A static compaction type coarse aggregate triaxial test specimen preparation device and its usage method

Abstract

The present invention discloses a static compaction type triaxial test specimen preparation device and a usage method thereof. The specimen preparation device includes a specimen preparation cylinder, a sealing device and a support frame. The specimen preparation cylinder is composed of two split molds spliced together. The specimen preparation device is provided with a static compaction device for compacting the soil sample in the specimen preparation cylinder. The static compaction device includes a compaction bottom plate and a compaction rod formed by connecting a plurality of compaction rod sections. The top end of the compaction rod is connected to an axial loading device on the axial loading platform of the triaxial testing machine; the support frame includes several vertical support rods arranged around the specimen preparation cylinder, and a transverse support rod for supporting the compaction rod is hinged to the upper part of each vertical support rod. A displacement sensor support platform is also provided on the support frame. The present invention uses a compaction method to prepare specimens. By using the triaxial test specimen preparation device and the axial loading platform of the triaxial testing machine, the particle breakage of the specimen during the specimen preparation process can be minimized to the greatest extent, ensuring the uniformity of the specimen and the accuracy of the volume change measurement.

Description

Technical Field

[0001] The present invention relates to the technical field of geotechnical engineering tests, and particularly to a static compaction type triaxial test sample preparation device for coarse-grained materials and a usage method thereof. Background Art

[0002] Coarse-grained materials such as graded crushed stones used for subgrade filling are granular materials filled with each other by particles of different particle sizes. Most of the internal particles are in point contact, and particle breakage is likely to occur under external loads, which has a significant impact on their engineering properties. At present, indoor geotechnical triaxial tests are the main method for studying the particle breakage characteristics of coarse-grained materials. The degree of particle breakage of coarse-grained materials can be obtained by measuring the particle gradation of the test sample before and after the test.

[0003] Indoor triaxial test samples are made by controlling the sample density, using the method of layered batching, layered filling, and layered compaction. The compaction method generally uses the heavy hammer compaction method. This method has a large disturbance to the structure of coarse-grained materials, is likely to cause particle breakage, and multiple parallel samples made by the same sample preparation method often show different degrees of breakage, thus affecting the analysis results of the particle breakage characteristics of coarse-grained materials. At the same time, when using layered sample loading, the compaction height of each layer of the sample is generally measured by visual inspection or using a steel ruler, but this measurement is not accurate enough and it is difficult to control the uniformity of the sample density. In addition, in order to improve the accuracy of volume change measurement as much as possible, it is necessary to control the good sealing of the sample. During the test, a rubber band is generally used to tie the outside of the latex film at both ends of the sample to prevent high-pressure water from seeping into the latex film. However, during the test, due to the change in the height and volume of the sample, the rubber band will be stretched. When stretched to a certain extent, it will cause loose bundling and water seepage, and ultimately affect the volume change measurement results. Chinese patent document with publication date of March 16, 2021 and publication number of CN 212722292U discloses a soil triaxial test sample compaction device, including a forming cylinder, a limiting mechanism, and a striking mechanism. The limiting mechanism includes a limiting ring fixed above the forming cylinder; the striking mechanism includes a hammer and a hammer rod. The hammer rod movably penetrates the limiting ring, and a limiting component is provided between the hammer rod and the limiting ring. The limiting component is used to allow the hammer rod to move downward. Pass the hammer rod of the striking mechanism through the limiting ring and strike the top of the hammer rod. The hammer rod moves downward so that the hammer can compact the soil sample. Due to the limitation of the limiting component, the striking mechanism that receives the reaction force of the soil sample will not rebound upward, greatly reducing the possibility of a gap appearing between the striking mechanism and the soil sample, ensuring that the internal structure of the sample is denser and facilitating the subsequent test. This soil triaxial test sample compaction device uses the heavy hammer compaction method, which has a large disturbance to the structure of coarse-grained materials, is likely to cause particle breakage, and multiple parallel samples made by the same sample preparation method often show different degrees of breakage, thus affecting the analysis results of the particle breakage characteristics of coarse-grained materials. Summary of the Invention

[0004] The object of the present invention is to solve the problems existing in the specimen preparation method by using a heavy hammer compaction method in the existing geotechnical triaxial test, and to provide a static compaction type triaxial test specimen preparation device for coarse-grained materials and a using method thereof. By using the triaxial test specimen preparation device and the axial loading platform of the triaxial testing machine, specimens are prepared by compaction, so as to achieve the purpose of minimizing particle breakage of the specimens during the specimen preparation process to the greatest extent, ensuring the uniformity of the specimens and the accuracy of volume change measurement.

[0005] The technical solution adopted by the present invention to solve the above technical problems is a static compaction type triaxial test specimen preparation device for coarse-grained materials, which is arranged on the axial loading platform of the triaxial testing machine, and includes a base and a specimen preparation cylinder, a sealing device and a support frame arranged on the base. The specimen preparation cylinder is composed of two split dies. The specimen preparation cylinder includes a cylinder body and an annular platform horizontally arranged at the bottom of the cylinder body. A static compaction device for pressing the soil sample in the specimen preparation cylinder is provided on the specimen preparation device. The static compaction device includes a compaction bottom plate and a compaction rod connected to the compaction bottom plate. The diameter of the compaction bottom plate is adapted to the inner diameter of the specimen preparation cylinder. The compaction rod is composed of a plurality of compaction rod sections with equal diameters. The top end of the compaction rod is connected to the axial loading device on the axial loading platform of the triaxial testing machine. The base includes an upper convex platform with an outer diameter adapted to the inner diameter of the specimen preparation cylinder and a lower convex platform for fixing the support frame. The support frame includes a plurality of vertical support rods arranged around the specimen preparation cylinder. A horizontal support rod for supporting the compaction rod is hinged to the upper part of each vertical support rod. A displacement sensor support platform corresponding to the axial displacement sensor on the axial loading platform of the triaxial testing machine is also provided on the support frame.

[0006] The sample preparation tube of the present invention is composed of two split molds. A horizontal semi-annular platform is added to the bottom end of each split mold to ensure that the sample preparation tube is in an upright state when placed. The static compaction device includes a compaction base plate and a compaction rod connected to the compaction base plate. The compaction rod is composed of a plurality of compaction rod sections of equal diameter. The length can be adjusted according to the soil sample in the sample tube to ensure the compaction of the layered soil sample. It is easy to assemble and disassemble. Combined with the axial loading system, it can achieve precise control of the layer height, control the total density of the coarse aggregate, and ensure uniform sample preparation. The support frame is mainly used to support the compaction rod, ensure that the compaction rod is vertical and the compaction base plate is horizontal, and prevent the compaction rod of the multi-section structure from shifting in the horizontal direction; the axial loading platform of the triaxial testing machine is used to statically compact the soil sample in the sample tube, and the axial displacement sensor detects the axial displacement. The rise, fall and axial displacement of the axial loading device can be controlled and displayed by the axial loading platform of the triaxial testing machine. Thus, the present invention fully utilizes the axial loading platform of the triaxial testing machine to achieve static compaction of triaxial specimens of coarse aggregate, thereby evenly applying force to the coarse aggregate, causing minimal structural disturbance to the coarse aggregate, and significantly reducing particle breakage during the sample preparation process. This is highly beneficial for experimental research on coarse aggregate particle breakage. The present invention solves the problem that prior art geotechnical triaxial testing sampling devices employ a heavy hammer compaction method, which significantly disturbs the structure of the coarse aggregate and easily causes particle breakage, and that multiple sets of parallel specimens prepared using the same sample preparation method often exhibit different degrees of breakage, thereby affecting the analytical results of the coarse aggregate particle breakage characteristics.

[0007] Preferably, the sealing device includes a latex film arranged on the inner wall of the sample preparation tube, the height of the latex film being greater than the height of the sample preparation tube, and an air extraction hole being provided on the side wall of the sample preparation tube, the outer side of the air extraction hole being connected to a rubber suction ball, and the air extraction hole being in a mesh structure. The latex film, which is greater in height than the sample preparation tube, is used to cover the sample, thereby resolving the sealing problem of the sample and improving the accuracy of volume change measurement and the success rate of the test; the air extraction hole is used in conjunction with the rubber suction ball to remove air between the sample preparation tube and the latex film, ensuring that the latex film is tightly attached to the sample preparation tube; the air extraction hole is in a mesh-like form on the air-facing surface to prevent sharp particles from piercing the latex film.

[0008] Preferably, the sealing device further comprises a cover plate adapted to the inner diameter of the sample preparation cylinder. The cover plate and the upper boss of the base are both provided with an annular groove. An elastic rubber ring is provided on the periphery of the latex membrane at the annular groove for securing the latex membrane. A sealing band is provided on the outer side of the elastic rubber ring, and a buckle is provided on the sealing band for locking the sealing band. The annular grooves on the cover plate and the upper boss cooperate with the elastic rubber ring to seal the sample, and the sealing band provides the final fixation, thereby resolving the sealing problem of the sample.

[0009] Preferably, the middle section of the compaction rod has a threaded hole at the upper end of its main body and a protruding bolt at the lower end of its main body. The protruding bolt is adapted to the threaded hole. The length of the main body of the middle section of the compaction rod is the same as the height of the layered soil sample. The top section of the compaction rod at the uppermost end is provided with a rubber joint, and the bottom section of the compaction rod at the lowermost end is fixed to the compaction bottom plate. The length of the main body of the compaction rod section is the same as the height of the layered soil sample, which is convenient for layered sample filling and compaction. The screw connection between the compaction rod sections is convenient for assembly and disassembly.

[0010] Preferably, the support frame includes an annular bottom plate connected to the base. The inner diameter of the annular bottom plate is adapted to the outer diameter of the annular platform at the bottom end of the sample preparation cylinder. The vertical support rods of the support frame are fixed to the annular bottom plate. There is a support rod connection head at the connection of the vertical support rod and the horizontal support rod. The horizontal support rod is pivotally connected upwardly to the support rod connection head. A cross-bar fixing bayonet for fixing the horizontal support rod is sleeved on the top end of the vertical support rod. An arc-shaped flap die is provided at the suspended end of the horizontal support rod. When the horizontal support rods are in a horizontal support state, the arc-shaped flap dies on all the horizontal support rods form a cylinder with an inner diameter adapted to the outer diameter of the compaction rod. The cylinder formed by the arc-shaped flap dies on the horizontal support rods is used to limit the horizontal movement of the compaction rod and ensure that the compaction rod is perpendicular to the compaction bottom plate.

[0011] Preferably, a connecting rod is horizontally provided on the support rod connection head. One end of the horizontal support rod is pivotally connected to the support rod connection head through the connecting rod. A horizontal rod for limiting the downward rotation of the horizontal support rod is provided at the bottom of the support rod connection head on the side away from the vertical support rod. When the horizontal support rod rotates around the connecting rod and abuts against the horizontal rod, the horizontal support rod is in a horizontal state; when the horizontal support rod rotates upward to a vertical state, the horizontal support rod is buckled with the arc-shaped bayonet on the cross-bar fixing bayonet. When the horizontal support rod is in a horizontal state, it can limit the horizontal movement of the compaction rod and ensure that the compaction rod is perpendicular to the compaction bottom plate, which is suitable for the static compaction mode used; and when the horizontal support rod is in a vertical state, there is no obstruction above the sample cylinder, so the traditional impact compaction mode can also be adopted, serving two purposes with one object.

[0012] Preferably, there are 3 - 4 vertical support rods. The displacement sensor support platform is arranged at the top of one of the vertical support rods. The displacement sensor support platform includes a vertically arranged rotating shaft and a horizontal plate arranged on the rotating shaft. A rotating shaft hole is provided at the top end of the vertical support rod. The rotating shaft is rotatably connected to the vertical support rod. The displacement sensor support platform of the present invention can rotate around the circumference and cannot move up and down, which is convenient for docking with the axial displacement sensor while ensuring the detection accuracy.

[0013] Preferably, the loading platform of the triaxial testing machine comprises a control panel, a bottom platform and columns fixed to both sides of the bottom platform. A cross beam is provided at the top of the columns. The axial loading device is arranged below the cross beam, and the lower end of the axial loading device is connected to the axial displacement sensor.

[0014] Preferably, the splicing joints of the cylinders on the two split dies are both provided with mutually adapted concave-convex interfaces. An elastic gasket is provided between the butting surfaces of the concave-convex interfaces. A collar for fastening the split dies of the sample preparation cylinder is provided on the outer circumference of the sample preparation cylinder. The collar is used to splice and fix the cylinders on the two split dies; and an elastic gasket is arranged between the butting surfaces of the split dies, so that the split dies can be tightly closed under the action of the collar.

[0015] The using method of the static compaction type coarse-grained soil triaxial test sample preparation device comprises the following steps:

[0016] a. Place the permeable stone and the filter paper on the upper convex platform of the base in sequence, put a latex film on the outer wall of the upper convex platform, tie the latex film tightly at the annular groove of the upper convex platform with an elastic rubber ring, splice the two split dies and install them on the upper convex platform of the base, and use a collar to sleevethe outer circumference of the sample preparation cylinder to fix the two split dies into one body. Turn the latex film protruding above the sample preparation cylinder outwards to the outer wall of the sample preparation cylinder. Use a rubber suction balloon to pump out the air between the latex film and the sample preparation cylinder through the air extraction hole, and then insert the deflated rubber suction balloon at the outer end of the air extraction hole to make the latex film tightly adhere to the inner wall of the sample preparation cylinder.

[0017] b. Place the annular bottom plate of the support frame on the lower convex platform of the base and connect it with the base as a whole through connecting bolts. Place the static compaction device in the sample preparation cylinder, where the compaction bottom plate is in close contact with the filter paper. Operate the control panel of the triaxial testing machine to make the rubber joint at the top of the compaction rod contact the bottom end of the axial loading device. Adjust the axial displacement sensor and the displacement sensor support platform so that the end of the axial displacement sensor supports on the displacement sensor support platform. At this time, zero the axial displacement value displayed on the control panel, and then take out the static compaction device.

[0018] c. Rotate the transverse support rod of the support frame upwards and fix it in the cross bar fixing bayonet. Fill the first layer of coarse-grained soil sample prepared in layers into the sample preparation cylinder. Remove a small section of the compaction rod with a main body length equal to the height of the layered soil sample from the compaction rod and reassemble it, and place it in the sample preparation cylinder. Lower the transverse support rod to make it in a horizontal state. The arc-shaped flap die at the suspended end of the transverse support rod forms a cylinder with an inner diameter adapted to the outer diameter of the compaction rod to limit the horizontal movement of the compaction rod. Operate the control panel to make the compaction rod and the compaction bottom plate descend as a whole through the axial loading device of the triaxial testing machine to compact the soil sample, and stop descending when the axial displacement is displayed as 0 again.

[0019] d. Repeat the above steps to load the remaining soil samples in the same way. After each layer of soil samples is loaded, a compaction rod section with a main body length equal to the height of the layered soil sample must be disassembled and reassembled. The compaction standard for each layer of soil samples is to take the axial displacement value as 0 until the last layer of soil samples is loaded, and the support frame and static compaction device are removed.

[0020] e. Place the filter paper, permeable stone and cover plate on the top of the sample in sequence, straighten the latex film outside the sample preparation cylinder upwards, remove the sample preparation cylinder, tie the elastic rubber ring to the outside of the latex mold at the groove of the cover plate, and wrap sealing tape around the outside of the two elastic rubber rings at the top and bottom of the sample respectively, and lock them with buckles. After the sample preparation is completed, the coarse-grained triaxial sample can be used for triaxial compression test.

[0021] The beneficial effects of the present invention are as follows: first, the axial loading platform of the triaxial testing machine is fully utilized to realize the static compaction of the triaxial specimens of coarse aggregate, so that the coarse aggregate can be subjected to uniform force, the structural disturbance to the coarse aggregate is small, and the particle breakage of the coarse aggregate during the sample preparation process is greatly reduced, which is very beneficial to the experimental research on the particle breakage of coarse aggregate. Second, the compaction rod is connected in sections, which is convenient for assembly and disassembly. The control panel combined with the axial loading system can realize precise control of the layer height, control the total density of the coarse aggregate, and prepare the sample uniformly. The 90° rotation of the horizontal support rod of the support frame is convenient for both sample loading and compaction. Third, the elastic rubber ring combined with the sealing tape and the buckle solves the sealing problem of the sample, improves the accuracy of the volume change measurement and the success rate of the test. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 A structural schematic diagram of the present invention together with a loading platform of a triaxial testing machine;

[0023] Figure 2 This is a schematic diagram of a three-dimensional exploded structure of the base, sample preparation cylinder, static compaction device and support frame of the present invention;

[0024] Figure 3 A schematic diagram of the structure of the present invention during static compaction;

[0025] Figure 4 for Figure 3 A top view of

[0026] Figure 5 This is a schematic structural diagram of the present invention when loading soil samples;

[0027] Figure 6 Schematic diagram of the structure and structural decomposition of the static compaction device of the present invention;

[0028] Figure 7 This is a schematic diagram of the structure before the first layer of soil sample is loaded in the present invention;

[0029] Figure 8 It is a schematic structural diagram after filling the last layer of soil sample for the invention;

[0030] Figure 9-1 It is a top view of the support rod connector of the present invention;

[0031] Figure 9-2 It is a front view of the support rod connector of the present invention;

[0032] Figure 10 It is a top view of the crossbar fixing bayonet of the present invention;

[0033] Figure 11 It is a schematic structural diagram of an air extraction hole of the present invention;

[0034] Figure 12 It is a schematic structural diagram of the control panel of the axial loading platform of the triaxial testing machine of the present invention;

[0035] Figure 13 It is a front view of the test sample when the sample preparation is completed;

[0036] Figure 14 It is a top view of the test sample when the sample preparation is completed;

[0037] Figure 15-1 It is a schematic structural diagram of the sealing tape when the buckle of the present invention is locked;

[0038] Figure 15-2 It is a schematic structural diagram of a buckle of the present invention.

[0039] In the figure: 1. Annular bottom plate, 2. Vertical support rod, 3. Horizontal support rod, 4. Support rod connector, 4-a. Connecting rod, 4-b. Horizontal rod, 5. Crossbar fixing bayonet, 5-a. Fixed ring, 5-b. Arc-shaped bayonet, 6. Arc-shaped flap die, 7. Displacement sensor support platform, 8. Lower convex platform, 9. Middle convex platform, 10. Upper convex platform, 11. Connecting bolt, 12. Permeable stone, 13. Latex film, 14. Sample preparation cylinder, 14-a. Split die, 14-b. Concave-convex interface, 15. Annular platform, 16. Sleeve ring, 17. Air extraction hole, 18. Rubber suction balloon, 19. Compaction bottom plate, 20. Compaction rod, 20-a. Rubber joint, 20-b. Protruding bolt, 20-c. Threaded hole, 20-d. Small section of compaction rod, 21. Bottom platform, 22. Column, 23. Axial loading device, 24. Axial displacement sensor, 25. Control panel, 26. Sealing tape, 26-a. Elastic rubber ring, 27. Buckle, 27-a. Buckle ring, 27-b. Tightening cover, 27-c. Connecting shaft, 27-d. Tightening platform, 28. Soil sample, 29. Cover plate. Detailed implementation mode

[0040] The following is a further description of the specific implementation of the technical solution of the present invention through embodiments in combination with the accompanying drawings. Structures or methods not described in detail in the embodiments all adopt the prior art in the technical field of the present invention.

[0041] Embodiment 1

[0042] In Embodiment 1 as shown in Figure 1 Figure 2 , a static compaction type coarse aggregate triaxial test sample preparation device is arranged on the axial loading platform of a triaxial testing machine. The loading platform of the triaxial testing machine includes a control panel Figure 12 25 (see

[0043] ), a bottom platform 21 and columns 22 fixed on both sides of the bottom platform. A cross beam is provided at the top of the columns. An axial loading device 23 is arranged below the cross beam, and an axial displacement sensor 24 is connected to the lower end of the axial loading device. Figure 4 The sample preparation device includes a base and a sample preparation cylinder 14 arranged on the base, a sealing device, and a support frame arranged on the outer periphery of the sample preparation cylinder. The base is a cylindrical boss including upper, middle, and lower layers with different diameters, including an upper boss 10 with an outer diameter adapted to the inner diameter of the sample preparation cylinder and a lower boss 8 for fixing the support frame. A middle boss 9 is provided between the upper boss and the lower boss. The sample preparation cylinder is composed of two split molds 14-a joined together. The sample preparation cylinder includes a cylinder body and an annular platform 15 horizontally arranged at the bottom of the cylinder body. The annular platform is used to ensure the uprightness of the sample preparation cylinder. Convex and concave interfaces 14-b (see

[0044] The sample preparation device is provided with a static compaction device for compressing the soil sample 28 in the sample cylinder. The static compaction device includes a circular compaction bottom plate 19 and a compaction rod 20 connected to the compaction bottom plate. The diameter of the compaction bottom plate is adapted to the inner diameter of the sample cylinder. The compaction rod is composed of multiple compaction rod segments 20-d with the same diameter. In this embodiment, the number of segments of the compaction rod 20 is the number of sample loading layers + 2 layers. In this embodiment, the number of soil sample layers is 5 layers, and the number of segments of the compaction rod is 7 segments. The top of the compaction rod segment at the uppermost end is provided with a rubber joint 20-a. The top end of the compaction rod is connected to the axial loading device 23 on the axial loading platform of the triaxial testing machine. The compaction rod segment at the lowermost end is fixed to the compaction bottom plate. The main body of the compaction rod segment in the middle of the compaction rod is provided with a threaded hole 20-c at the upper end and a protruding bolt 20-b at the lower end. The protruding bolt and the threaded hole are adapted to each other. All the compaction rod segments are connected by threads. Except for the compaction rod segment at the uppermost end and the compaction rod segment at the lowermost end, the main body lengths of the other 5 compaction rod segments in the middle of the compaction rod are the same as the height of the layered soil sample (see Figure 6 ).

[0045] The support frame includes 3 vertical support rods 2 arranged around the sample cylinder. Each upper part of the vertical support rod is hinged with a horizontal support rod 3 for supporting the compaction rod. The support frame is also provided with a displacement sensor support platform 7 corresponding to the axial displacement sensor 24 on the axial loading platform of the triaxial testing machine (see Figure 3 ). The displacement sensor support platform is arranged at the top of one of the vertical support rods. The displacement sensor support platform includes a vertically arranged rotating shaft and a horizontal plate arranged on the rotating shaft. The top end of the vertical support rod is provided with a rotating shaft hole, and the rotating shaft is rotatably connected with the vertical support rod. The displacement sensor support platform can rotate around and cannot move up and down, which facilitates the docking with the axial displacement sensor while ensuring the detection accuracy. The support frame also includes an annular bottom plate 1 connected to the base. The inner diameter of the annular bottom plate is adapted to the outer diameter of the annular platform at the bottom end of the sample cylinder. The vertical support rods of the support frame are fixed on the annular bottom plate. A support rod connection head 4 is provided at the connection between the vertical support rod and the horizontal support rod (see Figure 9-1 . Figure 9-2 ). The horizontal support rod is rotatably hinged upward on the support rod connection head. A connecting rod 4-a is horizontally arranged on the support rod connection head. One end of the horizontal support rod is hinged to the support rod connection head through the connecting rod. A horizontal rod 4-b for restricting the downward rotation of the horizontal support rod is provided at the bottom of the support rod connection head away from the vertical support rod. When the horizontal support rod rotates around the connecting rod and abuts against the horizontal rod, the horizontal support rod is in a horizontal state.

[0046] A crossbar fixing bayonet 5 for fixing the horizontal support rod is sleeved on the top end of the vertical support rod (see Figure 10), the crossbar fixing bayonet is made of plastic and is fixed to the vertical support rod through the fixing ring 5-a. The arc diameter of the fixing ring is the same as the diameter of the vertical support rod. When the horizontal support rod rotates upward by 90° to the vertical state, the horizontal support rod is buckled with the arc-shaped bayonet 5-b on the crossbar fixing bayonet (see Figure 5 ). The suspended end of the horizontal support rod is provided with an arc-shaped flap die 6. When the horizontal support rod is in the horizontal support state, the arc-shaped flap dies on all the horizontal support rods form a cylinder with an inner diameter adapted to the outer diameter of the compaction rod (see Figure 3 Figure 4 ). When the horizontal support rod is in the horizontal state, it can limit the horizontal movement of the compaction rod, ensure that the compaction rod is perpendicular to the compaction bottom plate, and is suitable for the static compaction mode used; when the horizontal support rod is in the vertical state, there is no obstacle above the sample cylinder, so the traditional impact compaction mode can also be adopted, which has two functions in one.

[0047] The sealing device includes a latex film 13 provided on the inner wall of the sample preparation cylinder. The height of the latex film is greater than the height of the sample preparation cylinder. The latex film with a height greater than the sample preparation cylinder is used to wrap the sample, solve the sealing problem of the sample, and improve the accuracy of volume change measurement and the success rate of the test; an air extraction hole 17 is provided on the side wall of the sample preparation cylinder (see Figure 11 ). The outside of the air extraction hole is connected to a rubber suction balloon 18. The air extraction hole is in a mesh structure. The air extraction hole cooperates with the rubber suction balloon to remove the air between the sample preparation cylinder and the latex film, ensuring that the latex film is closely attached to the sample preparation cylinder; the air-facing surface of the air extraction hole is in a mesh form, which can prevent the sharp edges and corners of the particles from piercing the latex film. The sealing device also includes a cover plate 29 adapted to the inner diameter of the sample preparation cylinder. Annular grooves are provided on the upper convex platforms of the cover plate and the base. An elastic rubber ring 26-a for fixing the latex film is provided on the outer periphery of the latex film at the annular groove. A sealing belt 26 is provided on the outside of the elastic rubber ring. A buckle 27 for locking the sealing belt is provided on the sealing belt. The buckle is made of metal and includes a buckle ring 27-a, a connecting shaft 27-c, and a fastening cover 27-b. The buckle ring 27-a is tightly buckled on the fastening platform 27-d at the other end of the sealing belt, and the buckle is locked by pressing down the fastening cover (see Figure 15-1 、 Figure 15-2 ). The annular grooves on the cover plate and the upper convex platform cooperate with the elastic rubber ring to seal the sample, and the sealing belt plays a final fixing role to solve the sealing problem of the sample.

[0048] A method for using a static compaction type coarse-grained soil triaxial test sample preparation device includes the following steps:

[0049] a. Place the permeable stone 12 and filter paper on the upper boss 10 of the base in sequence, put a latex film 13 on the outer wall of the upper boss, tie the latex film tightly at the annular groove of the upper boss with an elastic rubber ring 26-a, assemble the two split dies 14-a and install them on the upper boss of the base, and fix the two split dies into one body by sleeving a collar 16 on the outer periphery of the sample preparation cylinder. Turn the latex film protruding above the sample preparation cylinder 14 outwards to the outer wall of the sample preparation cylinder, use a rubber suction balloon 18 to extract the air between the latex film and the sample preparation cylinder through the air extraction hole 17, and then insert the deflated rubber suction balloon at the outer end of the air extraction hole to make the latex film closely adhere to the inner wall of the sample preparation cylinder (see Figure 7 )

[0050] b. Place the annular base plate 1 of the support frame on the lower boss 8 of the base and connect it to the base as a whole through a connecting bolt 11. Place the static compaction device in the sample preparation cylinder, where the compaction base plate 19 is in close contact with the filter paper. Operate the control panel 25 of the triaxial testing machine to make the rubber joint 20-a at the top of the compaction rod 20 contact the bottom end of the axial loading device 23. Adjust the axial displacement sensor 24 and the displacement sensor support platform 7 so that the end of the axial displacement sensor is supported on the displacement sensor support platform. At this time, zero the axial displacement value displayed on the control panel and take out the static compaction device.

[0051] c. Rotate the horizontal support rod 3 of the support frame upwards and fix it in the crossbar fixing bayonet 5. Fill the first layer of coarse-grained soil sample 28 prepared in layers into the sample preparation cylinder. Remove a small section 20-d of the compaction rod with a main body length equal to the height of the layered soil sample from the compaction rod and reassemble it, and place it in the sample preparation cylinder. Lower the horizontal support rod to make it in a horizontal state. The arc-shaped flap molds 6 at the suspended end of the horizontal support rod form a cylinder with an inner diameter adapted to the outer diameter of the compaction rod to limit the horizontal movement of the compaction rod. Operate the control panel to lower the compaction rod and the compaction base plate as a whole through the axial loading device of the triaxial testing machine to compact the soil sample, and stop lowering when the axial displacement is displayed as 0 again.

[0052] d. Repeat the above steps to fill the remaining soil samples in the same way. After each layer of soil sample is filled, remove a small section of the compaction rod with a main body length equal to the height of the layered soil sample and reassemble it. The compaction standard for each layer of soil sample is to take the axial displacement value as 0 until the last layer of soil sample is filled (see Figure 8 ) and remove the support frame and the static compaction device.

[0053] e. Place the filter paper, permeable stone and cover plate 29 on the top of the specimen in sequence. Straighten the latex film outside the sample preparation cylinder upwards, remove the sample preparation cylinder, tie an elastic rubber ring on the outside of the latex film at the groove of the cover plate, and wind sealing tapes 26 on the outside of the elastic rubber rings at the top and bottom ends of the specimen respectively, and lock them through buckles 27 (see Figure 13 Figure 14), after sample preparation, the triaxial sample of coarse aggregate can be used for triaxial compression test.

[0054] The sample preparation cylinder of the present invention is composed of two split molds. A horizontal semi-circular platform is added to the bottom end of each split mold to ensure that the sample preparation cylinder is in an upright state when placed. The static compaction device includes a compaction bottom plate and a compaction rod connected to the compaction bottom plate. The compaction rod is composed of multiple compaction rod segments with equal diameters and can be adjusted in length according to the soil sample situation in the sample cylinder to ensure the compaction of the layered soil sample, which is convenient for assembly and disassembly. Combined with the axial loading system, it can accurately control the layered height, control the total density of the coarse aggregate, and ensure uniform sample preparation. The support frame is used to support the compaction rod to ensure that the compaction rod is vertical and the compaction bottom plate is horizontal, preventing the multi-segment compaction rod from shifting in the horizontal direction; the axial loading platform of the triaxial testing machine is used to statically compact the soil sample in the sample cylinder. The axial displacement sensor detects the axial displacement, and the rise, fall, and axial displacement of the axial loading device can all be controlled and the data can be displayed through the axial loading platform of the triaxial testing machine. The present invention uses the triaxial test sample preparation device and the axial loading platform of the triaxial testing machine, and adopts the compaction method to make samples, achieving the purpose of minimizing particle breakage of the sample during the sample preparation process, ensuring the uniformity of the sample, and the accuracy of volume change measurement to the greatest extent.

[0055] In addition to the above embodiments, within the scope disclosed in the claims and the specification of the present invention, the technical features or technical data of the present invention can be reselected and combined to form new embodiments, which can be realized by those skilled in the art without creative labor. Therefore, these embodiments not detailedly described in the present invention should also be regarded as specific embodiments of the present invention and within the protection scope of the present invention.

Claims

1. A static compaction type coarse aggregate triaxial test specimen preparation device is arranged on the axial loading platform of a triaxial testing machine, and is characterized in that It includes a base, a sample preparation cylinder (14) arranged on the base, a sealing device, and a support frame arranged on the outer periphery of the sample preparation cylinder. The sample preparation cylinder is composed of two split molds (14-a) joined together. The sample preparation cylinder includes a cylinder body and an annular platform (15) horizontally arranged at the bottom of the cylinder body. A static compaction device for compacting the soil sample (28) inside the sample preparation cylinder is provided on the sample preparation device. The static compaction device includes a compaction bottom plate (19) and a compaction rod (20) connected to the compaction bottom plate. The diameter of the compaction bottom plate is adapted to the inner diameter of the sample preparation cylinder. The compaction rod is composed of a plurality of compaction rod segments (20-d) with the same diameter. A threaded hole (20-c) is provided at the upper end of the main body of the compaction rod segment located in the middle of the compaction rod, and a protruding bolt (20-b) is provided at the lower end of the main body. The protruding bolt and the threaded hole are adapted to each other. The length of the main body of the compaction rod segment located in the middle of the compaction rod is the same as the height of the layered soil sample. The top of the compaction rod is connected to an axial loading device (23) on the axial loading platform of the triaxial testing machine. The base includes an upper convex platform (10) with an outer diameter adapted to the inner diameter of the sample preparation cylinder and a lower convex platform (8) for fixing the support frame. The support frame includes several vertical support rods (2) arranged around the sample preparation cylinder. A horizontal support rod (3) for supporting the compaction rod is hinged to the upper part of each vertical support rod. A displacement sensor support platform (7) corresponding to the axial displacement sensor (24) on the axial loading platform of the triaxial testing machine is also provided on the support frame.

2. The static compaction type coarse aggregate triaxial test sample preparation device according to claim 1, characterized in that, The sealing device includes a latex film (13) arranged on the inner wall of the sample preparation cylinder. The height of the latex film is greater than the height of the sample preparation cylinder. An air extraction hole (17) is provided on the side wall of the sample preparation cylinder. The outside of the air extraction hole is connected to a rubber suction balloon (18). The air extraction hole is in a mesh structure.

3. The static compaction type coarse aggregate triaxial test specimen preparation device according to claim 2, characterized in that, The sealing device further includes a cover plate (29) adapted to the inner diameter of the sample preparation cylinder. Annular grooves are provided on both the cover plate and the upper convex platform of the base. An elastic rubber ring (26-a) for fixing the latex film is provided on the outer periphery of the latex film at the annular groove. A sealing strip (26) is provided on the outside of the elastic rubber ring. A buckle (27) for locking the sealing strip is provided on the sealing strip.

4. The static compaction type coarse aggregate triaxial test sample preparation device according to claim 1, characterized in that, A rubber joint (20-a) is provided at the top of the compaction rod segment located at the uppermost end. The compaction rod segment located at the lowermost end is fixed on the compaction bottom plate.

5. The static compaction type coarse aggregate triaxial test sample preparation device according to claim 1, wherein The support frame includes an annular bottom plate (1) connected to the base. The inner diameter of the annular bottom plate is adapted to the outer diameter of the annular platform at the bottom end of the sample preparation cylinder. The vertical support rods of the support frame are fixed on the annular bottom plate. A support rod connection head (4) is provided at the connection between the vertical support rod and the horizontal support rod. The horizontal support rod is rotatably hinged upward on the support rod connection head. A cross-bar fixing bayonet (5) for fixing the horizontal support rod is sleeved on the top end of the vertical support rod. An arc-shaped flap mold (6) is provided at the suspended end of the horizontal support rod. When the horizontal support rod is in a horizontal support state, the arc-shaped flap molds on all the horizontal support rods form a cylinder with an inner diameter adapted to the outer diameter of the compaction rod.

6. The static compaction type coarse aggregate triaxial test specimen preparation device according to claim 5, wherein, A connecting rod (4-a) is horizontally provided on the support rod connector head. One end of the horizontal support rod is hinged to the support rod connector head through the connecting rod. A horizontal rod (4-b) for restricting the downward rotation of the horizontal support rod is provided at the bottom of the support rod connector head on the side away from the vertical support rod. When the horizontal support rod rotates around the connecting rod and abuts against the horizontal rod, the horizontal support rod is in a horizontal state. When the horizontal support rod rotates upward to a vertical state, the horizontal support rod is buckled with an arc-shaped bayonet (5-b) on the crossbar fixed bayonet.

7. The static compaction type coarse aggregate triaxial test sample preparation device according to claim 1, characterized in that The number of the vertical support rods is 3 - 4. The displacement sensor support platform is arranged at the top of one of the vertical support rods. The displacement sensor support platform includes a vertically arranged rotating shaft and a horizontal plate arranged on the rotating shaft. A rotating shaft hole is arranged at the top end of the vertical support rod. The rotating shaft is rotatably connected with the vertical support rod.

8. The static compaction type coarse aggregate triaxial test sample preparation device according to claim 1, wherein, The triaxial testing machine loading platform includes a control panel (25), a bottom platform (21) and columns (22) fixed on both sides of the bottom platform. A cross beam is arranged at the top end of the column. The axial loading device is arranged below the cross beam. The lower end of the axial loading device is connected with the axial displacement sensor.

9. The static compaction type coarse aggregate triaxial test sample preparation device according to claim 1, wherein Convex-concave interfaces (14-b) which are matched with each other are provided at the splicing places of the cylinders on the two split dies. An elastic gasket is arranged between the butting surfaces of the convex-concave interfaces. A collar (16) for fastening the split dies of the sample preparation cylinder is arranged on the outer periphery of the sample preparation cylinder.

10. A method for using the static compaction type coarse aggregate triaxial test sample preparation device according to any one of claims 1-9, characterized in that It includes the following steps: a. Place the permeable stone (12) and the filter paper on the upper convex platform (10) of the base in sequence, and put a latex film (13) on the outer wall of the upper convex platform. Tie the latex film tightly at the annular groove of the upper convex platform with an elastic rubber ring (26-a). Combine the two split dies (14-a) and install them on the upper convex platform of the base, and fix the two split dies into one body by sleeving a collar (16) on the outer periphery of the sample preparation cylinder. Turn the latex film protruding above the sample preparation cylinder (14) to the outer wall of the sample preparation cylinder. Use a rubber suction balloon (18) to extract the air between the latex film and the sample preparation cylinder through the air extraction hole (17), and then insert the shriveled rubber suction balloon into the outer end of the air extraction hole to make the latex film closely adhere to the inner wall of the sample preparation cylinder. b. Place the annular bottom plate (1) of the support frame on the lower convex platform (8) of the base and connect it with the base as a whole through a connecting bolt (11). Place the static compaction device in the sample preparation cylinder, where the compaction bottom plate (19) is in close contact with the filter paper. Operate the control panel (25) of the triaxial testing machine to make the rubber joint (20-a) at the top end of the compaction rod (20) contact with the bottom end of the axial loading device (23). Adjust the axial displacement sensor (24) and the displacement sensor support platform (7) so that the end of the axial displacement sensor supports on the displacement sensor support platform. At this time, clear the axial displacement value displayed on the control panel, and take out the static compaction device. c. Rotate the horizontal support rod (3) of the support frame upward and fix it in the crossbar fixing bayonet (5). Load the first layer of coarse-grained soil sample (28) prepared in layers into the sample preparation cylinder. Remove a small section of the compaction rod (20-d) with a main body length equal to the height of the layered soil sample from the compaction rod, reassemble it, and place it in the sample preparation cylinder. Lower the horizontal support rod to make it in a horizontal state. The arc-shaped flap molds (6) at the suspended end of the horizontal support rod form a cylinder with an inner diameter adapted to the outer diameter of the compaction rod to limit the horizontal movement of the compaction rod. The operation control panel uses the axial loading device of the triaxial testing machine to make the compaction rod and the compaction bottom plate descend as a whole to achieve the compaction of the soil sample. Stop descending when the axial displacement is displayed as 0 again; d. Repeat the above steps to load the remaining soil samples in the same way. After each layer of soil sample is loaded, a small section of the compaction rod with a main body length equal to the height of the layered soil sample needs to be removed and reassembled. The compaction standard for each layer of soil sample is to take the axial displacement value as 0 until the last layer of soil sample is loaded, and then remove the support frame and the static compaction device; e. Place the filter paper, permeable stone, and cover plate (29) on the top of the specimen in sequence. Straighten the latex film outside the sample preparation cylinder upward, remove the sample preparation cylinder, tie the elastic rubber ring around the outside of the latex mold at the groove of the cover plate, and wind the sealing tape (26) around the outside of the elastic rubber rings at the top and bottom ends of the specimen respectively, and lock it with the buckle (27). After the sample preparation is completed, the coarse-grained soil triaxial specimen can be used for the triaxial compression test.

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