CN108333060B - Testing machine for measuring clay rock shear fracture permeability coefficient evolution by adopting steady-state method - Google Patents
Testing machine for measuring clay rock shear fracture permeability coefficient evolution by adopting steady-state method Download PDFInfo
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- CN108333060B CN108333060B CN201810259148.5A CN201810259148A CN108333060B CN 108333060 B CN108333060 B CN 108333060B CN 201810259148 A CN201810259148 A CN 201810259148A CN 108333060 B CN108333060 B CN 108333060B
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- 239000011435 rock Substances 0.000 title claims abstract description 177
- 239000004927 clay Substances 0.000 title claims abstract description 152
- 230000035699 permeability Effects 0.000 title claims abstract description 52
- 238000000034 method Methods 0.000 title claims abstract description 47
- 238000012360 testing method Methods 0.000 title claims abstract description 36
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 183
- 238000010008 shearing Methods 0.000 claims abstract description 71
- 238000006073 displacement reaction Methods 0.000 claims abstract description 45
- 239000011148 porous material Substances 0.000 claims abstract description 34
- 238000007789 sealing Methods 0.000 claims description 11
- 239000003822 epoxy resin Substances 0.000 claims description 8
- 229920000647 polyepoxide Polymers 0.000 claims description 8
- 229910001220 stainless steel Inorganic materials 0.000 claims description 3
- 239000010935 stainless steel Substances 0.000 claims description 3
- 230000008569 process Effects 0.000 description 12
- 230000009286 beneficial effect Effects 0.000 description 7
- 238000004080 punching Methods 0.000 description 6
- 239000000463 material Substances 0.000 description 5
- 238000004891 communication Methods 0.000 description 3
- 239000002689 soil Substances 0.000 description 3
- 230000008859 change Effects 0.000 description 2
- 238000007906 compression Methods 0.000 description 2
- 230000008878 coupling Effects 0.000 description 2
- 238000010168 coupling process Methods 0.000 description 2
- 238000005859 coupling reaction Methods 0.000 description 2
- 238000010586 diagram Methods 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 230000036571 hydration Effects 0.000 description 2
- 238000006703 hydration reaction Methods 0.000 description 2
- 239000012466 permeate Substances 0.000 description 2
- 238000012545 processing Methods 0.000 description 2
- 239000004575 stone Substances 0.000 description 2
- 230000009471 action Effects 0.000 description 1
- 230000004888 barrier function Effects 0.000 description 1
- 229910000278 bentonite Inorganic materials 0.000 description 1
- 239000000440 bentonite Substances 0.000 description 1
- SVPXDRXYRYOSEX-UHFFFAOYSA-N bentoquatam Chemical compound O.O=[Si]=O.O=[Al]O[Al]=O SVPXDRXYRYOSEX-UHFFFAOYSA-N 0.000 description 1
- 238000004364 calculation method Methods 0.000 description 1
- 230000006835 compression Effects 0.000 description 1
- 238000004880 explosion Methods 0.000 description 1
- 230000005251 gamma ray Effects 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 230000003204 osmotic effect Effects 0.000 description 1
- 238000002360 preparation method Methods 0.000 description 1
- 238000011160 research Methods 0.000 description 1
- 239000002699 waste material Substances 0.000 description 1
Classifications
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N3/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N3/24—Investigating strength properties of solid materials by application of mechanical stress by applying steady shearing forces
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume or surface-area of porous materials
- G01N15/08—Investigating permeability, pore-volume, or surface area of porous materials
- G01N15/082—Investigating permeability by forcing a fluid through a sample
- G01N15/0826—Investigating permeability by forcing a fluid through a sample and measuring fluid flow rate, i.e. permeation rate or pressure change
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- Dispersion Chemistry (AREA)
- Investigating Strength Of Materials By Application Of Mechanical Stress (AREA)
Abstract
The invention relates to a testing machine for measuring clay rock shear fracture permeability coefficient evolution by adopting a steady-state method, which comprises a shear box, a water pressure servo loader, a water pressure sensor and an LVDT displacement sensor, wherein the shear box is arranged on the shear box; the clay rock sample is of a flat cylindrical structure with the thickness of 1-2 cm, the hydraulic servo loader is communicated to the upper side of the clay rock sample through a pipeline, pore water is provided for the clay rock sample, pore water pressure is applied, the lower side of the clay rock sample is communicated to the atmosphere through the pipeline, and the shearing direction of the clay rock sample is parallel to the permeation path of the pore water in the clay rock sample. And when the shearing displacement is applied, pore water pressure is applied to the upper part of the clay rock sample with the flat cylindrical structure with the thickness of 1-2 cm, and the lower part of the clay rock sample is communicated to the atmosphere through a pipeline, so that a constant water head difference can be formed above and below the sheared clay rock sample, thereby generating steady-state seepage, and further, the permeability coefficient of the clay rock with low permeability can be accurately measured by adopting a steady-state method.
Description
Technical Field
The invention relates to geotechnical engineering test equipment, in particular to a test machine for measuring clay rock shear fracture permeability coefficient evolution by adopting a steady-state method.
Background
Clay rock is a soft rock with material properties between rock and soil, and often has certain plasticity and low permeability coefficient, and internal cracks can be closed slowly under the hydration effect. Due to this property, clay rocks (including bentonite blocks) are often used as barrier materials, and more often as parent and buffer materials for high level nuclear waste reservoirs around the world. Shear cracks are a common crack form in clay rock underground caverns, so that research on permeability coefficient evolution of clay rock in a shearing process is an important subject.
The permeability evolution of the rock and soil material in shear failure is currently measured by adopting a seepage-stress coupling triaxial tester for test: the permeability coefficient was measured by directly applying a water pressure differential at the top and bottom of a cylindrical sample during triaxial shear (or triaxial compression) of the sample. The method is more suitable for rock-soil mediums with relatively large permeability, such as sandstone, and the like, and is very low for clay rock, and the rock mass with strong self-closing characteristic of cracks, if the rock mass is prepared into a common triaxial sample, the permeation coefficient cannot be measured by adopting a steady-state method due to a long permeation path, but can only be measured by adopting a pulse method. The permeability coefficient measured by the pulse method has larger error, so that the method cannot generally obtain test results with better regularity. And the shear cracks of triaxial shear tend not to penetrate up and down, which results in a measured permeability coefficient that is much smaller than the actual value. If the clay rock sample is prepared into a flat cylinder, triaxial shearing cannot be performed, and the test purpose cannot be achieved.
The pages 47-58 of volume 124 of Engineering Geology published in 1 of 2012 introduce a seepage-stress coupling hollow cylinder triaxial apparatus capable of measuring the permeability coefficient of clay rock shear cracks, and the change rule of the permeability of the clay rock sample in the shearing process can be calculated by measuring water pressure and flow on the inner side and the outer side of the hollow cylinder sample respectively in the triaxial compression process. The wall thickness of the hollow sample is smaller, the permeability coefficient can be measured by adopting a steady state method, the measured data is more accurate, and the permeability coefficient change in the clay rock shearing process can be better reflected. However, the method has the advantages that the test instrument is complex, the top and the bottom of the hollow cylinder are required to be sealed in the test process, the inner and outer walls of the sample are required to be wrapped with rubber films and the sensor is required to be installed, and the method is difficult and takes a long time. In addition, the processing difficulty of the hollow cylindrical sample of the clay rock is also high. In addition, the location of the shear fracture is also difficult to control.
Pages 87-99 of volume 47, volume 1, no. 1, rock Mechanics and Rock Engineering, published in month 1 of 2014, describe a method for measuring the permeability coefficient of clay-rock shear cracks by using a prefabricated-crack sample, which is a wafer sample with a small thickness (1 cm-2 cm) due to the relatively low permeability of clay-rock. By adopting the method, only the permeability of the cracks of the clay rock and the characteristic that the cracks are self-closed and gradually reduced under the action of water can be measured, the permeability evolution in the shearing process can not be measured, and the loss of rock scraps on the crack surface of the pre-shearing can also influence the accuracy of a test result.
Disclosure of Invention
The invention aims to solve the technical problem of providing a testing machine for measuring the evolution of the permeability coefficient of a clay rock shear fracture by adopting a steady-state method, which can realize the measurement of the law of the permeability coefficient evolution of the clay rock in the shearing process by adopting simpler experimental equipment with higher precision.
The technical scheme for solving the technical problems is as follows: the testing machine for measuring the clay rock shear fracture permeability coefficient evolution by adopting a steady-state method comprises a shear box for punching and shearing clay rock samples, a water pressure servo loader, a water pressure sensor and an LVDT displacement sensor; the clay rock sample is arranged in the shearing box, and is of a flat cylindrical structure with the thickness of 1-2 cm, and the shearing box is used for shearing the clay rock sample by hydraulically driving a piston to move; the hydraulic servo loader is communicated to the upper part of a clay rock sample in the shearing box through a pipeline, pore water is provided for the clay rock sample, pore water pressure is applied, the lower part of the clay rock sample is communicated to the atmosphere through a pipeline, and the shearing direction of the shearing box on the clay rock sample is parallel to the permeation path of the pore water in the clay rock sample; the hydraulic pressure sensor comprises a pore water pressure sensor and a piston cylinder hydraulic pressure sensor, the pore water pressure sensor is arranged on a pipeline of the hydraulic servo loader, which is communicated to the upper part of the clay rock sample, and the piston cylinder hydraulic pressure sensor is used for measuring the shearing pressure of the shearing box on the clay rock sample; the LVDT displacement sensor is mounted on the shear box and is used for measuring the shear displacement of the shear box on the clay rock sample.
The beneficial effects of the invention are as follows: in the tester for measuring the evolution of the permeability coefficient of the clay rock shear cracks by adopting the steady-state method, the clay rock sample is processed into a flat cylindrical structure with the thickness of 1-2 cm, the pore water pressure is applied above the clay rock sample while the shear displacement is applied, and the lower part of the clay rock sample is communicated to the atmosphere through a pipeline, so that a constant water head difference is formed above and below the sheared clay rock sample, thereby generating steady-state seepage, and further accurately measuring the permeability coefficient of the clay rock with low permeability by adopting the steady-state method; the shearing displacement of the clay rock sample is controllable because the clay rock sample is sheared by adopting a punching shearing mode; because the shearing direction of the shearing box on the clay rock sample is parallel to the permeation path of pore water in the clay rock sample, the influence of the shearing crack on the permeation coefficient of the clay rock sample can be accurately estimated, and the influence rule of shearing deformation on the permeation coefficient of the sample can be obtained by respectively measuring the permeation coefficients of the clay rock sample under different shearing displacements; meanwhile, the shear stress-strain relation of the clay rock sample can be calculated by reading readings of the LVDT displacement sensor and the piston cylinder water pressure sensor in the shearing process; in addition, after the shear cracks are formed, the shear displacement of the clay rock sample is controlled to be kept constant, so that the cracks of the clay rock sample are gradually self-closed, the permeability coefficient of the clay rock sample is measured at different times, and the permeability coefficient evolution rule in the clay rock sample self-closing process can be obtained.
On the basis of the technical scheme, the invention can be improved as follows.
Further comprises a computer, a controller and an amplifier, wherein the computer is connected with the water pressure servo loader through the controller, the LVDT displacement sensor is connected with the computer through the amplifier, and the pore water pressure sensor and the piston cylinder water pressure sensor are both connected with the controller.
The beneficial effects of adopting the further scheme are as follows: the computer can read data such as pressure and displacement, and can control the pressure and the displacement, so that the test is convenient to carry out.
Further, the shear box includes shear box top cap and shear box base, the shear box top cap is installed shear box base is last, the bottom of shear box top cap is equipped with the decurrent upper portion piston cylinder of opening, the top of shear box base is equipped with the decurrent lower part piston cylinder of opening, just upper portion piston cylinder with the position of lower part piston cylinder is relative, slide in the upper portion piston cylinder and be equipped with upper portion piston, the lateral wall of upper portion piston with seal between the lateral wall of upper portion piston cylinder, slide in the lower part piston cylinder and be equipped with the lower part piston, the lateral wall of lower part piston with seal between the lateral wall of lower part piston cylinder, the clay rock sample is located between upper portion piston and the lower part piston, and through the drive upper portion piston and under the cooperation of lower part piston to clay rock sample is sheared.
The beneficial effects of adopting the further scheme are as follows: the upper piston and the lower piston are driven to perform punching shear type shearing on the clay rock sample, so that the controllable shearing displacement of the clay rock sample can be ensured.
The hydraulic servo loader is further communicated with the upper piston cylinder and the lower piston cylinder respectively through pipelines, injects hydraulic pressure into the upper piston cylinder and the lower piston cylinder through the pipelines, drives the upper piston through the hydraulic pressure and shears the clay rock sample under the cooperation of the lower piston; the two piston cylinder water pressure sensors are correspondingly arranged on pipelines of the water pressure servo loader, which are respectively communicated with the upper piston cylinder and the lower piston cylinder.
The beneficial effects of adopting the further scheme are as follows: the shearing cracks of the clay rock sample are formed in a punching shear mode, and the punching shear is realized by driving the upper piston and the lower piston to move by water pressure, so that the boundary conditions of a test are not destroyed when the shearing cracks are formed, and the shape and the direction of the shearing cracks can be ensured, thereby improving the precision of a test result.
Further, the top end of the upper piston extends out of the shear box top cover, the LVDT displacement sensor is mounted on the top end of the upper piston, and the sensing end of the LVDT displacement sensor is in contact with the upper end face of the shear box top cover.
Further, the clay rock sample is arranged in the lower piston cylinder through a lower water permeable plate, an upper water permeable plate is arranged in the upper piston cylinder, and the clay rock sample is clamped between the upper water permeable plate and the lower water permeable plate; the upper water permeable plate and the lower water permeable plate respectively comprise a circular water permeable plate and an annular water permeable plate, and the circular water permeable plates are positioned in circular holes of the annular water permeable plates; the circular water permeable plate in the upper water permeable plate is opposite to the upper piston, the area of the circular water permeable plate in the upper water permeable plate is equal to the sectional area of the upper piston, the circular water permeable plate in the lower water permeable plate is opposite to the lower piston, the area of the circular water permeable plate in the lower water permeable plate is equal to the sectional area of the lower piston, and meanwhile the sectional area of the upper piston is equal to the sectional area of the lower piston.
The beneficial effects of adopting the further scheme are as follows: the top and the bottom of the clay rock sample are respectively provided with a water permeable plate, and the sample needs to be sheared along the vertical direction, so that the upper water permeable plate and the lower water permeable plate are respectively divided into a circular water permeable plate and an annular water permeable plate along the shearing edges; meanwhile, the shearing position is arranged in the center of the clay rock sample, so that the sealing of the clay rock sample is not influenced; in addition, the circular impermeable plate has the same cross section as the upper and lower pistons, thereby avoiding the obstruction of the permeable stone to shearing.
Further, the upper piston cylinder and the lower piston cylinder are respectively provided with a threaded clamping ring for limiting the displacement of the upper piston and the lower piston, the clamping rings in the upper piston cylinder and the lower piston cylinder are respectively correspondingly connected with the annular water permeable plates in the upper water permeable plate and the lower water permeable plate, and sealing rings are respectively arranged between the clamping rings and the corresponding upper piston cylinder, upper piston, lower piston cylinder and lower piston.
Further, the gap between the side edge of the clay rock sample and the inner side edge of the shear box base is filled with epoxy resin for sealing.
The beneficial effects of adopting the further scheme are as follows: the epoxy resin ensures the water-impermeable boundary condition of the side surface of the clay rock sample, thereby improving the test precision.
Further, filter paper is respectively paved between the upper water permeable plate and the lower water permeable plate and the clay rock sample.
The beneficial effects of adopting the further scheme are as follows: in order to avoid the loss of the rock scraps of the clay rock sample and the blockage of the pipeline, filter papers with equal areas can be filled between the upper water permeable plate and the clay rock sample and between the lower water permeable plate and the clay rock sample.
Further, the pipe is a stainless steel capillary.
Drawings
FIG. 1 is a schematic diagram of the overall structure of a testing machine for measuring clay rock shear fracture permeability coefficient evolution by adopting a steady state method;
FIG. 2 is a schematic diagram of an explosion structure of a water permeable plate in a testing machine for measuring the evolution of the permeability coefficient of a clay rock shear fracture by adopting a steady state method.
In the drawings, the list of components represented by the various numbers is as follows:
1. the hydraulic servo loading device comprises a computer, 2, a controller, 3, a hydraulic servo loader, 3a, a first hydraulic servo loader, 3b, a second hydraulic servo loader, 3c, a third hydraulic servo loader, 4, a hydraulic sensor, 4a, a first piston cylinder hydraulic sensor, 4b, a pore water hydraulic sensor, 4c, a second piston cylinder hydraulic sensor, 5, a pipeline, 5a, a first pipeline, 5b, a second pipeline, 5c, a third pipeline, 5d, a fourth pipeline, 6, an LVDT displacement sensor, 7, an amplifier, 8, an upper piston, 9, a sealing ring, 10, a shear box top cover, 11, an upper piston cylinder, 12, a bolt, 13, a clamping ring, 14, an annular water permeable plate, 15, a circular water permeable plate, 16, epoxy resin, 17, a clay rock sample, 18, a lower piston, 19, a lower piston cylinder, 20, a shear box base, 21 and a water receiving container.
Detailed Description
The principles and features of the present invention are described below with reference to the drawings, the examples are illustrated for the purpose of illustrating the invention and are not to be construed as limiting the scope of the invention.
As shown in fig. 1, the tester for measuring the evolution of the permeability coefficient of the clay rock shear fracture by adopting a steady-state method comprises a computer 1, a controller 2, a hydraulic servo loader 3, a hydraulic sensor 4, a pipeline 5, an LVDT displacement sensor 6, an amplifier 7, an upper piston 8, a sealing ring 9, a shear box top cover 10, an upper piston cylinder 11, bolts 12, a clamping ring 13, an annular water permeable plate 14, a circular water permeable plate 15, epoxy resin 16, a clay rock sample 17, a lower piston 18, a lower piston cylinder 19, a shear box base 20 and a water receiving container 21. In this specific embodiment, the hydraulic servo loader 3 includes a first hydraulic servo loader 3a, a second hydraulic servo loader 3b, and a third hydraulic servo loader 3c; the controller 2 includes a first controller 2a, a second controller 2b, and a third controller 3c; the water pressure sensor 4 comprises a pore water pressure sensor 4b and a piston cylinder water pressure sensor, wherein the piston cylinder water pressure sensor comprises a first piston cylinder water pressure sensor 4a and a second piston cylinder water pressure sensor 4c; the pipes 5 include a first pipe 5a, a second pipe 5b, a third pipe 5c, and a fourth pipe 5d.
In this specific embodiment, the clay rock sample 17 is arranged in the shearing box, and the shearing box is used for punching and shearing the clay rock sample 17, specifically, the shearing box makes the clay rock sample shear through the movement of the hydraulic driving piston; the clay rock sample 17 is of a flat cylindrical structure with the thickness of 1-2 cm, the clay rock sample 17 is placed on the base of the shearing box after being processed, the permeation direction of the clay rock sample 17 is the thickness direction, and the permeation coefficient of the clay rock sample 17 can be accurately measured by adopting a steady-state method due to the short permeation path.
In this embodiment, the hydraulic servo loader 3 is connected to the upper side of the clay-rock sample 17 through a pipe (specifically, the second hydraulic servo loader 3b is connected to the upper side of the clay-rock sample 17 through a second pipe 5b, and the pore water pressure sensor 4b is disposed on the second pipe 5 b), and pore water is provided for the clay-rock sample 17; the lower part of the clay rock sample 17 is communicated to the atmosphere through a pipeline 5 (specifically, the lower part of the clay rock sample 17 is communicated to the atmosphere through a fourth pipeline 5d, and the tail end of the fourth pipeline 5d is also provided with a water receiving container 21, wherein the water receiving container 21 is used for collecting pore water permeated and flowed out of the clay rock sample 17); when the second hydraulic servo loader 3b applies pore water pressure to the upper side of the clay-rock sample 17 through the second pipe 5b, a constant head difference is formed between the upper and lower sides of the clay-rock sample 17, so that steady-state seepage can be generated, and the permeability coefficient of the clay-rock sample 17 with low permeability can be accurately measured by a steady-state method.
In this embodiment, the direction of the crack formed by shearing the clay rock sample 17 by the shearing box is parallel to the permeation path of the pore water in the clay rock sample 17, so that the influence of the shearing crack on the permeability coefficient of the clay rock sample can be accurately estimated.
In this specific embodiment, the piston cylinder water pressure sensor is used to measure the shear pressure of the shear box on the clay rock sample 17 (specifically, the first piston cylinder water pressure sensor 4a and the second piston cylinder water pressure sensor 4c are used to measure the shear pressure of the shear box on the clay rock sample 17). The LVDT displacement sensor 6 is mounted on the shear box and is adapted to measure the shear displacement of the shear box on the clay rock sample 17, in this particular embodiment the LVDT displacement sensor 6 is in particular an LVDT sensor.
In the present embodiment, the first hydraulic servo loader 3a is connected to a computer through the first controller 2a, the second hydraulic servo loader 3b is connected to a computer through the second controller 2b, and the third hydraulic servo loader 3c is connected to a computer through the third controller 2 c; the first piston cylinder water pressure sensor 4a is connected with the first controller 2a, the pore water pressure sensor 4b is connected with the second controller 2b, and the second piston cylinder water pressure sensor 4c is connected with the third controller 2 c; the LVDT displacement sensor 6 is connected to the computer 1 via the amplifier 7.
In this particular embodiment, the shear box comprises a shear box top cover 10 and a shear box base 20, wherein the shear box top cover 10 is mounted on the shear box base 20, and the shear box top cover 10 can be fixed on the shear box base 20 by bolts 12; the bottom of the shear box top cover 10 is provided with an upper piston cylinder 11 with a downward opening, the top of the shear box base 20 is provided with a lower piston cylinder 19 with an upward opening, and the upper piston cylinder 11 is opposite to the lower piston cylinder 19; an upper piston 8 is slidably arranged in the upper piston cylinder 11, and a seal is formed between the side wall of the upper piston 8 and the side wall of the upper piston cylinder 10; a lower piston 18 is slidably arranged in the lower piston cylinder 19, and a seal is formed between the side wall of the lower piston 18 and the side wall of the lower piston cylinder 19; the clay-rock sample 17 is located between the upper piston 8 and the lower piston 18, and the clay-rock sample 17 is sheared by driving the upper piston 8 and under the cooperation of the lower piston 18.
In this particular embodiment, the hydraulic servo-actuator 3 is also in communication with the upper and lower piston cylinders 11, 19 via the conduit 5 (specifically: the first hydraulic servo-actuator 3a is in communication with the upper and lower piston cylinders 11 via the first conduit 5a, the third hydraulic servo-actuator 3c is in communication with the lower piston cylinder 19 via the third conduit 5c, and the first piston cylinder hydraulic sensor 4a is disposed on the first conduit 5a, the second piston cylinder hydraulic sensor 4c is disposed on the third conduit 5 c), the hydraulic servo-actuators 3 (first and third hydraulic servo-actuators 3a, 3 c) inject hydraulic pressure into the upper and lower piston cylinders 11, 19 via the conduit 5 (first and third conduits 5a, 5 c), and the upper piston 8 is hydraulically driven and the clay sample 17 is sheared in cooperation with the lower piston 18.
In this embodiment, the top end of the upper piston 8 extends out of the shear box top cover 10, the LVDT displacement sensor 6 is mounted on the top end of the upper piston 8, and the sensing end of the LVDT displacement sensor 6 is in contact with the upper end surface of the shear box top cover 10.
In this embodiment, the clay rock sample 17 is disposed in the lower piston cylinder 19 through a lower water permeable plate, an upper water permeable plate is disposed in the upper piston cylinder 11, and the clay rock sample 17 is sandwiched between the upper water permeable plate and the lower water permeable plate; as shown in fig. 2, the upper water permeable plate and the lower water permeable plate (both made of water permeable stone material) respectively comprise a circular water permeable plate 15 and an annular water permeable plate 14, and the circular water permeable plate 15 is positioned in the circular holes of the annular water permeable plate 14; the circular water permeable plate 15 in the upper water permeable plate is opposite to the upper piston 8, the area of the circular water permeable plate 15 in the upper water permeable plate is equal to the sectional area of the upper piston 8, the circular water permeable plate 15 in the lower water permeable plate is opposite to the lower piston 18, the area of the circular water permeable plate 15 in the lower water permeable plate is equal to the sectional area of the lower piston 18, and meanwhile the sectional area of the upper piston 8 is equal to the sectional area of the lower piston 18; in the process of shearing the clay rock sample 17, the circular water permeable plate 15 in the upper water permeable plate moves along with the upper piston 8; the hydraulic servo loader 3 (the first hydraulic servo loader 3a and the third hydraulic servo loader 3 c) is filled with water into the upper piston cylinder 11 and the lower piston cylinder 19 through the pipeline 5 (the first pipeline 5a and the third pipeline 5 c), so that the movable pressure of the upper piston 8 and the lower piston 18 is provided, the upper piston 8 moves downwards to enable the clay rock sample 17 to generate downward shearing, and the lower piston 18 provides upward counterforce to enable the circular water permeable plate 15 in the lower water permeable plate to be closely attached to the bottom of the clay rock sample 17.
In this embodiment, threaded snap rings 13 are respectively disposed in the upper piston cylinder 11 and the lower piston cylinder 19, the snap rings 13 in the upper piston cylinder 11 and the lower piston cylinder 19 are respectively connected with the annular water permeable plates 14 in the upper water permeable plate and the lower water permeable plate correspondingly, and sealing rings 9 are respectively disposed between the snap rings 13 and the corresponding upper piston cylinder 11, upper piston 8, lower piston cylinder 19 and lower piston 18. A sealing ring 9 is also provided between the side wall of the upper piston 8 and the side wall of the shear box top cap 10.
In this embodiment, the gap between the lateral edge of the clay rock sample 17 and the lower piston cylinder 19 is filled with epoxy resin 16, and a sealing ring 9 is also arranged between the epoxy resin 16 and the lower piston cylinder 19.
In this embodiment or other embodiments, filter papers are respectively laid between the upper water permeable plate and the lower water permeable plate and the clay rock sample 17. The pipe 5 is a stainless steel capillary.
The testing steps performed by using the testing machine of the invention are as follows:
step 1: processing a clay rock sample 17 into a flat cylindrical structure with the thickness of 1-2 cm, mounting the clay rock sample on a shear box base 20, and sealing a gap at the outer side of the sample by adopting epoxy resin 16;
step 2: water is injected into the upper piston cylinder 11 and the lower piston cylinder 19 through the water pressure servo loader 3 (the first water pressure servo loader 3a and the third water pressure servo loader 3 c) so that about 20kPa pressure is respectively applied above and below the clay rock sample 17, and the upper piston 8 and the lower piston 18 are respectively tightly attached to the circular water permeable plates 15 in the upper water permeable plate and the lower water permeable plate;
step 3: the positions of the upper piston 8 and the lower piston 18 are controlled to be unchanged, pore water pressure is applied to the upper part of the clay rock sample 17 through the water pressure servo loader 3 (the second water pressure servo loader 3 b), a water head difference can be formed on the upper surface and the lower surface of the clay rock sample 17, water permeates from the top to the bottom through the clay rock sample 17 and flows into the water receiving container 21 through a pipeline (the fourth pipeline 5 d), the pore water pressure is measured through the pore water pressure sensor 4b, and when the seepage state reaches a steady state, the permeability coefficient of the clay rock sample 17 can be calculated;
step 4: reducing the water head above the clay-rock sample 17 to atmospheric pressure, after the pore pressure dissipates for about 20 minutes, injecting water into the upper piston cylinder 11 and the lower piston cylinder 19 through the water pressure servo loader 3 (the first water pressure servo loader 3a and the third water pressure servo loader 3 c) so as to drive the upper piston and the lower piston to 20kPa, balancing the upper pressure and the lower pressure of the clay-rock sample 17, keeping the lower piston pressure unchanged, enabling the lower water permeable plate to be tightly attached to the clay-rock sample, injecting water into the upper piston cylinder 11 through the water pressure servo loader 3 (the first water pressure servo loader 3 a), driving the upper piston to downwards move and punch the clay-rock sample 17, forming a circular shear crack in the middle of the clay-rock sample 17 (the shear position is in the center of the clay-rock sample 17, the shear position, the circumference and the width are all controllable), and simultaneously measuring the shear crack displacement and the upper piston pressure by the LVDT displacement sensor 6 and the piston cylinder water pressure sensor (the first piston cylinder water pressure sensor 4 a);
step 5: when the upper piston is sheared to different displacements, the position of the upper piston is controlled to be unchanged, the step 3 is repeated, and the evolution of the permeability coefficient of the clay rock sample 17 at different shearing stages is measured.
Step 6: when the upper piston is sheared to a certain displacement, the shearing displacement is controlled to be kept constant, so that the cracks of the clay rock sample 17 are gradually self-closed, the step 3 is repeated at different time, and the evolution of the permeability coefficient in the self-closing process of the cracks of the clay rock sample 17 after shearing is measured.
In the invention, pore water pressure is applied to the upper part of a clay rock sample 17 through a water pressure servo loader 3, a water head difference can be formed on the upper surface and the lower surface of the clay rock sample 17, water permeates from the top to the bottom through the clay rock sample 17 and flows into a water receiving container 21 through a pipeline, the pore water pressure is measured through a water pressure sensor, and when a seepage state reaches a steady state, a seepage coefficient can be calculated; the clay rock sample 17 can be sheared by driving the upper piston 8 and the lower piston 18 to move through the hydraulic servo loader 3, an annular shearing crack is formed in the middle of the clay rock sample 17, the shearing force is converted after being measured through a piston cylinder hydraulic sensor, and the shearing displacement can be measured through an LVDT displacement sensor; and when the shearing is carried out to different displacements, stopping the movement of the upper piston, controlling the only constant, applying pore water pressure at the top of the clay rock sample, and measuring the evolution of the permeability coefficient of the clay rock sample at different shearing stages. When shearing to a certain displacement, the piston displacement can be controlled to be kept constant, and the piston displacement is placed for a period of time, so that the crack of the clay rock sample is gradually self-closed under the hydration effect, pore water pressure applied to the top of the clay rock sample is subjected to different time, and the evolution of the permeability coefficient in the clay rock crack self-closing engineering is measured.
The osmotic coefficient calculation method comprises the following steps:
wherein Q is the amount of water passing through the sample in unit time; l is the sample thickness (m); gamma ray w Is the volume weight of water (kN/m 3); Δp w A is the pressure difference between the upper and lower ends of the sample, and A is the cross-sectional area (m 2) of the sample.
And in the shearing process, reading of the LVDT displacement sensor and the piston cylinder water pressure sensor is read in real time by a computer, and the shearing stress-strain relation of the clay rock sample can be obtained. Wherein the shear stress is:
wherein DeltaP is the difference between the axial pressures at the upper end and the lower end of the sample; d is the diameter of the shear fracture.
The shear strain is:
where Δu is the sample piston displacement.
The tester for measuring the permeability coefficient evolution of the clay rock shear fracture by adopting a steady-state method can completely measure the permeability coefficient evolution of a sample in the shear fracture forming and self-closing process; the permeability coefficient of the rock mass is measured by adopting a steady-state method, so that the precision is high; the sample preparation process is simple, the efficiency is high, and the success rate is high; the stress-strain relationship of the shear of the test specimen can be measured simultaneously.
The foregoing description of the preferred embodiments of the invention is not intended to limit the invention to the precise form disclosed, and any such modifications, equivalents, and alternatives falling within the spirit and scope of the invention are intended to be included within the scope of the invention.
Claims (9)
1. The tester for measuring the clay rock shear fracture permeability coefficient evolution by adopting a steady-state method is characterized in that: the device comprises a shearing box for shearing clay rock samples, a hydraulic servo loader, a hydraulic sensor and an LVDT displacement sensor; the clay rock sample is arranged in the shearing box, the clay rock sample is of a flat cylindrical structure, and the shearing box enables the clay rock sample to be sheared through hydraulic driving of piston movement; the hydraulic servo loader is communicated to the upper part of a clay rock sample in the shearing box through a pipeline, pore water is provided for the clay rock sample, pore water pressure is applied, the lower part of the clay rock sample is communicated to the atmosphere through a pipeline, and the shearing direction of the shearing box on the clay rock sample is parallel to the permeation path of the pore water in the clay rock sample; the hydraulic pressure sensor comprises a pore water pressure sensor and a piston cylinder hydraulic pressure sensor, the pore water pressure sensor is arranged on a pipeline of the hydraulic servo loader, which is communicated to the upper part of the clay rock sample, and the piston cylinder hydraulic pressure sensor is used for measuring the shearing pressure of the shearing box on the clay rock sample; the LVDT displacement sensor is arranged on the shear box and is used for measuring the shear displacement of the shear box on the clay rock sample;
the shearing box comprises a shearing box top cover and a shearing box base, an upper piston cylinder with a downward opening is arranged at the bottom of the shearing box top cover, a lower piston cylinder with an upward opening is arranged at the top of the shearing box base, an upper piston is slidably arranged in the upper piston cylinder, and a lower piston is slidably arranged in the lower piston cylinder;
the clay rock sample is arranged in the lower piston cylinder through a lower water permeable plate, an upper water permeable plate is arranged in the upper piston cylinder, and the clay rock sample is clamped between the upper water permeable plate and the lower water permeable plate; the upper water permeable plate and the lower water permeable plate respectively comprise a circular water permeable plate and an annular water permeable plate, and the circular water permeable plates are positioned in circular holes of the annular water permeable plates; the circular water permeable plate in the upper water permeable plate is opposite to the upper piston, the area of the circular water permeable plate in the upper water permeable plate is equal to the sectional area of the upper piston, the circular water permeable plate in the lower water permeable plate is opposite to the lower piston, the area of the circular water permeable plate in the lower water permeable plate is equal to the sectional area of the lower piston, and meanwhile the sectional area of the upper piston is equal to the sectional area of the lower piston.
2. The testing machine for measuring clay rock shear fracture permeability coefficient evolution by adopting a steady state method according to claim 1, wherein the testing machine is characterized in that: the hydraulic servo loader is characterized by also comprising a computer, a controller and an amplifier, wherein the computer is connected with the hydraulic servo loader through the controller, the LVDT displacement sensor is connected with the computer through the amplifier, and the pore water pressure sensor and the piston cylinder water pressure sensor are both connected with the controller.
3. The testing machine for measuring the evolution of the permeability coefficient of a clay rock shear fracture by adopting a steady-state method according to claim 1 or 2, wherein: the shearing box top cover is installed on the shearing box base, the upper piston cylinder is opposite to the lower piston cylinder in position, the side wall of the upper piston is sealed with the side wall of the upper piston cylinder, the side wall of the lower piston is sealed with the side wall of the lower piston cylinder, the clay rock sample is located between the upper piston and the lower piston, and the clay rock sample is sheared by driving the upper piston and under the cooperation of the lower piston.
4. The testing machine for measuring clay rock shear fracture permeability coefficient evolution by adopting a steady state method according to claim 3, wherein the testing machine is characterized in that: the hydraulic servo loader is also communicated with the upper piston cylinder and the lower piston cylinder respectively through pipelines, injects hydraulic pressure into the upper piston cylinder and the lower piston cylinder through the pipelines, drives the upper piston through the hydraulic pressure and shears the clay rock sample under the cooperation of the lower piston; the two piston cylinder water pressure sensors are correspondingly arranged on pipelines of the water pressure servo loader, which are respectively communicated with the upper piston cylinder and the lower piston cylinder.
5. The testing machine for measuring clay rock shear fracture permeability coefficient evolution by adopting a steady state method according to claim 3, wherein the testing machine is characterized in that: the top end of the upper piston extends out of the shear box top cover, the LVDT displacement sensor is mounted on the top end of the upper piston, and the sensing end of the LVDT displacement sensor is in contact with the upper end face of the shear box top cover.
6. The testing machine for measuring clay rock shear fracture permeability coefficient evolution by adopting a steady state method according to claim 1, wherein the testing machine is characterized in that: the upper piston cylinder and the lower piston cylinder are respectively provided with a threaded clamping ring used for limiting the displacement of the upper piston and the lower piston, the clamping rings in the upper piston cylinder and the lower piston cylinder are respectively correspondingly connected with the annular water permeable plates in the upper water permeable plate and the lower water permeable plate, and sealing rings are respectively arranged between the clamping rings and the corresponding upper piston cylinder, upper piston, lower piston cylinder and lower piston.
7. The testing machine for measuring the evolution of the permeability coefficient of a clay rock shear fracture by adopting a steady-state method according to claim 1 or 6, wherein the testing machine is characterized in that: and the gap between the side edge of the clay rock sample and the inner side edge of the shear box base is filled with epoxy resin for sealing.
8. The testing machine for measuring the evolution of the permeability coefficient of a clay rock shear fracture by adopting a steady-state method according to claim 1 or 6, wherein the testing machine is characterized in that: filter paper is respectively paved between the upper water permeable plate and the lower water permeable plate and the clay rock sample.
9. The testing machine for measuring clay rock shear fracture permeability evolution by adopting a steady state method according to any one of claims 1-2 and 4-6, wherein: the pipeline is a stainless steel capillary.
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