True triaxial multifunctional pipe soil test device and method

Abstract

The invention discloses a true triaxial multifunctional pipe soil test device and method, and belongs to the technical field of buried pipeline tests. The device comprises a rack, a true triaxial loading chamber, a test piece box, a hydraulic servo control system and a fluid injection device, the rack comprises a counter-force frame, a transfer slide rail, a test piece box lifting transfer platform and a right counter-force frame; the true triaxial loading chamber is arranged in the counter-force frame, sixteen groups of loading devices are arranged in the front, left, rear and upper directions of the loading chamber, and each group of loading device comprises a hydraulic cylinder, a pressure transmission rod and a pressure transmission plate; the right counter-force frame provides sixteen groups of right loading devices; the fluid injection device is a liquid injection or gas injection device, is connected with the nitrogen storage tank for gas injection when a gas buried pipeline needs to be simulated, and is connected with the water storage tank for liquid injection when a liquid buried pipeline needs to be simulated; and the hydraulic servo control system is connected with each hydraulic cylinder and is an independent hydraulic control device. The device can be used for simulating the influence of different loads on the stress, deformation and damage of the buried pipeline under actual conditions.

Description

Technical Field

[0001] The invention relates to a true triaxial multifunctional pipe-soil testing device and method, belonging to the technical field of buried pipeline testing. Background Art

[0002] Buried pipelines are one of the channels for transporting oil and gas resources, but they are frequently affected by natural disasters or engineering disturbances along the buried pipelines, and various pipeline geological disasters occur frequently. Therefore, it is necessary to conduct mechanical tests on the combination formed by the pipeline and the surrounding soil to explore the effects of different loads on the stress, deformation and damage of buried pipelines.

[0003] Existing pipe-soil test methods are divided into field tests and laboratory model tests. Field tests can truly reflect the stress and deformation of pipelines in natural environments and can be monitored for a long time, but field tests usually require a large investment of manpower and funds. At the same time, due to the complexity of the environment, it is difficult to accurately control and change a single variable, and data processing and analysis are difficult, which affects the accuracy of the test results. The use of model box tests in the laboratory has strong controllability and relatively low cost, but it is difficult to accurately control the stress state in multiple directions, and the boundary effect will affect the accuracy of the test results.

[0004] The true triaxial testing machine can independently apply and accurately control stress in three orthogonal directions, and can simulate the stress state under actual geological conditions. The true triaxial loading chamber can provide a uniform stress field and eliminate stress concentration in the specimen. Therefore, a large-scale true triaxial pipe-soil testing device and method are proposed to improve the accuracy of pipe-soil testing. Summary of the invention

[0005] The present invention aims to provide a true triaxial multifunctional pipe-soil testing device and method, by which the influence of different loads on the stress, deformation and damage of buried pipelines under actual conditions can be simulated; true triaxial stress is applied to the pipe-soil specimen, gas or liquid is injected into the pipeline, and the changes in pressure field and temperature field are controlled to carry out pipe-soil testing.

[0006] The present invention uses a true triaxial testing machine and a pipe-soil combination specimen to conduct experimental research. Combining the three stress states of compression, shearing and bending of the pipeline in the soil, the true triaxial testing machine is modified to realize the study of the mechanical behavior of the pipeline in the soil. The true triaxial testing machine has sixteen sets of loading devices in the five directions of front, back, left, right and top, which can provide a more complex stress state for the pipe-soil combination specimen. When filling the pipe-soil combination specimen, fully considering the different inclination angles of the pipeline in the soil is more in line with the application background of the pipeline in actual engineering.

[0007] The present invention provides a true triaxial multifunctional pipe-soil testing device, comprising a frame, a true triaxial loading chamber, a test piece box, a hydraulic servo control system, and a fluid injection device; The frame includes a reaction frame, a transfer slide, a specimen box lifting and transfer platform and a right reaction frame. The reaction frame is fixed on the base, the column supports the base, and the bottom of the column has anchor bolts to fix the reaction frame on the ground, and the crossbeam passes through the reaction frame. The transfer slide is on the right side of the reaction frame, and the transfer slide is provided with a linear guide rail slot, the length of which can extend to the bottom of the reaction frame, and the width of the transfer slide is less than the width of the reaction frame. The specimen box lifting and transfer platform and the right reaction frame are installed on the transfer slide. The specimen box lifting and transfer platform consists of a sliding base, a lifting hydraulic cylinder, a guide column and a transfer platform. The bottom of the sliding base contacts the roller on the linear guide rail slot and can slide horizontally along the transfer slide. The bottom and upper piston rod of the lifting hydraulic cylinder are respectively welded to the upper surface of the sliding base and the lower surface of the transfer platform. The bottom of the guide column is welded to the four corners of the sliding base, and the top of the guide column is connected to the transfer platform through a sliding sleeve. The transfer platform is provided with a linear guide rail slot and a corresponding spiral clamping mechanism.

[0008] The right reaction force frame is composed of a right sliding base, a right vertical plate, a right hydraulic cylinder and a right pressure transmission rod. The bottom of the right sliding base contacts the roller on the linear guide rail and can slide horizontally along the transfer rail. The right vertical plate is connected to the right sliding base through a crossbeam. The right hydraulic cylinder is fixed to the right vertical plate through bolts. The end of the piston rod of the right hydraulic cylinder has a thread that can be connected to the internal thread of the right pressure transmission rod.

[0009] The test box is a cubic structure, including a base, four side panels (front, rear, left and right), and ear panels. The ear panels fix the four side panels together. The bottom of the base is connected to the spiral clamping mechanism on the transfer platform, and can slide horizontally along the linear guide rail on the transfer platform. There is a circular opening in the center of each side panel, and the connecting wires of the fluid injection pipeline and the monitoring equipment pass through the opening. A pulley clamp is provided on the upper edge of each side panel. The pulley clamp is used to fix the thin rope to adjust the position and inclination of the pipeline in the pipe-soil specimen through the thin rope (polyester rope or polypropylene rope). The test box is connected to the temperature regulating device.

[0010] When conducting a pipeline shear test, two test boxes need to cooperate with each other, that is, two test boxes are set up. First, test box one is assembled and pushed into the true triaxial loading chamber. A bottom guard plate is added to the bottom of test box one, and the bottom guard plate is tightly connected to the side plate by using the ear plate. Test box one is lifted by a hydraulic jack installed at the bottom of the true triaxial loading chamber for a distance s (so that there is a height difference between the two test boxes), the right side plate of test box one is removed, test box two is assembled and its left side plate is removed, and a pre-prepared baffle (the length and thickness are the same as those of the left side plate of the test box, and the width is s) is installed on the left side of test box two close to the lower surface, and test box two is moved so that its left side is tightly fitted with the right side of test box one, and the hydraulic jack at the bottom of the true triaxial loading chamber is retracted so that test box one is suspended between the shear side plate and test box two. The shear side plate is fixed vertically on the base, and two connecting ribs are respectively arranged in the front and rear directions to connect the shear side plate, the test box one and the test box two. The test box one is used as the test box and is located between the shear side plate and the test box two. The connecting ribs, the shear side plate and the test box two are connected by bolts.

[0011] The bottom guard plate is set at the bottom of the specimen box 1 to prevent the soil of the specimen box 1 from falling off from the bottom of the specimen box due to the upper extrusion force. When the pressure transmission plate above the true triaxial pressure chamber is pressed downward, it is squeezed together with the side plate and the bottom guard plate, and the entire specimen box 1 slides downward in the space connecting the rib plate, the shear side plate and the specimen box 2.

[0012] The true triaxial loading chamber is inside the reaction force frame, and sixteen groups of loading devices are arranged in the front, left, rear and top directions of the loading chamber. Each group of loading devices includes a hydraulic cylinder, a pressure transmission rod and a pressure transmission plate.

[0013] The structure of the loading device is as follows: the hydraulic cylinder is fixed to the reaction frame by bolts. The hydraulic cylinder and the pressure transmission rod are connected by threads. The pressure transmission rod is a hollow rod, and a hollow hole is arranged circumferentially on the side of the pressure transmission rod of the loading device close to the hydraulic cylinder. The right reaction frame provides sixteen sets of right loading devices, which are combined with the true triaxial loading chamber to surround the specimen box in the middle. The structure of the loading device in the right reaction frame is the same as that of the loading device in the above reaction frame.

[0014] After the specimen box is placed in the true triaxial loading chamber, the ear plates are removed and the side plates of the specimen box are pulled out. The length of the pressure transmission rod is adjusted so that the pressure transmission plate contacts the specimen but does not squeeze it. The piston of the hydraulic cylinder drives the pressure transmission rod, which squeezes the pressure transmission plate to generate load on the specimen. There is a silicone rubber film on the contact surface between the pressure transmission plate and the specimen to prevent the soil in the specimen from being squeezed out of the true triaxial pressure chamber due to the mutual displacement of the pressure transmission plates.

[0015] After the specimen box lifting and transfer platform is raised, the specimen can be pushed into the true triaxial loading chamber along the linear guide rail on the transfer platform. After the specimen box lifting and transfer platform is lowered, it can be pushed under the true triaxial loading chamber along the transfer slide rail. The right reaction frame can slide along the transfer slide rail to the right side of the true triaxial loading chamber, and the right vertical plate can be tightly connected to the reaction frame by high-strength bolts. The lifting hydraulic cylinder is connected to the lifting motor. The specimen box transfer platform, the right reaction frame and the specimen box move horizontally on the slide rail through the slide rail motor.

[0016] The fluid injection device is a liquid injection or gas injection device. Water or nitrogen is used as a conventional simulation fluid in the laboratory. That is, when it is necessary to simulate a gas buried pipeline (such as a natural gas pipeline), it is connected to a nitrogen storage tank for gas injection; when it is necessary to simulate a liquid buried pipeline (such as an oil pipeline), it is connected to a water storage tank for liquid injection.

[0017] The fluid injection device consists of a fluid storage tank, a booster pump, a fluid injection pipeline, a return pipeline, a control valve, a flow meter and a temperature control device. The booster pump extracts gas or liquid from the fluid storage tank and pumps it to the fluid injection pipeline. The gas or liquid flows along the outlet of the booster pump, passes through the hollow hole on the pressure transmission rod and the circular opening on the side plate of the test box, and then flows to the test pipeline in the pipe soil test piece; one end of the return pipeline is connected to the test pipeline in the pipe soil test piece, and the other end passes through the circular opening on the side plate of the test box and the hollow hole on the pressure transmission rod to connect to the fluid storage tank, and the gas (liquid) finally flows back to the fluid storage tank. The interfaces of the fluid injection pipeline, the return pipeline and the test pipeline must ensure sealing and consistency, especially for tested pipelines of different diameters, it is necessary to combine a reducer with a flange to connect the fluid injection pipeline and the tested pipeline, and add a gasket between the flanges to ensure the sealing effect. The fluid injection device can control the flow state of the gas (liquid) by adjusting the gas (liquid) injection speed or adding an orifice at the end of the fluid injection pipeline.

[0018] The fluid storage tank is a nitrogen storage tank or a water storage tank. A flow meter is provided in the fluid injection device, and the device is connected to the hydraulic servo control system to monitor the flow and pressure of the gas (liquid).

[0019] The temperature regulating device includes a refrigeration mechanism, a heating mechanism and a temperature regulating mechanism. The refrigeration mechanism consists of a refrigerant and a refrigeration pipeline, which can reduce the temperature to -10°C or lower to simulate low-temperature frozen soil; the heating mechanism consists of an electric heating plate and a heating wire, which can heat the temperature to 50°C to simulate a high-temperature soil layer. The temperature regulating mechanism uses a computer to achieve real-time temperature control.

[0020] The hydraulic servo control system is an independent hydraulic control device, which is connected to each hydraulic cylinder of the true triaxial loading chamber through a fluid injection pipeline and a return pipeline. Stress monitoring is completed by the pressure sensor in the hydraulic servo control system: a pressure sensor is provided in the hydraulic servo control system, and the load to be applied is monitored in real time through the pressure sensor. The output force is corrected by using the data feedback of the pressure sensor. While the corrected force is output, the stress data is also monitored. Deformation monitoring is completed by a number of displacement sensors installed on the top, bottom, surroundings and pipeline surface of the specimen. The deformation of the specimen can be obtained by analyzing the displacement of each point. In deformation monitoring, the sensor only monitors and outputs data. Unlike stress monitoring, which requires feedback of pressure output, the displacement sensor in deformation monitoring is not connected to the control system.

[0021] The present invention provides a true triaxial multifunctional pipe-soil test method, comprising the following steps: S1, assemble the test box, adjust the test box according to the test requirements, so that the pipeline to be tested can be completely placed in the box, fill the box with soil samples and compact them; S2, adjust the height of the specimen box lifting and transfer platform, and push the specimen box into the true triaxial loading chamber; S3, lower the height of the specimen box lifting and transfer platform, and push the specimen box transfer frame under the reaction force frame; S4, push the right reaction frame to the true triaxial loading chamber, tightly connect the right vertical plate and the reaction frame with high-strength bolts, and remove the ear plate of the specimen box; S5, start the fluid injection device, wait for the flow meter reading to stabilize, start the temperature adjustment device to make the fluid temperature reach the target value, and start the heating module built into the side plate until the temperature of the test piece reaches the target value and remains unchanged; S6, start the hydraulic servo control system until the triaxial pressure reaches the load required for the test and remains constant; S7, after the test, collect monitoring data and shut down the fluid injection device and hydraulic servo control system; S8: Take the reverse process of S2, S3, and S4 to remove the pipe-soil specimen.

[0022] The specifications of the pipe-soil specimen are 500×500×500mm. The axial pressure and confining pressure of the pipe-soil specimen can reach 4MPa. The temperature of the pipe-soil specimen can be adjusted between -10°C and 50°C. The inclination angle of the pipe can be adjusted within the range of 0° to 90°.

[0023] The specific operations of step S1 are as follows: Assemble the specimen box and pipe-soil combination specimen according to different test requirements: ① When there is a requirement for the inclination of the pipeline in the pipe-soil test, use two thin ropes (polyester rope or polypropylene rope) to hang the pipe in the specimen box through the pulley. One end of the thin rope is connected to the pipeline, and the other end is lapped on the pulley clamp. The position and inclination of the pipe are adjusted by adjusting the pulley clamp; ② When conducting a pipeline shear test, two specimen boxes need to cooperate with each other. First, assemble specimen box one and push specimen box one into the true triaxial loading chamber. Add a bottom guard plate to the bottom of specimen box one, use the ear plate to tightly connect the bottom guard plate with the side plate, and use the hydraulic jack installed at the bottom of the true triaxial loading chamber to lift specimen box one by a distance of s, and remove the specimen box one. The right side plate, assemble the specimen box two and remove its left side plate, install the pre-prepared baffle (the length and thickness are the same as the left side plate of the specimen box, and the width is s) on the left side of the specimen box two close to the lower surface, move the specimen box two so that its left side fits tightly with the right side of the specimen box one, retract the hydraulic jack at the bottom of the true triaxial loading chamber, so that the specimen box one is suspended between the shear side plate and the specimen box two, and use a thin rope to suspend the pipeline horizontally in the specimen box; ③ When conducting the pipeline compression bending test, after assembling the pipe-soil combination specimen, adjust each hydraulic cylinder to output different forces in different areas on the same surface of the specimen through the hydraulic servo control system. For the compression bending test, the force in the surrounding area should be greater than the force in the central area.

[0024] The specific operation method of adjusting the position and inclination of the tube is as follows: Use two thin ropes (polyester rope or polypropylene rope) to hang the pipe in the specimen box through the pulley, and use the pulley clamp 22 to adjust the position and inclination of the pipe. After the position of the pipe is determined, fix the free end of the rope. Take another thin rope and fix one end in the middle of the pipe, and the other end on the D-shaped ring buckle at the bottom center of the specimen box. There are shearing devices on the three ropes. When externally stimulated, the blades of the shearing devices will quickly cut the ropes. Fill the box with soil samples and compact them; the inclination of the pipeline is determined by the purpose of the test simulation: the simulated pipeline length a, inclination b, the angle c between the pipeline and its projection on the front side plate, and the angle d between the pipeline and its projection on the right side plate are used. Assume that the box is a cubic structure with the length, width and height of its inner wall all being A. The pipeline can be completely placed in the box, the center of the pipeline coincides with the geometric center of the box, and the rope and the pipeline are on the same plane. Then the lengths L1 and L2 of the two ropes are respectively: ; ; The two pulley holders, the rope and the measured pipe are in the same plane, and the distance between the left pulley holder and the front side plate is L3: ; The distance between the right pulley clamp and the rear side plate is the same as the distance between the left pulley clamp and the front side plate, which is L3.

[0025] The above calculation formula corresponds to the case where the pulley clamp is fixed on the upper edge of the left and right side plates. The case where the pulley clamp is on the front and rear side plates can be obtained by replacing c and d. The box can only realize the assembly of pipe specimens with an inclination b of 0~45°. If it is necessary to assemble 45°~90°, the remaining angles should be selected. Taking the assembly of a 60° inclination pipe as an example, it is impossible to hoist it to an angle of 60°. Only the remaining angle of 30° can be selected, and then the specimen is regarded as being rotated 90° for testing. The pipe-soil specimen is assembled at a 30° inclination, and then the left and right sides are regarded as the bottom and top surfaces in the true triaxial pressure chamber, and the bottom and top surfaces are regarded as the sides for testing.

[0026] Beneficial effects of the present invention: (1) For large specimen boxes, a specimen box lifting and transfer platform and a transfer slide rail shared by the loading unit are designed; after the specimen box lifting and transfer platform is raised, the specimen can be pushed into the true triaxial loading chamber along the linear guide rail on the transfer platform; after the specimen box lifting and transfer platform is lowered, it can be pushed under the true triaxial loading chamber along the transfer slide rail; the right reaction frame can slide along the transfer slide rail to the right side of the true triaxial loading chamber, and the right reaction frame can be tightly connected to the reaction frame through high-strength bolts; at the same time, the specimen box transfer platform, the right reaction frame and the specimen box move horizontally on the slide rail through an electric control system, which is easy to operate and has a high degree of automation.

[0027] (2) The large-scale true triaxial pipe-soil test device of the present invention can provide stress and temperature conditions that are consistent with actual conditions for the pipe-soil specimen. The size of the pipe-soil specimen is 500×500×500mm. The axial pressure and confining pressure of the true triaxial loading chamber can reach 4MPa, and the temperature of the pipe-soil specimen can be adjusted between -10℃ and 50℃. The device can be used to simulate the pipe-soil specimen under actual conditions, apply true triaxial stress to the pipe-soil specimen, inject gas or liquid into the pipeline, and control the changes in pressure field and temperature field. It can also monitor and record the stress, strain, temperature of the pipe-soil specimen, and the flow rate, flow rate, pressure and other parameters of the liquid or gas injected into the pipeline in real time. Various test parameters are controlled, measured and displayed by a computer, with high integration and simple and convenient use. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a schematic diagram of the true triaxial soil pipe test device of the present invention; Figure 2 It is a cross-sectional view (top view) of the working state of the loading device in the true triaxial loading chamber; Figure 3 It is the structural schematic diagram of the test box; Figure 4 This is a structural schematic diagram of the test piece box lifting and transfer platform; Figure 5 It is a structural schematic diagram of the right reaction frame; Figure 6 This is the state diagram of the specimen box during the pipeline shear test; Figure 7 This is a schematic diagram of the pipes in the test box being placed horizontally and parallel to the front and rear side plates.

[0029] Figure 8 It is a schematic diagram showing that the pipe in the test box has an inclination angle of b and is parallel to the front and rear side plates.

[0030] Fig. 9 This is a schematic diagram showing that the pipes in the test chamber are placed horizontally and are not parallel to the front and rear side plates.

[0031] Fig.10 It is a schematic diagram showing that the pipe in the test box has an inclination angle of b and is not parallel to the front and rear side plates.

[0032] In the figure: 1, reaction frame; 2, transfer rail; 3, specimen box lifting and transfer platform; 4, right reaction frame; 5, base; 6, column; 7, anchor bolt; 8, crossbeam; 9, sliding base; 10, lifting hydraulic cylinder; 11, guide column; 12, transfer platform; 13, sliding sleeve; 14, right sliding base; 15, right vertical plate; 16, right hydraulic cylinder; 17, right pressure transmission rod; 18, base; 19, side plate; 20, ear plate; 21 , circular opening; 22, pulley clamp; 23, hydraulic cylinder; 24, pressure transmission rod; 25, hollow hole; 26, hydraulic servo control system; 27, fluid storage tank; 28, booster pump; 29, control valve; 30, flow meter; 31, temperature regulating device; 32, pressure transmission plate; 33, lifting motor; 34, slide rail motor; 35, connecting rib plate; 36, shear side plate; 37, baffle; 38, test piece box one; 39, test piece box two. DETAILED DESCRIPTION

[0033] The present invention is further illustrated by the following examples, but is not limited to the following examples. Example 1

[0034] This embodiment provides a true triaxial multifunctional pipe-soil test device, such as Figures 1 to 6 As shown, the test device includes a frame, a true triaxial loading chamber, a specimen box, a hydraulic servo control system, and a fluid injection device; The frame includes a reaction frame 1, a transfer slide 2, a specimen box lifting and transfer platform 3 and a right reaction frame 4. The reaction frame 1 is fixed on a base 5, and a column 6 supports the base 5. An anchor bolt 7 is provided at the bottom of the column to fix the reaction frame to the ground, and a crossbeam 8 passes through the reaction frame. The transfer slide 2 is on the right side of the reaction frame 1. The transfer slide 2 is provided with a linear guide groove, and its length can extend to the bottom of the reaction frame 1. The width of the transfer slide 2 is smaller than the width of the reaction frame 1. The specimen box lifting and transfer platform 3 and the right reaction frame 4 are installed on the transfer slide 2. The specimen box lifting and transfer platform 3 is composed of a sliding base 9, a lifting hydraulic cylinder 10, a guide column 11 and a transfer platform 12. The bottom of the sliding base 9 contacts the rollers on the linear guide groove and can slide horizontally along the transfer slide rail 2. The bottom and upper piston rod of the lifting hydraulic cylinder 10 are respectively welded to the upper surface of the sliding base 9 and the lower surface of the transfer platform 12. The bottom of the guide column 11 is welded to the four corners of the sliding base 9. The top of the guide column 11 is connected to the transfer platform 12 through a sliding sleeve 13. There are linear guide grooves and corresponding spiral clamping mechanisms on the transfer platform 12.

[0035] The right reaction force frame 4 is composed of a right sliding base 14, a right vertical plate 15, a right hydraulic cylinder 16 and a right pressure transmission rod 17. The bottom of the right sliding base 14 contacts the roller on the linear guide rail slideway and can slide horizontally along the transfer slide rail 2. The right vertical plate 15 is connected to the right sliding base 14 through a crossbeam. The right hydraulic cylinder 16 is fixed to the right vertical plate 15 by bolts. The end of the piston rod of the right hydraulic cylinder 16 has a thread that can be connected to the internal thread of the right pressure transmission rod 17.

[0036] The test box is a cubic structure, including a base 18, four side panels 19 at the front, rear, left and right, and ear panels 20. The ear panels fix the four side panels together. The bottom of the base 18 is connected to the spiral clamping mechanism on the transfer platform 12, and can slide horizontally along the linear guide rail groove on the transfer platform 12. There is a circular opening 21 in the center of each side panel, and the connecting wires of the fluid injection pipeline and the monitoring equipment pass through the opening. A pulley clamp 22 is provided on the upper edge of each side panel. The pulley clamp 22 is used to fix a thin rope to adjust the position and inclination of the pipeline in the pipe-soil specimen through the thin rope (polyester rope or polypropylene rope). The test box is connected to a temperature regulating device.

[0037] When conducting a pipeline shear test, two test boxes need to cooperate with each other, that is, two test boxes are set up, first assemble test box one 38 and push test box one into the true triaxial loading chamber, add a bottom guard plate to the bottom of test box one, use ear plates to tightly connect the bottom guard plate and the side plate, use the hydraulic jack installed at the bottom of the true triaxial loading chamber to lift test box one for a distance s (so that there is a height difference between the two test boxes), remove the right side plate of test box one 38, assemble test box two 39 and remove its left side plate, install a pre-prepared baffle 37 (the length and thickness are the same as the left side plate of the test box, and the width is s) on the left side of test box two 39 close to the lower surface, move test box two so that its left side fits tightly with the right side of test box one, and retract the hydraulic jack at the bottom of the true triaxial loading chamber so that test box one is suspended between the shear side plate and test box two. The shear side plate 36 is vertically fixed on the base 18, and two connecting ribs 35 are respectively provided in the front and rear directions to connect the shear side plate, the test box 1 and the test box 2. The test box 1 is used as the test box and is located between the shear side plate and the test box 2. The connecting ribs 35 are connected to the shear side plate and the test box 2 by bolts. Figure 6 shown.

[0038] The bottom guard plate is set at the bottom of the specimen box 1 to prevent the soil of the specimen box 1 from falling off from the bottom of the specimen box due to the upper extrusion force. When the pressure transmission plate above the true triaxial pressure chamber is pressed downward, it is squeezed together with the side plate and the bottom guard plate, and the entire specimen box 1 slides downward in the space connecting the rib plate, the shear side plate and the specimen box 2.

[0039] The true triaxial loading chamber is inside the reaction frame 1, and sixteen groups of loading devices are provided in the front, left, rear and top directions of the loading chamber. Each group of loading devices includes a hydraulic cylinder 23, a pressure transmission rod 24 and a pressure transmission plate 32. The structure of the loading device is as follows: the hydraulic cylinder 23 is fixed to the reaction frame 1 by bolts. The hydraulic cylinder 23 and the pressure transmission rod 24 are connected by threads. The structure of the loading device in the right reaction frame is the same as that of the loading device in the reaction frame 1 mentioned above. The right reaction frame 4 provides sixteen groups of right loading devices, such as Figure 5 As shown, the right hydraulic cylinder 16 and the right pressure transmission rod 17 are respectively provided with sixteen groups, forming sixteen groups of loading devices. Figure 2 It is a top view. Figure 2 The loading condition shown is a schematic diagram of placing the specimen box as a whole into a true triaxial loading chamber and subjecting the specimen box to loading in four directions: front, back, left, and right.

[0040] The pressure transmission rod 24 is a hollow rod, and a hollow hole 25 is circumferentially arranged on one side of the pressure transmission rod close to the hydraulic cylinder 23. In this embodiment, two pressure transmission rods on the front side and the right side are respectively provided with hollow holes 25 (two hollow holes can meet the requirements), and the hollow holes are connected to the circular openings 21 on the corresponding side plates, so that the fluid injection pipeline and the connecting wires of the monitoring equipment can pass through the holes. Figure 2 shown.

[0041] After the specimen box is placed in the true triaxial loading chamber, the ear plates are removed and the side plates 19 of the specimen box are pulled out. The length of the pressure transmission rod is adjusted so that the pressure transmission plate contacts the specimen but does not squeeze the specimen. The piston of the hydraulic cylinder 23 drives the pressure transmission rod 24, and the pressure transmission rod 24 squeezes the pressure transmission plate to generate load on the specimen. There is a silicone rubber film on the contact surface between the pressure transmission plate and the specimen to prevent the soil in the specimen from being squeezed out of the true triaxial pressure chamber due to the mutual displacement of the pressure transmission plates.

[0042] After the specimen box lifting and transfer platform 3 is raised, the specimen can be pushed into the true triaxial loading chamber along the linear guide rail groove on the transfer platform. After the specimen box lifting and transfer platform 3 is lowered, it can be pushed under the true triaxial loading chamber along the transfer slide rail 2. The right reaction frame 4 can slide along the transfer slide rail 2 to the right side of the true triaxial loading chamber, and the right vertical plate 15 can be tightly connected to the reaction frame 1 by high-strength bolts. The lifting hydraulic cylinder 10 is connected to the lifting motor 33. The specimen box transfer platform 3, the right reaction frame 4 and the specimen box move horizontally on the slide rail through the slide rail motor 34.

[0043] The fluid injection device is a liquid injection or gas injection device. Water or nitrogen is used as a conventional simulation fluid in the laboratory. That is, when it is necessary to simulate a gas buried pipeline (such as a natural gas pipeline), it is connected to a nitrogen storage tank for gas injection; when it is necessary to simulate a liquid buried pipeline (such as an oil pipeline), it is connected to a water storage tank for liquid injection.

[0044] The fluid injection device is composed of a fluid storage tank 27, a booster pump 28, a fluid injection pipeline, a return pipeline, a control valve 29, a flow meter 30 and a temperature regulating device 31. The booster pump 28 extracts gas or liquid from the fluid storage tank 27 and pumps it to the fluid injection pipeline. The gas or liquid flows along the outlet of the booster pump 28, passes through the hollow hole 25 on the pressure transmission rod 24, and the circular opening 21 on the side plate 19 of the test box to the test pipeline in the pipe soil test piece; one end of the return pipeline is connected to the test pipeline in the pipe soil test piece, and the other end passes through the circular opening 21 on the side plate 19 of the test box and the hollow hole 25 on the pressure transmission rod 24 to connect to the fluid storage tank 27, and the gas (liquid) finally flows back to the fluid storage tank 27. The interfaces of the fluid injection pipeline, the return pipeline and the test pipeline must ensure sealing and consistency, especially for tested pipelines of different diameters, a reducer is required to connect the fluid injection pipeline and the tested pipeline in combination with a flange, and a gasket is added between the flanges to ensure the sealing effect. The fluid injection device can control the flow state of the gas (liquid) by adjusting the gas (liquid) injection speed or adding an orifice plate at the end of the fluid injection pipeline.

[0045] The fluid storage tank is a nitrogen storage tank or a water storage tank. A flow meter 30 is provided in the fluid injection device, and the device is connected to the hydraulic servo control system 26 to monitor the flow and pressure of the gas (liquid).

[0046] The temperature regulating device 31 includes a refrigeration mechanism, a heating mechanism and a temperature regulating mechanism. The refrigeration mechanism is composed of a refrigerant and a refrigeration pipeline, which can reduce the temperature to -10°C or lower to simulate low-temperature frozen soil; the heating mechanism is composed of an electric heating plate and a heating wire, which can heat the temperature to 50°C to simulate a high-temperature soil layer. The temperature regulating mechanism realizes real-time temperature control with the help of a computer.

[0047] The hydraulic servo control system 26 is an independent hydraulic control device, which is connected to each hydraulic cylinder of the true triaxial loading chamber through a fluid injection pipeline and a return pipeline. A pressure sensor is provided in the hydraulic servo control system, which monitors the load to be applied in real time through the pressure sensor, and uses the data feedback of the pressure sensor to correct the output force. While outputting the corrected force, the stress data is also monitored. Stress monitoring is completed by the pressure sensor in the hydraulic servo control system 26. Deformation monitoring is completed by a number of displacement sensors installed on the top, bottom, surroundings and pipeline surface of the specimen. The deformation of the specimen can be obtained by analyzing the displacement of each point. A number of displacement sensors are set on the top, bottom, surroundings and pipeline surface of the specimen to monitor the change of displacement. Example 2

[0048] This embodiment provides a method for performing a true triaxial multifunctional pipe-soil test (under pressure) using the device described in Embodiment 1, comprising the following steps: S1, assemble the test box, adjust the test box according to the test requirements, so that the pipeline to be tested can be completely placed in the box, fill the box with soil samples and compact them; S2, adjust the height of the specimen box lifting and transfer platform 3, and push the specimen box into the true triaxial loading chamber; S3, lowering the height of the specimen box lifting and transfer platform 3, and pushing the specimen box transfer frame under the reaction force frame 1; S4, push the right reaction frame 4 to the true triaxial loading chamber, tightly connect the right vertical plate 15 to the reaction frame 1 through high-strength bolts, and remove the ear plate of the specimen box; S5, start the fluid injection device, wait for the flow meter 30 reading to stabilize, start the temperature adjustment device 31 to make the fluid temperature reach the target value, and start the heating module built into the side plate until the temperature of the test piece reaches the target value and remains unchanged; S6, starting the hydraulic servo control system 26 until the triaxial pressure reaches the load required for the test and remains constant; S7, after the test, collect monitoring data, and turn off the fluid injection device and the hydraulic servo control system 26; S8: Take the reverse process of S2, S3, and S4 to remove the pipe-soil specimen.

[0049] The specifications of the pipe-soil specimen are 500×500×500mm. The axial pressure and confining pressure of the pipe-soil specimen can reach 4MPa. The temperature of the pipe-soil specimen can be adjusted between -10°C and 50°C. The inclination angle of the pipe can be adjusted within the range of 0° to 90°.

[0050] The specific operation of step S1 is as follows: when there is a requirement for the inclination of the pipe in the pipe-soil test, two thin ropes (polyester rope or polypropylene rope) are used to hang the pipe in the test box through a pulley, one end of the thin rope is connected to the pipe, and the other end is overlapped on the pulley clamp 22, and the position and inclination of the pipe are adjusted by adjusting the pulley clamp 22; the specific operation method of adjusting the position and inclination of the pipe is as follows: two thin ropes (polyester rope or polypropylene rope) are used to hang the pipe in the test box through a pulley, and the position and inclination of the pipe are adjusted by the pulley clamp 22. After the position of the pipe is determined, the free end of the rope is fixed. Another thin rope is taken, one end is fixed in the middle of the pipe, and the other end is fixed to the D-shaped ring buckle at the bottom of the test box. There is a small mechanical shearing device on the rope. When externally stimulated, the blade of the shearing device will quickly cut the rope. Fill the soil sample into the box and compact it; the inclination of the pipe is determined by the purpose of the test simulation. The direction and inclination of the pipe placement are adjusted as follows: (1) Horizontally placed pipe: The pipe is parallel to the front and rear side plates, and two pulley clamps are fixed at the top center of the left and right side plates respectively, as shown in the attached figure. Figure 7 shown.

[0051] (2) The pipeline is inclined at an angle of b and is parallel to the front and rear side panels: Fix the pipeline to the pulley with a thin rope. The pulley is fixed by two pulley clamps. The pipeline is parallel to the front and rear side panels. The two pulley clamps are fixed at the top center of the left and right side panels respectively. The angle between the pipeline and its projection on the right side panel is d. At this time, the sum of b and d is 90°. Figure 8 shown.

[0052] (3) Horizontally placed pipe, but not parallel to the front and rear side plates: Fix the pipe to the pulley with a thin rope. The pulley is fixed by two pulley clamps. The distance between the left pulley clamp and the front side plate is L3. The angle between the pipe and its projection on the front side plate is c. Fig. 9 shown.

[0053] (4) The pipeline is tilted at an angle of b, but the pipeline is not parallel to the front and rear side plates: Fix the pipeline to the pulley with a thin rope. The pulley is fixed by two pulley clamps. The distance between the left pulley clamp and the front side plate is L3. The angle between the pipeline and its projection on the front side plate is c, and the angle between the pipeline and its projection on the right side plate is d. Fig.10 shown.

[0054] The simulated pipeline length is a, the inclination is b, the angle between the pipeline and its projection on the front side plate is c, and the angle between the pipeline and its projection on the right side plate is d. Assume that the box is a cubic structure with the length, width and height of its inner wall all being A. The pipeline can be completely placed in the box, the center of the pipeline coincides with the geometric center of the box, and the rope and the pipeline are on the same plane. The lengths of the two ropes L1 and L2 are: ; ; The two pulley holders, the rope and the measured pipe are in the same plane, and the distance between the left pulley holder and the front side plate is L3: ;

[0055] The distance between the right pulley clamp and the rear side plate is the same as the distance between the left pulley clamp and the front side plate, which is L3.

[0056] The above calculation formula corresponds to the case where the pulley clamp is fixed on the upper edges of the left and right side plates. The case where the pulley clamp is on the front and rear side plates can be obtained by replacing c and d.

[0057] In the four cases described above, the box can only realize the assembly of pipe specimens with an inclination angle b of 0~45°. If it is necessary to simulate the assembly of inclination angles b of 45°~90°, the remaining angles (i.e. 90°-b) should be selected to assemble the pipe-soil specimens, and then the left and right sides should be regarded as the bottom and top surfaces in the true triaxial pressure chamber, and the bottom and top surfaces should be regarded as the sides for testing. Example 3

[0058] This embodiment provides a method for conducting compression and bending tests on pipe-soil specimens using the above-mentioned device. When conducting the pipeline compression and bending test, after assembling the pipe-soil combination specimen, each hydraulic cylinder is adjusted by the hydraulic servo control system to output different forces in different areas on the same surface of the specimen. In order to conduct the compression and bending test, the force in the surrounding areas should be greater than the force in the central area.

[0059] The following steps are involved: (1) Place the specimen box lifting and transfer platform 3 and the right reaction frame 4 on the right side of the transfer slide rail 2, as shown in the attached figure. Figure 1 The lifting hydraulic cylinder 10 of the specimen box transfer platform 3 is lowered to the lowest position, so that the transfer platform 12 reaches the lowest position.

[0060] (2) Assemble the specimen box on the transfer platform 12 and tightly connect the side panels of the specimen box using the ear plates 20.

[0061] (3) Use two thin ropes (polyester rope or polypropylene rope) to hang the tube in the specimen box through the pulley, and use the pulley clamp 22 to adjust the position and inclination of the tube. After the position of the tube is determined, fix the free end of the rope. Take another thin rope and fix one end in the middle of the tube, and the other end to the D-shaped ring buckle at the bottom of the specimen box. Install small mechanical shearing devices on all three ropes; Note: The inclination angle of the pipeline is determined by the purpose of the test simulation: assuming that the length of the simulated pipeline is a, the inclination angle is b, the angle between the pipeline and its projection on the front side plate is c, and the angle between the pipeline and its projection on the right side plate is d, and the length, width and height of the cube box are A, the pipeline can be completely placed in the box, the center of the pipeline coincides with the geometric center of the box, and the rope and the pipeline are on the same plane, then the lengths of the two ropes are: ; ;

[0062] The two pulley holders, the rope and the measured pipe are in the same plane, and the distance between the left pulley holder and the front side plate is L3: ;

[0063] The distance between the right pulley clamp and the rear side plate is the same as the distance between the left pulley clamp and the front side plate, which is L3.

[0064] The above calculation formula corresponds to the case where the pulley clamp is fixed on the upper edge of the left and right side plates. The case where the pulley clamp is on the front and rear side plates can be obtained by replacing c and d. This box can only realize the assembly of pipe specimens with an inclination angle b of 0~45°. If assembly of 45°~90° is required, the remaining angles should be selected to assemble the pipe-soil specimens, and then the left and right sides are regarded as the bottom and top surfaces in the true triaxial pressure chamber, and the bottom and top surfaces are regarded as the sides for testing.

[0065] (4) Connect the injection pipeline and the return pipeline at both ends of the pipeline, fill the soil sample into the box and compact it, and activate the small mechanical shearing device on the rope to cut the rope; (5) Raise the height of the lifting hydraulic cylinder 10, and slowly raise the transfer platform 12 until the slide rail on the transfer platform 12 is at the same height as the slide rail inside the true triaxial pressure chamber. Slide the specimen box lifting transfer platform 3 along the slide rail toward the true triaxial pressure chamber, so that the slide rail on the transfer platform 12 fits with the slide rail inside the true triaxial pressure chamber. Fine-tune the height of the transfer platform, and push the specimen box into the true triaxial pressure chamber. (6) Lower the height of the specimen box lifting and transfer platform 3, and push the specimen box lifting and transfer platform 3 along the slide rail to the bottom of the reaction frame 1; (7) Push the right reaction frame into the true triaxial loading chamber and tightly connect the right reaction frame to the crossbeam in reaction frame 1 using high-strength bolts; (8) Start the hydraulic servo control system and the heating device built into the side plate to make the temperature of the pipe-soil specimen reach the target value and keep the temperature constant; (9) Remove the ear plates of the specimen box and pull the side plates of the specimen box out of the gap of the reaction frame 1. Each time a side plate is pulled out, the pressure transmission plate in the corresponding direction is controlled by the hydraulic servo control system to fit the side wall of the pipe-soil specimen, but the side wall of the pipe-soil specimen is not squeezed by the pressure transmission plate. For the side plates with injection or return lines extending out, the quick-connect connectors on the injection or return lines can be disconnected first to disconnect the injection or return lines. After the side plates are pulled out, the quick-connect connectors can be connected; (10) Start the fluid injection device, wait for the flow meter 30 reading to stabilize, and start the temperature adjustment device to make the fluid temperature reach the target value; (11) The specimen pressure is applied to the pipe-soil specimen by using a hydraulic servo control system. The pressure transmission plates in the horizontal direction of the specimen tube can provide horizontal pressures with different horizontal gradients. If only the pipe-soil specimen is subjected to a compression test, the forces output by the nine pressure transmission plates on the pipe-soil specimen should be controlled to be the same. If a compression bending test is conducted on the pipe-soil specimen, the forces output by the pressure transmission plates on the pipe-soil specimen should be controlled to be different, in which the force output by the central pressure transmission plate is greater than the forces output by the surrounding pressure transmission plates. (12) Obtain test data through pressure sensors, flow meters, etc.; turn off the fluid injection device and the hydraulic servo control system, push the right reaction frame away from the true triaxial loading chamber, adjust the specimen box lifting and transfer platform, and unload the pipe-soil specimen. Example 4

[0066] This embodiment provides a method for carrying out compression and shear tests on pipe-soil specimens using the above-mentioned device. When carrying out the pipeline shear test, two specimen boxes need to cooperate with each other. First, assemble the specimen box one and push the specimen box one into the true triaxial loading chamber. Add a bottom guard plate to the bottom of the specimen box one, and use the ear plate to tightly connect the bottom guard plate with the side plate. Use the hydraulic jack installed at the bottom of the true triaxial loading chamber to lift the specimen box one by a distance s, remove the right side plate of the specimen box one, assemble the specimen box two and remove its left side plate, install a pre-prepared baffle (with the same length and thickness as the left side plate of the specimen box and a width of s) on the left side of the specimen box two close to the lower surface, move the specimen box two so that its left side is tightly fitted with the right side of the specimen box one, retract the hydraulic jack at the bottom of the true triaxial loading chamber, so that the specimen box one is suspended between the shear side plate and the specimen box two, and use a thin rope to horizontally suspend the pipeline in the specimen box; The following steps are involved: (1) Place the specimen box lifting and transfer platform 3 and the right reaction frame 4 on the right side of the transfer slide rail 2, as shown in the attached figure. Figure 1 The lifting hydraulic cylinder 10 of the specimen box transfer platform 3 is lowered to the lowest position, so that the transfer platform 12 reaches the lowest position; (2) Assemble the specimen box 1 on the transfer platform 12. In addition to the side panels, a bottom guard plate is added to the bottom of the specimen box 1. A hydraulic jack is preset under the bottom guard plate. The bottom guard plate is tightly connected to the side panels using ear plates. (3) Raise the height of the lifting hydraulic cylinder 10 and slowly raise the transfer platform 12 until the slide rail on the transfer platform 12 is at the same height as the slide rail inside the true triaxial pressure chamber; slide the specimen box lifting transfer platform 3 along the slide rail toward the true triaxial pressure chamber so that the slide rail on the transfer platform 12 fits the slide rail inside the true triaxial pressure chamber, and fine-tune the height of the transfer platform to ensure that the specimen box 1 can smoothly enter the true triaxial pressure chamber along the slide rail; push the specimen box 1 into the true triaxial pressure chamber; remove the right side panel of the specimen box 1; (4) Repeat step (1), assemble the specimen box 2 on the transfer platform 12 and remove its left side plate, and install the pre-prepared baffle (with the same length and thickness as the left side plate of the specimen box and a height of s) on the left side of the specimen box 2 close to the lower surface. (5) Raise the height of the lifting hydraulic cylinder 10, and slowly raise the transfer platform 12 until the slide rail on the transfer platform 12 is at the same height as the slide rail in the true triaxial pressure chamber. Slide the specimen box lifting transfer platform 3 along the slide rail toward the true triaxial pressure chamber, so that the slide rail on the transfer platform 12 fits with the slide rail in the true triaxial pressure chamber. Fine-tune the height of the transfer platform, and push the specimen box 2 into the true triaxial pressure chamber. The left side of the specimen box 2 fits with the right side of the specimen box 1. (6) Adjust the hydraulic jack preset under the bottom guard plate to raise the test box 1 by s compared with the test box 2; (7) Install connecting ribs and shear side plates, such as Figure 6 , withdraw the hydraulic jack; (8) Use two thin ropes (polyester rope or polypropylene rope) to hang the tube in the specimen box through the pulley, and use the pulley clamp 22 to adjust the position and inclination of the tube. After the position of the tube is determined, fix the free end of the rope. Take another thin rope and fix one end in the middle of the tube, and the other end to the D-shaped ring buckle at the bottom of the specimen box. Install a small mechanical shearing device on all three ropes; Note: In the pipe soil pressure shear test, the pipe should be kept horizontal in the test box and parallel to the front and rear side panels of the box. The height of the pipe can be roughly at the center height of test box one and test box two.

[0067] (9) Connect the injection pipeline and the return pipeline at both ends of the pipeline, fill the soil sample into the box and compact it, and activate the small mechanical shearing device on the rope to cut the rope; (10) Lower the height of the specimen box lifting and transfer platform 3, and push the specimen box lifting and transfer platform 3 along the slide rail to the bottom of the reaction frame 1; (11) Push the right reaction frame into the true triaxial loading chamber and tightly connect the right reaction frame to the crossbeam in reaction frame 1 using high-strength bolts; (12) Start the hydraulic servo control system and the heating device built into the side plate to make the temperature of the pipe-soil specimen reach the target value and keep the temperature constant; (13) Start the fluid injection device, wait for the flow meter 30 reading to stabilize, and start the temperature adjustment device to make the fluid temperature reach the target value; (14) A hydraulic servo control system is used to apply specimen pressure to the pipe-soil specimen. The pressure transmission plates in the horizontal direction of the specimen tube can provide horizontal pressures with different horizontal gradients. The nine pressure transmission plates above the specimen output the same force and displacement, squeezing the specimen box downward to perform a compression shear test. (15) Obtain test data through pressure sensors, flow meters, etc.; turn off the fluid injection device and the hydraulic servo control system, push the right reaction frame away from the true triaxial loading chamber, adjust the specimen box lifting and transfer platform, and unload the pipe-soil specimen.

[0068] It should be noted that, in this article, relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In addition, "front", "back", "left", "right", "upper" and "lower" in this article are all referenced to the placement states shown in the accompanying drawings. Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention is described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions recorded in the aforementioned embodiments, or replace some of the technical features therein with equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A true triaxial multifunctional pipe-soil testing device, characterized in that: It includes a frame, a true triaxial loading chamber, a specimen box, a hydraulic servo control system, and a fluid injection device; The rack includes a reaction frame, a transfer slide rail, a specimen box lifting and transfer platform and a right reaction frame; the reaction frame is fixed on the base, the column supports the base, the bottom of the column has anchor bolts to fix the reaction frame on the ground, and the crossbeam passes through the reaction frame; the transfer slide rail is on the right side of the reaction frame, the transfer slide rail is provided with a linear guide rail slot, the length of which can extend to the bottom of the reaction frame, the width of the transfer slide rail is smaller than the width of the reaction frame, and the specimen box lifting and transfer platform and the right reaction frame are installed on the transfer slide rail; the specimen box lifting and transfer platform consists of a sliding base, a lifting hydraulic cylinder, a guide column and a transfer platform; The test box is a cubic structure, including a base, four side panels at the front, rear, left and right, and ear panels, and the ear panels fix the four side panels together; the bottom of the base is connected to the spiral clamping mechanism on the transfer platform, and can slide horizontally along the linear guide rail groove on the transfer platform; there is a circular opening in the center of each side panel, and the connecting wires of the fluid injection pipeline and the monitoring equipment pass through the opening; the upper edge of each side panel is provided with a pulley clamp, which is used to fix the thin rope, so as to adjust the position and inclination of the pipeline in the pipe-soil test piece through the thin rope; the test box is connected to the temperature adjustment device; The true triaxial loading chamber is inside the reaction force frame, and sixteen groups of loading devices are arranged in the front, left, rear and upper directions of the loading chamber, and each group of loading devices includes a hydraulic cylinder, a pressure transmission rod and a pressure transmission plate; the structure of the loading device is as follows: the hydraulic cylinder is fixed to the reaction force frame by bolts; the hydraulic cylinder and the pressure transmission rod are connected by threads; the pressure transmission rod is a hollow rod, and a hollow hole is arranged on the circumference of the pressure transmission rod of each group of loading devices close to the hydraulic cylinder; the right reaction force frame provides sixteen groups of right loading devices, which are combined with the true triaxial loading chamber; After the specimen box lifting and transfer platform is raised, the specimen is pushed into the true three-axis loading chamber along the linear guide rail on the transfer platform. After the specimen box lifting and transfer platform is lowered, it is pushed under the true three-axis loading chamber along the transfer slide rail; the right reaction frame slides along the transfer slide rail to the right side of the true three-axis loading chamber, and the lifting hydraulic cylinder is connected to the lifting motor; the specimen box transfer platform, the right reaction frame and the specimen box move horizontally on the slide rail through the slide rail motor; The fluid injection device is composed of a fluid storage tank, a booster pump, a fluid injection pipeline, a return pipeline, a control valve, a flow meter and a temperature regulating device; The hydraulic servo control system is an independent hydraulic control device, which is connected to each hydraulic cylinder of the true triaxial loading chamber through a fluid injection pipeline and a return pipeline.

2. The true triaxial multifunctional soil-pipe test device according to claim 1 is characterized in that: The bottom of the sliding base contacts the rollers on the linear guide groove and can slide horizontally along the transfer slide rail. The bottom and upper piston rod of the lifting hydraulic cylinder are welded to the upper surface of the sliding base and the lower surface of the transfer platform respectively. The bottom of the guide column is welded to the four corners of the sliding base. The top of the guide column is connected to the transfer platform through a sliding sleeve. There are linear guide grooves and corresponding spiral clamping mechanisms on the transfer platform.

3. The true triaxial multifunctional soil-pipe test device according to claim 1 is characterized in that: The right reaction force frame consists of a right sliding base, a right vertical plate, a right hydraulic cylinder and a right pressure transmission rod; the bottom of the right sliding base contacts the roller on the linear guide rail groove and can slide horizontally along the transfer slide rail. The right vertical plate is connected to the right sliding base through a cross beam, and the right hydraulic cylinder is fixed to the right vertical plate through bolts. The end of the piston rod of the right hydraulic cylinder is threaded and can be connected to the internal thread of the right pressure transmission rod.

4. The true triaxial multifunctional soil-pipe testing device according to claim 1 is characterized in that: When conducting a pipe shear test, two test boxes need to cooperate with each other, that is, two test boxes are set up. First, test box one is assembled and pushed into the true triaxial loading chamber. A bottom guard plate is added to the bottom of test box one, and the bottom guard plate is tightly connected to the side plate by using the ear plate. The hydraulic jack installed at the bottom of the true triaxial loading chamber is used to lift test box one for a distance s, so that there is a height difference between the two test boxes. The right side plate of test box one is removed, and test box two is assembled and its left side plate is removed. The pre-prepared baffle is installed on the left side of test box two close to the lower surface. The length and thickness are the same as the left side plate of the specimen box, and the width is s. Move the specimen box 2 so that its left side fits tightly with the right side of the specimen box 1, and retract the hydraulic jack at the bottom of the true triaxial loading chamber so that the specimen box 1 is suspended between the shear side plate and the specimen box 2; the shear side plate is vertically fixed on the base, and two connecting ribs are respectively provided in the front and rear directions to connect the shear side plate, the specimen box 1 and the specimen box 2. The specimen box 1 is used as the tested specimen box and is located between the shear side plate and the specimen box 2. The connecting ribs, the shear side plate and the specimen box 2 are connected by bolts.

5. The true triaxial multifunctional soil-pipe testing device according to claim 1 is characterized in that: After the specimen box is placed in the true triaxial loading chamber, the ear plates are released and the side plates of the specimen box are pulled out. The length of the pressure transmission rod is adjusted so that the pressure transmission plate contacts the specimen but does not squeeze it. The piston of the hydraulic cylinder drives the pressure transmission rod, which squeezes the pressure transmission plate to generate load on the specimen. There is a silicone rubber film on the contact surface between the pressure transmission plate and the specimen to prevent the soil in the specimen from being squeezed out of the true triaxial pressure chamber due to the mutual displacement of the pressure transmission plates.

6. The true triaxial multifunctional soil-pipe testing device according to claim 1 is characterized in that: In the fluid injection device, a booster pump extracts gas or liquid from a fluid storage tank and pumps it to a fluid injection pipeline; the gas or liquid passes through the outlet of the booster pump, through the hollow hole on the pressure transmission rod, and through the circular opening on the side plate of the test box, and then to the test pipeline in the pipe soil test piece; one end of the return pipeline is connected to the test pipeline in the pipe soil test piece, and the other end passes through the circular opening on the side plate of the test box and the hollow hole on the pressure transmission rod, and is connected to the fluid storage tank, and the gas or liquid finally flows back to the fluid storage tank; the fluid injection device controls the flow state of the gas or liquid by adjusting the injection speed of the gas or liquid or adding an orifice plate at the end of the fluid injection pipeline; The fluid injection device is a liquid injection or gas injection device, and the fluid storage tank is a nitrogen storage tank or a water storage tank; a flow meter is provided in the fluid injection device, and the device is connected to a hydraulic servo control system for monitoring the flow and pressure of the gas or liquid.

7. The true triaxial multifunctional soil-pipe testing device according to claim 1 is characterized in that: The temperature regulating device includes a refrigeration mechanism, a heating mechanism and a temperature regulating mechanism; the refrigeration mechanism is composed of a refrigerant and a refrigeration pipeline, and can reduce the temperature to -10°C or lower to simulate low-temperature frozen soil; the heating mechanism is composed of an electric heating plate and a heating wire, and can heat the temperature to 50°C to simulate a high-temperature soil layer; A pressure sensor is provided in the hydraulic servo control system, which monitors the load to be applied in real time through the pressure sensor, and uses the data feedback of the pressure sensor to correct the output force. While outputting the corrected force, the stress data is also monitored at the same time. Deformation monitoring is completed by several displacement sensors installed on the top, bottom, surroundings and pipeline surface of the specimen. The deformation of the specimen can be obtained by analyzing the displacement of each point.

8. A true triaxial multifunctional soil-pipe test method, using the true triaxial multifunctional soil-pipe test device according to any one of claims 1 to 7, characterized in that The following steps are involved: S1, assemble the test box, adjust the test box according to the test requirements, so that the pipeline to be tested can be completely placed in the box, fill the box with soil samples and compact them; S2, adjust the height of the specimen box lifting and transfer platform, and push the specimen box into the true triaxial loading chamber; S3, lower the height of the specimen box lifting and transfer platform, and push the specimen box transfer frame under the reaction force frame; S4, push the right reaction frame to the true triaxial loading chamber, tightly connect the right vertical plate and the reaction frame with high-strength bolts, and remove the ear plate of the specimen box; S5, start the fluid injection device, wait for the flow meter reading to stabilize, start the temperature adjustment device to make the fluid temperature reach the target value, and start the heating module built into the side plate until the temperature of the test piece reaches the target value and remains unchanged; S6, start the hydraulic servo control system until the triaxial pressure reaches the load required for the test and remains constant; S7, after the test, collect monitoring data and shut down the fluid injection device and hydraulic servo control system; S8, take the reverse process of S2, S3, and S4 and remove the pipe-soil specimen; The specifications of the pipe-soil specimen are 500×500×500mm; the axial pressure and confining pressure of the pipe-soil specimen can reach 4MPa; the temperature of the pipe-soil specimen is adjusted between -10°C and 50°C, and the inclination angle of the pipeline is adjusted within the range of 0° to 90°.

9. The true triaxial multifunctional pipe-soil test method according to claim 8, characterized in that: The specific operation method of step S1 is as follows: assemble the specimen box and the pipe-soil combination specimen according to different test requirements: ① When there is a requirement for the inclination of the pipeline in the pipe-soil test, use two thin ropes to hang the pipe in the specimen box through a pulley, one end of the thin rope is connected to the pipeline, and the other end is overlapped on the pulley clamp, and the position and inclination of the pipe are adjusted by adjusting the pulley clamp; ② When conducting a pipeline shear test, the two specimen boxes need to cooperate with each other. First, assemble specimen box one and push specimen box one into the true triaxial loading chamber. Add a bottom guard plate to the bottom of specimen box one, use the ear plate to tightly connect the bottom guard plate with the side plate, and use the hydraulic jack installed at the bottom of the true triaxial loading chamber to lift specimen box one by a distance s, and remove the specimen box. 1, assemble the right side plate of specimen box 2 and remove its left side plate, install a pre-prepared baffle on the left side of specimen box 2 close to the lower surface, the length and thickness are the same as the left side plate of the specimen box, and the width is s, move specimen box 2 so that its left side fits tightly with the right side of specimen box 1, retract the hydraulic jack at the bottom of the true triaxial loading chamber, so that specimen box 1 is suspended between the shear side plate and specimen box 2, and the pipeline is suspended horizontally in the specimen box with a thin rope; ③ When conducting the pipeline compression bending test, after assembling the pipe-soil combination specimen, adjust each hydraulic cylinder to output different forces in different areas on the same surface of the specimen through the hydraulic servo control system. For the compression bending test, the force in the surrounding area should be greater than the force in the central area.

10. The true triaxial multifunctional pipe-soil test method according to claim 9, characterized in that: When adjusting the inclination angle of the pipeline, the specific operation is as follows: Use two thin ropes to hang the pipe in the test box through the pulley, and use the pulley clamp to adjust the position and inclination of the pipe. After the position of the pipe is determined, fix the free end of the rope; take another thin rope and fix one end in the middle of the pipe, and the other end on the D-shaped ring buckle at the bottom center of the test box. There are shearing devices on the three ropes. When externally stimulated, the blades of the shearing devices will quickly cut the ropes; fill the box with soil samples and compact it; the inclination of the pipeline is determined by the purpose of the test simulation: the simulated pipeline length a, inclination b, the angle c between the pipeline and its projection on the front side plate, and the angle d between the pipeline and its projection on the right side plate are assumed. Assume that the box is a cubic structure with the length, width and height of its inner wall all being A. The pipeline can be completely placed in the box, the center of the pipeline coincides with the geometric center of the box, and the rope and the pipeline are on the same plane. Then the lengths L1 and L2 of the two ropes are: ； ； The two pulley holders, the rope and the measured pipe are in the same plane, and the distance between the left pulley holder and the front side plate is L3: ； The distance between the right pulley clamp and the rear side plate is the same as the distance between the left pulley clamp and the front side plate, which is L3; The above calculation formula corresponds to the situation where the pulley clamp is fixed on the upper edge of the left and right side plates. The situation where the pulley clamp is on the front and rear side plates can be obtained by replacing c and d. The box can only realize the assembly of pipeline test pieces with an inclination angle b of 0~45°. If assembly of 45°~90° is required, the angles of other angles should be selected.

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