In-ring direct pressing device and method for simulating joint-containing compacted bentonite combination

Abstract

The invention provides an in-ring direct pressing device and method for simulating a joint-containing compacted bentonite combination, and the method comprises a sample pressing part and a reserved steel sheet taking-out part: before the sample pressing, a base, a steel sheet, a sample ring and a sample pressing ring are sequentially assembled; the design of the through groove is used for ensuring the stability of the steel sheet and the fixity of the preset joint position and supporting the extrusion of the subsequent reserved steel sheet; after sample pressing is finished, the sample pressing assembly is inverted, the steel sheet is pressed out at a constant speed by means of the universal press, the original pressing assembly is converted into the supporting assembly, and soil body tension cracks caused by friction force in the steel sheet pressing-out process are effectively reduced. According to the invention, in-ring direct pressing of the joint-containing compacted bentonite assembly is realized, joint width change and structural damage at corners of the sample caused by transfer of the sample from a sample pressing mold to a test ring are avoided, and uniformity and stability of the directly-pressed assembly sample are ensured; and technical support is provided for research on construction joints of the bentonite buffer layer in the high-level radioactive waste deep geological repository.

Description

Technical Field

[0001] The present invention relates to the technical fields of civil engineering (geotechnical) and geological engineering, and particularly relates to a direct pressing device and method inside a ring for simulating a compacted bentonite combination body with joints. Background Art

[0002] Currently, it is internationally recognized to use the deep geological disposal method to achieve the permanent disposal of high-level radioactive waste, that is: in the rock mass about 500 to 1000 meters below the ground surface, a multi-barrier system composed of natural surrounding rock barriers and engineering barriers is constructed to seal high-level radioactive waste. Among them, compacted bentonite is regarded as the preferred material for constructing engineering barriers due to its characteristics such as high expansibility, low permeability, good thermal conductivity, and adsorption. In actual engineering, the precast block stacking method is used to fill bentonite, that is, the bentonite combination body is pre-pressed and then filled between the waste canister body and the surrounding rock roadway. This method inevitably generates joints between the bentonite combination body and the blocks, becoming a weak area in the mechanical properties of the engineering barrier in the disposal repository and even a preferential channel for groundwater infiltration, affecting the buffering performance of the engineering barrier. Based on this, conducting research on the compacted bentonite combination body containing joints is very important for the design and long-term performance evaluation of the engineering barrier in the disposal repository. Currently, most of the research on the pressing of bentonite combination bodies is based on complete specimens, and devices for quickly and simply pressing combination body blocks containing joints are relatively rare. Summary of the Invention

[0003] The purpose of the present invention is to provide a sample pressing device that can achieve direct pressing inside a ring, thereby avoiding the change in joint width caused by the transfer of the pressed sample.

[0004] To achieve the above purpose, the present invention proposes a direct pressing device inside a ring for simulating a compacted bentonite combination body with joints, including a press, a sample pressing assembly, and a reserved steel sheet pressing-out assembly. The sample pressing assembly presses the bentonite sample through the press.

[0005] The sample pressing assembly includes a sample pressing column, a sample pressing ring, a sample ring, a reserved steel sheet, and a base: one end of the sample ring is fixed on the base, and the other end is connected to the sample pressing ring to form a sample pressing chamber, and bentonite powder is pressed in the sample pressing chamber.

[0006] A groove is provided at the center of the base, so that the reserved steel sheet is inserted into the groove of the base, evenly dividing the sample pressing chamber into two symmetrical half-chambers, ensuring the uniformity of the soil on both sides of the longitudinal joint and realizing the control of the longitudinal joint width.

[0007] The sample pressing column is arranged directly below the press. One end of the sample pressing column facing the base groove is provided with a seam groove corresponding to the base groove, so that during the process of sample pressing after the sample pressing column is pressed by the press, the reserved steel sheet standing upright in the sample pressing chamber is embedded in the seam groove, ensuring the upright stability of the reserved steel sheet, the fixity of the preset seam position, and the removal method of the reserved steel sheet.

[0008] The reserved steel sheet pressing-out assembly includes a support assembly and a pressure conduction sheet. The support assembly is composed of the sample pressing assembly inverted after pressing, and is used to limit the bottom boundary of the sample, effectively reducing the soil body cracking caused by friction during the process of steel sheet extraction. One end of the pressure conduction sheet is connected to the press, and the other end is connected to the support assembly, which is used to solve the problem of removing the reserved steel sheet between high dry density combinations, and ensure the stability of the bottom boundary of the sample during the process of pressing out the reserved steel sheet, preventing the soil body from cracking caused by friction.

[0009] Furthermore, the bottom edge of the sample pressing ring is a secondary cutting and is provided with a groove of a certain height; the diameter of the groove on the outer edge of the sample pressing ring is the same as the outer diameter of the sample ring, which is used to fix the sample ring, so that the sample ring just fits into the outer edge of the sample pressing ring, ensuring that the bentonite powder does not overflow during the pressing process, and providing a lateral confinement boundary for the sample pressing column to reduce the risk of deformation and failure of the sample pressing column. The sample ring is a rigid ring directly used in the hydration test of the bentonite combination sample. The sample is directly pressed in the ring, avoiding the change of the seam width caused by transferring it from the sample pressing mold to the sample ring.

[0010] Furthermore, the inner diameters of the sample pressing ring and the sample ring are the same; the diameter of the sample pressing column is the same as the inner diameter of the sample ring; the outer surface of the sample pressing column is respectively in contact with the inner walls of the sample pressing ring and the sample ring.

[0011] Furthermore, the sample pressing column is used to bear the pressure applied by the press and transfer the pressure to the bentonite powder in the chamber to form a bentonite combination; one end of the sample pressing column is provided with a seam groove according to the size of the reserved steel sheet, so that the too long reserved steel sheet can just be embedded during the sample pressing process, ensuring the stability of the upright steel sheet, the fixity of the preset seam position, and the removal method of the reserved steel sheet; the other end is provided with a threaded drill hole along the central axis of the sample pressing column, which is used to screw in a screw rod to eject the reserved steel sheet, preventing the steel sheet pushed out from the combination from being embedded in the groove of the sample pressing column and being unable to be disassembled.

[0012] Furthermore, before pressing the bentonite powder, an active baffle is placed above the reserved steel sheet, which is used to evenly pour the bentonite powder on both sides and reduce the overflow of the soil powder during the stirring process.

[0013] Furthermore, the pressure applied by the press is transmitted through the pressure transmission sheet to separate the reserved steel sheet in the bentonite sample assembly from the soil on both sides. The thickness of the pressure transmission sheet is less than the thickness of the reserved steel sheet, with a minimum of 1.5 mm, and has sufficient compressive and bending strength. The pressure of the press can be transmitted to the reserved steel sheet, solving the problem of removing the blocking material between high dry density assemblies.

[0014] Furthermore, the press is a CNC universal press with a maximum pressure of 300 kN, which meets the pressing requirements of high-density samples in the test and includes two modes: pressure control and displacement control.

[0015] Furthermore, the sample pressing assembly and the reserved steel sheet extrusion assembly are both made of 316L stainless steel to ensure sufficient mechanical strength and low friction during the pressing process, and are used to press the bentonite powder into bentonite blocks through static displacement control technology.

[0016] The reserved steel sheet is made of 316L stainless steel material. The original steel sheet is polished to a target thickness by a surface polishing method to reduce the influence of the side wall friction of the steel sheet during the sample pressing process, thereby achieving control of the longitudinal seam width.

[0017] Furthermore, the sample pressing column and the reserved steel sheet can freely adjust the joint width, joint type and joint quantity according to the test requirements, and support the pressing of compacted bentonite assemblies with different joint widths, types and quantities.

[0018] The present invention also provides a method for directly pressing a bentonite assembly in a ring by simulating compaction of bentonite with joints, which is performed by using the device for directly pressing a bentonite assembly in a ring by simulating compaction of bentonite with joints. The method comprises the following steps:

[0019] S1: Based on the gas phase method, the bentonite powder is subjected to suction control to determine the initial moisture content of the powder;

[0020] S2: The reserved steel sheet is embedded in the base, and the sample ring, the sample pressing ring, and the sample pressing column are assembled on the base in sequence, wherein the inner walls of the sample ring and the sample pressing ring are fitted with the outer wall of the sample pressing column, and the sample ring is embedded in the groove of the sample pressing ring and fixed to form a sample pressing chamber. At this time, the reserved steel sheet divides the sample pressing chamber into two symmetrical half chambers;

[0021] S3: Calculate the required mass of bentonite powder, weigh it in batches and pour it into the half chamber evenly divided by the reserved steel sheet;

[0022] S4: The sample pressing column is connected to the reserved steel sheet through the joint groove, and the sample is pressed in the sample ring using a universal press according to the displacement control method;

[0023] S5: After the pressing is completed, reverse the sample pressing assembly, fix the pressure conduction plate at the center of the base, and slowly push out the reserved steel sheet to form a bentonite combination containing a joint.

[0024] Through the device and method of the present invention, the in-ring direct pressing of the compacted bentonite combination with joints is realized, avoiding the change in joint width caused by the transfer of the sample from the sample pressing mold to the sample ring, and ensuring the uniformity and stability of the combination. By appropriately modifying the through-joint of the sample pressing column, the type and width of the reserved steel sheet, the in-ring direct pressing of bentonite combinations with different joint numbers / types can be realized, providing experimental support for the subsequent research on the buffering performance of the sample of the combination with joints.

[0025] Compared with the prior art, the advantages of the present invention are as follows:

[0026] 1. Through the in-ring direct pressing device of the present invention, the in-ring direct pressing of the compacted bentonite combination with joints is realized, avoiding the change in joint width caused by the transfer of the sample from the sample pressing mold to the test ring and the structural damage at the corners of the sample, and ensuring the uniformity and stability of the combination.

[0027] 2. By appropriately modifying the joint groove of the sample pressing column and the type and width of the reserved steel sheet, the present invention realizes the in-ring direct pressing of bentonite combinations with different joint numbers / types, provides experimental support for the subsequent research on the buffering performance of the sample of the combination with joints, and has sufficient stability and applicability.

[0028] 3. In the device of the present invention, by using steel sheets of different thicknesses, the precise control of different widths of a single longitudinal joint is realized, and the influence of boundary friction on the compacted sample is effectively reduced.

[0029] 4. The sample of the bentonite combination with joints prepared by the method of the present invention can be used to carry out the self-sealing / healing test of the bentonite-bentonite indirect joint and the research on the buffering performance of the engineering barrier during the evolution of the joint, so as to evaluate the sealing effect of the compacted bentonite and provide a theoretical basis for the design and optimization of the joint. Description of the Drawings

[0030] Figure 1 It is a schematic diagram of the sample pressing process of the present invention;

[0031] Figure 2 It is a schematic diagram of the process of taking out the reserved steel sheet of the present invention;

[0032] Figure 3 (a) is the auxiliary disassembly step of the present invention, (b) is the top view of the sample pressing assembly of the present invention:

[0033] 1 - sample pressing column, 2 - sample pressing ring, 3 - sample ring, 4 - reserved steel sheet, 5 - base, 6 - soil powder, 7 - pressure conduction plate, 8 - auxiliary screw. Specific Embodiment

[0034] To make the objectives, technical solutions and advantages of the present invention clearer, the technical solutions of the present invention will be further described below.

[0035] This embodiment provides a direct pressing device inside a ring for simulating a compacted bentonite combination with seams. As Figure 1 shown, the device includes a universal testing machine and a reserved steel sheet pressing-out assembly. The sample pressing assembly presses bentonite samples through the universal testing machine.

[0036] In this embodiment, the universal testing machine is a DDL-200 type numerically controlled universal testing machine with a maximum pressure of 300 kN, including two modes of pressure control and displacement control.

[0037] The sample pressing assembly includes a sample pressing column 1, a sample pressing ring 2, a sample ring 3, a reserved steel sheet 4 and a base 5. Among them, one end of the sample ring 2 is fixed on the base 5, and the other end is connected to the sample pressing ring 2 to form an annular sample pressing chamber, and bentonite powder 6 is pressed in the sample pressing chamber;

[0038] A groove is provided at the center of the base 5, and the reserved steel sheet 4 is inserted into the groove of the base, evenly dividing the annular sample pressing chamber into two symmetrical nearly semi-circular chambers, which is used to ensure the uniformity of the soil on both sides of the longitudinal joint and realize the control of the longitudinal joint width.

[0039] As Figure 1 shown, the sample pressing column 1 is arranged directly below the universal testing machine. One end of the sample pressing column facing the groove of the base is provided with a joint groove corresponding to the groove of the base. When the sample pressing column 1 presses the sample under the pressure of the universal testing machine, the reserved steel sheet 4 standing upright in the sample pressing chamber is embedded in the joint groove, which not only ensures the upright stability of the reserved steel sheet, but also presets the fixity of the joint position and the removal method of the reserved steel sheet.

[0040] In this embodiment, as Figure 2 shown, the reserved steel sheet pressing-out assembly includes a support assembly and a pressure conduction sheet 7. The support assembly is composed of the sample pressing assembly inverted after pressing, which is used to limit the bottom boundary of the sample and effectively reduce the soil cracking caused by friction during the extraction of the steel sheet. One end of the pressure conduction sheet 7 is connected to the universal testing machine, and the other end is connected to the support assembly. The pressure of the universal testing machine is transmitted to the reserved steel sheet 4 through the pressure conduction sheet 7, separating the reserved steel sheet in the bentonite sample combination from the soil on both sides, solving the problem of removing the reserved steel sheet 4 between high dry density combinations, and ensuring the stability of the bottom boundary of the sample during the pressing-out process of the reserved steel sheet 4 and preventing soil cracking caused by friction. The thickness of the pressure conduction sheet 7 is less than the thickness of the reserved steel sheet 4, with a minimum of 1.5 mm, and it has sufficient compressive and bending strength.

[0041] In this embodiment, a groove with a certain height is provided by secondary cutting at the bottom edge of the sample pressing ring 2; the diameter of the groove at the outer edge of the sample pressing ring 2 is the same as the outer diameter of the sample ring 3, which is used to fix the sample ring 3 so that the sample ring 3 just fits into the groove at the outer edge of the sample pressing ring 3, ensuring that the bentonite powder 6 does not overflow during the pressing process and providing a lateral confinement boundary for the sample pressing column 1 to reduce the risk of deformation and failure of the sample pressing column. In this embodiment, the sample ring 2 is a rigid ring directly used in the hydration test of the bentonite composite sample. The sample is directly pressed inside the ring, avoiding the change in the joint width caused by transferring it from the sample pressing mold to the sample ring.

[0042] In addition, the inner diameters of the sample pressing ring 2 and the sample ring 3 are the same; the diameter of the sample pressing column 1 is the same as the inner diameter of the sample ring 3, and the outer surface of the sample pressing column 1 fits with the inner walls of the sample pressing ring 2 and the sample ring 3 respectively.

[0043] In this embodiment, the sample pressing column 1 is used to bear the pressure applied by the universal testing machine and transfer the pressure to the bentonite powder 6 in the chamber to form a bentonite composite; one end of the sample pressing column 1 is provided with a joint groove according to the size of the reserved steel sheet 4, facilitating the exact embedding of the overlong reserved steel sheet 4 during the sample pressing process, ensuring the stability of the upright steel sheet, the fixation of the preset joint position, and the removal method of the reserved steel sheet; the other end of the sample pressing column 1 is provided with a threaded hole along the central axis of the sample pressing column, as Figure 3 (a) and Figure 3 (b) show that by screwing in the screw 8, the reserved steel sheet is pushed out to prevent the steel sheet pushed out from the composite from being embedded in the groove of the sample pressing column and being unable to be disassembled. During the removal process of the reserved steel sheet 4, the reserved steel sheet pressing-out assembly is used to press the reserved steel sheet 4 in the composite into the longitudinal joint groove of the sample pressing column 1 to achieve the purpose of "removing the reserved steel sheet". However, after this process, the steel sheet 4 will be stuck in the joint groove of the sample pressing column due to a small amount of floating soil and be difficult to disassemble. At this time, the steel sheet 4 is smoothly taken out from the sample pressing column 1 through the long screw 8 screwed into the top of the sample pressing column 1.

[0044] In this embodiment, before pressing the bentonite powder, an active baffle is placed above the reserved steel sheet 4, which is used to evenly pour the bentonite powder into the nearly semi-circular chambers on both sides and reduce the overflow of the bentonite powder during the stirring process.

[0045] In this embodiment, the sample pressing column 1, the sample pressing ring 2, the sample ring 3, the reserved steel sheet 4, the base 5, and the pressure conduction sheet 7 in the reserved steel sheet pressing-out assembly of the sample pressing assembly are all made of 316L stainless steel material.

[0046] The joint width, joint type, and number of joints of the sample pressing column 1 and the reserved steel sheet 4 can be freely adjusted according to the test requirements, supporting the pressing of compacted bentonite composites with different joint widths, types, and numbers.

[0047] Based on the above-mentioned in-ring direct pressing device for simulating a compacted bentonite assembly with seams, the in-ring direct pressing of the compacted bentonite assembly with seams is carried out as follows:

[0048] 1) Suction control of bentonite powder: Based on the gas phase method, the bentonite powder 6 is placed in a sealed glass drying dish with a specific saturated salt solution at the bottom and sealed. When the total mass hardly changes anymore, it is considered that the suction has reached the equilibrium state, and the initial moisture content of the powder is measured by the drying method.

[0049] 2) Preparation of the device before sample pressing: Assemble the sample pressing assembly. Insert the 2-mm steel sheet 4 into the central groove of the base 5. The sample ring 3, the sample pressing ring 2, and the sample pressing column 1 are fixed to the base 5 in sequence, keeping the inner walls of the sample ring 3 and the sample pressing ring 2 in contact with the outer wall of the sample pressing column 1. The sample ring 3 is embedded in the bottom edge groove of the sample pressing ring 2 for fixation, forming an annular pressing chamber. At this time, the reserved steel sheet 4 divides the annular pressing chamber into two nearly semi-circular sample pressing chambers of equal size on average.

[0050] 3) Weighing of bentonite powder: According to the target dimensions of the sample, namely a diameter of 61.8 mm, a height of 20 mm, and a seam width of 2 mm, calculate the mass of the bentonite powder 6 required under the conditions of the target dry density and moisture content, and weigh it in portions and pour it into the two nearly semi-circular sample pressing chambers on both sides evenly divided by the steel sheet 4.

[0051] 4) Pressing of the bentonite assembly: Align the seam groove of the sample pressing column 1 with the reserved steel sheet 4 and carefully fit it against the inner wall of the sample pressing ring 2 and enter the pressing chamber. Using a universal testing machine, according to the displacement control method, press the sample at a descending rate of 0.5 mm / min to prevent the bentonite powder 6 from overflowing due to too fast a speed. After reaching the target displacement, let it stand for 1 h to avoid sample rebound.

[0052] 5) Pushing out the steel sheet: Subsequently, invert the sample pressing assembly, fix the pressure conduction sheet 7 at the center of the base 5, and push out the steel sheet at a rate of 1 mm / min to form a bentonite assembly with a seam. After pressing the sample, measure the height, mass, and seam width of the sample to ensure that the dry density of the bentonite assembly is between the target dry density ± 0.01 g / cm3.

[0053] The above is only the preferred embodiment of the present invention and does not impose any limitation on the present invention. Any person skilled in the art within the technical field, without departing from the technical solution of the present invention, makes any form of equivalent replacement or modification and other changes to the technical solution and technical content disclosed by the present invention, all of which fall within the content of the technical solution of the present invention and still belong to the protection scope of the present invention.

Claims

1. A direct pressing device for simulating a joint-containing compacted bentonite assembly, characterized in that: It includes a press, a sample pressing assembly and a reserved steel sheet extrusion assembly, wherein the sample pressing assembly is used to press the bentonite sample through the press; The sample pressing assembly includes a sample pressing column, a sample pressing ring, a sample ring, a reserved steel sheet and a base: one end of the sample ring is fixed to the base, and the other end is connected to the sample pressing ring to form a sample pressing chamber, in which bentonite powder is pressed; A groove is provided in the center of the base, so that the reserved steel sheet is inserted into the groove of the base to evenly divide the sample pressing chamber into two symmetrical half chambers; The sample pressing column is arranged directly below the press, and one end of the sample pressing column facing the base groove is provided with a joint groove corresponding to the base groove, so that during the sample pressing process after the sample pressing column is pressed by the press, the reserved steel sheet standing upright in the sample pressing chamber is embedded in the joint groove; The reserved steel sheet extrusion assembly includes a support assembly and a pressure transmission sheet. The support assembly is composed of a sample pressing assembly that is inverted after pressing. One end of the pressure transmission sheet is connected to the press, and the other end is connected to the support assembly.

2. The in-ring direct pressing device for simulating a joint-containing compacted bentonite assembly according to claim 1, characterized in that: The bottom edge of the sample pressing ring is secondarily cut, and the diameter of the groove on the outer edge of the sample pressing ring is the same as the outer diameter of the sample ring, so that the sample ring is just embedded in the outer edge of the sample pressing ring.

3. The in-ring direct pressing device for simulating a joint-containing compacted bentonite assembly according to claim 1, characterized in that: The inner diameters of the sample compression ring and the sample ring are the same; the diameter of the sample compression column is the same as the inner diameter of the sample ring; and the outer surface of the sample compression column fits with the inner walls of the sample compression ring and the sample ring respectively.

4. The in-ring direct pressing device for simulating a joint-containing compacted bentonite assembly according to claim 1, characterized in that: One end of the sample pressing column is provided with a joint groove, and the other end is provided with a threaded hole along the central axis for screwing in a screw rod to eject the reserved steel sheet.

5. The in-ring direct pressing device for simulating a joint-containing compacted bentonite assembly according to claim 1, characterized in that: Before pressing the bentonite powder, a movable baffle is placed above the reserved steel sheet.

6. The in-ring direct pressing device for simulating a joint-containing compacted bentonite assembly according to claim 1, characterized in that: The pressure applied by the press is transmitted through the pressure transmission sheet to separate the reserved steel sheet in the bentonite sample assembly from the soil bodies on both sides. The thickness of the pressure transmission sheet is smaller than that of the reserved steel sheet, and the minimum thickness is 1.5 mm.

7. The in-ring direct pressing device for simulating a joint-containing compacted bentonite assembly according to claim 1, characterized in that: The press is a CNC universal press with a maximum pressure of 300kN, including two modes: pressure control and displacement control.

8. The in-ring direct pressing device for simulating a joint-containing compacted bentonite assembly according to claim 1, characterized in that: The sample pressing assembly and the reserved steel sheet pressing assembly are both made of 316L stainless steel.

9. A method for directly pressing a bentonite assembly in a ring by simulating compaction with joints, using the device for directly pressing a bentonite assembly in a ring by simulating compaction with joints as claimed in any one of claims 1 to 8, characterized in that: The steps include: S1: Control the suction of bentonite powder and measure the initial moisture content of the powder; S2: The reserved steel sheet is embedded in the base, and the sample ring, the sample pressing ring, and the sample pressing column are assembled on the base in sequence, wherein the inner walls of the sample ring and the sample pressing ring are fitted with the outer wall of the sample pressing column, and the sample ring is embedded in the groove of the sample pressing ring and fixed to form a sample pressing chamber. At this time, the reserved steel sheet divides the sample pressing chamber into two symmetrical half chambers; S3: Calculate the required mass of bentonite powder, weigh it in batches and pour it into the half chamber evenly divided by the reserved steel sheet; S4: The sample pressing column is connected to the reserved steel sheet through the joint groove, and the sample is pressed in the sample ring using a universal press according to the displacement control method; S5: After the pressing is completed, invert the sample pressing assembly, fix the pressure transmission sheet at the center of the base, and slowly push out the reserved steel sheet to form a bentonite assembly with joints.

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