A method and system for measuring ground stress using a thermal-mechanical coupling model

Abstract

The present invention belongs to the field of geostress measurement, and specifically relates to a method and system for measuring geostress using a thermomechanical coupling model. The system comprises: a heating device arranged below the rock mass in the geostress measurement area, a borehole on the rock mass in the geostress measurement area, an acoustic emission device, and an infrared temperature sensor; the acoustic emission probe of the acoustic emission device is arranged on the wall of the borehole; and the infrared temperature sensor is arranged on the wall of the borehole to measure the wall temperature of the borehole. The method provided by the present invention does not require separate drilling, and uses the existing thermomechanical coupling model to analyze the temperature of thermal cracking of the rock mass, which is an effective auxiliary method for measuring geostress.

Description

Technical Field

[0001] The present invention belongs to the field of ground stress measurement, and in particular relates to a method and a system for measuring ground stress by using a thermal-mechanical coupling model. Background Art

[0002] Geostress is the fundamental force that causes deformation and destruction in mining and other underground geotechnical engineering projects. The size and direction of the geostress field have a significant impact on deep resource development. So far, there are more than 20 methods for measuring geostress, mainly including the flat jack method, the casing stress relief method, the hydraulic fracturing method, the acoustic emission method, and the rigid inclusion stress gauge. Among them, the casing stress relief method, the hydraulic fracturing method, and the acoustic emission method are the most widely used geostress measurement methods. However, the casing stress relief method and the hydraulic fracturing method are complex, expensive, and time-consuming for geostress measurement. The acoustic emission method requires directional core processing tests, which is simple, economical, and intuitive and is widely used, but the measurement accuracy is limited due to the problem of rock mass stress history. Summary of the invention

[0003] In view of the above technical problems, the present invention provides a method and system for measuring ground stress using a thermal-mechanical coupling model. The method does not require drilling a hole separately, but uses an existing thermal-mechanical coupling model to analyze the temperature of thermal cracking of rock mass, which is an effective auxiliary method for measuring ground stress.

[0004] In order to achieve the above technical objectives, the present invention provides the following technical solutions:

[0005] A system for measuring ground stress using a thermal-mechanical coupling model, the system comprising: a heating device arranged below a rock mass in a region to be measured for ground stress, a drill hole on the rock mass in the region to be measured for ground stress, an acoustic emission device, and an infrared temperature sensor;

[0006] The acoustic emission probe of the acoustic emission device and the infrared temperature sensor are both arranged on the wall of the borehole; the heating device is used to heat the rock mass; the acoustic emission device is used to detect and collect the acoustic signal generated during the rock mass heating process; the infrared temperature sensor is used to measure the wall temperature of the borehole;

[0007] When the system measures the ground stress, a heating device is used to heat the rock mass, and the acoustic emission probe of the acoustic emission device detects the fracture sound waves of the rock mass. The thermal stress of the borehole wall at the moment when the rock mass begins to fracture is: ;in, is the thermal stress of the borehole wall; and is the two-dimensional stress field of the borehole; is the tensile strength of the rock sample;

[0008] The heating device is used to heat until the intensity of the acoustic signal obtained by the acoustic emission device is less than 5% of the intensity of the rock mass fracture acoustic signal obtained when the rock mass begins to fracture, and then the heating is stopped, the time of stopping the heating is recorded, and the infrared temperature sensor is used to measure the corresponding borehole wall temperature during the heating process in real time;

[0009] The temperature of the borehole wall and the conductivity coefficient of the rock sample corresponding to the entire heating process ,density Specific heat capacity Input the temperature simulation software to obtain the temperature distribution curve of the rock mass around the borehole when the temperature rise stops. Based on the temperature distribution curve, the crack development position is obtained. Directional pressure ,and ;

[0010] According to the measured tensile strength of the rock mass , and the calculated , , the two-dimensional stress field of the borehole is obtained and size.

[0011] Furthermore, when installing the heating device, the heating device is connected to the drill rod, and the drill rod brings the heating device to the heating position, and the heating position is below the rock mass in the area where the ground stress is to be measured.

[0012] Furthermore, an electromagnetic coil is provided in the heating device to heat the rock mass.

[0013] A method for measuring ground stress using a thermal-mechanical coupling model, the method comprising the following steps:

[0014] (1) Take rock samples from the area where the ground stress is to be measured and measure the tensile strength of the rock samples , conductivity ,density Specific heat capacity ;

[0015] (2) The system for measuring ground stress using the thermal-mechanical coupling model is set up in the ground stress test area, and the initial temperature of the rock mass before heating is recorded by an infrared temperature sensor, and the temperature of the borehole wall corresponding to the entire heating process is measured; when the heating device is heating, the acoustic emission probe of the acoustic emission device is used to detect the fracture sound wave of the rock mass;

[0016] (3) judging whether the rock mass has cracked according to the acoustic signal detected by the acoustic emission device, and when the acoustic emission device detects the acoustic signal of rock mass cracking, recording the time corresponding to the first detection of the acoustic signal of rock mass cracking as the time when the rock mass starts to crack;

[0017] At the moment when the rock mass begins to break, ;

[0018] in, is the thermal stress of the borehole wall; and is the two-dimensional stress field of the borehole; is the tensile strength of the rock sample;

[0019] (4) the heating device is used to heat until the intensity of the acoustic signal obtained by the acoustic emission device is less than 5% of the intensity of the rock mass fracture acoustic signal obtained when the rock mass begins to fracture, and then the heating is stopped, the time of stopping the heating is recorded, and the infrared temperature sensor is used to measure the corresponding borehole wall temperature during the heating process in real time;

[0020] (5) Inputting the borehole wall temperature corresponding to the entire heating process and the rock sample parameters obtained in step (1) into the temperature simulation software to obtain the temperature distribution curve of the rock mass around the borehole when the heating is stopped;

[0021] The crack development location is calculated based on the temperature distribution curve. Directional pressure ,and ;

[0022] (6) Based on the measured tensile strength of the rock sample , and the calculated , , we can conclude and size.

[0023] Furthermore, in step (3), when the intensity of the acoustic signal acquired by the acoustic emission device is less than 5% of the peak acoustic signal intensity acquired when the rock mass begins to fracture, the fracture depth reaches more than 3 times the borehole diameter.

[0024] Furthermore, in step (5), the borehole wall temperature and the rock sample conductivity corresponding to the entire heating process are calculated. ,density Specific heat capacity Input the temperature simulation software to obtain the temperature distribution curve of the rock mass around the borehole when the heating stops.

[0025] Furthermore, the horizontal axis of the temperature distribution curve represents the distance of the rock mass around the borehole from the center of the borehole, and the vertical axis represents the temperature of the rock mass.

[0026] Furthermore, the temperature simulation software is finite element analysis software.

[0027] Furthermore, the temperature simulation software is COMSOL simulation software.

[0028] Furthermore, in step (5), the first point on the side of the temperature distribution curve close to the vertical axis that is consistent with the initial temperature of the rock mass before heating is calculated to obtain the crack development location. Directional pressure .

[0029] The beneficial effects of the present invention are:

[0030] The method for measuring ground stress provided by the present invention can assist other ground stress measurement means and does not require separate drilling, so it is a relatively economical auxiliary means.

[0031] The method for measuring ground stress provided by the present invention utilizes the existing thermal-mechanical coupling model to analyze the temperature data of thermal cracking of rock mass, thereby summarizing a set of effective auxiliary ground stress measurement methods. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a schematic diagram of the original problem in the present invention;

[0033] Figure 2 It is a schematic diagram of the problem of the present invention;

[0034] Figure 3 This is a schematic diagram of the second problem of the present invention;

[0035] Figure 4 Schematic diagram of a system for measuring ground stress using a thermal-mechanical coupling model in an embodiment of the present invention;

[0036] Figure 5 Schematic diagram of the temperature distribution of the rock mass around the borehole in an embodiment of the present invention;

[0037] Figure 6 is a temperature distribution curve of the rock mass around the borehole when the temperature rise is stopped in the embodiment of the present invention;

[0038] Figure 7 It is a curve showing the change of pressure and acoustic emission ringing count over time in an embodiment of the present invention;

[0039] Figure numerals: 1. Drilled hole wall; 2. Acoustic emission probe; 3. Infrared temperature sensor; 4. Heating device. DETAILED DESCRIPTION

[0040] The technical solution of the present invention is further described below in conjunction with specific embodiments and drawings.

[0041] The present invention simplifies the rock mass stress problem (i.e. the original problem) into an infinite body with boundary stresses q1 and q2 and a radius of The temperature on the hole wall is Tf, and the infinite body heat conduction coefficient is , the density is The specific heat capacity is , For time; infinite body The temperature at the moment is Celsius, such as Figure 1 As shown;

[0042] Split the original question into question 1 and question 2; question 1 (such as Figure 2 ) Specifically: There is a circular hole with a radius of R in an infinite body with boundary stress, and the inner wall of the hole is stress-free; Problem 2 (such as Figure 3 ) Specifically: In an infinite body with no boundary stress, there is a radius The temperature of the hole wall is Tf;

[0043] Ziers's answer to question 1:

[0044] ;

[0045] ;

[0046] ;

[0047] in, is the tangential normal stress at a point in the infinite body; is the axial normal stress at a point in the infinite body; is the shear stress at a point in the infinite body; is the hole radius; is the distance between a point in the infinite body and the center of the circle; is the angle between a point in the infinite body and the x-axis;

[0048] Problem 2: The temperature function is solved using the temperature stress formula (i.e. the existing thermal-mechanical coupling model mentioned in the present invention):

[0049] ;

[0050] ;

[0051] ;

[0052] in, is the tangential normal stress at a point in the infinite body; is the axial normal stress at a point in the infinite body; is the shear stress at a point in the infinite body; is the radius of a hole at a point in the infinite body; Take positive infinity; is the distance between a point in the infinite body and the center of the circle; is the angle between a point in the infinite body and the x-axis; is the temperature distribution function of the cross section at a certain point in the infinite body;

[0053] The above calculation principle is used to explain the equations and data acquisition method of the geostress measurement method in the present invention; if related concepts are mentioned below, they will be used directly.

[0054] Principle of geostress measurement: From the above calculation principle, it can be seen that the borehole is located in an infinite rock mass and is subject to a two-dimensional stress field. and The role of;

[0055] The stress around the drill hole is:

[0056] ;

[0057] ;

[0058] ;

[0059] in, is the tangential stress at a certain point around the borehole; is the radial stress at a certain point around the borehole; is the angle between a certain point around the borehole and the σ1 axis;

[0060] when hour, Take the minimum value, , applying heat source in the hole to generate thermal stress ,when When the minimum compressive stress at the hole wall exceeds the sum of the tensile strength of the rock mass, the hole wall will break. direction, i.e. The directions of the axes that will produce the cracks are:

[0061] ;

[0062] If heating is continued until the crack depth reaches more than 3 times the borehole diameter, the crack is close to the original rock stress state, and the temperature is stopped (when the intensity of the acoustic signal obtained by the acoustic emission device is less than 5% of the peak acoustic signal intensity obtained when the rock mass begins to crack, the crack depth reaches more than 3 times the borehole diameter). Directional pressure is recorded as , and Phase equilibrium, that is

[0063] ;

[0064] According to the experimental results obtained on site, combined with the rock sample parameters obtained by sampling, the temperature distribution curve is obtained through simulation software; because it is an axisymmetric problem, it is only necessary to derive the temperature function of the interface through the center of the circle (see Problem 2 for the temperature function formula) to obtain ;

[0065] Measure the tensile strength of rock mass and recorded and , calculated from (3) and (4) and ; and size.

[0066] The following are specific embodiments:

[0067] Embodiment 1: A system for measuring ground stress using a thermal-mechanical coupling model, such as Figure 4 As shown, the system comprises:

[0068] A heating device 4 is arranged below the rock mass in the area to be tested for ground stress, a drilling hole, an acoustic emission device, and an infrared temperature sensor are arranged on the rock mass in the area to be tested for ground stress;

[0069] The acoustic emission probe 2 and the infrared temperature sensor 3 of the acoustic emission device are both arranged on the borehole wall 1; the heating device is used to heat the rock mass; the acoustic emission device is used to detect and collect the acoustic signal generated during the rock mass heating process; the infrared temperature sensor is used to measure the borehole wall temperature;

[0070] When the system measures the ground stress, a heating device is used to heat the rock mass, and the acoustic emission probe of the acoustic emission device detects the fracture sound waves of the rock mass. The thermal stress of the borehole wall at the moment when the rock mass begins to fracture is: ;in, is the thermal stress of the borehole wall; and is the two-dimensional stress field of the borehole; is the tensile strength of the rock sample;

[0071] The heating device is used to heat until the intensity of the acoustic signal obtained by the acoustic emission device is less than 5% of the intensity of the rock mass fracture acoustic signal obtained when the rock mass begins to fracture, and then the heating is stopped, the time of stopping the heating is recorded, and the infrared temperature sensor is used to measure the corresponding borehole wall temperature during the heating process in real time;

[0072] The temperature of the borehole wall and the conductivity coefficient of the rock sample corresponding to the entire heating process ,density Specific heat capacity Input the temperature simulation software to obtain the temperature distribution curve of the rock mass around the borehole when the temperature rise stops. Based on the temperature distribution curve, the crack development position is obtained. Directional pressure ,and ;

[0073] According to the measured tensile strength of the rock mass , and the calculated , , the two-dimensional stress field of the borehole is obtained and size.

[0074] In this embodiment, when installing the heating device, the heating device is connected to the drill rod, and the drill rod brings the heating device to the heating position, which is below the rock mass in the area where the ground stress is to be measured; the heating device has an electromagnetic coil to heat the rock mass.

[0075] Embodiment 2: A method for measuring ground stress using a thermal-mechanical coupling model, the method comprising the following steps:

[0076] (1) Take rock samples from the area where the ground stress is to be measured and measure the tensile strength of the rock samples , conductivity ,density Specific heat capacity ; Specifically, taking rock samples from the heating area;

[0077] (2) The system described in Example 1 is set up in the area to be tested for ground stress, and an infrared temperature sensor is used to record the initial temperature of the rock mass before heating and to measure the borehole wall temperature corresponding to the entire heating process; when the heating device is heating, the acoustic emission probe of the acoustic emission device is used to detect the fracture sound waves of the rock mass;

[0078] (3) Since rock mass destruction will generate sound waves, whether the rock mass is destroyed is determined based on the sound signal detected by the acoustic emission device. When the acoustic emission device detects the rock mass fracture sound signal, the time corresponding to the first detection of the rock mass fracture sound signal is recorded as the time when the rock mass begins to fracture. Figure 7 In the ring count-time curve, a clear step can be observed; Figure 7 The medium ring count represents the acoustic signal strength;

[0079] At the moment when the rock mass begins to break, ;

[0080] in, is the thermal stress of the borehole wall; and is the two-dimensional stress field of the borehole; is the tensile strength of the rock sample;

[0081] (4) The heating device is used to heat until the intensity of the acoustic signal obtained by the acoustic emission device is less than 5% of the intensity of the rock mass fracture acoustic signal obtained when the rock mass begins to fracture, and then the heating is stopped. The time of stopping the heating is recorded, and the infrared temperature sensor is used to measure the corresponding borehole wall temperature during the heating process in real time; wherein, when the intensity of the acoustic signal obtained by the acoustic emission device is less than 5% of the peak acoustic signal intensity obtained when the rock mass begins to fracture, the crack depth reaches more than 3 times the borehole diameter, and at this time, the crack is close to the original rock stress state, and the heating is stopped;

[0082] (5) Temperature curve:

[0083] The borehole wall temperature corresponding to the entire heating process and the rock sample parameters obtained in step (1) are input into the temperature simulation software to obtain a temperature distribution curve of the rock mass around the borehole at the moment when the heating is stopped; the horizontal axis of the temperature distribution curve represents the distance of the rock mass around the borehole from the center of the borehole (the starting point of the horizontal axis is the radius of the borehole, that is, the distance of the borehole wall from the center of the borehole), and the vertical axis represents the rock mass temperature (the starting point of the vertical axis is the borehole wall temperature corresponding to the moment when the heating is stopped); Figure 5-6 As shown, Figure 6 for Figure 5 The temperature distribution curve at the position indicated by the horizontal line;

[0084] The first point on the side of the temperature distribution curve close to the vertical axis that is consistent with the initial temperature of the rock mass before heating is taken for calculation to obtain the crack development location. Directional pressure ,and ;

[0085] (6) Based on the measured tensile strength of the rock mass , and the calculated , , we can conclude and size.

[0086] In step (3) of this embodiment, It is calculated using the temperature stress formula corresponding to the drilling (see the temperature stress formula given in Question 2).

[0087] In step (3) of this embodiment, when the intensity of the acoustic signal obtained by the acoustic emission device is less than 5% of the peak acoustic signal intensity obtained when the rock mass begins to fracture, the crack depth reaches more than 3 times the borehole diameter; at this time, the crack is close to the original rock stress state and the temperature stops rising.

[0088] In this embodiment, the temperature simulation software may use COMSOL simulation or other finite element analysis software.

[0089] In step (5) of this embodiment, the first point on the side of the temperature distribution curve close to the vertical axis that is consistent with the initial temperature of the rock mass before heating is calculated to obtain the crack development location. Directional pressure Specifically, after obtaining the temperature of the first point, the temperature stress formula is used to obtain the crack development location. Directional pressure .

[0090] Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. For ordinary technicians in this field, they can still modify or transform the technical solutions described above, which all fall within the scope of protection of the present invention.

Claims

1. A system for measuring ground stress using a thermal-mechanical coupling model, characterized in that: The system comprises: a heating device arranged under the rock mass in the area to be tested for ground stress, a drilling hole on the rock mass in the area to be tested for ground stress, an acoustic emission device, and an infrared temperature sensor; The acoustic emission probe of the acoustic emission device and the infrared temperature sensor are both arranged on the wall of the borehole; the heating device is used to heat the rock mass; the acoustic emission device is used to detect and collect the acoustic signal generated during the rock mass heating process; the infrared temperature sensor is used to measure the wall temperature of the borehole; When the system measures the ground stress, a heating device is used to heat the rock mass, and the acoustic emission probe of the acoustic emission device detects the fracture sound waves of the rock mass. The thermal stress of the borehole wall at the moment when the rock mass begins to fracture is: ;in, is the thermal stress of the borehole wall; and is the two-dimensional stress field of the borehole; is the tensile strength of the rock sample; The heating device is used to heat until the intensity of the acoustic signal obtained by the acoustic emission device is less than 5% of the intensity of the rock mass fracture acoustic signal obtained when the rock mass begins to fracture, and then the heating is stopped, the time of stopping the heating is recorded, and the infrared temperature sensor is used to measure the corresponding borehole wall temperature during the heating process in real time; when the intensity of the acoustic signal obtained by the acoustic emission device is less than 5% of the peak acoustic signal intensity obtained when the rock mass begins to fracture, the fracture depth reaches more than 3 times the borehole diameter; The temperature of the borehole wall and the conductivity coefficient of the rock sample corresponding to the entire heating process ,density Specific heat capacity Input the temperature simulation software to obtain the temperature distribution curve of the rock mass around the borehole when the temperature rise stops. Based on the temperature distribution curve, the crack development position is obtained. Directional pressure ,and ; According to the measured tensile strength of the rock mass , and the calculated , , the two-dimensional stress field of the borehole is obtained and size.

2. According to claim 1, a system for measuring ground stress using a thermal-mechanical coupling model is characterized in that: When installing the heating device, the heating device is connected to the drill rod, and the drill rod brings the heating device to the heating position, which is below the rock mass in the area where the ground stress is to be measured.

3. The system for measuring ground stress using a thermal-mechanical coupling model according to claim 1, characterized in that: The heating device is provided with an electromagnetic coil to heat the rock mass.

4. A method for measuring ground stress using a thermal-mechanical coupling model, characterized in that: The method comprises the following steps: (1) Take rock samples from the area where the ground stress is to be measured and measure the tensile strength of the rock samples , conductivity ,density Specific heat capacity ; (2) The system described in any one of claims 1 to 3 is set up in the area to be tested for ground stress, and an infrared temperature sensor is used to record the initial temperature of the rock mass before heating and to measure the borehole wall temperature corresponding to the entire heating process; when the heating device is heating, the acoustic emission probe of the acoustic emission device is used to detect the fracture sound waves of the rock mass; (3) judging whether the rock mass has cracked according to the acoustic signal detected by the acoustic emission device, and when the acoustic emission device detects the acoustic signal of rock mass cracking, recording the time corresponding to the first detection of the acoustic signal of rock mass cracking as the time when the rock mass starts to crack; At the moment when the rock mass begins to break, ; in, is the thermal stress of the borehole wall; and is the two-dimensional stress field of the borehole; is the tensile strength of the rock sample; (4) the heating device is used to heat until the intensity of the acoustic signal obtained by the acoustic emission device is less than 5% of the intensity of the rock mass fracture acoustic signal obtained when the rock mass begins to fracture, and then the heating is stopped, the time of stopping the heating is recorded, and the infrared temperature sensor is used to measure the corresponding borehole wall temperature during the heating process in real time; (5) Inputting the borehole wall temperature corresponding to the entire heating process and the rock sample parameters obtained in step (1) into the temperature simulation software to obtain the temperature distribution curve of the rock mass around the borehole when the heating is stopped; The crack development location is calculated based on the temperature distribution curve. Directional pressure ,and ; (6) Based on the measured tensile strength of the rock sample , and the calculated , , we can conclude and size; In step (5), the borehole wall temperature and the rock sample conductivity corresponding to the entire heating process are ,density Specific heat capacity Input the temperature simulation software to obtain the temperature distribution curve of the rock mass around the borehole when the heating stops.

5. The method for measuring ground stress using a thermomechanical coupling model according to claim 4, characterized in that: In step (3), when the intensity of the acoustic signal acquired by the acoustic emission device is less than 5% of the peak acoustic signal intensity acquired when the rock mass begins to fracture, the fracture depth reaches more than 3 times the borehole diameter.

6. The method for measuring ground stress using a thermomechanical coupling model according to claim 5, characterized in that: The horizontal axis of the temperature distribution curve represents the distance between the rock mass around the borehole and the center of the borehole, and the vertical axis represents the temperature of the rock mass.

7. The method for measuring ground stress using a thermomechanical coupling model according to claim 5, characterized in that: The temperature simulation software is finite element analysis software.

8. The method for measuring ground stress using a thermomechanical coupling model according to claim 7, characterized in that: The temperature simulation software is COMSOL simulation software.

9. The method for measuring ground stress using a thermomechanical coupling model according to claim 4, characterized in that: In step (5), the first point on the side of the temperature distribution curve close to the vertical axis that is consistent with the initial temperature of the rock mass before heating is taken for calculation to obtain the crack development location. Directional pressure .

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