Device for testing the unsaturated expansion force of high-compacted bentonite assemblies

Abstract

A device for testing the unsaturated swelling force of a high-compacted bentonite assembly includes four parts: a constant volume experimental device, a suction control device, a swelling force measuring device, and a sample pressing auxiliary device. The constant volume experimental device provides functions such as sample preparation, sample combination, and deformation limitation. The suction control device uses a gas phase method to control the target suction achieved by the sample. The swelling force measuring device provides functions such as swelling force measurement and recording under the action of the target suction. The sample pressing auxiliary device provides functions such as blocking and inspection required for the sample preparation and sample combination process. The present invention realizes the automated testing of the unsaturated swelling force of a high-compacted bentonite assembly, as well as the exploration of the self-healing conditions of the assembly interface. The method of the present invention is simple, has a large amount 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 deep geological disposal repository engineering barrier system, and has important engineering significance and practical value.

Description

Technical Field

[0001] The invention belongs to the technical field of civil engineering (geotechnical engineering) and geological engineering, and relates to a device for testing the unsaturated expansion force of a high-compacted bentonite assembly. Background Art

[0002] High-level radioactive waste has the characteristics of strong radioactivity and long half-life, and deep geological disposal is recognized as an effective and feasible means of high-level radioactive waste disposal. This method is to seal the solidified body of high-level radioactive waste in deep rock formations and use multiple barriers (including engineering barriers and natural barriers) to block the migration of nuclides to the external environment. The buffer backfill material in the engineering barrier should have key functions such as maintaining structural stability, blocking groundwater seepage, and blocking the migration of nuclides. After comparative research, compacted bentonite has been preferred by various countries as a buffer backfill material due to its properties such as strong expansion, low permeability and strong adsorption.

[0003] In the concept of deep geological disposal, the engineering barrier is usually made of high-compacted bentonite blocks. As a result, three types of interfaces will be formed in the engineering barrier: the interface between the 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 three types of interfaces play a decisive role in the physical and mechanical integrity of the engineering barrier, and ultimately affect its chemical-hydraulic-mechanical buffering properties. After the disposal hole is closed, the compacted bentonite in the engineering barrier will continue to absorb moisture and hydrate from the surrounding environment, generating swelling force. Studies have shown that the magnitude of swelling force plays a key role in the stability of the waste tank and biochemical inhibition. In addition, under the action of pressure (swelling force) and humidity (suction), the interface of the high-compacted bentonite assembly will gradually cement and heal, and this process plays a positive role in enhancing the hydraulic barrier capacity. Therefore, it is necessary to study the evolution of the swelling force of the high-compacted bentonite assembly with humidity (suction) and the suction conditions for interface healing, and then evaluate the hydraulic and mechanical buffering properties of the engineering barrier system.

[0004] In terms of interface problems in engineering barriers, existing studies have mainly conducted indoor experiments to explore the swelling force and saturated permeability properties of the waste tank-compacted bentonite interface and the compacted bentonite-surrounding rock interface. However, there is no healing effect between the two types of interfaces, which is different from the change in swelling force caused by the healing of the interface between compacted bentonites. At present, no relevant research has been conducted on the unsaturated swelling force of high-compacted bentonite assemblies. Summary of the invention

[0005] The purpose of the present invention is to provide a device for testing the unsaturated swelling force of a high-compacted bentonite assembly, to carry out indoor experimental research, and to provide a scientific basis for the research work of deep geological disposal repositories. Furthermore, for the buffer backfill material in the deep geological disposal repository, the swelling force evolution and interface healing conditions of the high-compacted bentonite assembly under suction control conditions are analyzed to provide a basis for studying the evolution of the hydraulic state of the engineering barrier system.

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

[0007] A device for testing the unsaturated expansion force of a high-compacted bentonite assembly, comprising four parts: a constant volume experimental device, a suction control device, an expansion force measuring 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 suction control device uses the gas phase method to control the target suction achieved by the sample;

[0010] The expansion force measuring device provides functions such as expansion force measurement and recording under target suction;

[0011] The sample pressing auxiliary device provides the functions of sealing and inspection required in the sample preparation and sample combination process;

[0012] The constant volume experimental device is the main part of the test device and is used during the entire test phase. The sample pressing auxiliary device is used during the sample pressing phase and is embedded on the left and right sides of the constant volume experimental device. The suction control device is used during the experimental phase and is connected to the left side of the constant volume experimental device using a pipeline. The expansion force measuring device is used during the experimental phase and is installed on the top of the constant volume experimental device using screws. The above components are installed and used as needed.

[0013] further:

[0014] 1) The constant volume experimental device includes a base, a lower sample ring, an upper sample ring, a top cover, a stud, a piston, a sealing ring, a filter paper, a permeable stone, and a sample. The base, the lower sample ring, the upper sample ring, the top cover, the stud, and the piston are all made of stainless steel. The lower sample ring, the upper sample ring, and the top cover are respectively provided with four through holes, and are connected to the base by four studs, wherein the upper sample ring and the lower sample ring are fixed to the base by nuts. The top cover is fixed to the top of the stud by nuts. The lower sample ring is provided with a group of horizontal through holes symmetrical along the axis at the middle position of the height. A connecting channel is provided inside the base, and the first and second base pneumatic quick-connect connectors are provided at the left and right ends of the channel respectively. A connecting channel is provided inside the piston, and the first and second piston pneumatic quick-connect connectors are provided at the left and right ends of the channel respectively. The sample is located inside the lower sample ring, and is formed by closely splicing the upper and lower parts. Filter paper and permeable stone are placed in the upper part of the upper sample and the lower part of the lower sample respectively. The piston is embedded inside the upper sample ring and pressed on the upper permeable stone. Annular sealing grooves are respectively arranged between the upper sample ring and the piston, between the upper sample ring and the lower sample ring, and between the lower sample ring and the base, and sealing rings are installed.

[0015] 2) The suction control device includes a diaphragm air pump, a saturated salt solution bottle, and a steam purification bottle. The diaphragm air pump is connected to the first piston pneumatic quick-connect connector on the piston through a conduit, and the steam purification bottle is connected to the first base pneumatic quick-connect connector on the base through a conduit. The diaphragm air pump, the saturated salt solution bottle, and the steam purification bottle are connected in sequence through conduits. The second base pneumatic quick-connect connector on the base and the second piston pneumatic quick-connect connector on the piston are connected by a conduit. The saturated salt solution bottle is used to place a saturated salt solution. The diaphragm air pump agitates the saturated salt solution to generate steam with corresponding humidity (suction value) to enter the steam purification bottle, and the steam purification bottle filters the liquid entering the pipeline. The steam enters the constant volume experimental device through the first base pneumatic quick-connect connector on the base, and then returns to the diaphragm air pump through the second piston pneumatic quick-connect connector on the piston, forming a steam circulation path, and finally making the suction of the sample the same as the suction controlled by the saturated salt solution.

[0016] 3) The expansion force measuring device includes a pressure sensor, a sensor screw, and a paperless recorder. 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 through 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 through holes on the lower sample ring. The outer end of the plunger is connected to the middle of the connecting piece through a thread. The two ends of the connecting piece are horizontally fixed to the lower sample ring by connecting piece screws.

[0018] The present invention can respectively press the lower sample and the upper sample in the lower sample ring and the upper sample ring, push the upper sample in the upper sample ring into the lower sample ring, complete the close splicing with the lower sample, and form a high-pressure compacted bentonite assembly.

[0019] The suction control device (including diaphragm air pump, saturated salt solution bottle, steam purification bottle) and gas phase method are used for suction control, and the suction control range can reach 3~309MPa.

[0020] The pressure sensor is used to measure the unsaturated expansion force of the high-compacted bentonite assembly, and the paperless recorder displays and stores the expansion force data in real time.

[0021] The horizontal through hole of the lower sample ring is blocked by a sample pressing auxiliary device (plunger, connecting piece, connecting piece screw) to press the lower sample in the lower sample ring.

[0022] The present invention can carry out both single-stage suction controlled expansion force experiments and multi-stage suction controlled expansion force experiments.

[0023] The invention can be used for measuring the unsaturated expansion force of a high-compacted bentonite assembly, and can also be used for exploring the self-healing suction conditions 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 separate pressing and tight splicing of high-compacted bentonite assemblies;

[0026] 2) The present invention realizes the automated test of the unsaturated expansion force of a high-compacted bentonite assembly under constant volume, single-stage or multi-stage suction control conditions;

[0027] 3) The present invention realizes the evolution of unsaturated swelling force under constant volume and multi-stage suction control conditions, and determines the suction conditions for the healing effect of the interface of the high-compacted bentonite assembly;

[0028] 4) The test method of the present invention is easy, the test device is inexpensive, the degree of automation is high, and it is generally reliable and easy to operate. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a schematic diagram of the structure of an embodiment of the testing device of the present invention.

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

[0031] Figure 3 Schematic diagram of the structure of the sample pressing auxiliary device according to an embodiment of the present invention.

[0032] Wherein: 1 base; 2 lower sample ring; 3 upper sample ring; 4 top cover; 5 stud; 6 piston; 7a first sealing ring; 7b second sealing ring; 7c third sealing ring; 8a first filter paper; 8b second filter paper; 9a first permeable stone; 9b second permeable stone; 10a upper sample, 10b lower sample; 11a first base pneumatic quick-connect connector; 11b second base pneumatic quick-connect connector; 12a first piston pneumatic quick-connect connector; 12b second piston pneumatic quick-connect connector; 13 diaphragm air pump; 14 saturated salt solution bottle; 15 air purification bottle; 16 pressure sensor; 17 sensor screw; 18 paperless recorder; 19 stud; 20 connecting plate; 21 connecting plate screw. DETAILED DESCRIPTION

[0033] The present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0034] like Figures 1 to 3 As shown, the present invention provides a device for testing the unsaturated expansion force of a high-compacted bentonite assembly, comprising four parts: a constant volume experimental device, a suction control device, an expansion force measuring device, and a sample pressing auxiliary device:

[0035] 1) The constant volume experimental device comprises a base 1, a lower sample ring 2, an upper sample ring 3, a top cover 4, a stud 5, a piston 6, a first sealing ring 7a, a second sealing ring 7b, a third sealing ring 7c, a first filter paper 8a, a second filter paper 8b, a first permeable stone 9a, a second permeable stone 9b, an upper sample 10a, and a lower sample 10b.

[0036] The lower sample ring 2, the upper sample ring 3, and the top cover 4 are respectively provided with four through holes, and are connected to the base 1 by four studs 5, wherein the lower sample ring 2 and the upper sample ring 3 are fixed to the base 1 by nuts. The top cover 4 is fixed to the top of the stud 5 by nuts. The lower sample ring 2 is provided with a group of horizontal through holes symmetrical along the axis at the middle height position. A connecting channel is provided inside the base 1, and the first base pneumatic quick-connect fitting 11a and the second base pneumatic quick-connect fitting 11b are provided at the left and right ends of the channel respectively. A connecting channel is provided inside the piston 6, and the first piston pneumatic quick-connect fitting 12a and the second piston pneumatic quick-connect fitting 12b are provided at the left and right ends of the channel respectively. The sample is located inside the lower sample ring 2, and is formed by the upper sample 10a and the lower sample 10b being tightly spliced ​​together. The first filter paper 8a, the second filter paper 8b, the first permeable stone 9a, and the second permeable stone 9b are placed in sequence on the upper part of the upper sample 10a and the lower part of the lower sample 10b. The piston 6 is embedded in the upper sample ring 3 and pressed on the first permeable stone 9a. Annular sealing grooves are respectively provided between the upper sample ring 3 and the piston 6, between the upper sample ring 3 and the lower sample ring 2, and between the lower sample ring 2 and the base 1, and the first sealing ring 7a, the second sealing ring 7b, and the third sealing ring 7c are installed.

[0037] 2) The suction control device includes a diaphragm air pump 13, a saturated salt solution bottle 14, and a steam purification bottle 15. The diaphragm air pump 13 is connected to the first piston pneumatic quick-connect connector 12a on the piston 6 through a conduit, and the steam purification bottle 15 is connected to the first base pneumatic quick-connect connector 11a on the base 1 through a conduit. The diaphragm air pump 13, the saturated salt solution bottle 14, and the steam purification bottle 15 are connected in sequence through conduits. The second base pneumatic quick-connect connector 11b on the base 1 and the second piston pneumatic quick-connect connector 12b on the piston 6 are connected by a conduit. The saturated salt solution bottle 14 is used to place a saturated salt solution. The diaphragm air pump 13 agitates the saturated salt solution to generate steam with a corresponding humidity (suction value) to enter the steam purification bottle 15, and the steam purification bottle 15 filters the liquid that may enter the pipeline. The steam enters the constant volume experimental device through the first base pneumatic quick-connect connector 11a on the base 1, and then returns to the diaphragm air pump 13 through the second piston pneumatic quick-connect connector 12a on the piston 6, forming a steam circulation path, and finally making the suction of the sample the same as the suction controlled by the saturated salt solution.

[0038] 3) The expansion force measuring device includes a pressure sensor 16, a sensor screw 17, and a paperless recorder 18. The pressure sensor 16 is fixed to the lower part of the top cover 4 and the upper part of the piston 6 by four sensor screws 17. The probe of the pressure sensor 16 is embedded in the groove at the top of the piston 6. The paperless recorder 18 is connected to the pressure sensor 16 via a cable to automatically record and store the expansion force data.

[0039] 4) The sample pressing auxiliary device includes a plunger 19, a connecting piece 20, and a connecting piece screw 21. The plunger 19 can be inserted into and block the two horizontal through holes on the lower sample ring 2. The outer end of the plunger 19 is connected to the middle of the connecting piece 20 through a thread. The two ends of the connecting piece 20 are horizontally fixed to the lower sample ring 2 by connecting piece screws 21.

[0040] The working mode of the device for testing the unsaturated expansion force of a high-compacted bentonite assembly of the present invention is as follows:

[0041] 1) Preparation of lower sample: The size of the lower sample is 50mm in diameter, 10mm in height, and the dry density is 1.7g / cm 3 . Calculate the mass of bentonite powder required based on the dry density and moisture content of bentonite powder. First, disassemble the test device and use only the lower sample ring and the upper sample ring for sample compression and sample combination. Use the sample compression auxiliary device (plunger, connecting piece and connecting piece screw) to seal the horizontal through holes on both sides of the lower sample ring, and adjust and fix the position of the plunger. Then, combine the lower sample ring with the upper sample ring, pour the bentonite powder into it, put in the pressure rod, and use the 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, take out the pressure rod, and clean the surface of the lower sample.

[0042] 2) Preparation of upper sample: The upper sample size is 50mm in diameter, 10mm in height, and the dry density is 1.7g / cm 3 After the lower sample is pressed, separate the upper sample ring from the lower sample ring. The upper sample is pressed in the upper sample ring. Weigh the same mass of bentonite powder as the lower sample, pour it into the upper sample ring, put in the pressing rod, use the same loading rate, standing time and unloading rate, complete the pressing of the upper sample, and clean the surface of the upper sample.

[0043] 3) Combination of upper and lower specimens: Combine the lower specimen ring containing the lower specimen with the upper specimen ring containing the upper specimen, and remove the sample pressing auxiliary devices on both sides of the lower specimen ring. Insert the pressure rod, use the electronic universal testing machine to push the upper specimen downward at a rate of 0.2mm / min, and combine it with the lower specimen. During the downward pushing and combining process, record the stable pushing resistance, and check the ventilation of the interface through the horizontal through hole on the lower specimen ring. When the interface contacts, bears a pressure of about 0.2MPa, and the interface is no longer breathable, it is considered that the upper specimen has been pushed into the lower specimen ring and spliced ​​with the lower specimen to form a combination.

[0044] 4) Unsaturated expansion force test of the assembly: After the sample is assembled, the components are assembled according to Figure 1 The structural connection shown in the figure applies an initial pressure of 0.2MPa. Start the diaphragm air pump and use different saturated salt solutions to control the suction force under the moisture absorption path step by step. After the expansion force under each level of suction reaches stability, the next level of suction control can be carried out. In addition, single-stage suction can also be used to complete low suction control. After the multi-stage suction control is completed, the suction value at which the combination interface begins to heal is judged based on the evolution of the expansion force.

[0045] In summary, the method of the present invention is simple, has a large amount 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 deep geological disposal repository engineering barrier system, which has important engineering significance and practical value.

[0046] 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 unsaturated expansion force of a high-compacted bentonite assembly, characterized in that: It includes four parts: constant volume experimental device, suction control device, expansion force measuring device and sample pressing auxiliary device; The constant volume experimental device provides sample preparation, sample combination and deformation limiting functions, and can respectively press the lower sample (10b) and the upper sample (10a) in the lower sample ring (2) and the upper sample ring (3), push the upper sample (10a) in the upper sample ring (3) into the lower sample ring (2), complete the tight splicing with the lower sample (10b), and form a high-pressure compacted bentonite assembly; The suction control device uses a gas phase method to control the target suction achieved by the sample; The expansion force measuring device provides expansion force measurement and recording functions under target suction force; The sample pressing auxiliary device provides the sealing and inspection functions required for the sample preparation and sample combination process; the sample pressing auxiliary device is used to seal the horizontal through hole of the lower sample ring (2) and press the lower sample (10b) inside the lower sample ring (2); the sample pressing auxiliary device comprises a plunger (19), a connecting piece (20), and a connecting piece screw (21); the plunger (19) can be inserted into and seal the two horizontal through holes on the lower sample ring (2); the outer end of the plunger (19) is connected to the middle of the connecting piece (20) through a thread; the two ends of the connecting piece (20) are horizontally fixed to the lower sample ring (2) by connecting piece screws (21); the sample pressing auxiliary device is respectively installed on the left and right sides of the constant volume experimental device in an embedded manner; the suction control device is connected to the left side of the constant volume experimental device by a pipeline; and the expansion force measuring device is installed on the top of the constant volume experimental device by a movable connection structure.

2. The device for testing the unsaturated expansion force of a high-compacted bentonite assembly according to claim 1, characterized in that: The constant volume experimental device comprises a base (1), a lower sample ring (2), an upper sample ring (3), a top cover (4), a stud (5), a piston (6), a first sealing ring (7a), a second sealing ring (7b), a third sealing ring (7c), a first filter paper (8a), a second filter paper (8b), a first permeable stone (9a), a second permeable stone (9b), an upper sample (10a), and a lower sample (10b); The lower sample ring (2), the upper sample ring (3) and the top cover (4) are respectively provided with four through holes and connected to the base (1) by four studs (5), wherein the lower sample ring (2) and the upper sample ring (3) are fixed to the base (1) by nuts; the top cover (4) is fixed to the top of the studs (5) by nuts; the lower sample ring (2) is provided with a group of horizontal through holes symmetrical along the axis at the middle position of the height; a connecting channel is provided inside the base (1), and a first base pneumatic quick-connect connector (11a) and a second base pneumatic quick-connect connector (11b) are respectively provided at both ends of the channel; a connecting channel is provided inside the piston (6), and a first piston pneumatic quick-connect connector (12a) and a second piston pneumatic quick-connect connector (12b) are respectively provided at both ends of the channel. b); the sample is located inside the lower sample ring (2), and is composed of an upper sample (10a) and a lower sample (10b) that are tightly spliced ​​together; a first filter paper (8a), a second filter paper (8b), a first permeable stone (9a), and a second permeable stone (9b) are placed in sequence on the upper part of the upper sample (10a) and the lower part of the lower sample (10b); a piston (6) is embedded inside the upper sample ring (3) and pressed on the first permeable stone (9a); annular sealing grooves are provided between the upper sample ring (3) and the piston (6), between the upper sample ring (3) and the lower sample ring (2), and between the lower sample ring (2) and the base (1), and a first sealing ring (7a), a second sealing ring (7b), and a third sealing ring (7c) are installed.

3. The device for testing the unsaturated expansion force of a high-compacted bentonite assembly according to claim 1, characterized in that: The suction control device comprises a diaphragm air pump (13), a saturated salt solution bottle (14), and a steam purification bottle (15); the diaphragm air pump (13) is connected to a first piston pneumatic quick-connect connector (12a) on the piston (6) via a conduit; the steam purification bottle (15) is connected to a first base pneumatic quick-connect connector (11a) on the base (1) via a conduit; the diaphragm air pump (13), the saturated salt solution bottle (14), and the steam purification bottle (15) are connected in sequence via conduits; a second base pneumatic quick-connect connector (11b) on the base (1) is connected to a second piston pneumatic quick-connect connector (11a) on the piston (6) The joint (12b) is connected by a conduit; the saturated salt solution bottle (14) is used to place the saturated salt solution, and the diaphragm air pump (13) agitates the saturated salt solution to generate steam with a corresponding humidity / suction value, which enters the steam purification bottle (15); the steam purification bottle (15) filters the liquid entering the pipeline; the steam enters the constant volume experimental device through the first base pneumatic quick connector (11a) on the base (1), and then returns to the diaphragm air pump (13) through the second piston pneumatic quick connector (12b) on the piston (6), forming a steam circulation path, and finally making the suction of the sample and the suction controlled by the saturated salt solution reach the same.

4. The device for testing the unsaturated expansion force of a high-compacted bentonite assembly according to claim 1, characterized in that: The expansion force measuring device comprises a pressure sensor (16), a sensor screw (17), and a paperless recorder (18); the pressure sensor (16) is fixed to the lower part of the top cover (4) and the upper part of the piston (6) by four sensor screws (17); the probe of the pressure sensor (16) is embedded in the groove at the top end of the piston (6); the paperless recorder (18) is connected to the pressure sensor (16) via a cable to automatically record and store the expansion force data.

5. The device for testing the unsaturated expansion force of a high-compacted bentonite assembly according to claim 1, characterized in that: The suction control device and the gas phase method are used to control the suction, and the suction control range reaches 3~309MPa.

6. The device for testing the unsaturated expansion force of a high-compacted bentonite assembly according to claim 1, characterized in that: The pressure sensor is used to measure the unsaturated expansion force of the high-compacted bentonite assembly, and the paperless recorder displays and stores the expansion force data in real time.

7. The device for testing the unsaturated expansion force of a high-compacted bentonite assembly according to claim 1, characterized in that: It can be used to carry out expansion force experiments with single-stage suction control, as well as expansion force experiments with multi-stage suction control; or, it can be used to measure the unsaturated expansion force of high-compacted bentonite assemblies, as well as to explore the self-healing suction conditions of the assembly interface.

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