An in-situ direct compression apparatus and method for simulating a jointed compacted bentonite assembly

Abstract

The application provides a device and method for directly pressing a sample in a ring, which simulates a jointed compacted bentonite assembly, and comprises two parts of sample pressing and reserved steel sheet taking out; before sample pressing, a base, a steel sheet, a sample ring and a sample pressing ring are assembled in sequence, and a through groove is designed to ensure stability of the steel sheet, fixation of a preset joint position and support for subsequent pressing of the reserved steel sheet; after sample pressing, the sample pressing assembly is inverted, the steel sheet is pressed out at a constant speed by means of a universal testing machine, the original pressing assembly is converted into a supporting assembly, and soil body tearing caused by friction during pressing of the steel sheet is effectively reduced. The application realizes direct pressing of the jointed compacted bentonite assembly in a ring, avoids changes in joint width and structural damage at edges and corners of the sample caused by sample transfer from a sample pressing mold to a test ring, ensures uniformity and stability of the directly pressed assembly sample, and provides technical support for research on construction joints of a bentonite buffer layer in a high-level radioactive waste deep geological repository.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of civil engineering (geotechnical) and geological engineering, and particularly relates to a ring-in direct pressing device and method for simulating a joint-containing compacted bentonite assembly. BACKGROUND

[0002] At present, it is internationally recognized that the deep geological disposal method is used to realize permanent disposal of high-level waste, that is, a multi-barrier system composed of a natural surrounding rock barrier and an engineering barrier is constructed in a rock mass about 500-1000 meters below the ground surface to store high-level waste. The compacted bentonite is considered as the first choice for building the engineering barrier due to its high swelling property, low permeability, and good thermal conductivity and adsorption property. In actual engineering, the precast block stacking method is used to fill the bentonite, that is, the bentonite assembly is pressed in advance and then filled between the waste tank body and the surrounding rock roadway. This method inevitably produces a joint between the bentonite assembly and the block, which becomes a weak area in the mechanical properties of the disposal repository engineering barrier and an advantageous channel for groundwater infiltration, affecting the buffering performance of the engineering barrier. Based on this, research on the compacted bentonite assembly containing joints is very important for the design and long-term performance evaluation of the engineering barrier in the disposal repository. At present, most of the compacted bentonite assembly is based on complete samples, and there are few devices for quickly and simply pressing the assembly block containing joints. SUMMARY

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

[0004] To achieve the above purpose, the present application provides a ring-in direct pressing device for simulating a joint-containing compacted bentonite assembly, which comprises a pressing machine, a sample pressing assembly, and a reserved steel sheet pressing-out assembly. The sample pressing assembly is used for pressing the bentonite sample through the pressing machine.

[0005] The sample pressing assembly comprises 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. The bentonite powder is pressed in the sample pressing chamber.

[0006] The base is provided with a groove in the center, so that the reserved steel sheet is inserted into the groove of the base, and the sample pressing chamber is evenly divided into two symmetrical half-chambers, which ensures the uniformity of the soil on both sides of the longitudinal joint and controls the width of the longitudinal joint.

[0007] The pressure sample column is arranged directly below the press, and one end of the pressure sample column opposite to the base groove is provided with a joint groove corresponding to the base groove, so that the reserved steel sheet standing in the pressure sample chamber is embedded in the joint groove during the process of the pressure sample column after being pressed by the press, and the standing stability of the reserved steel sheet, the fixing of the preset joint position and the taking-out mode of the reserved steel sheet are ensured.

[0008] The reserved steel sheet pressing-out assembly comprises a support assembly and a pressure transmission sheet, the support assembly is composed of the inverted sample pressing assembly after pressing, and is used for limiting the bottom boundary of the sample, and effectively reducing the soil body tearing caused by friction during the extraction of the steel sheet. One end of the pressure transmission sheet is connected with the press, and the other end is connected with the support assembly, which is used to solve the problem of taking out the reserved steel sheet between the high dry density combination, and ensure the stability of the bottom boundary of the sample during the process of the reserved steel sheet being pressed out, and prevent the soil body from being torn by friction.

[0009] Further, the bottom edge of the pressure sample ring is two-stage cutting and is provided with a groove with a certain height; the outer edge groove of the pressure sample ring has the same diameter as the outer diameter of the sample ring, which is used to fix the sample ring, so that the sample ring is embedded in the outer edge of the pressure sample ring, the bentonite powder is prevented from overflowing during the pressing process, and the pressure sample column is provided with a lateral limit boundary to reduce the risk of deformation and damage of the pressure sample column. The sample ring is a rigid ring directly used in the hydration test of the bentonite combination sample, and the sample is directly pressed in the ring, avoiding the change of the joint width caused by the transfer of the sample from the pressure sample mold to the sample ring.

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

[0011] Further, the pressure sample column is used to bear the pressure applied by the press, and transmit the pressure to the bentonite powder in the chamber to form a bentonite combination; one end of the pressure sample column is provided with a joint groove according to the size of the reserved steel sheet, so that the reserved steel sheet which is too long can be embedded during the process of pressing, and the stability of the standing steel sheet, the fixing of the preset joint position and the taking-out mode of the reserved steel sheet are ensured; the other end is provided with a threaded drill hole along the central axis of the pressure sample column, which is used to screw in a screw rod to push out the reserved steel sheet, so that the steel sheet pushed out from the combination cannot be embedded in the groove of the pressure sample column and cannot be disassembled.

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

[0013] Further, the reserved steel sheet in the bentonite sample assembly is separated from the soil on both sides by conducting the pressure of the pressure machine, the thickness of the pressure conducting sheet is less than the thickness of the reserved steel sheet, and the minimum is 1.5 mm, which has sufficient compression and bending strength, and can conduct the pressure of the pressure machine to the reserved steel sheet, so that the problem of taking out the interlayer blocking material of the high dry density assembly is solved.

[0014] Further, the pressure machine is a numerical control universal pressure machine, and the maximum pressure is 300kN, which meets the pressing requirements of the high-density sample in the test and includes pressure control and displacement control modes.

[0015] Further, the sample pressing assembly and the reserved steel sheet pressing-out assembly are made of 316L stainless steel material, so as to ensure sufficient mechanical strength and low boundary friction influence in the pressing process, and the bentonite powder is pressed into a bentonite block by the static force method displacement control technology.

[0016] The reserved steel sheet is made of 316L stainless steel material, and the original steel sheet is polished to the target thickness by the surface polishing method, so as to reduce the influence of the side wall friction of the steel sheet in the sample pressing process, and the control of the longitudinal joint width is realized.

[0017] Further, the sample pressing column and the reserved steel sheet can freely adjust the joint width, joint type and joint number according to the test requirements, and support the pressing of the compacted bentonite assembly with different joint widths, types and numbers.

[0018] The application also provides a ring-in direct pressing method for simulating a joint-containing compacted bentonite assembly, and the method is pressed by using the ring-in direct pressing device for simulating the joint-containing compacted bentonite assembly, and the method comprises the following steps:

[0019] S1: based on the gas phase method, the suction control of the bentonite powder is carried out, and the initial water content of the powder is measured;

[0020] S2: the reserved steel sheet is embedded into the base, and the sample ring, the sample pressing ring and the sample pressing column are sequentially assembled on the base, wherein the inner wall of the sample ring and the sample pressing ring is attached to the outer wall of the sample pressing column, the sample ring is embedded into the groove of the sample pressing ring and fixed, and the sample pressing cavity is formed, at this time, the reserved steel sheet divides the sample pressing cavity into two symmetrical half cavities;

[0021] S3: the required bentonite powder mass is calculated, and the bentonite powder is weighed and poured into the half cavities divided by the reserved steel sheet in batches;

[0022] S4: the sample pressing column is sleeved with the reserved steel sheet through the joint groove, and the universal pressure machine is used to press the sample in the sample ring according to the displacement control method;

[0023] S5: After the completion of pressing, the sample pressing assembly is turned upside down, the pressure conducting sheet is fixed in the center of the base, and the reserved steel sheet is slowly pushed out to form a bentonite combination containing a joint.

[0024] Through the device and method of the application, the in-ring direct pressing of the joint-containing compacted bentonite combination is realized, the joint width change caused by the transfer of the sample from the sample pressing mold to the sample ring is avoided, and the uniformity and stability of the combination are ensured. By appropriately modifying the type and width of the joint groove of the sample pressing column and the reserved steel sheet, the in-ring direct pressing of the bentonite combination with different numbers / types of joints can be realized, which can provide experimental support for the subsequent buffer performance research of the joint-containing combination sample.

[0025] Compared with the prior art, the application has the following advantages:

[0026] 1. The in-ring direct pressing device of the application realizes the in-ring direct pressing of the joint-containing compacted bentonite combination, avoids the joint width change caused by the transfer of the sample from the sample pressing mold to the sample ring and the structural damage at the corners of the sample, and ensures the uniformity and stability of the combination.

[0027] 2. The application realizes the in-ring direct pressing of the bentonite combination with different numbers / types of joints by appropriately modifying the type and width of the joint groove of the sample pressing column and the reserved steel sheet, which provides experimental support for the subsequent buffer performance research of the joint-containing combination sample, has sufficient stability and applicability.

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

[0029] 4. The joint-containing bentonite combination sample prepared in the method of the application can be used to carry out the self-sealing / healing test of the bentonite-bentonite indirect joint and the buffer performance research of the engineering barrier in the joint evolution process, so as to evaluate the sealing effect of the compacted bentonite and provide a theoretical basis for the design and optimization of the joint. BRIEF DESCRIPTION OF DRAWINGS

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

[0031] Figure 2 It is a schematic diagram of the reserved steel sheet removal process of the application;

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

[0033] 1-sample pressing column, 2-sample pressing ring, 3-sample ring, 4-reserved steel sheet, 5-base, 6-soil powder, 7-pressure conducting sheet, 8-assistant screw. DETAILED DESCRIPTION

[0034] In order to make the purpose, technical solutions and advantages of the present application clearer, the technical solutions of the present application will be further described below.

[0035] The present embodiment proposes a device for directly pressing in a ring containing a jointed compacted bentonite assembly, as shown in the figure, which comprises a universal testing machine and a reserved steel sheet pressing-out assembly, and the sample pressing assembly is used for pressing the bentonite sample through the universal testing machine. Figure 1

[0036] In the present embodiment, the universal testing machine is a DDL-200 numerical control universal testing machine, with a maximum pressure of 300 kN, including pressure control and displacement control modes.

[0037] The sample pressing assembly comprises a sample pressing column 1, a sample pressing ring 2, a sample ring 3, a reserved steel sheet 4 and a base 5, wherein the sample ring 3 is fixed at one end on the base 5 and connected at the other end to the sample pressing ring 2 to form a ring-shaped sample pressing chamber, and the bentonite powder 6 is pressed in the sample pressing chamber.

[0038] The base 5 is provided with a groove in the center, and the reserved steel sheet 4 is inserted into the groove of the base to evenly divide the ring-shaped sample pressing chamber into two symmetrical semi-circular chambers, which are used to ensure the uniformity of the soil on both sides of the longitudinal joint and realize the control of the width of the longitudinal joint.

[0039] As shown in the figure, the sample pressing column 1 is arranged directly below the universal testing machine, and one end of the sample pressing column opposite to the groove of the base is provided with a joint groove corresponding to the groove of the base, so that when the sample pressing column 1 is pressed by the universal testing machine, the reserved steel sheet 4 standing in the sample pressing chamber is embedded in the joint groove, which not only ensures the stability of the standing reserved steel sheet, but also presets the fixation of the joint position and the removal mode of the reserved steel sheet. Figure 1 In the present embodiment, as shown in the figure, the reserved steel sheet pressing-out assembly comprises a support assembly and a pressure transmission sheet 7, wherein the support assembly is composed of the inverted sample pressing assembly after pressing, which is used to limit the boundary of the bottom of the sample and effectively reduce the soil tearing caused by friction during the extraction of the steel sheet. One end of the pressure transmission 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 transmission sheet 7, so as to separate the reserved steel sheet from the soil on both sides in the bentonite sample assembly, solve the problem of taking out the reserved steel sheet 4 in the high dry density assembly, and ensure the stability of the boundary of the bottom of the sample during the pressing-out process of the reserved steel sheet 4, preventing the soil from being torn by friction. The thickness of the pressure transmission sheet 7 is less than the thickness of the reserved steel sheet 4, and the minimum thickness is 1.5 mm, which has sufficient compressive and bending strength.

[0040] Figure 2

[0041] ​​​In this embodiment, the bottom edge of the sample ring 2 is provided with a certain height groove by two-stage cutting; the outer edge groove diameter of the sample 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 is just clamped into the outer edge groove of the sample ring 2, ensuring that the bentonite powder 6 does not overflow during the pressing process, and providing a side limit boundary for the pressed sample column 1 to reduce the risk of deformation and damage of the pressed sample column. In this embodiment, the sample ring 3 is a rigid ring directly used in the hydration test of the bentonite assembly sample, and the sample is directly pressed in the ring to avoid the change of the joint width caused by the transfer of the sample from the pressing mold to the sample ring.

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

[0043] In this embodiment, the pressed sample column 1 is used to bear the pressure applied by the universal testing machine, and the pressure is transmitted to the bentonite powder 6 in the chamber to form a bentonite assembly; one end of the pressed sample column 1 is provided with a joint groove according to the size of the reserved steel sheet 4, which facilitates the embedding of the excessively long reserved steel sheet 4 during the pressing process, and ensures the stability of the upright steel sheet, the fixation of the preset joint position and the removal mode of the reserved steel sheet; the other end of the pressed sample column 1 is provided with a threaded drill hole along the central axis of the pressed sample column, as shown in Figure 3 (a) and Figure 3 (b), the reserved steel sheet is ejected by screwing in the screw rod 8, preventing the steel sheet from being embedded in the pressed sample column groove and being difficult to disassemble. During the removal of the reserved steel sheet 4, the reserved steel sheet pressing assembly is used to press the reserved steel sheet 4 in the longitudinal joint groove of the pressed sample column 1, so as to achieve the purpose of "reserved steel sheet removal", but after this process, the steel sheet 4 will be difficult to disassemble due to a small amount of floating soil being stuck in the joint groove of the pressed sample column, at this time, the long screw rod 8 screwed into the top of the pressed sample column 1 successfully removes the steel sheet 4 from the pressed sample column 1.

[0044] In this embodiment, before pressing the bentonite powder, a movable baffle is placed above the reserved steel sheet 4, which is used to uniformly pour the bentonite powder into the two side semi-circular chambers and reduce the overflow of the bentonite powder during the stirring process.

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

[0046] The pressed sample column 1 and the reserved steel sheet 4 can freely adjust the joint width, joint type and joint number according to the test requirements, and support the pressing of the compacted bentonite assembly with different joint widths, types and numbers.

[0047] Based on the above-mentioned simulation of the ring-in direct pressing device of the joint-containing compacted bentonite assembly, the ring-in direct pressing of the joint-containing compacted bentonite assembly is carried out, and the method is as follows:

[0048] 1) Bentonite powder suction control: 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. When the total mass hardly changes, it is considered that the suction has reached the equilibrium state, and the initial moisture content of the powder is determined by the drying method.

[0049] 2) Device preparation before sample pressing: assemble the sample pressing assembly, insert the 2mm steel sheet 4 into the center groove of the base 5, and fix the sample ring 3, the sample pressing ring 2 and the sample pressing column 1 on the base 5 in turn. The inner wall of the sample ring 3 and the sample pressing ring 2 is in close 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 to form a ring-shaped pressing chamber. At this time, the reserved steel sheet 4 divides the ring-shaped pressing chamber into two equal semi-circular sample chambers.

[0050] 3) Bentonite powder weighing: according to the target size of the sample, i.e. diameter 61.8mm, height 20mm, joint width 2mm, calculate the mass of bentonite powder 6 required under the condition of target dry density and moisture content, and weigh and pour into the two semi-circular sample chambers divided by the steel sheet 4.

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

[0052] 5) Steel sheet pushing out: then reverse the sample pressing assembly, fix the pressure conducting sheet 7 at the center of the base 5, and push out the steel sheet at a rate of 1mm / min to form a bentonite assembly containing a joint. After the sample pressing is completed, measure the sample height, mass and joint width to ensure that the dry density of the bentonite assembly is within the target dry density ±0.01g / cm3.

[0053] The above is only the preferred embodiment of the present application, and does not limit the present application in any way. Any person skilled in the art can make any form of equivalent replacement, modification or change to the technical solutions and technical contents disclosed in the present application without departing from the scope of the technical solutions of the present application, which still belongs to the protection scope of the present application.

Claims

1. A ring-internal direct-pressing apparatus for simulating a joint-containing compacted bentonite assembly, characterized by, The device comprises a press, a sample pressing assembly and a reserved steel sheet pressing-out assembly, and the sample pressing assembly is pressed by the press to press the bentonite sample; The sample pressing assembly comprises 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, the other end is connected with the sample pressing ring to form a sample pressing chamber, and the bentonite powder is pressed in the sample pressing chamber; The center of the base is provided with a groove, 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 opposite to the groove of the base is provided with a joint groove corresponding to the groove of the base, so that the reserved steel sheet standing in the sample pressing chamber is embedded into the joint groove during the pressing process of the sample pressing column after the press is pressed; The reserved steel sheet pressing-out assembly comprises a support assembly and a pressure transmission sheet, the support assembly is composed of the inverted sample pressing assembly after the pressing is completed, one end of the pressure transmission sheet is connected with the press, and the other end is connected with the support assembly; 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 a screw rod to push out the reserved steel sheet; The pressure transmission sheet transmits the pressure of the press to separate the reserved steel sheet from the soil on both sides in the bentonite sample assembly, the thickness of the pressure transmission sheet is less than that of the reserved steel sheet, and the minimum thickness is 1.5 mm.

2. The in-ring direct press apparatus for simulating a jointed compacted bentonite assemblage of claim 1, wherein, The bottom edge of the sample pressing ring is two-stage cutting, the outer edge groove of the sample pressing ring has the same diameter as the outer diameter of the sample ring, so that the sample ring is embedded into the outer edge of the sample pressing ring.

3. The in-ring direct press apparatus that simulates a jointed compacted bentonite assembly of claim 1, wherein, 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, and the outer surface of the sample pressing column is in contact with the inner walls of the sample pressing ring and the sample ring.

4. The in-ring direct press apparatus that simulates a jointed compacted bentonite assembly of claim 1, wherein, Before the bentonite powder is pressed, a movable baffle is placed above the reserved steel sheet.

5. The in-ring direct press apparatus that simulates a jointed compacted bentonite assembly of claim 1, wherein, The press is a numerical control universal press, and the maximum pressure is 300 kN, which includes pressure control and displacement control modes.

6. The in-ring direct press apparatus that simulates a jointed-compacted bentonite assembly of claim 1, wherein, The sample pressing assembly and the reserved steel sheet pressing-out assembly are made of 316L stainless steel.

7. A method of ring-rolling a simulated jointed compacted bentonite assembly by using the ring-rolling apparatus for a simulated jointed compacted bentonite assembly according to any one of claims 1 to 6, characterized by, The method comprises the following steps: S1: The bentonite powder is controlled by suction force, and the initial water content of the powder is measured; S2: The reserved steel sheet is embedded into 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 in contact with the outer wall of the sample pressing column, the sample ring is embedded into the groove of the sample pressing ring to be fixed, a sample pressing chamber is formed, and the reserved steel sheet divides the sample pressing chamber into two symmetrical half chambers; S3: The required mass of the bentonite powder is calculated, and the bentonite powder is weighed and poured into the half chamber divided by the reserved steel sheet in batches; S4: The sample pressing column is sleeved with the reserved steel sheet through the joint groove, a universal press is used, and the sample pressing is carried out in the sample ring according to the displacement control method; S5: After the pressing is completed, the sample pressing assembly is inverted, the pressure transmission sheet is fixed at the center of the base, the reserved steel sheet is slowly pushed out, and a bentonite assembly containing a joint is formed.

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