Testing Method and Device for Water-Thermal-Mechanical Coupling Earth Pressure in Multi-Directional Stress Field of Cold Region Soil

Abstract

Testing method and device for water - heat - force coupling earth pressure of multi - directional stress field in cold region soil. There are horizontal and vertical loading systems on the test platform. The horizontal force - transmitting rod pushes and pulls the propulsion plate. The propulsion plate compresses the equivalent constraint module, pushing the loading frame and the cold end of the heat exchange module. In front of the cold end are the test specimen and the warm end. There are lateral restraint plates at the cold and warm ends, and a cover plate on the test specimen. There are also a water supply system and a camera system. The test specimen is placed on the test platform for horizontal and vertical loading, and the temperature is loaded to be stable at the air temperature at the depth of the simulated foundation pit, and test data are obtained. There are also horizontal axial force acquisition sensors, horizontal displacement sensors, vertical load sensors, vertical displacement sensors, temperature and earth pressure sensors to collect data. It can realize the research on the frost heave coupling characteristics of water - containing (especially water - rich) soil under negative temperature environment in cold regions under certain stress conditions and constraint conditions, which is of great significance for studying the frost heave force distribution and the development law of frost heave force of over - wintering deep foundation pits.

Description

Technical Field

[0001] The present invention belongs to the field of frozen soil engineering, a branch of geotechnical engineering, and particularly relates to a method and device for testing water-heat-mechanical coupling earth pressure in a multi-directional stress field of soil in cold regions. It is a testing method and device applicable to the research of water-heat-mechanical coupling under the condition of a multi-directional stress field of soil. Background Art

[0002] For the overwintering deep foundation pit engineering in cold regions, due to the continuous decrease in temperature. The negative temperature state causes the soil to freeze, and its frost heave is particularly obvious in a water-rich (close to or reaching the saturated water content) environment. The soil on the free face of the deep foundation pit meets the water-rich condition, so the frost heave of the soil will cause a great load on the foundation pit support structure, seriously affecting the safety of the deep foundation pit project and surrounding buildings and structures. Using the device and method of the present invention can simulate the soil environmental conditions in the natural state, realize the research on the frost heave coupling characteristics of soil under multi-directional stress fields and different temperature gradients, explore the relationship between restraint and frost heave force, understand the development law of frost heave in space and time, and provide a reference for the subsequent evaluation of frost heave force in deep foundation pits. Summary of the Invention

[0003] One object of the present invention is to provide a method for testing water-heat-mechanical coupling earth pressure in a multi-directional stress field of soil in cold regions, and another object of the present invention is to provide a device for testing water-heat-mechanical coupling earth pressure in a multi-directional stress field of soil in cold regions, which can realize the research on the frost heave coupling characteristics of water-containing (especially water-rich) soil under certain stress conditions and certain restraint conditions in the negative temperature environment of cold regions.

[0004] The adopted technical solution is as follows:

[0005] When using the method for testing water-heat-mechanical coupling earth pressure in a multi-directional stress field of soil in cold regions, it is characterized by including the following steps:

[0006] Step 1: Fabricate a test specimen, install it on the test platform, set the left lateral restraint plate and the right lateral restraint plate, and the sensors on the left lateral restraint plate and the right lateral restraint plate.

[0007] Step 2: Simulate the multi-directional stress field of the deep foundation pit soil, and perform vertical loading, horizontal loading and consolidation on the test specimen.

[0008] Step 3: Perform temperature loading on the test specimen, and simulate the temperature field and temperature gradient in the soil of the test specimen according to the actual engineering situation.

[0009] Step 4: Simulate the deformation stiffness of the deep foundation pit support structure in the actual project through the equivalent restraint module. The equivalent stiffness value needs to be calculated according to the actual situation of the deep foundation pit support structure.

[0010] Step 5: Record the water replenishment amount of the test specimen during the test. After the test, slice the test specimen to analyze the change in water content of the test specimen before and after the test.

[0011] Step 6: Through multiple groups of tests with different temperature gradients, the overall frost heave development characteristics and distribution laws of the deep foundation pit in terms of time and space can be obtained.

[0012] Lubricate both the left lateral restraint plate and the right lateral restraint plate around the test specimen to reduce the lateral friction during the frost heave of the test specimen. At the same time, place the cold end and the warm end of the heat exchange module at the rear and front ends of the test specimen and press them tightly to limit the displacement of the warm end of the heat exchange module.

[0013] Final value of vertical load in vertical loading: N 竖 = ρ pj ·g·H·a·L (1).

[0014] Among them, ρ pj is the average density of all soil layers above the simulated position.

[0015] g is the acceleration due to gravity.

[0016] H is the depth of the simulated position.

[0017] a is the side length of the horizontal plane of the test specimen, and L is the longitudinal side length of the test specimen.

[0018] Through conversion, the test specimen will reach the initial stress state of σ1 vertically:

[0019] σ1 = ρ pj ·g·H (2).

[0020] Final value of horizontal load in horizontal loading:

[0021] For the state of static earth pressure:

[0022] N sp = K0·σ1·a·b (3).

[0023] Among them, K0 = 1 - sinφ.

[0024] For the state of active earth pressure:

[0025] N sp = (tan 2 (45 - φ / 2)·σ a - 2c·tan(45 - φ / 2))·a·b (4).

[0026] Among them, σ a is the active earth pressure at the simulated position.

[0027] Consolidation: After the test specimen is placed, the loading control system is used to achieve equal-proportion loading in the vertical and horizontal directions or loading along a certain path for the test specimen, so as to achieve the target state of stress in the lateral and horizontal orthogonal directions of the test specimen at the initial stage.

[0028] During the loading, start the data acquisition system to collect the vertical and horizontal deformations Δ1 and Δ2 of the test specimen.

[0029] The automatic loading control system will automatically adjust the loading according to the soil sample size or soil stress change, and keep the position of the test specimen unchanged after consolidation in the horizontal loading direction.

[0030] Temperature loading: By adjusting the cold bath at the cold end and the cold bath at the warm end, the cold end of the heat exchange module and the warm end of the heat exchange module both reach a low temperature of 0-2°C, and the overall temperature field of the test specimen is monitored by temperature sensors distributed on both sides of the test specimen. When the overall temperature field of the test specimen is consistent and evenly distributed, the temperature of the cold bath at the cold end is reduced to lower the cold end of the heat exchange module. Finally, the temperature of the cold end of the heat exchange module is stabilized at the simulated environmental temperature. As the temperature of the cold end of the heat exchange module decreases, the test specimen begins to gradually freeze at this end and frost heave occurs due to water migration and phase change. The total frost heave Δ should be estimated before the test. 冻 , the frost heave compressible deformation Δ of the equivalent constraint module should meet the following conditions:

[0031] Δ≥2(N sp / K eq -N sp ·L / (a·b·E 土 )+Δ 冻 ) (5).

[0032] The initial length of the equivalent constraint module (10) should meet the following conditions:

[0033] L0≥n·d 弹 +Δ (6).

[0034] Among them, Δ is the compressible deformation of the equivalent constraint module.

[0035] N sp is the initial loading value of the horizontal loading system.

[0036] K eq is the spring Hooke stiffness equivalent to the deep foundation pit support system.

[0037] E 土 is the compression modulus of the test specimen. a and b are the cross-sectional dimensions of the test specimen respectively.

[0038] Δ 冻 is the estimated frost heave. L is the longitudinal length of the test specimen.

[0039] L0 is the initial length of the equivalent constraint module.

[0040] N is the number of coils of the spring of the equivalent constraint module. d 弹 is the diameter of the spring.

[0041] Calculation of equivalent stiffness: This test method is designed using the elastic fulcrum method. The test method can be used to evaluate the earth pressure on the side wall of deep foundation pits in cold regions. The test method involves equivalenting the support stiffness of the deep foundation pit support structure to the constraint stiffness on the test device. This device comprehensively simulates the support structure constraint and the passive earth pressure at the embedded end on the inner side of the foundation pit by a spring with equivalent constraint stiffness, and performs equivalent calculation considering the parameter characteristics of the deep foundation pit support structure between the ground and the bottom of the deep foundation pit to obtain the equivalent deformation stiffness K eq .

[0042] K eq = K 总 / C k (7).

[0043] Among them, K 总 is the comprehensive stiffness of the support structure constraint and the passive earth pressure at the embedded end of the foundation pit.

[0044] C k is the spring stiffness similarity coefficient.

[0045] The comprehensive stiffness of the support structure constraint and the passive earth pressure at the embedded end of the deep foundation pit should be calculated according to the following formula.

[0046]

[0047] Among them, α1, α2, α3, α4 are stiffness adjustment coefficients

[0048] k i is the deformation stiffness of the i-th cable anchor.

[0049] k′ i is the deformation stiffness of each steel collar.

[0050] n is the number of cable anchor lines.

[0051] Ks is the equivalent stiffness of the passive earth pressure at the embedded end of the support pile body.

[0052] Kp is the constraint stiffness of the support pile body.

[0053] Kg is the constraint stiffness of the capping beam.

[0054] Water supply system: The water supply bottle is connected to the inlet of the drip tube. A filter paper is provided between the rear of the warm end housing of the heat exchange module and the test specimen. A permeable stone is provided below the test specimen. The permeable stone is arranged in the groove of the test platform, and a water collecting tank is provided below the permeable stone. The water collecting tank is fixed below the test platform. Water enters the drip tube from the water supply bottle by gravity and wets the filter paper at the contact point between the test specimen and the warm end housing of the heat exchange module at the water supply hole. Water is continuously introduced into the drip tube through external water supply, and the excess water enters the water collecting tank through the permeable stone at the test specimen end under the action of gravity.

[0055] Both the water supply bottle and the water collecting tank are respectively provided with water volume scales, and the water volume absorbed by the soil body is calculated according to the water supply volume and the water collection volume during the test process.

[0056] During the test process, record the water replenishment volume of the specimen. After the test is completed, slice the test specimen. Analyze the change of the water content of the specimen before and after the test, and deeply analyze the law of water migration to facilitate the verification of the numerical analysis results.

[0057] The horizontal loading system includes a horizontal power device, a horizontal force transmission rod, a horizontal axial force acquisition sensor, a horizontal displacement sensor, a directional plate, a propulsion plate, an equivalent constraint module, a horizontal guide rail, a loading frame, the cold end of the heat exchange module, a lateral constraint plate, and the warm end of the heat exchange module.

[0058] The output part of the horizontal power device is connected to the rear end of the horizontal force transmission rod.

[0059] The horizontal power device is fixedly arranged on the test platform.

[0060] The directional plate is fixed on the test platform, and the horizontal force transmission rod passes through the force transmission rod hole in the middle of the directional plate.

[0061] The front end of the horizontal force transmission rod is fixedly connected to the propulsion plate. The propulsion plate is located in front of the directional plate.

[0062] The propulsion plate is sleeved on the horizontal guide rail through the propulsion plate hole, and the horizontal guide rail passes through the directional plate guide rail hole on the directional plate.

[0063] A horizontal axial force acquisition sensor is provided on the horizontal force transmission rod.

[0064] The horizontal displacement sensor is located between the directional plate and the propulsion plate.

[0065] The front end of the horizontal guide rail is fixedly connected to the loading frame.

[0066] The front end of the loading frame contacts the outer shell of the cold end of the heat exchange module.

[0067] The area for placing the test specimen is in front of the cold end of the heat exchange module.

[0068] An equivalent constraint module is provided on the horizontal guide rail, and the equivalent constraint module is located between the propulsion plate and the loading frame.

[0069] A heat exchange module warm end is fixedly arranged in front of the area where the test specimen is placed.

[0070] Vertical lateral restraint plates are fixedly arranged on the left and right sides of the area where the test specimen is placed.

[0071] Temperature sensors and earth pressure sensors are arranged on the lateral restraint plates.

[0072] Vertical loading system: The vertical loading system includes a reaction frame, a vertical power device, a vertical load sensor, a vertical loading rod, a cover plate, and a vertical displacement sensor.

[0073] A vertical power device is fixedly arranged below the transverse bracket of the reaction frame.

[0074] The output part of the vertical power device is connected to the upper part of the vertical loading rod.

[0075] A cover plate is fixedly arranged at the lower end of the vertical loading rod.

[0076] The vertical load sensor is located on the vertical loading rod.

[0077] The vertical displacement sensor is located between the upper part of the cover plate and the bracket fixed on the test platform.

[0078] The cover plate is located in the area above where the test specimen is placed.

[0079] A water replenishing system is arranged in the area where the test specimen is placed.

[0080] Water replenishing system: A plurality of water supply holes are opened at the rear of the housing of the warm end of the heat exchange module, and a plurality of drip tubes are arranged inside the housing of the warm end of the heat exchange module. The outlets of the drip tubes are correspondingly connected to the water supply holes.

[0081] A water supply bottle is connected to the inlet of the drip tube.

[0082] A filter paper is arranged between the rear of the housing of the warm end of the heat exchange module and the test specimen.

[0083] A permeable stone is arranged below the test specimen. The permeable stone is arranged in the groove opened on the test platform.

[0084] A water collecting tank is arranged below the permeable stone.

[0085] The horizontal power device is a horizontal stepping guide rail, and the rear end of the horizontal force transmission rod is fixedly arranged at the output part of the horizontal stepping guide rail.

[0086] The vertical power device is a vertical loading motor, which is threadedly connected to the upper part of the vertical loading rod.

[0087] A guide block is arranged on the vertical loading rod, a guide frame is arranged below the transverse bracket, a vertical guide groove is opened on the guide frame, and the guide block is located in the guide groove.

[0088] The equivalent constraint module is a spring. A camera is set on the test platform.

[0089] Its advantages are as follows:

[0090] The present invention provides a research device and a research idea for the study of frozen soil characteristics of deep foundation pits, slopes, etc. overwintering in cold regions, and can realize the study of the frost heave coupling characteristics of water-containing (especially water-rich) soil under negative temperature environment in cold regions under certain stress conditions and certain constraint conditions, which is of great significance for studying the distribution and development law of frost heave force of overwintering deep foundation pits. Description of the Drawings

[0091] Figure 1 It is the front view of the device.

[0092] Figure 2 It is Figure 1 the structural schematic diagram of the main components in

[0093] Figure 3 It is the top view of the device.

[0094] Figure 4 It is the front view of the left lateral restraint plate ( Figure 3 the left side in

[0095] Figure 5 It is the front view of the right lateral restraint plate ( Figure 3 the right side in

[0096] Figure 6 It is the front view of the propulsion plate.

[0097] Figure 7 It is the top view of the propulsion plate.

[0098] Figure 8 It is the front view of the positioning plate.

[0099] Figure 9 It is the top view of the positioning plate.

[0100] Figure 10 It is the structural schematic diagram of the water replenishing system.

[0101] Figure 11 It is the structural schematic diagram of the water supply hole and the warm end of the heat exchange module.

[0102] Figure 12 It is the side view of the deep foundation pit.

[0103] Figure 13 It is Figure 12 the front view in

[0104] Figure 14 It is the schematic diagram of the equivalent constraint stiffness of the anchor cable, waist beam and retaining pile structure of the simulated deep foundation pit.

[0105] Figure 15 It is a system block diagram.

[0106] Figure 16 It is a stress state diagram of the soil sample (test specimen) (at normal temperature).

[0107] Figure 17 It is a stress state diagram of the soil sample (test specimen) (from active earth pressure to at-rest earth pressure).

[0108] Figure 18 Stress state diagram of the soil sample (test specimen) (transition from active earth pressure to at-rest earth pressure, and even to passive earth pressure).

[0109] Reaction frame 1, transverse support 1a, vertical support 1b, vertical loading motor 2, horizontal axial force acquisition sensor 3, cover plate 4, upper cover plate 4a, lower heat insulation cover plate 4b, lateral restraint plate 5, left lateral restraint plate 5a, right lateral restraint plate 5b, lateral support 6, orientation plate 7, horizontal stepping guide rail 8, push plate 9, equivalent restraint module 10, horizontal guide rail 11, loading frame 12, cold end of heat exchange module 13, warm end of heat exchange module 14, heat preservation cover 15, temperature sensor 16, test specimen 17, loading controller 18, cold end cold bath 19, warm end cold bath 20, test platform 21, water replenishing system 22, horizontal displacement sensor 23, horizontal loading motor 24, horizontal force transfer rod 25, hole groove of lateral restraint plate 26, camera 27, hole of force transfer rod 28, hole of orientation plate guide rail 29, anchor cable 30, retaining pile 31, waist beam 32, ground 33, foundation pit bottom 34, vertical displacement sensor 35, vertical load sensor 36, vertical loading rod 37, loading control system 38, data acquisition system 39, image shooting system 40, temperature control system 41, earth pressure sensor 42, hole of push plate 43, support 44, water supply hole 45, drip tube 46, water supply bottle 47, filter paper 48, permeable stone 49, water collecting tank 50, crown beam 51, guide block 52, guide frame 53, guide groove 54, frozen layer 55, heat insulation layer 56, metal layer 57. Detailed implementation manners

[0110] Embodiment 1

[0111] The multi-directional stress field water-heat-mechanical coupling earth pressure testing device for cold region soil has a test platform 21.

[0112] A horizontal loading system and a vertical loading system are arranged on the test platform 21.

[0113] The horizontal loading system includes a horizontal power device (horizontal loading motor 24 and horizontal stepping guide rail 8), a horizontal force transfer rod 25, a horizontal axial force acquisition sensor 3, a horizontal displacement sensor 23, a horizontal guide rail 11, an orientation plate 7, a propulsion plate 9, an equivalent constraint module 10, a loading frame 12, the cold end 13 of a heat exchange module, a lateral constraint plate 5, a lateral support 6, and the warm end 14 of a heat exchange module.

[0114] The output part of the horizontal power device is connected to the rear end of the horizontal force transfer rod 25.

[0115] The horizontal stepping guide rail 8 and its horizontal loading motor 24 (stepping) are fixedly arranged on the test platform 21.

[0116] The rear end of the horizontal force transfer rod 25 is fixed to the output part of the horizontal stepping guide rail 8.

[0117] Two orientation plates 7 arranged front and rear are fixed on the test platform 21, and the horizontal force transfer rod 25 passes through the force transfer rod hole 28 in the middle of the orientation plate 7.

[0118] The front end of the horizontal force transfer rod 25 is fixedly connected to the propulsion plate 9. The propulsion plate 9 is located in front of the two orientation plates 7.

[0119] The propulsion plate 9 is sleeved on the two horizontal guide rails 11 through two propulsion plate holes 43, and each horizontal guide rail 11 passes through the corresponding orientation plate guide rail hole 29 on the orientation plate 7.

[0120] The horizontal force transfer rod 25 is located between the two horizontal guide rails 11.

[0121] A horizontal axial force acquisition sensor 3 is provided on the horizontal force transfer rod 25 (the specific installation method can divide the horizontal force transfer rod 25 into front and rear ends, and the horizontal axial force acquisition sensor 3 is arranged in the middle) to collect the axial force value of the horizontal force transfer rod 25 at any time.

[0122] The horizontal axial force acquisition sensor 3 is between the front orientation plate 7 and the propulsion plate 9.

[0123] The horizontal displacement sensor 23 is between the front orientation plate 7 and the propulsion plate 9 and is located outside the horizontal guide rail 11.

[0124] Horizontal displacement sensors 23 are respectively arranged on both sides of the propulsion plate 9, and the average value of the collected displacements is taken.

[0125] The housing of the horizontal displacement sensor 23 is fixed in front of the front orientation plate 7, and the probe of the horizontal displacement sensor 23 is connected to the rear of the propulsion plate 9.

[0126] The front ends of the two horizontal guide rails 11 are fixedly connected to the loading frame 12.

[0127] The front end of the loading frame 12 contacts the outer shell of the cold end 13 of the heat exchange module.

[0128] A test specimen 17 is placed in front of the cold end 13 of the heat exchange module.

[0129] An equivalent constraint module 10 is provided on the horizontal guide rail 11. The equivalent constraint module 10 is located between the propulsion plate 9 and the loading frame 12, and the equivalent constraint module 10 is a spring.

[0130] The warm end 14 of the heat exchange module is fixedly arranged in front of the area where the test specimen 17 is placed.

[0131] Vertical lateral constraint plates 5 are fixedly provided on the left and right sides of the area where the test specimen 17 is placed.

[0132] Lateral supports 6 are provided outside both lateral constraint plates 5.

[0133] The warm end 14 of the heat exchange module, the lateral constraint plates 5 and the lateral supports 6 are all fixed on the test platform 21.

[0134] A plurality of lateral constraint plate hole slots 26 are transversely opened along the horizontal center line on the lateral constraint plate 5 for inserting the temperature sensor 16.

[0135] The lateral constraint plates 5 on both sides are respectively the left lateral constraint plate 5a and the right lateral constraint plate 5b, and the upper lateral constraint plate hole slots 26 (reserved holes) are arranged in a staggered plum blossom shape.

[0136] A plurality of lateral constraint plate pressure sensor holes are opened along the horizontal direction on the lateral constraint plate 5 (left lateral constraint plate 5a) for arranging the earth pressure sensor 42.

[0137] A camera 27 is also arranged on the test platform 21, located on the left side of the test specimen 17.

[0138] Both the lateral constraint plates 5 and the lateral supports 6 are made of transparent organic glass.

[0139] The heat preservation cover 15 is fixed on the test platform 21 to cover the test specimen 17, the lateral constraint plates 5, the lateral supports 6, the cold end 13 of the heat exchange module, the warm end 14 of the heat exchange module, the loading frame 12 and the camera 27.

[0140] The front ends of the horizontal guide rail 11 and the equivalent constraint module 10 extend into the heat preservation cover 15.

[0141] The contact surface between the cold end 13 of the heat exchange module and the loading frame 12 is covered with nylon material to form a heat insulation layer 56 (nylon layer), aiming to isolate the heat exchange between the test specimen 17 and the outside air.

[0142] The contact surface between the cold end 13 of the heat exchange module and the test specimen 17 is a metal layer 57 (made of brass). Brass has a high heat conduction efficiency, which is convenient for controlling the temperature of the test specimen 17.

[0143] The front end of the test specimen 17 is the warm end 14 of the heat exchange module. The two sides of the test specimen 17 are constrained by the lateral constraint plates 5. Under normal temperature conditions, a state of static earth pressure σ2 is formed laterally. A vertical load is applied on the upper part to form a σ1 stress state, and a horizontal load is applied at the cold end 13 of the heat exchange module to form a σ3 active earth pressure stress state, as Figure 16 shown.

[0144] The axis of the horizontal force transfer rod 25 is coaxial with the center line of the test specimen 17 and parallel to the axis of the horizontal guide rail 11 to ensure a constant direction during the loading process.

[0145] Three holes are reserved in the middle of the orientation plate 7 (the axes of the two orientation plate guide holes 29 and one force transfer rod hole 28 are parallel to each other), through which the two horizontal guide rails 11 and the horizontal force transfer rod 25 pass respectively. The diameter of the holes is 0.5 mm to 1.0 mm larger than the diameters of the horizontal guide rail 11 and the horizontal force transfer rod 25, and grease is applied on the horizontal guide rail 11 and the horizontal force transfer rod 25.

[0146] Two reserved holes (push plate holes 43) are provided on the push plate 9. The distance between the two holes is the same as the center distance and the hole diameter of the orientation plate guide hole 29 to facilitate the passage of the horizontal guide rail 11. An equivalent constraint stiffness spring is provided between the push plate 9 and the loading frame 12, and its stiffness is K eq .

[0147] The horizontal loading motor 24 drives the horizontal force transfer rod 25 on the horizontal stepping guide rail 8 to move back and forth along the horizontal stepping guide rail 8 through screw transmission, pushing the push plate 9. The horizontal guide rail 11 slides inside the orientation plate 7, compressing the equivalent constraint module 10 (spring). The horizontal force is loaded onto the loading frame 12 and the heat exchange module 13 (cold end) through the equivalent constraint module 10 (spring) to load the test specimen 17. To ensure uniform loading, the horizontal force transfer rod 25, the push plate 9, the horizontal guide rail 11 and the loading frame 12 can only slide back and forth along the three holes of the orientation plate 7.

[0148] The two sides of the test specimen 17 are supported by the lateral supports 6 and constrained by the lateral constraint plates 5 to ensure no lateral deformation and displacement of the test specimen 17. The rear of the test specimen 17 is constrained by the warm end 14 of the heat exchange module.

[0149] The orientation plate 7 is fixed on the test platform 21 to play a guiding role. The horizontal guide rail 11 passes through the orientation plate guide hole 29 of the orientation plate 7, and all the components moving in the horizontal direction can only move in the direction of the orientation plate guide hole 29 of the orientation plate 7.

[0150] The camera 27 is correspondingly connected to the image capturing system 40, and the development law of the freezing-heaving process of the test specimen 17 is observed through the transparent lateral constraint plate 5.

[0151] The temperature sensor 16 and the earth pressure sensor 42 are inserted into the test specimen 17.

[0152] The equivalent constraint module 10 is a simulation component. The device simulates the deformation stiffness of the crown beam 51, the cable anchor 30, the steel support, the retaining pile 31, the steel collar or the waist beam 32 in actual engineering through the equivalent constraint module 10. A reserved space is provided between the loading frame 12 and the cold end 13 of the heat exchange module, facilitating the connection of the refrigerant circulation pipe of the cold bath 19 at the cold end to the cold end 13 of the heat exchange module.

[0153] Each lateral constraint plate 5 reserves 5 - 8 lateral constraint plate holes and grooves 26 on its long axis center line. The left lateral constraint plate 5a and the right lateral constraint plate 5b are cross - grooved. The lateral constraint plate holes and grooves 26 have an axial spacing of 1 - 3 cm and a grooving length of 2 - 4 cm. Temperature sensors 16 and earth pressure sensors 42 are arranged at the contact positions of the left lateral constraint plate 5a and the right lateral constraint plate 5b on both sides of the test specimen 17 (soil sample). The grooving is for reserving displacement space during frost heaving. The grooving of the lateral constraint plates 5a and 5b Figure 4 and 5 are staggered as shown, and the grooving of the two plates is distributed in a plum blossom shape.

[0154] The thickness of the lateral constraint plate 5 is 2 - 4 cm, and transparent and low - thermal - conductivity materials such as plexiglass plates are used. The two outer sides of the lateral constraint plate 5 use a method of uniform lateral support 6 (support plates) to limit the lateral deformation of the lateral constraint plate 5.

[0155] The horizontal loading system is covered by a heat - insulating and heat - preserving box 15 to reduce heat exchange and maintain a constant temperature within a certain range around the test specimen 17. The dimensional characteristics of the cold end 13 of the heat exchange module and the warm block 14 at the cold end of heat exchange: the horizontal dimension is 0.5 - 2 mm smaller than that of the test specimen 17, and the vertical dimension is 2 - 5 mm smaller than that of the test specimen 17 to prevent the module from restricting the movement of the loading system during the initial consolidation process.

[0156] The cold end 13 of the heat exchange module is correspondingly connected to the cold bath 19 at the cold end.

[0157] The warm end 14 of the heat exchange module is correspondingly connected to the warm bath 20 at the warm end.

[0158] Vertical loading system: The vertical loading system includes a reaction frame 1, a vertical power device (vertical loading motor 2), a vertical load sensor 36, a vertical loading rod 37, a cover plate 4, and a vertical displacement sensor 35.

[0159] The reaction frame 1 is fixed on the test platform 21.

[0160] The reaction frame 1 is a frame structure, including two vertical supports 1b (located outside the left and right sides of the heat - insulating cover 15) and a horizontal support 1a fixed on them (located outside the upper side of the heat - insulating cover 15)

[0161] A vertical power device is fixed below the horizontal bracket 1a.

[0162] The output part of the vertical power device (the threaded part of the power shaft of the vertical loading motor 2) is connected above the vertical loading rod 37.

[0163] A guide block 52 is provided on the vertical loading rod 37, and a guide frame 53 is provided below the horizontal bracket 1a. The guide frame 53 is provided with a vertical guide groove 54, and the guide block 52 is located in the guide groove 54.

[0164] A cover plate 4 is fixed to the lower end of the vertical loading rod 37.

[0165] The cover plate 4 includes an upper cover plate 4a (made of steel) and a lower heat-insulating cover plate 4b (made of plexiglass with low heat conduction material to reduce the temperature field interference caused by heat conduction) which are fixedly connected. The vertical load sensor 36 is located on the vertical loading rod 37. The specific installation method is: the vertical load sensor 36 is located between the upper and lower ends of the vertical loading rod 37.

[0166] The vertical loading rod 37 penetrates into the heat-insulating cover 15. The vertical load sensor 36 is located inside the heat-insulating cover 15.

[0167] The vertical displacement sensor 35 is located between the cover plate 4 above and the bracket 44 fixed on the test platform 21.

[0168] The bracket 44 is located inside the heat-insulating cover 15.

[0169] The housing of the vertical displacement sensor 35 is fixedly supported by the bracket 44 fixed on the test platform 21, and the probe of the vertical displacement sensor 35 is fixed above the cover plate 4 (upper cover plate 4a).

[0170] The cover plate 4 is located inside the heat-insulating cover 15 and above the test specimen 17.

[0171] The reaction frame 1, the vertical loading motor 2, the vertical load sensor 36 and the vertical loading rod 37 are on the same axis and coincide with the plane center of the test specimen 17 (test soil sample).

[0172] The lower end of the vertical loading rod 37 is hemispherical and contacts the equal-diameter hemispherical groove on the upper surface of the upper cover plate 4a. The hemispherical contact area is large, the force is more uniform, and it is beneficial for positioning.

[0173] The widths of the upper cover plate 4a (made of steel) and the lower heat-insulating cover plate 4b are the same as the width of the test specimen 17.

[0174] The power shaft of the vertical loading motor 2 is threadedly connected above the vertical loading rod 37.

[0175] When the power shaft of the vertical loading motor 2 rotates, under the guiding action of the guide block 52 and the guide groove 54, the vertical loading rod 37 drives the cover plate 4 to move up and down.

[0176] Water supply system 22: A plurality of water supply holes 45 are formed in the rear of the housing of the warm end 14 of the heat exchange module. A plurality of drip tubes 46 are arranged in the housing of the warm end 14 of the heat exchange module, and the outlets of the drip tubes 46 are correspondingly connected to the water supply holes 45.

[0177] The water supply bottle 47 is connected to the inlet of the drip tube 46.

[0178] A filter paper 48 is provided between the rear of the housing of the warm end 14 of the heat exchange module and the test specimen 17.

[0179] A permeable stone 49 is provided below the test specimen 17. The permeable stone 49 is arranged in the slot of the test platform 21, and a water collecting tank 50 is provided below the permeable stone 49. The water collecting tank 50 is fixed below the test platform 21.

[0180] Water enters the drip tube 46 from the water supply bottle 47 by gravity and wets the filter paper 48 at the contact position between the test specimen 17 and the housing of the warm end 14 of the heat exchange module from the water supply hole 45.

[0181] Water is continuously introduced into the drip tube 46 through external water supply, and the excess water enters the water collecting tank 50 through the permeable stone 49 at the lower end of the test specimen 17 under the action of gravity.

[0182] The water supply system 22 replenishes water for the test specimen 17. Only water needs to be provided to contact the bottom of the test specimen 17, and the water is absorbed and dispersed evenly through the capillary principle of the test specimen 17.

[0183] Both the water supply bottle 47 and the water collecting tank 50 are provided with water volume scales, and the water volume absorbed by the soil body can be calculated according to the water supply volume and the water collection volume during the test.

[0184] 1. Loading control system 38: The loading control system 38 mainly includes a loading controller 18, a vertical loading system and a horizontal loading system. The loading controller 18 can control the loading values of the vertical loading and horizontal loading systems and automatically keep them constant. At the same time, the horizontal loading system has a displacement control function (position locking).

[0185] The loading controller 18 is powered by an independent power supply and is connected to a computer through RS232 / 485. The input end is connected to the data acquisition system 39, and the output end is connected to the two motors of the vertical loading and horizontal loading systems.

[0186] The loading controller 18 is mainly a PLC controller, and the loading value can be preset through software. The software will feedback-adjust the motors of the loading system according to the data collected by the data acquisition system 39, load or unload the soil body of the test specimen 17, and keep the soil body load constant at the software preset value.

[0187] Among them, the equivalent constraint module 10 should be calculated based on the deformation stiffness of the deep foundation pit support structure, and the equivalent deformation stiffness E at a certain point of the foundation pit is obtained by equivalent calculation considering the parameters such as the anchor cable 30, the retaining pile 31 or the collar beam 32 between the ground 33 and the bottom of the foundation pit 34. eq , such as Figure 12 , 13 , as shown in Figure 14.

[0188] 2. Temperature control system 41: The temperature control system 41 mainly includes two low-temperature constant temperature circulating baths as the cold-end cold bath 19 and the warm-end cold bath 20. One is responsible for controlling the temperature of the cold end 13 of the heat exchange module of the test specimen 17 to control the cold-end temperature of the test specimen 17, and the other is responsible for controlling the temperature of the warm end 14 of the heat exchange module, so as to form a temperature gradient in the axial direction of the test specimen 17. Among them, the lateral restraint plates 5 on both sides of the test specimen 17 are made of transparent organic glass, which also effectively reduces the influence of heat conduction and radiation. The temperature fluctuation is further reduced by the outer heat insulation cover 15.

[0189] After the soil sample is consolidated and the temperature condition starts, due to the freezing phase change of the test specimen 17 on the cold end side, the stress state changes from the active earth pressure to the at-rest earth pressure, and even to the passive earth pressure state, as shown in Figure 17 and 18 .

[0190] In the temperature control system 41, the temperature can be set through software. The software will control the operation of the high and low temperature circulating device according to the data of the temperature sensor 16 in the system. The refrigerant and heat medium are both high-purity anhydrous alcohol for temperature control equipment. The temperature control equipment components of the temperature control system 41 are finished products purchased.

[0191] 3. Data acquisition system 39: It mainly includes a data acquisition instrument and multiple sensors. The data acquisition instrument includes a static strain acquisition instrument and a temperature acquisition instrument. The sensors include a horizontal axial force acquisition sensor 3, a horizontal displacement sensor 23, an earth pressure sensor 42, a vertical displacement sensor 35, a vertical load sensor 36 and a temperature sensor 16, all of which are connected to the corresponding data acquisition instrument.

[0192] In the loading control system 38, the loading force is set through software. The software will control the corresponding loading motor to load or unload according to the output data of the horizontal axial force acquisition sensor 3, the horizontal displacement sensor 23, the vertical displacement sensor 35 and the vertical load sensor 36. At the same time, the software will collect the displacement data of the test specimen 17, and the displacement data can also be set. The software will control the corresponding loading motor (step, servo) to load to the set position. At the same time, the magnitude of the earth pressure is collected.

[0193] Embodiment 2

[0194] The multi-directional stress field water-heat-mechanical coupling earth pressure test method for cold region soil includes the following steps:

[0195] Step 1: Fabricate a test specimen, install it on the test platform, set the left lateral restraint plate and the right lateral restraint plate, as well as the sensors (earth pressure sensor 42 and temperature sensor 16) on the left lateral restraint plate and the right lateral restraint plate.

[0196] Step 2: Simulate the multi-directional stress field of deep foundation pit soil, and perform vertical loading, horizontal loading and consolidation on the test specimen.

[0197] Step 3: Apply temperature loading to the test specimen, and simulate the temperature field and temperature gradient in the soil body of the test specimen according to the actual engineering situation.

[0198] Step 4: Simulate the deformation stiffness of the deep foundation pit support structure in the actual project through the equivalent constraint module. The equivalent stiffness value needs to be calculated according to the actual situation of the deep foundation pit support structure.

[0199] Step 5: Record the water replenishment amount of the test specimen during the test. After the test, slice the test specimen to analyze the change in the water content of the test specimen before and after the test.

[0200] Step 6: Through multiple groups of tests with different temperature gradients, the overall frost heave development characteristics and distribution laws of the deep foundation pit in time and space can be obtained.

[0201] Specifically:

[0202] Before the multi-stress field coupling frost heave test, a series of conventional auxiliary tests need to be carried out, mainly including density test, moisture content test, compaction test, triaxial test and consolidation test, etc., to obtain the original density ρ of the soil, natural moisture content ω1 and convert the dry density ρ d1 , maximum dry density ρ dmax , optimum moisture content ω opt , soil friction angle φ and compression modulus E 土 and other parameters, and record the depth of the soil sampling location.

[0203] The obtained soil samples are crushed and dried to facilitate the preparation of soil with the target moisture content ω2 (ω2 can be ω1 to ω 饱和 ), after preparation, soak for no less than 24h, and detect 3 times again before sample preparation. Use a sampler to fabricate the test specimen 17 (cuboid soil sample) with the target dry density ρ d2 , the dry density ρ d2 can be selected in the range of ρ d1 ~ρ d3 , where ρ d3 =(0.8~0.9)ρ dmax .

[0204] The test specimen 17 was completed and demolded, and then installed on the test platform 21. The left lateral restraint plate 5a, the right lateral restraint plate 5b, and the earth pressure sensors 42 thereon were set up.

[0205] Among them, the left lateral restraint plate 5a and the right lateral restraint plate 5b around the test specimen 17 were smeared with lubricants such as vaseline to reduce the lateral friction during the frost heaving of the test specimen 17. At the same time, the cold end 13 and the warm end 14 of the heat exchange module were placed against the rear and front ends of the test specimen 17 respectively to limit the displacement of the warm end 14 of the heat exchange module. The values of the upper vertical load and the horizontal load were set according to the simulated position depth.

[0206] Final value of vertical load: N 竖 = ρ pj ·g·H·a·L (1).

[0207] Where, ρ pj is the average density of all soil layers above the simulated position.

[0208] g is the acceleration of gravity.

[0209] H is the depth of the simulated position.

[0210] a is the side length of the horizontal plane of the test specimen 17, and L is the longitudinal side length of the test specimen 17.

[0211] Through conversion, it can be obtained that the test specimen 17 will reach the initial stress state of σ1 vertically:

[0212] σ1 = ρ pj ·g·H (2).

[0213] Final value of horizontal load:

[0214] For the state of static earth pressure:

[0215] N sp = K0·σ1·a·b (3).

[0216] Where, K0 = 1 - sinφ.

[0217] For the state of active earth pressure:

[0218] N sp =(tan 2 (45 - φ / 2)·σ a - 2c·tan(45 - φ / 2))·a·b (4).

[0219] Where, σ a is the active earth pressure at the simulated position.

[0220] Consolidation: After the test specimen 17 is placed, the loading control system 38 is used to apply synchronous and proportional loading to the test specimen 17 in the vertical and horizontal (axial) directions or to load it according to a certain path, so as to achieve the target state of the stress of the test specimen 17 in the two orthogonal directions of the lateral and axial directions at the initial stage (each direction can be in the active, static or passive earth pressure state).

[0221] During the loading, the data acquisition system 39 is started to collect the deformations Δ1 and Δ2 of the test specimen 17 in the vertical and axial directions (vertical displacement sensor 35 and horizontal displacement sensor 23).

[0222] The automatic loading control system 38 will automatically adjust the loading according to the soil sample size or the change of soil body stress. After the loading is stable, the temperature sensor 16 is inserted into the test specimen 17 along the lateral restraint plate hole groove 26 of the two lateral restraint plates 5, and the position after consolidation in the horizontal loading direction remains unchanged. Or the temperature sensor 16 can also be inserted on the lateral restraint plate 5 together with the earth pressure sensor 42.

[0223] Temperature loading: After consolidation, the temperature loading is carried out by adjusting the cold end cold bath 19 and the warm end cold bath 20, so that both the cold end 13 and the warm end 14 of the heat exchange module reach a low temperature of (0 - 2) °C, and the overall temperature field of the test specimen 17 is monitored by the temperature sensors 16 distributed on both sides of the test specimen 17. When the overall temperature field of the test specimen 17 reaches consistency and uniform distribution, the temperature of the cold end cold bath 19 is reduced to lower the temperature of the cold end 13 of the heat exchange module, and the cooling rate is (0.5 - 1.5) °C / h. Finally, the temperature of the cold end 13 of the heat exchange module is stabilized at the simulated ambient temperature. As the temperature of the cold end 13 of the heat exchange module decreases, the test specimen 17 begins to gradually freeze at this end and produces frost heave due to the migration and phase change of water. The total frost heave amount Δ should be estimated before the test. 冻 , the frost heave compressible deformation amount Δ of the equivalent restraint module 10 (spring) should meet the following conditions:

[0224] Δ≥2(N sp / K eq -N sp ·L / (a·b·E 土 )+Δ 冻 ) (5).

[0225] The initial length of the equivalent restraint module 10 should meet the following conditions:

[0226] L0≥n·d 弹 +Δ (6).

[0227] Among them, Δ is the compressible deformation amount of the equivalent restraint module 10 (spring).

[0228] N spis the initial loading value of the horizontal loading system.

[0229] K eq is the spring Hooke's stiffness equivalent to the deep foundation pit support system.

[0230] E 土 is the compression modulus of the test specimen 17 (soil). a and b are the cross-sectional dimensions of the test specimen 17 (soil), respectively.

[0231] Δ 冻 is the estimated frost heave amount. L is the longitudinal length of the test specimen 17.

[0232] L0 is the initial length of the equivalent constraint module 10.

[0233] N is the number of coil turns of the spring of the equivalent constraint module 10. d 弹 is the diameter of the spring.

[0234] This test method is designed using the elastic fulcrum method. The test method can be used to evaluate the earth pressure on the side wall of deep foundation pits in cold regions. The test method involves equivalent conversion of the support stiffness of the foundation pit support structure (support piles 31, anchor cables 30, steel supports, steel girders, capping beams 51, and waist beams 32, etc.) into the constraint stiffness on the test device. This device comprehensively simulates the support structure constraint and passive earth pressure at the embedded end on the inner side of the deep foundation pit through a spring with equivalent constraint stiffness, and performs equivalent calculation considering the parameter characteristics of the anchor cables 30, support piles 31, and waist beams 32, etc. between the ground and the bottom of the foundation pit to obtain the equivalent deformation stiffness K at a certain point of the deep foundation pit eq .

[0235] K eq = K 总 / C k (7).

[0236] Among them, K 总 is the comprehensive stiffness of the support structure constraint and passive earth pressure at the embedded end of the foundation pit.

[0237] C k is the spring stiffness similarity coefficient.

[0238] The comprehensive stiffness of the support structure constraint and passive earth pressure at the embedded end of the foundation pit should be calculated according to the following formula.

[0239]

[0240] Among them, α1, α2, α3, and α4 are stiffness adjustment coefficients.

[0241] k i is the deformation stiffness of the i-th anchor cable 30.

[0242] k′ iis the deformation stiffness of each steel purlin.

[0243] n is the number of 30 anchor cables.

[0244] Ks is the equivalent stiffness of the passive earth pressure at the fixed end of the retaining pile body.

[0245] Kp is the restraint stiffness of the retaining pile body.

[0246] Kg is the restraint stiffness of the capping beam 51.

[0247] According to the on-site monitoring data, it is found that there are significant differences in the temperature at different depths of the deep foundation pit. Through multiple groups of tests with different temperature gradients, the overall frost heave development characteristics and distribution laws of the deep foundation pit in time and space can be obtained. The temperature gradient range of the test sample 17 for the test is (0.05 - 1) °C / cm. The stress state of the soil after frost heave of the soil loaded at the cold end 13 of the heat exchange module is Figure 17 As shown, the stress state of the soil sample changes from the initial stress state with the lateral stress being σ2 and the axial stress being σ3 at normal temperature to the state with the axial stress being σ2 and the lateral stress being σ3 after negative temperature loading, and even the axial and lateral stresses are both σ2.

[0248] During the test process, the horizontal axial force acquisition sensor 3, horizontal displacement sensor 23, temperature sensor 16, earth pressure sensor 42, vertical displacement sensor 35, and vertical load sensor 36 collect the corresponding data and transmit it to the data acquisition system 39.

[0249] During the test process, the water replenishment amount of the sample is recorded. After the test, the test sample 17 is sliced to analyze the change in the water content of the sample before and after the test, and the law of water migration is deeply analyzed to facilitate verifying the numerical analysis results. The water replenishment system 22 can replenish water from the start of cooling at the cold end 13 and the warm end 14 of the heat exchange module until the end of the test.

Claims

1. A test method for water - heat - force coupling earth pressure in multi - directional stress field of cold region soil, characterized in that It includes the following steps: Step 1: Fabricate a test specimen (17), install it on a test platform (21), set up the left lateral restraint plate (5a) and the right lateral restraint plate (5b), as well as the sensors on the left lateral restraint plate (5a) and the right lateral restraint plate (5b). Step 2: Simulate the multi-directional stress field of deep foundation pit soil mass, and perform vertical loading, horizontal loading and consolidation on the test specimen (17). Step 3: Apply temperature loading to the test specimen (17), and simulate the temperature field and temperature gradient in the soil mass of the test specimen (17) according to the actual engineering situation. Step 4: Simulate the deformation stiffness of the deep foundation pit support structure in actual engineering through the equivalent restraint module (10) in the horizontal loading system; the equivalent stiffness value is calculated according to the actual situation of the deep foundation pit support structure. Step 5: Record the water replenishment amount of the test specimen (17) during the test; after the test, slice the test specimen (17) to analyze the change in water content of the test specimen (17) before and after the test. Step 6: Through multiple groups of tests with different temperature gradients, the overall frost heave development characteristics and distribution laws of the deep foundation pit in time and space can be obtained. Temperature loading: By adjusting the cold bath at the cold end (19) and the cold bath at the warm end (20), the low temperature of 0 - 2 °C is achieved at both the cold end (13) and the warm end (14) of the heat exchange module. The overall temperature field of the test specimen (17) is monitored by the temperature sensors (16) distributed on both sides of the test specimen (17). When the overall temperature field of the test specimen (17) reaches consistency and uniform distribution, the temperature of the cold bath at the cold end (19) is reduced to lower the temperature of the cold end (13) of the heat exchange module. Finally, the temperature of the cold end (13) of the heat exchange module stabilizes at the simulated ambient temperature; as the temperature of the cold end (13) of the heat exchange module decreases, the test specimen (17) starts to gradually freeze at this end and frost heave occurs due to water migration and phase change; the total frost heave amount Δ should be estimated before the test 冻 , and the frost heave compression deformable amount Δ of the equivalent constraint module (10) should meet the following conditions: Δ≥2(N sp / K eq - N sp· L / (a·b·E 土 )+Δ 冻 ) (5); The initial length of the equivalent restraint module (10) should meet the following conditions: L0≥ n·d 弹 +Δ (6); Where, Δ is the frost heave compression deformable amount of the equivalent restraint module (10); N sp is the initial loading value of the horizontal loading system; Keq is the equivalent deformation stiffness; E 土 For testing the compression modulus of the test specimen (17); Δ 冻 is the estimated total frost heave amount; L is the longitudinal length of the test specimen (17); L0 is the initial length of the equivalent restraint module (10); n is the number of turns of the spring of the equivalent constraint module (10); d 弹 is the diameter of the spring; Calculation of equivalent stiffness: The constraints of the retaining structure on the inner side of the foundation pit and the passive earth pressure at the fixed end of the pile are comprehensively simulated by a spring with equivalent constraint stiffness, and the equivalent deformation stiffness K at a certain point in the deep foundation pit is obtained through equivalent calculation considering the parameter characteristics of the deep foundation pit retaining structure between the ground and the bottom of the deep foundation pit. eq ; K eq = K 总 / C k (7); Among them, K 总 is the comprehensive stiffness of the restraint of the deep foundation pit support structure and the passive earth pressure at the embedded end; C k is the spring stiffness similarity coefficient; The comprehensive stiffness of the restraint and passive earth pressure at the fixed end of the deep foundation pit support structure should be calculated according to the following formula; （8）； Among them, is the stiffness adjustment coefficient; k i is the deformation stiffness of the i-th cable bolt (30); is the deformation stiffness of each steel waling; n is the number of cable bolts (30); Ks is the equivalent stiffness of the passive earth pressure at the fixed end of the support pile body; Kp is the restraint stiffness of the support pile body; Kg is the restraint stiffness of the capping beam (51).

2. The multi-directional stress field water-thermal-mechanical coupled earth pressure test method for cold region soil masses according to claim 1, characterized in that It includes the following steps: Lubricate both the left lateral restraint plate (5a) and the right lateral restraint plate (5b) around the test specimen (17) to reduce the side friction during the frost heave of the test specimen (17). At the same time, place the cold end (13) and the warm end (14) of the heat exchange module at the rear and front ends of the test specimen (17) and press them tightly to limit the displacement of the warm end (14) of the heat exchange module.

3. The multi-directional stress field water-heat-mechanical coupling earth pressure test method for cold region soil mass according to claim 1, characterized in that It includes the following steps: Vertical load: Final value of vertical load during vertical loading: N 竖 = ρ pj ·g·H·a·L (1); where ρ pj is the average density of all soil layers above the simulated position; g is the acceleration of gravity; H is the depth of the simulated position; a is the side length of the horizontal plane of the test specimen (17), and L is the longitudinal length of the test specimen (17); Through conversion, the test specimen (17) will reach the initial stress state of σ1 vertically: σ1 = ρ pj ·g·H (2); The final value of horizontal loading in horizontal loading: For the state of static earth pressure: N sp = K0·σ1·a·b (3); Where, K0 = 1 - sinφ; For the state of active earth pressure: N sp = (tan 2 (45 - φ / 2) · σ a - 2c · tan(45 - φ / 2)) · a · b (4); Among them, σ a is the active earth pressure at the simulated position.

4. The multi-directional stress field water-thermal-mechanical coupled earth pressure test method for cold region soil masses according to claim 1, wherein It includes the following steps: Consolidation: After the test specimen (17) is placed, through the loading control system (38), realize synchronous and proportional loading in the vertical and horizontal directions of the test specimen (17) or load according to a certain path, so as to achieve the target state of the stress of the test specimen (17) in the two orthogonal directions of lateral and horizontal at the initial stage. During the loading, start the data acquisition system (39) to collect the vertical and horizontal deformations Δ1 and Δ2 of the test specimen (17). The loading control system (38) will automatically adjust the loading according to the soil sample size or soil stress change, and keep the position unchanged after consolidation in the horizontal loading direction.

5. The method for testing the water - heat - force coupling earth pressure in a multi - directional stress field of frozen soil according to claim 1, characterized in that It includes the following steps: Water supply system (22): The water supply bottle (47) is connected to the inlet of the drip tube (46); a plurality of water supply holes (45) are opened at the rear of the housing of the warm end (14) of the heat exchange module, and a plurality of drip tubes (46) are arranged in the housing of the warm end (14) of the heat exchange module. The outlet of the drip tube (46) is correspondingly connected to the water supply hole (45). A filter paper (48) is provided between the rear of the housing of the warm end (14) of the heat exchange module and the test specimen (17); a permeable stone (49) is provided below the test specimen (17); the permeable stone (49) is arranged in the groove of the test platform (21), and a water collecting tank (50) is provided below the permeable stone (49); the water collecting tank (50) is fixed below the test platform (21); water enters the drip tube (46) from the water supply bottle (47) by gravity, and wets the filter paper (48) at the contact between the test specimen (17) and the housing of the warm end (14) of the heat exchange module at the water supply hole (45); water is continuously introduced through the drip tube (46) by external water supply, and the excess water enters the water collecting tank (50) through the permeable stone (49) at the lower end of the test specimen (17) under the action of gravity. Both the water supply bottle (47) and the water collecting tank (50) are provided with water volume scales, and the water volume absorbed by the soil body is calculated according to the water supply volume and the water collection volume during the test. During the test, record the water supply volume of the specimen. After the test, slice the test specimen (17); analyze the change in the water content of the specimen before and after the test, and deeply analyze the law of water migration to facilitate verifying the numerical analysis results.

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