A preparation device and method for circular bentonite blocks based on multi-step displacement control

Abstract

The present invention provides a preparation device and method for circular bentonite blocks based on multi-step displacement control. The device includes a hydraulic universal testing machine, a sample pressing ring, a sleeve, a central column, a base, a sample pushing column, and a sample pushing ring. Using the multi-step displacement control method with the universal testing machine, the target displacement is evenly divided into multiple parts and pressed sequentially. Whenever the single-part target displacement is reached, a constant pressure is maintained to fully adjust the spatial arrangement of bentonite particles. After the sample pressing is completed, the sample pushing column and the sample pushing ring are assembled, and the block is evenly pushed out from between the sleeve and the central column by means of the universal testing machine, reducing the disturbance to the uniformity of the block during the sample pushing process. The present invention provides an experimental device and method for effectively preparing circular bentonite blocks, ensuring the integrity and uniformity of the blocks while controlling the sample pressing accuracy within 1%. The circular bentonite blocks prepared can effectively replace the sector-shaped bentonite blocks, reducing the adverse impact of the construction joints formed during the splicing process on the buffering performance of the engineering barrier.

Description

Technical Field

[0001] The present invention belongs to the technical field of civil engineering, and particularly relates to a device and method for preparing circular bentonite blocks based on multi-step displacement control. Background Art

[0002] The rapid development of nuclear energy will inevitably generate a large amount of high-level radioactive waste (hereinafter referred to as "HLW"). How to safely dispose of it has become the key to restricting the sustainable development of nuclear energy. Currently, deep geological disposal is generally considered the most feasible and reliable disposal solution internationally, that is: placing HLW in mine tunnels or tunnels about 250 to 1000 meters below the ground surface, and realizing the effective isolation of HLW from the biosphere through a multi-barrier system composed of surrounding rock natural barriers, engineering barriers, and metal cans. Among them, compacted bentonite is regarded as the preferred engineering barrier material due to its excellent properties such as high swelling, low permeability, and strong radionuclide adsorption.

[0003] During the actual construction of the disposal repository, bentonite powder is often pre-pressed into 1 / 6 or 1 / 2 sector-shaped blocks, and then spliced and stacked between the surrounding rock natural barrier and the metal can to form an engineering barrier. However, during the process of splicing and stacking the blocks to form an engineering barrier, a large number of construction joints / interfaces will inevitably be formed between the bentonite blocks. When groundwater infiltrates, although these construction joints / interfaces will be spontaneously sealed / healed due to the hydration swelling behavior of bentonite, on an extremely long time scale, the initial construction joint / interface area will still exist as a preferential seepage channel and mechanical weakness, thus affecting the effective play of the buffer function of the engineering barrier. If circular bentonite blocks can be prepared and replace the sector-shaped blocks during actual construction, the adverse effects of block construction joints on the buffer performance of the engineering barrier can be effectively avoided. Unfortunately, currently, there is no reported preparation method for circular bentonite block specimens. In addition, research on hydraulic fracturing related to bentonite, research on the self-sealing behavior of the circumferential joint between the block and the metal can, etc., also face the need to prepare circular bentonite blocks. Based on the above, it is of great practical significance to develop a test device that can be used to prepare circular bentonite blocks.

[0004] Existing soil compaction technologies, such as dynamic compaction vibration, spinning loading, air pump action, etc., all have certain defects when applied to the preparation of bentonite blocks, mainly reflected in:

[0005] 1) The target dry density of bentonite blocks is relatively high, showing a high compaction state, and conventional compaction technologies are difficult to reach the required pressure;

[0006] 2) The pressing accuracy is not high, the specimen size error is relatively large, and it is mostly inhomogeneously distributed along the compaction direction. The disposal repository aims at operating for tens of thousands of years, and has extremely high requirements for construction quality.

[0007] Therefore, ensuring the accuracy, integrity, and uniformity of the compacted blocks is also an important technical issue. Summary of the Invention

[0008] The object of the present invention is to provide a preparation device for circular bentonite blocks based on multi-step displacement control, which is characterized by including a sample pressing control component, a sample pushing control component, and a hydraulic universal testing machine. The sample pressing control component presses the sample through the hydraulic universal testing machine and takes out the sample through the sample pushing control component.

[0009] The sample pressing control component includes a base, a through hole is provided in the middle of the base; a central column is placed above the through hole; a sleeve is placed around the central column; on the upper surface of the base, a circular sample pressing chamber is formed between the sleeve and the central column, and the sample pressing chamber is used to place bentonite powder; a sample pressing ring is movably inserted into the sample pressing chamber.

[0010] The hydraulic universal testing machine is installed above the sample pressing control component and is used to drive the sample pressing ring to displace downward in the sample pressing chamber.

[0011] Further, two layers of step layers are coaxially provided on the upper surface of the base. The inner diameter of the first step layer at the top is larger than the inner diameter of the second step layer at the bottom. The inner diameter of the second step layer is larger than the diameter of the through hole, and the middle parts of the two step layers are communicated with the through hole.

[0012] Further, the diameter of the central column is the same as the inner diameter of the second step layer and is movably embedded in the second step layer;

[0013] The outer diameter of the sleeve is the same as the inner diameter of the first step layer, and one end of the sleeve is embedded in the first step layer;

[0014] The ring width of the sample pressing ring is the same as the ring width of the circular sample pressing chamber. When pressing the bentonite block, the sum of the height of the bentonite block and the height of the sample pressing ring is greater than the depth of the sample pressing chamber.

[0015] Further, the sample pushing control component includes a columnar sample pushing column and a circular sample pushing ring. The diameter of the sample pushing column is smaller than the diameter of the through hole; the ring width of the sample pushing ring is smaller than the ring width of the sample pressing chamber. The outer diameter of the sample pushing ring is smaller than the outer diameter of the sample pressing chamber, the inner diameter of the sample pushing ring is larger than the inner diameter of the sample pressing chamber, and the height of the sample pushing ring is greater than the height of the bentonite block.

[0016] Further, by changing the inner diameter of the sleeve and the diameter of the central column, circular bentonite blocks with different inner and outer diameter sizes can be prepared.

[0017] Further, the sample pressing ring, the sleeve, the central column, the base, the sample pushing column, and the sample pushing ring are all made of 316L stainless steel.

[0018] Further, the hydraulic testing machine for completion is a DDL-200 type numerically controlled universal press, including a pressure control operation mode and a displacement control operation mode.

[0019] A preparation method of a circular bentonite block based on multi-step displacement control is completed by using a preparation device for a circular bentonite block based on multi-step displacement control, and is characterized by including the following steps:

[0020] S1: Embed the central column into the second step layer of the base, and embed one end of the sleeve into the first step of the base to form a sample pressing chamber;

[0021] S2: Pour the bentonite powder that has completed suction balance in advance into the sample pressing chamber, and insert the sample pressing ring into the sample pressing chamber;

[0022] S3: Use a hydraulic universal testing machine to drive the sample pressing ring to displace towards the bentonite powder in the sample pressing chamber to complete the pressing of the circular bentonite block;

[0023] S4: Take out the circular bentonite block from the sample pressing control component through the hydraulic universal testing machine and the sample pushing control component to complete the preparation of the circular bentonite block.

[0024] Further, in S3, the pressing of the circular bentonite block is specifically as follows: Based on the multi-step displacement control method, calculate the target pressing displacement, divide the target displacement into multiple equal parts, and successively use the hydraulic universal testing machine to press at a descending rate of 0.5 mm / min; Whenever the single-target displacement is reached, stand still for 1 h to fully adjust the spatial arrangement of the bentonite particles to avoid sample rebound and uneven distribution along the compaction direction.

[0025] Further, in S4, taking out the circular bentonite block from the sample pressing control component specifically includes the following steps:

[0026] S41: After the sample pressing is completed, invert the sample pressing control component, insert the sample pushing column into the through hole of the base, and use the hydraulic universal testing machine to push the central column out of the pressed circular bentonite block at a descending rate of 1 mm / min, so as to reduce the disturbance to the uniformity of the block during the sample pushing process;

[0027] S42: Disassemble the base, place the sample pushing ring on the top of the sleeve, and use the hydraulic universal testing machine to push the pressed circular bentonite block out of the sleeve at a descending rate of 1 mm / min to obtain the circular bentonite block.

[0028] Compared with the prior art, the beneficial effects of the present invention are mainly reflected in:

[0029] 1. Effective preparation of circular bentonite blocks: The test device and the sample preparation method based on multi-step displacement control proposed in the present invention can meet the requirements for preparing high-quality circular bentonite blocks. While controlling the sample pressing accuracy within 1%, the integrity of the blocks and the uniformity along the compaction direction are ensured. The pressed circular bentonite blocks can effectively replace the fan-shaped bentonite blocks, reducing the adverse effects of construction joints formed during the splicing process on the buffering performance of the engineering barrier.

[0030] 2. Flexible adjustment of block size: By changing the inner diameter of the sleeve and the diameter of the central column, circular bentonite blocks of different sizes can be prepared. When the inner diameter size is small, it is equivalent to preparing a specimen with a central hole, which is suitable for the study of hydraulic fracturing tests of compacted bentonite or other situations where a central hole is required.

[0031] 3. Self-sealing / healing test research: The circular bentonite blocks prepared according to the present invention can be used to carry out self-sealing / healing test research on the circumferential joint between bentonite and the metal can, so as to evaluate the sealing effect of the compacted bentonite and provide a theoretical basis for the design and optimization of the circumferential joint.

[0032] 4. The technical solution of the present invention is of great significance in the preparation and test research of circular bentonite blocks. It can not only provide a method to effectively replace the fan-shaped blocks, avoiding the adverse effects caused by construction joints / interfaces, but also provide substantial support for the research on the hydraulic fracturing characteristics of compacted bentonite and the self-sealing / healing characteristics of the circumferential joint between bentonite and the metal can. These beneficial effects will promote the optimization of the engineering barrier design and construction schemes in the field of deep geological disposal of high-level radioactive waste. Description of the Drawings

[0033] Figure 1 It is a schematic structural diagram of a device for preparing circular bentonite blocks based on multi-step displacement control according to the present invention.

[0034] Figure 2 It is a three-dimensional structure diagram of the sample pressing control component according to the present invention.

[0035] Figure 3 It is the front view and top view of the base according to the present invention.

[0036] Figure 4 It is a three-dimensional schematic flow diagram of a method for preparing circular bentonite blocks based on multi-step displacement control according to the present invention.

[0037] Among them, 1. Hydraulic universal testing machine; 2. Sample pressing ring; 3. Sleeve; 4. Central column; 5. Specimen; 6. Base; 7. Sample pushing column; 8. Sample pushing ring; 9. First step layer; 10. Second step layer. Detailed Embodiments

[0038] The following will describe in more detail a preparation device and method for circular bentonite blocks based on multi-step displacement control of the present invention with reference to schematic diagrams, in which the preferred embodiments of the present invention are shown. It should be understood that those skilled in the art can modify the present invention described herein while still achieving the advantageous effects of the present invention. Therefore, the following description should be understood as a broad guidance for those skilled in the art and not as a limitation to the present invention.

[0039] As Figure 1 and 2 shown, the present invention provides a preparation device for circular bentonite blocks based on multi-step displacement control, which includes a hydraulic universal testing machine 1, a sample pressing control component, and a sample pushing control component.

[0040] The hydraulic universal testing machine 1 is a DDL-200 type numerical control universal press with a maximum pressure of 300 kN, supporting two operating modes of pressure control and displacement control. The hydraulic universal testing machine 1 is erected above the sample pressing control component.

[0041] The sample pressing control component includes a sample pressing ring 2, a sleeve 3, a central column 4, and a base 6.

[0042] Both the sleeve 3 and the central column 4 are arranged on the upper surface of the base 6. Among them, the sleeve 3 is arranged on the outer periphery of the central column 4, and the diameter of the central column 4 is smaller than the inner diameter of the sleeve 3, so as to form an annular sample pressing chamber between the sleeve 3 and the central column 4 for placing the bentonite powder for preparing circular bentonite blocks. The ring width of the sample pressing ring 2 is the same as the ring width of the sample pressing chamber. By inserting the sample pressing ring 2 into the sample pressing chamber and bearing the downward pressure applied by the hydraulic universal testing machine 1, the sample pressing ring 2 moves downward in the sample pressing chamber and transmits the pressure to the bentonite powder, so that it is compacted into a circular bentonite block.

[0043] It should be noted that when pressing the circular bentonite block, the inner wall and outer wall of the sample pressing ring 2 need to be respectively attached to the outer wall of the central column 4 and the inner wall of the sleeve 3, and the sum of the height of the sample pressing ring 2 and the height of the prepared target circular bentonite block needs to be greater than the depth of the sample pressing chamber. The present invention can prepare circular bentonite blocks with different inner and outer diameter sizes by changing the inner diameter of the sleeve 3 and the diameter of the central column 4.

[0044] The sample pushing control component is used to cooperate with the hydraulic universal testing machine 1 to disassemble the sample pressing control component, so as to take out the prepared circular bentonite block without affecting the integrity and precision requirements of the block.

[0045] Referring to Figure 3 , to meet the above requirements, the sample pushing control component includes a sample pushing column 7 and a sample pushing ring 8. The upper surface of the base 6 is coaxially concaved inward with 2 layers of steps, and a through hole is provided through the 2 layers of steps and the center of the base 6.

[0046] Specifically, a through hole is provided at the center of the base 6. The upper surface of the base is recessed inward to form a first stepped layer 9 and an upwardly protruding border. The sleeve 3 is then movably inserted into the first stepped layer 9 on the upper surface of the base through the border.

[0047] At the through hole at the center within the first stepped layer 9, a second stepped layer 10 is recessed inward. The inner diameter of the second stepped layer 10 is smaller than the inner diameter of the first stepped layer 9 and larger than the diameter of the through hole. Correspondingly, the diameter of the central column 4 is the same as the inner diameter of the second stepped layer 10. When the central column 4 is inserted into the second stepped layer 10, the outer circumference of the central column 4 fits against the inner wall of the second stepped layer 10.

[0048] The diameter of the sample pushing column 7 in the sample pushing control assembly is smaller than the through hole and is used to push the central column 4 (the diameter of the central column is larger than the through hole) out of the second stepped layer 10 from the through hole. The ring width of the sample pushing ring 8 in the sample pushing control assembly is smaller than the ring width of the sample pressing chamber, and its outer diameter is smaller than its outer diameter, its inner diameter is larger than its inner diameter, and its height is not less than the height of the bentonite block. When using the sample pushing ring, by abutting the end face of one end of the sample pushing ring against the middle of the end face of the sleeve 3 and cooperating with the hydraulic universal testing machine 1, the disassembly of the sample pressing ring 2 is completed.

[0049] In the present invention, the sample pressing ring 2, the sleeve 3, the central column 4, the base 6 that constitute the sample pressing control assembly, and the sample pushing column 7 and the sample pushing ring 8 that constitute the sample pushing control assembly are all made of 316L stainless steel with good wear resistance and high stiffness.

[0050] The test device and the sample preparation method based on multi-step displacement control proposed by the present invention can meet the requirements for preparing high-quality circular bentonite blocks. While controlling the sample pressing accuracy within 1%, it ensures the integrity of the blocks and the uniformity along the compaction direction. The prepared specimen 5 can be used to replace the fan-shaped blocks, reducing the existence of construction joints / interfaces inside the engineering barrier and their adverse effects on the buffering performance of the engineering barrier. At the same time, it can be used to carry out experimental studies on the self-sealing / healing of the circumferential joints between bentonite and metal cans to evaluate the sealing effect of the compacted bentonite. When the inner diameter size is small, it is equivalent to preparing a specimen with a central hole and can be used for experimental studies on the hydraulic fracturing of compacted bentonite.

[0051] As Figure 4 shown, the test method of the present invention applied to the preparation of circular bentonite blocks is as follows:

[0052] 1) Sample pressing chamber construction: Insert the central column 4 into the second stepped layer 10 of the base 6, and insert the sleeve 3 into the first stepped layer 9 at the top of the base 6 to assemble and form a sample pressing chamber, corresponding to Figure 4 Steps Ⅰ - Ⅲ in

[0053] 2) Compression of Specimen 5: Pour the bentonite powder that has completed the suction balance in advance into the sample pressing chamber, and cover it with the sample pressing ring 2; Based on the multi-step displacement control method, calculate the target pressing displacement. Divide the target displacement into multiple equal parts, and successively use the hydraulic universal testing machine 1 to press at a descending rate of 0.5 mm / min; Whenever the single-part target displacement is reached, let it stand for 1 h to fully adjust the spatial arrangement of the bentonite particles, avoiding sample rebound and uneven distribution along the compaction direction, corresponding to Figure 4 Step Ⅳ in

[0054] 3) Pushing out of the Central Column 4: Invert the device, insert the sample pushing column 7 into the through hole of the base 6, and use the hydraulic universal testing machine 1 to push out the central column 4 from the pressed circular bentonite block at a descending rate of 1 mm / min, reducing the disturbance to the uniformity of the block during the sample pushing process. Then disassemble the base 6, corresponding to Figure 4 Steps Ⅵ-Ⅴ in

[0055] 4) Pushing out of Specimen 5: Place the sample pushing ring 8 on the top of the sleeve 3, and use the hydraulic universal press 1 to push out the pressed circular bentonite block from the sleeve 3 at a descending rate of 1 mm / min, and then a circular bentonite block can be obtained, corresponding to Figure 4 Steps Ⅶ-Ⅷ in

[0056] Taking the circular specimen 5 with a dry density of 1.7 g / cm3, a height of 20 mm, and inner and outer diameters of 61.8 mm and 100 mm respectively as an example. After the sample preparation is completed, the circular bentonite block is evenly divided into 4 equal parts horizontally, and then each equal part is divided into 3 equal parts vertically, a total of 12 equal parts, which are respectively used for dry density and microstructure tests. The results show that the maximum dry density in the horizontal direction is 1.706 g / cm3, the minimum is 1.694 g / cm3, and the average is 1.701 g / cm3; The maximum dry density in the vertical direction is 1.711 g / cm3, the minimum is 1.692 g / cm3, and the average is 1.704 g / cm3. The microscopic pore structure obtained from the mercury intrusion test also shows a similar pore size distribution characteristic, which indicates that the sample preparation device and method provided by the present invention can ensure the accuracy, integrity, and uniformity of the pressed circular bentonite block specimens.

[0057] The above are only the preferred embodiments of the present invention and do not impose any limitation on the present invention. Any person skilled in the art, within the scope of 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 belong to the content within the scope of the technical solution of the present invention and still fall within the protection scope of the present invention.

Claims

1. A preparation method of a circular bentonite block based on multi-step displacement control, characterized in that The preparation is completed by using a circular bentonite block preparation device based on multi-step displacement control, including the following steps: S1: Embed one end of the central column into the second step layer of the base, and embed one end of the sleeve into the first step layer of the base to form a sample pressing chamber; S2: Pour the pre-completed bentonite powder with balanced suction into the sample pressing chamber, and insert the sample pressing ring into the sample pressing chamber; S3: Use a hydraulic universal testing machine to drive the sample pressing ring to displace towards the bentonite powder in the sample pressing chamber to complete the pressing of the circular bentonite block; S4: Take out the circular bentonite block from the sample pressing control component through the hydraulic universal testing machine and the sample pushing control component to complete the preparation of the circular bentonite block; In S3, the pressing of the circular bentonite block is specifically as follows: Based on the multi-step displacement control method, calculate the target pressing displacement, divide the target displacement into multiple equal parts, and successively use the hydraulic universal testing machine to press at a descending rate of 0.5 mm / min; Whenever the single-target displacement is reached, let it stand for 1 h to fully adjust the spatial arrangement of the bentonite particles to avoid sample rebound and uneven distribution along the compaction direction; The circular bentonite block preparation device based on multi-step displacement control includes a sample pressing control component, a sample pushing control component, and a hydraulic universal testing machine (1). The sample pressing control component presses the sample (5) through the hydraulic universal testing machine and takes out the sample through the sample pushing control component; In S4, taking out the circular bentonite block from the sample pressing control component specifically includes the following steps: S41: After the sample pressing is completed, invert the sample pressing control component, insert the sample pushing column into the through hole of the base, and use the hydraulic universal testing machine to push the central column out of the completed circular bentonite block at a descending rate of 1 mm / min, so as to reduce the disturbance of the uniformity of the block during the sample pushing process; S42: Disassemble the base, place the sample pushing ring on the top of the sleeve, and use the hydraulic universal testing machine to push the completed circular bentonite block out of the sleeve at a descending rate of 1 mm / min to obtain the circular bentonite block The sample pressing control component includes a base (6), and a through hole is provided in the middle of the base; Above the through hole, a central column (4) is placed on the upper surface of the base; A sleeve (3) is placed on the outer circumference of the central column; On the upper surface of the base, a circular sample pressing chamber is formed between the sleeve and the central column, and the sample pressing chamber is used to place bentonite powder; The sample pressing ring (2) is movably inserted into the sample pressing chamber; The hydraulic universal testing machine is installed above the sample pressing control component and is used to drive the sample pressing ring to displace downward in the sample pressing chamber.

2. The preparation method of the circular bentonite block based on multi-step displacement control according to claim 1, characterized in that, Two step layers are coaxially provided on the upper surface of the base. The inner diameter of the first step layer (9) at the top is larger than the inner diameter of the second step layer (10) at the bottom. The inner diameter of the second step layer is larger than the diameter of the through hole, and the middle parts of the two step layers are communicated with the through hole.

3. The preparation method of the circular bentonite block based on multi-step displacement control according to claim 2, characterized in that, The diameter of the central column is the same as the inner diameter of the second step layer and is movably embedded in the second step layer; The outer diameter of the sleeve is the same as the inner diameter of the first step layer, and one end of the sleeve is embedded in the first step layer; The ring width of the sample pressing ring is the same as that of the annular sample pressing chamber. When pressing bentonite blocks, the sum of the height of the bentonite block and the height of the sample pressing ring is greater than the depth of the sample pressing chamber.

4. The preparation method of the circular bentonite block based on multi-step displacement control according to claim 2, wherein The sample pushing control assembly includes a columnar sample pushing column (7) and an annular sample pushing ring (8). The diameter of the sample pushing column is smaller than the diameter of the through hole; the ring width of the sample pushing ring is smaller than the ring width of the sample pressing chamber, the outer diameter of the sample pushing ring is smaller than the outer diameter of the sample pressing chamber, and the inner diameter of the sample pushing ring is larger than the inner diameter of the sample pressing chamber; the height of the sample pushing ring is greater than the height of the bentonite block.

5. The preparation method of the annular bentonite block based on multi-step displacement control according to claim 2, characterized in that, By changing the inner diameter of the sleeve and the diameter of the central column, circular bentonite cut blocks with different inner and outer diameter sizes are prepared.

6. The preparation method of the circular bentonite block based on multi-step displacement control according to claim 2, characterized in that, The sample pressing ring, sleeve, central column, base, sample pushing column and sample pushing ring are all made of 316L stainless steel.

7. The preparation method of the circular bentonite block based on multi-step displacement control according to claim 1, characterized in that, The hydraulic testing machine is a DDL-200 type numerical control universal testing machine, including a pressure control operation mode and a displacement control operation mode.

Images