Device and use for testing interface permeability of high-compacted bentonite composites

Abstract

A device for testing the interface permeability of a high-compacted bentonite assembly, the testing device mainly includes four parts: a constant volume experimental device, a permeability auxiliary device, a control and measurement device, and a sample pressing auxiliary device. The constant volume experimental device provides functions such as sample preparation, sample combination, and deformation restriction. The permeability auxiliary device provides functions such as positioning, channeling, and filtering required for seepage along the interface. The control and measurement device provides functions such as water pressure / flow rate control, flow / water pressure measurement and recording, and expansion force measurement and recording. The sample pressing auxiliary device provides functions such as blocking required for sample preparation. The present invention realizes the automated testing of the constant volume expansion force of a high-compacted bentonite assembly, the interface permeability properties of the assembly, and the hydraulic splitting and self-healing properties of the assembly interface. The present invention can be used for the study of the expansion-permeability properties of a high-compacted bentonite assembly, and can also be used for the study of the hydraulic splitting and self-healing properties of the assembly interface.

Description

Technical Field

[0001] The invention belongs to the technical field of civil engineering (geotechnical) and geological engineering, and relates to a device for testing the interface permeability properties of a high-density bentonite assembly. Background Art

[0002] High-level radioactive waste is characterized by strong radioactivity, long half-life and high toxicity. At present, deep geological disposal is a recognized and feasible disposal method, which seals it in deep rock formations and uses multiple barriers to block the migration of nuclides to the external environment. In the concept of deep geological disposal, the buffer backfill materials in the engineering barrier should have key functions such as maintaining the stability of the engineering structure, preventing groundwater seepage, and blocking the migration of nuclides. After years of comparative research, bentonite-based materials have been selected by various countries as buffer and backfill materials for deep geological disposal repositories due to their properties such as strong expansion, low permeability and strong adsorption.

[0003] In the concept of deep geological disposal, the engineering barrier system is usually built with high-compacted bentonite blocks. Three types of interfaces will be formed in the engineering barrier system: the interface between the high-level waste tank and the compacted bentonite, the interface between the compacted bentonite assembly, and the interface between the compacted bentonite and the surrounding rock. These interfaces determine the physical and mechanical integrity of the engineering barrier and will affect its chemical-hydraulic-mechanical buffering capacity to a certain extent. After the disposal repository is closed, groundwater in the surrounding rock continues to infiltrate the engineering barrier. Various interfaces, as dominant seepage channels, determine the saturation process of the engineering barrier system. On the other hand, due to the special self-sealing-healing ability of high-compacted bentonite, the interface of the high-compacted bentonite assembly will gradually close, cement, and heal during the seepage process, which plays a positive role in enhancing the hydraulic barrier capacity. At the same time, the existence of the interface will lead to a decrease in the saturated expansion force and an increase in the permeability coefficient, and the interface of the high-compacted bentonite assembly after healing may still be a hydraulically weak position. Therefore, it is necessary to study the expansion-permeability properties of the interface of the high-compacted bentonite assembly, and then evaluate the hydraulic healing capacity of the engineering barrier system.

[0004] In view of the interface problem in the engineering barrier system, the existing research mainly conducts indoor experiments to explore the expansion-permeability properties of the waste tank-compacted bentonite interface and the compacted bentonite-surrounding rock interface, and the seepage medium used is water or air. However, no research has been conducted on the expansion-permeability properties of the interface between high-pressure compacted bentonites (combinations). Summary of the invention

[0005] The purpose of the present invention is to provide a testing device for studying the interface permeability properties of high-compacted bentonite assemblies, to carry out indoor experimental research, and to provide a scientific basis for the research work of deep geological disposal repositories.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is:

[0007] A device for testing the interface permeability of a high-compression bentonite assembly includes four parts: a constant volume experimental device, a permeability auxiliary device, a control and measurement device, and a sample pressing auxiliary device:

[0008] The constant volume experimental device provides functions such as sample preparation, sample combination and deformation limitation;

[0009] The infiltration assist device provides the positioning, channeling and filtering functions required for seepage along the interface;

[0010] The control and measurement device provides functions such as water pressure / flow rate control, flow / water pressure measurement and recording, expansion force measurement and recording, etc.

[0011] The sample pressing auxiliary device provides functions such as sealing required for sample preparation.

[0012] The constant volume experimental device is the main part of the test device and is used in the entire test stage; the sample pressing auxiliary device is only used in the sample pressing stage, and is installed in an embedded manner on the left and right sides of the constant volume experimental device, and is removed after the sample pressing is completed; the penetration auxiliary device is used in the penetration stage, and is installed in an embedded manner on the left and right sides of the constant volume experimental device; the control and measurement device is used in the penetration stage, and is connected to the left and top of the constant volume experimental device by pipelines and threads. The above components are installed and used as needed.

[0013] further:

[0014] 1) The constant volume experimental device includes a base, a sample ring, a top cover, a stud, a piston, a sealing ring, and a sample. The base, sample ring, top cover, piston, and stud are all made of stainless steel. The sample ring and the top cover are respectively provided with four through holes, and are connected to the base with four bolts, wherein the sample ring is fixed to the base with nuts and is in close contact with the base, and the top cover is fixed to the top of the bolts with nuts. The sample is located inside the base, and is composed of upper and lower parts tightly spliced ​​together. The piston is embedded in the sample ring and pressed on the sample. Annular sealing grooves are respectively provided between the sample ring and the piston, and between the sample ring and the base, and sealing rings are installed.

[0015] 2) The penetration auxiliary device includes a pipe joint, a thin-walled tube, a water-permeable block, and filter paper. The pipe joint and the thin-walled tube are made of stainless steel, and the water-permeable block is made of sintered copper. Two sets of auxiliary penetration devices are respectively installed in two horizontal penetration holes symmetrically distributed along the axis on the base. From the outside to the inside, they are the pipe joint, the thin-walled tube, the water-permeable block, and the filter paper, and they are in close contact. The filter paper is in direct contact with the sample.

[0016] 3) The control and measurement device includes computer control software, water pressure / flow controller, pressure sensor, sensor screw, and paperless recorder. The water pressure / flow controller is connected to the pipe joint by a polytetrafluoroethylene hose, connected to the computer by a cable, and the water pressure / flow is controlled by the control software, and the permeation flow / pressure is automatically recorded. The pressure sensor is fixed to the lower part of the top cover and the upper part of the piston by four screws. The probe of the pressure sensor is embedded in the groove at the top of the piston. The paperless recorder is connected to the pressure sensor by a cable to automatically record and store the expansion force data.

[0017] 4) The sample pressing auxiliary device includes a plunger, a connecting piece, and a connecting piece screw. The plunger can be inserted into and block the two horizontal penetration holes on the base. The outer end of the plunger is connected to the upper end of the connecting piece through a thread. The lower end of the connecting piece is fixed to the base by a connecting piece screw.

[0018] Optionally, the device for high-pressure compacted bentonite assembly interface permeability testing can press a lower sample to be tested and an upper sample to be tested in a base and a sample ring, respectively, and push the upper sample in the sample ring into the base to complete a tight splicing with the lower sample, thereby avoiding the formation of a dominant seepage channel other than the splicing interface.

[0019] Optionally, the device for testing the interface permeability of a high-density bentonite assembly has horizontal permeable holes on both sides of the joint interface, and uses the permeability auxiliary device so that the hydration and permeation of the sample are preferentially carried out along the interface of the assembly.

[0020] Optionally, a computer control software module and a water pressure / flow controller are used to control the water pressure / flow rate, measure and record the corresponding flow / water pressure, use a pressure sensor to measure the expansion force of the assembly, and a paperless recorder to display and store the expansion force data in real time.

[0021] Optionally, the sample pressing auxiliary device is used to block the horizontal penetration holes and press the lower sample in the base.

[0022] The invention can carry out both constant pressure controlled interface permeation experiments and constant flow controlled interface permeation experiments.

[0023] The invention can be used for the research of the expansion-permeability property of the high-compression bentonite assembly, and can also be used for the research of the hydraulic splitting and self-healing property of the assembly interface.

[0024] Due to the adoption of the above technical solution, the beneficial effects obtained by the present invention include:

[0025] 1) The present invention realizes the automated testing of the interfacial permeability properties of high-compacted bentonite assemblies under constant water pressure or constant flow rate conditions.

[0026] 2) The present invention realizes the automated testing of the self-healing properties of the interface of a high-compacted bentonite assembly under constant water pressure or constant flow rate conditions.

[0027] 3) The present invention realizes the automated test of the expansion force evolution of high-compacted bentonite assemblies under constant water pressure or constant flow rate conditions.

[0028] 4) The test device of the present invention is low in price, has a high degree of automation, is generally reliable and easy to use, and is practical in this field. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a front view of a constant volume experimental device, a permeation auxiliary device, and a control and measurement device according to an embodiment of the present invention.

[0030] Figure 2 for Figure 1 AA' cross-sectional view of the illustrated embodiment.

[0031] Figure 3 This is a structural diagram of an embodiment of the penetration assist device provided by the present invention.

[0032] Figure 4 A structural diagram of an embodiment of the sample pressing auxiliary device provided by the present invention.

[0033] Among them: 1 base; 2 sample ring; 3 top cover; 4 bolts; 5 piston; 6a first sealing ring; 6b second sealing ring; 7a upper sample; 7b upper sample; 8 pipe joint; 9 thin-walled tube; 10 water-permeable block; 11 filter paper; 12 computer control software module; 13 water pressure / flow controller; 14 pressure sensor; 15 sensor screw; 16 paperless recorder; 17 plunger; 18 connecting piece; 19 connecting piece screw. DETAILED DESCRIPTION

[0034] The present invention aims at the interface of the buffer backfill material assembly in the deep geological disposal repository, and invents a high-density bentonite assembly interface permeability property testing device, which analyzes the expansion-permeability property of the high-density bentonite assembly interface under the action of groundwater seepage from the perspective of indoor experiments, and provides a basis for studying the hydraulic state evolution of the engineering barrier system. The method of the present invention is simple, has a lot of automated sampling data, is reliable and easy to implement, and the results can provide a basic basis for the design, construction and safety assessment of the engineering barrier system of the high-level waste disposal repository, and has important engineering significance and practical value.

[0035] The present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0036] like Figures 1 to 4As shown, the present invention provides a testing device for the interfacial permeability properties of a high-compressed bentonite assembly, comprising four parts: a constant volume experimental device, a permeability auxiliary device, a control and measurement device, and a sample pressing auxiliary device:

[0037] 1) The constant volume experimental device includes a base 1, a sample ring 2, a top cover 3, a bolt 4, a piston 5, a sealing ring (including a first sealing ring 6a, a second sealing ring 6b), and a sample (including an upper sample 7a and a lower sample 7b). The base 1, the sample ring 2, the top cover 3, the bolt 4, and the piston 5 are all made of stainless steel. The sample ring 2 and the top cover 3 are respectively provided with four through holes, and are connected to the base 1 by four bolts 4, wherein the sample ring 2 is fixed on the base 1 by nuts and is in close contact with the base 1, and the top cover 3 is fixed to the top of the bolt 4 by nuts. The sample is located inside the base 1, and is formed by closely splicing the upper sample 7a and the lower sample 7b. The piston 5 is embedded in the sample ring 2 and pressed on the sample 7a. Annular sealing grooves are respectively provided between the sample ring 2 and the piston 5, and between the sample ring 2 and the base 1, and the first sealing ring 6a and the second sealing ring 6b are respectively installed in the annular sealing grooves.

[0038] 2) The infiltration auxiliary device includes a pipe joint 8, a thin-walled tube 9, a water-permeable block 10, and a filter paper 11. The pipe joint 8 and the thin-walled tube 9 are made of stainless steel, and the water-permeable block 10 is made of metal, and in this embodiment, it is made of sintered copper. The two sets of auxiliary infiltration devices are respectively installed in two horizontal infiltration holes symmetrically distributed along the axis (A-A') on the base. From the outside to the inside, they are the pipe joint 8, the thin-walled tube 9, the water-permeable block 10, and the filter paper 11, and they are in close contact. The filter paper 11 is in contact with the sample.

[0039] 3) The control and measurement device includes a computer control software module 12, a water pressure / flow controller 13, a pressure sensor 14, a sensor screw 15, and a paperless recorder 16. The water pressure / flow controller 13 is connected to the pipe joint 8 by a polytetrafluoroethylene hose, and is connected to the computer control software module 12 through a cable to control the water pressure / flow and automatically record the permeation flow / pressure. The pressure sensor 14 is fixed to the lower part of the top cover 3 and the upper part of the piston 5 by four sensor screws 15. The probe of the pressure sensor 14 is embedded in the groove at the top of the piston 5. The paperless recorder 16 is connected to the pressure sensor 14 by a cable to automatically record and store the expansion force data.

[0040] 4) The sample pressing auxiliary device includes a plunger 17, a connecting piece 18, and a connecting piece screw 19. The plunger 17 can be inserted into and block the two horizontal penetration holes on the base 1. The outer end of the plunger 17 is connected to the upper end of the connecting piece 18 through a thread. The lower end of the connecting piece 18 is fixed to the base 1 by a connecting piece screw 19.

[0041] The working mode of the high-density bentonite assembly interface permeability test device of the present invention is as follows:

[0042] 1) Preparation of lower sample: The size of the lower sample is 50 mm in diameter, 10 mm in height, and the dry density is 1.7 g / cm 3 . Calculate the mass of bentonite powder required based on the dry density and moisture content of bentonite powder. After the base and sample ring are connected with studs and tightened with nuts, the sample pressing auxiliary device (plunger, connecting piece and connecting piece screw) is used to block the penetration holes on both sides of the base, and the position of the plunger is adjusted and fixed to just block the penetration holes. Pour the bentonite powder into the base, put in a 50mm diameter stainless steel sample pressing rod, and use an electronic universal testing machine to press it to the preset position at a loading rate of 0.5mm / min; after standing for one hour, unload the pressure at a rate of 20kN / min and remove the sample pressing rod.

[0043] 2) Preparation of upper sample: The upper sample size is 50 mm in diameter, 10 mm in height, and has a dry density of 1.7 g / cm 3 After the lower sample is pressed, the sample ring is separated from the base. The upper sample is pressed in the sample ring. Weigh the same mass of bentonite powder as the lower sample, pour it into the sample ring, and use the same loading rate, standing time and unloading rate as the lower sample to complete the pressing of the upper sample.

[0044] 3) Combination of the upper sample and the lower sample: Connect the base containing the lower sample and the sample ring containing the upper sample with studs, tighten the nuts, and then remove the sample pressing auxiliary devices on both sides of the base. Insert the sample pressing rod, use an electronic universal testing machine to push the upper sample downward at a rate of 0.2mm / min, and combine it with the lower sample. During the process of pushing the sample downward, record the stable sample pushing resistance, and check the ventilation of the interface through the horizontal penetration holes on the base. Wait for the interface to contact, bear a pressure of about 0.2MPa, and the interface is no longer breathable, then it is considered that the upper sample has been pushed into the base and spliced ​​with the lower sample to form a combination.

[0045] 4) Assembled body interface self-healing experiment: After the sample is assembled, separate the sample ring and the base, and then put the components together according to Figure 1 The structure is connected as shown. Set the water pressure / flow controller to a constant pressure of 1MPa, start the experiment, and observe the water outflow from outlet A'. If there is a continuous water flow, it means that interfacial hydraulic fracturing has occurred; stop water injection, wait for about 5 minutes, and then inject water again at a water pressure of 1MPa to observe whether interfacial hydraulic fracturing has occurred. Adjust the waiting time or water injection pressure, and repeat this process to explore the hydraulic fracturing and self-healing ability of the interface of the high-compacted bentonite assembly. In addition, a constant flow rate can also be used to explore the hydraulic fracturing and self-healing ability of the assembly interface.

[0046] 5) Assemblies interface permeability test: After the self-healing experiment of the assembly interface, apply a water pressure that can produce hydraulic fracture of the interface; then, stop the water pressure control and allow the water pressure to drop freely, eventually reaching a certain stable value. Select a water pressure slightly lower than the stable value, start the interface permeability experiment with constant water pressure, and automatically record the permeability flow. At the same time, the pressure sensor measures the expansion force generated by the hydration expansion of the assembly, which is recorded by a paperless recorder. Finally, when the permeability flow reaches a linear relationship with the controlled water pressure and the expansion force reaches a stable value, the sample reaches a saturated state. The expansion-permeability properties of the high-compacted bentonite assembly are analyzed through the evolution of the permeability flow and the expansion force.

[0047] The above description of the embodiments is to facilitate the understanding and application of the present invention by those skilled in the art. Those skilled in the art can make appropriate adjustments to these embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the embodiments described herein. Improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the scope of protection of the present invention.

Claims

1. A device for testing the interface permeability of a high-compacted bentonite assembly, characterized in that: It includes constant volume experimental device, penetration auxiliary device, control and measurement device, and sample pressing auxiliary device; The constant volume experimental device provides sample compression, sample splicing and deformation limitation; The infiltration auxiliary device provides the positioning, channel and filtering functions required for seepage along the splicing interface; The control and measurement device provides water pressure / flow rate control, flow / water pressure measurement and recording, and expansion force measurement and recording functions; The sample pressing auxiliary device provides the sealing function required for sample preparation; The sample pressing auxiliary device is used in the sample pressing stage, and is respectively installed in an embedded manner on the left and right sides of the constant volume experimental device, and is removed after the sample pressing is completed; the infiltration auxiliary device is used in the infiltration stage, and is respectively installed in an embedded manner on the left and right sides of the constant volume experimental device; the control and measurement device is used in the infiltration stage, and is connected to the left and top of the constant volume experimental device by pipelines and threads; The device for high-pressure compaction bentonite assembly interface permeability test can respectively press the lower sample to be tested and the upper sample to be tested in the base and the sample ring, push the upper sample in the sample ring into the base, complete the splicing with the lower sample, thereby avoiding the formation of a dominant seepage channel other than the splicing interface; The device for testing the interface permeability of a high-density bentonite assembly is provided with horizontal permeable holes on both sides of the joint interface, and the permeability auxiliary device is used so that the hydration and permeation of the sample are preferentially performed along the joint interface of the assembly.

2. The device for testing the interface permeability of a high-compacted bentonite assembly according to claim 1, characterized in that: The constant volume experimental device comprises a base (1), a sample ring (2), a top cover (3), bolts (4), a piston (5), a first sealing ring (6a) and a second sealing ring (6b); four through holes are respectively arranged on the sample ring (2) and the top cover (3), and four bolts (4) are used to connect the sample ring (2) and the base (1), wherein the sample ring (2) is fixed on the base (1) by nuts and is in close contact with the base (1), and the top cover (3) is fixed on the top of the bolt (4) by nuts; a sample to be tested can be installed inside the base 1; the piston (5) is embedded inside the sample ring (2); annular sealing grooves are respectively arranged between the sample ring (2) and the piston (5), and between the sample ring (2) and the base (1) to install the first sealing ring (6a) and the second sealing ring (6b).

3. The device for testing the interface permeability of a high-compacted bentonite assembly according to claim 1, characterized in that: The infiltration auxiliary device comprises a pipe joint (8), a thin-walled tube (9), a water-permeable block (10), and filter paper (11); two sets of auxiliary infiltration devices are respectively installed in two horizontal infiltration holes symmetrically distributed along the axis (A-A') on the base; from the outside to the inside, they are the pipe joint (8), the thin-walled tube (9), the water-permeable block (10), and the filter paper (11), which are in close contact; the filter paper (11) is in contact with the sample (7) to be tested.

4. The device for testing the interface permeability of a high-compacted bentonite assembly according to claim 3, characterized in that: The pipe joint (8), the thin-walled pipe (9), and the water-permeable block (10) are all made of metal; or, the pipe joint (8) and the thin-walled pipe (9) are made of stainless steel, and the water-permeable block (10) is made of sintered copper.

5. The device for testing the interface permeability of a high-compacted bentonite assembly according to claim 1, characterized in that: The control and measurement device comprises a computer control software module (12), a water pressure / flow controller (13), a pressure sensor (14), screws (15), and a paperless recorder (16); the water pressure / flow controller (13) and the pipe joint (8) are connected by a polytetrafluoroethylene hose and connected to the computer control software module (12) via a cable to control the water pressure / flow and automatically record the permeation flow / pressure; the pressure sensor (14) is fixed to the lower part of the top cover (3) and the upper part of the piston (5) by four sensor screws (15); the probe of the pressure sensor (14) is embedded in the groove at the top end of the piston (5); the paperless recorder (16) is connected to the pressure sensor (14) via a cable to automatically record and store the expansion force data.

6. The device for testing the interface permeability of a high-compacted bentonite assembly according to claim 1, characterized in that: The sample pressing auxiliary device comprises a plunger (17), a connecting piece (18), and a connecting piece screw (19); the plunger (17) can be inserted into and block two horizontal penetration holes on the base (1); the outer end of the plunger (17) is connected to the upper end of the connecting piece (18) through a thread; the lower end of the connecting piece (18) is fixed to the base (1) by a connecting piece screw (19).

7. The device for testing the interface permeability of a high-compacted bentonite assembly according to claim 2, characterized in that: The lower sample (7a) to be tested and the upper sample (7b) to be tested can be pressed in the base (1) and the sample ring (2) respectively, and the upper sample (7b) in the sample ring (2) is pushed into the base (1) to complete the splicing with the lower sample (7a), thereby avoiding the formation of a dominant seepage channel other than the splicing interface.

8. The device for testing the interface permeability of a high-compacted bentonite assembly according to claim 3, characterized in that: Horizontal penetration holes are arranged on both sides of the joint interface, and the penetration auxiliary device is used so that the hydration and penetration of the sample (7) are preferentially carried out along the joint interface of the assembly.

9. The device for testing the interface permeability of a high-compacted bentonite assembly according to claim 5, characterized in that: A computer control software module (12) and a water pressure / flow controller (13) are used to control the water pressure / flow rate, and to measure and record the corresponding flow / water pressure; a pressure sensor (14) is used to measure the expansion force of the assembly, and a paperless recorder (16) is used to display and store the expansion force data in real time.

10. The device for testing the interface permeability of a high-compacted bentonite assembly according to claim 6, characterized in that: The sample pressing auxiliary device is used to block the horizontal penetration hole, and the lower sample (7a) to be tested is pressed inside the base (1).

11. The device for testing the interface permeability of a high-compacted bentonite assembly according to claim 1, characterized in that: It can carry out interface permeation experiments under constant pressure control or constant flow control.

12. Use of the device for testing the interface permeability of a high-compacted bentonite assembly according to any one of claims 1 to 11, characterized in that: It can be used to study the expansion-permeability properties of high-compacted bentonite assemblies, and can also be used to study the hydraulic fracturing and self-healing properties of the assembly interface.

Images