Prestressed anchor cable tensioning and protection integrated construction method in alpine region

Abstract

The application discloses a prestressed anchor cable tensioning and protection integrated construction method in high-cold regions, and belongs to the technical field of slope reinforcement engineering. The method solves the problem that it is difficult to accurately determine the stable stage of frost heaving action in the construction of anchor cables in high-cold regions, which leads to improper construction timing of protection. The method comprises the following steps: drilling an anchor cable hole and installing a prestressed anchor cable; pouring a cement-based slurry into the anchoring section; installing an anchor cable dynamometer at the tensioning end to continuously monitor the anchor cable axial force; tensioning and locking the anchor cable and calculating the axial force change rate; burying a temperature sensor at the hole opening to continuously monitor the temperature and calculate the temperature change rate; comprehensively determining that the frost heaving action has reached the stable decay stage through multiple conditions; then, applying a protective coating, setting a sheath pipe and injecting sealant, and heating and solidifying by using an electric heating tape. The method realizes the integrated construction of tensioning and protection, accurately determines the stable timing of frost heaving, ensures the long-term safety of the anchor cable, and is suitable for slope reinforcement engineering in high-cold regions.

Description

Technical Field

[0001] This invention belongs to the field of slope reinforcement engineering technology. More specifically, this invention relates to an integrated construction method for prestressed anchor cable tensioning and protection of slopes in high-altitude and cold regions. Background Technology

[0002] In slope reinforcement projects in high-altitude and cold regions, prestressed anchor cables are a widely used technique. Anchor cables apply prestress to the soil and rock mass through tensioning and locking, effectively controlling slope deformation and improving stability. However, in seasonally frozen soil areas or high-altitude cold regions, the low-temperature environment presents unique challenges for anchor cable construction.

[0003] In the existing construction process, after the anchor cables are installed, tensioned, and locked, an anti-corrosion coating needs to be applied to the exposed sections of the anchor cables, a protective sleeve needs to be installed, and sealant needs to be injected to form a permanent protective structure. The protective layer is quite sensitive to temperature changes, and the injection and curing of the sealant usually require positive temperature conditions to ensure material performance and bonding quality. If construction is carried out in a low-temperature environment, the protective material may not cure properly, or after curing, defects such as cracking and debonding may occur due to freeze-thaw expansion and contraction, leading to anchor cable corrosion, prestress loss, and ultimately affecting the long-term safety of the slope.

[0004] On the other hand, the soil and rock mass surrounding the anchorage section of the anchor cable undergoes frost heave and thaw settlement during seasonal changes. When the temperature drops, the pore water in the soil and rock freezes and expands, generating additional frost heave force on the anchorage section, increasing the axial force of the anchor cable; when the temperature rises, the frozen soil thaws, the frost heave force gradually dissipates, and the axial force of the anchor cable decreases accordingly. The generation and dissipation of this frost heave force is a slow dynamic process, the duration of which is affected by factors such as temperature changes, soil and rock type, and water content, ranging from several weeks to several months.

[0005] Constructing protective measures before frost heave has stabilized poses two risks: First, if construction is carried out during the frost heave intensification stage, the continued increase in frost heave force may break the anchor cables or cause bond slippage between the anchor cables and the surrounding soil and rock, leading to anchorage failure. Second, if construction is carried out during the frost heave attenuation stage but before it has stabilized, the protective layer may experience additional stress due to the continued changes in the axial force of the anchor cables, leading to cracking or debonding of the protective layer. Therefore, determining a suitable time for protective construction is crucial.

[0006] Currently, the methods used in engineering practice to determine the timing of anchor cable protection construction are rather crude. A common approach is to estimate the time required for frost heave stabilization based on local climate data, for example, waiting a fixed number of days after spring temperatures have stabilized before commencing construction. This method fails to consider the differences in temperature fluctuations across different years and does not monitor the stress state of specific anchor cables, making it prone to misjudgment. If the waiting time is too short, construction may proceed before frost heave has stabilized, potentially leading to anchor cable failure; if the waiting time is too long, it prolongs the construction period and increases construction costs.

[0007] Another approach is to simply observe the borehole temperature and begin construction once the air temperature rises to positive levels and remains so for a certain period. However, borehole temperature only reflects the shallow surface conditions and cannot represent the frost heave state of the surrounding soil and rock. Since the anchorage section is located at a certain depth, the generation and dissipation of frost heave forces lag behind changes in surface temperature; therefore, it is difficult to accurately determine the actual stress state of the anchorage section based solely on surface temperature.

[0008] A few projects have attempted to install strain gauges or force gauges on anchor cables to monitor changes in axial force, but this is usually only used for control during the tensioning process or as a long-term monitoring method after construction. There is a lack of systematic methods and quantitative indicators for determining the specific point of frost heave stability. Simply observing the rate of change in axial force makes it difficult to distinguish between frost heave attenuation and axial force fluctuations caused by other factors; short-term observations alone cannot determine whether frost heave has entered a stable attenuation phase.

[0009] Furthermore, the construction window in high-altitude and cold regions is short, and the time when the temperature is suitable for construction is limited. If the protective construction is delayed due to inaccurate assessment of frost heave stability, the best construction season of the year may be missed, resulting in a one-year delay in the overall project schedule and bringing enormous time pressure and cost burden.

[0010] Therefore, how to scientifically and accurately determine whether the frost heave of the surrounding soil and rock has reached a stable attenuation stage, and thus determine the appropriate timing for protective construction, has become a pressing technical challenge in anchor cable construction in high-altitude and cold regions. The core of this problem lies in the fact that the evolution of frost heave force is a complex, multi-factor coupled process, influenced by factors such as the rate of temperature change, the thermophysical properties of the soil and rock, and moisture migration, making it difficult to accurately determine using a single parameter or simple threshold. A comprehensive determination method that can reflect the evolution of frost heave is needed, ensuring reliability while also considering the feasibility and timeliness of on-site implementation. Summary of the Invention

[0011] The purpose of this invention is to provide an integrated construction method for prestressed anchor cable tensioning and protection of slopes in high-altitude and cold regions. This method can solve the problem of improper timing of protection construction caused by the difficulty in accurately judging the stable stage of frost heave during anchor cable construction in high-altitude and cold regions.

[0012] To address the aforementioned problems and achieve the objectives and other advantages of this invention, an integrated construction method for prestressed anchor cable tensioning and protection of slopes in high-altitude and cold regions is provided, comprising: S1, Drill anchor cable holes and install prestressed anchor cables. The prestressed anchor cables have an anchoring section located at the bottom of the anchor cable hole and a tensioning section extending from the opening of the anchor cable hole to the outside. S2, inject cement-based grout into the entire length of the anchoring section and cure until the compressive strength of the stone reaches more than 80% of the design compressive strength; S3. Install an anchor cable force gauge at the tensioning end to continuously monitor the axial force of the anchor cable. P ; S4, Tension and lock the anchor cable, record axial force data and calculate the rate of change of axial force. dP / dt ; S5. A temperature sensor is installed at the orifice of the anchor cable hole to continuously monitor the ambient temperature at the orifice. T Record temperature data and calculate the rate of temperature change. dT / dt ; S6. When the following conditions are met simultaneously, it is determined that the frost heave of the surrounding soil and rock mass has reached the stable decay stage: Condition 1 dP / dt The value changes from a positive value that continuously crosses zero to a negative value; Condition 2, within 72 consecutive hours after condition 1 is met | dP / dt |<0.05kN / h; Condition 3: Calculate the ratio R =| dP / dt | / | dT / dt |, calculation R rate of change of value dR / dt ,when R The value changed from a continuous rise to a continuous fall, and remained so for 48 hours after the change. R The difference between the maximum and minimum values ​​is less than R 15% of the average value; Condition 4: After satisfying condition 3, within 48 consecutive hours R The second derivative of the value d 2 R / dt 2 It is a negative value, and | d 2 R / dt 2 |<0.0005 kN / (℃·h 2 ), at the same time | dR / dt |<0.005 kN / (℃·h); S7. After the conditions in S6 are met, apply a protective coating to the exposed part of the tensioning section. S8, a protective sleeve is installed on the outside of the protective coating, and sealant is injected between the protective sleeve and the anchor cable; S9. After the sealant is injected, an electric heating tape is used to cure it, completing the protective construction.

[0013] Preferably, in the integrated construction method for prestressed anchor cable tensioning and protection of slopes in high-altitude and cold regions, after completing all steps S1 to S5, a frost heave force-axial force regression model is established and deviation monitoring and judgment are performed according to the following steps: Step 1) Drill three holes of different depths in the rock and soil around the anchor hole opening. The three holes are radially distributed with the anchor hole axis as the center. The horizontal angle between adjacent holes is 120°. The hole depths are 30cm, 60cm and 90cm respectively. A miniature earth pressure sensor is buried at the bottom of each hole. The sensing surface of the miniature earth pressure sensor faces the anchor hole axis. The lead wire of the miniature earth pressure sensor is led out to the ground surface by an armored cable and the armored cable is covered with a polyethylene sheath. Step 2) Continuously monitor the horizontal frost heave force at a depth of 30cm using three miniature earth pressure sensors. F 1. Horizontal frost heave force at a depth of 60cm F 2 and 90cm depth horizontal frost heave force F 3. Simultaneously, the axial force of the anchor cable is continuously monitored using an anchor cable dynamometer. P The acquisition frequency of all monitoring data is set to no less than 0.5Hz; Step 3), continuous data acquisition F 1. F 2. F 3 and P The data must be at least 7 days old. After aligning the collected data by timestamp, ... F 1. F 2. F 3 is the independent variable. P Using the least squares method as the dependent variable, a multiple linear regression model was established to fit the frost heave force-axial force regression model: Among them, the regression coefficient a 1. a 2. a 3 and b The predicted values ​​for all data points are obtained by calculating using the least squares method. a 1 F 1+ a 2 F 2+ a 3 F 3+ b Compared with measured values P The sum of squared residuals is minimized; after the initial calculation of regression coefficients is completed, starting from the time the initial calculation is completed, when the cumulative monitoring data duration reaches 14 days, the regression coefficients are recalculated every 24 hours using the monitoring data of the 7 days closest to the current time, so as to realize the dynamic updating of regression coefficients; Step 4), during the process of determining whether the frost heave effect has reached the stable attenuation stage in S6, the following verification operations are performed simultaneously: based on real-time monitoring F 1. F 2. F 3 and the latest regression coefficients a 1. a 2. a 3. b According to the formula Calculate frost heave force to predict axial force P pred ;Will P pred Anchor cable axial force monitored in real time by anchor cable force gauge P Compare the two and calculate the average relative deviation over a continuous 24 hours. in, N This represents the number of sampling points within 24 hours. P pred，i For the first i Predicting axial force based on frost heave force at each sampling point. P i For the first i Measured values ​​of anchor cable axial force at each sampling point; Step 5), when δ If ≤15%, continue with S6 judgment; when δ When the value is greater than 15%, it is determined that the anchor cable force gauge has zero-point drift or that there is bond slip between the rock and soil and the anchor cable. At this time, the S6 determination is paused and the compensation tensioning program is started. The compensation tensioning procedure includes the following steps: Step A: Determine the compensation tension, which is 1.05-1.10 times the design locking tension value; Step B: Reinstall the tensioning jack onto the anchor cable tensioning end, ensuring that the jack axis coincides with the anchor cable hole axis during installation; Step C: Perform graded tensioning, apply the compensating tension force in three to five levels, with equal increments for each level, and stabilize the pressure for 5-10 minutes after each level of tensioning reaches the target value. Step D: After completing all levels of tensioning and stabilizing, lock the working anchorage and record the axial force of the anchor cable after compensation tensioning as the new initial tension force reference value; Step E: After the compensation tension is completed, the current time is reset to the new monitoring zero point, and the judgment of conditions 1 to 4 in S6 is restarted based on this zero point. If the average relative deviation obtained by repeating step 4) is completed within 24 hours after the compensation tensioning is completed, δ If the percentage still exceeds 15%, a reassessment process will be initiated. The re-evaluation procedure is as follows: Set the moment when the compensation tensioning is completed and locked as the new zero point, and re-execute steps 2) to 4) from the new zero point. When the average relative deviation is obtained from re-executing step 4), δ When ≤15%, based on newly collected measured values ​​of anchor cable axial force. P and synchronously monitored wellhead ambient temperature T Re-execute all the judgment steps of conditions 1 to 4 in S6; if conditions 1 to 4 are not fully met after two consecutive re-executions of S6, it is determined that there is irreversible damage to the anchoring system, and engineering treatment is carried out by installing additional anchor cables or grouting reinforcement.

[0014] Preferably, in the integrated construction method for prestressed anchor cable tensioning and protection of slopes in high-altitude and cold regions, the absolute value of the temperature change rate is monitored simultaneously during the determination process of S6. dT / dt |; When | dT / dt When the temperature is ≥0.01℃ / h, all conditions in S6 are applied for a comprehensive judgment. When | dT / dt When | < 0.01℃ / h, suspend all conditions in S6 and instead perform the following frost heave stability determination steps: Step a: Continuously collect horizontal frost heave force at a depth of 30cm. F 1. Horizontal frost heave force at a depth of 60cm F 2 and 90cm depth horizontal frost heave force F 3. The data acquisition frequency is not less than 0.5Hz; Step b: Using a 72-hour time window, calculate the difference between the maximum and minimum values ​​of each frost heave force data within that window, and obtain Δ... F 1. △ F 2 and △ F 3; Step c, calculate the average value of each frost heave force data within the window, and obtain the results respectively. F 1avg , F 2avg and F 3avg ; Step d, when △ F 1≤0.05 F 1avg , △ F 2≤0.05 F 2avg and △ F 3≤0.05F 3avg When it is determined that the frost heave of the surrounding rock and soil has reached a stable decay stage, proceed with S7 and subsequent steps. Step e: If any of the conditions in step d are not met, it is determined that the frost heave effect has not yet stabilized, and monitoring continues until the above conditions are met before proceeding to S7. Step f, when | dT / dt When the temperature rises to ≥0.01℃ / h, resume all conditions in S6 and re-determine the frost heave stability based on real-time monitoring data.

[0015] Preferably, in the integrated construction method for prestressed anchor cable tensioning and protection of slopes in cold regions, the cement-based grout in S2 is a low-temperature early-strength cement-based grout, composed of the following components by weight: 100 parts of G-grade oil well cement, 32-45 parts of water, 3-5 parts of calcium formate, 1-2 parts of triethanolamine, and 1-3 parts of sodium nitrite; before grouting, a composite mineral admixture is added to the cement-based grout, which is composed of the following components by weight: 60-80 parts of slag powder, 10-20 parts of nano-silica, and 5-15 parts of anhydrous calcium sulfoaluminate; wherein, the specific surface area of ​​the slag powder is ≥600 m². 2 / kg, D90≤30μm; nano-silica with a particle size of 10-30nm and a specific surface area ≥200 m² 2 / g; based on 100 parts by weight of G-grade oil well cement, the amount of composite mineral admixture is 8-15 parts by weight; the method of adding composite mineral admixture is as follows: add it to the cement-based grout 5-10 minutes before the start of grouting and stir, the stirring speed is not less than 1200 r / min, and the stirring time is 3-5 minutes; the grouting adopts the bottom return grouting method, the return grouting flow rate is 20-50L / min until the grout consistent with the grouting grout overflows from the anchor cable hole and then stops, after grouting is completed and cured for 5 days, the subsequent tensioning operation can be carried out.

[0016] Preferably, in the integrated construction method for prestressed anchor cable tensioning and protection of slopes in high-altitude and cold regions, tensioning in S4 is graded tensioning, including initial tensioning, intermediate tensioning and final tensioning. The initial tension force is 10%-20% of the design locking tension force value and is held for 5-15 minutes. The intermediate tensioning is divided into three to five levels, starting from the tension force after the initial tensioning ends. The increase in tension force at each level is 15%-25% of the design locking tension force value, and each level is held for 8-20 minutes. The final tensioning reaches 1.05-1.10 times the design locking tension force value and is then locked.

[0017] Preferably, in the integrated construction method for prestressed anchor cable tensioning and protection of slopes in high-altitude and cold regions, the temperature sensor in S5 is embedded in the soil and rock at the edge of the anchor cable hole opening to a depth of 10-30 cm. The embedding method is as follows: drill a hole with a diameter of 30-50 mm and a depth of 10-30 cm at the edge of the anchor cable hole opening, place the temperature sensor at the bottom of the hole, fill the area around the temperature sensor with fine sand, and use armored cable to lead out the temperature sensor lead wire. The cable is covered with a polyethylene sheath, and the outlet of the sheath is sealed with waterproof sealant.

[0018] Preferably, in the integrated construction method for prestressed anchor cable tensioning and protection of slopes in high-altitude and cold regions, the protective coating in S7 includes a first protective coating and a second protective coating. The first protective coating is an epoxy zinc-rich primer with a coating thickness of 50-120μm, and the second protective coating is a polyurethane topcoat with a coating thickness of 60-150μm. In S8, the sheath is a polyethylene corrugated sheath with an inner diameter to outer diameter ratio of 1.2-1.6. The sealant is a flexible sealant. Before injecting the flexible sealant, the sheath is preheated with an electric heating tape at a temperature of 20-30℃ for 30-60 minutes, raising the temperature in the annular gap between the sheath and the prestressed anchor cable to above 5℃. Then, the flexible sealant is injected at a pressure of 0.2-0.6MPa for 10-30 minutes until the annular gap is completely filled and flexible sealant overflows from both ends of the sheath.

[0019] Preferably, in the integrated construction method for prestressed anchor cable tensioning and protection of slopes in cold regions, the winding spacing of the electric heating cable in S9 is 10-30cm, and the temperature of the sealant is maintained at 35-55℃ and cured for 45-90 minutes by electric heating.

[0020] Preferably, in the integrated construction method for prestressed anchor cable tensioning and protection of slopes in high-altitude and cold regions, after heating and curing in step S9, the electric heating cable is kept in a wound state, heating is stopped and the sealant is allowed to cool down naturally. During the cooling process, the change in tension force is continuously monitored by the anchor cable force gauge. A 10-minute sliding time window is taken as the sliding time window, and the difference between the maximum and minimum tension force in each sliding time window is calculated. When the difference between the maximum and minimum tension force in each sliding time window for three consecutive sliding time windows is divided by the design locking tension force value and is greater than 0.8%, it is determined that there is an adhesion defect in the protective layer. The electric heating cable is immediately restarted and heated to 40-50℃ and held at the temperature for 20-40 minutes for secondary curing. After the secondary curing is completed, the electric heating cable is removed.

[0021] Preferably, in the integrated construction method for prestressed anchor cable tensioning and protection of slopes in high-altitude and cold regions, S6... RThe method for determining whether a value changes from a continuously rising state to a continuously falling state is as follows: Real-time computing R Rate of change of value over time dR / dt When within 7 consecutive days dR / dt >0 and daily dR / dt The values ​​are all greater than the previous day's. dR / dt When determining numerical values, R The value is in an upward phase; When detected dR / dt The instant from a positive value to zero is called the moment. R The turning point where the value changes from rising to falling; After the turning point, within 7 consecutive days dR / dt <0 and daily dR / dt The absolute values ​​of all are greater than those of the previous day. dR / dt When the absolute value is used, determine R The value is in a downward phase.

[0022] The present invention has at least the following beneficial effects: This invention continuously monitors the axial force of the anchor cable and the ambient temperature at the orifice, and introduces multiple quantitative conditions such as the rate of change of axial force, the rate of change of temperature, and the derivative of their ratio R to make a comprehensive judgment. This accurately identifies the stable stage of frost heave in the surrounding soil and rock of the anchoring section, avoiding the defects of single-parameter judgment being easily affected by accidental factors. It provides a reliable decision-making basis for protective construction and fundamentally solves the problem of damage to the protective layer or delay in construction period caused by misjudgment of the frost heave stabilization time in anchor cable construction in high-altitude and cold regions.

[0023] This invention comprehensively covers the entire process of frost heave from enhancement to attenuation to complete stability by progressively constraining multiple conditions, such as the change of axial force rate from positive to negative, the threshold of the absolute value of the rate of change, the trend of the ratio R, and its second derivative. The judgment logic is highly consistent with the physical evolution law of frost heave force, ensuring the scientificity and accuracy of the judgment results. This allows the protective construction to be carried out at the moment when the frost heave effect truly ends, ensuring the long-term safety of anchor cables and the lasting stability of slope reinforcement.

[0024] This invention dynamically determines the frost heave status by monitoring data in real time, eliminating the need to rely on experience-based estimations or fixed waiting times. Once the frost heave effect has stabilized, protective construction can be carried out promptly, shortening the construction cycle and improving construction efficiency. At the same time, it integrates anchor cable tensioning, frost heave stability monitoring, and protective layer construction into a complete process chain, realizing continuous operation of tensioning and protection, reducing intermediate waiting and repeated site visits, and lowering the difficulty of construction organization.

[0025] This invention establishes a multi-depth frost heave force-axial force regression model and monitors deviations to effectively identify zero-point drift of anchor cable force gauges or abnormal bond slip between anchor cables and soil. By correcting these abnormalities in a timely manner through a compensation tensioning program, this invention endows the method with self-correction capabilities under abnormal sensor conditions, ensuring that the same accurate judgment results and engineering effects can be obtained under adverse conditions as under normal conditions, significantly improving the reliability and engineering applicability of the technical solution.

[0026] This invention introduces a temperature change rate threshold triggering mechanism, which switches to direct stability determination based on multi-depth frost heave force measured data when the temperature change rate is extremely small. This avoids the numerical instability problem of the original ratio criterion during the temperature stable period, makes full use of the data of the buried sensors, does not require additional hardware, ensures the continuity and accuracy of the determination under special weather conditions, and avoids the delay in construction period caused by waiting for the temperature change rate to recover.

[0027] This invention employs a low-temperature, early-strength cement-based grout. Through the synergistic effect of G-grade oil well cement with multiple components such as calcium formate, triethanolamine, sodium nitrite, slag powder, nano-silica, and anhydrous calcium sulfoaluminate, the hydration reaction is significantly accelerated under low-temperature conditions in high-altitude and cold regions, greatly shortening the curing time. At the same time, the filling effect of ultrafine mineral admixtures and the activity of volcanic ash make the stone body more compact, resulting in better bonding performance between the anchoring section and the soil and rock mass. This improves construction efficiency while ensuring the long-term durability of the anchoring section.

[0028] This invention employs a graded tensioning process, which combines initial tensioning, multi-stage intermediate tensioning, and final over-tensioning with sufficient holding time to ensure uniform stress distribution in each strand of the anchor cable, reasonable shear stress distribution in the anchoring section, and full development of ground deformation. This effectively reduces prestress loss after tensioning and locking, making the axial force of the anchor cable after locking closer to the design value, and providing a reliable prestressed foundation for subsequent frost heave stability assessment and protective construction.

[0029] This invention features a specially designed method for burying temperature sensors. Through measures such as reasonable burial depth, dense filling with fine sand, protection of armored cables with polyethylene conduits, and sealing with waterproof sealant, the sensor is ensured to form good thermal contact with the soil and rock in harsh environments of high-altitude and cold regions. The leads are protected by multiple layers, enabling long-term stable acquisition of representative temperature data and providing an accurate and reliable data foundation for determining frost heave stability.

[0030] This invention employs an epoxy zinc-rich primer and a polyurethane topcoat to form a double-layer protective coating, combined with a polyethylene corrugated sheath and flexible sealant to form a multi-layer protective system. The sealant has an elongation at break of ≥200% at -40℃, ensuring its flexibility under extreme low temperatures. The preheating and pressure injection process ensures that the sealant forms a tight bond with the sheath and anchor cable, and the annular gap is filled densely, effectively preventing water vapor intrusion and significantly extending the service life of the anchor cable in high-altitude and cold regions.

[0031] This invention provides a quantitative definition for the determination of the R-value state. By continuously monitoring the sign and value changes of the R-value change rate dR / dt, an objective judgment standard is established from continuous rise, peak inflection and continuous decline. This effectively eliminates short-term fluctuation interference, accurately captures the peak inflection point, and is highly consistent with the law that the frost heave force first accelerates and then accelerates its decline during the frost heave evolution process. This provides a reliable basis for the accurate determination of condition 3 and the overall frost heave stability determination.

[0032] Other advantages, objectives and features of the present invention will become apparent in part from the following description, and in part from those skilled in the art through study and practice of the invention. Detailed Implementation

[0033] The present invention will now be described in further detail so that those skilled in the art can implement it based on the description.

[0034] It should be noted that, unless otherwise specified, the experimental methods described in the following implementation plan are all conventional methods, and the reagents and materials described are all commercially available unless otherwise specified.

[0035] This invention provides an integrated construction method for prestressed anchor cable tensioning and protection of slopes in high-altitude and cold regions, comprising: S1, drilling anchor cable holes and installing prestressed anchor cables, wherein the prestressed anchor cables have an anchoring section located at the bottom of the anchor cable hole and a tensioning section extending from the opening of the anchor cable hole to the outside; S2, injecting cement-based grout into the entire length of the anchoring section and curing until the compressive strength of the aggregate reaches more than 80% of the design compressive strength; S3, installing an anchor cable force gauge at the tensioning end (the end of the tensioning section, i.e., the location where the anchor, anchor cable force gauge, and tensioning operation are performed) to continuously monitor the axial force of the anchor cable. P S4, Tension and lock the anchor cable, record axial force data and calculate the rate of change of axial force. dP / dt S5. Install a temperature sensor at the borehole opening of the anchor cable to continuously monitor the ambient temperature at the borehole opening. T Record temperature data and calculate the rate of temperature change. dT / dt S6, When the following conditions are met simultaneously, it is determined that the frost heave of the surrounding soil and rock mass of the anchorage section has reached the stable decay stage: Condition 1, dP / dt From positive values ​​continuously crossing zero to becoming negative values; Condition 2, within 72 hours after satisfying Condition 1 | dP / dt | < 0.05 kN / h; Condition 3, calculate the ratio R =| dP / dt | / | dT / dt |, calculationR rate of change of value dR / dt ,when R The value changed from a continuous rise to a continuous fall, and remained so for 48 hours after the change. R The difference between the maximum and minimum values ​​is less than that within 48 hours. R 15% of the average value; Condition 4: After satisfying condition 3, within 48 consecutive hours R The second derivative of the value d 2 R / dt 2 It is a negative value, and | d 2 R / dt 2 |<0.0005 kN / (℃·h 2 ), at the same time | dR / dt |<0.005 kN / (℃·h); S7, after meeting the conditions in S6, apply a protective coating to the exposed part of the tensioning section; S8, install a sheath outside the protective coating and inject sealant between the sheath and the anchor cable; S9, after the sealant is injected, use an electric heating tape to cure it, and complete the protective construction.

[0036] In the construction of prestressed anchor cables on slopes in high-altitude and cold regions, existing technologies typically rely on empirical judgment to determine the timing of protective construction. Construction workers, based on local meteorological data, wait a fixed number of days (e.g., 30 days) after the spring temperature rises, or simply observe that the borehole temperature remains above 0°C for several consecutive days before commencing the construction of the protective layer on the exposed sections of the anchor cables. Some projects also install dynamometers on the anchor cables to monitor axial force, but this is only used for tensioning process control or long-term monitoring, without establishing a systematic index for determining frost heave stability. These methods have significant shortcomings: empirical waiting cannot adapt to temperature fluctuations and geological differences from year to year, easily leading to construction before frost heave has stabilized due to insufficient waiting time, or delays due to excessive waiting time; relying solely on temperature judgment cannot reflect the actual stress state of the anchorage section, as the generation and dissipation of frost heave force lag behind changes in surface temperature. Therefore, existing technologies struggle to accurately determine whether the frost heave effect on the surrounding soil and rock has reached a stable attenuation stage, resulting in inappropriate timing of protective construction and causing problems such as anchor cable breakage, protective layer cracking, or project delays.

[0037] This method achieves accurate identification of the frost heave stabilization stage by continuously monitoring the anchor cable axial force and borehole temperature, and setting multiple quantitative conditions for comprehensive judgment. Step S1 involves drilling anchor cable holes and installing prestressed anchor cables to provide a foundation for subsequent construction. Step S2 involves injecting cement-based grout along the entire length of the anchorage section and curing it to over 80% of its design strength to ensure sufficient load-bearing capacity. Step S3 involves installing an anchor cable dynamometer at the tensioning end to acquire axial force data in real time. Step S4 involves tensioning and locking the anchor cable, recording the axial force data, and calculating the rate of change of axial force. dP / dt The rate of change of axial force is a key indicator reflecting the dynamic changes caused by frost heave. Step S5 involves embedding a temperature sensor at the orifice of the anchor cable hole to continuously monitor the ambient temperature T at the orifice and calculate the rate of change of temperature. dT / dt This is used to eliminate the influence of the rate of temperature change on the change in axial force. The four conditions in step S6 constitute the core judgment logic for frost heave stability: Condition 1 requires the axial force change rate to continuously cross zero from a positive value to a negative value, indicating that the frost heave effect of the surrounding soil and rock mass has transitioned from the strengthening stage to the attenuation stage. During frost heave strengthening, the expansion of the soil and rock mass compresses the anchor cable, increasing the axial force. dP / dt The result is positive; as the frost heave begins to subside, the axial force gradually decreases. dP / dt The condition changes from positive to negative, thus marking the beginning of the decline phase of frost heave.

[0038] Condition 2 requires that, after satisfying Condition 1, the absolute value of the axial force change rate must be less than 0.05 kN / h for 72 consecutive hours. This is to confirm that the decay process has entered a slow and stable state, and the axial force no longer fluctuates drastically. 0.05 kN / h is a relatively small threshold. For example, for an anchor cable with a design locking tension of 500 kN, this change rate is equivalent to an axial force change of no more than 0.01% per hour, indicating that the frost heave force has essentially dissipated.

[0039] Condition 3 introduces the ratio R, which is equal to the absolute value of the rate of change of axial force divided by the absolute value of the rate of change of temperature. This ratio eliminates the influence of the rate of temperature change and reflects the magnitude of axial force change caused by a unit temperature change, thus more purely characterizing the intensity of frost heave. Calculation R rate of change of value dR / dt ,when R When the temperature shifts from a continuous increase to a continuous decrease, it indicates that the sensitivity of frost heave to temperature changes has reached its peak and begun to weaken. Within 48 hours following this shift, R The difference between the maximum and minimum values ​​within that 48-hour period is less than R 15% of the average value, which indicates RThe value fluctuation range is very small, and the frost heave effect has entered a stable decline phase. For example, if within 48 hours... R If the average value is 0.2 kN / ℃, then its fluctuation range should be less than 0.03 kN / ℃.

[0040] Condition 4: After satisfying condition 3, calculate. R The second derivative of the value d 2 R / dt 2 When both of the following conditions are met simultaneously within 48 consecutive hours, it indicates that... R The rate of decline of the value has slowed sufficiently and entered a stable phase: ① d 2 R / dt 2 The absolute value is negative. d 2 R / dt 2 |<0.0005 kN / (℃·h 2 );② | dR / dt |<0.005 kN / (℃·h). Wherein, condition ① reflects... R The rate of change of the value's rate of decrease approaches zero, meaning the downward trend is leveling off; condition ② is further confirmed. R The change in the value itself is also extremely small. With all four conditions met, it is determined that the frost heave effect on the surrounding soil and rock has reached a stable attenuation stage, and subsequent protective construction can proceed safely. Steps S7 to S9 complete the application of the protective coating, the installation of the sheath, the injection of sealant, and the curing of the electric heating tape, achieving integrated tensioning and protection operations.

[0041] The effectiveness of this method is further illustrated below through examples and comparative examples.

[0042] Example 1 (Sensor is normal, temperature change is normal, judged according to 4 conditions) A slope reinforcement project in a high-altitude, cold region employed prestressed anchor cables with a designed locking tension of 600 kN. During the installation of these anchor cables, the anchor cable dynamometer functioned normally without any zero-point drift. The construction process was strictly carried out in accordance with the method described in this invention.

[0043] Anchor cable holes were drilled in S1, with a depth of 20m and a diameter of 150mm. After drilling, the hole walls were cleaned with pressurized water for 10 minutes at a pressure of 1.2MPa. Prestressed anchor cables were then installed, consisting of 7 strands of steel wire. The anchoring section was located at the bottom of the hole, and the tensioning section extended to the outside of the hole opening.

[0044] Low-temperature early-strength cement-based grout was injected along the entire length of the S2 anchorage section. The grout formula was: 100 parts P.O42.5 ordinary Portland cement, 40 parts water, 2 parts sodium nitrite, 1 part triethanolamine, and 0.5 parts lithium carbonate (an early-strength agent). The grouting was performed using the bottom-return grouting method, with a return flow rate of 30 L / min, continuing until uniform grout overflowed from the borehole opening. After 7 days of curing, the aggregate strength reached 85% of the design strength.

[0045] S3. Install the anchor cable dynamometer. First, pre-embed anchor plates on the surface of the slope soil and rock. The anchor plates are square steel plates with a central hole. Align the central hole of the anchor plate with the axis of the anchor cable hole, and grind the surface of the anchor plate smooth. Then, mount the anchor cable dynamometer onto the prestressed anchor cable, pushing the dynamometer along the anchor cable to the anchor plate, ensuring the dynamometer is flush with the outer end face of the anchor plate. Adjust the position of the dynamometer so that its axis coincides with the axis of the anchor cable hole, requiring an inclination of less than 0.5° and an eccentricity of less than 0.5mm. Next, install the working anchor plate, a circular steel plate 40mm thick, with a diameter matching the outer diameter of the anchor cable dynamometer. The working anchor plate has multiple conical holes in its central area, the number of which matches the number of anchor cable strands (7 in this embodiment). The conical holes are truncated cones, with larger diameters on the side closer to the dynamometer and smaller diameters on the other side. Place the working anchor plate firmly against the outer end face of the anchor cable dynamometer, ensuring the center of the working anchor plate coincides with the center of the anchor cable dynamometer. Pass the seven steel strands through the corresponding conical holes on the working anchor plate, with the strands entering from the smaller diameter side and exiting from the larger diameter side. Insert the working clamps into the conical holes of the working anchor plate, placing two semi-circular ring-shaped clamps in each conical hole, with the outer surface of the clamps fitting against the inner wall of the conical hole, and the teeth on the inner surface of the clamps securing the steel strands. Gently tap the ends of the clamps with a sleeve and a hammer to initially clamp the steel strands. Before tensioning begins, continuously measure the initial value of the anchor cable dynamometer three times. If the difference between the maximum and minimum values ​​of the three readings is less than 1% of the full scale of the anchor cable dynamometer, take the average of the three readings as the initial tension force reference value. Thereafter, continuously monitor the axial force of the anchor cable. P .

[0046] S4 underwent graded tensioning. The initial tension was 15% of the design locking tension, i.e., 90 kN, held for 10 minutes. Intermediate tensioning was divided into four stages, starting from the initial 90 kN, with each stage increasing the tension by 20% of the design locking tension, i.e., 120 kN, sequentially reaching 210 kN, 330 kN, 450 kN, and 570 kN, each held for 15 minutes. The final tension reached 1.08 times the design locking tension, i.e., 648 kN, and was locked. At the moment of locking, the anchor cable axial force was recorded as 645 kN. Subsequently, the axial force was continuously monitored, and the rate of change of axial force was calculated. dP / dt .

[0047] S5 involves embedding a temperature sensor within the soil and rock at the edge of the anchor cable borehole. A 40mm diameter, 20cm deep hole is drilled, and the temperature sensor is placed at the bottom of the hole. The surrounding area is then filled with fine sand. The sensor lead is led out using an armored cable, which is sheathed in a polyethylene conduit. The conduit outlet is sealed with waterproof sealant. The ambient temperature at the borehole opening is continuously monitored. T And calculate the rate of temperature change. dT / dt .

[0048] S6 determines frost heave stability based on continuous monitoring data. Monitoring lasted for 60 days, and the data recorded during this period is as follows: 24th day dP / dt The value changes from positive to negative, satisfying condition 1. This continues for the next 72 hours, from day 24 to day 27. dP / dt The absolute value is at most 0.04 kN / h and less than 0.05 kN / h, thus satisfying condition 2.

[0049] On day 30, calculate the ratio. R =| dP / dt | / | dT / dt |, Discover R The value rose continuously from day 26, reaching its peak on day 30, and was detected. dR / dt The moment the value changes from positive to zero is the turning point. Calculations are performed at this point. d 2 R / dt 2 -0.0009kN / (℃•h) 2 ),show R Although the value has begun to decrease, the rate of decrease is still changing. Over the next 7 days... dR / dt If all values ​​are less than 0 and the absolute value of each day is greater than the previous day, then the judgment is made. R The value is in a downward phase. Within a consecutive 48-hour period following the turning point, i.e., from day 31 to day 33... R The maximum value is 0.22 kN / ℃, the minimum value is 0.19 kN / ℃, the average value is 0.205 kN / ℃, the difference is 0.03 kN / ℃, which is less than 15% of the average value, i.e., 0.03075 kN / ℃, thus satisfying condition 3.

[0050] On day 36, the determination of condition 4 began. Monitoring data showed that within the following 48 hours, R The second derivative of the value d 2 R / dt 2The value remains negative and its absolute value is less than 0.0005 kN / (℃·h). 2 It should be noted that the calculation of the second derivative in discrete sampling exhibits some fluctuations, starting from 08:15 on day 36. d 2 R / dt 2 The calculated values ​​are stable between -0.0003 and -0.0004 kN / (℃·h). 2 Between ), the calculated value at 14:23 on the 36th day is -0.00035, satisfying | d 2 R / dt 2 The threshold requirement is | < 0.0005. Meanwhile, | dR / dt The monitored value of | fluctuated between 0.002 and 0.004 kN / (℃·h) within the 48 hours, all less than the threshold of 0.005 kN / (℃·h). Thus, both sub-conditions of condition 4 were satisfied for 48 consecutive hours. On day 38, it was determined that the frost heave of the surrounding soil and rock had reached a stable attenuation stage, and protective construction from S7 to S9 was subsequently carried out.

[0051] S7 applies a protective coating to the exposed portion of the tensioning section. First, apply an epoxy zinc-rich primer with a thickness of 80 μm; then apply a polyurethane topcoat with a thickness of 100 μm.

[0052] S8 features a protective sleeve on the outside of the protective coating, made of corrugated polyethylene with an inner diameter to outer diameter ratio of 1.4. The sealant is a flexible sealant with an elongation at break of ≥200% at -40℃. Before injection, the sleeve is preheated with an electric heating tape at 25℃ for 45 minutes, raising the temperature within the annular gap to above 5℃. Then, the flexible sealant is injected at a pressure of 0.4MPa for 20 minutes until the annular gap is completely filled and sealant overflows from both ends of the sleeve.

[0053] After the S9 sealant is injected, it is cured using an electric heating cable. The heating cable is wound at 20cm intervals, and the sealant temperature is maintained at 45℃ by heating for 60 minutes. After curing, the heating cable is kept in its wound state, and heating is stopped to allow it to cool naturally. During the cooling process, the tension change is monitored using an anchor cable force gauge. A 10-minute sliding window is used, and the difference between the maximum and minimum tension values ​​in each window is calculated. If the difference between three consecutive windows divided by the design locking tension value is less than 0.8%, it is determined that there are no adhesion defects in the protective layer, and the heating cable is removed. The protective construction is complete.

[0054] Forty days after tensioning and locking, a sharp drop in temperature occurred, falling to -18℃. Observational data showed that during this cooling process, the anchor cable axial force briefly increased from 620kN to 623kN, a change of 3kN, before quickly returning to its normal fluctuation range. Throughout the six-month observation period, the anchor cable axial force remained stable between 615kN and 633kN, with a difference of 18kN between the maximum and minimum values. At the end of the six months, prestress testing was conducted on the anchor cable, with a measured value of 619kN, compared to the initial locking value of 645kN. The prestress retention rate was 619 / 645 × 100% = 96.0%. Inspection of the end sealant of the sheath and the exposed section of the anchor cable at the end of the six months revealed no signs of cracking or corrosion.

[0055] Comparative Example 1 (Empirical Method) For adjacent areas on the same slope, anchor cables with the same design parameters were used, and the timing of protection was determined according to traditional experience methods. These anchor cables were constructed concurrently with those in Example 1, and the terrain, geology, and sunlight conditions at the location were identical to those in Example 1. Based on local meteorological data accumulated over many years, the construction team waited 30 days after the temperature had stably risen above 0°C before commencing protection work.

[0056] Monitoring data shows that the anchor cable at 24 days dP / dt The change from positive to negative is consistent with Example 1. On day 30, dP / dt The absolute value has dropped to 0.04 kN / h, satisfying condition 2. However, the ratio at this point... R The value is 0.24 kN / ℃, still in the late stage of the rising phase, not yet reaching the peak, and certainly not yet entering the stable declining phase. Because the method of this invention was not used for real-time monitoring and quantitative determination, the construction personnel did not pay attention to the ratio. R Based on the trend of its changes, protective construction will be carried out on the 30th day as originally planned, and the construction process will be the same as in Example 1.

[0057] Forty days after the tensioning and locking date, the area experienced the same sharp temperature drop as in Example 1, with the temperature falling to -18°C. At this time, because the deep frost heave had not completely subsided during the protective construction, there were still unthawed frozen soil layers within the rock and soil mass. This temperature drop triggered further frost heave in the deep rock and soil mass, causing the axial force of the anchor cable to rise from 622kN to 658kN, a change of 36kN. dP / dt The axial force reached 0.13 kN / h. Changes in axial force caused shear stress at the interface between the protective layer and the anchor cable. An inspection conducted 100 days after tensioning and locking (70 days after protective construction) revealed fine cracks in the sealant at the end of the sheath and slight signs of corrosion on the exposed section of the anchor cable. Testing showed that the anchor cable's prestress loss reached 3.5%, which, while not requiring immediate re-tensioning, already adversely affected its long-term durability.

[0058] Comparison of effects: Example 1 demonstrates that, under normal sensor operation, the basic method of this invention can accurately determine the timing of frost heave stabilization, successfully complete construction, and achieve good long-term performance—the axial force fluctuation was 3kN on the 40th day after the tensioning and locking date, the axial force fluctuation range was 18kN after 6 months, the prestress retention rate was 96.0% after 6 months, and the protective layer remained intact at the end of 6 months.

[0059] Comparative Example 1 reveals the consequences of not using this method to determine frost heave stability: early construction led to instability of deep frost heave, and subsequent cooling caused a large fluctuation of axial force of 36kN. As a result, damage to the protective layer and loss of prestress were found on the 100th day after tensioning and locking, i.e., the 70th day after protective construction, and the long-term durability was significantly reduced.

[0060] In another approach, the integrated construction method for prestressed anchor cable tensioning and protection of slopes in high-altitude and cold regions involves establishing a frost heave force-axial force regression model and monitoring and judging deviations after completing all steps S1 to S5, following these steps: Step 1) Drill three holes of different depths in the rock and soil around the anchor hole opening. The three holes are radially distributed with the anchor hole axis as the center. The horizontal angle between adjacent holes is 120°. The hole depths are 30cm, 60cm and 90cm respectively. A miniature earth pressure sensor is buried at the bottom of each hole. The sensing surface of the miniature earth pressure sensor faces the anchor hole axis. The lead wire of the miniature earth pressure sensor is led out to the ground surface by an armored cable and the armored cable is covered with a polyethylene sheath. Step 2) Continuously monitor the horizontal frost heave force at a depth of 30cm using three miniature earth pressure sensors. F 1. Horizontal frost heave force at a depth of 60cm F 2 and 90cm depth horizontal frost heave force F 3. Simultaneously, the axial force of the anchor cable is continuously monitored using an anchor cable dynamometer. P The acquisition frequency of all monitoring data is set to no less than 0.5Hz; Step 3), continuous data acquisition F 1. F 2. F 3 and P The data must be at least 7 days old. After aligning the collected data by timestamp, ... F 1. F 2. F 3 is the independent variable. P Using the least squares method as the dependent variable, a multiple linear regression model was established to fit the frost heave force-axial force regression model: Among them, the regression coefficient a 1. a 2.a 3 and b The predicted values ​​for all data points are obtained by calculating using the least squares method. a 1 F 1+ a 2 F 2+ a 3 F 3+ b Compared with measured values P The sum of squared residuals is minimized; after the initial calculation of regression coefficients is completed, starting from the time the initial calculation is completed, when the cumulative monitoring data duration reaches 14 days, the regression coefficients are recalculated every 24 hours using the monitoring data of the 7 days closest to the current time, so as to realize the dynamic updating of regression coefficients; Step 4), during the process of determining whether the frost heave effect has reached the stable attenuation stage in S6, the following verification operations are performed simultaneously: based on real-time monitoring F 1. F 2. F 3 and the latest regression coefficients a 1. a 2. a 3. b According to the formula Calculate frost heave force to predict axial force P pred ;Will P pred Anchor cable axial force monitored in real time by anchor cable force gauge P Compare the two and calculate the average relative deviation over a continuous 24 hours. in, N This represents the number of sampling points within 24 hours. P pred，i For the first i Predicting axial force based on frost heave force at each sampling point. P i For the first i Measured values ​​of anchor cable axial force at each sampling point; Step 5), when δ If ≤15%, continue with S6 judgment; when δ When the value is greater than 15%, it is determined that the anchor cable force gauge has zero-point drift or that there is bond slip between the rock and soil and the anchor cable. At this time, the S6 determination is paused and the compensation tensioning program is started. The compensation tensioning procedure includes the following steps: Step A, determine the compensation tension force, which is 1.05-1.10 times the design locking tension force; Step B, reinstall the tensioning jack onto the anchor cable tensioning end, ensuring that the jack axis coincides with the anchor cable hole axis during installation; Step C, perform graded tensioning, applying the compensation tension force in three to five levels, with equal increments for each level, and stabilizing the tension for 5-10 minutes after each level reaches the target value; Step D, after completing all levels of tensioning and stabilizing, lock the working anchorage and record the anchor cable axial force after compensation tensioning as the new initial tension force benchmark value; Step E, after the compensation tensioning is completed, reset the current time to the new monitoring zero point, and restart the judgment of conditions 1 to 4 in S6 based on this zero point. If the average relative deviation obtained by repeating step 4) is completed within 24 hours after the compensation tensioning is completed, δ If the percentage still exceeds 15%, a reassessment process will be initiated. The re-evaluation procedure is as follows: Set the moment when the compensation tensioning is completed and locked as the new zero point, and re-execute steps 2) to 4) from the new zero point. When the average relative deviation is obtained from re-executing step 4), δ When ≤15%, based on newly collected measured values ​​of anchor cable axial force. P and synchronously monitored wellhead ambient temperature T Repeat all judgment steps from conditions 1 to 4 in S6; if two consecutive re-judgments fail, it is determined that there is irreversible damage to the anchoring system, and engineering treatment is carried out by installing additional anchor cables or grouting reinforcement.

[0061] In the construction of prestressed anchor cables on slopes in high-altitude and cold regions, accurate monitoring of the anchor cable axial force is fundamental to determining frost heave stability. However, in actual engineering projects, anchor cable dynamometers are exposed to low-temperature environments for extended periods, which may cause zero-point drift, resulting in axial force readings deviating from the true value. Simultaneously, adhesion and slippage may occur between the anchor cable and the surrounding soil and rock mass due to frost heave cycles or grouting defects, preventing the anchor cable axial force from accurately reflecting changes in frost heave force. All these factors can lead to deviations in axial force data relying solely on anchor cable dynamometer monitoring, thereby rendering the frost heave stability assessment based on the rate of change of axial force unreliable and potentially causing misjudgments.

[0062] To address the aforementioned issues, this method, building upon previous steps, further involves drilling three holes of varying depths (30cm, 60cm, and 90cm) within the surrounding soil and rock around the anchor cable borehole. These holes are radially distributed with adjacent holes at a 120° angle. A miniature earth pressure sensor is embedded at the bottom of each hole, with its sensing surface facing the anchor cable borehole axis. These three sensors continuously monitor the horizontal frost heave force at different depths. F 1. F 2. F 3. Simultaneously, the axial force monitored by the anchor cable dynamometer PSynchronous acquisition, with an acquisition frequency of not less than 0.5Hz.

[0063] After continuously collecting data for at least 7 days, F 1. F 2. F 3 is the independent variable. P Using the least squares method as the dependent variable, a multiple linear regression model was established to fit the frost heave force-axial force regression. Regression coefficients a 1. a 2. a 3 and b The regression coefficients are calculated using the least squares method to minimize the sum of squared residuals between the predicted and measured values. After the initial calculation, starting from the moment the initial calculation is completed, once the accumulated monitoring data period reaches 14 days, the regression coefficients are recalculated every 24 hours using the monitoring data from the 7 days most recent to the current moment, achieving dynamic updates to track changes in the mechanical properties of the soil and rock.

[0064] During the subsequent determination of frost heave stability, a verification operation is performed simultaneously: based on real-time monitoring. F 1. F 2. F 3. Using the latest regression coefficients, calculate the frost heave force to predict the axial force. .Will P pred Axial force monitored in real time by anchor cable force gauge P Compare the two and calculate the average relative deviation over a continuous 24 hours. ,in N This represents the number of sampling points within 24 hours. When... δ When the frost heave is ≤15%, the anchor cable dynamometer data is considered reliable, and the frost heave stability assessment can continue; when δ When the value is greater than 15%, it is determined that the anchor cable force gauge may have zero-point drift or that there is bond slip between the soil and the anchor cable. At this time, the original frost heave stability determination is suspended and the compensation tensioning procedure is started.

[0065] The compensation tensioning procedure aims to restore the prestress in the anchor cable and re-establish a reliable stress state. The compensation tension force is 1.05-1.10 times the design locking tension force. The tensioning jack is reinstalled on the anchor cable tensioning end, ensuring the jack axis coincides with the anchor cable hole axis. Tensioning is performed in stages, with the compensation tension force applied in three to five stages, each stage having an equal increase in tension force. After each stage reaches the target value, the pressure is stabilized for 5-10 minutes. After all tensioning is completed and stabilized, the working anchor is locked, and the anchor cable axial force after compensation tensioning is recorded as the new initial tension force reference value. After compensation tensioning is completed, the current time is reset to the new monitoring zero point, and the judgments for conditions 1 to 4 in S6 are restarted based on this zero point.

[0066] If the average relative deviation is recalculated within 24 hours after the compensation tension is completed, δ If the frost heave force and axial force data still exceed 15%, a re-evaluation procedure is initiated: the moment when the compensation tensioning is completed and locked is set as the new zero point. Starting from the new zero point, frost heave force and axial force data are collected again for at least 7 days, a new regression model is established, and the frost heave stability determination is re-executed based on the new data. If conditions 1 to 4 are not fully met after two consecutive re-executions of the S6 determination, the anchoring system is determined to have irreversible damage, and engineering treatment is required by installing additional anchor cables or grouting reinforcement.

[0067] Through the above steps, this method introduces multi-depth frost heave force monitoring as an independent reference, establishes a correlation model between frost heave force and axial force, can effectively identify anomalies in anchor cable force gauges or slippage in the anchoring system, and corrects them in a timely manner through compensation tension, ensuring the accuracy of frost heave stability determination and avoiding the risk of misjudgment caused by sensor failure or soil deformation.

[0068] It's important to note that the principle behind compensatory tensioning to correct sensor drift is not to repair the sensor itself, but rather to re-establish the correspondence between the actual stress state of the anchor cable and the sensor readings through re-tensioning. When a sensor experiences zero-point drift, its readings have a fixed deviation, but the sensor's sensitivity to changes in force usually remains normal. Compensatory tensioning adjusts the anchor cable prestress to near the design value, allowing the sensor to operate at the new stress point, and simultaneously re-recording the reading at that point as a new reference value, thus eliminating the influence of the original zero-point drift. The rate of change of axial force is then monitored based on this new reference value. dP / dt It can accurately reflect changes in stress, thus restoring the frost heave stability assessment to normal.

[0069] Example 2 (Sensor drift, but with deviation verification mechanism) In a slope reinforcement project in a high-altitude, cold region, another prestressed anchor cable with the same design parameters as Example 1 was designed with a locking tension of 600 kN. This anchor cable was constructed concurrently with the one in Example 1, and its location had identical topographical, geological, and sunlight conditions. The difference from Example 1 was that the anchor cable dynamometer experienced zero-point drift on day 22. After completing steps S1 to S5, the frost heave force monitoring and deviation verification steps added to this method were followed.

[0070] Three holes with depths of 30cm, 60cm, and 90cm were drilled in the soil surrounding the anchor cable borehole, with an angle of 120° between adjacent holes. A miniature earth pressure sensor was embedded at the bottom of each hole, with the sensing surface facing the axis of the anchor cable borehole. The sensor leads were led to the ground surface using armored cables, which were then sheathed in polyethylene conduits. The horizontal frost heave force was continuously monitored using the three miniature earth pressure sensors. F 1.F 2. F 3. Simultaneously, the axial force of the anchor cable is continuously monitored using an anchor cable dynamometer. P The sampling frequency was set to 0.5Hz.

[0071] After collecting data continuously for 10 days, with F 1. F 2. F 3 is the independent variable. P Using the frost heave force as the dependent variable, a multiple linear regression model was established using the least squares method to fit the data and obtain the regression coefficients. a 1 = 0.31 a 2 = 0.46 a 3 = 0.22 b =11.2, model goodness of fit R 2 =0.94. The regression coefficients are then recalculated every 24 hours using the latest 7-day data, achieving dynamic updates.

[0072] During the subsequent frost heave stability assessment, deviation monitoring was conducted simultaneously. On day 22, the axial force measured by the anchor cable dynamometer was recorded. P The displayed value is 580kN, while the real-time monitoring data shows... F 1 = 200kN F 2 = 170kN F Substituting 3=140kN into the current regression model, the predicted axial force is calculated. P pred =0.31×200+0.46×170+0.22×140+11.2=62+78.2+30.8+11.2=182.2kN. P pred Axial force monitored in real time by anchor cable force gauge P Comparing the values ​​of 580kN and calculating the average relative deviation of the two over a continuous 24-hour period. δ The rate reached 68.6%, far exceeding the 15% threshold. Based on this, it was determined that the anchor cable force gauge had zero-point drift, the frost heave stability assessment was suspended, and the compensation tensioning procedure was initiated.

[0073] The compensating tension was set at 1.08 times the design locking tension value of 600kN, i.e., 648kN. The tensioning jack was reinstalled on the anchor cable tensioning end, ensuring axis alignment. Compensating tensioning was performed in four stages, with each stage increasing the tension by 162kN, sequentially reaching 162kN, 324kN, 486kN, and 648kN. After each stage reached the target value, the tension was stabilized for 8 minutes. After completing all tensioning and stabilization, the working anchor was locked, and the axial force of the anchor cable after compensating tensioning was recorded as 647kN. This compensating tensioning re-established the anchor cable's stress state, allowing the sensor to operate at the new stress point and eliminating the influence of the original zero-point drift.

[0074] After the tensioning compensation is completed, deviation monitoring resumes. The average relative deviation is recalculated over a continuous 24-hour period from day 23 to day 24. δ The value was 4.9%, less than 15%, indicating that the anchor cable's stress state had returned to normal. Subsequently, frost heave stability was assessed according to four conditions. Compensatory tensioning not only corrected data deviations caused by sensor drift but also helped eliminate minor gaps in the anchorage section that might have been caused by previous frost heave cycles, thus optimizing the anchor cable's stress state. On day 24, dP / dt The change from positive to negative occurred synchronously with Example 1. On the 30th day... R The value reached its peak and then began to decline on day 35. d 2 R / dt 2 The value changed from negative to positive on day 38, and all four conditions were met, indicating that the frost heave was stable. Subsequently, S7 to S9 protective measures were implemented, using the same process as in Example 1.

[0075] On the 40th day after tensioning and locking, the same severe cooling as in Example 1 occurred, with the temperature dropping to -18°C. Observational data showed that during this cooling process, the anchor cable axial force only briefly increased from 621kN to 622kN, a change of only 1kN, a 67% decrease compared to the 3kN in Example 1. Throughout the 6-month observation period, the anchor cable axial force remained stable between 620kN and 632kN, with a difference of 12kN between the maximum and minimum values, a 33% decrease compared to the 18kN in Example 1. At the end of the 6-month period, the anchor cable prestress was tested, and the measured value was 625kN. The initial value after compensation tensioning was 647kN, and the prestress retention rate was 625 / 647×100%=96.6%, an increase of 0.6 percentage points compared to 96.0% in Example 1. At the end of the 6-month period, the sealant at the end of the sheath and the exposed section of the anchor cable were inspected, and no cracks or corrosion were found.

[0076] Comparison of effects: Example 1 demonstrates that, under normal sensor operation, the basic method of this invention can accurately determine the timing of frost heave stabilization, successfully complete construction, and achieve good long-term performance—the axial force fluctuation was 3kN on the 40th day after the tensioning and locking date, the axial force fluctuation range was 18kN after 6 months, the prestress retention rate was 96.0% after 6 months, and the protective layer remained intact at the end of 6 months.

[0077] Example 2 demonstrates the value of the added frost heave monitoring and deviation verification mechanism under adverse conditions of sensor zero-point drift: by timely identifying anomalies and performing compensatory tensioning, the compensatory tensioning successfully corrected the data deviation caused by sensor drift, restoring the anchor cable axial force monitoring to normal. Simultaneously, the re-tensioning helps eliminate minor gaps in the anchorage section that may have been caused by previous frost heave cycles, optimizing the stress state of the anchor cable. Ultimately, its long-term monitoring data (axial force fluctuation range 12kN, prestress retention rate 96.6%) is essentially equivalent to that of Example 1 (fluctuation range 18kN, retention rate 96.0%), both at excellent levels. This indicates that the deviation verification and compensatory tensioning mechanism of the present invention can effectively cope with abnormal sensor conditions, ensuring that the anchor cable performance is restored to the normal design level.

[0078] Comparative Example 1 and Example 1 were located in the same engineering area, with consistent geological conditions, anchor cable parameters, and construction techniques. Monitoring data showed that after protective construction was carried out on day 30, a sharp drop in temperature on day 40 caused a significant fluctuation in axial force, reaching 36 kN, far exceeding the 3 kN in Example 1. Damage to the protective layer was also observed on day 100. Although anchor cable performance in actual engineering is affected by a combination of factors, this comparative result strongly demonstrates that carrying out protective construction before the frost heave effect has fully stabilized significantly increases the risk of subsequent environmental disturbances to the anchor cable. Therefore, using the precise determination method of this invention to determine the timing of protection is of great value in ensuring the long-term safety of anchor cables.

[0079] The three sets of comparisons demonstrate that the basic method in Example 1 can accurately determine the timing of frost heave stabilization, avoiding the risk of premature construction. The frost heave force monitoring and deviation verification mechanism added in Example 2 further enhances the method's fault tolerance, enabling it to identify and promptly correct problems under abnormal sensor conditions, ensuring the anchor cable performance returns to normal levels and improving the reliability and engineering applicability of the technical solution. This is precisely the core value of Example 2.

[0080] In another approach, the integrated construction method for prestressed anchor cable tensioning and protection of slopes in high-altitude and cold regions involves simultaneously monitoring the absolute value of the temperature change rate during the S6 determination process. dT / dt |, when| dT / dt When |≥0.01℃ / h, perform a comprehensive judgment based on all conditions in S6 (conditions 1 to 4); when | dT / dt When | < 0.01℃ / h, pause all conditions in S6 and instead execute the following frost heave stability determination steps: Step a, continuously collect horizontal frost heave force at a depth of 30cm. F 1. Horizontal frost heave force at a depth of 60cm F 2 and 90cm depth horizontal frost heave force F3. For the data, the data acquisition frequency should not be less than 0.5Hz; in step b, using 72h as a time window, calculate the difference between the maximum and minimum values ​​of each frost heave force data within that window, and obtain Δ... F 1. △ F 2 and △ F 3; Step c, calculate the average value of each frost heave force data within the window, and obtain the following: F 1avg , F 2avg and F 3avg Step d, when △ is satisfied simultaneously F 1≤0.05 F 1avg , △ F 2≤0.05 F 2avg and △ F 3≤0.05 F 3avg When the frost heave of the surrounding soil and rock mass is determined to have reached a stable attenuation stage, proceed to step S7 and subsequent steps; in step e, if any condition in step d is not met, it is determined that the frost heave has not yet stabilized, and monitoring continues until the above conditions are met before proceeding to step S7; in step f, when | dT / dt When the temperature rises to ≥0.01℃ / h, resume all conditions in S6 and re-determine the frost heave stability based on real-time monitoring data.

[0081] In the construction of prestressed anchor cables on slopes in high-altitude and cold regions, the ratio of axial force change rate to temperature change rate is used as a basis for... R The method for determining the stability of frost heave and its derivatives will lead to problems when the rate of temperature change is extremely small, as the denominator approaches zero. R The drastic fluctuations in values ​​render subsequent determinations for conditions 2, 3, and 4 unreliable. This numerical instability can lead to misjudgments or delays in determining the stable state of frost heave; for example, during periods of stable temperature, even if frost heave has stabilized, R The value may also fluctuate abnormally due to slight temperature variations, causing construction workers to mistakenly believe that it has not yet stabilized and continue to wait, thus affecting the construction period. To address this technical challenge, this method, based on the previously established multi-depth frost heave force monitoring, further introduces a temperature change rate threshold triggering mechanism. When the temperature change rate is extremely small, it switches to direct stability determination based on measured frost heave force data, thereby compensating for the blind spots of the original determination logic.

[0082] This method simultaneously monitors the absolute value of the rate of temperature change during the frost heave stability determination process. dT / dt |。When| dT / dt When |≥0.01℃ / h, perform a comprehensive judgment based on all conditions in S6; when| dT / dt When | < 0.01℃ / h, suspend all conditions in the original judgment and instead execute the following frost heave stability judgment steps. Step a, continuously collect horizontal frost heave force at a depth of 30cm. F 1. Horizontal frost heave force at a depth of 60cm F 2 and 90cm depth horizontal frost heave force F For step 3, the data acquisition frequency should be no less than 0.5Hz to ensure that subtle fluctuations in frost heave force can be captured. Step b: Using a 72-hour time window, calculate the difference between the maximum and minimum values ​​of each frost heave force data point within that window, and obtain Δ... F 1. △ F 2 and △ F 3. The 72-hour window length is sufficient to eliminate short-term random fluctuations and reflect the true range of change in frost heave force. Step c: Calculate the average value of each frost heave force data within this window, and obtain... F 1avg , F 2avg and F 3avg Step d, when △ is satisfied simultaneously F 1≤0.05 F 1avg , △ F 2≤0.05 F 2avg and △ F 3≤0.05 F 3avg When the frost heave of the surrounding soil and rock mass is determined to have reached a stable attenuation stage, subsequent protective construction continues. A threshold of 0.05 indicates that the fluctuation range of the frost heave force does not exceed 5% of the average value, which is a small fluctuation range, indicating that the frost heave force has basically stabilized. For example, if the average frost heave force at a certain depth is 200kN, then its fluctuation range should be less than 10kN. Step e: If any condition in step d is not met, it is determined that the frost heave effect has not yet stabilized, and monitoring continues until the above conditions are met before construction proceeds. Step f: When | dT / dt When the temperature rises to ≥0.01℃ / h, all conditions in the original judgment are restored, and the frost heave stability judgment is re-performed based on real-time monitoring data. This mechanism achieves environmental adaptive switching of the judgment logic, avoiding numerical instability when the temperature change rate is extremely small, and making full use of the data from the already embedded frost heave force sensors. It requires no additional hardware and is simple and efficient.

[0083] Example 3 (Sensor is normal, encountering a period of stable temperature, threshold switching mechanism is activated) Another anchor cable on the same slope, using the exact same construction parameters as in Example 1, functioned normally with the anchor cable dynamometer, without any zero-point drift. This anchor cable, based on Example 1, added frost heave force monitoring and deviation verification steps, as well as a temperature change rate threshold switching mechanism, thus possessing both the frost heave force monitoring system of Example 2 and the threshold switching function of Example 3.

[0084] Three holes with depths of 30cm, 60cm, and 90cm were drilled in the soil and rock surrounding the anchor cable borehole. The horizontal angle between adjacent holes was 120°. A miniature earth pressure sensor was embedded at the bottom of each hole, with the sensing surface facing the axis of the anchor cable borehole. The horizontal frost heave force was continuously monitored using the three miniature earth pressure sensors. F 1. F 2. F 3. Simultaneously, the axial force of the anchor cable is continuously monitored using an anchor cable dynamometer. P The sampling frequency was set to 0.5Hz. After collecting data continuously for 10 days, a frost heave force-axial force regression model was established to achieve dynamic updates.

[0085] From day 20 to day 34 after the tensioning and locking, the area experienced continuous cloudy weather with stable temperatures and a temperature change rate of | dT / dt |Continued below 0.01℃ / h. At this time, conditions 2, 3, and 4 in the original judgment are no longer valid. R The value fluctuates drastically and cannot be used reliably. According to the threshold switching mechanism, the original judgment is paused and the frost heave stability judgment step is started.

[0086] Continuous data collection was performed within a 72-hour window from day 31 to day 34. F 1. F 2. F 3. Data. F 1. The maximum value within 72 hours is 202 kN, and the minimum value is 198 kN. △ F 1 = 4kN, average value F 1avg =200kN, △ F 1 / F 1avg =2.0% is less than 5%. F 2. The maximum value is 172kN, and the minimum value is 168kN. △ F 2 = 4kN, average value F 2avg =170kN, Δ F 2 / F 2avg =2.4% is less than 5%. F 3. The maximum value is 146kN, and the minimum value is 143kN. △ F 3 = 3kN, average value F3avg =144.5kN, Δ F 3 / F 3avg =2.1% is less than 5%. The simultaneous fulfillment of all three conditions indicates that the frost heave of the surrounding soil and rock has reached a stable attenuation stage.

[0087] 35th day, although | dT / dt The temperature was still less than 0.01℃ / h, but based on the frost heave force assessment results, it was determined that the frost heave had reached a stable level. Subsequently, protective construction was carried out, and the process was the same as in Example 1.

[0088] If the threshold switching mechanism is not enabled (i.e., only the frost heave monitoring system of Example 2 is available but threshold switching is not enabled), then because R If conditions 3 and 4 cannot be met for an extended period, we can only wait for the temperature change rate to recover. Based on the actual monitoring data in this embodiment, it is estimated that the temperature remained stable from day 35 to day 37. R Value determination could not be performed; it was not until the temperature began to fluctuate on the 37th day. R Value determination can only be restored after this process. If the threshold switching mechanism is not enabled, it will take time. R If the value is restored and all four conditions are met, the construction time will be delayed by approximately 3 days. Therefore, the threshold switching mechanism advances the construction time by approximately 3 days, effectively avoiding delays caused by the temperature stabilization period.

[0089] Post-construction observation: On the 40th day, when the temperature dropped sharply to -18℃, the axial force of the anchor cable briefly increased from 621kN to 622kN, a change of 1kN; throughout the 6-month observation period, the axial force of the anchor cable remained stable between 620kN and 631kN, with a difference of 11kN between the maximum and minimum values; at the end of the 6 months, the prestress retention rate was 96.5%, and the protective layer was intact.

[0090] Comparison of effects: Example 1 demonstrates the operation of the sensor under normal working conditions and without special weather conditions, according to the original... R The value determination process was carried out on the 38th day of construction, and good long-term performance was achieved: the axial force fluctuation was 3kN on the 40th day of cooling, the fluctuation was 18kN after 6 months, and the prestress retention rate was 96.0%.

[0091] Example 2 demonstrates that when the sensor experiences zero-point drift, the deviation verification mechanism can promptly identify the anomaly and perform compensatory tensioning. Construction was ultimately carried out on the 38th day, with the same results as in Example 1, proving the method's fault tolerance capability.

[0092] Example 3 uses the same sensor operating conditions as Example 1, but adds a frost heave monitoring system and a threshold switching mechanism to the system described in Example 1. When encountering a period of stable temperature, the original... RWhile the threshold determination method was unusable, the threshold switching mechanism directly determined the frost heave stability time on day 35, 3 days earlier than in Example 1, thus avoiding delays caused by waiting for the temperature change rate to recover. Simultaneously, the earlier completion of protective construction reduced the impact of subsequent temperature fluctuations on the anchor cables. The core value of Example 3 lies in demonstrating that the threshold switching mechanism can solve the problem of the original temperature stabilization period. R To address the issue of value determination failure and ensure the continuity of the determination process, this embodiment directly determines the value based on frost heave force. In this example, frost heave stability was confirmed and construction completed on day 35, which is more efficient than simply relying on... R The theoretical waiting time for value determination (day 38) was advanced by 3 days, effectively shortening the construction period. The observed axial force fluctuation was 1 kN, which is excellent, similar to the 3 kN in Example 1, with minor differences within the normal fluctuation range for engineering projects. The core value of this example lies in demonstrating that the threshold switching mechanism can solve the problem of temperature stabilization during the original... R To address the issue of value determination failure, ensure the continuity of the determination process.

[0093] The comparison of the three sets of embodiments shows that: Embodiment 1 serves as the baseline scheme, proving the effectiveness of the basic judgment method; Embodiment 2 demonstrates the fault tolerance capability of the deviation verification mechanism; and Embodiment 3, based on Embodiment 1, adds a threshold switching mechanism, demonstrating the timeliness improvement and performance optimization brought by this mechanism under special weather conditions. The three embodiments progressively demonstrate the adaptability and superiority of the technical solution of this invention under different working conditions.

[0094] In another embodiment, in the integrated construction method for prestressed anchor cable tensioning and protection of slopes in cold regions, the cement-based grout in S2 is a low-temperature early-strength cement-based grout, composed of the following components by weight: 100 parts of G-grade oil well cement, 32-45 parts of water, 3-5 parts of calcium formate, 1-2 parts of triethanolamine, and 1-3 parts of sodium nitrite; before grouting, a composite mineral admixture is added to the cement-based grout, which is composed of the following components by weight: 60-80 parts of slag powder, 10-20 parts of nano-silica, and 5-15 parts of anhydrous calcium sulfoaluminate; wherein, the specific surface area of ​​the slag powder is ≥600 m². 2 / kg, D90≤30μm; nano-silica with a particle size of 10-30nm and a specific surface area ≥200 m² 2 / g; Based on 100 parts by weight of G-grade oil well cement, the amount of composite mineral admixture is 8-15 parts by weight; The method of adding composite mineral admixture is as follows: Add it to the cement-based grout 5-10 minutes before the start of grouting and stir, with a stirring speed of not less than 1200 r / min and a stirring time of 3-5 minutes; The grouting adopts the bottom return grouting method, with a return grouting flow rate of 20-50 L / min until the grout that is consistent with the grouting grout overflows from the anchor cable hole, and then stop. After grouting is completed, it can be cured for 5 days before subsequent tensioning operations can be carried out.

[0095] In the construction of prestressed anchor cables on slopes in high-altitude and cold regions, the quality of the cement-based grout injection in the anchoring section directly affects the bearing capacity and long-term stability of the anchor cable. Conventional cement-based grouts undergo slow hydration reactions and significantly prolonged setting times in low-temperature environments, resulting in insufficient early strength development. This leads to the anchoring section failing to provide sufficient anchoring force in a timely manner, forcing subsequent tensioning operations to be postponed until the grout strength reaches the required standard. For example, the P.O42.5 ordinary silicate cement grout used in Example 1, despite the addition of early-strength antifreeze components such as sodium nitrite and triethanolamine, still requires 7 days of curing to reach 85% of its design strength. Furthermore, high-altitude and cold regions have frigid climates. According to building climate zoning, the average January temperature in severely cold regions can reach -31 to -10℃, with extreme minimum temperatures generally below -35℃. For example, Maduo County in Qinghai Province, at an altitude of 4300m, has an average annual temperature of -4.1℃, an average January temperature of -16.8℃, and an extreme minimum temperature of -48.1℃; Tashkurgan County in Xinjiang has an average annual temperature of 3.7℃, with a minimum temperature reaching -43℃. In such low-temperature environments, the curing time of conventional cement grout will be further extended, and the effective construction window will be extremely limited. To address this technical challenge, this method uses a low-temperature, early-strength cement-based grout. By optimizing the material composition and grouting process, the hydration reaction is accelerated under low-temperature conditions, significantly shortening the curing time and improving construction efficiency.

[0096] In this method, step S2 uses a low-temperature early-strength cement-based grout, which consists of the following components by weight: 100 parts of Grade G oil well cement, 32-45 parts of water, 3-5 parts of calcium formate, 1-2 parts of triethanolamine, and 1-3 parts of sodium nitrite. Grade G oil well cement has good low-temperature hydration performance, and its mineral composition is suitable for hydration under low-temperature conditions. Calcium formate, as an early-strength agent, can accelerate the cement hydration reaction and promote early strength development. Triethanolamine, as a grinding aid and early-strength accelerator, can improve the dispersibility of cement particles and accelerate the hydration process. Sodium nitrite, as an antifreeze agent, can lower the freezing point of the grout and prevent the grout from being damaged by freezing before hardening. Before grouting, a composite mineral admixture is added to the cement-based grout. This admixture consists of 60-80 parts of slag powder, 10-20 parts of nano-silica, and 5-15 parts of anhydrous calcium sulfoaluminate by weight. Slag powder possesses pozzolanic activity, enabling it to undergo a secondary reaction with calcium hydroxide, a cement hydration product, to form hydrated calcium silicate gel, filling the pores of cement stone. Nano-silica exhibits extremely high specific surface area and pozzolanic activity, significantly promoting early hydration and reacting with calcium hydroxide to form additional gel. Anhydrous calcium sulfoaluminate can react with aluminates and sulfates in cement to form ettringite, providing an early strength skeleton. Based on 100 parts by weight of Grade G oil well cement, the dosage of composite mineral admixtures is 8-15 parts by weight.

[0097] The composite mineral admixture is added to the cement-based grout 5-10 minutes before grouting begins and stirred using a high-speed shear mixer at a speed of no less than 1200 r / min for 3-5 minutes. High-speed stirring ensures thorough dispersion of the ultrafine particles, preventing agglomeration and maximizing its active effect. Grouting employs the bottom-return grouting method, with a return flow rate of 20-50 L / min until grout of the anchor cable hole overflows, consistent with the grouting grout. This bottom-return grouting method ensures uniform filling from the bottom of the hole upwards, expelling air and water from the hole and preventing voids or segregation. Due to the low-temperature early-strength characteristics of this grout, the curing time is significantly shorter than that of conventional grouts under cold climate conditions.

[0098] Example 4 In a slope reinforcement project in a high-altitude cold region, a prestressed anchor cable with the same design parameters as in Example 1 was designed with a locking tension of 600 kN. This anchor cable was constructed according to the method in Example 1, i.e., frost heave stability was determined using four conditions, and the anchor cable dynamometer functioned normally. The difference from Example 1 is that, in step S2, the low-temperature early-strength cement-based grout used in this method was employed.

[0099] The project site is located at an altitude of approximately 3500m, in a typical high-altitude cold climate zone, with an average annual temperature of -2℃, an average January temperature of -18℃, and an extreme minimum temperature reaching -35℃. The S2 slurry mix ratio is: 100 parts G-grade oil well cement, 38 parts water, 4 parts calcium formate, 1.5 parts triethanolamine, and 2 parts sodium nitrite. The composite mineral admixture, by weight, consists of 70 parts slag powder, 15 parts nano-silica, and 10 parts anhydrous calcium sulfoaluminate, wherein the slag powder has a specific surface area ≥600 m². 2 / kg, D90≤30μm; nano-silica with a particle size of 10-30nm and a specific surface area ≥200 m² 2 / g; Based on 100 parts by weight of G-grade oil well cement, the amount of composite mineral admixture is 12 parts. Add it to the cement-based grout 8 minutes before the start of grouting and stir at 1500 r / min for 4 minutes. Grouting adopts the bottom-of-hole grout return method, with a return flow rate of 35 L / min, stopping when uniform grout overflows from the borehole opening. After grouting, it is cured for 5 days under natural climatic conditions in a high-altitude cold region, during which the average daily temperature is -15 to -10℃ and the lowest nighttime temperature is -30℃. Testing shows that the stone body strength reaches 85% of the design strength, meeting the tension requirements. In Example 1, using P.O42.5 ordinary silicate cement grout, it requires 7 days of curing under the same climatic conditions to reach 85% of the design strength.

[0100] S3 Install anchor cable force gauge; S4 Perform graded tensioning, and record the anchor cable axial force as 646kN at the moment of locking; S5 Install temperature sensor; S6 Determine frost heave stability based on four conditions, and the monitoring data is basically consistent with Example 1: Day 24 dP / dt From positive to negative, on the 30th day R The value reached its peak on the 35th day. d 2 R / dt 2 The value changed from negative to positive. All four conditions were met on the 38th day. The frost heave was determined to be stable and protective construction was carried out. The process was the same as in Example 1.

[0101] On the 40th day after tensioning and locking, the same severe cooling as in Example 1 occurred, with the temperature dropping to -18°C. Observational data showed that during this cooling process, the anchor cable axial force briefly increased from 620kN to 623kN, a change of 3kN, the same as in Example 1. Throughout the 6-month observation period, the anchor cable axial force remained stable between 615-633kN, with a difference of 18kN between the maximum and minimum values. At the end of the 6-month period, the prestress of the anchor cable was tested, and the measured value was 620kN, while the initial locking value was 646kN. The prestress retention rate was 620 / 646 × 100% = 96.0%, the same as 96.0% in Example 1. At the end of the 6-month period, the sealant at the end of the sheath and the exposed section of the anchor cable were inspected, and no cracks or corrosion were found.

[0102] Comparison of effects: Example 1 uses P.O42.5 ordinary silicate cement grout, which requires 7 days of curing under cold climate conditions to reach 85% of the design strength before tensioning. Example 4 uses the low-temperature early-strength cement-based grout of this method, which only requires 5 days of curing under the same cold climate conditions to reach the strength required for tensioning, shortening the curing time by 2 days and improving construction efficiency. In terms of long-term performance, the anchor cable of Example 4 is completely equivalent to that of Example 1: the axial force fluctuation range at the same strength and temperature drop on day 40 is 3kN, the axial force fluctuation range within the 6-month observation period is 18kN, and the prestress retention rate after 6 months is 96.0%. This shows that the low-temperature early-strength cement-based grout can maintain long-term performance comparable to conventional grouts while shortening the curing time. This grout formulation, through the synergistic effect of multiple components, accelerates the hydration reaction under low-temperature conditions in cold regions without sacrificing later strength, effectively solving the contradiction between long curing time and short construction window in anchor cable construction in cold regions.

[0103] In another scheme, in the integrated construction method of prestressed anchor cable tensioning and protection for slopes in high-altitude and cold regions, tensioning in S4 is graded tensioning, including initial tensioning, intermediate tensioning and final tensioning. The initial tension force is 10%-20% of the design locking tension force value and is held for 5-15 minutes. The intermediate tensioning is divided into three to five levels, starting from the tension force after the initial tensioning ends. The increase in tension force at each level is 15%-25% of the design locking tension force value, and each level is held for 8-20 minutes. The final tensioning reaches 1.05-1.10 times the design locking tension force value and is then locked.

[0104] In the construction of prestressed anchor cables for slopes in high-altitude and cold regions, the quality of anchor cable tensioning and locking directly affects the long-term stability of the anchoring effect. Conventional tensioning methods often involve tensioning to the design load in one go and then locking directly. This operation easily leads to uneven stress distribution among the steel strands of the anchor cable, concentrated shear stress distribution in the anchoring section, and significant prestress loss in the short term after tensioning and locking. Engineering practice shows that debonding and slippage at the front end of the anchor cable is an important cause of initial tensioning and locking loss. Applying the tension load too quickly or holding it for too short a time will prevent the prestress loss caused by ground creep from being fully released, resulting in the actual prestress of the anchor cable after locking being lower than the design locking value, thus affecting the slope reinforcement effect. To address this technical challenge, this method adopts a staged tensioning process, applying prestress gradually through three stages: initial tensioning, intermediate tensioning, and final tensioning, combined with sufficient holding time. This ensures close contact and uniform stress distribution among the anchor cable components, allowing for full development of ground deformation, thereby effectively controlling prestress loss and ensuring stable and reliable axial force of the anchor cable after locking.

[0105] In this method, step S4 employs graded tensioning, including initial tensioning, intermediate tensioning, and final tensioning. The initial tension force is 10%-20% of the design locking tension value, held for 5-15 minutes. The purpose of initial tensioning is to gradually tighten the anchor cable from a relaxed state, eliminate initial relaxation differences between the steel strands, ensure uniform initial stress on each strand, and simultaneously ensure the working anchor, wedges, and other components are properly positioned and secured. The design locking tension value refers to the prestress value that the anchor cable must ultimately maintain according to design requirements. For example, if the design locking tension is 600kN, then the initial tension force is 90-120kN. Holding the load for 5-15 minutes allows the anchor cable to initially stabilize under low stress, laying the foundation for subsequent tensioning.

[0106] Intermediate tensioning is divided into three to five stages, starting from the tension force after the initial tensioning. Each stage increases the tension force by 15%-25% of the design locking tension value, with each stage held for 8-20 minutes. Intermediate tensioning is the core stage of applying prestress in stages. By gradually increasing the load, the shear stress in the anchorage section of the anchor cable is gradually transferred to the deeper layers, avoiding stress concentration at the front end of the anchorage section due to excessive loading at once, which could lead to debonding and slippage. For example, if the design locking tension is 600 kN, intermediate tensioning can be carried out in four stages, increasing by 120-150 kN each stage, sequentially reaching 210 kN, 330 kN, 450 kN, and 570 kN. Holding each stage for 8-20 minutes allows the strata to deform sufficiently under each load, releasing prestress loss caused by ground creep during the tensioning process, rather than waiting until locking. This gradual loading and stabilization method significantly improves the shear stress distribution on the anchorage body and reduces the initial loss rate.

[0107] The final tensioning is achieved by reaching 1.05-1.10 times the design locking tension value before locking. Over-tensioning is used in the final tensioning process, with an over-tensioning ratio of 1.05-1.10 times to compensate for prestress losses caused by wedge retraction and strand slack during the tensioning and locking process. For example, if the design locking tension is 600kN, the final tensioning is increased to 630kN to 660kN, and then locked after holding and stabilizing the load. After locking, the anchor cable axial force returns to near the design locking value. The selection of the over-tensioning range needs to comprehensively consider factors such as the strand material, anchor performance, and geological conditions. It should not be too small, resulting in insufficient compensation, nor too large, causing anchor cable damage or geological disruption.

[0108] Through the above-mentioned graded tensioning process, this method achieves precise control of the anchor cable prestress, making the anchor cable more uniformly stressed, allowing the stratum deformation to develop fully, effectively reducing the prestress loss after tensioning and locking, and ensuring the long-term stable working state of the anchor cable.

[0109] Effects Description: Compared to direct locking after a single tensioning to the design load, the staged tensioning process offers the following advantages: First, by initially tensioning and gradually loading, the initial relaxation differences between steel strands are eliminated, ensuring uniform stress on each strand and preventing overloading or relaxation of individual strands due to uneven stress. Second, holding each load for 8-20 minutes allows the stratum to fully deform under each load, releasing prestress losses caused by stratum creep during tensioning and reducing prestress losses after locking. Third, locking after a final overtension of 1.05-1.10 times effectively compensates for losses caused by factors such as wedge retraction and steel strand relaxation, resulting in an anchor cable axial force closer to the design locking value after locking. Fourth, staged tensioning leads to a more reasonable distribution of shear stress in the anchorage section, preventing debonding and slippage at the anchorage front due to stress concentration and improving the long-term stability of the anchorage system. Therefore, this method significantly improves the quality of anchor cable tensioning and locking through graded tensioning and appropriate load holding, providing a reliable prestressed foundation for subsequent frost heave stability assessment and protective construction.

[0110] In another embodiment, in the integrated construction method of prestressed anchor cable tensioning and protection for slopes in high-altitude and cold regions, the temperature sensor in S5 is embedded in the soil and rock at the edge of the anchor cable hole opening to a depth of 10-30cm. The embedding method is as follows: drill a hole with a diameter of 30-50mm and a depth of 10-30cm at the edge of the anchor cable hole opening, place the temperature sensor at the bottom of the hole, fill the area around the temperature sensor with fine sand, and use armored cable to lead out the temperature sensor lead wire. The cable is covered with a polyethylene sheath, and the outlet of the sheath is sealed with waterproof sealant.

[0111] Step S5 of this method specifies the installation method of the temperature sensor. The temperature sensor is buried in the soil and rock at the edge of the anchor cable hole, at a depth of 10-30 cm. This depth range is selected based on the following considerations: if the burial is too shallow (less than 10 cm), the sensor is easily affected by surface air temperature fluctuations and solar radiation, resulting in overly drastic temperature changes that cannot represent the actual temperature of the soil and rock around the hole; if the burial is too deep (greater than 30 cm), the measured temperature changes are too delayed, inconsistent with the thermal response characteristics of the soil and rock near the anchor cable hole, and increase the drilling workload. A depth of 10-30 cm avoids strong surface interference, accurately reflects the temperature changes of the soil and rock around the hole, and matches the response characteristics of the anchor cable axial force to temperature changes.

[0112] The specific installation procedure is as follows: Drill holes with a diameter of 30-50mm and a depth of 10-30cm at the edge of the anchor cable hole. Place the temperature sensor at the bottom of the hole and fill the area around the sensor with fine sand. Fine sand has good thermal conductivity and is easy to compact, ensuring close contact between the sensor and the surrounding soil and rock, smooth heat conduction, and avoiding temperature measurement lag caused by air gaps. At the same time, fine sand has minimal volume change during freeze-thaw cycles, reducing pressure damage to the sensor. The temperature sensor lead is led out using an armored cable, with a polyethylene sheath. The outlet of the sheath is sealed with waterproof sealant. The armored cable has tensile, compressive, and bending resistance, effectively protecting the internal conductors from breakage during soil frost heave. The polyethylene sheath has good low-temperature resistance and corrosion resistance, further protecting the cable from abrasion by soil particles and water erosion. Sealing the outlet of the sheath with waterproof sealant prevents surface water from seeping into the hole along the cable, avoiding water accumulation and freezing damage to the sensor.

[0113] Through the above-mentioned burial method, the temperature sensor forms good thermal contact with the rock and soil, and the lead wire is protected by multiple layers, enabling it to work stably for a long time in harsh environments in high-altitude and cold regions and continuously collect reliable borehole ambient temperature data.

[0114] Results Description: This method optimizes the burial method of the temperature sensor. Compared with the conventional simple burial method, it has the following effects: First, the burial depth of 10-30cm allows the sensor to avoid strong surface temperature interference, enabling it to accurately reflect the temperature changes of the surrounding soil and rock, and to represent the temperature change rate. dT / dt First, the system provides accurate data for calculations. Second, the fine sand filling ensures close contact between the sensor and the soil, resulting in high heat transfer efficiency and timely temperature response, avoiding temperature lag caused by air gaps. Third, the multiple protective structures of the armored cable and polyethylene conduit effectively resist the pulling of the lead wire by soil frost heave, ensuring the sensor's continuous operation during long-term freeze-thaw cycles in cold regions. Fourth, waterproof sealant prevents moisture infiltration, avoiding water accumulation and freezing that could damage the sensor. These measures collectively guarantee the reliability and data accuracy of the temperature monitoring system, providing a solid data foundation for determining frost heave stability based on the rate of temperature change, thereby improving the stability and reliability of the entire construction method.

[0115] In another embodiment, in the integrated construction method of prestressed anchor cable tensioning and protection for slopes in high-altitude and cold regions, the protective coating in S7 includes a first protective coating and a second protective coating. The first protective coating is an epoxy zinc-rich primer with a coating thickness of 50-120μm, and the second protective coating is a polyurethane topcoat with a coating thickness of 60-150μm. The sheath in S8 is a polyethylene corrugated sheath with an inner diameter to outer diameter ratio of 1.2-1.6. The sealant is a flexible sealant with an elongation at break of ≥200% after curing at -40℃. Before injecting the flexible sealant, the sheath is preheated with an electric heating tape at 20-30℃ for 30-60 minutes to raise the temperature in the annular gap between the sheath and the prestressed anchor to above 5℃. Then, the flexible sealant is injected at a pressure of 0.2-0.6MPa using a dedicated pneumatic or electric plunger pump. The injection tube should be sealed to the injection port of the sheath. The injection time is 10-30 minutes until the annular gap is completely filled and flexible sealant overflows from both ends of the sheath.

[0116] In the construction of prestressed anchor cables on slopes in high-altitude and cold regions, the protective layer of the exposed section of the anchor cable is the last line of defense to ensure its long-term durability. Conventional protection methods often use a single coating or direct application of ordinary sealant, which is prone to cracking and debonding in low-temperature environments, leading to moisture infiltration and anchor cable corrosion. Furthermore, freeze-thaw cycles further exacerbate the damage to the protective layer. In addition, if the annular gap between the sheath and the anchor cable is not properly filled, it can easily become a channel for moisture intrusion. To address this technical challenge, this method specifically designs the material properties and construction process of the protective coating, sheath, and sealant. Through multi-layer composite protection, the selection of flexible sealant, and a preheated injection process, it ensures that the protective layer remains intact for a long time in harsh, cold environments.

[0117] In this method, step S7 specifies the protective coating: the protective coating consists of a first protective coating and a second protective coating. The first protective coating is an epoxy zinc-rich primer with a thickness of 50-120 μm; the second protective coating is a polyurethane topcoat with a thickness of 60-150 μm. The epoxy zinc-rich primer uses epoxy resin as a base material and adds a large amount of zinc powder, providing excellent cathodic protection. When the coating is partially damaged, the zinc powder preferentially sacrifices itself to protect the steel strand substrate. Simultaneously, this primer has strong adhesion and can form a firm bond with the surface of the steel strand. In practical engineering, solvent-free, low-temperature, fast-curing epoxy zinc-rich primer 1140 can be selected. This product is specifically designed for application in low-temperature winter environments, can be applied at around 5°C and dries quickly, has good coating adhesion, and is suitable for long-term rust prevention. Alternatively, TEKNOPLAST PRIMER 7 two-component solvent-based epoxy primer can be used. When applying at temperatures below 10°C, a special winter curing agent can be used to ensure curing effectiveness. Polyurethane topcoats possess excellent weather resistance, low-temperature resistance, and corrosion resistance, effectively resisting ultraviolet radiation, wind, snow, and freeze-thaw erosion. GritatopPU 882 acrylic polyurethane topcoat is a good option; this product can cure at temperatures as low as -10℃, exhibits excellent color and gloss retention, and is not prone to chalking, making it suitable as a long-lasting anti-corrosion topcoat for severely corrosive atmospheric environments. Alternatively, S04-1060 high-solids polyurethane topcoat can be selected; this product passed a -53℃ low-temperature impact test, showing no cracking or peeling of the film. The sum of the thicknesses of the two coating layers is typically controlled between 110-270μm, ensuring sufficient protection without being too thick and causing the coating to become brittle.

[0118] Step S8 specifies the materials and injection process for the sheath and sealant. The sheath is made of corrugated polyethylene, with the ratio of its inner diameter to the outer diameter of the prestressed anchor cable being 1.2-1.6. The corrugated polyethylene sheath has good flexibility and low-temperature resistance, allowing it to bend with slight deformation of the anchor cable without cracking due to low temperatures. The ratio of its inner diameter to the outer diameter of the anchor cable is between 1.2 and 1.6, ensuring that the sheath can be smoothly fitted into the anchor cable without excessive gaps leading to excessive sealant usage or incomplete filling.

[0119] The sealant is a flexible sealant with an elongation at break of ≥200% after curing at -40℃. This performance indicator ensures that the sealant maintains sufficient flexibility in extremely low temperature environments. When the anchor cable undergoes slight displacement due to temperature changes or load fluctuations, the sealant can stretch accordingly without cracking, thus preventing the formation of moisture penetration channels. JS-2000 weather-resistant silicone sealant can be selected. This product has an elongation at break greater than 200%, maintains good elasticity in environments ranging from -50℃ to 150℃ after curing, and has a displacement capacity of ±35%. It is suitable for weather-resistant and waterproof sealing of building curtain walls. Alternatively, SG305 polyurethane insulating sealant can be selected. This product has an elongation at break ≥200%, does not crack at -60℃, and can be used for a long time in environments ranging from -40℃ to 90℃. It also has good adhesion to various materials such as steel, concrete, and plastics. For projects with higher elasticity requirements, Huachishi QIS-5705 elastic sealant can be considered. This product has an elongation at break ≥200%, a temperature resistance range of -55℃ to 260℃, and is soft and elastic after curing. It is suitable for bonding and sealing plastic, metal, and non-metal materials.

[0120] Before injecting the flexible sealant, the sheath is preheated using an electric heating cable at 20-30℃ for 30-60 minutes, raising the temperature within the annular gap between the sheath and the prestressed anchor cable to above 5℃. Preheating increases the surface temperature of both the sheath and the anchor cable, preventing the sealant from becoming less fluid at low temperatures and ensuring the sealant fully fills every corner of the annular gap. Simultaneously, the increased temperature aids in the adhesion between the sealant and the substrate, reducing air bubble formation. A preheating temperature of 20-30℃ ensures the gap temperature reaches above 5℃ without being excessively high and causing deformation of the sheath.

[0121] After preheating, inject flexible sealant at a pressure of 0.2-0.6 MPa for 10-30 minutes until the annular gap is completely filled and sealant overflows from both ends of the sheath. Pressure injection ensures uniform distribution of the sealant within the gap, eliminates air, and prevents voids. Insufficient pressure may result in incomplete filling, while excessive pressure may cause the sheath to burst. Adjust the injection time according to the gap volume and injection speed, ensuring the gap is completely filled by sealant overflowing from both ends.

[0122] Through the above steps, this method forms a multi-layered protective system consisting of primer, topcoat, flexible sealant, and sheath. The layers work together to effectively resist adverse factors such as low temperature, freeze-thaw cycle, and ultraviolet radiation in cold regions.

[0123] Effects Description: Compared to conventional single-coat or ordinary sealant protection methods, the optimized design of the protective layer materials and processes in this method offers the following advantages: First, the double-coat structure combines the cathodic protection of the epoxy zinc-rich primer with the weather resistance of the polyurethane topcoat, significantly improving the corrosion resistance of the exposed section of the anchor cable. Second, the combination of the polyethylene corrugated sheath and flexible sealant can adapt to the minute displacements of the anchor cable under temperature changes and load fluctuations, preventing sealant cracking. Third, the sealant's elongation at break of ≥200% at -40℃ ensures that it maintains its flexibility at extreme low temperatures, fundamentally solving the problem of low-temperature brittleness. Fourth, the preheating and pressure injection process ensures a tight bond between the sealant, sheath, and anchor cable, with the annular gap completely filled, eliminating channels for moisture intrusion. These measures collectively guarantee the long-term reliability of the protective layer for the exposed section of the anchor cable, significantly extending the service life of the anchor cable in cold regions and reducing subsequent maintenance costs.

[0124] In another embodiment, in the integrated construction method of prestressed anchor cable tensioning and protection for slopes in cold regions, the winding spacing of the electric heating cable in S9 is 10-30cm, and the temperature of the sealant is maintained at 35-55℃ and cured for 45-90 minutes by electric heating.

[0125] In this method, step S9 specifies the heating parameters for the electric heating cable: the wrapping spacing of the electric heating cable is 10-30cm, and the temperature of the sealant is maintained at 35-55℃ by electric heating, with curing time of 45-90 minutes. A wrapping spacing of 10-30cm ensures uniform heating without causing localized overheating due to too small a spacing or insufficient heating due to too large a spacing. The heating temperature of 35-55℃ is determined based on the curing characteristics of the flexible sealant; too low a temperature results in slow and incomplete curing, while too high a temperature may cause sealant decomposition or deformation of the sheath. The heating time of 45-90 minutes needs to be adjusted according to the type of sealant, ambient temperature, and gap size to ensure complete curing of the sealant.

[0126] In another scheme, in the integrated construction method of prestressed anchor cable tensioning and protection for slopes in high-altitude and cold regions, after the heating and curing in S9 is completed, the electric heating cable is kept in a wrapped state, heating is stopped and the sealant is allowed to cool down naturally. During the cooling process, the change of tension force is continuously monitored by the anchor cable force gauge. A 10-minute sliding time window is taken as the sliding time window, and the difference between the maximum and minimum tension force in each sliding time window is calculated. When the difference between the maximum and minimum tension force in each sliding time window for three consecutive sliding time windows is divided by the design locking tension force value and is greater than 0.8%, it is determined that there is an adhesion defect in the protective layer. The electric heating cable is immediately restarted and heated to 40-50℃ and held at the temperature for 20-40 minutes for secondary curing. After the secondary curing is completed, the electric heating cable is removed.

[0127] Step S9 of this method specifies the monitoring and judgment of the cooling process. After heating and curing, keep the electric heating cable wrapped and stop heating to allow the sealant to cool naturally. Keeping the electric heating cable wrapped allows for restarting heating if needed, eliminating the need for reinstallation. During the cooling process, the tension change is continuously monitored using an anchor cable force gauge at a sampling frequency of not less than 0.5Hz. High-frequency sampling can capture instantaneous fluctuations in tension, providing detailed data for defect judgment.

[0128] A 10-minute sliding time window was used to calculate the difference between the maximum and minimum tension values ​​within each window. The sliding window refers to a time period 10 minutes prior to the current moment; the window slides forward with each new data point, enabling continuous monitoring. The 10-minute sliding time window length was chosen based on considerations of the sealant's cooling rate and stress release characteristics; a window that is too short would fail to reflect effective fluctuations, while a window that is too long would mask transient anomalies.

[0129] If the difference between the maximum and minimum tension values ​​within each of three consecutive sliding time windows, divided by the design locking tension value, is greater than 0.8%, then the protective layer is considered to have an adhesion defect. The design locking tension value refers to the prestress value that the anchor cable must ultimately maintain according to design requirements; for example, 600kN, then 0.8% corresponds to 4.8kN. That is, if the tension fluctuation range exceeds 4.8kN within each of three consecutive 10-minute sliding time windows, it indicates that uneven stress was generated during the sealant shrinkage process, which may lead to localized debonding from the anchor cable. The condition of three consecutive sliding time windows can eliminate single, accidental fluctuations and improve the reliability of the judgment.

[0130] Once an adhesion defect is identified, immediately restart the electric heating cable to 40-50℃ and hold this temperature for 20-40 minutes for secondary curing. The heating temperature of 40-50℃ is consistent with the initial curing temperature of 35-55℃, allowing the sealant to soften and flow again to fill the detached areas without deteriorating material properties due to excessive temperature. Holding the temperature for 20-40 minutes allows the sealant to fully flow in its softened state, penetrate the detachment gaps, and re-cures during the subsequent cooling process to form a complete bond. After the secondary curing is complete, remove the electric heating cable.

[0131] Through the aforementioned cooling monitoring and secondary curing mechanism, this method can automatically identify and repair bonding defects after the sealant has cured, ensuring that the protective layer and anchor cable form a reliable whole.

[0132] Effect Description: This method introduces real-time monitoring and a secondary curing mechanism during the cooling process. Compared to the conventional method of directly removing the electric heating cable after curing, it has the following advantages: First, continuous monitoring of tension changes using an anchor cable force gauge can capture stress fluctuations generated during sealant shrinkage, allowing for timely detection of bonding defects. Second, the 10-minute sliding window design allows for real-time tracking of tension changes, avoiding misjudgments caused by data discretization. Third, setting a threshold of 0.8% fluctuation for three consecutive windows locks the tension value as the judgment threshold, eliminating interference from random fluctuations while ensuring the sensitivity of defect identification. Fourth, the secondary curing process softens and flows the sealant by reheating, filling the debonded areas before curing again, effectively repairing defects that may have occurred during the initial curing. Fifth, the secondary curing temperature of 40-50℃ matches the initial curing temperature, avoiding the adverse effects of excessively high temperatures on sealant performance. These measures collectively ensure the bonding quality of the cured sealant, forming a tight bond between the protective layer and the anchor cable, effectively preventing moisture intrusion and significantly extending the service life of the anchor cable in cold regions.

[0133] In another embodiment, in the integrated construction method for prestressed anchor cable tensioning and protection of slopes in high-altitude and cold regions, S6... R The method for determining whether a value changes from a continuously rising state to a continuously falling state is: real-time calculation. R Rate of change of value over time dR / dt When within 7 consecutive days dR / dt >0 and daily dR / dt The values ​​are all greater than the previous day's. dR / dt When determining numerical values, R The value is in an upward phase; when it is detected dR / dt The instant from a positive value to zero is called the moment. R The turning point where the value changes from rising to falling; after the turning point, within 7 consecutive days... dR / dt <0 and daily dR / dt The absolute values ​​of all are greater than those of the previous day. dR / dt When the absolute value is used, determine R The value is in a downward phase.

[0134] In this method, S6 is paired with R The method for determining whether a value changes from a continuously rising state to a continuously falling state is specifically defined. Real-time calculation. R Rate of change of value over time dR / dt This value reflectsR The rate and direction of change of the value; positive values ​​indicate an increase, negative values ​​indicate a decrease, and the absolute value indicates the rate of change. When within 7 consecutive days... dR / dt A value greater than 0 and each day's dR / dt value is greater than the previous day's value. dR / dt When determining numerical values, R The value is in an upward phase. The requirement of 7 consecutive days eliminates short-term, accidental fluctuations and ensures the reliability of the upward trend; each day's value being greater than the previous day indicates a continuously accelerating rate of increase, rather than a volatile increase. For example, if the first day... dR / dt The value is 0.03 on the first day, 0.04 on the second day, 0.05 on the third day, and so on until it reaches 0.09 on the seventh day. Then it is determined that... R The value is in an upward phase.

[0135] When detected dR / dt The instant from a positive value to zero is called the moment. R The turning point where the value changes from rising to falling. dR / dt From positive to zero R When the upward trend of the value stops and is about to turn downward, this zero point is the peak position. Real-time monitoring can accurately capture this moment and avoid missing the turning point due to excessively large sampling intervals.

[0136] After the turning point, within 7 consecutive days dR / dt Less than 0 and daily dR / dt The absolute values ​​of all are greater than those of the previous day. dR / dt When the absolute value is used, determine R The value is in a downward phase. The requirement of 7 consecutive days is also used to confirm the stability of the downward trend; a daily absolute value greater than the previous day indicates that the rate of decline is accelerating, rather than a decrease in volatility. For example, the first day after the turning point. dR / dt The value is -0.02 on the first day, -0.03 on the second day, -0.04 on the third day, and so on until the seventh day when it reaches -0.08. Then it is determined... R The value is in a downward phase.

[0137] Based on the above dR / dt The method for determining changes in sign and value will be... R The identification of value states is transformed into a quantifiable calculation process, eliminating the uncertainty of subjective judgment and ensuring that the identification of turning points is accurate and reliable.

[0138] Effect description: This method is effective for RThe quantitative definition of value state determination, compared to relying on manual observation or simple thresholds, has the following advantages: First, through continuous 7 days... dR / dt First, comparing signs and values ​​effectively eliminates short-term fluctuations, ensuring the authenticity of upward and downward trends; second, real-time monitoring... dR / dt The instant the value changes from positive to zero accurately captures the peak inflection point, avoiding delays or overshoots caused by subjective judgment or sampling intervals. Third, the requirement for daily values ​​to increase compared to the previous day reflects the characteristic of a continuously accelerating rate of change, consistent with the pattern of frost heave force initially accelerating and then accelerating its decline during frost heave evolution. Fourth, this determination method is entirely based on real-time monitoring data for automatic calculation, resulting in an objective and unique outcome. Different operators using the same data can arrive at the same conclusion, eliminating discrepancies arising from human judgment. These measures collectively ensure the accuracy and consistency of condition 3, providing a reliable foundation for satisfying condition 4 and determining overall frost heave stability.

[0139] Although the embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. They can be applied to various fields suitable for the present invention. For those skilled in the art, other modifications can be easily made. Therefore, without departing from the general concept defined by the claims and their equivalents, the present invention is not limited to the specific details.

Claims

1. An integrated construction method for prestressed anchor cable tensioning and protection of slopes in high-altitude and cold regions, characterized in that, include: S1, Drill anchor cable holes and install prestressed anchor cables. The prestressed anchor cables have an anchoring section located at the bottom of the anchor cable hole and a tensioning section extending from the opening of the anchor cable hole to the outside. S2, inject cement-based grout into the entire length of the anchoring section and cure until the compressive strength of the stone reaches more than 80% of the design compressive strength; S3. Install an anchor cable force gauge at the tensioning end to continuously monitor the axial force of the anchor cable. P ; S4, Tension and lock the anchor cable, record axial force data and calculate the rate of change of axial force. dP / dt ; S5. A temperature sensor is installed at the orifice of the anchor cable hole to continuously monitor the ambient temperature at the orifice. T Record temperature data and calculate the rate of temperature change. dT / dt ; S6. When the following conditions are met simultaneously, it is determined that the frost heave of the surrounding soil and rock mass has reached the stable decay stage: Condition 1 dP / dt The value changes from a positive value that continuously crosses zero to a negative value; Condition 2, within 72 consecutive hours after condition 1 is met | dP / dt |<0.05kN / h; Condition 3: Calculate the ratio R =| dP / dt | / | dT / dt |, calculation R rate of change of value dR / dt ,when R The value changed from a continuous rise to a continuous fall, and remained so for 48 hours after the change. R The difference between the maximum and minimum values ​​is less than R 15% of the average value; Condition 4: After satisfying condition 3, within 48 consecutive hours R The second derivative of the value d 2 R / dt 2 It is a negative value, and | d 2 R / dt 2 |<0.0005kN / (℃·h 2 ), at the same time | dR / dt |<0.005 kN / (℃·h); S7. After the conditions in S6 are met, apply a protective coating to the exposed part of the tensioning section. S8, a protective sleeve is installed on the outside of the protective coating, and sealant is injected between the protective sleeve and the anchor cable; S9. After the sealant is injected, an electric heating tape is used to cure it, completing the protective construction.

2. The integrated construction method for prestressed anchor cable tensioning and protection of slopes in high-altitude and cold regions as described in claim 1, characterized in that, After completing all steps S1 to S5, establish the frost heave force-axial force regression model and monitor and determine the deviation according to the following steps: Step 1) Drill three holes of different depths in the rock and soil around the anchor hole opening. The three holes are radially distributed with the anchor hole axis as the center. The horizontal angle between adjacent holes is 120°. The hole depths are 30cm, 60cm and 90cm respectively. A miniature earth pressure sensor is buried at the bottom of each hole. The sensing surface of the miniature earth pressure sensor faces the anchor hole axis. The lead wire of the miniature earth pressure sensor is led out to the ground surface by an armored cable and the armored cable is covered with a polyethylene sheath. Step 2) Continuously monitor the horizontal frost heave force at a depth of 30cm using three miniature earth pressure sensors. F 1. Horizontal frost heave force at a depth of 60cm F 2 and 90cm depth horizontal frost heave force F 3. Simultaneously, the axial force of the anchor cable is continuously monitored using an anchor cable dynamometer. P The acquisition frequency of all monitoring data is set to no less than 0.5Hz; Step 3), continuous data acquisition F 1. F 2. F 3 and P The data must be at least 7 days old. After aligning the collected data by timestamp, ... F 1. F 2. F 3 is the independent variable. P Using the least squares method as the dependent variable, a multiple linear regression model was established to fit the frost heave force-axial force regression model: Among them, the regression coefficient a 1. a 2. a 3 and b The predicted values ​​for all data points are obtained by calculating using the least squares method. a 1 F 1+ a 2 F 2+ a 3 F 3+ b Compared with measured values P The sum of squared residuals is minimized; after the initial calculation of regression coefficients is completed, starting from the time the initial calculation is completed, when the cumulative monitoring data duration reaches 14 days, the regression coefficients are recalculated every 24 hours using the monitoring data of the 7 days closest to the current time, so as to realize the dynamic updating of regression coefficients; Step 4), during the process of determining whether the frost heave effect has reached the stable attenuation stage in S6, the following verification operations are performed simultaneously: based on real-time monitoring F 1. F 2. F 3 and the latest regression coefficients a 1. a 2. a 3. b According to the formula Calculate frost heave force to predict axial force P pred ;Will P pred Anchor cable axial force monitored in real time by anchor cable force gauge P Compare the two and calculate the average relative deviation over a continuous 24 hours. in, N This represents the number of sampling points within 24 hours. P pred，i For the first i Predicting axial force based on frost heave force at each sampling point. P i For the first i Measured values ​​of anchor cable axial force at each sampling point; Step 5), when δ If ≤15%, continue with S6 judgment; when δ When the value is greater than 15%, it is determined that the anchor cable force gauge has zero-point drift or that there is bond slip between the rock and soil and the anchor cable. At this time, the S6 determination is paused and the compensation tensioning program is started. The compensation tensioning procedure includes the following steps: Step A: Determine the compensation tension, which is 1.05-1.10 times the design locking tension value; Step B: Reinstall the tensioning jack onto the anchor cable tensioning end, ensuring that the jack axis coincides with the anchor cable hole axis during installation; Step C: Perform graded tensioning, apply the compensating tension force in three to five levels, with equal increments for each level, and stabilize the pressure for 5-10 minutes after each level of tensioning reaches the target value. Step D: After completing all levels of tensioning and stabilizing, lock the working anchorage and record the axial force of the anchor cable after compensation tensioning as the new initial tension force reference value; Step E: After the compensation tension is completed, the current time is reset to the new monitoring zero point, and the judgment of conditions 1 to 4 in S6 is restarted based on this zero point. If the average relative deviation obtained by repeating step 4) is completed within 24 hours after the compensation tensioning is completed, δ If the percentage still exceeds 15%, a reassessment process will be initiated. The re-evaluation procedure is as follows: Set the moment when the compensation tensioning is completed and locked as the new zero point, and re-execute steps 2) to 4) from the new zero point. When the average relative deviation is obtained from re-executing step 4), δ When ≤15%, based on newly collected measured values ​​of anchor cable axial force. P and synchronously monitored wellhead ambient temperature T Re-execute all the judgment steps of conditions 1 to 4 in S6; if conditions 1 to 4 are not fully met after two consecutive re-executions of S6, it is determined that there is irreversible damage to the anchoring system, and engineering treatment is carried out by installing additional anchor cables or grouting reinforcement.

3. The integrated construction method for prestressed anchor cable tensioning and protection of slopes in high-altitude and cold regions as described in claim 2, characterized in that, During the S6 determination process, the absolute value of the temperature change rate is monitored simultaneously. dT / dt |; When | dT / dt When the temperature is ≥0.01℃ / h, all conditions in S6 are applied for a comprehensive judgment. When | dT / dt When | < 0.01℃ / h, suspend all conditions in S6 and instead perform the following frost heave stability determination steps: Step a: Continuously collect horizontal frost heave force at a depth of 30cm. F 1. Horizontal frost heave force at a depth of 60cm F 2 and 90cm depth horizontal frost heave force F 3. The data acquisition frequency is not less than 0.5Hz; Step b: Using a 72-hour time window, calculate the difference between the maximum and minimum values ​​of each frost heave force data within that window, and obtain Δ... F 1. △ F 2 and △ F 3; Step c, calculate the average value of each frost heave force data within the window, and obtain the results respectively. F 1avg , F 2avg and F 3avg ; Step d, when △ F 1≤0.05 F 1avg , △ F 2≤0.05 F 2avg and △ F 3≤0.05 F 3avg When it is determined that the frost heave of the surrounding rock and soil has reached a stable decay stage, proceed with S7 and subsequent steps. Step e: If any of the conditions in step d are not met, it is determined that the frost heave effect has not yet stabilized, and monitoring continues until the above conditions are met before proceeding to S7. Step f, when | dT / dt When the temperature rises to ≥0.01℃ / h, resume all conditions in S6 and re-determine the frost heave stability based on real-time monitoring data.

4. The integrated construction method for prestressed anchor cable tensioning and protection of slopes in high-altitude and cold regions as described in claim 1, characterized in that, The cement-based grout in S2 is a low-temperature, early-strength cement-based grout, composed of the following components by weight: 100 parts of Grade G oil well cement, 32-45 parts of water, 3-5 parts of calcium formate, 1-2 parts of triethanolamine, and 1-3 parts of sodium nitrite. Before injection, a composite mineral admixture is added to the cement-based grout. This admixture is composed of the following components by weight: 60-80 parts of slag powder, 10-20 parts of nano-silica, and 5-15 parts of anhydrous calcium sulfoaluminate. The slag powder has a specific surface area ≥ 600 m². 2 / kg, D90≤30μm; nano-silica with a particle size of 10-30nm and a specific surface area ≥200 m² 2 / g; Based on 100 parts by weight of G-grade oil well cement, the amount of composite mineral admixture is 8-15 parts by weight; The method of adding composite mineral admixture is as follows: add it to the cement-based grout 5-10 minutes before the start of grouting and stir, with a stirring speed of not less than 1200 r / min and a stirring time of 3-5 minutes; The grouting adopts the bottom return grouting method, with a return grouting flow rate of 20-50 L / min until the grout that is consistent with the grouting grout overflows from the anchor cable hole, and then stop. After grouting is completed, it can be cured for 5 days before subsequent tensioning operations can be carried out.

5. The integrated construction method for prestressed anchor cable tensioning and protection of slopes in high-altitude and cold regions as described in claim 1, characterized in that, In S4, tensioning is performed in stages, including initial tensioning, intermediate tensioning, and final tensioning. The initial tension force is 10%-20% of the design locking tension force value and is held for 5-15 minutes. The intermediate tensioning is divided into three to five levels, starting from the tension force after the initial tensioning ends. The tension force of each level increases by 15%-25% of the design locking tension force value, and each level is held for 8-20 minutes. The final tensioning reaches 1.05-1.10 times the design locking tension force value and is then locked.

6. The integrated construction method for prestressed anchor cable tensioning and protection of slopes in high-altitude and cold regions as described in claim 1, characterized in that, In S5, the temperature sensor is buried in the soil and rock at the edge of the anchor cable hole, with a burial depth of 10-30 cm. The burial method is as follows: drill a hole with a diameter of 30-50 mm and a depth of 10-30 cm at the edge of the anchor cable hole, place the temperature sensor at the bottom of the hole, fill the area around the temperature sensor with fine sand, and use armored cable to lead out the temperature sensor lead wire. The cable is covered with a polyethylene protective tube, and the outlet of the protective tube is sealed with waterproof sealant.

7. The integrated construction method for prestressed anchor cable tensioning and protection of slopes in high-altitude and cold regions as described in claim 1, characterized in that, The protective coating in S7 includes a first protective coating and a second protective coating. The first protective coating is an epoxy zinc-rich primer with a coating thickness of 50-120μm, and the second protective coating is a polyurethane topcoat with a coating thickness of 60-150μm. In S8, the sheath is a polyethylene corrugated sheath with an inner diameter to outer diameter ratio of 1.2-1.

6. The sealant is a flexible sealant. Before injecting the flexible sealant, the sheath is preheated with an electric heating tape at a temperature of 20-30℃ for 30-60 minutes, raising the temperature in the annular gap between the sheath and the prestressed anchor cable to above 5℃. Then, the flexible sealant is injected at a pressure of 0.2-0.6MPa for 10-30 minutes until the annular gap is completely filled and flexible sealant overflows from both ends of the sheath.

8. The integrated construction method for prestressed anchor cable tensioning and protection of slopes in high-altitude and cold regions as described in claim 7, characterized in that, The wrapping spacing of the electric heating tape in S9 is 10-30cm. The temperature of the sealant is maintained at 35-55℃ and cured for 45-90 minutes by electric heating.

9. The integrated construction method for prestressed anchor cable tensioning and protection of slopes in high-altitude and cold regions as described in claim 1, characterized in that, After the S9 heating curing is completed, keep the electric heating cable wrapped and stop heating to allow the sealant to cool down naturally. During the cooling process, continuously monitor the change in tension force using an anchor cable force gauge. Take 10 minutes as the sliding time window and calculate the difference between the maximum and minimum tension force in each sliding time window. When the difference between the maximum and minimum tension force in each sliding time window for three consecutive sliding time windows is greater than 0.8% by the design locking tension force value, it is determined that there is an adhesion defect in the protective layer. Immediately restart the electric heating cable to heat to 40-50℃ and hold the temperature for 20-40 minutes for secondary curing. After the secondary curing is completed, remove the electric heating cable.

10. The integrated construction method for prestressed anchor cable tensioning and protection of slopes in high-altitude and cold regions as described in claim 1, characterized in that, S6 R The method for determining whether a value changes from a continuously rising state to a continuously falling state is as follows: Real-time computing R Rate of change of value over time dR / dt When within 7 consecutive days dR / dt >0 and daily dR / dt The values ​​are all greater than the previous day's. dR / dt When determining numerical values, R The value is in an upward phase; When detected dR / dt The instant from a positive value to zero is called the moment. R The turning point where the value changes from rising to falling; After the turning point, within 7 consecutive days dR / dt <0 and daily dR / dt The absolute values ​​of all are greater than those of the previous day. dR / dt When the absolute value is used, determine R The value is in a downward phase.

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