True triaxial stress relief test device and method under large-scale hydraulic coupling conditions

Abstract

The application discloses a true triaxial stress relief test device and method under large-scale hydraulic coupling conditions, which comprises a high-pressure water tank, two groups of opposite horizontal reserved holes and two groups of opposite lateral reserved holes are arranged on the side wall of the high-pressure water tank, opposite vertical reserved holes are arranged on the top and bottom of the high-pressure water tank, a stress relief reserved hole is arranged on the top of the high-pressure water tank, a strain gauge is arranged in the test rock sample, the strain gauge is electrically connected with a data acquisition device, a three-way force loading device is used for applying three-way force to the test rock sample, a stress relief device comprises a drilling machine, a drill rod connected with the drilling machine and located on the top of the tank body and a drill tool arranged on the end side of the drill rod, the drilling machine is started, the drill rod pushes the drill tool to drill a hole in the test rock sample subjected to three-way stress to realize stress relief, the strain gauge senses stress data on the test rock sample and transmits the stress data to the data acquisition device. The application can simulate the real stress condition and water environment of the rock mass, so that the stress condition of the rock mass can be accurately obtained.

Description

Technical Field

[0001] This invention belongs to the technical field of rock mechanics testing, specifically relating to a test device and method for true triaxial stress relief under large-scale hydraulic coupling conditions. Background Technology

[0002] In-situ stress refers to a natural force objectively present within the Earth's crustal rock mass and undisturbed by engineering projects; also known as in-situ rock stress, it is the fundamental force causing deformation, fracture, folding, and even earthquakes in the Earth's crustal rock mass. In-situ stress measurement is a crucial issue in major construction projects. Accurately determining the in-situ stress of rock mass is the basis for correctly and rationally calculating the excavation load of underground engineering projects; therefore, in-situ stress measurement is extremely important. Currently, there are two main methods for in-situ in-situ stress testing: stress relief method and hydraulic fracturing method. However, existing testing equipment and theories contain many fundamental assumptions. It is difficult to accurately evaluate whether the in-situ stress results obtained using existing instruments and methods conform to the actual stress conditions of the surrounding rock. Evaluation can only be achieved through extensive field experiments combined with different testing methods. Therefore, how to accurately measure in-situ stress and whether the use of existing instruments and equipment for in-situ stress measurement is a problem that must be solved when conducting research related to rock mass in-situ stress. Summary of the Invention

[0003] One objective of this invention is to address the shortcomings of existing technologies by providing a large-scale true triaxial stress relief test device under hydraulic coupling conditions. This device can simulate the actual stress conditions of rock samples and accurately obtain the in-situ in-situ stress conditions in the high-stress zone during the true triaxial stress relief process under high stress conditions.

[0004] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0005] A large-scale, hydraulically coupled true triaxial stress relief test apparatus includes:

[0006] The high-pressure water tank has two sets of opposing horizontal reserved holes and two sets of opposing lateral reserved holes on its side wall, with the arc between the lateral reserved holes and the horizontal reserved holes being 90°. It also has opposing vertical reserved holes at the top and bottom of the high-pressure water tank and a stress relief reserved hole at the top. During the test, the test rock sample is placed in the high-pressure water tank and filled with high-pressure water. A strain gauge is installed inside the test rock sample, and the strain gauge is electrically connected to the data acquisition device.

[0007] The three-dimensional force loading device includes a horizontal force loading device, a vertical force loading device, and a lateral force loading device that is perpendicular to both the horizontal and vertical forces. The horizontal force loading device applies a horizontal force to the test rock sample through a horizontal pre-drilled hole on the high-pressure water tank. The vertical force loading device applies a vertical load to the test rock sample through a horizontal pre-drilled hole on the high-pressure water tank. The lateral force loading device applies a lateral force to the test rock sample through a lateral pre-drilled hole on the high-pressure water tank.

[0008] The stress relief device includes a drilling rig, a drill rod connected to the drilling rig and located at the top of the tank, and a drill bit set at the end of the drill rod. During the stress relief simulation test, the drilling rig is turned on, and the drill rod pushes the drill bit through the stress relief reserved hole to drill through the test rock sample under triaxial stress to achieve stress relief. The strain gauge senses the stress data on the rock sample during the stress relief process and transmits it to the data acquisition device.

[0009] Furthermore, the system includes a main frame with a hollowed-out area for accommodating the high-pressure tank during the test, and a through hole at the top of the main frame connecting the hollowed-out area. The drill rod drives the drill bit through the through hole from the top of the main frame to relieve stress on the test rock sample.

[0010] Furthermore, it also includes a horizontal loading frame, which is equipped with a receiving groove for fixing high pressure through a through hole at the top of the main frame. In addition, a slide rail is provided on the main frame that traverses the hollow area. The horizontal loading frame slides on the slide rail. During the test, the horizontal loading frame moves the high-pressure water tank to the test position in the hollow area for testing.

[0011] Furthermore, a horizontal force loading device is provided on the opposite two sides of the horizontal loading frame. The horizontal force loading device includes a first loading cylinder fixed on the side of the horizontal loading frame, a first force transmission column that passes through a horizontal reserved hole and is in contact with the first loading cylinder, and a first force transmission plate connected to the first force transmission column. During the test, the first force transmission plate is located in a high-pressure water tank and presses against the test rock sample. The first loading cylinder pushes the first force transmission column and the first force transmission plate to apply a horizontal force to the test rock sample.

[0012] Furthermore, vertical force loading devices are provided at the top and bottom of the hollowed-out area. The vertical force loading devices include a second loading cylinder fixed on the top or bottom surface, a second force transmission column that passes through a vertical pre-drilled hole and is in contact with the second loading cylinder, and a second force transmission plate connected to the second force transmission column. During the test, the second force transmission plate is located in a high-pressure water tank and presses against the test rock sample. The second loading cylinder pushes the second force transmission column and the second force transmission plate to apply a vertical force to the test rock sample.

[0013] Furthermore, lateral force loading devices are fixed on both opposite sidewalls of the hollow area. The lateral force loading devices include a third loading cylinder fixed on the sidewall of the hollow area, a third force transmission column that passes through the lateral reserved hole and is in contact with the third loading cylinder, and a third force transmission plate connected to the third force transmission column. During the test, the third force transmission plate is located in the high-pressure water tank and presses against the test rock sample. The third loading cylinder pushes the third force transmission column and the third force transmission plate to apply lateral force to the test rock sample.

[0014] Furthermore, it also includes a water pressure application device connected to the high-pressure water tank and used to inject water and pressurize the high-pressure water tank, and a water pressure measuring device for measuring the water pressure of the high-pressure water tank, the water pressure measuring device being installed inside the high-pressure water tank.

[0015] Furthermore, the high-pressure water tank includes a hollow tank body and a sealing cover that is closed and sealed on the tank body. Horizontal and lateral reserved holes are provided on the side wall of the tank body, while vertical reserved holes and stress relief reserved holes are fixed on the sealing cover.

[0016] Another object of the present invention is to provide a test method for a true triaxial stress relief test apparatus under large-scale hydraulic coupling conditions as described above, comprising the following steps:

[0017] Step 1: Prepare a strain gauge mounting hole in the center of the test rock sample, install the strain gauge in the hole, and connect the strain gauge to the data acquisition device;

[0018] Step 2: At the installation station, place the test rock sample obtained in Step 1 in high-pressure water and seal the high-pressure water tank;

[0019] Step 3: Install the horizontal force loading device, vertical force loading device and lateral force loading device, move the horizontal loading frame to the test position, start the triaxial force loading device to apply triaxial force to the test rock sample in the high pressure tank, and at the same time inject water into the high pressure tank to the specified water pressure value.

[0020] Step 4: When the stress in each direction is loaded to the preset value, the stress relief device is activated to relieve the stress on the test rock sample in the high-pressure water tank. The data acquisition device collects the data sensed by the strain gauge throughout the process until the stress relief is completed.

[0021] Step 5: Calculate the strain changes obtained before and after stress relief to obtain the three-dimensional stress state at the drill hole.

[0022] Furthermore, the method for calculating the three-dimensional stress at the borehole is as follows:

[0023] One of the three stress loading directions is taken as the X-axis, and the others are the Y-axis and Z-axis, respectively;

[0024] The strain bundle embedded on the surface of the strain gauge is denoted by the number i and the corresponding polar angle is θ.i Each strain bundle includes multiple strain gauges, denoted by the number j, with the corresponding angle being... Based on the strain observation value ε of each strain gauge k The relationship between the rock mass stress state and the observed values ​​yielded the following set of equations:

[0025] E·ε k =A k1 σ x +A k2 σ y +A k3 σ z +A k4 τ xy +A k5 τ yz +A k6 τ zx

[0026] k = 4(i-1) + j;

[0027] In the formula:

[0028]

[0029] In the formula: σ x Normal stress in the X direction, σ y The normal stress in the Y direction, σ z The normal stress is in the Z direction, while τ xy Let τ be the shear stress on the xy plane. yz τ is the shear stress on the yz plane. zx , respectively, are the shear stresses on the zx plane, K1, K2, K3, and K4 are correction coefficients, R is the borehole radius, R1 is the strain gauge inner diameter, ρ is the radius of the strain gauge embedded part, E is the elastic modulus of the surrounding rock, μ is Poisson's ratio and E1 is the elastic modulus of the epoxy resin layer, μ1 is Poisson's ratio;

[0030] Based on the above method, the equations for each strain gauge are obtained. Using the principle of least squares, the normal equations for solving the optimal values ​​of the stress components are obtained:

[0031]

[0032] After obtaining the multiple stress components of the rock mass expressed in the borehole coordinate system, they are transformed to the geodetic coordinate system, and then the three principal stresses are solved according to the following formula:

[0033]

[0034] In the formula, n represents the number of strain gauges involved in the calculation of three-dimensional stress;

[0035]

[0036] In the formula: J1, J2, and J3 correspond to the first, second, and third invariants of the stress tensor, respectively; the principal stress directions are represented by the following formula:

[0037] (σ x -σ i )l i +τ xy m i +τ zx n i =0

[0038] τ xy l i +(σ y -σ i )m i +τ yz n i =0

[0039] τ zx l i +τ yz m i +(σ z -σ i )n i =0

[0040] Among them, the two equations and the direction cosine relation are:

[0041]

[0042] Solving the equations simultaneously, we obtain the inclination angle α of the principal stresses. i and azimuth β i for:

[0043] α i =sin -1 n i

[0044]

[0045] In the formula, l i σ i The direction cosine on the X-axis, m i σ i The direction cosine on the Y-axis, n i σ i The direction cosine on the Z-axis, β0 is the azimuth angle of the X-axis in the geodetic coordinate system. If the X-axis is due north, then β0 = 0.

[0046] Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention can simulate the actual stress state of rock mass and water environment by using a triaxial stress device and applying high-pressure water to a high-pressure water tank. Then, stress relief is performed on the rock sample, and the strain value during the stress relief process is obtained. The three-dimensional stress state at the borehole can be accurately obtained through experiments. The present invention can not only conduct simulation experiments of the true triaxial stress relief process under high stress conditions, with a maximum stress of up to 100 MPa, but also considers high external water pressure (up to 5 MPa, equivalent to a water head pressure of 500 m). The sample size can reach 50 cm × 50 cm × 100 cm. By conducting simulation experiments of the true triaxial stress relief process under high stress conditions, the field stress test results of high stress areas can be verified, and strain gauge calibration tests can also be performed. Attached Figure Description

[0047] Figure 1 This is a schematic diagram of the structure of the true triaxial stress relief test device under large-scale hydraulic coupling conditions according to an embodiment of the present invention;

[0048] Figure 2 This is a vertical cross-sectional schematic diagram of the stress relief simulation test device according to an embodiment of the present invention;

[0049] Figure 3 This is a schematic horizontal cross-sectional view of the stress relief simulation test device according to an embodiment of the present invention;

[0050] Figure 4 This is a vertical cross-sectional view of the rock sample under load according to an embodiment of the present invention;

[0051] Figure 5 This is a horizontal cross-sectional view of a rock sample under load according to an embodiment of the present invention. Detailed Implementation

[0052] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0053] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0054] The present invention will be further described below with reference to specific embodiments, but these are not intended to limit the scope of the invention.

[0055] like Figure 1 , Figure 2 , Figure 3As shown in the figure, this invention discloses a true triaxial stress relief test device under large-scale hydraulic coupling conditions, including a high-pressure water tank, a triaxial force loading device, and a stress relief device. The high-pressure water tank 1 includes a hollow tank body 100 and sealing caps 101 that cover and seal both ends of the tank body 100. Two sets of opposing horizontal pre-drilled holes and two sets of opposing lateral pre-drilled holes are provided on the side wall of the tank body 100, with a 90° arc between the lateral and horizontal pre-drilled holes. Opposing vertical pre-drilled holes are provided on the two sealing caps 101. These pre-drilled holes facilitate the triaxial force loading device to load the test rock sample 2. The test rock sample 2 can be a similar material sample or a rock sample retrieved from the field. During the stress relief test, the test rock sample 2 is placed in the high-pressure water tank 1, and high-pressure water 104 is added to it. The high-pressure water tank 1 provides a water pressure environment for the test rock sample 2. To this end, a water pressure application device connected to the high-pressure water tank 1 for injecting and pressurizing the high-pressure water tank 1, and a water pressure measuring device for measuring the water pressure of the high-pressure water tank are also provided. The water pressure measuring device is located inside the tank body 100. In addition, a stress relief reserved hole 102 is provided on the sealing cover at the top of the tank body. In order to facilitate the acquisition of stress and strain conditions on the test rock sample during stress relief, an installation hole is pre-made inside the test rock sample, and then the strain gauge 3 is fixed in the installation hole. The installed strain gauge 3 is connected to the data acquisition device 4 via a cable 400. Multiple strain bundles are embedded on the surface of the strain gauge 3, and each strain bundle includes multiple strain gauges. During the test, the data acquisition device 4 collects the strain data of each strain gauge.

[0056] To facilitate the fixing of the triaxial force loading device and the high-pressure water tank 1, the system also includes a main frame 5, a horizontal loading frame 6, and an auxiliary frame 9 positioned opposite the horizontal loading frame. The main frame 5 is a frame structure with a hollow area 500 at its center to provide testing space for the high-pressure water tank 1. A slide rail 501 traverses the bottom of the hollow area 500. Both the horizontal loading frame 6 and the auxiliary frame 9 are slidably connected to the slide rail 501 via pulleys or sliders. A groove 600 for fixing the high-pressure water tank 1 is provided on the horizontal loading frame 6. During the test, the high-pressure water tank 1 is fixed in the groove 600, and the horizontal loading frame 6 is pushed. The horizontal loading frame 6 moves the high-pressure water tank 1 along the slide rail 501 to the testing position in the hollow area 500.

[0057] The triaxial force loading device includes a horizontal force loading device, a vertical force loading device, and a lateral force loading device that is perpendicular to both the horizontal and vertical forces. The horizontal force loading device is fixed to the horizontal loading frame 6 and the auxiliary frame 9, with the horizontal force loading device fixed to the horizontal loading frame 6 and the horizontal force loading device fixed to the auxiliary frame 9 positioned opposite each other. The horizontal force loading device includes a first loading cylinder 700 fixed to the side of the horizontal loading frame 6 or the auxiliary frame 9, a first force transmission column 701 passing through a pre-drilled horizontal hole and connected to the first loading cylinder 700, and a first force transmission plate 702 connected to the first force transmission column 701. During the test, the first force transmission plate 702 is located in the high-pressure water tank 1 and presses against two opposite sides of the test rock sample 2. The first loading cylinder 700 pushes the first force transmission column 701 and the first force transmission plate 702 to apply a horizontal force to the test rock sample 2.

[0058] The lateral force loading device is installed on the side wall of the hollow area 500 of the main frame 5. Specifically, a lateral force loading device is fixed on each of the two opposite side walls of the hollow area 500. The lateral force loading device includes a third loading cylinder 703 fixed on the side wall of the hollow area 500, a third force transmission column 704 that passes through the lateral reserved hole and is in contact with the third loading cylinder 703, and a third force transmission plate 705 connected to the third force transmission column 704. During the test, the third force transmission plate 705 is located in the high-pressure water tank 1 and presses against the other two opposite sides of the test rock sample 2. The third loading cylinder 703 pushes the third force transmission column 704 and the third force transmission plate 705 to apply lateral force to the test rock sample 2. In addition, the vertical force loading device is also fixed on the main frame 5. Specifically, the vertical force loading device is set opposite to the top and bottom of the hollow area 500. The vertical force loading device includes a second loading cylinder 706 fixed on the top or bottom surface of the hollow area 500, a second force transmission column 707 that passes through the vertical reserved hole and is in contact with the second loading cylinder 706, and a second force transmission plate 708 connected to the second force transmission column 707. During the test, the second force transmission plate 708 is located in the high-pressure water tank 1 and presses against the top and bottom surfaces of the test rock sample 2. The second loading cylinder 706 pushes the second force transmission column 707 and the second force transmission plate 708 to apply a vertical force to the test rock sample 2.

[0059] The stress relief device includes a drill rig 800 mounted on the main frame, a drill rod 801 connected to the drill rig 800 and located at the top of the main frame 3, and a drill bit 802 located at the end of the drill rod 801. Correspondingly, a through hole 103 is provided at the top of the main frame 5, connecting to the hollow area 500 and allowing the drill rod 801 to pass through. During stress relief, the drill rod 801 drives the drill bit 802 through the through hole from the top of the main frame 5 to drill a hole in the test rock sample 2 in the high-pressure water tank 1 to achieve stress relief. In order to facilitate stress relief of the test rock sample, a stress relief reserved hole 102 is provided on the sealing cover 101 at the top of the tank 100. The drill rod 801 pushes the drill bit through the stress relief hole to relieve the stress on the test rock sample 2.

[0060] This invention also discloses a method for conducting stress relief simulation tests using the aforementioned stress relief simulation test apparatus, comprising the following steps:

[0061] Step 1: Prepare a strain gauge mounting hole in the center of the test rock sample 2, install the strain gauge 3 in the hole, and connect the strain gauge 3 to the data acquisition device 4.

[0062] Step 2: Move the horizontal loading frame 6 away from the hollow area 500 (i.e., the installation position), place the test rock sample 2 obtained in Step 1 in the groove 600 of the horizontal loading frame 6, and fit the tank body 100 over the test rock sample 2. Install force transmission plates on the 6 faces of the test rock sample 2 and connect the force transmission plates to the transmission columns. The first transmission column 701 passes through the horizontal reserved hole on the tank body 1, and the third transmission column 704 passes through the lateral reserved hole on the tank body. Cover the two ends of the tank body 100 with sealing caps 101, and the second transmission column 707 passes through the vertical reserved hole on the sealing cap.

[0063] Step 3: Push the horizontal loading frame 6 to the test position in the hollow area 500, and push the auxiliary frame 9 into the hollow area so that the two horizontal force loading devices are in place. Set the drill and drill rod 801 on the top of the main frame 5, wherein the drill rod 801 is set to correspond to the through hole on the main frame 5.

[0064] Step 4: Simultaneously activate the first loading cylinder 700, the second loading cylinder 703, the third loading cylinder 706, and the loading cylinders in each direction. Each loading cylinder pushes the transmission column and force transmission plate to apply load to the test rock sample in each direction. Alternatively, one loading cylinder can be activated first, and when the preset stress is reached, the second loading cylinder can be activated, and so on. While applying the three-dimensional load, water is injected into the high-pressure water tank 1 to the specified water pressure value.

[0065] Step 5, see Figure 4 and Figure 5When the stress in each direction is loaded to the preset value, the drilling machine is started. The drilling machine pushes the drill rod 801 to drive the drill tool 802 through the through hole and the stress relief reserved hole on the sealing cover 101 to drill the test rock sample 2 in the high pressure tank 1 to relieve the stress. The data acquisition device 4 collects the data sensed by each strain gauge on the strain gauge throughout the process until the stress is relieved.

[0066] Step 5: Calculate the strain changes obtained before and after stress relief to obtain the three-dimensional stress state at the drill hole; the calculation method for the three-dimensional stress state at the drill hole is as follows:

[0067] First, based on the determined coordinate axes, in this embodiment, the coordinate axes are defined as follows: the horizontal loading direction σ2 is the X-axis, the lateral loading direction σ3 is the Y-axis, and the vertical loading direction σ1 is the Z-axis;

[0068] In this embodiment, three strain bundles are embedded in the surface of the strain gauge, denoted by the number i, and corresponding to polar angles θ. i Each strain bundle consists of three strain gauges, denoted by the number j, and corresponding to an angle of . Based on strain observation value ε k The relationship between the rock mass stress state and the observed values ​​yields the following set of equations:

[0069] E·ε k =A k1 σ x +A k2 σ y +A k3 σ z +A k4 τ xy +A k5 τ yz +A k6 τ zx (1)

[0070] k=4(i-1)+j, i=1~3, j=1~3

[0071] In the formula:

[0072]

[0073] In the formula: σ x Normal stress in the X direction, σ y The normal stress in the Y direction, σ z The normal stress is in the Z direction, while τ xy Let τ be the shear stress on the xy plane. yz τ is the shear stress on the yz plane. zxLet R be the shear stress on the zx plane, K1, K2, K3, and K4 be correction coefficients, R be the borehole radius, R1 be the strain gauge inner diameter, ρ be the radius of the strain gauge embedding part, E be the elastic modulus of the surrounding rock, μ be Poisson's ratio, and E1 be the elastic modulus of the epoxy resin layer (the material of the strain gauge), μ1 be Poisson's ratio; where, the following calculations are used to determine:

[0074]

[0075] In the formula:

[0076] d1=1 / [1-2μ1+m 2 +ζ(1-m 2 )]

[0077] d2=12(1-ζ)m 2 (1-m 2 ) / (R 2 D)

[0078] d3=[m 4 (4m 2 -3)(1-ζ)+χ1+ζ] / D(4)

[0079] d4 = -4R1 2 [m 6 [(1-ζ)+χ1+ζ] / D

[0080] d5 = 3R1 4 [m 4 [(1-ζ)+χ1+ζ] / D

[0081] d6=1 / [1+m 2 +ζ(1-m 2 )]

[0082] D=(1+χζ)[χ1+ζ+(1-ζ)(3m 2 -6m 4 +4m 6 )]+(χ1-χζ)m 2 [(1-ζ)m 6 +(χ1+ζ)]

[0083] ζ=[E1(1+μ)] / [E(1+μ1)], m=R1 / R, χ=3-4μ, χ1=3-4μ1

[0084] In the formula, χ is a constant determined based on the Poisson's ratio of the surrounding rock, χ1 is a constant determined based on the Poisson's ratio of the epoxy resin, and m is a constant determined based on the ratio of the strain gauge inner diameter to the borehole radius.

[0085] A single measurement using a 3-cluster, 9-element hollow-enclosed borehole triaxial strain gauge yields 9 observation equations, allowing for the solution of 6 unknowns in the stress components. Using the least squares method, the normal equations for finding the optimal values ​​of the stress components are obtained:

[0086]

[0087] In the formula, n represents the number of strain gauges involved in the calculation of three-dimensional stress;

[0088] After obtaining the six stress components of the rock mass expressed in the borehole coordinate system, we transform them to the geodetic coordinate system and then solve for its three principal stresses using the following formula:

[0089]

[0090] In the formula:

[0091]

[0092] In the formula: J1, J2 and J3 correspond to the first, second and third invariants of the stress tensor, respectively.

[0093] The direction of the principal stress is represented by the following formula:

[0094]

[0095] Among them, the two equations and the direction cosine relation are:

[0096]

[0097] Solving the equations simultaneously, we obtain the inclination angle α of the principal stresses. i and azimuth β i for:

[0098]

[0099] In the formula, l i σ i The direction cosine on the X-axis, m i σ i The direction cosine on the Y-axis, n i σ i The direction cosine on the Z-axis, i = 1 to 3, and β0 is the azimuth angle of the X-axis in the geodetic coordinate system. If the X-axis is due north, then β0 = 0.

[0100] This experimental setup can not only simulate the true triaxial stress relief process under high stress conditions, with a maximum stress of 100 MPa, but also consider high external water pressure (up to 5 MPa, equivalent to a water head pressure of 500 m); the sample size can reach 50 cm × 50 cm × 100 cm. By conducting simulation tests of the true triaxial stress relief process under high stress conditions, the results of in-situ ground stress tests in high stress zones can be verified.

[0101] This experimental setup can also be used to calibrate strain gauges and study the variation of the four correction coefficients of strain gauges under true triaxial conditions.

[0102] The above are merely preferred embodiments of the present invention and are not intended to limit the implementation methods and protection scope of the present invention. Those skilled in the art should recognize that any equivalent substitutions and obvious changes made based on the content of this specification should be included within the protection scope of the present invention.

Claims

1. A true triaxial stress unloading test device under large-scale hydraulic coupling conditions, characterized in that, The utility model relates to a three-dimensional stress release simulation test device for rock sample, which comprises the following parts: a high-pressure water tank, two sets of opposite horizontal reserved holes and two sets of opposite lateral reserved holes are arranged on the side wall of the high-pressure water tank, the angle between the lateral reserved hole and the horizontal reserved hole is 90 degrees, and opposite vertical reserved holes are arranged on the top and bottom of the high-pressure water tank, and a stress release reserved hole is arranged on the top of the high-pressure water tank; during the stress release test, the test rock sample is arranged in the high-pressure water tank, and high-pressure water is filled in the tank; a strain gauge is arranged in the test rock sample, and the strain gauge is electrically connected with a data acquisition device; a three-dimensional force loading device, which comprises a horizontal force loading device, a vertical force loading device and a lateral force loading device perpendicular to the horizontal force and the vertical force; the horizontal force loading device passes through the horizontal reserved hole on the high-pressure water tank to apply a horizontal force to the test rock sample; the vertical force loading device passes through the horizontal reserved hole on the high-pressure water tank to apply a vertical force to the test rock sample; and the lateral force loading device passes through the lateral reserved hole on the high-pressure water tank to apply a lateral force to the test rock sample; a stress release device, which comprises a drilling machine, a drill rod connected with the drilling machine and located on the top of the high-pressure water tank, and a drill tool arranged on the end side of the drill rod; during the stress release simulation test, the drilling machine is started, the drill rod pushes the drill tool to drill a hole in the test rock sample subjected to three-dimensional stress through the stress release reserved hole to realize stress release, and the strain gauge senses the stress data of the test rock sample during the stress release process and transmits the stress data to the data acquisition device.

2. The apparatus according to claim 1, wherein The main frame is provided with a hollow area for providing a test space for the high-pressure water tank, and a through hole is arranged on the top of the main frame and communicates with the hollow area; during the test, the drill rod drives the drill tool to pass through the through hole on the top of the main frame to release the stress of the test rock sample.

3. The apparatus according to claim 2, wherein The horizontal loading frame and the auxiliary frame are oppositely arranged, and the high-pressure water tank is fixed in the accommodation groove on the horizontal loading frame; in addition, a slide rail is arranged on the main frame and crosses the hollow area; the horizontal loading frame and the auxiliary frame are slidably connected to the slide rail; during the test, the horizontal loading frame drives the high-pressure water tank to move to the test position in the hollow area for testing.

4. The apparatus according to claim 3, wherein The horizontal force loading device is oppositely arranged on the horizontal loading frame and the auxiliary frame, and comprises a first loading oil cylinder fixed on the side surface of the horizontal loading frame or the auxiliary frame, a first force transmission column in contact with the first loading oil cylinder and passing through the horizontal reserved hole, and a first force transmission plate connected with the first force transmission column; during the test, the first force transmission plate is located in the high-pressure water tank and abuts against the test rock sample, and the first loading oil cylinder drives the first force transmission column and the first force transmission plate to apply a horizontal force to the test rock sample.

5. The apparatus according to claim 2, wherein The vertical force loading device is oppositely arranged on the top and bottom of the hollow area, and comprises a second loading oil cylinder fixed on the top surface or the bottom surface, a second force transmission column in contact with the second loading oil cylinder and passing through the vertical reserved hole, and a second force transmission plate connected with the second force transmission column; during the test, the second force transmission plate is located in the high-pressure water tank and abuts against the test rock sample, and the second loading oil cylinder drives the second force transmission column and the second force transmission plate to apply a vertical force to the test rock sample.

6. The apparatus according to claim 2, wherein The lateral force loading device is fixed on the opposite side walls of the hollowed-out area, and comprises a third loading oil cylinder fixed on the side wall of the hollowed-out area, a third force transmission column in contact connection with the third loading oil cylinder through the lateral reserved hole, and a third force transmission plate connected with the third force transmission column; during the test, the third force transmission plate is located in the high-pressure water tank and presses on the test rock sample, and the third loading oil cylinder pushes the third force transmission column and the third force transmission plate to exert lateral force on the test rock sample.

7. The apparatus according to claim 1, wherein The water pressure applying device for pressurizing the high-pressure water tank and the water pressure measuring device for measuring the water pressure of the high-pressure water tank are further included, and the water pressure measuring device is arranged in the high-pressure water tank.

8. The apparatus according to claim 1, wherein The high-pressure water tank comprises a hollow tank body and sealing covers sealingly covering two ends of the tank body, and the horizontal reserved hole and the lateral reserved hole are arranged on the side wall of the tank body, and the vertical reserved hole and the stress relief reserved hole are fixed on the sealing covers.

9. The apparatus for true triaxial stress unloading test under large-scale hydro-coupling conditions according to any one of claims 1-8, characterized in that, The method comprises the following steps: Step 1: a strain gauge mounting hole is prepared in the center of the test rock sample, and a strain gauge is arranged in the hole, and the strain gauge is connected with a data acquisition device; Step 2: the test rock sample obtained in step 1 is placed in high-pressure water, and the high-pressure water tank is sealed; Step 3: the horizontal force loading device, the vertical force loading device and the lateral force loading device are installed, the three-direction force loading device is started to load the test rock sample in the high-pressure tank body, and water is injected into the high-pressure water tank to a specified water pressure value; Step 4: when the stress in each direction is loaded to a preset value, the stress relief device is started to relieve the stress of the test rock sample in the high-pressure water tank, and the data acquisition device collects the data sensed by the strain gauge during the whole process until the relief is completed; Step 5: the strain change values obtained before and after the stress relief are calculated to obtain the three-dimensional stress state of the drilling tool at the drilling hole.

10. The apparatus according to claim 9, wherein The calculation method of the three-dimensional stress at the drilling hole is as follows: One of the three-direction stress loading directions is taken as the X axis, and the others are taken as the Y axis and the Z axis respectively; Strain gage surface-embedded strain cluster, serial number is represented by i, and the corresponding polar angle is θ i Each strain cluster includes a plurality of strain gauges, serial number is represented by j, and the corresponding angle is According to the strain observation value ε k The relationship with the stress state of rock mass, the following observation equation group is obtained: E ε k = A k1 σ x + A k2 σ y + A k3 σ z + A k4 τ xy + A k5 τ yz + A k6 τ zx k = 4(i-1) + j; In the formula: wherein: σ x is the normal stress in the X direction, σ y is the normal stress in the Y direction, σ z is the normal stress in the Z direction, and τ xy is the shear stress in the xy plane, τ yz is the shear stress in the yz plane, τ zx is the shear stress in the zx plane, K1, K2, K3, K4 are correction coefficients, R is the borehole radius, R1 is the strain gauge inner diameter, p is the radius of the strain gauge embedding site, E is the elastic modulus of the surrounding rock, μ is the Poisson's ratio, and E1 is the elastic modulus of the epoxy resin layer, μ1 is the Poisson's ratio; According to the equation group of each strain gauge obtained by the above method, the normal equation group for solving the optimal value of the stress component is obtained by using the least square method principle: After the multiple stress components of the rock mass expressed by the drilling coordinate system are solved, they are converted into the geodetic coordinate system, and then the three principal stresses are solved according to the following formula: In the formula, n represents the number of strain gauges participating in the calculation of the three-dimensional stress; In the formula: J1, J2 and J3 respectively correspond to the first, second and third invariants of the stress tensor; the principal stress direction is represented by the following formula: (σ x -σ i )l i +τ xy m i +τ zx n i =0 τ xy l i +(σ y -σ i )m i +τ yz n i =0 τ zx l i +τ yz m i +(σ z -σ i )n i =0 Wherein, the direction cosine relationship of any two formulas is: The inclination angle α of the principal stress is obtained by simultaneous solution i and the azimuth angle β is i : a i = sin -1 n i wherein l i denotes σ i directional cosine of the direction in the X axis, m i denotes σ i directional cosine of the direction in the Y axis, n i denotes σ i directional cosine of the direction in the Z axis, β0is the azimuth angle of the X axis of the geodetic coordinate system. If the X axis is the north direction, then β0= 0.

Images