A method for testing tangential frost heaving force of pile foundation in cold region

Abstract

The application discloses a kind of tangential frost heaving force test methods of cold region pile foundation, belong to cold region pile foundation frost heaving prevention and control technical field, the test method of the application is in the top of test pile Design load is applied and is kept, and in the time point when freezing depth and frost heaving reach maximum, obtain annual maximum unit tangential frost heaving force, by the determination of dangerous section, obtain the maximum tangential frost heaving force that pile body bears, namely the most unfavorable load state that pile foundation faces in a year, can be directly used as the key design control value of pile foundation security guarantee, fundamentally avoid the problem of data randomness and insufficient representation caused by improper test timing, so that key design parameter originates from real annual most unfavorable working condition, provide more scientific and reliable basis for subsequent frost heaving prevention and control and stability checking.

Description

Technical Field

[0001] This invention relates to the field of frost heave prevention and control technology for pile foundations in cold regions, and in particular to a method for testing the tangential frost heave force of pile foundations in cold regions. Background Technology

[0002] Pile foundations, with their outstanding advantages such as minimal construction disturbance, excellent bearing capacity, and strong geological adaptability, are widely used in cold-region engineering construction. With the continued increase in bearing capacity requirements for cold-region engineering under the background of climate change, the application of pile foundations will become even more widespread. However, under repeated shallow freeze-thaw cycles, the long-term stability of pile foundations faces severe threats, and frost pull-out defects occur frequently, such as… Figure 1 As shown, this has become a critical issue jeopardizing the safe operation of pile foundation projects in cold regions.

[0003] Frost pull-out is a common form of damage to underground structures in seasonally frozen soil regions. Its mechanism is as follows: Figure 2 As shown: In the early stages of winter freezing, the soil around the pile freezes and cements with the pile body, causing frost heave. The tangential frost heave force pulls the pile upwards. When the soil thaws in spring, the shallow thawed soil recedes, while the deeper frozen soil remains frozen to the pile body, preventing the pile from fully returning to its original position and resulting in residual vertical displacement. This process repeats annually, with the amount of frost pull-out accumulating until it eventually leads to pile foundation instability. Figure 3 As shown, from a mechanical perspective, shallow normal frost soil exerts both horizontal and tangential frost heave forces on pile foundations, with the tangential frost heave force being the primary cause of frost pull-out failure. This force value is the product of the pile-soil contact area within the seasonal freeze-thaw layer and the unit tangential frost heave force. Therefore, the value of the unit tangential frost heave force becomes a core parameter for the frost pull-out resistance design and safety control of pile foundations in cold regions.

[0004] Currently, the measured data of unit tangential frost heave force exhibits significant dispersion, primarily due to the complexity of its formation mechanism and the coupled influence of multiple factors such as natural conditions, constraint states, and structural characteristics. This results in insufficient comparability and reference value between different test results. While existing standards recommend prioritizing in-situ testing to determine design values, they lack specific on-site quantification methods, monitoring procedures, and guidelines for testing timing. Existing testing methods largely focus on indoor experiments; a few on-site testing methods are often conducted under conditions that completely suppress pile foundation frost pull-out, which can easily lead to overestimation of results. Although this ensures safety, it often results in wasted engineering costs, making it difficult to balance safety and economy, thus hindering the optimized development of pile foundation technology in major linear projects in cold regions.

[0005] To address the above problems, this invention proposes a method for testing the unit tangential frost heave force of pile foundations in cold regions. This method, based on specific engineering design data, conducts a "one project, one test" approach for the target project's pile foundation structure, directly obtaining the design value of the unit tangential frost heave force that closely matches the actual working conditions, thereby significantly improving the accuracy and applicability of frost pull-out control design. The equipment and materials used are all mature market products, easy for frontline technicians to master and promote, and have good prospects for engineering application. At the innovation level, this invention represents a practical creation that advances the field by "half a step," emphasizing integration with existing technological systems and avoiding disconnection from upstream and downstream standards. It provides a more reliable and practical parameter testing method for frost pull-out control design and stability verification of pile foundations in cold regions. Summary of the Invention

[0006] The purpose of this invention is to address the technical deficiencies in the existing technology by providing a method for testing the tangential frost heave force of pile foundations in cold regions.

[0007] The technical solution adopted to achieve the purpose of this invention is:

[0008] A method for testing the tangential frost heave force of pile foundations in cold regions includes the following steps:

[0009] Step 1: Estimate the maximum seasonal freezing depth, the time of occurrence of the maximum seasonal freezing depth, and the freeze-thaw cycle;

[0010] Step 2: Determine the design load of the pile foundation, design the test pile foundation, and divide the test pile foundation into M layers from top to bottom. Install strain gauges on the upper and lower sections of each layer. Carry out construction in the target project area. Install a static level at the top of the test pile foundation, and set up frost heave gauges, a row of temperature sensors along the depth direction, a row of moisture sensors, and a reference point static level connected to the static level at the top of the pile foundation on the natural site.

[0011] Step 3: Apply the designed pile load to the top of the test pile foundation in one go and monitor the data.

[0012] Step 4: Within the time frame of the estimated maximum seasonal frost depth in Step 1 and the freeze-thaw cycle, determine the time point when both frost heave and frost depth reach their maximum based on the monitored data, and evaluate the validity of the data through the operational status of the test pile foundations;

[0013] Step 5: Based on the cross-sectional area of ​​the test pile foundation, the cross-sectional area and elastic modulus of the concrete and steel reinforcement, and the strain data monitored by the strain gauge, calculate the axial force of the pile foundation at each section during the freezing period. Take the strain data corresponding to the time point in Step 4 to calculate the vertical distribution of the pile foundation axial force and the annual maximum unit tangential frost heave force of each layer.

[0014] Step 6: Analyze the changes in axial force of pile foundation at each section during the freezing period, take the section with the largest change as the critical section, and calculate the maximum tangential frost heave force borne by the pile body above the critical section as the tangential frost heave force of the pile foundation.

[0015] In the above technical solution, in step 1, engineering environmental data of the target engineering area are collected. The engineering environmental data includes engineering geological and hydrogeological data, meteorological data and seasonal freeze-thaw process records.

[0016] In the above technical solution, in step 1, the geological structure, soil characteristics and duration of positive and negative temperatures in the target project area are analyzed based on engineering environmental data to estimate the maximum seasonal freezing depth, the time of occurrence of the maximum seasonal freezing depth, and the freeze-thaw cycle.

[0017] In the above technical solution, in step 2, the temperature sensor and moisture sensor located at the bottom are flush with the bottom of the test pile foundation.

[0018] In the above technical solution, in step 2, the strain gauge, temperature sensor, moisture sensor, frost heave gauge, pile top static level and benchmark point static level are respectively connected to the data acquisition unit to acquire data and store it in the data storage unit.

[0019] In the above technical solution, the evaluation process of the operation status of the test pile foundation in step 4 is as follows: calculate the frost pull-out displacement of the test pile foundation based on the data monitored by the static level instrument at the pile top and the static level instrument at the benchmark point, evaluate whether the frost pull-out displacement is within the allowable safe range of the project, and at the same time carry out the integrity test of the pile body. If it meets the safety requirements, the monitored data is determined to be valid and used for the subsequent calculation of the unit tangential frost heave force.

[0020] In the above technical solution, in step 4, the frost heave development is determined based on the data monitored by the frost heave meter, and the soil temperature and moisture content data are monitored by the temperature sensor and moisture sensor to plot the curve of moisture content changing with temperature, and to determine the time point when both frost heave and freezing depth have developed to their maximum.

[0021] In the above technical solution, in step 5, the elastic modulus of the test pile foundation... E The calculation formula is as follows:

[0022] ;

[0023] In the formula, E c , E a These are the elastic modulus of concrete and the elastic modulus of steel reinforcement, respectively. A c , A a , AThese are the cross-sectional areas of the concrete in the test pile foundation, the cross-sectional areas of all steel bars in the test pile foundation, and the cross-sectional area of ​​the pile foundation, respectively.

[0024] In the above technical solution, in step 5, the axial force of the pile foundation N The calculation formula is as follows:

[0025] ;

[0026] In the formula, E The elastic modulus of the pile foundation; A This represents the cross-sectional area of ​​each section of the pile foundation; ε Let be the strain at each cross section.

[0027] In the above technical solution, in step 5, when both frost heave and freezing depth have developed to their maximum, any area within the seasonal freeze-thaw layer... k Maximum annual unit tangential frost heave force of pile foundation in stratum test :

[0028] ;

[0029] In the formula, D The diameter of the test pile foundation; N k , N k+1 For any k Axial forces in pile foundations at the upper and lower sections of the story level; l k For any k The height of the pile foundation for the stratum test.

[0030] In the above technical solution, the formula for calculating the maximum tangential frost heave force borne by the pile body in the layer above the dangerous section in step 6 is as follows:

[0031] ;

[0032] In the formula, The annual maximum unit tangential frost heave force for the first layer closest to the ground. The height of the first level closest to the ground. n The layer containing the dangerous section. The maximum annual unit tangential frost heave force at the layer where the critical section is located. The height of the layer containing the critical section is given, where the critical section is the lower section of the layer.

[0033] Compared with the prior art, the beneficial effects of the present invention are:

[0034] 1. This invention explicitly proposes that while applying and maintaining the design load at the top of the test pile foundation, the displacement at the pile top must only be within the safe range allowed by engineering specifications, rather than completely suppressing the displacement. This ensures that the obtained tangential frost heave force reflects the actual tangential frost heave force borne by the pile foundation during normal operation, thereby significantly improving the economic rationality of the design while strictly ensuring safety.

[0035] 2. This invention significantly improves the engineering representativeness and design reliability of the obtained critical section locations and maximum tangential frost heave forces by precisely setting the testing time to the end of the negative temperature cycle and when the freezing depth and frost heave reach their maximum values. The testing method of this invention combines the pile-soil interaction mechanism in frozen soil regions with the physical law that tangential frost heave force develops with freezing depth and does not reach its annual extreme value during the freezing period. Therefore, the obtained unit tangential frost heave force essentially represents the most unfavorable load state faced by the pile foundation in a year, and can be directly used as a key design control value for ensuring the safety of the pile foundation. This fundamentally avoids the problems of data randomness and insufficient representativeness caused by improper testing timing, ensuring that key design parameters originate from the actual most unfavorable annual working conditions, providing a more scientific and reliable basis for subsequent frost pull-out control and stability verification.

[0036] 3. This invention constructs a complete technical chain from environmental analysis to mechanical quantification, significantly enhancing the relevance and reliability of the results. The method begins with a systematic analysis of the geology, meteorology, and freeze-thaw processes of the engineering area. Then, based on the preliminary design of the engineering pile foundation, a customized test pile foundation and its surrounding monitoring system are established. Finally, synchronous data acquisition and calculation are performed at critical mechanical moments. The resulting unit tangential frost heave force value is a true reflection of the interaction between the specific site environment and the specific pile structure, overcoming the shortcomings of traditional empirical formulas or isolated tests that are severely disconnected from engineering practice and have poor universality.

[0037] 4. This invention significantly improves the reliability and engineering applicability of the obtained design parameters by simultaneously implementing data validity assessment during field testing. This invention determines whether the pile top frost-pull-out displacement is within the safe range allowed by the engineering requirements while simultaneously monitoring the integrity of the test pile foundation. That is, only when the pile foundation response is both safe and intact is the currently monitored data considered valid and usable for subsequent calculations. This field assessment step ensures that the key design parameters ultimately used are derived from the normal and healthy working state of the pile-soil system, avoiding the risk of mistakenly using test values ​​under abnormal or dangerous conditions as design basis, thereby greatly improving the reliability of the design parameters and the overall safety level of the design.

[0038] 5. This invention emphasizes practicality and operability, facilitating frontline promotion and seamless integration with existing standards. The monitoring equipment used is comprised of general-purpose engineering monitoring products, requiring no special instruments, and the procedures are clear and easy to follow. Its testing philosophy aligns with the current standards' encouragement of in-situ testing, and the output results can directly serve existing design verification systems, significantly lowering the barrier to method adoption and facilitating its rapid application in engineering practice, effectively improving the design and operation and maintenance level of pile foundation engineering in cold regions.

[0039] 6. This invention systematically outputs two key design parameters for frost pullback control design, significantly improving the integrity of the design process and the synergy between parameters. The first parameter is for pile strength verification, namely the critical section determined based on the location of maximum axial force change and its maximum tangential frost heave force; the second parameter is for overall stability control, namely the design value of unit tangential frost heave force according to the standard. These two key design parameters are both derived from on-site measurements and simultaneous calculations at the same time (when the frost depth is maximum), forming a logically self-consistent and mutually supportive design parameter package. This ensures that the integrity verification and frost pullback stability verification of the pile foundation are based on the same set of reliable and consistent on-site data, avoiding design deviations caused by different parameter sources or different judgment standards, and greatly enhancing the coordination and overall reliability of the final design scheme.

[0040] 7. Compared to simply using 0℃ as the criterion for determining frost depth, this method comprehensively judges the frost depth by considering the coupling relationship between temperature and moisture content changes. This more accurately reflects the phase change process of soil moisture and avoids misjudgments caused by factors such as soil salinity, texture, or temperature lag. It can not only identify the temperature range where phase change is occurring but also visually display the advancement of the freezing front, improving the accuracy and reliability of frost depth monitoring and providing a more scientific basis for on-site judgment of frost heave prevention and related research in cold-region engineering. Attached Figure Description

[0041] Figure 1 This is a schematic diagram of pile foundation frost pull-out deformation in the background art, wherein: σ t For tangential frost heave, σ h For horizontal frost heave, q 0 represents the side friction resistance.

[0042] Figure 2 This is a schematic diagram of the freeze-pull failure mechanism in the background art.

[0043] Figure 3 This is a schematic diagram of the interaction between frozen soil and pile foundation.

[0044] Figure 4 This is a flowchart illustrating the testing method of the present invention.

[0045] Figure 5 This is a schematic diagram of pile foundation and soil monitoring.

[0046] Figure 6 This is a diagram of the monitoring system architecture.

[0047] Figure 7 This is a schematic diagram of the stress caused by frost pull-out of pile foundations in cold regions.

[0048] Figure 8 This is a curve showing the relationship between ground temperature and water content. Detailed Implementation

[0049] The present invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0050] like Figure 4 As shown, a method for testing the tangential frost heave force of pile foundations in cold regions includes the following steps:

[0051] Step 1: Collect engineering environmental data of the target project area. Analyze the geological structure, soil characteristics, and duration of positive and negative temperatures in the target project area based on the engineering environmental data, and estimate the maximum seasonal freezing depth, the time of occurrence of the maximum seasonal freezing depth, and the freeze-thaw cycle, thereby providing necessary basic data support for the implementation of subsequent steps. The engineering environmental data includes: engineering geological and hydrogeological data, meteorological data, and records of seasonal freeze-thaw processes.

[0052] Step 2, Test Pile Installation: Based on the preliminary design data of the project's pile foundation (including pile type, structural form, pile length, pile diameter, material, reinforcement, etc.), determine the design load of the pile foundation and design the test pile foundation. The dimensions of the test pile foundation are consistent with those of the target project's intended pile foundation to ensure the representativeness and applicability of the test results.

[0053] like Figure 5As shown, the test pile foundation is divided into M layers from top to bottom (the layer closest to the ground surface is called the first layer, the upper surface of the layer is called the first section, the lower surface is called the second section, and so on). A strain gauge is arranged in the upper and lower sections of each layer to monitor the strain of the pile foundation. The designed test pile foundation is constructed and installed in the target engineering area. Frost heave gauges are set up in the natural site (in this embodiment, the natural site is located more than 20 meters away from the test pile foundation) to monitor the frost heave deformation of the soil. At the same time, a row of temperature sensors and a row of moisture sensors are set up along the depth direction in the natural site to monitor the soil temperature and moisture content. The moisture and soil temperature monitoring data are comprehensively analyzed to determine the frost depth development. Then, a static level instrument is installed on the top of the test pile foundation. A benchmark point is set in the natural site, and a benchmark point static level instrument connected to the pile top static level instrument is set at the benchmark point (the benchmark point static level instrument is installed on a benchmark rod, which is inserted into the natural site and anchored at the bottom). The benchmark point static level instrument at the benchmark point is used as a reference to monitor the frost pull-out displacement of the pile top, thus completing the construction and installation.

[0054] Furthermore, the temperature and moisture sensors located at the very bottom are flush with the bottom of the test pile foundation.

[0055] like Figure 6 As shown, furthermore, the strain gauge, temperature sensor, moisture sensor, frost heave gauge, pile top static level and benchmark point static level are respectively connected to the data acquisition unit to acquire data and store it in the data storage unit.

[0056] Step 3, Target Parameter Monitoring and Load Arrangement: The pile foundation design load obtained in Step 2 is applied to the top of the test pile foundation in one go to ensure that the final obtained tangential frost heave force reflects the actual tangential frost heave force borne by the pile foundation during normal operation. Data is monitored by installing strain gauges, frost heave gauges, pile top static level, benchmark point static level, temperature sensor and moisture sensor.

[0057] Step 4: During the estimated maximum seasonal frost depth and freeze-thaw cycle in Step 1, collect data from frost heave gauges, temperature sensors, and moisture sensors to obtain the time point when both frost heave and frost depth reach their maximum. At this time, the frost pull-out force (tangential frost heave force) reaches its annual maximum value, and record the strain data of the strain gauges at this time. Calculate the frost pull-out displacement of the test pile foundation based on the data monitored by the pile top static level and the benchmark static level, and assess whether the frost pull-out displacement is within the allowable safe range of the project. At the same time, conduct pile integrity testing using the low-strain method. If it meets the safety requirements, the monitored data is deemed valid and can be used for subsequent calculation of the unit tangential frost heave force.

[0058] like Figure 7As shown, step 5, calculation of unit tangential frost heave force of pile foundation: Based on the preliminary design data of the pile foundation in step 2, determine the cross-sectional area of ​​the pile foundation, the cross-sectional area and elastic modulus of the concrete and steel reinforcement, and calculate the elastic modulus of the pile foundation. E The calculation formula is as follows:

[0059] (1);

[0060] In the formula, E c , E a These are the elastic modulus of concrete and the elastic modulus of steel reinforcement, respectively. A c , A a , A These are the cross-sectional areas of the concrete, the steel reinforcement, and the pile foundation, respectively.

[0061] Based on the elastic modulus of the pile foundation E Based on the strain data monitored by strain gauges at each section in step 3, the axial force of the test pile foundation at each section is calculated. N The calculation formula is as follows:

[0062] (2);

[0063] In the formula, E The elastic modulus of the pile foundation; A This represents the cross-sectional area of ​​each section of the pile foundation; ε Let be the strain at each cross section.

[0064] Based on the axial force of each section of the test pile foundation N Calculate any t Unit tangential frost heave force of test pile foundation at different times and depths The calculation formula is as follows:

[0065] (3);

[0066] In the formula, D The diameter of the test pile foundation; N ( z , t )for t The corresponding time level of each layer z Axial force of pile foundation at depth z For depth.

[0067] To better assist frontline technicians in calculating the differences in axial force between pile foundations at various cross-sections, formula (3) is simplified. Combining the strain data from strain gauges at each cross-section recorded in step 4 with formula (2), the maximum seasonal freeze-thaw layer range is calculated when frost heave and frost depth reach their maximum. k Maximum annual unit tangential frost heave force of pile foundation in layer test q k :

[0068] (4);

[0069] In the formula, N k , N k+1 For any k Axial forces in pile foundations at upper and lower cross sections of the layer; l k For any k The height of the pile foundation for the stratum test.

[0070] Step 6: Provide key design parameters: Based on the calculation results of Step 5, analyze the changes in axial force of pile foundations at each section during the freezing period, take the section with the largest change as the critical section, and calculate the maximum tangential frost heave force borne by the pile body above the critical section as the tangential frost heave force of the pile foundation. At the same time, based on the relevant technical standard requirements (JGJ 118 Code for Design of Building Foundations in Frozen Soil Areas), and combined with the annual maximum unit tangential frost heave force obtained in Step 5, propose the design value of unit tangential frost heave force. The critical section and the maximum tangential frost heave force are the two key design parameters that provide the basis for pile integrity verification. The design value of unit tangential frost heave force is used as the key design parameter for the design of actual pile foundations in cold regions.

[0071] The formula for calculating the maximum tangential frost heave force borne by the pile body in the layers above the critical section is as follows:

[0072] (5);

[0073] In the formula, The annual maximum unit tangential frost heave force for the first layer closest to the ground. The height of the first level closest to the ground. n The layer containing the dangerous section. The maximum annual unit tangential frost heave force at the layer where the critical section is located. The height of the layer containing the critical section is given, where the critical section is the lower section of the layer.

[0074] Furthermore, the time when the frost depth reaches its maximum was obtained through data monitored by temperature and moisture sensors: soil temperature and moisture content data were monitored in-situ using temperature and moisture sensors, and the relationship curve between the two was plotted. Figure 8 This method can effectively determine the development of soil frost depth. Soil moisture content is calculated from the dielectric constant measured by a moisture sensor. When the temperature drops to near the freezing point, liquid water in the soil gradually freezes into ice, and the water molecule structure transforms into ice crystals, leading to a significant decrease in conductivity and a noticeable reduction in the calculated moisture content. Therefore, in the relationship curve between soil temperature and moisture content... Figure 8 The range where the water content decreases sharply with decreasing temperature corresponds to the water phase transition process and reflects the actual freezing state of the soil. By analyzing the changes in the shape of this curve, the stable freezing temperature of the soil can be determined. (The stable freezing temperature refers to the temperature state or lower limit of the range at which the drastic phase change of a large amount of water within the soil is essentially complete during the freezing process, and the system temperature change is mainly controlled by sensible heat, with the release of latent heat of phase change being negligible. Under this state, the macroscopic thermophysical properties of the soil tend to be stable, but a small amount of residual unfrozen water may still exist.) This allows for the determination of the true location and progress of freezing depth development. This method, based on the actual response of the soil moisture state, is more accurate and reliable than traditional methods.

[0075] The above description is only a preferred embodiment of the present invention. It should be noted that, for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for testing the tangential frost heave force of pile foundations in cold regions, characterized in that, Includes the following steps: Step 1: Estimate the maximum seasonal freezing depth, the time of occurrence of the maximum seasonal freezing depth, and the freeze-thaw cycle; Step 2: Determine the design load of the pile foundation and design the test pile foundation. Divide the test pile foundation into M layers from top to bottom. Install a strain gauge on the upper and lower sections of each layer. Carry out construction in the target project area. Install a pile top static level on the top of the test pile foundation. Set up frost heave gauges, a row of temperature sensors along the depth direction, a row of moisture sensors, and a reference point static level connected to the pile top static level in the natural site. Step 3: Apply the designed pile load to the top of the test pile foundation in one go and monitor the data. Step 4: Within the estimated maximum seasonal frost depth and freeze-thaw cycle from Step 1, determine the time point when both frost heave and frost depth reach their maximum based on monitored data, and evaluate the validity of the data through the operational status of the test pile foundation. The evaluation process for the operational status of the test pile foundation is as follows: Calculate the frost pull-out displacement of the test pile foundation based on data monitored by the pile top static level and the benchmark static level, assess whether the frost pull-out displacement is within the allowable safe range for the project, and simultaneously conduct pile integrity testing. If it meets safety requirements, the monitored data is deemed valid and used for subsequent calculation of the unit tangential frost heave force. Determine the frost heave development based on data monitored by the frost heave meter; plot the curve of moisture content versus temperature based on data monitored by temperature and moisture sensors, and determine the time point when both frost heave and frost depth reach their maximum. Step 5: Based on the cross-sectional area of ​​the test pile foundation, the cross-sectional area and elastic modulus of the concrete and steel reinforcement, and the strain data monitored by the strain gauge, calculate the axial force of the pile foundation at each section during the freezing period. Take the strain data corresponding to the time point in Step 4 to calculate the vertical distribution of the pile foundation axial force and the annual maximum unit tangential frost heave force of each layer. Step 6: Analyze the changes in axial force of pile foundation at each section during the freezing period, take the section with the largest change as the critical section, and calculate the maximum tangential frost heave force borne by the pile body above this section as the tangential frost heave force of the pile foundation.

2. The method for testing the tangential frost heave force of pile foundations in cold regions according to claim 1, characterized in that, In step 1, engineering environmental data of the target project area are collected, including engineering geological and hydrogeological data, meteorological data and seasonal freeze-thaw process records; based on the engineering environmental data, the stratigraphic structure, soil characteristics and duration of positive and negative temperatures in the target project area are analyzed, and the maximum seasonal freezing depth, the time of occurrence of the maximum seasonal freezing depth and the freeze-thaw cycle are estimated.

3. The method for testing the tangential frost heave force of pile foundations in cold regions according to claim 1, characterized in that, In step 2, the temperature sensor and moisture sensor at the bottom are flush with the bottom of the test pile foundation.

4. The method for testing the tangential frost heave force of pile foundations in cold regions according to claim 1, characterized in that, In step 2, the strain gauge, temperature sensor, moisture sensor, frost heave gauge, pile top static level and benchmark point static level are respectively connected to the data acquisition unit to acquire data and store it in the data storage unit.

5. The method for testing the tangential frost heave force of pile foundations in cold regions according to claim 4, characterized in that, In step 5, the elastic modulus of the test pile foundation is... E The calculation formula is as follows: In the formula, E c , E a These are the elastic modulus of concrete and the elastic modulus of steel reinforcement, respectively. A c , A a , A These are the cross-sectional areas of the concrete in the test pile foundation, the cross-sectional areas of all steel bars in the test pile foundation, and the cross-sectional area of ​​the pile foundation, respectively.

6. The method for testing the tangential frost heave force of pile foundations in cold regions according to claim 5, characterized in that, In step 5, the axial force of the pile foundation N The calculation formula is as follows: In the formula, E The elastic modulus of the pile foundation; A This represents the cross-sectional area of ​​each section of the pile foundation; ε Let be the strain at each cross section.

7. The method for testing the tangential frost heave force of pile foundations in cold regions according to claim 6, characterized in that, In step 5, when both frost heave and frost depth have reached their maximum, any area within the seasonal freeze-thaw layer... k Maximum annual unit tangential frost heave force of pile foundation in stratum test q k : In the formula, D The diameter of the test pile foundation; N k , N k+1 For any k Axial forces in pile foundations at the upper and lower sections of the story level; l k For any k The height of the pile foundation for the stratum test.

8. The method for testing the tangential frost heave force of pile foundations in cold regions according to claim 7, characterized in that, In step 6, the formula for calculating the maximum tangential frost heave force borne by the pile body in the layers above the critical section is as follows: In the formula, q 1 represents the annual maximum unit tangential frost heave force in the first layer closest to the ground. l 1 represents the height of the first floor closest to the ground. n The layer containing the dangerous section. q n The maximum annual unit tangential frost heave force at the layer where the critical section is located. l n The height of the layer containing the critical section is given, where the critical section is the lower section of the layer.

Images