CN110220834B - Triaxial seepage test method for visual single-fracture rock stress-seepage coupling sample - Google Patents

Triaxial seepage test method for visual single-fracture rock stress-seepage coupling sample Download PDF

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Publication number
CN110220834B
CN110220834B CN201910461877.3A CN201910461877A CN110220834B CN 110220834 B CN110220834 B CN 110220834B CN 201910461877 A CN201910461877 A CN 201910461877A CN 110220834 B CN110220834 B CN 110220834B
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crack
sample
seepage
rock
rock stress
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CN201910461877.3A
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Chinese (zh)
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CN110220834A (en
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牛子豪
刘承
朱珍德
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河海大学
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    • GPHYSICS
    • G01MEASURING; TESTING
    • G01NINVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N15/00Investigating characteristics of particles; Investigating permeability, pore-volume, or surface-area of porous materials
    • G01N15/08Investigating permeability, pore-volume, or surface area of porous materials
    • G01N15/082Investigating permeability by forcing a fluid through a sample
    • G01N15/0826Investigating permeability by forcing a fluid through a sample and measuring fluid flow rate, i.e. permeation rate or pressure change

Abstract

The invention discloses a triaxial seepage test method of a visual single-fracture rock stress-seepage coupling sample, which comprises the following steps of 1, manufacturing a transparent rock matrix sample; step 2, manufacturing cracks and prefabricated cracks; step 3, manufacturing a single-crack rock stress-seepage coupling sample; step 4, manufacturing a standard gypsum sample; step 5, determining an initial permeability coefficient; step 6, clamping the single-crack rock stress-seepage coupling sample with a true triaxial apparatus; step 7, carrying out a true triaxial seepage test; and 8, comparing the seepage test. The method can prepare a visual single-crack rock stress-seepage coupling sample, can track and record the whole test process, and can accurately describe the crack development process of the single-crack sample under the stress-seepage coupling condition and the corresponding permeability coefficient change.

Description

Triaxial seepage test method for visual single-fracture rock stress-seepage coupling sample

Technical Field

The invention relates to the field of rock mechanics and rock mechanics tests, in particular to a triaxial seepage test method for a visual single-crack rock stress-seepage coupling sample.

Background

Rock is a natural seepage medium produced in nature, and is an anisotropic multi-phase body formed by rock matrix and various defects. The defects mainly comprise faults, joints, cracks, pores and the like. The change of the stress field of the rock mass accelerates the crack expansion occurring in the rock mass, which in turn affects the permeability of the rock mass and accelerates the destruction of the rock mass, and the mutual influence is defined as the coupling effect of seepage and stress. In recent years, with the construction and the operation of a series of large hydroelectric projects such as the three gorges dam, the white crane beach hydropower station and the like, the research on the pressure stress-seepage coupling of rock mass under high confining pressure and high seepage water pressure becomes a key research subject in the field of rock mechanics research at present, and the process from cracking to penetrating of cracks in the rock mass becomes extremely important.

The scholars at home and abroad carry out preliminary research on the seepage characteristics of the cracks in the rock body and the cracking of the cracks under the stress-seepage coupling condition to obtain certain research results, but the expansion of the cracks in the rock body still stays in a theoretical derivation stage and a numerical simulation stage, and no visual test result comparison exists.

In the aspect of a test instrument, the Chinese patent with the publication number of CN 109253962A discloses a rock triaxial mechanical permeability characteristic tester and a test method.

The patent of Chinese utility model with publication number CN 208334085U discloses a triaxial seepage test device.

Both of the above patents propose a stress-seepage coupling instrument for rock samples and a corresponding test method, which can obtain the permeability coefficient of the rock sample under corresponding conditions, but have the following disadvantages:

1. the cylindrical sample can only be added with the same magnitude confining pressure all around, and can not well reflect the working conditions of different circumferential stresses.

2. The test methods are all used for carrying out stress-seepage coupling tests under the closed condition of the sample, the visibility is poor, the development condition of the internal cracks of the sample cannot be known, and only the final damage form of the sample can be obtained, so that the later numerical simulation damage process cannot be verified in a contrasting manner.

3. The seepage path in the rock sample cannot be accurately obtained, and only the change rule of the permeability coefficient of the rock sample can be obtained.

Therefore, the preparation and test method of the rock mass seepage sample with high visualization degree becomes a problem to be solved urgently in the field of rock seepage mechanics at present.

Disclosure of Invention

The invention aims to solve the technical problem of the prior art, and provides a triaxial seepage test method for a visual single-fracture rock stress-seepage coupling sample, which can be used for preparing the visual single-fracture rock stress-seepage coupling sample, tracking and recording the whole test process and accurately describing the crack development process of the single-fracture sample under the stress-seepage coupling condition and the corresponding permeability coefficient change.

In order to solve the technical problems, the invention adopts the technical scheme that:

a triaxial seepage test method for a visual single-crack rock stress-seepage coupling sample comprises the following steps.

Step 1, preparing a transparent rock matrix sample: cutting modified organic glass as material to form two cuboid transparent rock matrix samples with length, width and height of a mm x b mm x a mm; wherein a > 2 b; in each transparent rock matrix sample, the two sides with the largest area are both transparent observation sides.

Step 2, crack and prefabricated crack production: placing the two transparent rock matrix samples prepared in the step 1 in parallel and fixing the positions of the two transparent rock matrix samples to form a cube with the side length of a mm, and forming a crack with the thickness of c mm between the transparent observation side surfaces of the two transparent rock matrix samples; wherein c = a-2 b; at least one piece of borneol with a set angle is preset at the position of the prefabricated crack in the crack, and two ends of the borneol are in pressing contact with the transparent observation side surfaces at two sides.

And 3, manufacturing a single-crack rock stress-seepage coupling sample, which comprises the following steps.

Step 31, forming a fracture medium filling cavity: sealing the openings at the two sides of the crack formed in the step 2 by adopting a sealant to form a crack medium filling cavity.

Step 32, filling a fracture medium: filling the uniformly stirred gypsum mortar in the crack medium filling cavity, wherein the gypsum hydration reaction generates heat, so that the gypsum mortar is quickly bonded with the transparent observation side surfaces of the two transparent rock matrix samples to form a cubic integral sample with side length of a mm; meanwhile, melting the borneol preset in the step 2 to form a preset crack.

Step 33, sample maintenance: and (3) placing the cubic integral sample into a constant-temperature curing box with the temperature of 20 +/-1 ℃ and the humidity of more than or equal to 90% for curing for not less than 7 days, wherein the cured cubic integral sample is the manufactured single-crack rock stress-seepage coupling sample.

Step 4, standard gypsum sample preparation: adopting the gypsum mortar in the step 32 to prepare a standard gypsum sample with side length of a mm, and curing according to the method in the step 33; wherein the standard gypsum sample has the same pre-cracks therein as the single-crack rock stress-seepage coupling sample.

Step 5, determining an initial permeability coefficient: and (4) clamping the standard gypsum sample prepared in the step (4) in a true triaxial apparatus, performing a penetration test under a set penetration condition, and determining the penetration coefficient of the obtained standard gypsum sample to be the initial penetration coefficient.

And 6, clamping the single-crack rock stress-seepage coupling sample with a true triaxial apparatus: clamping the single-crack rock stress-seepage coupling sample manufactured in the step (3) in a sample placing cavity of a true triaxial apparatus, and enabling each side face of the single-crack rock stress-seepage coupling sample to be provided with a loading device, so that the single-crack rock stress-seepage coupling sample can be subjected to axial pressure loading in the X direction, the Y direction and the Z direction; wherein, a camera is arranged in one or two loading devices which are in contact with the transparent observation side; the loading device contacted with the top of the crack is a Z-direction osmotic pressure loading head, the Z-direction osmotic pressure loading head is connected with a high-pressure osmotic water tank of a true triaxial apparatus, and macromolecular organic dye is added into a water body in the high-pressure osmotic water tank.

Step 7, true triaxial seepage test: the true triaxial apparatus in the step 6 performs a penetration test on the single-crack rock stress-seepage coupling sample according to the same set conditions as the step 5; and (3) shooting a seepage path image in the seepage test process in real time by the camera and transmitting the image to the computer, wherein the computer also collects the permeability coefficient of the single-crack rock stress-seepage coupling sample in real time, and when the permeability coefficient of the single-crack rock stress-seepage coupling sample reaches more than two orders of magnitude of the initial permeability coefficient determined in the step (6), the single-crack rock stress-seepage coupling sample is considered to be completely damaged, and the true triaxial seepage test set is finished.

Further comprising step 8 of comparing seepage tests: changing the set permeation conditions, repeating the steps 1 to 7, and comparing and analyzing the expansion of cracks of the fractured rock mass and the influence condition of the permeation coefficient under different set permeation conditions; wherein, the different set infiltration conditions are any one or combination of different precast crack inclination angles, infiltration water pressures, axial pressures or lateral pressures.

In step 32, the gypsum mortar comprises the components of gypsum, fine sand, water, a gypsum naphthalene water reducer and a polysiloxane water repellent in a weight ratio of 1:1:0.5:0.02: 0.05.

In step 8, the inclination angle of the pre-crack is 0 °, 45 °, 90 ° or 135 °.

In step 8, the osmotic water pressure is increased in a gradient manner, and the osmotic water pressure gradient is 0.5MP, 1MP, 2MP and 4 MP.

In the step 2, two parallel borneol pieces are preset at the position of the prefabricated crack in the crack, and the borneol pieces form a set angle with the horizontal plane.

And adjusting the thickness value of the crack by changing the width b value of the transparent rock matrix sample.

In step 6, water blocking devices are arranged between the single-crack rock stress-seepage coupling sample and the loading devices at the top and the bottom, and each water blocking device comprises a water blocking steel plate and a rubber gasket; the middle part of the water-blocking steel plate is provided with a water permeable area formed by a plurality of water permeable holes, the water permeable area is positioned at the top or the bottom of the crack, and the rubber gasket is nested at the periphery of the water permeable area.

The camera is a high-speed dynamic capture micro camera.

The modified organic glass is organic glass containing 7 percent of barium methacrylate.

The invention has the following beneficial effects:

1. the method can prepare a visual single-crack rock stress-seepage coupling sample which is cubic, can simulate the cracking process and the permeability coefficient change process of the single-crack rock stress-seepage coupling sample under the working conditions of different water pressures and X, Y, Z three-direction axial pressures, and simultaneously solves the problem that the lateral stresses of cylindrical stress-seepage coupling samples are the same.

2. According to the invention, a water-impermeable film does not need to be wrapped outside the stress-seepage coupling sample of the single-crack rock, a water blocking device is arranged on the upper and lower seepage surfaces, a water flow path can be controlled in the single crack, a colored tracer (namely, a high-molecular organic dye) and a camera built in a loading device are used for tracking and recording the whole test process in an auxiliary manner, the crack development process and the corresponding seepage coefficient change of the single-crack sample under the stress-seepage coupling condition can be accurately described, and the problem of large error of the traditional acoustic emission method is solved.

3. The addition mode of the prefabricated cracks can reduce the influence on the sample to the maximum extent and better ensure the physical and mechanical properties of the sample.

4. The invention greatly enriches the visualization degree in the field of true triaxial seepage samples.

Drawings

FIG. 1 is a flow chart of a triaxial seepage test method for a visual single-fracture rock stress-seepage coupling sample.

FIG. 2 shows a schematic representation of two transparent rock matrix samples placed in parallel.

FIG. 3 shows a structural diagram of a single fracture rock stress-seepage coupled sample after fracture medium filling.

FIG. 4 shows a schematic angle diagram of several different pre-crack inclinations.

FIG. 5 shows a schematic diagram of clamping a single-crack rock stress-seepage coupling sample with a true triaxial apparatus.

Fig. 6 shows a schematic structural diagram of the Y-axis loading device.

Fig. 7 shows a schematic view of the water blocking device.

Fig. 8 shows a graph of the PFC2D numerical simulation.

Among them are: 1. a transparent rock matrix sample; 2. borneol; 3. a flange plate; 4, a Y-axis loading device; an X-axis loading device; 6, a Z-axis loading device; 7. a sample placement chamber; 8. a data transmission line; 9. a flange plate; 10. pressurizing the steel joint; 11. a camera; 12. a transparent sealing plate; 13. water permeable holes; 14. a rubber gasket; 15. a water-blocking steel plate.

Detailed Description

The present invention will be described in further detail with reference to the accompanying drawings and specific preferred embodiments.

In the description of the present invention, it is to be understood that the terms "left side", "right side", "upper part", "lower part", etc., indicate orientations or positional relationships based on those shown in the drawings, and are only for convenience of describing the present invention and simplifying the description, but do not indicate or imply that the referred device or element must have a specific orientation, be constructed in a specific orientation, and be operated, and that "first", "second", etc., do not represent an important degree of the component parts, and thus are not to be construed as limiting the present invention. The specific dimensions used in the present example are only for illustrating the technical solution and do not limit the scope of protection of the present invention.

As shown in figure 1, a triaxial seepage test method for visualizing a single-crack rock stress-seepage coupling sample comprises the following steps.

Step 1, preparing a transparent rock matrix sample: cutting modified organic glass as material to form two cuboid transparent rock matrix samples with length, width and height of a mm x b mm x a mm; wherein a > 2 b. In the present invention, a =100mm and b =48mm are exemplified.

Polymethyl methacrylate is commonly called organic glass, is the best variety with transmittance and transmittance of more than 92 percent in the current plastics, and is widely applied to the aspects of buildings, culture and education, navigation, aviation, daily life and the like. Organic glass has excellent optical performance, and also has good weather resistance, acid and alkali resistance, dimensional stability, insulating property and mechanical strength. Because of the good physical and mechanical properties of the organic glass, the organic glass can be applied to the field of rock seepage. The modified organic glass applied in the method is prepared by adopting an ionic crosslinking modification method, and each parameter is similar to that of rock. The waterproof rock matrix is simulated by the modified organic glass, and the water-permeable fracture is simulated by the gypsum mortar, so that the sample method of the current similar material test is developed.

The method for modifying the organic glass mainly improves the heat resistance and the toughness of the organic glass by copolymerization, crosslinking and oriented stretching, introduces strong polar groups or forms hydrogen bonds to enhance the acting force among polymer molecules, and achieves the aim of improving the thermal stability and certain strength of the polymer. Compared with chemical crosslinking, physical crosslinking can improve certain physical properties of the polymer, maintain a linear structure and does not influence the molding processability of the polymer. The modified organic glass adopted by the method is the organic glass containing 7% of the barium methacrylate, prepared from the xuwenying and the like, the visible light transmittance is 85%, the glass transition temperature is 200 ℃, the surface hardness is improved by 44% compared with the common organic glass, and the modified organic glass has stronger radiation resistance and solvent resistance.

The physical and mechanical properties of the modified organic glass and the weakly weathered basalt are compared as follows:

comparison table of physical and mechanical properties of modified organic glass and rock

As can be seen from the above table, the modified organic glass material has a great similarity to the weakly weathered basalt in terms of physical and mechanical properties. Simultaneously, the modified organic glass is the same as a rock medium, is also a viscoelastic plastic material, has a stress-strain curve conforming to the viscoelastic rule, and has a very strong visualization degree.

In each of the transparent rock matrix samples, the two sides having the largest area were both transparent observation sides. The transparent viewing side is preferably mechanically polished by a polishing machine to enhance the transparency of the transparent rock matrix sample.

And 2, manufacturing cracks and prefabricated cracks.

Placing the two transparent rock matrix samples prepared in the step 1 on the ground or a platform in parallel and fixing the positions of the two transparent rock matrix samples to form a cube with the side length of a mm, and forming a crack with the thickness of c mm as shown in figure 2 between the transparent observation side surfaces of the two transparent rock matrix samples; where c = a-2b, c is preferably 4mm in the present invention. The slit thickness values can be adjusted as desired. The specific adjusting method comprises the following steps: and adjusting the thickness value of the crack by changing the width b value of the transparent rock matrix sample.

At least one piece of borneol with a set angle is preset at the position of the prefabricated crack in the crack, and two ends of the borneol are in pressing contact with the transparent observation side surfaces at two sides.

As shown in FIG. 4, two parallel ice pieces are preset at the position of the crack in advance, and the ice pieces and the horizontal plane form a set angle. The diagrams a, b, c and d in fig. 4 respectively show that the ice piece is at 0 degree, 45 degrees, 90 degrees and 135 degrees from the horizontal plane.

The thickness of the borneol is preferably 5mm, the borneol is placed in a reserved position (namely a prefabricated crack position) according to design angles (such as 0 degree, 45 degree, 90 degree and 135 degree), the transparent rock matrix samples on two sides are fixed by a metal clamp, and the metal clamping force is not too large so as to prevent the prefabricated borneol from being damaged.

And 3, manufacturing a single-crack rock stress-seepage coupling sample, which comprises the following steps.

Step 31, forming a fracture medium filling cavity: sealing the openings at the two sides of the crack formed in the step 2 by adopting a sealant (such as a water stop glue) to form a crack medium filling cavity.

Step 32, filling a fracture medium: the gypsum mortar which is uniformly stirred is filled in the crack medium filling cavity, and the gypsum hydration reaction generates heat, so that the gypsum mortar is quickly bonded with the transparent observation side surfaces of the two transparent rock matrix samples to form a cubic integral sample with side length of a mm as shown in figure 3.

The components of the gypsum mortar are preferably gypsum, fine sand, water, a gypsum naphthalene water reducing agent and a polysiloxane water repellent, and the weight ratio of the components is 1:1:0.5:0.02: 0.05. The configuration method is preferably as follows: the gypsum, the fine sand, the water reducing agent and the polysiloxane water repellent are stirred uniformly, water is slowly added until the standard requirement is met, and the stirring is stopped when the gypsum mortar is free from caking and has high fluidity.

The gypsum hydration reaction generates a large amount of heat, and the gypsum hydration reaction is fast in solidification, so that the gypsum hydration reaction ice block has certain strength when the ice blocks are melted. The ice blocks are melted to form preset cracks, the melted water body seeps out along with the pores, and the single-crack sample with the preset cracks has good physical properties and can not change in shape.

Step 33, sample maintenance: and (3) placing the cubic integral sample into a constant-temperature curing box with the temperature of 20 +/-1 ℃ and the humidity of more than or equal to 90% for curing for not less than 7 days, wherein the cured cubic integral sample is the manufactured single-crack rock stress-seepage coupling sample.

Step 4, standard gypsum sample preparation: adopting the gypsum mortar in the step 32 to prepare a standard gypsum sample with the side length of a =100mm, and curing according to the method in the step 33; wherein the standard gypsum sample has the same pre-cracks therein as the single-crack rock stress-seepage coupling sample.

Step 5, determining an initial permeability coefficient: and (4) clamping the standard gypsum sample prepared in the step (4) in a true triaxial apparatus, performing a penetration test under a set penetration condition, and determining the penetration coefficient of the obtained standard gypsum sample to be the initial penetration coefficient.

And 6, clamping the single-crack rock stress-seepage coupling sample with a true triaxial apparatus.

As shown in fig. 5, the single-crack rock stress-seepage coupling sample manufactured in step 3 is clamped in a sample placing cavity 7 of a true triaxial apparatus, so that a loading device is respectively installed on six side surfaces of the single-crack rock stress-seepage coupling sample, and further, axial compression loading in the X direction, the Y direction and the Z direction can be realized on the single-crack rock stress-seepage coupling sample. The pressure range of each loading device can be adjusted within 0.5 MP-20 MP.

In fig. 5, two loading devices attached in contact with the transparent viewing side (also referred to as left and right side surfaces) are referred to as Y-axis loading devices 4, two loading devices attached in contact with the front and rear side surfaces are referred to as X-axis loading devices 5, and two loading devices attached in contact with the upper and lower side surfaces are referred to as Z-axis loading devices 6.

As shown in fig. 6, the Y-axis loading device includes a pressure steel joint 10, in which a camera 11 or a camera is built in a central portion facing the transparent observation side surface, and the camera is preferably a high-speed motion capture micro camera. The outer side of the camera is preferably provided with a transparent sealing plate 12 which can avoid damage to the camera during loading.

The pressurizing steel joint is preferably connected with a jack through a flange plate 9, the control of oil pressure in the jack and a camera file in the camera are preferably connected with a control terminal (a computer) through a data transmission line 8, and integrated processing of three-way pressure, seepage pressure, test data and test dynamic progress videos in the true triaxial apparatus is achieved.

During loading, gradient unloading loading is preferably selected as the loading mode of the Y-axis loading device, and the crack propagation and permeability coefficient change conditions of the single-crack pre-crack test sample at three different stages of elasticity, elastoplasticity and plasticity are researched.

The Z-axis loading device positioned at the top of the single-crack rock stress-seepage coupling sample is connected with the osmotic pressure loading head, so the Z-direction osmotic pressure loading head is also called as a Z-direction osmotic pressure loading head and provides Z-direction osmotic pressure, and the osmotic pressure range and the pressure loading range are adjustable.

The Z-direction osmotic pressure loading head is connected with a high-pressure osmotic water tank of a true triaxial apparatus, and a high-molecular organic dye is added into a water body in the high-pressure osmotic water tank.

The macromolecular organic dye has larger molecular particle size, is not easy to pass through compact pores in the gypsum, can seep out through cracks generated by pressurization, can trace the expansion process of the cracks in the whole sample, and avoids the condition of whole dyeing of the crack surface of the whole gypsum.

As shown in fig. 7, water-blocking devices are respectively arranged between the upper and lower bottom surfaces of the single-crack rock stress-seepage coupling sample and the Z-axis loading device, and preferably comprise a water-blocking steel plate 15 and a rubber gasket 14; the region of permeating water that forms by a plurality of hole 13 of permeating water is seted up at the steel sheet middle part that blocks water, and the region of permeating water is located the top or the bottom of crack, and rubber packing ring nestification is in the periphery that is located the region of permeating water. The planar area of the water-blocking steel plate is preferably the same as the top surface area of the single-crack rock stress-seepage coupling sample, the thickness of the rubber gasket is larger than that of a circular clamping groove reserved on the water-blocking steel plate, after axial stress is applied, the rubber gasket is squeezed and compacted, the Z-direction seepage water pressure is ensured to enter a sample crack through a water-permeable hole, crack inner cracks are developed and communicated together with confining pressure, and high-pressure water leakage is avoided. Meanwhile, the camera records the expansion process of the colored water flow and the microscopic through process of the whole crack.

Step 7, true triaxial seepage test: the true triaxial apparatus in the step 6 performs a penetration test on the single-crack rock stress-seepage coupling sample according to the same set conditions as the step 5; and (3) shooting a seepage path image in the seepage test process in real time by the camera and transmitting the image to the computer, wherein the computer also collects the permeability coefficient of the single-crack rock stress-seepage coupling sample in real time, and when the permeability coefficient of the single-crack rock stress-seepage coupling sample reaches more than two orders of magnitude (namely 100 times) of the initial permeability coefficient determined in the step (6), the single-crack rock stress-seepage coupling sample is considered to be completely damaged, and the true triaxial seepage test is finished.

Step 8, comparing seepage tests: changing the set permeation conditions, repeating the steps 1 to 7, and comparing and analyzing the expansion of cracks of the fractured rock mass and the influence condition of the permeation coefficient under different set permeation conditions; wherein, the different set infiltration conditions are any one or combination of different precast crack inclination angles, infiltration water pressures, axial pressures or lateral pressures. Wherein the inclination angle of the prefabricated crack is 0 degree, 45 degrees, 90 degrees or 135 degrees, etc. The osmotic water pressure is increased in a gradient manner, and the osmotic water pressure gradient is 0.5MP, 1MP, 2MP, 4MP and the like.

After the test is finished, numerical simulation is carried out through particle flow software PFC2D, the model is as shown in fig. 8, a black area simulates a crack medium binding material, a gray area is a prefabricated parallel crack, and the model is subjected to triaxial compression simulation in PFC software. According to different test conditions, different simulation schemes are set, the simulation result is compared with the image shot by the high-definition camera, and the accuracy of the crack expansion process result obtained by the verification test under different conditions is high.

Although the preferred embodiments of the present invention have been described in detail, the present invention is not limited to the details of the embodiments, and various equivalent modifications can be made within the technical spirit of the present invention, and the scope of the present invention is also within the scope of the present invention.

Claims (10)

1. The triaxial seepage test method of the visual single-fracture rock stress-seepage coupling sample is characterized by comprising the following steps of: the method comprises the following steps:
step 1, preparing a transparent rock matrix sample: cutting modified organic glass as material to form two cuboid transparent rock matrix samples with length, width and height of amm × b mm × a mm; wherein a > 2 b; in each transparent rock matrix sample, two side surfaces with the largest area are transparent observation side surfaces;
step 2, crack and prefabricated crack production: placing the two transparent rock matrix samples prepared in the step 1 in parallel and fixing the positions of the two transparent rock matrix samples to form a cube with the side length of a mm, and forming a crack with the thickness of cmm between the transparent observation side surfaces of the two transparent rock matrix samples; wherein c = a-2 b; at least one piece of borneol with a set angle is preset at the position of the prefabricated crack in the crack, and two ends of the borneol are in pressing contact with the transparent observation side faces of the transparent rock matrix samples at two sides;
step 3, manufacturing a single-crack rock stress-seepage coupling sample, which comprises the following steps:
step 31, forming a fracture medium filling cavity: sealing openings at two sides of the crack formed in the step 2 by adopting a sealant to form a crack medium filling cavity;
step 32, filling a fracture medium: filling the uniformly stirred gypsum mortar in the crack medium filling cavity, wherein the gypsum hydration reaction generates heat, so that the gypsum mortar is quickly bonded with the transparent observation side surfaces of the two transparent rock matrix samples to form a cubic integral sample with side length of a mm; meanwhile, melting the borneol preset in the step 2 to form a preset crack;
step 33, sample maintenance: placing the cubic integral sample into a constant-temperature curing box with the temperature of 20 +/-1 ℃ and the humidity of more than or equal to 90% for curing for at least 7 days, wherein the cured cubic integral sample is the manufactured single-crack rock stress-seepage coupling sample;
step 4, standard gypsum sample preparation: adopting the gypsum mortar in the step 32 to prepare a standard gypsum sample with side length of a mm, and curing according to the method in the step 33; wherein the standard gypsum sample has the same prefabricated crack as the single-crack rock stress-seepage coupling sample;
step 5, determining an initial permeability coefficient: clamping the standard gypsum sample prepared in the step 4 in a true triaxial apparatus, performing a penetration test under a set penetration condition, and determining the penetration coefficient of the obtained standard gypsum sample as an initial penetration coefficient;
and 6, clamping the single-crack rock stress-seepage coupling sample with a true triaxial apparatus: clamping the single-crack rock stress-seepage coupling sample manufactured in the step (3) in a sample placing cavity of a true triaxial apparatus, and enabling each side face of the single-crack rock stress-seepage coupling sample to be provided with a loading device, so that the single-crack rock stress-seepage coupling sample can be subjected to axial pressure loading in the X direction, the Y direction and the Z direction; wherein, a camera is arranged in one or two loading devices which are in contact with the transparent observation side; the loading device contacted with the top of the crack is a Z-direction osmotic pressure loading head, the Z-direction osmotic pressure loading head is connected with a high-pressure osmotic water tank of a true triaxial apparatus, and macromolecular organic dye is added into a water body in the high-pressure osmotic water tank;
step 7, true triaxial seepage test: the true triaxial apparatus in the step 6 performs a penetration test on the single-crack rock stress-seepage coupling sample according to the same set conditions as the step 5; and (3) shooting a seepage path image in the seepage test process in real time by the camera and transmitting the image to the computer, wherein the computer also collects the permeability coefficient of the single-crack rock stress-seepage coupling sample in real time, and when the permeability coefficient of the single-crack rock stress-seepage coupling sample reaches more than two orders of magnitude of the initial permeability coefficient determined in the step (6), the single-crack rock stress-seepage coupling sample is considered to be completely damaged, and the true triaxial seepage test set is finished.
2. The triaxial seepage test method for visualizing the single-fracture rock stress-seepage coupling sample according to claim 1, wherein the method comprises the following steps: further comprising step 8 of comparing seepage tests: changing the set permeation conditions, repeating the steps 1 to 7, and comparing and analyzing the expansion of cracks of the fractured rock mass and the influence condition of the permeation coefficient under different set permeation conditions; wherein, the different set infiltration conditions are any one or combination of different precast crack inclination angles, infiltration water pressures, axial pressures or lateral pressures.
3. The triaxial seepage test method for visualizing the single-fracture rock stress-seepage coupling sample according to claim 1 or 2, wherein: in step 32, the gypsum mortar comprises the components of gypsum, fine sand, water, a gypsum naphthalene water reducer and a polysiloxane water repellent in a weight ratio of 1:1:0.5:0.02: 0.05.
4. The triaxial seepage test method for visualizing the single-fracture rock stress-seepage coupling sample according to claim 2, wherein the method comprises the following steps: in step 8, the inclination angle of the pre-crack is 0 °, 45 °, 90 ° or 135 °.
5. The triaxial seepage test method for visualizing the single-fracture rock stress-seepage coupling sample according to claim 2, wherein the method comprises the following steps: in step 8, the osmotic water pressure is increased in a gradient manner, and the osmotic water pressure gradient is 0.5MP, 1MP, 2MP and 4 MP.
6. The triaxial seepage test method for visualizing the single-fracture rock stress-seepage coupling sample according to claim 1, wherein the method comprises the following steps: in the step 2, two parallel borneol pieces are preset at the position of the prefabricated crack in the crack, and the borneol pieces form a set angle with the horizontal plane.
7. The triaxial seepage test method for visualizing the single-fracture rock stress-seepage coupling sample according to claim 1, wherein the method comprises the following steps: and adjusting the thickness value of the crack by changing the width b value of the transparent rock matrix sample.
8. The triaxial seepage test method for visualizing the single-fracture rock stress-seepage coupling sample according to claim 1, wherein the method comprises the following steps: in step 6, water blocking devices are arranged between the single-crack rock stress-seepage coupling sample and the loading devices at the top and the bottom, and each water blocking device comprises a water blocking steel plate and a rubber gasket; the middle part of the water-blocking steel plate is provided with a water permeable area formed by a plurality of water permeable holes, the water permeable area is positioned at the top or the bottom of the crack, and the rubber gasket is nested at the periphery of the water permeable area.
9. The triaxial seepage test method for visualizing the single-fracture rock stress-seepage coupling sample according to claim 1, wherein the method comprises the following steps: the camera is a high-speed dynamic capture micro camera.
10. The triaxial seepage test method for visualizing the single-fracture rock stress-seepage coupling sample according to claim 1, wherein the method comprises the following steps: the modified organic glass is organic glass containing 7 percent of barium methacrylate.
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