A method for determining reinforcement timing of rock mass slope

Abstract

The application discloses a method for determining the reinforcement time of a rock mass slope. The rock mass and excavation parameters are determined through geological survey of the rock mass slope; two prestressed monitoring anchor cables are arranged in the key area of the rock mass slope to monitor the prestress loss rate in the excavation process in real time; a prestress loss rate-excavation time relation curve is drawn, and the intersection point of the two relation curves in the rapid reduction stage is determined as the best supporting time of the rock mass slope; and the anchor cable support is carried out on the excavation area of the slope according to the time. The method accurately quantitatively characterizes the self-organizing adjustment process of the stress of the rock mass slope in the excavation process through the prestressed monitoring anchor cable, provides an important basis for determining the reinforcement time of the rock mass slope, and provides a safe and economic double guarantee for the reinforcement design of the rock mass slope.

Description

Technical Field

[0001] This invention relates to the technical field of rock slope support timing determination, and in particular to a method for determining the timing of rock slope reinforcement. Background Technology

[0002] With the continuous advancement of major hydropower and transportation infrastructure construction in mountainous areas of my country, the number of rock slope excavation projects is increasing, while stability control still faces severe challenges. Currently, prestressed anchor cable reinforcement is a common method, but the timing of support mainly relies on engineering experience, which has significant shortcomings: if support is applied too early, the internal stress of the slope is still undergoing drastic adjustments, and the anchor cables bear continuously increasing additional stress, leading to rapid prestress loss, anchor cable fatigue, or even failure; if support is applied too late, the slope may have already undergone irreversible deformation or localized damage, greatly reducing the support effect and drastically increasing costs. Existing research mainly focuses on slope stability evaluation and support structure design itself, lacking scientific criteria for determining the timing of support based on the self-organized adjustment process of prestress within the slope. This often leads to problems such as untimely or excessive reinforcement in engineering practice, causing safety hazards or waste of resources. Summary of the Invention

[0003] To address the shortcomings of existing technologies, the technical problem this invention aims to solve is to propose a method for determining the timing of rock slope reinforcement. This method characterizes the stress redistribution process within the slope by monitoring the prestress loss rate of prestressed anchor cables during slope excavation, thereby scientifically determining the optimal support timing.

[0004] The technical solution of the present invention to solve the aforementioned technical problem is: A method for determining the timing of rock mass slope reinforcement, the method comprising the following four steps: Step 1: Conduct engineering geological survey of the rock mass slope system to obtain the physical and mechanical parameters and conditions of the rock mass, and determine the slope excavation design parameters. The slope excavation design parameters include the total excavation height, the graded excavation height, and the excavation ratio determined based on the rock mass type, weathering degree, and slope height. Step 2: Based on the exploration results and rock physical and mechanical parameters in Step 1, the slope top turning area and the upper part of the excavation free face are identified as key stress areas. A prestressed monitoring anchor cable is installed in each of the two key stress areas, and a load sensor is installed to form a dual-point real-time monitoring system. At the same time, the influence range of the prestressed monitoring anchor cable is determined, and the prestress loss of the prestressed monitoring anchor cable is monitored. Step 3: Excavate in an orderly manner according to the graded excavation height determined in Step 1. After each grade of excavation is completed, construction is suspended and a monitoring period is entered. During this period, the prestress values ​​of the two prestressed monitoring anchor cables are monitored, and the real-time prestress loss rate is calculated. At the same time, the correlation data between excavation time and prestress loss rate is established, and the relationship curve between prestress loss rate and excavation time of the two prestressed monitoring anchor cables is plotted. Step 4: Based on the prestress loss rate-excavation time relationship curve drawn in Step 3, identify the intersection point of the curves of the two prestress monitoring anchor cables during the rapid deceleration stage. The time corresponding to this intersection point is the optimal support time for the rock slope.

[0005] Furthermore, in step 1, the vertical height difference between the prestressed monitoring anchor points in the slope crest transition area and the slope crest is 0.1 to 0.3 times the total excavation height; the vertical height difference between the prestressed monitoring anchor points in the upper part of the excavated free face and the slope crest is 0.4 to 0.6 times the total excavation height; the spacing between two prestressed monitoring anchors is determined based on the rock mass integrity and joint development degree, and is controlled within the range of 0.1 to 0.3 times the total excavation height.

[0006] Furthermore, the safe distance between the prestressed monitoring anchor cable placement points in the upper part of the excavated face and the upper end of the excavation area. It shall not be less than 1.5 times the height of the staged excavation.

[0007] Furthermore, in step 2, the influence range of the prestressed monitoring anchor cable is estimated based on the stress diffusion theory, wherein the influence radius R is related to the stress diffusion angle, the borehole diameter, and the anchorage length of the prestressed monitoring anchor cable.

[0008] Furthermore, the prestress loss rate-excavation time relationship curve identifies and divides three typical stages of stress self-organization adjustment within the slope: the first stage is the rapid loss stage, the second stage is the rapid deceleration stage, and the third stage is the stable stage. The rapid loss stage is characterized by a continuously rapid increase in the prestress loss rate; the rapid deceleration stage is characterized by a significant decrease in the prestress loss rate; and the stable stage is characterized by a prestress loss rate approaching zero and the prestress loss rate approaching a constant value.

[0009] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) This invention is the first to quantify the internal self-organizing adjustment process during the excavation of rock slope by using the prestress loss rate of the prestress monitoring anchor cable, which provides an important basis for the selection of the best support time for rock slope.

[0010] (2) The present invention determines the support timing by the intersection of two relationship curves, which avoids the limitations of single-point monitoring and improves the scientificity and reliability of decision-making. In addition, the present invention is applicable to rock slopes with different geological conditions and engineering scales, and has good engineering applicability and promotion value. Attached Figure Description

[0011] Figure 1 A schematic diagram of the key technical process of the method for determining the timing of rock mass slope reinforcement in this invention; Figure 2 A schematic diagram showing the placement of the two prestressed monitoring anchor cables; Figure 3 A schematic diagram of the relationship between the prestress loss rate and excavation time of the prestress monitoring anchor cable; Figure 4 Schematic diagram of parameters for rock mass slope excavation area; Figure 5 Schematic diagram of calculation parameters related to prestressed monitoring anchor cables; Figure 6 Example 1: Calculation model diagram; Figure 7 Example 1: Schematic diagram of the relationship curve between prestress loss rate and excavation time for prestressed monitoring anchor cables; Figure 8 Example 1: Comparison of safety factors of reinforced slopes at different support times.

[0012] In the diagram: 1. First prestressed monitoring anchor cable; 2. Second prestressed monitoring anchor cable; 3. Excavation area. Detailed Implementation

[0013] The present invention will be further explained below with reference to the embodiments and accompanying drawings, but this is not intended to limit the scope of protection of this application.

[0014] The method for determining the timing of rock mass slope reinforcement in this invention is mainly applicable to rock mass slope engineering under excavation and unloading conditions, and is particularly suitable for determining the timing of slope support for steep slopes with complex geological conditions. Specific steps (see...) Figure 1 )yes: Step 1: Conduct a comprehensive geological survey of the rock slope to obtain rock mass parameters and slope excavation design parameters; The exploration content includes: rock strata occurrence, lithological distribution, rock mass type, mineral composition, weathering degree, structural features, groundwater distribution, rock and soil structure, occurrence, degree of geological structural development, slope, slope height, and slope shape. The physical and mechanical parameters of the rock mass are determined through laboratory tests and field tests. These parameters include physical parameters and strength parameters. Physical parameters include rock density, porosity, and water absorption; strength parameters include cohesion, internal friction angle, and shear strength, primarily obtained through laboratory triaxial shear tests on rock samples or in-situ direct shear tests. Rock mass parameters include physical and mechanical parameters as well as rock mass conditions.

[0015] Determine the slope excavation design parameters: The slope excavation design parameters include the total excavation height, the staged excavation height, and the excavation ratio. The total excavation height is determined according to the engineering design requirements. h The staged excavation height is adjusted based on the obtained rock mass conditions (such as rock mass type and weathering degree). h i The typical excavation height is 5 to 15 m, and the sum of all the excavation heights is the total excavation height. Considering the rock mass type, weathering degree, and slope height H, the slope excavation ratio is determined according to Table 1: Table 1. Influence of Excavation Ratio on Rock Mass Slope

[0016] Step 2: Based on the exploration results and rock physical and mechanical parameters in Step 1, the slope crest turning area and the upper part of the excavation free face are identified as key stress areas. A prestressed monitoring anchor cable is installed in each of these two key stress areas of the slope, and a load sensor is installed to clarify the influence range of the anchor cable. One prestressed monitoring anchor cable 2 is installed in the slope crest transition area, where potential deformation is relatively large (the slope crest area will experience the largest deformation first during the excavation of the rock mass slope), and its installation point is denoted as B; another prestressed monitoring anchor cable 1 is installed in the middle and upper part of the excavated free face, and its installation point is denoted as A; the vertical height difference of installation point B from the slope crest is... h B Approximately 0.1 h ~0.3 h When selecting point A, the vertical height difference from the top of the slope is... h A Approximately 0.4 h ~0.6 h It is located in the upper part of the current excavation step.

[0017] Assuming an ideal state, with the slope running horizontally downwards and the slope surface relatively gentle, the vertical difference between the top of the slope (slope top line) and the placement point of the corresponding prestressed monitoring anchor cable is recorded as the standard distance of the placement point.

[0018] Safety distance between deployment point A and the upper end of excavation area 3 It should satisfy equation (1): (1) in, For staged excavation height, Figure 4 The height of the excavated steps (i.e., the vertical height) is used as the level of excavation height.

[0019] Based on the slope gradient, slope height, and slope shape obtained from the geological survey, determine whether the slope excavation area is a convex or concave slope. Based on this, the location of the placement points can be adjusted accordingly: when it is a convex slope, placement points A and B are offset from the excavation area by 10% to 15% of the standard distance; when it is a concave slope, placement points A and B are offset from the free face by 5% to 10% of the standard distance.

[0020] Excavation methods are divided into blasting excavation and mechanical excavation. Depending on the excavation method, the location of the excavation points can be adjusted: when blasting excavation is used, the excavation points A and B are moved back, that is, they are both moved 20-30% of the standard distance away from the excavation area 3; when mechanical excavation is used, the excavation points A and B are arranged at the standard distance.

[0021] The spacing between the two prestressed monitoring anchor cables should be determined based on the rock mass integrity, joint development degree, and the obtained spacing range (0.1). h <d<0.3 h A suitable value should be selected, where d is the distance between the placement points of the first and second prestressed monitoring anchor cables, i.e., the spacing between them, to avoid interference from the "group anchor effect". A smaller value should be used when the rock mass has poor integrity and dense joint development, and a larger value should be used when the rock mass is intact and structural planes are sparse. In relevant engineering examples, when there is significant structural plane control, anchor cables should be avoided at least 1.0 m above the main structural plane. The anchor cable inclination angle should preferably be 10°~35° to optimize the stress state.

[0022] Both the first prestressed monitoring anchor cable 1 and the second prestressed monitoring anchor cable 2 include an anchorage section and a free section. When installing the first prestressed monitoring anchor cable 1 and the second prestressed monitoring anchor cable 2, the following technical requirements must be met: anchorage section length... It should penetrate deep into stable rock mass, typically 3-10 m; free section length The excavation disturbance area must be covered, and equation (2) must be satisfied simultaneously: (1) in, The anchor cable inclination angle; The excavation height is determined by stages.

[0023] By combining specific engineering examples with theoretical calculations, the influence range of prestressed monitoring anchor cables is clarified. The influence range can be defined from different perspectives. According to the stress bubble / pressure cone theory, the prestress is regarded as a concentrated force or distributed force acting on the midpoint of the anchorage section. According to elastic theory (such as Mindlin solution) or stress diffusion theory, a compressive stress zone similar to a "light bulb" or "cone" is formed around the anchorage section.

[0024] According to the stress diffusion theory, assuming a stress diffusion angle β with a value of 30°~45°, the influence radius R satisfies equation (3): (3) in: D The borehole diameter; This refers to the length of the anchorage section.

[0025] The unfavorable cluster anchoring effect is avoided by controlling the anchor spacing, and a continuous reinforcement zone is ensured. Therefore, the horizontal influence range is considered to be approximately 0.5 to 1.0 times the anchor spacing.

[0026] Simultaneously, the stress distribution around the anchor cable was measured; inclinometer tubes were installed to monitor changes in the displacement field, thereby verifying the influence range of the anchor cable on site.

[0027] Finally, high-precision load sensors are installed at the anchorages to monitor the prestress loss of the prestressed anchor cables in a timely and accurate manner, preparing for subsequent data processing and curve acquisition. Simultaneously, the load sensor's range should meet the design prestress requirements. 1.5 to 2.0 times that of the standard, with an accuracy of no less than 0.5%. .

[0028] Step 3: Excavate step by step according to the graded excavation height. After each level of excavation is completed, construction is suspended to monitor the prestress of the two anchor cables and the slope displacement, and plot the relationship curve between prestress loss rate and excavation time. The construction process employed a "staged excavation, intermittent monitoring" technique. Excavation proceeded in layers from top to bottom, with each layer having a specific excavation height. The typical excavation height is 5-15 m, which can be adjusted in real time according to the construction conditions. Construction is suspended for 7-15 days after each excavation stage to monitor and record changes in prestress using high-precision load sensors. Monitoring is conducted 2-4 times daily during excavation and 1-2 times daily during the suspension period. Data records include: excavation time t, the excavation height of each stage during excavation time t, and the prestress value. p Anchor cable prestress loss value Based on the monitored data, a prestress loss rate-excavation time relationship curve was plotted, with the vertical axis representing the prestress loss rate. The horizontal axis represents the excavation time t. Excavation of the slope will cause stress redistribution within the rock mass, resulting in deformation and displacement. Excessive deformation can lead to disasters such as collapse and landslides on high slopes. Therefore, it is necessary to monitor the displacement and deformation of the slope surface in real time during this process.

[0029] The relationship curve characteristics were identified into three distinct stages: three typical stages of stress self-organization adjustment within the slope were identified and divided: the first stage is the "rapid loss stage," in which the prestress loss rate increases rapidly and continuously, reflecting a violent redistribution of stress within the slope, lasting for t1; the second stage is the "rapid deceleration stage," in which the prestress loss rate begins to decrease significantly, indicating that the stress adjustment trend is slowing down and the system is transitioning to a new equilibrium state, lasting for t2; the third stage is the "stable stage," in which the prestress loss rate increases close to zero and approaches a constant value, marking the basic establishment of a new round of equilibrium, lasting for t3.

[0030] Step 4: Identify the intersection of the curves of the two prestressed monitoring anchors during the rapid deceleration phase. The time corresponding to this intersection is the optimal support time for the rock slope. In the plotted prestress loss rate-excavation time relationship curve, determine the intersection point of the two curves during the rapid deceleration phase. Based on the intersection point of the curves obtained from the first and second prestress monitoring anchor cables during the rapid deceleration phase, record the corresponding time and prestress loss rate at the intersection point. The moment corresponding to this intersection is the optimal time for support.

[0031] The second prestress monitoring anchor is located far from the excavation area, while the first prestress monitoring anchor is located close to the excavation area. When the stress inside the rock mass is redistributed after excavation, the first prestress monitoring anchor will experience prestress loss first, while the second prestress monitoring anchor, being far away, will have a lag effect. Therefore, the curves of the two prestress monitoring anchors will only intersect during the rapid deceleration phase.

[0032] Systematic anchor cable reinforcement was carried out at the determined optimal support time. After reinforcement, slope deformation and stress changes were continuously monitored to verify the support effect. Subsequent construction plans were adjusted based on the monitoring results.

[0033] Example 1 A finite element numerical model of a high rock slope was established using ABAQUS software to verify the effectiveness of the method described in this invention. The parameters of the finite element numerical model of the high rock slope are shown in Table 2. Table 2 Material parameters of the finite element numerical model for rocky high slopes

[0034] Based on geological surveys, the relevant parameters were determined. The model slope is classified as Class II moderately weathered rock, with a slope height H of 24m. The excavation ratio is 1:0.5, and the excavation height of each stage is 8m, selected based on engineering experience during slope excavation. Prestressed monitoring anchors are installed at the slope crest inflection point (point B) and the midpoint of the free face of the slope (point A). The prestressed monitoring anchors have an inclination angle of 30° and a spacing of 20m. The anchorage length of the prestressed monitoring anchor is 6m, and the free section length is 54m. The support anchors have an inclination angle of 30°, an anchorage length of 6m, and a free section length of 24m.

[0035] The process of staged excavation was simulated, with a 5-day pause after each stage to monitor changes in anchor cable prestress. Subsequently, a prestress loss rate versus excavation time curve was plotted (e.g., ...). Figure 7 As shown in the figure, the curves were used to identify the stages. The curves show that the rapid loss stage lasts from 0 to 20 days, during which the prestress loss rate increases continuously; the rapid deceleration stage lasts from 20 to 50 days, during which the prestress loss rate begins to decrease significantly, indicating a slowdown in stress adjustment and the system transitioning to a new equilibrium state; the stable stage occurs after 50 days, where the prestress loss rate increases close to zero and approaches a constant value. The two curves intersect on day 30 of the rapid deceleration stage, at which point the prestress loss rate is 10.3%.

[0036] Simultaneously, the timing of support was determined and verified. Support simulations were conducted on days 10, 20, 30 (at the intersection, with a prestress loss rate of 10.3%), 40, and 50, and the stability coefficient for each condition was calculated using the strength reduction method. The stability coefficient was 1.17 on day 10, 1.32 on day 20, 1.44 on day 30 (the intersection of the two curves), 1.21 on day 40, and 1.14 on day 50. The slope stability coefficient obtained by support at the intersection of the two curves was the highest. Figure 8 As shown, this verifies the scientific validity of the optimal support timing determined by the method of the present invention.

[0037] Simultaneously, the influence range of the prestressed monitoring anchor cable was verified, and the stress distribution around the anchor cable was monitored. The results showed that the influence radius R was approximately 8-10m, which is basically consistent with the theoretical calculation value. Through this embodiment, it is verified that the method of the present invention can scientifically determine the optimal support timing based on the dynamic information of stress adjustment within the slope, achieving the best balance between engineering safety and economy.

[0038] This invention provides a precise quantitative characterization of the self-organized adjustment process of rock slope stress during excavation using prestressed monitoring anchor cables. This provides an important basis for determining the timing of rock slope reinforcement and offers both safety and economic assurance for rock slope reinforcement design.

[0039] Any aspects not covered in this invention are applicable to existing technologies.

Claims

1. A method for determining the timing of rock mass slope reinforcement, characterized in that, The method includes the following steps: Step 1: Conduct engineering geological survey of the rock mass slope system to obtain the physical and mechanical parameters and conditions of the rock mass, and determine the slope excavation design parameters. The slope excavation design parameters include the total excavation height, the graded excavation height, and the excavation ratio determined based on the rock mass type, weathering degree, and slope height. Step 2: Based on the exploration results and rock physical and mechanical parameters in Step 1, the slope top turning area and the upper part of the excavation free face are identified as key stress areas. A prestressed monitoring anchor cable is installed in each of the two key stress areas, and a load sensor is installed to form a dual-point real-time monitoring system. At the same time, the influence range of the prestressed monitoring anchor cable is determined, and the prestress loss of the prestressed monitoring anchor cable is monitored. Step 3: Excavate in an orderly manner according to the graded excavation height determined in Step 1. After each grade of excavation is completed, construction is suspended and a monitoring period is entered. During this period, the prestress values ​​of the two prestressed monitoring anchor cables are monitored, and the real-time prestress loss rate is calculated. At the same time, the correlation data between excavation time and prestress loss rate is established, and the relationship curve between prestress loss rate and excavation time of the two prestressed monitoring anchor cables is plotted. Step 4: Based on the prestress loss rate-excavation time relationship curve drawn in Step 3, identify the intersection point of the curves of the two prestress monitoring anchors during the rapid deceleration stage. The time corresponding to this intersection point is the optimal support time for the rock slope. The prestress loss rate-excavation time relationship curve identifies and divides three typical stages of stress self-organization adjustment within the slope: the first stage is the rapid loss stage, the second stage is the rapid mitigation stage, and the third stage is the stabilization stage.

2. The method for determining the timing of rock mass slope reinforcement according to claim 1, characterized in that, In step 1, the vertical height difference between the prestressed monitoring anchor points in the slope crest transition area and the slope crest is 0.1 to 0.3 times the total excavation height; the vertical height difference between the prestressed monitoring anchor points in the upper part of the excavated free face and the slope crest is 0.4 to 0.6 times the total excavation height; the spacing between two prestressed monitoring anchors is determined based on the rock mass integrity and joint development degree, and is controlled within the range of 0.1 to 0.3 times the total excavation height.

3. The method for determining the timing of rock mass slope reinforcement according to claim 2, characterized in that, Safety distance between the prestressed monitoring anchor cable placement points in the upper part of the excavated face and the upper end of the excavation area It shall not be less than 1.5 times the height of the staged excavation.

4. The method for determining the timing of rock mass slope reinforcement according to claim 1, characterized in that, In step 2, the influence range of the prestressed monitoring anchor cable is estimated based on the stress diffusion theory, wherein the influence radius R is related to the stress diffusion angle, the borehole diameter, and the anchorage length of the prestressed monitoring anchor cable.

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