Pile foundation negative friction coefficient-displacement full curve testing device and method under dry-wet cycle condition
By developing a testing device and method for the full curve of negative skin friction coefficient-displacement of pile foundations under dry-wet cycle conditions, and utilizing cyclic operations of vacuuming and water saturation, rapid testing of the full curve of negative skin friction coefficient-displacement of pile foundations was achieved. This solved the problem of rapidly obtaining key design parameters in high-fill structures in hydropower station reservoir areas and met the project schedule requirements.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-10
- Publication Date
- 2026-04-10
AI Technical Summary
Existing technologies struggle to quickly obtain the full curve of negative skin friction coefficient-displacement of pile foundations under wet-dry cycle conditions, especially in high-fill structures in hydropower station reservoir areas where construction schedules are tight and the settlement of the soil around the piles is complex, and there is a lack of rapid testing equipment and methods.
A pile foundation negative skin friction coefficient-displacement full curve testing device under dry and wet cycle conditions is adopted, including a test chamber, a vacuum chamber, a seepage drainage module and a testing module. Through the cyclic operation of vacuuming and water saturation, combined with pile side earth pressure gauges and settlement monitoring gauges, the device can achieve rapid soil settlement and precise testing of negative skin friction coefficient.
It enables rapid testing of the full curve of negative skin friction coefficient-displacement of pile foundation under wet-dry cycle conditions, breaking through the limitations of single skin friction coefficient testing, and provides a refined constitutive model of negative skin friction coefficient of pile side, providing key design parameters for high embankment buildings and meeting the project schedule requirements.
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Figure CN121827397A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of high-end equipment and testing in geotechnical engineering, specifically relating to a device and method for testing the full curve of negative skin friction coefficient-displacement of pile foundation under wet-dry cycle conditions. Background Technology
[0002] With the vigorous advancement of national water conservancy and hydropower projects, the formation of large-scale reservoirs in high mountain and canyon areas has brought about the need for resettlement of displaced persons. Therefore, building high-fill towns on both sides of the reservoir area to solve the resettlement problem has become an inevitable path for the development of the times. Under these conditions, the high fill undergoes a series of wet-dry cycles of repeated infiltration, drainage, re-infiltration, and re-drying by the reservoir water level, resulting in long-term settlement. At this time, when buildings are constructed on the high fill, the part of the building pile foundation that penetrates the fill body will inevitably interact with the fill soil and rock. The wet-dry cycle settlement of the soil and rock relative to the pile foundation moves downward, thus generating a downward drag force along the pile side (and negative skin friction of the pile foundation), causing a qualitative change in the bearing capacity characteristics of the pile foundation. How to accurately test the characteristics of negative skin friction and obtain a quantitative curve relationship between negative skin friction and pile-soil shear displacement has become a new technical challenge in the industry.
[0003] Currently, some technologies exist for testing the negative skin friction of pile foundations, but these are mostly based on a single, slow settlement of the soil around the pile, resulting in a very inefficient testing process. This is time-consuming and generally limited to testing only the coefficient of negative skin friction; there are few experimental equipment and technologies that can quickly obtain continuous negative skin friction coefficient-displacement curves for pile foundations. For high-fill infrastructure in hydropower station reservoirs, due to frequent rises and falls in reservoir water levels, significant and complex settlement of the fill around the piles, coupled with tight construction schedules, there is an urgent need to develop relevant technical equipment to achieve rapid testing of the complete negative skin friction coefficient-displacement curve of pile foundations under wet-dry cycle conditions. Summary of the Invention
[0004] The first objective of this invention is to provide a full curve testing device for negative skin friction coefficient-displacement of pile foundation under dry-wet cycle conditions, addressing the aforementioned problems.
[0005] To achieve the above objectives, the present invention adopts the following technical solution:
[0006] A pile foundation negative skin friction coefficient-displacement full curve testing device under dry and wet cycle conditions includes a test chamber, a vacuum chamber, a test platform base, a seepage drainage module, and a testing module. The test platform base is equipped with the test chamber, vacuum chamber, seepage drainage module, and testing module.
[0007] The test chamber is barrel-shaped, with a water inlet at the top and a pile foundation penetrating the bottom of the test chamber inserted in the center. The chamber is filled with soil around the pile foundation to simulate a high embankment.
[0008] The vacuum cavity is arranged between the test cabin bottom and the test bed base, and an air extraction pump is arranged at the edge of the vacuum cavity.
[0009] The water seepage and drainage module comprises a test cabin bottom seepage channel, a test bed base water drainage channel and a water drainage device.
[0010] The test module comprises a pile side soil pressure gauge, a soil pressure signal optical fiber, a pile bottom pressure sensor, a steel bar gauge, a settlement monitoring gauge and a settlement signal optical fiber.
[0011] In addition to the above technical solutions, the present application can also adopt or combine the following technical solutions:
[0012] As a preferred technical solution of the present application, the test cabin bottom is provided with vertical seepage channels arranged in a ring scattering manner, and a filter layer is arranged on the upper side of the test cabin bottom.
[0013] As a preferred technical solution of the present application, the pile foundation is in a cylindrical shape, and vertical steel bars are arranged in the pile.
[0014] As a preferred technical solution of the present application, the test bed base is fixed on a solid ground, and a pile supporting platform is arranged at the central position of the test bed base.
[0015] As a preferred technical solution of the present application, the water in the soil layer seeps into the vacuum cavity through the test cabin bottom seepage channel, and the water in the vacuum cavity is drained into the water drainage device through the test bed base water drainage channel when the vacuum is extracted.
[0016] As a preferred technical solution of the present application, the pile side soil pressure gauges are arranged in the pile foundation side at equal intervals from bottom to top, and are exposed to contact with the surrounding soil, and the pile side soil pressure gauges are connected by the soil pressure signal optical fiber to transmit the measured pile side soil pressure data in the test to the computer terminal.
[0017] As a preferred technical solution of the present application, the pile bottom pressure sensor is arranged in the pile supporting platform and directly contacts with the pile bottom to measure the pile bottom pressure generated when the pile foundation is displaced downward during the test.
[0018] As a preferred technical solution of the present application, the steel bar gauges are divided into upper and lower steel bar gauges corresponding to the upper and lower steel bars of each pile side soil pressure gauge, and are used to monitor the strain of the steel bar during the test and to calculate the pile foundation axial force difference corresponding to the upper and lower ends of each pile side soil pressure gauge.
[0019] As a preferred technical scheme of the present application: the settlement monitoring meter is arranged at the same height corresponding to each pile side soil pressure meter, is buried in the soil layer at equal intervals from bottom to top, and is used for monitoring the settlement of each position in the soil layer; the settlement monitoring meter is connected by a settlement signal optical fiber, and the settlement data measured in the test can be transmitted to a computer terminal.
[0020] The second object of the present application is to provide a method for testing the negative skin friction coefficient-displacement full curve of a pile foundation under dry-wet cycle conditions.
[0021] To this end, the above object of the present application is achieved by the following technical scheme:
[0022] A method for testing the negative skin friction coefficient-displacement full curve of a pile foundation under dry-wet cycle conditions, which is based on the device as described above and comprises the following steps:
[0023] S1, sample loading and saturation: the pile foundation with a pile side soil pressure meter and a reinforcement meter is penetrated through the middle part of the test cabin and the pile bottom touches the pile supporting platform; the soil layer is filled in the test cabin layer by layer from bottom to top around the pile foundation; when filling reaches the position of a pile side soil pressure meter, a settlement monitoring meter is installed at the corresponding elevation, and the soil layer is continuously filled upwards; and the filling work is ended until the preset elevation position is reached. Then, the water injection faucet is opened to slowly inject water into the soil layer until the water level in the soil layer gradually rises to the top surface of the soil layer, and the soil body is in a saturated state;
[0024] S2, vacuum water abstraction and settlement full process test and monitoring: after the soil layer is saturated with water, the water collecting pipe valve is closed, the air pump is opened to perform air extraction, the vacuum cavity condition is created, the water in the soil layer in the test cabin penetrates into the vacuum cavity under the action of the external pressure difference, and the purpose of achieving soil layer dewatering to promote rapid soil layer settlement is achieved;
[0025] After the water in the soil layer completely penetrates out, the air pump is closed, and the water collecting pipe valve is opened to discharge the water in the vacuum cavity through the water collecting pipe, and thus one cycle of rapid soil layer dewatering and settlement based on vacuum is completed.
[0026] In this way, after the vacuum dewatering and settlement are completed, the process of water saturation, vacuum dewatering and soil layer settlement is started again, and the process of water saturation, vacuum dewatering and soil layer settlement is repeated for two or more times to achieve the rapid dry-wet cycle settlement process of the soil layer, and the test monitoring is carried out synchronously during the vacuum dewatering and settlement process.
[0027] S3, processing test monitoring data: according to the strain monitoring data of the steel bar meter corresponding to the upper and lower ends of each pile side soil pressure meter during the dry-wet cycle test, the pile foundation axial force data corresponding to the upper and lower ends of each pile side soil pressure meter is obtained, and then the pile side negative friction resistance corresponding to the position of each pile side soil pressure meter is quantified through force balance analysis, combined with each pile side soil pressure monitoring, the pile side negative friction resistance coefficient corresponding to the position of each pile side soil pressure meter is quantified and obtained, and combined with the settlement displacement monitoring of the settlement monitoring meter corresponding to each pile side soil pressure meter, the fine pile side negative friction resistance coefficient-displacement dry-wet cycle whole process curve of the pile foundation under dry-wet cycle condition is finally obtained.
[0028] The present application provides a kind of dry-wet cycle conditions under the negative friction resistance coefficient-displacement whole curve testing device and method of pile foundation, with the following beneficial effects:
[0029] 1) the present application first realizes the rapid generation of pile side negative friction resistance by the way of vacuum extraction to promote the settlement of soil around pile;
[0030] 2) the present application first realizes the rapid simulation of complex mechanical environment of pile side under dry-wet cycle condition through the repeated operation of water saturation-vacuum precipitation-soil settlement, solves the technical problem that key design parameters of pile foundation negative friction resistance cannot be quickly and efficiently obtained under the situation of tight construction period of high fill construction in reservoir area;
[0031] 3) the present application breaks through the limitation of previous technology only in testing single friction resistance coefficient, first realizes the whole process test of pile side negative friction resistance coefficient about settlement displacement whole curve, provides the possibility for constructing fine pile side negative friction resistance coefficient constitutive model. BRIEF DESCRIPTION OF DRAWINGS
[0032] Figure 1 It is the schematic diagram of the negative friction resistance coefficient-displacement whole curve testing device of pile foundation under dry-wet cycle condition provided by the present application.
[0033] Figure 2 It is Figure 1 the sectional view of A-A.
[0034] Figure 3 It is Figure 1 the sectional view of B-B.
[0035] Figure 4 It is Figure 1 the sectional view of C-C.
[0036] Figure 5 It is Figure 1 the sectional view of D-D.
[0037] Figure 6 It is the settlement schematic diagram from once precipitation to half.
[0038] Figure 7 The settlement after the completion of the first precipitation is shown.
[0039] Figure 8 The standard analysis section view of the negative skin friction of the pile foundation.
[0040] Figure 9 The full process curve of the negative skin friction coefficient-displacement of the pile foundation under the dry-wet cycle condition.
[0041] In the figure: 1 - right water tap, 2 - settlement monitoring meter, 21~28 - settlement monitoring meter from high to low 1~n, 3 - settlement signal optical fiber, 4 - pile side soil pressure meter, 41~48 - pile side soil pressure meter from high to low 1~n, 5 - soil pressure signal optical fiber, 6 - upper side steel bar meter, 7 - lower side steel bar meter, 8 - filling soil, 9 - high water level, 9a - precipitation to half water level, 10 - pile foundation, 11 - steel bar, 12 - left water tap, 13 - test cabin side wall, 13a - filling soil top surface original elevation, 14 - filter layer, 15 - test cabin bottom, 15a - test cabin bottom leakage passage, 15b - test cabin bottom pile surrounding control joint, 16 - vacuum air pump, 16a - air extraction, 16b - air extraction pipe, 17 - water collector surface of water drainer, 17a - water collector pipe valve of water drainer, 17b - water collector pipe of water drainer, 18 - vacuum cavity, 19 - pile supporting platform, 20 - pile bottom pressure sensor, 21 - leakage water drop, 22 - test platform base, 22a - water drainage passage of test platform base, 23 - settlement amount Δs1 of filling soil top surface after the first precipitation to half filling soil top surface, 24 - settlement amount Δs2 of filling soil top surface after the completion of the first precipitation, 25 - local analysis of pile foundation test, 26 - upper side axial force of pile section, 27 - lower side axial force of pile section, 28 - negative skin friction of pile side, 29 - soil pressure of pile side, 30 - radius of pile foundation, 31 - effective distance of upper and lower side steel bar meters. DETAILED DESCRIPTION
[0042] The application is described in further detail with reference to the drawings and specific embodiments.
[0043] As Figures 1-5 shown, a full curve test device of negative skin friction coefficient-displacement of pile foundation under dry-wet cycle condition, comprising a test cabin, a vacuum cavity, a test platform base, a water seepage and drainage module, and a test module, wherein the test platform base is provided with the test cabin, the vacuum cavity, the water seepage and drainage module, and the test module; the test platform base 22 is the basic part of the whole test device, and is fixed on a solid ground; a pile supporting platform 19 is arranged at the central position of the test platform base;
[0044] The test cabin is barrel-shaped, which is surrounded by the test cabin side wall 13 and the test cabin bottom 15, and water injection faucets (right faucet 1 and left faucet 12) are arranged above the test cabin, a pile foundation 10 is inserted into the middle of the test cabin, and soil layers are filled around the pile foundation to simulate high fill embankment; the test cabin bottom and the pile foundation penetrating therebetween have gap control to avoid friction therebetween; the test cabin bottom has vertically distributed vertical leakage passages in an annular scattering shape, and a filter layer 14 is arranged on the upper side of the test cabin bottom to prevent soil particles and other fine materials from being carried away during the downward seepage of water in the soil layer; the pile foundation is cylindrical, and vertical steel bars 11 are arranged in the pile foundation to facilitate the embedded implementation of the steel bar gauge for axial force monitoring.
[0045] The vacuum cavity 18 is arranged between the test cabin bottom and the test bench base, and a vacuum air pump 16 is arranged at the edge of the vacuum cavity; after the air pump is started, the air in the vacuum cavity can be pumped out through the air pump 16b, so that a vacuum cavity is formed.
[0046] The seepage and drainage module includes the test cabin bottom leakage passage 15a, the test bench base drainage passage 22a, and a water drainer; the water in the soil layer 8 seeps into the vacuum cavity through the test cabin bottom leakage passage, and the water seeping into the vacuum cavity is drained into the water drainer through the test bench base drainage passage when the vacuum is pumped.
[0047] The test cabin bottom leakage passage is directly connected to the vacuum cavity; when the vacuum is pumped in the cavity, the water in the soil layer in the test cabin will seep downward under the action of the external pressure difference and seep into the vacuum cavity through the test cabin bottom leakage passage.
[0048] The test bench base drainage passage is vertically arranged in the test bench base and connected to the vacuum cavity, and can drain the water seeping into the vacuum cavity when the vacuum is pumped into the water drainer.
[0049] The water drainer is arranged in the test bench base, and the upper side thereof is connected to the test bench base drainage passage to form a generally disc-shaped water drainer water collecting surface 17, which covers the bottoms of all the drainage passages, and the side is connected to the horizontal water collecting pipe to guide the water out of the test bench.
[0050] The water drainer water collecting pipe 17b side is provided with a water drainer water collecting pipe valve 17a; when the air pump is started to pump the vacuum, the valve needs to be closed to ensure that the inside of the vacuum cavity is disconnected from the atmosphere, so that the conditions for pumping the vacuum are met, the water in the soil layer in the upper test cabin seeps downward under the action of the external pressure difference and enters the vacuum cavity, and the water level in the soil layer is lowered. After the water in the soil layer completely seeps out, the air pump can be closed, the water drainer water collecting pipe valve can be opened, the water in the vacuum cavity can be drained through the water collecting pipe, and the soil layer precipitation and settlement based on vacuum pumping are completed.
[0051] The test module includes a pile side soil pressure gauge 4, a soil pressure signal optical fiber 5, a pile bottom pressure sensor 20, a steel bar gauge, a settlement monitoring gauge 2, a settlement signal optical fiber 3, and the like.
[0052] The pile side soil pressure gauges are arranged equidistantly from bottom to top in the side of the pile foundation, exposed and in contact with the surrounding soil, and connected by soil pressure signal optical fibers to transmit the measured pile side soil pressure data to the computer terminal.
[0053] The pile bottom pressure sensor is arranged in the pile bearing platform and in direct contact with the pile bottom to measure the pile bottom pressure generated when the pile foundation is displaced downward during the test.
[0054] The reinforcement gauges are divided into upper reinforcement gauges 6 and lower reinforcement gauges 7, corresponding to the upper and lower ends of each pile side soil pressure gauge, for monitoring the strain of the reinforcement during the test and converting the pile foundation axial force difference corresponding to the upper and lower ends of each pile side soil pressure gauge.
[0055] The settlement monitoring gauges are arranged at the same height corresponding to each pile side soil pressure gauge and equidistantly buried in the soil layer from bottom to top, for monitoring the settlement at each position in the soil layer, and connected by settlement signal optical fibers to transmit the measured settlement data to the computer terminal.
[0056] A method for testing the negative skin friction coefficient-displacement full curve of a pile foundation under dry-wet cycle conditions, based on the device described above, comprising the following steps:
[0057] S1, sample preparation and saturation: the pile foundation with pile side soil pressure gauges and reinforcement gauges is penetrated through the middle of the test chamber and the pile bottom touches the pile bearing platform, and the soil layer is filled in layers from bottom to top around the pile foundation in the test chamber, and whenever it is filled to the position of a pile side soil pressure gauge, a settlement monitoring gauge is installed at the corresponding elevation, and the soil layer is continuously filled upwards, and so on until the filling work is completed at the preset elevation. Then, the water inlet valve is opened to slowly inject water into the soil layer until the water level in the soil layer gradually rises to the top surface of the soil layer, and the soil is saturated;
[0058] S2, vacuum drainage and settlement full process test and monitoring: after the soil layer is saturated with water, the water collection pipe valve is closed and the air pump is opened to create a vacuum chamber condition, realizing the downward infiltration of water in the soil layer in the test chamber under the action of external pressure difference into the vacuum chamber, achieving the purpose of soil layer precipitation to promote rapid settlement of the soil layer;
[0059] After the water in the soil layer completely infiltrates, the air pump is closed and the water collection pipe valve is opened to discharge the water in the vacuum chamber through the water collection pipe, completing the soil layer precipitation and settlement based on vacuum.
[0060] Similarly, after the vacuum precipitation of water is completed, the process of water injection saturation of the soil layer, vacuum precipitation of water, and settlement of the soil layer is started again, and the process of water injection saturation, vacuum precipitation of water, and settlement of the soil layer is repeated for two or more times to realize the rapid dry-wet cycle settlement process of the soil layer, and the test monitoring is simultaneously carried out in the vacuum precipitation of water settlement process;
[0061] S3, processing of the test monitoring data: according to the strain monitoring data of the reinforcement gauges corresponding to the upper and lower positions of each pile side soil pressure gauge in the dry-wet cycle test process, the pile foundation axial force data corresponding to the upper and lower positions of each pile side soil pressure gauge are obtained, and then the pile side negative skin friction corresponding to the positions of each pile side soil pressure gauge is quantified through force balance analysis, the pile side negative skin friction coefficient corresponding to the positions of each pile side soil pressure gauge is quantified by combining the pile side soil pressure monitoring, and finally the fine pile side negative skin friction coefficient-displacement dry-wet cycle whole process curve of the pile foundation at different positions under the dry-wet cycle condition is obtained by combining the settlement displacement monitoring of the settlement monitoring gauges corresponding to each pile side soil pressure gauge.
[0062] As shown in Figures 6-7 , the settlement of the soil layer in the vacuum precipitation of water process is shown. It can be seen that when the water is half precipitated, the soil layer has an overall settlement, and the settlement amount of the top of the soil layer can be recorded as As123. When the water is precipitated to the bottom of the test cabin, the soil layer has an overall settlement, and the settlement amount of the top of the soil layer can be recorded as As224.
[0063] As shown in Figure 8 , the standard analysis section of the pile foundation negative skin friction is shown, which is obtained by intercepting the pile foundation with the reinforcement gauges on the upper and lower sides of the pile side soil pressure gauge as the benchmark. It can be seen that the axial force 26 of the upper pile section can be measured by the upper reinforcement gauge of the pile side soil pressure gauge, F’=πR 2 ε’E, the axial force 27 of the lower pile section can be measured by the lower reinforcement gauge of the pile side soil pressure gauge, F=πR 2 εE, and the pile side soil pressure σ can be measured according to the pile side soil pressure gauge. Wherein, ε’ is the strain measured by the upper reinforcement gauge, ε is the strain measured by the lower reinforcement gauge, E is the elastic modulus of the concrete pile foundation, and R is the radius 30 of the pile foundation. According to the vertical force balance analysis of the section, the sum of the pile side negative skin friction 28 of the section is balanced with the difference between the upper and lower section axial forces, i.e. the pile foundation negative skin friction τ=(F-F’) / (2πRΔL) is obtained, wherein ΔL31 is the height of the section. The pile foundation negative skin friction coefficient μ=τ / σ can be obtained by dividing the pile foundation negative skin friction by the pile side soil pressure 29.
[0064] As shown in Figure 9As shown, μ is the negative skin friction coefficient axis, S is the shear displacement axis, and the full process curve of the negative skin friction coefficient-displacement of the test pile at different positions under the dry-wet cycle condition is displayed, wherein the positions of the pile side soil pressure gauges represent different depth positions of the pile foundation, and the settlement displacement of the settlement monitoring gauge corresponding to the position of each pile side soil pressure gauge represents the settlement displacement between the pile foundation and the soil layer at the depth position. It can be seen that the measured negative skin friction coefficient of the pile foundation at different depth positions (the positions of the pile side soil pressure gauges) presents a regular change process of first increasing and then decreasing with the development of the settlement displacement at the position, and since the deeper the depth, the closer the pile foundation and the soil layer, the negative skin friction coefficient of the pile foundation generally presents an increasing trend with the increase of the depth. In addition, it can be seen that the negative skin friction coefficient presents a decreasing trend with the increase of the dry-wet cycle times.
[0065] The above specific embodiments are used to explain and illustrate the present application, and are only preferred embodiments of the present application, but not limit the present application, and any modification, equivalent replacement, improvement, etc. made to the present application falls within the protection scope of the present application.
Claims
1. A device for testing the full curve of the negative skin friction coefficient-displacement of a pile foundation under dry-wet cyclic conditions, characterized in that: The test cabin, the vacuum cavity, the test bed base, the seepage drainage module and the test module are arranged on the test bed base. The test cabin is barrel-shaped, and a water filling faucet is arranged above the test cabin. The vacuum cavity is arranged between the test cabin bottom and the test bed base, and an air suction pump is arranged at the edge of the vacuum cavity. The seepage drainage module comprises a test cabin bottom seepage channel, a test bed base drainage channel and a water drainer. The test module comprises a pile side soil pressure gauge, a soil pressure signal optical fiber, a pile bottom pressure sensor, a steel bar gauge and a settlement monitoring gauge.
2. The apparatus of claim 1, wherein: The test cabin bottom is provided with vertical seepage channels arranged in a ring scattering shape, and a filter layer is arranged on the upper side of the test cabin bottom.
3. The apparatus of claim 1, wherein: The pile base is cylindrical, and vertical steel bars are arranged in the pile.
4. The apparatus of claim 1, wherein: The test bed base is fixed on a solid ground, and a pile bearing platform is arranged at the central position of the test bed base.
5. The apparatus of claim 1, wherein: The water in the soil layer seeps into the vacuum cavity through the test cabin bottom seepage channel, and the water in the vacuum cavity is drained through the test bed base drainage channel and the water drainer.
6. The apparatus of claim 1, wherein: The pile side soil pressure gauges are arranged in the pile base side at equal intervals from bottom to top, and are exposed to contact with the surrounding soil.
7. The apparatus of claim 1, wherein: The pile bottom pressure sensor is arranged in the pile bearing platform and directly contacts with the pile bottom to measure the pile bottom pressure generated when the pile base is displaced downward during the test.
8. The apparatus of claim 1, wherein: The steel bar gauges are divided into upper and lower steel bar gauges corresponding to the upper and lower ends of each pile side soil pressure gauge, and are used to monitor the strain of the steel bars during the test and to calculate the axial force difference of the pile base at the upper and lower ends of each pile side soil pressure gauge.
9. The apparatus of claim 1, wherein: The settlement monitoring gauges are arranged at equal heights corresponding to each pile side soil pressure gauge, and are buried in the soil layer at equal intervals from bottom to top to monitor the settlement of each position in the soil layer.
10. A method for testing the full curve of the negative skin friction coefficient-displacement of a pile foundation under dry-wet cyclic conditions, characterized in that: The method is based on the device of any one of claims 1-9 and comprises the following steps: S1, sample loading and saturation: the pile base with the pile side soil pressure gauges and the steel bar gauges penetrates the central position of the test cabin bottom and touches the pile bearing platform, and the soil layer is filled in the test cabin from bottom to top in layers around the pile base, and the settlement monitoring gauges are installed at the corresponding elevations when the filling reaches the position of each pile side soil pressure gauge, and the soil layer is continuously filled upwards, and the filling work is ended when the filling reaches the preset elevation position. S2, vacuum drainage and settlement whole process test and monitoring: after the soil layer is saturated, the water collecting pipe valve is closed, the air suction pump is started to create a vacuum cavity condition, the water in the soil layer in the test cabin penetrates into the vacuum cavity under the action of external pressure difference, and the purpose of promoting the rapid settlement of the soil layer by reducing the water in the soil layer is achieved. After the water in the soil layer is completely discharged, the vacuum pump is closed, the valve of the water collecting pipe is opened, and the water in the vacuum cavity is discharged through the water collecting pipe, so that the rapid vacuum-based dewatering and settlement of the soil layer is completed; By analogy, after the vacuum dewatering and settlement is completed, the process of water saturation, vacuum dewatering and soil settlement is started again, and the process of water saturation, vacuum dewatering and soil settlement is repeated for two or more times, so that the rapid dry-wet cycle settlement process of the soil layer is realized, and the test monitoring is carried out simultaneously during the vacuum dewatering and settlement process; S3, processing the test monitoring data: according to the strain monitoring data of the reinforcement meter corresponding to the upper and lower positions of each pile side soil pressure meter during the dry-wet cycle test process, the pile foundation axial force data corresponding to the upper and lower positions of each pile side soil pressure meter is obtained, and then through force balance analysis, the negative skin friction of the pile side corresponding to the position of each pile side soil pressure meter is quantified, combined with the pile side soil pressure monitoring, the negative skin friction coefficient of the pile side corresponding to the position of each pile side soil pressure meter is quantified, and combined with the settlement displacement monitoring of the settlement monitoring meter corresponding to each pile side soil pressure meter, the fine pile side negative skin friction coefficient-displacement dry-wet cycle whole process curve of the pile foundation at different positions under the dry-wet cycle condition is finally obtained.