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

Abstract

The invention discloses a true triaxial stress relief test device and method under a large-scale hydraulic coupling condition, and the device comprises a high-pressure water tank, and the side wall of the high-pressure water tank is provided with two groups of opposite horizontal preformed holes and two groups of opposite lateral preformed holes. Opposite vertical preformed holes are formed in the top and the bottom of the high-pressure water tank, a stress relief preformed hole is formed in the top of the high-pressure water tank, and a strain gauge is arranged in the test rock sample and electrically connected with a data acquisition device; the three-way force loading device is used for applying three-way force to the test rock sample; the stress relieving device comprises a drilling machine, a drilling rod connected with the drilling machine and located at the top of the tank body and a drilling tool arranged on the end side of the drilling rod, the drilling machine device is started, the drilling rod pushes the drilling tool to drill holes in the test rock sample to which the three-dimensional stress is applied so as to relieve the stress, and a strainometer senses stress data on the test rock sample and transmits the stress data to the data acquisition device. According to the invention, the real stress condition and water environment condition of the rock mass can be simulated, so that the stress condition of the rock mass can be accurately obtained.

Description

Technical Field

[0001] The invention belongs to the technical field of rock mechanics testing, and in particular relates to a true triaxial stress relief test device and method under large-scale hydraulic coupling conditions. Background Art

[0002] Geostress refers to a natural force that objectively exists in the crust and rock mass and is not disturbed by engineering. It is also called original rock stress. It is the fundamental force that causes deformation, fracture, folding and even earthquakes in the crust and rock mass. Geostress measurement is a very important issue in major construction projects. Accurately measuring the geostress of the rock mass is the basis for correctly and reasonably calculating the excavation load of underground engineering. Therefore, geostress measurement is very important. There are two main methods for on-site geostress testing today: stress relief method and hydraulic fracturing method. However, the existing testing equipment and testing theories have many basic assumptions. It is difficult to accurately evaluate whether the geostress results measured by existing instruments and methods are consistent with the actual stress conditions of the surrounding rock. It can only be evaluated through a large number of field tests combined with different testing methods. Therefore, how to accurately measure geostress and whether the measurement of geostress with existing instruments and equipment is reliable are problems that must be solved when conducting research related to rock mass geostress. Summary of the invention

[0003] One purpose of the present invention is to address the deficiencies of the prior art and provide a true triaxial stress relief test device under large-scale hydraulic coupling conditions, which can simulate the actual stress conditions of rock samples and accurately obtain the on-site ground stress conditions in the high stress zone of the true triaxial stress relief process under high stress conditions.

[0004] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0005] A true triaxial stress relief test device under large-scale hydraulic coupling conditions, comprising:

[0006] A high-pressure water tank, wherein two groups of relative horizontal reserved holes and two groups of relative lateral reserved holes are arranged on the side wall of the high-pressure water tank, and the arc between the lateral reserved holes and the horizontal reserved holes is 90°, and relative vertical reserved holes are arranged on the top and bottom of the high-pressure water tank, and a stress relief reserved hole is arranged on the top thereof. During the test, the test rock sample is arranged in the high-pressure water tank and filled with high-pressure water, and a strain gauge is arranged inside the test rock sample, and the strain gauge is electrically connected to the data acquisition device;

[0007] A three-axis 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 force and the vertical force. The horizontal force loading device applies a horizontal force to the test rock sample through a horizontal reserved hole on the high-pressure water tank. The vertical force loading device applies a vertical load to the test rock sample through a horizontal reserved hole on the high-pressure water tank. The lateral force loading device applies a lateral force to the test rock sample through a lateral reserved 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 on the top of the tank body, and a drill tool arranged on the end side of the drill rod. During the stress relief simulation test, the drilling rig is turned on, and the drill rod pushes the drill tool through the stress relief reserved hole to drill a test rock sample to which three-dimensional stress is applied to achieve stress relief. The strain gauge senses the stress data on the test rock sample during the stress relief process and transmits it to the data acquisition device.

[0009] Furthermore, it comprises a main frame, on which a hollow area for accommodating a high-pressure tank body during testing is arranged, and a through hole connecting the hollow area is arranged on the top of the main frame, and a drill rod drives a drill tool from the top of the main frame through the through hole to relieve stress on the test rock sample.

[0010] Furthermore, it also includes a horizontal loading frame, on which a accommodating groove is provided for fixing high pressure through a through hole on the top of the main frame. In addition, a slide rail is provided on the main frame to cross the hollow area, and the horizontal loading frame is slidably connected to the slide rail. During the test, the horizontal loading frame drives the high-pressure water tank to move to the test station in the hollow area for testing.

[0011] Furthermore, a horizontal force loading device is arranged on two opposite side surfaces of the horizontal loading frame, and the horizontal force loading device includes a first loading cylinder fixed on the side surface of the horizontal loading frame, a first force transmission column connected to the first loading cylinder through a horizontal reserved hole, and a first force transmission plate connected to the first transmission column. During the test, the first force transmission plate is located in the high-pressure water tank and pressed against the test rock sample, and the first loading cylinder pushes the first transmission column and the first force transmission plate to apply horizontal force to the test rock sample.

[0012] Furthermore, vertical force loading devices are relatively arranged at the top and bottom of the hollow area, and the vertical force loading device includes a second loading cylinder fixed on the top surface or the bottom surface, a second force transmission column connected to the second loading cylinder through the vertical reserved hole, and a second force transmission plate connected to the second transmission column. During the test, the second force transmission plate is located in the high-pressure water tank and pressed against the test rock sample, and the second loading cylinder pushes the second transmission column and the second force transmission plate to apply vertical force to the test rock sample.

[0013] Furthermore, lateral force loading devices are fixed on two opposite side walls of the hollow area, and the lateral force loading device includes a third loading cylinder fixed on the side wall of the hollow area, a third force transmission column connected to the third loading cylinder through a lateral reserved hole, and a third force transmission plate connected to the third transmission column. During the test, the third force transmission plate is located in the high-pressure water tank and pressed against the test rock sample, and the third loading cylinder pushes the third 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 applying 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 used to measure the water pressure of the high-pressure water tank, and the water pressure measuring device is arranged in the high-pressure water tank.

[0015] Furthermore, the high-pressure water tank includes a hollow tank body and a sealing cover that covers and seals the tank body, the horizontal reserved holes and the lateral reserved holes are both arranged on the side wall of the tank body, and the vertical reserved holes and the stress relief reserved holes are fixed on the sealing cover.

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

[0017] Step 1: Prepare a strain gauge installation hole in the center of the test rock sample in advance, 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, the vertical force loading device and the lateral force loading device, move the horizontal loading frame to the test station, start the three-axis force loading device to load the test rock sample in the high-pressure tank with three-axis force, and at the same time, fill the high-pressure water tank with water to the specified water pressure value;

[0020] 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 stress relief is completed;

[0021] Step 5: Calculate the strain change values ​​obtained before and after stress relief to obtain the three-dimensional stress state of the drilling tool at the drilling hole.

[0022] Furthermore, the calculation method of the three-dimensional stress at the borehole is:

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

[0024] The strain bundle of the strain gauge surface is represented by i, and the corresponding polar angle is θi , each strain bundle includes multiple strain gauges, the serial number is represented by j, and the corresponding angle is According to the strain observation value ε of each strain gauge k The relationship between the rock mass stress state and the following set of observation equations is obtained:

[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] Where:

[0028]

[0029] Where: 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 on the xy plane, τ yz is the shear stress on the yz plane, τ zx are the shear stress on the zx plane, K 1 , K 2 , K 3 , K 4 is the correction coefficient, R is the drilling radius, R 1 is the inner diameter of the strain gauge, ρ is the radius of the embedded part of the strain gauge, E is the elastic modulus of the surrounding rock, μ is the Poisson's ratio and E 1 is the elastic modulus of the epoxy resin layer, μ 1 is Poisson’s ratio;

[0030] According to the above method, the equation group of each strain gauge is obtained. Using the principle of least squares method, the normal equation group for solving the optimal value of stress component is obtained:

[0031]

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

[0033]

[0034] Where n represents the number of strain gauges involved in calculating three-dimensional stress;

[0035]

[0036] Where: J 1 , J 2 and J 3 They correspond to the first, second and third invariants of the stress tensor respectively; the principal stress directions are expressed by the following formula:

[0037] (σ x -σ i ) 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 ) i =0

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

[0041]

[0042] The inclination angle α of the principal stress is obtained by simultaneous solution i and azimuth β i for:

[0043] α i =sin -1 n i

[0044]

[0045] In the formula, l i Represents σ i Direction cosines on the X axis, m i Represents σ i Direction cosines on the Y axis, n i Represents σ i Direction cosines about the Z axis, β 0is the azimuth of the X-axis of the geodetic coordinate system. If the X-axis is due north, then β 0 =0.

[0046] Compared with the prior art, the beneficial effects of the present invention are as follows: the present invention can simulate the real stress condition and water environment of the rock mass by means of a three-dimensional stress device and by applying high-pressure water to a high-pressure water tank, and then relieve the stress of the rock sample and obtain the strain value during the stress relief process, so that the three-dimensional stress state at the borehole can be accurately obtained through the experiment; the present invention can not only conduct a simulation test of the true triaxial stress relief process under high stress conditions, with the maximum stress reaching 100MPa; it also takes into account high external water pressure (up to 5MPa, equivalent to a head pressure of 500m); the sample size can reach 50cm×50cm×100cm, and the on-site ground stress test results in the high stress area can be verified by conducting a simulation test of the true triaxial stress relief process under high stress conditions, and the strain gauge can also be calibrated. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

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

[0050] Figure 4 A vertical cross-sectional view of a rock sample loaded according to an embodiment of the present invention;

[0051] Figure 5 This is a horizontal cross-sectional view of the loading of a rock sample according to an embodiment of the present invention. DETAILED DESCRIPTION

[0052] The technical solutions in the embodiments of the present invention will be described clearly and completely below in combination with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0053] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0054] The present invention will be further described below in conjunction with specific embodiments, but the present invention is not limited thereto.

[0055] like Figure 1 , Figure 2 , Figure 3 As shown, an embodiment of the present invention discloses a true triaxial stress relief test device under large-scale hydraulic coupling conditions, including a high-pressure water tank, a three-axis force loading device and a stress relief device. The high-pressure water tank 1 includes a hollow tank body 100 and a sealing cover 101 that covers and seals both ends of the tank body 100. Two groups of relative horizontal reserved holes and two groups of relative lateral reserved holes are arranged on the side wall of the tank body 100, and the arc between the lateral reserved holes and the horizontal reserved holes is 90°, and relative vertical reserved holes are arranged on the two sealing covers 101. The above-mentioned reserved holes facilitate the three-axis force loading device to load the test rock sample 2. The test rock sample 2 can be a sample of similar materials or a rock sample retrieved on site. 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 thereto. The high-pressure water tank 1 is used to provide a water pressure environment for the test rock sample 2. To this end, a water pressure applying device connected to the high-pressure water tank 1 and used to inject water and pressurize 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, wherein the water pressure measuring device is arranged in 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 the stress and strain conditions on the test rock sample during the stress relief process, a mounting hole is provided in advance inside the test rock sample, and then the strain gauge 3 is fixed in the mounting hole. The installed strain gauge 3 is connected to the data acquisition device 4 through a cable 400. A plurality of strain clusters are embedded on the surface of the strain gauge 3, each strain cluster includes a plurality of strain gauges. During the test, the data acquisition device 4 collects the strain data of each strain gauge.

[0056] In order to facilitate the fixation of the three-way force loading device and the high-pressure water tank 1, it also includes a main frame 5, a horizontal loading frame 6, and an auxiliary frame 9 arranged opposite to the horizontal loading frame. The main frame 5 is a frame structure, and a hollow area 500 is arranged at the center of the main frame to provide a test space for the high-pressure water tank 1, and a slide rail 501 is arranged at the bottom of the hollow area 500 to cross the hollow area. The horizontal loading frame 6 and the auxiliary frame 9 are both slidably connected to the slide rail 501 through pulleys or sliders. A groove 600 for fixing the high-pressure water tank 1 is arranged 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 drives the high-pressure water tank 1 to move on the slide rail 501 to the test station in the hollow area 500.

[0057] The three-way force loading device includes 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 is fixed on the horizontal loading frame 6 and the auxiliary frame 9, wherein the horizontal force loading device fixed on the horizontal loading frame 6 is arranged opposite to the horizontal force loading device fixed on the auxiliary frame 9. The horizontal force loading device includes a first loading cylinder 700 fixed on the side of the horizontal loading frame 6 or the auxiliary frame 9, a first force transmission column 701 that contacts and connects with the first loading cylinder 700 through a horizontal reserved hole, and a first force transmission plate 702 connected to the first transmission column 701. During the test, the first force transmission plate 702 is located in the high-pressure water tank 1 and pressed against two opposite sides of the test rock sample 2. The first loading cylinder 700 pushes the first transmission column 701 and the first force transmission plate 702 to apply horizontal force to the test rock sample 2.

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

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

[0060] The embodiment of the present invention further discloses a method for performing a stress relief simulation test using the stress relief simulation test device, comprising the following steps:

[0061] Step 1: prepare a strain gauge installation hole in the center of the test rock sample 2 in advance, 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 rack 6 away from the hollow area 500 (i.e., the installation station), place the test rock sample 2 obtained in step 1 in the groove 600 of the horizontal loading rack 6, and put the tank body 100 on the outside of the test rock sample 2, install the force transfer plates on the six surfaces of the test rock sample 2 respectively, and connect the force transfer plates with the transfer columns, the first transfer column 701 passes through the horizontal reserved hole on the tank body 1, and the third transfer column 704 passes through the lateral reserved hole on the tank body, cover the two ends of the tank body 100 with sealing covers 101, and the second transfer column 707 passes through the vertical reserved hole on the sealing cover;

[0063] Step 3, push the horizontal loading frame 6 to the test station in the hollow area 500, and push the auxiliary frame 9 into the hollow area to put the two horizontal force loading devices in place, and set the drill rig and drill rod 801 on the top of the main frame 5, wherein the drill rod 801 is set corresponding to the through hole on the main frame 5;

[0064] Step 4: Start the first loading cylinder 700, the second loading cylinder 703, the third loading cylinder, and the loading cylinder 706 at the same time. The loading cylinders in each direction push the transfer column and the force transfer plate to apply loads to the test rock sample in each direction. Of course, you can also start the loading cylinder in one direction first, and when the load reaches the preset stress, start the loading cylinder in the second direction, and so on. While applying the three-way load, fill the high-pressure water tank 1 with water 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 rig is started, and the drilling rig pushes the drill rod 801 to drive the drilling tool 802 to pass 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 body 1 to relieve the stress, and the data acquisition device 4 collects the data sensed by each strain gauge on the strain gauge during the whole process until the stress relief is completed;

[0066] Step 5: Calculate the strain change values ​​obtained before and after stress relief to obtain the three-dimensional stress state at the drilling hole of the drilling tool; wherein the calculation method of the three-dimensional stress state at the drilling hole is:

[0067] First, the coordinate axis is determined according to the present embodiment. In the present embodiment, the coordinate axis is defined as: horizontal σ 2 The loading direction is X-axis, and the lateral σ 3 The loading direction is the Y axis, and the vertical direction is σ 1 The loading direction is the Z axis;

[0068] In this embodiment, three strain clusters are embedded in the surface of the strain gauge, the serial number is represented by i, and the corresponding polar angle is θ i , each strain bundle consists of 3 strain gauges, the serial number is represented by j, and the corresponding angle is According to the strain observation value ε k The relationship between the rock mass stress state and the following set of observation equations can be obtained:

[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] Where:

[0072]

[0073] In the formula: In the formula: 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 on the xy plane, τ yz is the shear stress on the yz plane, τ zx are the shear stress on the zx plane, K1 , K 2 , K 3 , K 4 is the correction coefficient, R is the drilling radius, R 1 is the inner diameter of the strain gauge, ρ is the radius of the embedded part of the strain gauge, E is the elastic modulus of the surrounding rock, μ is the Poisson's ratio and E 1 is the elastic modulus of the epoxy resin layer (the material of the strain gauge), μ 1 is Poisson's ratio; where is determined by the following calculation:

[0074]

[0075] Where:

[0076] d 1 =1 / [1-2μ 1 +m 2 +ζ(1-m 2 )]

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

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

[0079] d 4 =-4R 1 2 [m 6 (1-ζ)+χ 1 +ζ] / D

[0080] d 5 =3R 1 4 [m 4 (1-ζ)+χ 1 +ζ] / D

[0081] d 6 =1 / [1+m 2 +ζ(1-m 2 )]

[0082] D = (1 + χζ) [χ 1 +ζ+(1-ζ)(3m 2 -6m 4 +4m 6 )]+(χ 1 -χζ)m 2 [(1-ζ)m6 +(χ 1 +ζ)]

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

[0084] In the formula, χ is a constant determined by the Poisson's ratio of the surrounding rock, 1 is a constant determined by the Poisson’s ratio of epoxy resin, and m is a constant determined by the ratio of the strain gauge inner diameter to the drill hole radius;

[0085] A single measurement of 3-cluster 9-piece hollow package-type borehole triaxial strain gauges can obtain 9 observation value equations and solve the unknown quantities of 6 stress components. Using the principle of least squares method, the normal equation group for solving the optimal value of stress components is obtained:

[0086]

[0087] Where n represents the number of strain gauges involved in calculating three-dimensional stress;

[0088] After solving the six stress components of the rock mass expressed by the borehole coordinate system, convert them to the geodetic coordinate system and then solve its three principal stresses according to the following formula:

[0089]

[0090] Where:

[0091]

[0092] Where: J 1 , J 2 and J 3 They correspond to the first, second and third invariants of the stress tensor respectively.

[0093] The principal stress directions are expressed by:

[0094]

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

[0096]

[0097] The inclination angle α of the principal stress is obtained by simultaneous solution i and azimuth β i for:

[0098]

[0099] In the formula, l i Represents σ i Direction cosines on the X axis, m i Represents σ i Direction cosines on the Y axis, n i Represents σ i Direction cosine on the Z axis, i = 1 to 3, β 0 is the azimuth of the X-axis of the geodetic coordinate system. If the X-axis is due north, then β 0 =0.

[0100] The test device can not only simulate the true triaxial stress relief process under high stress conditions, with a maximum stress of 100MPa, but also take into account high external water pressure (up to 5MPa, equivalent to a head pressure of 500m); the sample size can reach 50cm×50cm×100cm. By conducting a simulation test of the true triaxial stress relief process under high stress conditions, the on-site ground stress test results in high stress areas can be verified.

[0101] The test device can also perform calibration tests on strain gauges to study the changing rules of the four correction coefficients of the strain gauges under true triaxial conditions.

[0102] The above are only 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 be aware that all solutions obtained by equivalent substitutions and obvious changes made using the contents of the specification of the present invention should be included in the protection scope of the present invention.

Claims

1. A true triaxial stress relief test device under large-scale hydraulic coupling conditions, characterized in that: include: A high-pressure water tank, wherein two groups of relative horizontal reserved holes and two groups of relative lateral reserved holes are arranged on the side wall of the high-pressure water tank, and the arc between the lateral reserved holes and the horizontal reserved holes is 90°, and relative vertical reserved holes are arranged on the top and bottom of the high-pressure water tank, and a stress relief reserved hole is arranged on the top thereof. During the stress relief 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 inside the test rock sample, and the strain gauge is electrically connected to the data acquisition device; A three-axis 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 force and the vertical force. The horizontal force loading device applies a horizontal force to the test rock sample through a horizontal reserved hole on the high-pressure water tank. The vertical force loading device applies a vertical load to the test rock sample through a horizontal reserved hole on the high-pressure water tank. The lateral force loading device applies a lateral force to the test rock sample through a lateral reserved hole on the high-pressure water tank. The stress relief device includes a drilling rig, a drill rod connected to the drilling rig and located on the top of a high-pressure water tank, and a drill tool arranged on the end side of the drill rod. During the stress relief simulation test, the drilling rig is turned on, and the drill rod pushes the drill tool through a reserved hole for stress relief to drill a test rock sample to which triaxial stress is applied to achieve stress relief. The strain gauge senses stress data on the test rock sample during the stress relief process and transmits it to a data acquisition device.

2. The true triaxial stress release test device under large-scale hydraulic coupling conditions according to claim 1 is characterized in that: It comprises a main frame, on which a hollow area is arranged to provide a test space for a high-pressure water tank, and a through hole connected to the hollow area is arranged on the top of the main frame. During the test, the drill rod drives the drill tool from the top of the main frame through the through hole to relieve the stress of the test rock sample.

3. The true triaxial stress release test device under large-scale hydraulic coupling conditions according to claim 2 is characterized in that: It also includes a horizontal loading frame and an auxiliary frame arranged opposite to the horizontal loading frame. The horizontal loading frame is provided with a accommodating groove for fixing high pressure through a through hole from the top of the main frame. In addition, a slide rail crossing the hollow area is provided on the main frame. The horizontal loading frame and the auxiliary frame are both slidably connected to the slide rail. During the test, the horizontal loading frame drives the high-pressure water tank to move to the test station in the hollow area for testing.

4. The true triaxial stress release test device under large-scale hydraulic coupling conditions according to claim 3 is characterized in that: A horizontal force loading device is relatively arranged on the horizontal loading frame and the auxiliary frame, and the horizontal force loading device includes a first loading cylinder fixed on the side of the horizontal loading frame or the auxiliary frame, a first force transmission column passing through a horizontal reserved hole and contacting and connecting with the first loading cylinder, and a first force transmission plate connected with the first transmission column. During the test, the first force transmission plate is located in the high-pressure water tank and pressed against the test rock sample, and the first loading cylinder pushes the first transmission column and the first force transmission plate to apply horizontal force to the test rock sample.

5. The true triaxial stress release test device under large-scale hydraulic coupling conditions according to claim 2 is characterized in that: Vertical force loading devices are relatively arranged at the top and bottom of the hollow area, and the vertical force loading device includes a second loading cylinder fixed on the top surface or the bottom surface, a second force transmission column passing through a vertical reserved hole and contacting and connecting with the second loading cylinder, and a second force transmission plate connected with the second transmission column. During the test, the second force transmission plate is located in the high-pressure water tank and pressed against the test rock sample, and the second loading cylinder pushes the second transmission column and the second force transmission plate to apply vertical force to the test rock sample.

6. The true triaxial stress release test device under large-scale hydraulic coupling conditions according to claim 2 is characterized in that: A lateral force loading device is fixed on both opposite side walls of the hollow area, and the lateral force loading device includes a third loading cylinder fixed on the side wall of the hollow area, a third force transmission column connected to the third loading cylinder through a lateral reserved hole, and a third force transmission plate connected to the third transmission column. During the test, the third force transmission plate is located in the high-pressure water tank and pressed against the test rock sample, and the third loading cylinder pushes the third transmission column and the third force transmission plate to apply lateral force to the test rock sample.

7. The true triaxial stress release test device under large-scale hydraulic coupling conditions according to claim 1 is characterized in that: It also includes a water pressure applying 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 used to measure the water pressure of the high-pressure water tank. The water pressure measuring device is arranged in the high-pressure water tank.

8. The true triaxial stress release test device under large-scale hydraulic coupling conditions according to claim 1 is characterized in that: The high-pressure water tank comprises a hollow tank body and a sealing cover which covers and seals both ends of the tank body. The horizontal reserved holes and the lateral reserved holes are arranged on the side wall of the tank body, and the vertical reserved holes and the stress relief reserved holes are fixed on the sealing cover.

9. A true triaxial stress release test device under large-scale hydraulic coupling conditions according to any one of claims 1 to 8, characterized in that: The steps include: Step 1: Prepare a strain gauge installation hole in the center of the test rock sample in advance, install the strain gauge in the hole, and connect the strain gauge to the data acquisition device; Step 2, placing the test rock sample obtained in step 1 in high-pressure water and sealing the high-pressure water tank; Step 3: Install the horizontal force loading device, the vertical force loading device and the lateral force loading device, start the three-axis force loading device to load the test rock sample in the high-pressure tank with three-axis force, and at the same time, fill the high-pressure water tank with water to the 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 stress relief is completed; Step 5: Calculate the strain change values ​​obtained before and after stress relief to obtain the three-dimensional stress state of the drilling tool at the drilling hole.

10. The true triaxial stress release test device under large-scale hydraulic coupling conditions according to claim 9, characterized in that: The calculation method of the three-dimensional stress at the drilling hole is: One of the three stress loading directions is the X axis, and the others are the Y axis and the Z axis; The strain bundle of the strain gauge surface is represented by i, and the corresponding polar angle is θ i , each strain bundle includes multiple strain gauges, the serial number is represented by j, and the corresponding angle is According to the strain observation value ε of each strain gauge k The relationship between the rock mass stress state and the following set of observation equations is obtained: E·e k =A k1 s x +A k2 s y +A k3 s z +A k4 t xy +A k5 t yz +A k6 t zx k = 4(i-1) + j; Where: Where: 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 on the xy plane, τ yz is the shear stress on the yz plane, τ zx are the shear stress on the zx plane, K1, K2, K3, K4 are correction coefficients, R is the borehole radius, R1 is the inner diameter of the strain gauge, ρ is the radius of the strain gauge embedding part, 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 above method, the equation group of each strain gauge is obtained, and the normal equation group for solving the optimal value of the stress component is obtained by using the principle of least squares method: After solving the multiple stress components of the rock mass expressed by the borehole coordinate system, they are converted to the geodetic coordinate system, and then the three principal stresses are solved according to the following formula: Where n represents the number of strain gauges involved in calculating three-dimensional stress; Where: J1, J2 and J3 correspond to the first, second and third invariants of the stress tensor respectively; the principal stress direction is expressed by the following formula: (s x -s i )l i +t xy m i +t zx n i =0 t xy l i +(s y -s i )m i +t yz n i =0 t zx l i +t yz m i +(s z -s i )n i =0 Among them, any two equations and the direction cosine relationship are: The inclination angle α of the principal stress is obtained by simultaneous solution i and azimuth β i for: a i =sin -1 n i In the formula, l i Represents σ i Direction cosines on the X axis, m i Represents σ i Direction cosines on the Y axis, n i Represents σ i The direction cosine on the Z axis, β0 is the azimuth of the X axis of the geodetic coordinate system. If the X axis is due north, then β0=0.

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