Large-scale triaxial test chamber for coarse-grained soil and method for sample preparation and installation

Abstract

The present application relates to soil testing device technical field, especially to a kind of coarse-grained soil large triaxial confining pressure chamber, including confining pressure chamber cylinder component, sample installation assembly and auxiliary support seat;Wherein, sample installation assembly is the cylindrical structure of three layers of film, sample is placed in the inside of sample installation assembly, and the measurement of axial deformation generated to sample is completed;Confining pressure chamber cylinder component is fixed in the periphery of sample installation assembly, also complete the measurement of sample deformation;Confining pressure chamber cylinder component and sample installation assembly are fixed on auxiliary support seat.The triaxial confining pressure chamber of coarse-grained soil proposed in the present application uses inner and outer double-layer heat shrink film plus silica gel film as isolation layer, which not only easily maintains the form of sample, but also improves the resistance to confining pressure capacity;At the same time, two kinds of deformation measuring devices are used, which can accurately measure the axial deformation of sample.

Description

Technical Field

[0001] This invention relates to the field of soil testing equipment, and in particular to a large triaxial confining pressure chamber for coarse-grained soil and a method for sample preparation and installation. Background Technology

[0002] In nature, soil deformation can lead to engineering instability, and in severe cases, collapse and destruction. Therefore, simulating the mechanical properties of soil under its original stress state is an important basis for engineering design. Because deep soil is in a complex stress state, often triaxial, and is itself a highly complex natural material, stress tests under simple stress states often cannot fully reflect the actual stress state of soil in engineering projects. A thorough understanding of the mechanical properties of soil under complex stress states is essential for prevention. Therefore, conducting soil testing under triaxial conditions is extremely important.

[0003] Chinese patent application CN111103185A, published on May 5, 2020, entitled "Sampling Device and Method for Triaxial Testing of Coarse-grained Soil by Spinning," proposes a spun-compactor sampler and method for triaxial testing of coarse-grained soil. The sampler includes a base, a reaction frame, a rubber diaphragm, a sample preparation cylinder, a spinning device, a permeable plate, and a sample cap. However, the rubber diaphragm used has the problem of not easily maintaining the sample shape; once the sample preparation cylinder is removed, it is prone to instability and collapse, especially for... The above are large-scale samples; at the same time, due to the large gaps inside the coarse-grained soil, the single-layer rubber membrane cannot withstand large pressure, so the single-layer rubber membrane is prone to leakage when the confining pressure is large.

[0004] In the Chinese patent application CN104316380B, published on February 15, 2017, entitled "A sample preparation instrument for triaxial testing of coarse-grained soil and its usage method", the sample is wrapped with dry sand. However, the sample is also affected by the particle size of the dry sand when under confining pressure. After the cylinder in the pressure chamber is lifted out, a gap will be generated between the isolation cloth and the sample. The originally compacted sample may become somewhat loose, which has a certain impact on the sample. Summary of the Invention

[0005] To address the aforementioned problems, this invention provides a triaxial confining pressure chamber for coarse-grained soil. It employs an inner and outer double-layer heat-shrinkable film and a silicone film isolation layer, which not only easily maintains the shape of the sample but also improves its resistance to confining pressure. Simultaneously, it utilizes two devices for measuring deformation, enabling accurate measurement of the axial deformation of the sample.

[0006] The present invention proposes a large triaxial confining chamber for coarse-grained soil, comprising a confining chamber cylindrical component, a sample mounting assembly, and an auxiliary support base; wherein, the sample mounting assembly is a cylindrical structure with three layers of membrane, and the sample is placed inside the sample mounting assembly; the confining chamber cylindrical component is fixed to the periphery of the sample mounting assembly and together with the sample mounting assembly is fixed to the auxiliary support base, and together with the sample mounting assembly, the axial deformation generated by the sample is measured.

[0007] Furthermore, the confining pressure chamber cylinder components include a shut-off valve, a confining pressure container top cover, a cap, a pressure rod plate, a pull-wire optical encoder, the confining pressure chamber body, a bottom flange, a guide ring, a dustproof ring, and a piston rod seal; wherein: the confining pressure container top cover and the bottom flange are respectively fixed to the top and bottom ends of the confining pressure chamber body; the confining pressure container top cover is a hollow cylindrical structure used to install the pressure rod plate that matches the confining pressure container top cover, and a dustproof ring and a piston rod seal are used to seal the contact point between the confining pressure container top cover and the pressure rod plate; the guide ring is installed in a groove in the confining pressure container top cover, allowing the pressure rod plate to move axially along the inside of the confining pressure container top cover; the cap is fixed to the pressure rod plate with screws; one end of the pull-wire optical encoder is fixed to the cap, and the other end is fixed to the confining pressure chamber body; the shut-off valve is installed on the confining pressure container top cover.

[0008] Furthermore, one end of the pull wire in the pull wire encoder is fixed to the cap by a mounting bracket, and the other end of the pull wire is fixed inside the pull wire encoder.

[0009] Furthermore, the sample mounting assembly includes a magnetostrictive sensor, a position magnet, a magnetic ring mounting plate, a connecting block, a ball head seat, a ball head pressure plate, a locking collar, a water pipe, an isolation layer, a lower end cap, an upper pore water pressure plate, and a lower pore water pressure plate; wherein: the lower pore water pressure plate is fixed to the lower end cap; the isolation layer, from the inside out, consists of an inner heat-shrinkable sheath film, a silicone film, and an outer heat-shrinkable sheath film, and the isolation layer is fixed to the lower pore water pressure plate by the locking collar; the sample is located within the isolation layer, and the sample is mounted on the lower pore water pressure plate. A pore water pressure plate is placed above the sample. The upper pore water pressure plate is used to press the sample tightly using a ball head seat and a ball head pressure plate. A locking collar is used to fix the ball head pressure plate to the outer surface of the isolation layer, and an annealed copper strip is used to fix it to the joint of the locking collar to prevent leakage at the joint. One end of the water pipe is fixed to the water inlet of the ball head pressure plate, and the other end is fixed to the water inlet of the lower end cover. The magnetostrictive sensor is fixed on the lower end cover, and the position magnet is fixed to the ball head pressure plate through a magnetic ring mounting plate and a connecting block.

[0010] Furthermore, the lower end cover is equipped with an inlet and an outlet. The inlet is connected to the interior of the isolation layer, and the outlet is connected to the water pipe, so that the external water supply device enters the interior of the isolation layer through the inlet and then flows out through the outlet via the water pipe.

[0011] Furthermore, the surface of the magnetostrictive sensor is provided with external threads, which mate with the threaded holes in the lower end cover, allowing the measuring rod of the magnetostrictive sensor to pass through the lower end cover and fix the magnetostrictive sensor to the bottom of the lower end cover; the position magnet is fixed to the magnetic ring mounting plate by screws, and the measuring rod is inserted into the hole inside the position magnet; the magnetic ring mounting plate is fixed to the ball head seat by connecting blocks.

[0012] Furthermore, the auxiliary support base includes a bottom support frame, a confining pressure chamber support frame, and an oil receiving box; wherein, the oil receiving box is fixed on the bottom support frame, and the confining pressure chamber support frame is fixed in the oil receiving box.

[0013] Furthermore, the lower end cover is fixed to the confining pressure chamber support frame, and the bottom flange is fixed to the outer periphery of the lower end cover by screws, so that the confining pressure chamber cylinder component is fixed to the outer periphery of the sample mounting assembly, and the confining pressure chamber cylinder component and the sample mounting assembly are fixed to the auxiliary support base.

[0014] The present invention provides a large triaxial confining chamber for coarse-grained soil and proposes a corresponding method for sample preparation and installation. The method involves loading the sample into the large triaxial confining chamber for coarse-grained soil provided by the present invention, specifically including the following steps:

[0015] S1. Fix the lower end cap to the confining pressure chamber support frame and fix the lower pore water pressure plate to the lower end cap. Place the heat shrink tubing blow molding die on the lower pore water pressure plate. Place the inner sheath heat shrink film on the base of the heat shrink tubing blow molding die and the lower end cap. Use a hot air gun to evenly heat the inner sheath heat shrink film from bottom to top, so that the inner sheath heat shrink film is tightly shrunken on the outer surface of the heat shrink tubing blow molding die. Place the silicone film on the outside of the inner sheath heat shrink film, and then use a hot air gun to evenly heat the outer sheath heat shrink film from bottom to top. After the outer sheath heat shrink film is heated and shaped, an isolation layer is obtained. Use a locking collar to fix the isolation layer to the lower pore water pressure plate, and use annealed copper strip to seal the seam.

[0016] S2. Take out the heat shrink tubing blow molding die, place the sample inside the isolation layer, and tamp it with a tamping hammer until the required sample height is reached, and flatten the upper surface.

[0017] S3. Place the upper pore water pressure plate on the sample, install the ball head seat, fix the confining pressure chamber to the outer surface of the lower boss of the ball head seat with the locking collar, and seal the joint with annealed copper strip.

[0018] S4. Connect the sprue on the lower end cap and the sprue on the ball head seat with a spiral water pipe through a threaded connector to complete the installation of the sample mounting assembly.

[0019] S5. Lift the confining pressure chamber cylinder component and place it around the outside of the sample mounting assembly. Use screws to fasten the bottom flange to the lower end cover. The sample loading is now complete.

[0020] Compared with the prior art, the present invention can achieve the following beneficial effects:

[0021] (1) The isolation layer of double-layer heat shrink film and silicone film is used, which not only makes it easy to maintain the shape of the sample, but also improves the resistance to confining pressure.

[0022] (2) The three-layer isolation layer has a simple assembly process and ensures the sealing of the confining chamber cylinder components;

[0023] (3) Two devices for measuring deformation are used to accurately measure the axial deformation of the sample;

[0024] (4) The sample will not be affected by the isolation layer when it is under confining pressure, and no gap will be generated between the isolation layer and the sample after the confining pressure chamber cylinder component is lifted. Attached Figure Description

[0025] Figure 1 This is an overall structural diagram of a large triaxial confining chamber for coarse-grained soil provided according to an embodiment of the present invention;

[0026] Figure 2 This is an overall sectional view of a large triaxial confining chamber for coarse-grained soil provided according to an embodiment of the present invention;

[0027] Figure 3 This is a structural diagram of the confining pressure chamber cylinder component provided in an embodiment of the present invention;

[0028] Figure 4 This is a cross-sectional view of the confining pressure chamber cylinder component provided according to an embodiment of the present invention;

[0029] Figure 5 This is a structural diagram of the sample mounting assembly provided according to an embodiment of the present invention;

[0030] Figure 6 This is a cross-sectional view of the sample mounting assembly provided according to an embodiment of the present invention;

[0031] Figure 7 This is a side view of the sample mounting assembly provided according to an embodiment of the present invention;

[0032] Figure 8 This is a structural diagram of the auxiliary support base provided according to an embodiment of the present invention;

[0033] Figure 9 This is a front view of the auxiliary support base provided according to an embodiment of the present invention;

[0034] Figure 10 This is a flowchart of the sample preparation and installation method provided in the embodiments of the present invention;

[0035] Figure 11 This is a schematic diagram of an electronic scale measuring volume deformation according to an embodiment of the present invention.

[0036] Figure reference numerals: 1. Confining pressure chamber cylinder component; 1.1. Shut-off valve; 1.2. Confining pressure container top cover; 1.3. Cap; 1.4. Pressure rod plate; 1.5. Pull-wire optical encoder; 1.51. Mounting bracket; 1.52. Pull wire; 1.6. Confining pressure chamber body; 1.7. Bottom flange; 1.8. Guide ring; 1.9. Dustproof ring; 1.10. Piston rod seal; 2. Sample mounting assembly; 2.1. Magnetostrictive sensor; 2.2. Position magnet; 2.3. Magnetic ring mounting plate; 2.4. Connecting block; 2.5. Ball head seat; 2.6. Ball head pressure plate; 2.7. Locking collar; 2.8. Water pipe; 2.9. Isolation layer; 2.10. Lower end cover; 2.11. Upper pore water pressure plate; 2.12. Lower pore water pressure plate; 3. Auxiliary support seat; 3.1. Bottom support frame; 3.2. Confining pressure chamber support frame; 3.3. Oil receiving box; 4. Water pressure device; 5. Water pressure switch; 6. Measuring cup; 7. Electronic scale. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and do not constitute a limitation thereof.

[0038] This invention provides a triaxial confining chamber for coarse-grained soil, which uses an inner and outer double-layer heat-shrinkable film plus a silicone film isolation layer, which not only easily maintains the shape of the sample but also improves the resistance to confining pressure; at the same time, it uses two devices to measure deformation, which can accurately measure the axial deformation of the sample.

[0039] Figure 1 and Figure 2 The overall structure and cross-sectional structure of the large triaxial confining chamber for coarse-grained soil provided according to an embodiment of the present invention are shown respectively.

[0040] like Figure 1 and Figure 2 As shown, the large triaxial confining chamber for coarse-grained soil provided in this embodiment of the invention includes a confining chamber cylinder component 1, a sample mounting assembly 2, and an auxiliary support base 3.

[0041] The confining pressure chamber cylinder component 1 is fixed to the periphery of the sample mounting assembly 2, and the sample is placed inside the sample mounting assembly 2; the confining pressure chamber cylinder component 1 and the sample mounting assembly 2 are fixed on the auxiliary support base 3.

[0042] Figure 3 and Figure 4 The structure and cross-sectional view of the confining chamber cylinder component provided according to an embodiment of the present invention are shown respectively.

[0043] like Figure 3 and Figure 4As shown, the confining pressure chamber cylinder component 1 provided in this embodiment of the invention includes a shut-off valve 1.1, a confining pressure container cover 1.2, a cap 1.3, a pressure rod plate 1.4, a pull-wire optical encoder 1.5, a confining pressure chamber body 1.6, a bottom flange 1.7, a guide ring 1.8, a dustproof ring 1.9, and a piston rod seal 1.10.

[0044] The confining container cover 1.2 and bottom flange 1.7 are fixed to the top and bottom of the confining chamber body 1.6, respectively. The confining container cover 1.2 is a hollow cylindrical structure used to house the pressure rod plate 1.4, which is matched with the confining container cover 1.2. A dustproof ring 1.9 and a piston rod seal 1.10 are used to seal the contact between the confining container cover 1.2 and the pressure rod plate 1.4. A guide ring 1.8 is installed in a groove in the confining container cover 1.2, allowing the pressure rod plate 1.4 to move axially within the confining container cover 1.2. A cap 1.3 is fixed to the pressure rod plate 1.4 with screws.

[0045] like Figure 3 As shown, one end of the pull wire 1.52 in the pull wire encoder 1.5 is fixed to the cap by the mounting bracket 1.51, and the other end of the pull wire 1.52 is fixed inside the pull wire encoder 1.5.

[0046] When the medium is filled with confining pressure, the shut-off valve 1.1 is opened to discharge the internal gas. After the internal gas is discharged, the shut-off valve 1.1 is closed. Only then can confining pressure be applied to the inside of the confining pressure chamber cylinder component 1.

[0047] Figure 5 , Figure 6 and Figure 7 The structure, cross-sectional structure and side view of the sample mounting assembly provided according to an embodiment of the present invention are shown respectively.

[0048] like Figure 5 and Figure 6 As shown, the sample mounting assembly provided in this embodiment of the invention includes a magnetostrictive sensor 2.1, a position magnet 2.2, a magnetic ring mounting plate 2.3, a connecting block 2.4, a ball head seat 2.5, a ball head pressure plate 2.6, a locking collar 2.7, a water pipe 2.8, an isolation layer 2.9, a lower end cover 2.10, an upper pore water pressure plate 2.11, and a lower pore water pressure plate 2.12.

[0049] The lower pore water pressure plate 2.12 is fixed to the lower end cap 2.10. The isolation layer 2.9 consists of an inner heat-shrinkable film, a silicone film, and an outer heat-shrinkable film from the inside out. The isolation layer 2.9 is fixed to the lower pore water pressure plate 2.12 by a locking collar 2.7, and annealed copper strip is used at the joint of the locking collar 2.7 to prevent leakage. The sample is located inside the isolation layer 2.9, and the upper pore water pressure plate 2.11 is placed above the sample. The upper pore water pressure plate 2.11 is used to press the sample tightly using the ball head seat 2.5 and the ball head pressure plate 2.6, and the ball head pressure plate 2.6 is fixed to the outer surface of the isolation layer 2.9 using the locking collar 2.7. One end of the water pipe 2.8 is fixed to the outlet of the ball head pressure plate 2.6, and the other end is fixed to the inlet of the lower end cap 2.10.

[0050] like Figure 6 As shown, the lower end cover 2.10 has an inlet and an outlet. The inlet is connected to the isolation layer 2.9, and the outlet is connected to the water pipe 2.8, so that the external water supply device supplies water to the isolation layer 2.9 through the inlet and then discharges water from the outlet through the water pipe 2.8.

[0051] like Figure 7 As shown, the surface of the magnetostrictive sensor 2.1 is provided with external threads, which cooperate with the threaded hole opened in the lower end cover 2.10, so that the measuring rod of the magnetostrictive sensor 2.1 passes through the lower end cover 2.10 and fixes the magnetostrictive sensor 2.1 to the bottom of the lower end cover 2.10; the position magnet 2.2 is fixed to the magnetic ring mounting plate 2.3 by screws, and the measuring rod is inserted into the hole inside the position magnet 2.2; the magnetic ring mounting plate 2.3 is fixed to the ball head seat 2.5 by the connecting block 2.4.

[0052] Figure 8 and Figure 9 The structure and front view of the auxiliary support provided according to an embodiment of the present invention are shown respectively.

[0053] like Figure 8 and Figure 9 As shown, the auxiliary support 3 includes a bottom support frame 3.1, a confining pressure chamber support frame 3.2, and an oil receiving box 3.3.

[0054] The oil receiving box 3.3 is fixed on the bottom support frame 3.1, and the confining pressure chamber support frame 3.2 is fixed in the oil receiving box 3.3.

[0055] During the overall installation, the lower end cover 2.10 is fixed on the confining pressure chamber support frame 3.2, and the bottom flange 1.7 is fixed to the periphery of the lower end cover 2.10 with screws, so that the confining pressure chamber cylinder component 1 is fixed to the periphery of the sample mounting assembly 2, and the confining pressure chamber cylinder component 1 and the sample mounting assembly 2 are fixed on the auxiliary support seat 3.

[0056] Figure 10The steps of the sample preparation and installation method provided according to an embodiment of the present invention are shown.

[0057] like Figure 10 As shown, the sample preparation and installation method corresponding to the triaxial confining chamber for coarse-grained soil provided by this invention specifically includes the following steps:

[0058] S1. Fix the lower end cap 2.10 onto the confining pressure chamber support frame 3.2, and fix the lower pore water pressure plate 2.12 onto the lower end cap 2.10. Place the heat shrink tubing blow molding die onto the lower pore water pressure plate 2.12. Place the inner sheath heat shrink film onto the base of the heat shrink tubing blow molding die and the lower end cap 2.10. Use a hot air gun to evenly heat the inner sheath heat shrink film from bottom to top, so that the inner sheath heat shrink film is tightly shrunken onto the outer surface of the heat shrink tubing blow molding die. Place the silicone film onto the outside of the inner sheath heat shrink film, and then use a hot air gun to evenly heat the outer sheath heat shrink film from bottom to top. After the outer sheath heat shrink film is heated and shaped, the isolation layer 2.9 is obtained. Use the locking collar 2.7 to fix the isolation layer 2.9 onto the lower pore water pressure plate 2.12, and use annealed copper strip to seal the joint.

[0059] S2. Take out the heat shrink tubing blow molding die, place the sample in the isolation layer 2.9, and tamp it with a tamping hammer until the required sample height is reached, and flatten the upper surface.

[0060] S3. Place the upper pore water pressure plate 2.11 on the sample, install the ball head seat 2.5, fix the confining pressure chamber to the outer surface of the lower boss of the ball head seat 2.5 with the locking collar 2.7, and seal the joint with annealed copper strip.

[0061] S4. Connect the water inlet of the lower end cap 2.10 and the water inlet on the ball head seat 2.5 with a spiral water pipe 2.8 through a threaded connector to complete the installation of the sample installation assembly 2.

[0062] S5. Lift the confining pressure chamber cylinder component 1 and place it around the sample mounting assembly 2. Use screws to fasten the bottom flange 1.7 to the lower end cover 2.10. The sample loading is now complete.

[0063] According to the triaxial confining chamber for coarse-grained soil provided in the embodiments of the present invention, three methods for measuring deformation are obtained:

[0064] Measurement Method 1: Measurement of Axial Deformation using a Wire-Drawn Optical Encoder

[0065] In the confining chamber cylinder component 1, the cap 1.3 moves downward along with the pressure plate rod, which in turn causes the mounting bracket 1.52 to move downward together. The pull wire 1.51 is retracted under the action of the coil spring in the pull wire optical encoder 1.5, thereby causing the optical encoder disk in the pull wire optical encoder 1.5 to rotate, emitting an electrical pulse signal, which is converted into a displacement signal, thereby measuring the axial deformation of the sample.

[0066] Measurement Method 2: Magnetic Measurement of Axial Deformation

[0067] In the sample mounting assembly 2, the ball head seat 2.5 drives the magnetic ring mounting plate 2.3 to move downward, causing the connecting block 2.4 and the position magnet 2.2 to move downward together; when the relative positions of the position magnet 2.2 and the measuring rod change, the magnetostrictive sensor 2.1 will generate an electrical signal, which will then be converted into a displacement signal to measure the axial deformation of the sample.

[0068] Measurement Method 3: Measure volume deformation using an electronic scale.

[0069] Figure 11 A schematic diagram of an electronic scale measuring volume deformation according to an embodiment of the present invention is shown.

[0070] like Figure 11 As shown, before conducting the test, turn on the water pressure switch 5 and the water pressure device 4 adds water to the sample inside the isolation layer 2.9. When water flows out from the outlet of the lower end cover 2.10, it indicates that the sample is saturated with water. At this time, turn off the water pressure switch 5.

[0071] After the test begins, under the action of axial pressure and confining pressure, the volume of the sample will change, and the water inside the sample will be squeezed out and enter the measuring cup 6. The electronic scale 7 weighs the mass of the water in the measuring cup 6 and sends the mass of the water to the external device. Based on the change in weight, the volume change of the water will be calculated, thereby calculating the volumetric strain of the sample.

[0072] It should be understood that the various forms of processes shown above can be used to reorder, add, or delete steps. For example, the steps described in this invention disclosure can be executed in parallel, sequentially, or in different orders, as long as the desired result of the technical solution disclosed in this invention can be achieved, and this is not limited herein.

[0073] The specific embodiments described above do not constitute a limitation on the scope of protection of this invention. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A large triaxial confining chamber for coarse-grained soil, characterized in that, The system includes a confining pressure chamber cylindrical component, a sample mounting assembly, and an auxiliary support base. The sample mounting assembly is a three-layer membrane cylindrical structure. The sample is placed inside the sample mounting assembly, and the axial deformation of the sample is measured. The confining pressure chamber cylindrical component is fixed to the periphery of the sample mounting assembly, and also measures the axial deformation. The sample mounting assembly and the confining pressure chamber cylindrical component are jointly fixed to the auxiliary support base. The confining pressure chamber cylindrical component includes a shut-off valve, a top cover of the confining pressure container, a cap, a pressure rod plate, a pull-wire optical encoder, the confining pressure chamber body, a bottom flange, a guide ring, a dust seal, and a piston rod seal; wherein: The top cover of the confining pressure container and the bottom flange are respectively fixed to the top and bottom of the confining pressure chamber. The pressure vessel cover is a hollow cylindrical structure used to install a pressure rod plate that matches the pressure vessel cover. The contact point between the pressure vessel cover and the pressure rod plate is sealed using the dustproof ring and the piston rod seal. The guide ring is installed in the groove of the pressure vessel cover, allowing the pressure rod plate to move axially along the inside of the pressure vessel cover. The cap is fixed to the pressure plate with screws; one end of the pull-wire optical encoder is fixed to the cap, and the other end is fixed to the confining pressure chamber. The shut-off valve is installed on the top cover of the confining pressure container; The sample mounting assembly includes a magnetostrictive sensor, a position magnet, a magnetic ring mounting plate, a connecting block, a ball head seat, a ball head pressure plate, a locking collar, a water pipe, an isolation layer, a lower end cover, an upper pore water pressure plate, and a lower pore water pressure plate; wherein: The lower pore water pressure plate is fixed on the lower end cover; The isolation layer consists of an inner heat-shrinkable sheath film, a silicone film, and an outer heat-shrinkable sheath film from the inside out, and the isolation layer is fixed to the lower pore water pressure plate by the locking collar. The sample is located inside the isolation layer, and the upper pore water pressure plate is placed above the sample. The upper pore water pressure plate is pressed against the sample by the ball head seat and the ball head pressure plate. The ball head pressure plate is fixed on the outer surface of the isolation layer by the locking collar, and the joint of the locking collar is fixed by annealed copper strip to prevent leakage at the joint. One end of the water pipe is fixed at the water inlet of the ball head pressure plate, and the other end is fixed at the water inlet of the lower end cover; The magnetostrictive sensor is fixed on the lower end cover, and the position magnet is fixed on the ball head pressure plate by the magnetic ring mounting plate and the connecting block. The surface of the magnetostrictive sensor is provided with external threads, which cooperate with the threaded hole in the lower end cover, so that the measuring rod of the magnetostrictive sensor passes through the lower end cover and the magnetostrictive sensor is fixed to the bottom of the lower end cover; the position magnet is fixed to the magnetic ring mounting plate by screws, and the measuring rod is inserted into the hole inside the position magnet; the magnetic ring mounting plate is fixed to the ball head seat by the connecting block; The auxiliary support base includes a bottom support frame, a confining pressure chamber support frame, and an oil receiving box; wherein the oil receiving box is fixed on the bottom support frame, and the confining pressure chamber support frame is fixed in the oil receiving box.

2. The large triaxial confining chamber for coarse-grained soil according to claim 1, characterized in that, One end of the pull wire in the pull wire optical coder is fixed to the cap by a mounting bracket, and the other end of the pull wire is fixed inside the pull wire optical coder.

3. The large triaxial confining chamber for coarse-grained soil according to claim 1, characterized in that, The lower end cover is provided with an inlet and an outlet. The inlet is connected to the interior of the isolation layer, and the outlet is connected to the water pipe, so that the external water supply device enters the interior of the isolation layer through the inlet and then flows out through the outlet via the water pipe.

4. The large triaxial confining chamber for coarse-grained soil according to claim 1, characterized in that, The lower end cover is fixed on the confining pressure chamber support frame, and the bottom flange is fixed to the periphery of the lower end cover by screws, so that the confining pressure chamber cylinder component is fixed to the periphery of the sample mounting assembly, and the confining pressure chamber cylinder component and the sample mounting assembly are fixed on the auxiliary support base.

5. A method for sample preparation and installation, characterized in that, Loading the sample into the large triaxial confining chamber for coarse-grained soil as described in claim 1 specifically includes the following steps: S1. Fix the lower end cap to the support frame of the confining chamber and fix the lower pore water pressure plate to the lower end cap. Place the heat shrink tubing blow molding die on the lower pore water pressure plate. Cover the root of the heat shrink tubing blow molding die and the lower end cap with the inner sheath heat shrink film. Use a hot air gun to evenly heat the inner sheath heat shrink film from bottom to top, so that the inner sheath heat shrink film is tightly shrunken on the outer surface of the heat shrink tubing blow molding die. Cover the outer side of the inner sheath heat shrink film with a silicone film, and then use the hot air gun to evenly heat the outer sheath heat shrink film from bottom to top. After the outer sheath heat shrink film is heated and shaped, the isolation layer is obtained. Use the locking collar to fix the isolation layer to the lower pore water pressure plate, and use the annealed copper strip to seal the joint. S2. Take out the heat shrink tubing blow molding die, place the sample inside the isolation layer, and tamp it with a tamping hammer until the required sample height is reached, and flatten the upper surface. S3. Place the upper pore water pressure plate on the sample, install the ball head seat, fix the confining pressure chamber on the outer surface of the lower boss of the ball head seat with the locking collar, and seal the joint with the annealed copper strip. S4. Connect the water inlet of the lower end cap and the water inlet on the ball head seat with a spiral water pipe through a threaded connector to complete the installation of the sample mounting assembly. S5. Lift the confining pressure chamber cylinder component and place it around the sample mounting assembly. Use screws to fasten the bottom flange to the lower end cover. At this point, the sample loading is complete.

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