Visual seepage test device and method for shear fracture of rock structural surface under true triaxial condition

Abstract

The invention discloses a visual seepage test device and method for shear fracture of a rock structural surface under true triaxial. The visual seepage test device comprises a fixed base, a lower shear box, an upper shear box, a seepage water inlet pipe, a seepage water outlet pipe, a seepage water inlet shear head and a seepage water outlet shear head, the fixed base is connected with a normal loading block of a true triaxial testing machine through pin nails, the lower shear box is fixed on the fixed base, the upper shear box and the lower shear box are oppositely arranged, and the seepage water inlet shear head and the seepage water outlet shear head are respectively embedded into the lower shear box and the upper shear box to form a water injection cavity I and a water injection cavity II; after the lower shearing box and the upper shearing box are closed, a closed sample cavity for clamping a rock sample and a transparent block is formed, and meanwhile, the water injection cavity I and the water injection cavity II form a seepage cavity. According to the device and the method, the visual shear simulation of the rock mass structural surface under the multi-field coupling environment of true three-dimensional stress-high osmotic pressure-chemical corrosion and the like is realized.

Description

Technical Field

[0001] The present invention relates to the technical field of rock mechanics testing, and in particular to a device and method for visualizing seepage flow testing of shear fracture of rock structural surfaces under true triaxial testing. Background Art

[0002] As an important branch of geological engineering, rock mechanics plays an irreplaceable role in ensuring engineering safety and improving resource utilization efficiency. The rock structural surface is the interface between units with different mechanical properties within the rock mass. Its shear fracture process is often accompanied by the release of energy and the redistribution of stress, which has a significant impact on the overall mechanical behavior of the rock. The seepage process in the rock is closely related to factors such as the structure, porosity, and permeability of the rock, and has an important influence on the mechanical properties and hydrogeological conditions of the rock. In-depth research on the mechanical behavior and seepage characteristics of the rock structural surface during the shear fracture process has important guiding significance for revealing the failure mechanism of the rock, predicting the stability of the engineering structure, and optimizing the engineering design and construction.

[0003] Most of the existing rock shear fracture seepage test devices can only simulate uniaxial stress conditions and cannot truly reflect the mechanical behavior and seepage characteristics of rocks under complex stress environments. The test results under uniaxial stress conditions are often unable to accurately predict the performance of rocks in actual projects, resulting in errors and increased risks in engineering design and construction. In addition, the existing test devices also have certain limitations in observation methods. Traditional observation methods can often only obtain the deformation and fracture conditions of the rock surface, and cannot intuitively observe and analyze the seepage process and fluid flow conditions inside the rock. The above reasons have led to certain difficulties in deeply understanding the rock seepage mechanism. Therefore, the development of a true triaxial rock structural surface shear fracture visualization seepage test device is of great value for in-depth research on rock seepage mechanisms and improving the accuracy of rock strength predictions. Summary of the Invention

[0004] In order to solve the technical problems existing in the background technology, the present invention proposes a device and method for visualizing seepage test of shear fracture of rock structural surface under true triaxial conditions.

[0005] The present invention proposes a true triaxial rock structure surface shear fracture visualization seepage test device, which includes a fixed base, a lower shear box, an upper shear box, a seepage inlet pipe, a seepage outlet pipe, a seepage inlet shear head and a seepage outlet shear head; the fixed base is connected to the normal loading block of the true triaxial testing machine through dowels, the lower shear box is fixed on the fixed base, the upper shear box and the lower shear box are arranged relative to each other, and the seepage inlet shear head and the seepage outlet shear head are respectively embedded in the lower shear box and the upper shear box to form a first water injection cavity and a second water injection cavity. After the lower shear box and the upper shear box are closed, a closed sample cavity is formed for clamping the rock sample and the transparent block. At the same time, the water injection cavity one and the water injection cavity two form a seepage cavity. The inlet of the water injection cavity one is connected to one end of the seepage water inlet pipe, and the outlet of the water injection cavity two is connected to one end of the seepage water outlet pipe. The upper plate of the upper shear box is embedded with a transparent block, and the transparent block is in direct contact with the top surface of the rock sample. The upper cover of the upper shear box is rigidly connected to the upper pressure head. A slot is provided at the bottom of the upper pressure head. An endoscope is installed in the slot, and the endoscope lens is facing the top surface of the transparent block.

[0006] Preferably, the seepage chamber is integrated with at least two seepage water pressure measuring devices, at least two seepage flow measuring devices, at least two Ca 2+ and Cl - The solution ion concentration and pH measuring device, the seepage cavity, the seepage inlet pipe and the seepage outlet pipe form a seepage pipeline.

[0007] Preferably, a fill light with adjustable brightness is arranged in a ring around the endoscope, and an anti-reflection film is attached to the top surface of the transparent block.

[0008] Preferably, it also includes: a seepage water inlet seal, a lower sealing strip, an upper sealing strip, a partition plate, and a seepage water outlet seal. The lower sealing strip and the upper sealing strip are respectively embedded in the rectangular grooves of the lower and upper shear boxes. The partition plate is clamped between the upper shear box and the lower shear box by bolts. The edge of the partition plate fits tightly with the lower sealing strip and the upper sealing strip to form a double-layer sealing structure. The seepage water inlet seal and the seepage water outlet seal are fixed to the inlet / outlet of the seepage cavity by bolts, and form a multi-layer pressure-resistant sealing system with the lower sealing strip, the upper sealing strip, and the partition plate.

[0009] Preferably, the size of the transparent block and the rock sample is determined as follows:

[0010] The endoscope can be fine-tuned up and down in the upper pressure head and the diagonal field of view is 2 The bottom of the endoscope is set at a distance of h mm from the top of the transparent block. The length and width of the opening on the lower side of the upper pressure head are both 2b mm. According to the law of refraction of light, the value range of h is:

[0011] ;

[0012] The refractive index of the transparent block is n and the height is H. The refraction angle of the transparent block is determined according to the law of refraction of light: ;

[0013] in, is the angle of incidence, is the refraction angle, and further we can get the theoretical width L of the endoscope's field of view at the bottom of the transparent block as:

[0014] ;

[0015] The length of the transparent block should be less than L and greater than 0.5L and 1.5H, and the width of the transparent block should be half of the length; the length, width and height of the rock sample should be consistent with those of the transparent block.

[0016] Preferably, it also includes: a lateral pressure plate, a normal deformation measuring assembly, a tangential deformation measuring assembly, and a lateral deformation measuring assembly; one end of the normal deformation measuring assembly is fixedly connected to the upper pressure head, and the other end abuts against the upper cover surface of the upper shear box, and the upper pressure head fits with the transparent block. When the rock sample undergoes normal deformation, the upper pressure head moves with the transparent block, driving the normal deformation measuring assembly to expand and contract, and measure the normal displacement in real time; one end of the tangential deformation measuring assembly is fixedly connected to the force transmission block of the lower shear box, and the other end abuts against the upper shear box. On the surface of the upper cover, the upper shear box and the lower shear box undergo tangential relative displacement, and the shear force is transmitted through the force transmission block. The tangential deformation measurement assembly expands and contracts with the displacement, and the tangential displacement is measured in real time. The lateral pressure plate includes lateral pressure plate I and lateral pressure plate II. The two ends of the lateral deformation measurement assembly are respectively fixed to the pressure plate of lateral pressure plate I and the pressure plate of lateral pressure plate II by bolts. After the lateral pressure plate is subjected to lateral loading by the true triaxial testing machine, the pressure plate pushes the rock sample to generate lateral deformation, and the lateral deformation measurement assembly measures the lateral strain through the displacement difference at both ends.

[0017] A method for visualizing seepage flow through a rock structure surface under true triaxial shear fracture is applied to a device for visualizing seepage flow through a rock structure surface under true triaxial shear fracture, as described above. The method comprises the following steps:

[0018] S1: Install the rock specimen and the transparent block in the lower shear box, apply normal preload, lateral preload and tangential preload, and simultaneously apply normal stress, lateral stress and tangential shear force;

[0019] S2: injecting high-pressure acidic fluid into the seepage cavity through the seepage inlet pipe and controlling the water pressure difference between the seepage inlet pipe and the seepage outlet pipe;

[0020] S3: Record the seepage water pressure, flow rate, ion concentration, and pH value in the seepage pipeline every n minutes, calculate the permeability k based on Darcy's law, and calculate the damage degree Dc in combination with the stress-corrosion coupled damage model, where n ≥ 1;

[0021] S4: Based on the results calculated in the above steps, draw the permeability-time curve, damage degree-time curve and shear stress-strain curve to evaluate the rock failure mechanism.

[0022] Preferably, in step S1, during the test, normal pressure is first applied to the upper pressure head and the fixed base, which then apply normal pressure to the rock sample and the transparent block, and then lateral pressure is applied to lateral pressure plates I and II, which then apply lateral pressure to the rock sample and the transparent block.

[0023] Preferably, it also includes:

[0024] S5: During the test, adjust the distance between the endoscope and the top surface of the transparent block, and observe the seepage of high-pressure water and acidic fluid in the shear box and the real-time status of the rock structure surface sample through the endoscope.

[0025] Preferably, the permeability k is calculated based on Darcy's law as follows:

[0026] ;

[0027] in, for The average permeability of the rock over time; H is the average height of the rock sample, is the dynamic viscosity coefficient of water, =1×10 -3 Pa*s; for The volume of liquid that penetrates into the rock sample in a certain period of time; The water pressure difference at both ends of the sample is the osmotic pressure difference; is the time interval between recording points, and A is the cross-sectional area of ​​the sample.

[0028] Preferably, the damage degree Dc is calculated in combination with the stress-corrosion coupled damage model as follows:

[0029] ;

[0030] in, It is stress-corrosion coupling damage caused by chemical corrosion. and is the balancing coefficient, H at t minutes + The average concentration value of is Ca at t minutes 2+ The average concentration value of is the initial moment H + The average concentration value, M and is the chemical reaction coefficient, is the volume of the chemical solution.

[0031] In the present invention, the proposed device and method for visual seepage test of shear fracture of rock structural surface under true triaxial test realizes seepage shear test of rock structural surface under visual state, and the seepage situation of seepage water and the real-time situation of rock structural surface sample can be observed during the test; the present invention can adjust the water pressure difference on both sides of the rock structural surface sample during the test, and can quantitatively measure the permeability and chemical corrosion damage; the present invention adopts Hastelloy B-2 alloy to make the structural surface true triaxial shear box, and the structural surface true triaxial shear box adapts to the acidic fluid penetration corrosion environment under true three-dimensional stress loading; the present invention adopts a new sealing structure, taking into account the extrusion deformation of the sealing strip, through the cooperation of the shear box device, the high-pressure water seepage system and the sealing component, it can withstand higher seepage water pressure under large deformation shear conditions, and realize complete sealing of high-pressure water in the rock shear and seepage process; the present invention restores the real stress of the engineering site indoors to a higher degree through the multi-field coupling environment of true three-dimensional stress-high permeability pressure-chemical corrosion, and can more accurately understand the rock shear fracture mechanism and deformation law. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is a schematic diagram of the overall structure of the device for visualizing seepage flow testing of rock structure surface shear fracture under true triaxial conditions according to the present invention;

[0033] Figure 2 It is a side cross-sectional schematic diagram of the structure of the rock structure surface shear fracture visualization seepage test device for the present invention under true triaxial conditions;

[0034] Figure 3 It is a structural schematic diagram of the lower shear box of the present invention;

[0035] Figure 4 It is a structural schematic diagram of the upper pressurizing assembly of the present invention;

[0036] Figure 5 Schematic diagram of the structure of the normal deformation measurement assembly of the present invention;

[0037] Figure 6 Schematic diagram of the structure of the lateral deformation measurement assembly of the present invention;

[0038] Figure 7 is a stress path diagram of an embodiment of the present invention;

[0039] Figure 8 is a graph showing changes in permeability over time according to an embodiment of the present invention;

[0040] Figure 9 is a graph showing the stress-corrosion coupled damage degree of rock over time according to an embodiment of the present invention;

[0041] Figure 102 is a shear stress-strain curve diagram of an embodiment of the present invention.

[0042] Legend:

[0043] 1. Fixed base; 2. Lower shear box; 201. Base; 202. First shear pressure head; 203. First force transmission block; 204. Lower sealing strip; 205. Seepage inlet shear head; 206. First shear head; 207. First side pressure head; 208. First mixed row; 209. Spacer; 210. Tangential deformation measurement assembly; 211. Seepage inlet seal; 212. Seepage inlet pipe; 213. First seepage water pressure measurement device; 214. First seepage flow measurement device; 215. Ca 2+ and Cl - Solution ion concentration and pH measurement device 1; 3, upper shear box; 301, upper cover; 302, second shear pressure head; 303, second force transmission block; 304, upper sealing strip; 305, seepage water shear head; 306, second shear head; 307, second side pressure head; 308, second mixed row; 309, seepage water seal; 310, seepage water pipe; 311, second seepage water pressure measurement device; 312, second seepage flow measurement device; 313, Ca 2+ and Cl - Solution ion concentration and pH measurement device II; 314, rolling pad; 4, lateral pressure plate I; 401, fixed plate II; 402, first pressure plate; 403, first buckle plate; 404, lateral deformation measurement component; 5, lateral pressure plate II; 501, fixed plate I; 502, second pressure plate; 503, second buckle plate; 6, upper pressure component; 601, upper pressure head; 602, endoscope; 603, fill light; 604, normal deformation measurement component. DETAILED DESCRIPTION

[0044] Reference Figure 1-10The present invention proposes a true triaxial lower rock structure surface shear fracture visualization seepage test device, comprising a fixed base 1, a lower shear box 2, an upper shear box 3, a seepage inlet pipe 212, a seepage outlet pipe 310, a seepage inlet shear head 205 and a seepage outlet shear head 305; the fixed base 1 is connected to the normal loading block of the true triaxial testing machine through a pin, the lower shear box 2 is fixed on the fixed base 1, the upper shear box 3 and the lower shear box 2 are arranged relative to each other, and the seepage inlet shear head 205 and the seepage outlet shear head 305 are respectively embedded in the lower shear box 2 and the upper shear box 3 to form a water injection cavity 1 and a water injection cavity 2. Second, after the lower shear box 2 and the upper shear box 3 are closed, a sealed sample cavity for clamping the rock sample and the transparent block is formed. At the same time, the water injection cavity 1 and the water injection cavity 2 form a seepage cavity. The inlet of the water injection cavity 1 is connected to one end of the seepage water inlet pipe 212, and the outlet of the water injection cavity 2 is connected to one end of the seepage water outlet pipe 310. The upper plate of the upper shear box 3 is embedded with a transparent block, and the transparent block is in direct contact with the top surface of the rock sample. The upper cover 301 of the upper shear box 3 is rigidly connected to the upper pressure head 601. The lower part of the upper pressure head 601 is provided with a slot, and an endoscope 602 is installed in the slot. The lens of the endoscope 602 is facing the top surface of the transparent block.

[0045] Specifically, the shear box device includes a fixed base 1, a lower shear box 2, an upper shear box 3, a lateral pressure plate, and an upper pressure assembly 6. The lower shear box 2 includes a base 201, a first shear pressure head 202, a first force transmission block 203, a sealing strip bottom 204, a seepage water shear head 205, a first shear head 206, a first lateral pressure head 207, a first mixing row 208, a spacer 209, a tangential deformation measurement assembly 210, a seepage water seal 211, a seepage water inlet pipe 212, a first seepage water pressure measuring device 213, a first seepage flow measuring device 214, and a Ca 2+ and Cl -Solution ion concentration and pH measuring device 215; the first shear pressure head 202 and the first force transmission block 203 are fixed to the base 201 by bolt connection to apply tangential force; the sealing strip 204 is installed and fixed in the rectangular groove of the base 201 to achieve lateral and tangential sealing; the seepage water inlet shear head 205 is installed on the side of the seepage water inlet in the base 201 to achieve uniform pressure during high-pressure water seepage; the first shear head 206 is arranged relative to the seepage water inlet shear head 205, and the first shear head 206 is installed on the other side of the base 201 to apply shear force; the first side pressure head 207 and the first mixing row 208 are arranged on both sides of the base 201, and the first side pressure head 207 is installed on both sides of the base 201 to apply test force to the rock sample. Required lateral pressure; the first mixing row 208 is installed on the outside of the first lateral pressure head 207 close to the lateral pressure head to reduce friction and reduce the impact of friction on the test; the spacer 209 is installed between the lower shear box 2 and the upper shear box 3 to achieve sealing between the upper shear box 3 and the lower shear box 2 during the seepage test; the tangential deformation measurement component 210 is fixed on the first force transmission block 203 to measure the deformation size in the shear direction during the test; the seepage water inlet seal 211 is installed and fixed on the side of the base 201 where no force is applied in the shear direction to achieve sealing during water inlet; the seepage water inlet pipe 212 is connected to the seepage water inlet seal 211 to achieve injection of high-pressure water and acidic fluid; the first seepage water pressure measuring device 213, the first seepage flow measuring device 214, Ca 2+ and Cl - The solution ion concentration and pH measuring device 215 is installed on the seepage inlet pipe 212 to measure the water pressure, seepage flow rate, solution ion concentration and pH value of the rock structure surface sample on the water inlet side. The upper shear box 3 is arranged relative to the lower shear box 2. The upper shear box 3 includes an upper cover 301, a second shear pressure head 302, a second force transmission block 303, a sealing strip 304, a seepage outflow shear head 305, a second shear head 306, a second side pressure head 307, a second mixing row 308, a seepage outflow seal 309, a seepage outflow pipe 310, a second seepage water pressure measuring device 311, a second seepage flow measuring device 312, a Ca 2+ and Cl -Solution ion concentration and pH measuring device 2 313, rolling row 314; the second shear pressure head 302 and the second force transmission block 303 are fixed to the upper cover 301 by bolt connection, used to apply tangential force; the sealing strip 304 is installed and fixed in the rectangular groove of the upper cover 301, used to achieve lateral and tangential sealing; the seepage water shear head 305 is installed on the side of the seepage outlet in the upper cover 301, used to achieve uniform pressure during high-pressure water seepage; the second shear head 306 is arranged opposite to the seepage water shear head 305, and the second shear head 306 is installed on the other side of the tangential direction of the upper cover 301 to apply shear force; the second side pressure head 307 and the second mixed row 308 is set on both sides of the upper cover 301, and the second side pressure head 307 is installed on both sides of the upper cover 301 to apply the lateral pressure required for the test to the rock sample; the second mixing row 308 is installed on the outside of the second side pressure head 307 close to the side pressure head to reduce friction and reduce the impact of friction on the test; the seepage water seal 309 is installed and fixed on the side of the upper cover 301 where no force is applied in the shear direction to achieve sealing when water is entering; the seepage water pipe 310 is connected to the seepage water seal 309 to achieve high-pressure water and acidic fluid injection; the second seepage water pressure measuring device 311, the second seepage flow measuring device 312, and the Ca 2+ and Cl -The second solution ion concentration and pH measuring device 313 is installed on the seepage outlet pipe 310 to measure the water pressure, seepage flow, solution ion concentration and pH value of the rock structure surface sample on the water inlet side; the roller 314 is installed and fixed on both sides of the normal part of the upper cover 301 to reduce the friction force generated by the movement of the upper shear box 3 during the shear test. The lateral pressure plate includes a lateral pressure plate I4 and a lateral pressure plate II5; the lateral pressure plate II5 and the lateral pressure plate I4 are arranged opposite each other on the left and right sides of the shear box; the lateral pressure plate I4 includes a fixed plate I401, a first pressure plate 402, a first buckle plate 403, and a lateral deformation measuring assembly 404; the fixed plate I401 is installed on the right side of the shear box; the first pressure plate 402 is installed in the reserved hole of the fixed plate I401 to transmit lateral pressure; the first buckle plate 403 is connected to the fixed plate I401 by bolts and is attached to the roller 314 on the upper part of the upper shear box 3; the two ends of the lateral deformation measuring assembly 404 are respectively fixed on the first pressure plate 402 of the lateral pressure plate I4 and the second pressure plate 502 of the lateral pressure plate II5 to measure lateral deformation. The lateral pressure plate II includes a fixed plate II 501, a second pressure plate 502, and a second buckle plate 503. The fixed plate II 501 is installed on the left side of the shear box. The second pressure plate 502 is installed in the reserved hole of the fixed plate II 501 to transmit lateral pressure. The second buckle plate 503 is connected to the fixed plate II 501 by bolts and is close to the roller 314 on the upper part of the upper shear box 3. The upper pressure assembly 6 includes an upper pressure head 601, an endoscope 602, a fill light 603, and a normal deformation measurement assembly 604. The endoscope 602 is installed and fixed in the opening space below the upper pressure head 601 to observe the changes in the rock sample during the test and the seepage of high-pressure water and acidic fluid. The fill light 603 is installed around the endoscope 602. The normal deformation measurement assembly 604 has one end fixed to the upper pressure head 601 and the other end installed on the top of the upper cover 301 of the upper shear box 3 to measure the deformation in the shear direction during the test. The transparent block is made of transparent high-strength material and is tightly connected to the rock structure surface sample. It is used to transmit shear force to the rock structure surface sample and provide observation space for the endoscope 602. The anti-reflection colorless transparent film is attached to the top surface of the transparent block in the direction of the fill light 603 to increase the transmitted light and reduce the reflection.

[0046] In this embodiment, the seepage cavity is integrated with at least two seepage water pressure measuring devices, at least two seepage flow measuring devices, at least two Ca 2+ and Cl - The solution ion concentration and pH measuring device, the seepage cavity, the seepage water inlet pipe 212 and the seepage water outlet pipe 310 form a seepage pipeline.

[0047] Specifically, the high-pressure water and acidic fluid seepage assembly is arranged in the shear box device, including a seepage inlet pipe 212, a seepage inlet seal 211, a seepage inlet shear head 205, a seepage outlet shear head 305, a seepage outlet seal 309, a seepage outlet pipe 310, first seepage water pressure measuring devices 213 and 311, a first seepage flow measuring device 214 and a second seepage flow measuring device 312, a Ca 2+ and Cl - Solution ion concentration and pH measurement device - 215 and Ca 2+ and Cl - Solution ion concentration and pH measuring device 2 313; seepage water inlet pipe 212 is connected to seepage water inlet seal 211; the open end of the water injection chamber 1 arranged in the lower shear box 2 is the seepage water inlet of high-pressure water and acidic fluid, and the seepage water inlet seal 211 is connected to the water injection chamber 1, and the high-pressure water and acidic fluid enter the water injection chamber 1 from the seepage water inlet pipe 212 through the seepage water inlet seal 211, and then flow into the seepage water inlet shear head 205 from the water injection chamber 1, and then flow out from the other end of the seepage water inlet shear head 205, and high-pressure water and acidic fluid seepage are carried out in the shear box; the open end of the water injection chamber 2 arranged in the upper shear box 3 is the seepage outlet; the high-pressure water and acidic fluid seepage flows into the water injection chamber 2 from the seepage outlet shear head 305, and then flows into the seepage outlet pipe 310 from the water injection chamber 2 through the seepage outlet seal 309, and the high-pressure water and acidic fluid at the seepage end flow out from the seepage outlet pipe 310. The first seepage water pressure measuring devices 213 and 311 are used to measure the water pressure on both sides of the seepage inlet and outlet of the rock sample; the first seepage flow measuring device 214 and the second seepage flow measuring device 312 are used to measure the seepage inlet and outlet flow rates; 2+ and Cl - Solution ion concentration and pH measurement device - 215 and Ca 2+ and Cl - The second solution ion concentration and pH measuring device 313 is used to measure the solution ion concentration and pH value in high-pressure water and acidic fluid.

[0048] In this embodiment, a fill light 603 with adjustable brightness is arranged in a ring around the endoscope 602, and an anti-reflection film is attached to the top surface of the transparent block.

[0049] In this embodiment, it also includes: a seepage water inlet seal 211, a lower sealing strip 204, an upper sealing strip 304, a partition plate 209, and a seepage water outlet seal 309. The lower sealing strip 204 and the upper sealing strip 304 are respectively embedded in the rectangular grooves of the lower and upper shear boxes 3. The partition plate 209 is clamped between the upper shear box 3 and the lower shear box 2 by bolts. The edge of the partition plate 209 fits tightly with the lower sealing strip 204 and the upper sealing strip 304 to form a double-layer sealing structure. The seepage water inlet seal 211 and the seepage water outlet seal 309 are fixed to the inlet / outlet of the seepage cavity by bolts, and form a multi-layer pressure-resistant sealing system with the lower sealing strip 204, the upper sealing strip 304, and the partition plate 209.

[0050] Specifically, a multi-layer pressure-resistant sealing system is arranged in the shear box device, including a seepage water inlet seal 211, a lower sealing strip 204, an upper sealing strip 304, a partition plate 209, and a seepage water outlet seal 309; the two ends of the seepage water inlet seal 211 are respectively connected to the seepage water inlet pipe 212 and the seepage water inlet, for sealing during water inlet; the lower sealing strip 204 and the upper sealing strip 304 are respectively installed in the lower shear box 2 and the upper shear box 3, for sealing in the shear box during seepage; the partition plate 209 is installed between the upper shear box 3 and the lower shear box 2, for sealing between the upper shear box 3 and the lower shear box 2; the two ends of the seepage water outlet seal 309 are respectively connected to the seepage water outlet pipe 310 and the seepage water outlet, for sealing during water outlet.

[0051] It should be noted that the shear box device, high-pressure water and acidic fluid seepage components, and multi-layer pressure-resistant sealing system are made of Hastelloy B-2 alloy, which is resistant to corrosion by high-concentration hydrochloric acid under normal pressure. The melting point of Hastelloy B-2 alloy is 1330~1380℃.

[0052] In this embodiment, the dimensions of the transparent block and the rock sample are determined as follows:

[0053] The endoscope 602 can be fine-tuned up and down in the upper pressure head 601 and the diagonal field of view is 2 The bottom of the endoscope 602 is set at a distance of hmm from the top of the transparent block, and the length and width of the opening on the lower side of the upper pressure head 601 are both 2bmm. According to the law of refraction of light, the value range of h is:

[0054] ;

[0055] The refractive index of the transparent block is n and the height is H. The refraction angle of the transparent block is determined according to the law of refraction of light: ;

[0056] in, is the angle of incidence, is the refraction angle, and further, the theoretical width L of the field of view of the endoscope 602 at the bottom of the transparent block is:

[0057] ;

[0058] The length of the transparent block should be less than L and greater than 0.5L and 1.5H, and the width of the transparent block should be half of the length; the length, width and height of the rock sample should be consistent with those of the transparent block.

[0059] In this embodiment, it also includes: a lateral pressure plate, a normal deformation measurement component 604, a tangential deformation measurement component 210, and a lateral deformation measurement component 404; one end of the normal deformation measurement component 604 is fixedly connected to the upper pressure head 601, and the other end is in contact with the surface of the upper cover 301 of the upper shear box 3. The upper pressure head 601 is in contact with the transparent block. When the rock sample undergoes normal deformation, the upper pressure head 601 moves with the transparent block, driving the normal deformation measurement component 604 to expand and contract, and measuring the normal displacement in real time; one end of the tangential deformation measurement component 210 is fixedly connected to the force transmission block of the lower shear box 2, and the other end is fixedly connected to the force transmission block of the lower shear box 2. Abutting against the surface of the upper cover 301 of the upper shear box 3, the upper shear box 3 and the lower shear box 2 undergo tangential relative displacement, and the shear force is transmitted through the force transmission block. The tangential deformation measuring assembly 210 expands and contracts with the displacement to measure the tangential displacement in real time; the lateral pressure plate includes a lateral pressure plate I4 and a lateral pressure plate II5, and the two ends of the lateral deformation measuring assembly 404 are respectively fixed to the pressure plate of the lateral pressure plate I4 and the pressure plate of the lateral pressure plate II5 by bolts. After the lateral pressure plate is subjected to lateral loading by the true triaxial testing machine, the pressure plate pushes the rock sample to generate lateral deformation, and the lateral deformation measuring assembly 404 measures the lateral strain through the displacement difference at both ends.

[0060] Specifically, the deformation measuring device is arranged in the shear box device, including a normal deformation measuring component 604, a tangential deformation measuring component 210, and a lateral deformation measuring component 404; one end of the normal deformation measuring component 604 is installed and fixed on the upper pressure head 601, and the other end is pressed on the upper cover 301 of the upper shear box 3. During the test, the normal deformation measuring component 604 and the upper pressure head 601 are integrated. Since the upper pressure head 601 is tightly attached to the transparent block, when the rock structure surface sample below the transparent block undergoes normal deformation, the upper pressure head 601 also moves in the normal direction accordingly. The end of the normal deformation measuring component 604 fixed on the upper pressure head 601 also moves in the normal direction with the upper pressure head 601, and the end of the normal deformation measuring component 604 pressed on the upper cover 301 of the upper shear box 3 does not move, and is used to measure the normal deformation of the rock structure surface sample during the test by extending and retracting the deformation head toward the deformation measuring component 604; the tangential deformation measuring component 210 and the normal deformation measuring component 604 The components have the same structure, one end is fixed on the first force transmission block 203 of the lower shear box 2, and the other end is pressed on the upper cover 301 of the upper shear box 3. During the test, the tangential deformation measuring component 210 and the lower shear box 2 are integrated, and the end fixed on the lower shear box 2 does not move. When the upper shear box 3 moves tangentially due to shear, the end of the tangential deformation measuring component 210 pressing on the upper shear box 3 also moves tangentially. Through the expansion and contraction of the tangential deformation measuring component 210, it is used to measure the tangential deformation of the rock structure surface sample during the test; the lateral deformation measuring component 404, the two ends of which are respectively fixed on the first pressure plate 402 of the lateral pressure plate I4 and the second pressure plate 502 of the lateral pressure plate II5. During the test, the deformation head of the lateral deformation measuring component 404 also expands and contracts as the first pressure plate 402 and the second pressure plate 502 move laterally. Through the expansion and contraction of the deformation head of the lateral deformation measuring component 404, it is used to measure the lateral deformation of the rock structure surface sample during the test.

[0061] Reference Figure 1-10 The present invention proposes a true triaxial rock structure surface shear fracture visualization seepage test method, which is applied to any of the true triaxial rock structure surface shear fracture visualization seepage test devices described above. The method comprises the following steps:

[0062] S1: Install the rock sample and the transparent block in the lower shear box 2, apply normal preload, lateral preload and tangential preload, and simultaneously apply normal stress, lateral stress and tangential shear force.

[0063] In this embodiment, in step S1, during the test, normal pressure is first applied to the upper pressure head 601 and the fixed base 1, and the upper pressure head 601 and the fixed base 1 then apply normal pressure to the rock sample and the transparent block, and then lateral pressure is applied to the lateral pressure plates I4 and II5, and the lateral pressure plates I4 and II5 apply lateral pressure to the rock sample and the transparent block.

[0064] Specifically, before step S1, the method further includes:

[0065] First, place the fixed base 1 in the loading interval of the true triaxial testing machine and connect it to the normal loading block at the bottom of the true triaxial testing machine; fix the bottom surface of the base 201 of the lower shear box 2 on the fixed base 1 through pins; install the rock sample and the transparent block in the lower shear box 2, ensuring that the bottom surface of the rock sample is in close contact with the base 201 of the lower shear box 2; buckle the upper shear box 3 on the rock sample and the transparent block, ensuring that the upper cover 301 of the upper shear box 3 is in close contact with the transparent block; install the lateral pressure plate I4 and the lateral pressure plate II5 on the left and right sides of the upper shear box 3 and the lower shear box 2 respectively, and make the first buckle plate 403 and the second buckle plate 503 of the lateral pressure plate I4 and the lateral pressure plate II5 in close contact with the roller 314 of the upper shear box 3; adjust the position of the angle endoscope 602, the diagonal field of view (FOV) of the angle endoscope 602 is 1600, the bottom of the endoscope 602 is set at hmm from the top of the transparent block, and the length and width of the opening on the lower side of the upper pressure head 601 are both 40 mm, where the value range of h is obtained according to the law of refraction of light:

[0066]

[0067] The refractive index of the transparent block is 1.7 and the height is 50 mm. According to the law of refraction of light, the refractive angle of the transparent block is determined. :

[0068]

[0069] From the above formula, we can get =35.40. When the bottom of the endoscope 602 is set at 2.7 mm from the top of the transparent block, the width of the field of view of the endoscope 602 at the bottom of the transparent block is:

[0070] ,

[0071] After adjusting the position of the endoscope 602, place the upper pressurizing assembly 6 on the upper surface of the transparent block through the channel reserved at the top of the upper shear box 3, connect the external cable of the endoscope 602 to the computer, observe the clarity of the video shot by the endoscope 602, adjust the endoscope 602, and after the video shot by the endoscope 602 reaches the required clarity, connect the upper pressurizing assembly 6 to the normal loading block of the true triaxial testing machine to ensure that the upper pressurizing assembly 6 is in close contact with the transparent block, adjust the normal deformation measurement assembly 604, and further apply normal preload after the measurement accuracy of the normal deformation measurement assembly 604 meets the test requirements. After the normal preloading is completed, the lateral pressure plate I4 and the lateral pressure plate II5 are connected to the lateral loading block of the true triaxial testing machine to ensure that the lateral loading block of the true triaxial testing machine is in close contact with the lateral pressure plate I4 and the lateral pressure plate II5, and the lateral deformation measuring component 404 is adjusted to make the measurement accuracy of the lateral deformation measuring component 404 meet the test requirements before further applying lateral preloading; after the lateral preloading is completed, the tangential loading block of the true triaxial testing machine is connected to the first shear pressure head 202 and the second shear pressure head 302 tangential to the shear box to ensure that the tangential loading block of the triaxial testing machine is in close contact with the first shear pressure head 202 and the second shear pressure head 302 tangential to the shear box, and the tangential deformation measuring component 210 is adjusted to make the measurement accuracy of the tangential deformation measuring component 210 meet the test requirements before further applying tangential preloading; after the preloading is completed, the test is started, and the test adopts Figure 7 The stress path shown is loaded, where σ n is the normal stress, σ p is the lateral stress, P1 is the water pressure applied to the rock specimen and the transparent block on the water inlet side, P2 is the water pressure applied to the rock specimen and the transparent block on the water outlet side, and τ is the shear force. During the test, the normal pressure is first applied to the upper pressure assembly 6 and the fixed base 1, and the upper pressure assembly 6 and the fixed base 1 then apply the normal pressure to the rock specimen and the transparent block, and then the lateral pressure is applied to the lateral pressure plate I4 and the lateral pressure plate II5, and the lateral pressure plates I4 and II5 transfer the lateral pressure to the first pressure plate 402 and the second pressure plate 502, and the first pressure plate 402 and the second pressure plate 502 then apply the lateral pressure to the rock specimen and the transparent block.

[0072] S2: Injecting high-pressure acidic fluid into the seepage cavity through the seepage water inlet pipe 212 and controlling the water pressure difference between the seepage water inlet pipe 212 and the seepage water outlet pipe 310 .

[0073] S3: The seepage water pressure, flow rate, ion concentration, and pH value in the seepage pipeline are recorded every n minutes. The permeability k is calculated based on Darcy's law, and the damage degree Dc is calculated in combination with the stress-corrosion coupling damage model, where n ≥ 1.

[0074] In this embodiment, the permeability k is calculated based on Darcy's law as follows:

[0075] ;

[0076] in, for The average permeability of the rock over time; H is the average height of the rock sample, is the dynamic viscosity coefficient of water, =1×10 -3 Pa*s; for The volume of liquid that penetrates into the rock sample in a certain period of time; The water pressure difference at both ends of the sample is the osmotic pressure difference; is the time interval between recording points, and A is the cross-sectional area of ​​the sample.

[0077] In this embodiment, the damage degree Dc is calculated by combining the stress-corrosion coupled damage model as follows:

[0078] ;

[0079] in, It is stress-corrosion coupling damage caused by chemical corrosion. and is the balancing coefficient, H at t minutes + The average concentration value of is Ca at t minutes 2+ The average concentration value of is the initial moment H + The average concentration value, M and is the chemical reaction coefficient, is the volume of the chemical solution.

[0080] Specifically, the seepage water pressure is applied. During the test, the high-pressure water and acidic fluid prepared before the test are passed through the seepage water inlet pipe 212 and the seepage water inlet seal 211 into the water injection chamber 1. The water injection chamber 1 injects the high-pressure water and acidic fluid into the seepage water inlet shear head 205. The seepage water inlet shear head 205 applies the seepage water pressure to the rock sample and the transparent block. The high-pressure water and acidic fluid pass through the water injection chamber and enter the seepage water outlet pipe 310. The seepage water outlet pipe 310 flows out the high-pressure water and acidic fluid. During the test, the high-pressure water and acidic fluid are observed through the endoscope 602. The seepage conditions of pressurized water and acidic fluid in the shear box and the real-time conditions of the rock sample are measured. The seepage water pressure is read and recorded every minute through the first seepage water pressure measuring device 213 and the seepage water inlet seal 211. The water pressure on both sides of the rock sample and the transparent block is adjusted in time to meet the test requirements. During the test, the inflow and outflow flow rates of the seepage water are read and recorded every minute through the first seepage flow measuring device 214 and the second seepage flow measuring device 312. The Ca connected to the seepage outlet pipe 310 is opened every minute.2+ and Cl - Solution ion concentration and pH measurement device - 215 and Ca 2+ and Cl - Solution ion concentration and pH measuring device 2 313 valve, when the solution volume meets Ca 2+ and Cl - Solution ion concentration and pH measurement device - 215 and Ca 2+ and Cl - After the measurement requirements of solution ion concentration and pH measuring device 2 313 are met, close the valve and record the Ca 2+ ions, Cl - Ion concentration and pH value, open Ca after recording is completed 2+ and Cl - Solution ion concentration and pH measurement device - 215 and Ca 2+ and Cl - The solution ion concentration and pH measuring device 2 313 and the valve of the external drainage pipe are used to discharge the solution; when the seepage water pressure reaches the test requirements, shear force is applied to the first shear pressure head 202 and the second shear pressure head 302, and the first force transmission block 203 and the second force transmission block 303 transmit the shear force to the first shear head 206 and the second shear head 306, which then apply the shear force to the rock sample.

[0081] S4: Based on the results calculated in the above steps, draw the permeability-time curve, damage degree-time curve and shear stress-strain curve to evaluate the rock failure mechanism.

[0082] Specifically, after the test, the permeability and stress-corrosion coupling damage of the rock are calculated based on the data recorded during the test. During the test, the inflow and outflow of the seepage water are recorded in units of one minute. It can be considered that the recorded inflow and outflow rates do not change per unit time, which conforms to Darcy's law. The results calculated according to the above steps are plotted as a curve of permeability versus time, as shown in the figure below. Figure 8 As shown in the figure, the stress-corrosion coupled damage degree of rock changes with time. Figure 9 The shear stress-strain curve is shown in Figure 10 shown.

[0083] S5: During the test, the distance between the endoscope 602 and the top surface of the transparent block is adjusted, and the seepage of high-pressure water and acidic fluid in the shear box and the real-time condition of the rock sample are observed through the endoscope 602.

[0084] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A true triaxial rock structure surface shear fracture visualization seepage test device, characterized by: It includes a fixed base, a lower shear box, an upper shear box, a seepage inlet pipe, a seepage outlet pipe, a seepage inlet shear head and a seepage outlet shear head; the fixed base is connected to the normal loading block of the true triaxial testing machine through a pin, the lower shear box is fixed on the fixed base, the upper shear box and the lower shear box are relatively arranged, the seepage inlet shear head and the seepage outlet shear head are respectively embedded in the lower shear box and the upper shear box to form a water injection cavity 1 and a water injection cavity 2. After the lower shear box and the upper shear box are closed, a A sealed sample chamber is used to clamp the rock sample and the transparent block. At the same time, the water injection chamber 1 and the water injection chamber 2 form a seepage chamber. The inlet of the water injection chamber 1 is connected to one end of the seepage water inlet pipe, and the outlet of the water injection chamber 2 is connected to one end of the seepage water outlet pipe. The upper plate of the upper shear box is embedded with a transparent block, and the transparent block is in direct contact with the top surface of the rock sample. The upper cover of the upper shear box is rigidly connected to the upper pressure head. A slot is provided at the lower part of the upper pressure head. An endoscope is installed in the slot, and the endoscope lens is facing the top surface of the transparent block.

2. The true triaxial rock structure surface shear fracture visualization seepage test device according to claim 1 is characterized in that: The seepage cavity is integrated with at least two seepage water pressure measuring devices, at least two seepage flow measuring devices, at least two Ca 2+ and Cl - The solution ion concentration and pH measuring device, the seepage cavity, the seepage inlet pipe and the seepage outlet pipe form a seepage pipeline.

3. The true triaxial rock structure surface shear fracture visualization seepage test device according to claim 1 is characterized in that: A fill light with adjustable brightness is arranged in a ring around the endoscope, and an anti-reflection film is attached to the top surface of the transparent block.

4. The true triaxial rock structure surface shear fracture visualization seepage test device according to claim 1, characterized in that: Also includes: The seepage water inlet seal, the lower sealing strip, the upper sealing strip, the partition plate, and the seepage water outlet seal, the lower sealing strip and the upper sealing strip are respectively embedded in the rectangular grooves of the lower and upper shear boxes, and the partition plate is clamped between the upper shear box and the lower shear box by bolts. The edge of the partition plate fits tightly with the lower sealing strip and the upper sealing strip to form a double-layer sealing structure. The seepage water inlet seal and the seepage water outlet seal are fixed to the inlet / outlet of the seepage cavity by bolts, and form a multi-layer pressure-resistant sealing system with the lower sealing strip, the upper sealing strip and the partition plate.

5. The true triaxial rock structure surface shear fracture visualization seepage test device according to claim 1, characterized in that: The method for determining the dimensions of the transparent block and rock sample is as follows: The endoscope can be fine-tuned up and down in the upper pressure head and the diagonal field of view is 2 The bottom of the endoscope is set at a distance of h mm from the top of the transparent block. The length and width of the opening on the lower side of the upper pressure head are both 2b mm. According to the law of refraction of light, the value range of h is: ； The refractive index of the transparent block is n and the height is H. The refraction angle of the transparent block is determined according to the law of refraction of light: ; in, is the angle of incidence, is the refraction angle, and further we can get the theoretical width L of the endoscope's field of view at the bottom of the transparent block as: ； The length of the transparent block should be less than L and greater than 0.5L and 1.5H, and the width of the transparent block should be half of the length; the length, width and height of the rock sample should be consistent with those of the transparent block.

6. The true triaxial rock structure surface shear fracture visualization seepage test device according to claim 1, characterized in that: Also includes: Lateral compression plate, normal deformation measurement assembly, tangential deformation measurement assembly, lateral deformation measurement assembly; one end of the normal deformation measurement assembly is fixedly connected to the upper pressure head, and the other end abuts the upper cover surface of the upper shear box. The upper pressure head fits with the transparent block. When the rock sample undergoes normal deformation, the upper pressure head moves with the transparent block, driving the normal deformation measurement assembly to expand and contract, and measure the normal displacement in real time; one end of the tangential deformation measurement assembly is fixedly connected to the force transmission block of the lower shear box, and the other end abuts the upper cover surface of the upper shear box. The upper and lower shear boxes undergo tangential relative displacement, and the shear force is transmitted through the force transmission block. The tangential deformation measurement assembly expands and contracts with the displacement, and measures the tangential displacement in real time; the lateral compression plate includes lateral compression plate I and lateral compression plate II. The two ends of the lateral deformation measurement assembly are respectively fixed to the compression plate of lateral compression plate I and the compression plate of lateral compression plate II by bolts. After the lateral compression plate is subjected to lateral loading by the true triaxial testing machine, the compression plate pushes the rock sample to produce lateral deformation, and the lateral deformation measurement assembly measures the lateral strain through the displacement difference at both ends.

7. A visual seepage test method for shear fracture of rock structural surfaces under true triaxial conditions, characterized in that: The method is applied to the true triaxial rock structure surface shear fracture visualization seepage test device according to any one of claims 1 to 6, and comprises the following steps: S1: Install the rock specimen and the transparent block in the lower shear box, apply normal preload, lateral preload and tangential preload, and simultaneously apply normal stress, lateral stress and tangential shear force; S2: injecting high-pressure acidic fluid into the seepage cavity through the seepage inlet pipe and controlling the water pressure difference between the seepage inlet pipe and the seepage outlet pipe; S3: Record the seepage water pressure, flow rate, ion concentration, and pH value in the seepage pipeline every n minutes, calculate the permeability k based on Darcy's law, and calculate the damage degree Dc in combination with the stress-corrosion coupled damage model, where n ≥ 1; S4: Based on the results calculated in the above steps, draw the permeability-time curve, damage degree-time curve and shear stress-strain curve to evaluate the rock failure mechanism.

8. The method for visualizing seepage flow under true triaxial shear fracture of rock structure surface according to claim 7, characterized in that: In step S1, during the test, normal pressure is first applied to the upper pressure head and the fixed base, which then apply normal pressure to the rock sample and the transparent block, and then lateral pressure is applied to lateral pressure plates I and II, which then apply lateral pressure to the rock sample and the transparent block.

9. The method for visualizing seepage flow under true triaxial shear fracture of rock structure surface according to claim 7, characterized in that: Also includes: S5: During the test, adjust the distance between the endoscope and the top surface of the transparent block, and observe the seepage of high-pressure water and acidic fluid in the shear box and the real-time status of the rock structure surface sample through the endoscope.

10. The method for visualizing seepage flow in rock structure surface shear fracture under true triaxial testing according to claim 7, characterized in that: The permeability k is calculated based on Darcy's law as follows: ； in, for The average permeability of the rock over time; H is the average height of the rock sample, is the dynamic viscosity coefficient of water, =1×10 -3 Pa*s; for The volume of liquid that penetrates into the rock sample in a certain period of time; The water pressure difference at both ends of the sample is the osmotic pressure difference; is the time interval between recording points, and A is the cross-sectional area of ​​the sample.

11. The true triaxial shear fracture visualization seepage test method for rock structural surfaces according to claim 7, combined with the stress-corrosion coupled damage model, calculates the damage degree Dc as follows: ； in, It is stress-corrosion coupling damage caused by chemical corrosion. and is the balancing coefficient, H at t minutes + The average concentration value of is Ca at t minutes 2+ The average concentration value of is the initial moment H + The average concentration value, M and is the chemical reaction coefficient, is the volume of the chemical solution.

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