Device and method for testing bearing stability of friction pile in expansive soil area

Abstract

The invention discloses an expansive soil area friction pile bearing stability testing device and method, and relates to the technical field of civil engineering testing devices and methods, the expansive soil area friction pile bearing stability testing device comprises a multilayer soil body simulation system, a variable parameter friction pile body, a multidirectional dynamic loading system, a multiparameter monitoring system and an intelligent control system; by means of the detachable layered pressure chamber structure, layered filling and independent parameter control of the heterogeneous soil layer are achieved. Each layer of cavity can be independently filled with soil bodies with different water contents, compactness and grain composition, interlayer relative displacement is monitored through an interlayer flexible interface sensor, the spatial variation characteristic of an actual stratum is effectively simulated, in addition, the transparent organic glass materials of the layered cavities are matched with laser displacement monitoring, and the space variation characteristic of the stratum is effectively simulated. The soil deformation and pile-soil interface slippage process can be visually observed, and a visual research platform is provided for revealing the degradation mechanism of the bearing stability of the pile foundation in the heterogeneous soil layer.

Description

Technical Field

[0001] This invention belongs to the technical field of civil engineering testing devices and methods, specifically a testing device and method for the bearing stability of friction piles in expansive soil areas. Background Technology

[0002] Bridge construction in areas with expansive soil development generally faces three major challenges: First, the deteriorating characteristics of expansive soil, such as softening upon contact with water and cracking upon drying, lead to significant differences in foundation settlement. Traditional pile foundation + concrete beam structure systems are prone to uneven settlement, with cumulative settlement exceeding 300mm, seriously threatening the structural safety and driving comfort of bridges. Second, existing highways have high traffic volumes (over 100,000 vehicles per day). New bridges require temporary supports in the median strip of the roadbed. Traditional construction techniques cause significant disturbance to the existing road surface. Actual measurements show that the settlement joint opening caused by the support foundation construction can reach 5mm / day, posing a risk of inducing structural damage to the road. Third, the rainy season (annual rainfall of 1200mm) highly overlaps with the main construction period. Rainwater infiltration leads to an overconsolidation settlement rate of up to 20mm / day in expansive soil. In addition, restrictions on high-altitude welding operations extend the construction period of conventional steel-concrete composite beams with a single span of over 60m to more than 280 days, increasing labor and material consumption by 40% to 60% compared to plain areas.

[0003] The invention patent with announcement number CN117846045A discloses a pile foundation bearing capacity testing device and method. The main body is a pile body with a hydraulic jack at the bottom. In the end-bearing friction pile test, an upper static load is applied to the top of the pile body, and a load is applied at the bottom of the pile body by setting a hydraulic jack. Under the cooperation of the static load at the top of the pile body and the hydraulic jack at the bottom of the pile body, the mechanism of pile foundation service performance degradation under different ground temperatures and different pile side resistance and pile end resistance distribution ratios can be studied. Thus, the service performance of pile foundations under different pile side resistance and pile end resistance distribution ratios can be tested. Concrete is poured on the surface of the pile body of the pile foundation bearing capacity testing device to form a precast pile. After being driven into permafrost, the load service performance of the precast pile in the permafrost area can be tested. The pile foundation bearing capacity testing device is placed in the borehole and concrete is poured around the pile to achieve the service performance test of the bored cast-in-place pile.

[0004] However, existing testing equipment and methods focus on the bearing capacity testing of pile foundations in permafrost regions under single ground temperature conditions, without simulating the spatial heterogeneity of soil layers. The piles are directly placed into boreholes or molds, and the surrounding soil is usually uniformly filled, failing to reflect the influence of layered soil commonly seen in actual engineering on the distribution ratio of pile side resistance and pile end resistance. Furthermore, existing loading methods primarily rely on static loads at the pile top and axial loading using hydraulic jacks at the pile bottom, only enabling simple switching between axial static loads, pull-out loads, and end-bearing friction piles. They cannot simulate the horizontal cyclic loads that pile foundations may bear in actual engineering projects, thus failing to meet current needs. Summary of the Invention

[0005] The present invention aims to solve the technical problems existing in the prior art; to this end, the present invention proposes a test device and method for the bearing stability of friction piles in expansive soil areas.

[0006] A device for testing the bearing stability of friction piles in expansive soil areas includes: Multi-layer soil simulation system: It consists of a detachable layered pressure chamber, which contains at least 3 independent cavities. Each cavity can be independently filled with soil with different physical parameters (moisture content, density, particle size distribution), and flexible interface sensors are set between the layers to monitor the relative displacement between the layers. Variable parameter friction pile: The pile adopts a modular combination structure, including a detachable pile body outer sleeve. The surface of the outer sleeve is equipped with a roughness adjustment module, which can simulate the surface roughness of the pile by replacing the sleeve with different textures or adjusting the surface protrusion height (0.5~5mm). Multi-directional dynamic loading system: including axial hydraulic loading device and horizontal cyclic loading device. The axial loading device is located at the top of the pile, and the horizontal loading device is implemented by a miniature jack embedded in the middle of the pile body. It can apply sinusoidal cyclic loads with a frequency of 0.1 to 5 Hz. Multi-parameter monitoring system: includes pore pressure sensor, soil moisture sensor, pile strain gauge and three-dimensional laser displacement meter. Sensor signals are uploaded to data processing terminal in real time through wireless transmission module. Intelligent control system: integrates PLC controller and touch screen, can preset loading path (stress control / strain control), and dynamically adjust loading rate and load amplitude according to monitoring data.

[0007] As a further aspect of the present invention: the layered pressure chamber is made of transparent organic glass, and scale lines are set on the inner wall of the chamber to accurately control the thickness of the soil filling. Watertight isolation is achieved between the layers through rubber sealing rings.

[0008] As a further aspect of the present invention: the roughness adjustment module is a detachable threaded sleeve, a boss sleeve, or a smooth sleeve, which is fixed to the outside of the pile core shaft by bolts, and the three types of sleeves have different surface roughness.

[0009] As a further aspect of the present invention: the horizontal cyclic loading device includes two sets of orthogonally arranged miniature jacks, which are loaded by a servo motor driving a ball screw, and can simulate the horizontal thrust of soil or wave cyclic load.

[0010] As a further aspect of the present invention, the multi-parameter monitoring system also includes a temperature and humidity sensor for monitoring environmental parameters in the stratified pressure chamber, and a data processing terminal with a built-in BP neural network model that can invert the shear strength parameters of the pile-soil interface in real time.

[0011] As a further aspect of the present invention: a method for testing the bearing stability of friction piles in expansive soil areas, comprising the following steps: S1: Preparation of Heterogeneous Soil Layer Model Based on the target soil layer parameters, soils with different properties are filled into each cavity of the layered pressure chamber. The compaction error of each soil layer is controlled to be ≤1% during filling, and flexible displacement sensors are installed at the interlayer interface. S2: Friction pile installation and sensor deployment The assembled friction pile is vertically inserted into the center of the layered pressure chamber to ensure that the pile penetration depth meets the design requirements. The pile strain gauge, pore pressure sensor and moisture content sensor are connected in sequence, and the zero point is calibrated. S3: Saturation and Consolidation Treatment Airless water is injected into the pressure chamber through the bottom inlet, and the water level is controlled to 100mm above the pile top. An initial confining pressure of 50kPa is applied to saturate the soil. After the pore pressure coefficient B≥0.95, the consolidation pressure is applied in stages to the target value (50-500kPa). S4: Multi-condition loading test Static loading: Apply axial load at a rate of 0.02 mm / min until the pile top displacement reaches 10% of the pile diameter, and record the load-displacement curve; Cyclic loading: A horizontal cyclic load is superimposed on the axial static load, with 100 to 1000 cycles, and the changes in pile strain and soil pore pressure are monitored. S5: Data Acquisition and Analysis The intelligent control system collects sensor data in real time, analyzes the dynamic response of the soil under cyclic loading through Fourier transform, fits the distribution of pile side friction resistance based on hyperbolic model, and quantitatively evaluates the influence of heterogeneous soil layer on the bearing stability of friction pile. S6: Post-test processing The cavity was unloaded and disassembled to observe the pile-soil interface and analyze internal damage using CT scans.

[0012] As a further aspect of the present invention: in step S1, the physical parameters of the soil include cohesion (5-50 kPa), internal friction angle (10°-35°), and permeability coefficient (10⁻). 6 -10⁻ 2 (cm / s), and the hierarchical combination scheme was determined through orthogonal experimental design.

[0013] As a further aspect of the present invention: in step S3, the consolidation process adopts two modes: isotropic consolidation and K0 consolidation, and the natural stress state of the soil is simulated by adjusting the lateral constraint coefficient of the pressure chamber.

[0014] As a further aspect of the present invention: in step S4, the cyclic loading waveform includes sine wave, triangle wave and square wave, and the load amplitude is 20% to 80% of the static limit load, which is used to simulate actual working conditions such as vehicle load and wave load.

[0015] As a further aspect of the present invention: In step S6, after the test is completed, the pressure chamber is unloaded by controlling the PLC controller, the layered cavity is disassembled, the failure morphology of the pile-soil interface is observed, and the internal damage distribution of the soil is analyzed by combining CT scanning technology.

[0016] Compared with the prior art, the beneficial effects of the present invention are: (1) The friction pile bearing stability testing device and method in the expansive soil area of ​​the present invention realizes the layered filling and independent parameter control of heterogeneous soil layers through the detachable layered pressure chamber structure. Each cavity can be independently filled with soil with different moisture content, density and particle size distribution, and the interlayer relative displacement is monitored by the interlayer flexible interface sensor, which effectively simulates the spatial variation characteristics of the actual strata. In addition, the transparent organic glass material of the layered cavity, combined with laser displacement monitoring, allows for intuitive observation of soil deformation and pile-soil interface slippage process, providing a visual research platform for revealing the deterioration mechanism of pile foundation bearing stability in heterogeneous soil layers.

[0017] (2) The friction pile bearing stability testing device and method in expansive soil areas of this invention integrates multi-field coupled loading capabilities of axial static load, horizontal cyclic loading and temperature control. Through servo hydraulic jacks and micro horizontal loading devices, axial static load and horizontal sinusoidal / triangular wave cyclic load can be applied to simulate the effect of dynamic loads such as earthquakes and waves on the pile foundation. At the same time, the multi-parameter monitoring system synchronously collects data such as pore pressure, strain, displacement, temperature and humidity, and combines the BP neural network model to invert the shear strength parameters of the pile-soil interface in real time. Attached Figure Description

[0018] Figure 1 This is an overall structural diagram of the device of the present invention.

[0019] Figure 2This is a schematic diagram of the sensor layout of the multi-parameter monitoring system in this invention.

[0020] Figure 3 This is a schematic diagram of the method flow in this invention.

[0021] In the diagram: 1. Multi-layer soil simulation system; 11. Layered pressure chamber; 12. Base; 13. Top plate; 14. Flexible interface sensor; 2. Variable parameter friction pile; 21. Pile body; 22. Outer sleeve; 3. Multi-directional dynamic loading system; 31. Axial hydraulic loading device; 32. Horizontal cyclic loading device; 4. Multi-parameter monitoring system; 41. Pore pressure sensor; 42. Pile strain gauge; 43. Moisture content sensor; 44. Three-dimensional laser displacement meter; 45. Temperature and humidity sensor; 5. Intelligent control system. Detailed Implementation

[0022] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0023] Example 1 Please see Figure 1-3 This application provides a testing device for the bearing stability of friction piles in expansive soil areas, comprising a multi-layer soil simulation system 1: consisting of a detachable layered pressure chamber 11, containing at least three independent cavities. The cavities are connected by a combination of flanges and rubber sealing rings. The bottom of the upper cavity extends outward to form a flange, and the top of the lower cavity is correspondingly provided with a recessed flange groove to ensure tight connection and good sealing between layers. Each cavity is equipped with a porous support plate and a flexible sealing layer at its bottom. The porous support plate is made of stainless steel or high-strength plastic, with evenly distributed round holes or hollow grids, and a permeable non-woven fabric is laid on top of it. Alternatively, a rubber membrane can be used to prevent soil from falling off and to meet the testing requirements under saturated and unsaturated conditions. Each pressure chamber has an adjustable through hole at its geometric center for vertical insertion of the pile. The hole diameter is larger than the diameter of the pile 21. An elastic sealing sleeve made of silicone rubber or polyurethane is built into the hole wall. The inner wall of the sleeve is machined with an annular groove to embed an O-ring seal. This allows for vertical penetration of the pile 21 while effectively ensuring the sealing of the pressure chamber and the stability of the pile 21 under dynamic loading. The bottom chamber is fixed to the pressure chamber base 12, and the top of the top chamber is fixed with a pressure chamber top plate 13, forming a complete soil simulation space.

[0024] In this invention, each cavity can be independently filled with soil of different physical parameters (including moisture content, density, particle size distribution, cohesion, internal friction angle, permeability coefficient, etc.) to simulate a heterogeneous expansive soil layer. Flexible interface sensors 14 are installed between the layers to monitor relative displacement. Four to six probes of the flexible interface sensors 14 are evenly arranged around the circumference to contact the interlayer rubber sealing ring. Displacement gauge probes contact the bottom of the upper cavity and the top of the lower cavity to monitor relative sliding displacement between layers. A contact linear displacement sensor (LVDT) is used, and the sensor is fixed to a pressure... The chamber support has a micro-metal plate installed at the probe end, which contacts the interlayer rubber sealing rings at the bottom of the upper chamber and the top of the lower chamber respectively, to monitor the relative sliding displacement between layers in real time. The layered pressure chamber 11 is made of transparent plexiglass, and the inner wall of the chamber is set with scale lines to accurately control the soil filling thickness and ensure the accuracy of the test data. The layers are watertightly isolated by rubber sealing rings. Each layer of the chamber has an adjustable through hole at the center, with a hole diameter 2-3 mm larger than the diameter of the pile 21, and an internal elastic sealing sleeve (made of silicone rubber) to achieve vertical penetration and dynamic sealing of the pile.

[0025] In this invention, the variable parameter friction pile 2: The pile body 21 adopts a modular combination structure. The mandrel is made of stainless steel hollow cylinder with a pre-set wire groove inside for the laying and protection of sensor wires. The bottom end of the mandrel is fixed to the pressure chamber base 12 by a flange to ensure the stability of the pile body. The pile body 21 includes a detachable pile body outer sleeve 22. The surface of the outer sleeve 22 is provided with a roughness adjustment module. The surface roughness of the pile body can be simulated by changing the sleeve with different textures or adjusting the surface protrusion height. The roughness adjustment module is a detachable threaded sleeve, a boss sleeve, or a smooth sleeve. It is fixed to the outside of the pile body mandrel by an elastic positioning ring (rubber material) and bolts. The three sleeves have different surface roughnesses. Different surface roughnesses of the pile body 21 can be simulated by changing the sleeve or adjusting the surface protrusion height (range of 0.5 to 5 mm). An O-ring is provided between the sleeve and the mandrel. Two to three annular grooves are opened on the contact surface to prevent soil particles from intruding and ensure the reliability of the pile structure.

[0026] The multi-directional dynamic loading system 3 of this invention includes an axial hydraulic loading device 31 and a horizontal cyclic loading device 32. The axial loading device 31 uses a servo hydraulic jack, which is set in the center of the top plate 13 and fixed to the external base by a gantry frame to avoid disturbing the soil and can accurately apply axial loads. The horizontal loading device 32 is implemented by a miniature jack embedded in the middle of the pile body. It can apply cyclic loads of sine, triangular, or square waves with a frequency of 0.1 to 5 Hz. The load amplitude is 20% to 80% of the static ultimate load. The horizontal cyclic loading device 32 includes two sets of orthogonally arranged miniature jacks, which are respectively set at the connection of adjacent cavities. The loading is achieved by a ball screw driven by a servo motor. It can simulate various actual working conditions such as horizontal thrust of soil and wave cyclic load.

[0027] In this invention, the multi-parameter monitoring system 4 integrates multiple sensors to achieve real-time and accurate monitoring of multiple physical quantities during the experiment. The multi-parameter monitoring system 4 includes a pore pressure sensor 41, a soil moisture content sensor 43, a pile strain gauge 42, and a three-dimensional laser displacement gauge 44. Sensor signals are uploaded to the data processing terminal in real time via a wireless transmission module. The multi-parameter monitoring system 4 also includes a temperature and humidity sensor 45 for monitoring environmental parameters within the layered pressure chamber 11. The data processing terminal has a built-in BP neural network model that can invert the shear strength parameters of the pile-soil interface in real time. The pile strain gauge 42 is attached to the surface of the pile mandrel and positioned near the upper and lower ends of the roughness module and the horizontal loading point. The wires are led out through internal wire grooves.

[0028] In this invention, 1 to 2 pore pressure sensors 41 are arranged in the middle and bottom of each layer of the layered pressure chamber 11, specifically at half the height of each soil layer and 50 mm below the interlayer interface, to monitor the changes in pore water pressure in each layer of heterogeneous soil. The sensors in the layered soil are embedded in the soil during sample preparation using a "positioning before filling" method. They are fixed to pre-set holes in the side wall of the chamber by supports. The diameter of the holes is 2 to 3 mm larger than the outer diameter of the sensors, and the surrounding area is sealed with Vaseline to prevent water leakage.

[0029] In this invention, one set of pile strain gauges 42 is arranged 50mm below the loading end of the pile top and 100mm above the pile bottom to monitor stress concentration at the pile end; another set is arranged every 150-200mm along the pile axis, with a focus on the upper, middle and lower ends of the roughness adjustment module to capture the distribution of bending moment and shear force in the pile; before the strain gauges are pasted, the surface of the mandrel is polished, coated with special adhesive (such as cyanoacrylate), and covered with a waterproof protective layer (such as silicone rubber); the wires are led out through a pre-set spiral wire groove inside the mandrel, with a groove diameter of 3-5mm, and a certain amount of slack is reserved in the groove to prevent the pile from deforming and breaking the wires.

[0030] In this invention, one moisture content sensor 43 is arranged at the geometric center of each cavity, at a horizontal distance of 2-3 times the pile diameter, to avoid disturbance of soil moisture content by pile loading. An additional sensor is installed 10mm above the interface between two adjacent soil layers to monitor the water migration characteristics at the interface of heterogeneous soil layers. A needle-type sensor is used, which is vertically inserted into the soil to a set depth during sample preparation. The sensor wire is led out through a sealed joint on the side wall of the pressure chamber, and the joint is sealed with epoxy resin. The sensor is wrapped with water-permeable gauze to prevent soil particles from entering the electrode gap and affecting the measurement accuracy.

[0031] In this invention, a three-dimensional laser displacement meter 44 is set above the center of the pressure chamber top plate 13, aligned with the reflective target at the top of the pile, to monitor the axial displacement and horizontal offset of the pile top. On the transparent organic glass outer wall of the layered pressure chamber 11, laser measuring points are set every 50 mm along the radial direction of the pile body to monitor the settlement or heave deformation of the soil surface, with a measuring point spacing of 100-200 mm.

[0032] In this invention, one temperature and humidity sensor 45 is arranged at the top and one at the bottom of the layered pressure chamber 11 to monitor the temperature and humidity changes of the test environment and avoid the influence of environmental parameter fluctuations on the mechanical properties of the soil; a miniature integrated sensor is used and fixed to the side wall of the pressure chamber with double-sided adhesive.

[0033] The intelligent control system 5 in this invention integrates a PLC controller and a touch screen, which can preset the loading path (stress control / strain control) and dynamically adjust the loading rate and load amplitude according to monitoring data.

[0034] Example 2 Reference Figure 1 - Figure 3 This is the second embodiment of the present invention, wherein a method for testing the bearing stability of friction piles in expansive soil areas includes the following steps: S1: Preparation of Heterogeneous Soil Layer Model Based on the target soil layer parameters, orthogonal experimental design was used to determine the combination scheme of physical parameters of the layered soil, including cohesion, internal friction angle and permeability coefficient. Soil with different properties was filled into each of the 11 stratified pressure chambers. During the filling process, the compaction error of each soil layer was strictly controlled to be ≤1%. Flexible displacement sensors were installed at the interlayer interface to complete the construction of the heterogeneous soil layer model.

[0035] S2: Friction pile installation and sensor deployment The assembled variable parameter friction pile 2 is vertically inserted into the center of the layered pressure chamber 11 to ensure that the pile 21 penetrates the soil to the design depth. The pile strain gauge 42, pore pressure sensor 41 and moisture content sensor 43 are connected in sequence, and the zero point of each sensor is calibrated to ensure the accuracy of the monitoring data.

[0036] S3: Saturation and Consolidation Treatment Airless water is injected into the pressure chamber through the bottom inlet, and the water level is controlled to 100mm above the pile top. An initial confining pressure of 50kPa is applied to saturate the soil. After the pore pressure coefficient B≥0.95, consolidation pressure is applied in stages to the target value. The consolidation process can adopt two modes: isotropic consolidation and K0 consolidation. The natural stress state of the soil is simulated by adjusting the lateral constraint coefficient of the pressure chamber.

[0037] S4: Multi-condition loading test Static loading: Apply axial load at a rate of 0.02 mm / min and continuously record the load-displacement data at the top of the pile until the displacement at the top of the pile reaches 10% of the pile diameter, and obtain the static bearing capacity curve of the friction pile.

[0038] Cyclic loading: On the basis of axial static load, a horizontal cyclic load is superimposed, and the number of cycles is set to 100 to 1000 times; the loading waveforms such as sine wave, triangular wave or square wave can be selected, and the load amplitude is 20% to 80% of the static ultimate load to simulate actual working conditions such as vehicle load and wave load, and simultaneously monitor the changes in pile strain and soil pore pressure.

[0039] S5: Data Acquisition and Analysis The intelligent control system collects data from various sensors in real time and transmits it to the data processing terminal. It analyzes the dynamic response characteristics of the soil under cyclic loading through Fourier transform, fits the distribution curve of pile side friction based on hyperbolic model, quantitatively evaluates the influence of heterogeneous soil layer on the bearing stability of friction pile, and conducts in-depth research on the pile-soil interaction mechanism.

[0040] S6: Post-test processing After the test, the pressure chamber was slowly unloaded under the control of the PLC controller, and the layered cavities were disassembled in order from top to bottom. The friction pile was carefully removed, the failure morphology of the pile-soil interface was observed, and high-definition photos were taken to record the failure characteristics. The layered soil samples were subjected to CT scans, and the internal damage distribution of the soil was analyzed using professional image processing software. Combining the test data and analysis results, the bearing capacity law of friction piles in expansive soil areas was summarized, providing a scientific basis for the design and optimization of pile foundation engineering.

[0041] This invention, through the collaborative design of a layered pressure chamber, a variable roughness pile body, and a multi-parameter monitoring system, forms a set of friction pile bearing stability testing systems suitable for heterogeneous soil layers.

[0042] The above embodiments are only used to illustrate the technical methods of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical methods of the present invention without departing from the spirit and scope of the technical methods of the present invention.

Claims

1. A testing device for the bearing stability of friction piles in expansive soil areas, characterized in that, include: A multi-layer soil simulation system (1) was constructed, which consists of a detachable layered pressure chamber (11) for filling soil with different physical parameters and monitoring the relative displacement between layers; A variable parameter friction pile body (2) is set. The pile body adopts a modular combination structure and simulates different surface roughness of the pile body through the roughness adjustment module. A multi-directional dynamic loading system (3) is configured, which includes an axial hydraulic loading device (31) and a horizontal cyclic loading device (32) for applying axial loads and horizontal cyclic loads at different frequencies; Establish a multi-parameter monitoring system (4). This system monitors environmental and pile-soil interaction parameters through various sensors and uploads the signals to the data processing terminal in real time. An integrated intelligent control system (5) is used to preset the loading path and dynamically adjust the loading rate and load amplitude based on monitoring data.

2. The device for testing the bearing stability of friction piles in expansive soil areas according to claim 1, characterized in that, The number of the layered pressure chambers (11) is set to at least three groups; The layered pressure chamber (11) is made of transparent material and has scale lines on the inner wall to accurately control the thickness of the soil filling. The layers are separated by a sealing structure to achieve watertight isolation.

3. The device for testing the bearing stability of friction piles in expansive soil areas according to claim 1, characterized in that, The roughness adjustment module is a detachable sleeve that is fixed to the outside of the pile core shaft by bolts, and includes threads, bosses or smooth surfaces.

4. The bearing stability testing device for friction piles in expansive soil areas according to claim 1, characterized in that, The horizontal cyclic loading device (32) includes orthogonally arranged miniature jacks, and a ball screw driven by a servo motor to achieve multi-wave loading.

5. The device for testing the bearing stability of friction piles in expansive soil areas according to claim 1, characterized in that, The multi-parameter monitoring system (4) monitors environmental parameters through temperature and humidity sensors, and the terminal model inverts the shear strength of the pile-soil interface in real time.

6. A method for testing the bearing stability of friction piles in expansive soil areas, characterized in that, The friction pile bearing stability testing device for expansive soil areas according to any one of claims 1-5 is characterized by comprising the following steps: S1: Preparation of heterogeneous soil layer model, filling soil in layers according to target parameters, and installing interlayer displacement sensors; S2: Friction pile installation and sensor layout, vertically inserting into the pile and connecting and calibrating various sensors; S3: Saturation and consolidation treatment, water is injected into the pressure chamber to saturate the soil, and consolidation pressure is applied in stages after the conditions are met. S4: Multi-condition loading test, including static loading to obtain load-displacement curves, and superimposing horizontal cyclic load on the basis of axial static load and monitoring relevant parameters; S5: Data acquisition and analysis, using Fourier transform and hyperbolic model to evaluate the impact of heterogeneous soil layers on bearing stability.

7. The method for testing the bearing stability of friction piles in expansive soil areas according to claim 6, characterized in that, In step S1, the soil layer combination scheme is determined through experimental design, and the soil physical parameters include mechanical and permeability parameters.

8. The method for testing the bearing stability of friction piles in expansive soil areas according to claim 6, characterized in that, In step S3, an isotropic or K0 consolidation mode is used, and the lateral constraint coefficient is adjusted to simulate the natural stress state.

9. A method for testing the bearing stability of friction piles in expansive soil areas according to claim 6, characterized in that, In step S4, the cyclic loading uses multiple waveforms to simulate the actual working load with different amplitudes.

10. A method for testing the bearing stability of friction piles in expansive soil areas according to claim 6, characterized in that, It also includes step S6, after which the cavity is unloaded and disassembled after the test, the pile-soil interface is observed and the internal damage is analyzed in conjunction with CT scan.

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