Method for preparing and testing triaxial compression seismic test sample

Abstract

The invention belongs to the technical field of earthquake simulation tests, and particularly relates to a triaxial compression earthquake test sample preparation and test method which comprises a fault model. The fault model is composed of two beveled models which are in the same shape and are beveled along the diagonal line of the cross section on a cube with an ac * ac square cross section, the contact face of the two beveled models, namely the opposite face formed after beveled along the diagonal line, is a fault face, the size of the fault face is 1.414 ac * ac, and the size of the fault face is 1.414 ac * ac. By controlling the stress, temperature and water content conditions of the sample, the invention aims to improve the accuracy and reliability of earthquake simulation, and the control capability enables the earthquake simulation test under laboratory conditions to reproduce the mechanical behavior of deep rock in the earthquake process more truly. Therefore, more accurate data support is provided for understanding of an earthquake mechanism, assessment of earthquake risk and guidance of earthquake engineering practice.

Description

Technical Field

[0001] The present invention relates to the technical field of seismic simulation tests, and specifically to a method for preparing and testing samples for a triaxial compression seismic test. Background Art

[0002] In the fields of seismology and rock mechanics, a deep understanding of the response of deep rocks under seismic action is of great significance for revealing seismic mechanisms, assessing seismic hazards, and guiding seismic engineering practices. Byerly's law states in describing the friction characteristics of rocks that: under a certain normal stress, that is, below 200 Mpa, the shear stress is proportional to the friction coefficient. This law is of guiding significance for simulating the friction and fracture behavior of deep rocks during earthquakes and is an indispensable theoretical basis in seismological research.

[0003] Existing seismic simulation test methods usually cannot comprehensively simulate the complex stress states experienced by deep rocks during earthquakes, especially the lack of control over temperature and water content conditions.

[0004] The main drawback of the existing technology is the inability to simultaneously control the stress, temperature, and water content conditions of the samples, resulting in differences between the test results and the actual earthquake process. Specifically, existing seismic simulation test methods usually cannot comprehensively simulate the complex stress states experienced by deep rocks during earthquakes, especially the lack of control over temperature and water content conditions. This limitation may cause the experimental results to not accurately reflect the behavior of rocks during actual earthquakes, thus affecting the accuracy and reliability of seismic simulations.

[0005] The present invention can more realistically simulate the mechanical behavior of deep rocks during earthquakes by preparing samples with specific shapes and compositions and using a true triaxial testing machine for testing. Summary of the Invention

[0006] The purpose of the present invention is to provide a method for preparing and testing samples for a triaxial compression seismic test to solve the problems raised in the above background art.

[0007] To achieve the above purpose, the present invention provides the following technical solution: A method for preparing and testing samples for a triaxial compression seismic test: The triaxial compression seismic test sample includes the following fault models. The fault model is composed of two identically shaped beveled models obtained by obliquely cutting a cube with a square cross-section of a cm * a cm along its cross-sectional diagonal. The contact surface of the two beveled models, that is, the opposite surface formed after obliquely cutting along the diagonal, is the fault surface, and the size of the fault surface is 1.414a cm * a cm; The specific test method includes: Step 1: Obtain a preliminarily processed fault model: In this fault model, the cross-sections of the two inclined cutting models form a square with a side length of a cm * a cm, the model thickness is a cm, the size of the fault plane is 1.414a cm * a cm, and its four corners are all triangular chamfers of 15 mm * 15 mm * a mm; Step 2: Perform water content treatment on the specimen: Pre-treat the inclined cutting model to achieve the target water content; Step 3: Set up the experimental device: The experimental device includes: a fault model, a static loading system, a control system, a data measurement and acquisition system, and auxiliary testing instruments. The static loading system consists of a loading frame and three subsystems in each principal stress direction; the loading frame is designed with a high-rigidity integrated structure; the designed stiffness of the loading frame is 15 GN / m. Each subsystem includes two loading units, two hydraulic pistons, two oil cylinders, two force sensors, two linear variable differential transformers, two MOOG servo controllers, and four accumulators; among them, the piston push rods in the X and Y directions provide a load of 4000 KN, while the load in the Z direction is 2700 KN; the size of the specimen used in the true triaxial loading experiment is 100 mm x 100 mm x 100 mm, and correspondingly, stresses of 400 MPa, 400 MPa, and 270 MPa are generated in the X, Y, and Z directions of the specimen respectively; the data measurement and acquisition system relies on various indenter displacements, pressure sensors, and multi-channel acquisition cards; during the test loading process, each loading unit is equipped with a force sensor, so each loading unit conducts independent servo control through the computer with the data of the force sensor as the feedback signal. Two LVDTs are used to measure the displacements of the two hydraulic pistons in the oil cylinder. The stroke of the LVDT used for the hydraulic piston in the X and Y directions is 0 - 80.0 mm, while in the Z direction, the stroke is 0 - 50.0 mm, and the measurement error is less than 0.5%; in addition, each oil cylinder is equipped with a high-precision MOOG servo controller and a pair of accumulators to improve the stability, accuracy, and response speed during the loading process; the data is monitored by the sensor and then transmitted to the data acquisition card through the signal, and finally displayed and stored by the TTA software, realizing the automation of data acquisition and ensuring the reliability of data acquisition; Step 4: Apply prestress loading to the fault model: Fix the fault model at the center position of the heating chamber, place the fault model in the triaxial heating chamber for heating, and then apply a fixed-size quasi-static load to the fault model. For example, through displacement loading, the loading end is closely contacted with the four peripheral end faces of the fault model, change the loading method to force loading, load the two sides of the fault model to a fixed load, keep the axial pressure unchanged, and increase the vertical pressure to the set value to simulate the fault tectonic stress state.

[0008] Preferably, the fault model is prepared from sandstone.

[0009] Preferably, the fault model has chamfers at all its 12 edges, with a chamfer angle of 45° and a chamfer depth of 15 mm.

[0010] Preferably, in the preliminary processed fault model obtained in the first step, the rock block is processed into a standard cubic rock specimen with dimensions of 100 mm x 100 mm x 100 mm. Each side length of the specimen is greater than the side length of the indenter by 3 mm. This length is reserved as the distance for the indenter to prevent the indenter from colliding in different directions during the loading process. Subsequently, the standard cubic rock specimen is chamfered to reduce the stress concentration problem during the loading process.

[0011] Preferably, the processing process of the fault model includes: making a 45° oblique cut along the diagonal of the square cross-section of the fault model to obtain two oblique cut models.

[0012] Preferably, in the water content treatment of the specimen in the second step, the processing process of the water content treatment includes: cleaning the rock specimen to remove dust and loose particles on the surface, placing the specimen in an oven, drying it to a constant weight at a temperature of 105°C to 110°C; placing the dried specimen in a water container, first filling the water to 1 / 4 of the specimen height, and then filling the water to 1 / 2 and 3 / 4 of the specimen height every 2 hours respectively. After 6 hours, add water to 20 mm above the top surface of the specimen to facilitate the escape of air in the specimen. After the specimen is completely submerged in water, let it freely absorb water for 48 hours; use the boiling method to forcefully saturate the specimen after free water absorption. Place the specimen in a water tank, fill the water to half of the specimen height, let it stand for 2 hours, then add more water to submerge it, boil for more than 6 hours, and keep the water depth unchanged; place the forcefully saturated specimen on a weighing device in water, weigh the mass of the specimen in water, and measure the water temperature; calculate the water absorption rate and saturated water absorption rate of the rock according to the dry mass, mass after immersion, and mass after forced saturation of the specimen.

[0013] Compared with the prior art, the beneficial effects of the present invention are: By controlling the stress, temperature, and water content conditions of the sample, the present invention aims to improve the accuracy and reliability of earthquake simulation. This control ability will enable the earthquake simulation test under laboratory conditions to more realistically reproduce the mechanical behavior of deep rocks during earthquakes, thereby providing more accurate data support for the understanding of earthquake mechanisms, the assessment of earthquake hazards, and the guidance of earthquake engineering practices. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 is the fault model described in the embodiment; Figure 2 is the left view of the fault model; Figure 3 is the top view of the fault model; Figure 4It is a flow chart for water treatment. Detailed implementation manners

[0015] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0016] In the description of the present invention, it should be understood that the orientation or positional relationships indicated by the terms "upper", "lower", "front", "rear", "left", "right", "top", "bottom", "inner", "outer", etc. are based on the orientation or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as a limitation of the present invention.

[0017] Please refer to Figures 1-4 , the present invention provides a technical solution: A method for preparing and testing a triaxial compression seismic test sample: The triaxial compression seismic test sample includes a fault model, and the fault model is composed of two identically shaped beveled models obtained by obliquely cutting a cube with a square cross-section of acm * acm along its cross-sectional diagonal. The contact surface of the two beveled models, that is, the opposite surface formed after obliquely cutting along the diagonal, is the fault surface, and the size of the fault surface is 1.414acm * acm; The test method specifically includes: The first step is to obtain a preliminarily processed fault model: the cross-sections of the two beveled models in the fault model form a square with a side length of acm * acm, the model thickness is acm, the size of the fault surface is 1.414acm * acm, and the four corners are all triangular chamfers of 15mm * 15mm * amm; The second step is to perform water treatment on the specimen: pre-treat the beveled model to achieve the target water content; Step 3. Set up the experimental device: The experimental device includes a fault model, a static loading system (loading frame + six-direction static loading module), a control system, and a data measurement and acquisition system (data measurement and acquisition system), and auxiliary testing instruments. The static loading system consists of a loading frame and three subsystems in each principal stress direction (X, Y, Z). The loading frame is designed with a high-rigidity integrated structure to improve the response ability of the loading system. The designed rigidity of the loading frame is 15 GN / m. Each subsystem includes two loading units, two hydraulic pistons, two oil cylinders, two force sensors, two linear variable differential transformers (LVDTs), two MOOG servo controllers, and four accumulators. Among them, the piston push rods in the X and Y directions provide a load of 4000 KN, while the load in the Z direction is 2700 KN. The size of the specimen used in the true triaxial loading experiment is 100 mm x 100 mm x 100 mm, and corresponding stresses of 400 MPa, 400 MPa, and 270 MPa are generated in the X, Y, and Z directions of the specimen respectively. The data measurement and acquisition system relies on the displacement of each indenter, pressure sensors, and a multi-channel acquisition card. During the test loading process, each loading unit is equipped with a force sensor, so each loading unit conducts independent servo control through the computer with the data of the force sensor as the feedback signal. Two LVDTs are used to measure the displacements of the two hydraulic pistons in the oil cylinder. The stroke of the LVDT for the hydraulic piston in the X and Y directions is 0 - 80.0 mm, while the stroke in the Z direction is 0 - 50.0 mm, and the measurement error is less than 0.5%. In addition, each oil cylinder is equipped with a high-precision MOOG servo controller and a pair of accumulators to improve the stability, accuracy, and response speed during the loading process. The data is monitored by the sensor and then transmitted to the data acquisition card through the signal, and finally displayed and stored by the TTA software, realizing the automation of data acquisition and ensuring the reliability of data acquisition. Step 4. Apply prestress loading to the fault model: Fix the fault model at the center position of the heating chamber, place the fault model in the triaxial heating chamber for heating, and then apply a fixed-size quasi-static load to the fault model. For example, through displacement loading, the loading end is closely contacted with the four side faces of the fault model, change the loading method to force loading, load the two sides of the fault model to a fixed load, keep the axial pressure unchanged, and increase the vertical pressure to the set value to simulate the fault tectonic stress state.

[0018] The fault model is prepared from sandstone.

[0019] The fault model has chamfers at its 12 edges, with a chamfer angle of 45° and a chamfer depth of 15 mm.

[0020] In the first step of obtaining the preliminarily processed fault model, the rock block is processed into a standard cubic rock specimen with dimensions of 100 mm x 100 mm x 100 mm. Each side length of the specimen is greater than the indenter side length by 3 mm. This length is the reserved distance for the indenter to prevent the indenter from colliding in different directions during the loading process. Subsequently, the standard cubic rock specimen is chamfered to reduce the stress concentration problem during the loading process.

[0021] The processing of the fault model includes: making a 45° oblique cut along the diagonal of the square cross-section of the fault model to obtain two oblique cut models.

[0022] In the second step of water treatment for the specimen, the processing of water treatment includes: cleaning the rock specimen to remove dust and loose particles on the surface, putting the specimen into an oven, drying it to a constant weight at a temperature of 105 °C to 110 °C; placing the dried specimen in a water container, first filling water to 1 / 4 of the specimen height, and then filling water to 1 / 2 and 3 / 4 of the specimen height every 2 hours respectively. After 6 hours, add water to 20 mm above the top surface of the specimen to facilitate the escape of air inside the specimen. After the specimen is completely submerged in water, let it absorb water freely for 48 hours; use the boiling method to forcibly saturate the specimen after free water absorption. Put the specimen into a water tank, fill water to half of the specimen height, let it stand for 2 hours, then add more water to submerge it, boil for more than 6 hours, and keep the water depth unchanged; place the forcibly saturated specimen on a weighing device in water, weigh the mass of the specimen in water, and measure the water temperature; calculate the water absorption rate and saturated water absorption rate of the rock according to the dry mass, mass after immersion, and mass after forced saturation of the specimen. Example

[0023] The embodiment of this application provides a method for preparing a triaxial compression seismic test sample, and the steps are as follows: The first step: Obtain a fault model through preliminary processing. The planar structure of this fault model is as shown in the appendix Figure 1 The preliminary processing includes obtaining an oblique cut model and performing chamfer design; The specific processing process includes: Use sandstone, a rock material with good isotropy, to make a three-dimensional fault model with side lengths of 100 mm x 100 mm x 100 mm. Each side length of the specimen is greater than the indenter side length by 3 mm. This length is the reserved distance for the indenter to prevent the indenter from colliding in different directions during the loading process; at the same time, make an oblique cut along the diagonal of its cross-section into two identically shaped oblique cut models. The contact surface of these two oblique cut models, that is, the opposite surface formed after the oblique cut along the diagonal, is the fault surface. To prevent damage to the fault model during the triaxial loading process and avoid stress concentration at the corners, chamfer the corners of the fault model into a 15 mm * 15 mm chamfer; Example

[0024] Based on the initially processed fault model, perform water content treatment on the fault model to obtain the saturated water content of the fault model; Clean the rock specimens, removing the dust and loose particles on the surface; place the specimens in an oven and dry them to a constant weight at a temperature of 105°C to 110°C; place the dried specimens in a water container, first fill the water to 1 / 4 of the specimen height, and then fill the water to 1 / 2 and 3 / 4 of the specimen height every 2 hours respectively. After 6 hours, add water to 20 mm above the top surface of the specimen to facilitate the escape of air in the specimen. After the specimens are completely submerged in water, let them freely absorb water for 48 hours; Use the boiling method to forcibly saturate the specimens after free water absorption. Place the specimens in a water tank, fill the water to half of the specimen height, let it stand for 2 hours, then add more water to submerge it, boil for more than 6 hours, and keep the water depth unchanged.

[0025] Place the forcibly saturated specimens on a weighing device in water, weigh the mass of the specimens in water, and measure the water temperature; Calculate the water absorption rate and saturated water absorption rate of the rock according to the dry mass, mass after immersion, and mass after forced saturation of the specimens; Embodiment

[0026] Set up the experimental device, specifically including: The experimental device includes: the fault model, a static loading system (loading frame + six-direction static loading module), a control system, and a data measurement and acquisition system (data measurement and acquisition system), and auxiliary testing instruments.

[0027] Among them, the static loading system mainly consists of a loading frame and three subsystems in each principal stress direction (X, Y, Z). The loading frame adopts a high-rigidity integrated structure design, which can improve the response ability of the loading system. The designed rigidity of the loading frame is 15 GN / m. Each subsystem includes two loading units, two hydraulic pistons, two oil cylinders, two force sensors, two linear variable differential transformers (LVDTs), two MOOG servo controllers, and four accumulators. The piston push rods in the X and Y directions can provide a load of 4000 KN, while the load in the Z direction is 2700 KN. The size of the specimen used in the true triaxial loading experiment is 100 mm x 100 mm x 100 mm. Therefore, corresponding stresses of 400 MPa, 400 MPa, and 270 MPa can be generated in the X, Y, and Z directions of the specimen respectively. The data measurement and acquisition system relies on components such as the displacement of each indenter, pressure sensors, and multi-channel acquisition cards. During the test loading process, each loading unit is equipped with a force sensor. Therefore, each loading unit can perform independent servo control through the computer with the data of the force sensor as the feedback signal. Two LVDTs are used to measure the displacements of the two hydraulic pistons in the oil cylinder. The stroke of the LVDT for the hydraulic piston in the X and Y directions is 0 - 80.0 mm, while the stroke in the Z direction is 0 - 50.0 mm, and the measurement error is less than 0.5%. In addition, each oil cylinder is equipped with a high-precision MOOG servo controller and a pair of accumulators to improve the stability, accuracy, and response speed during the loading process. After being monitored by the sensor, the data is transmitted to the data acquisition card through the signal and is finally displayed and stored by the TTA software, realizing the automation of data acquisition and ensuring the reliability of data acquisition; Embodiment

[0028] Apply prestress loading to the fault model; It includes: fixing the fault model at the central position of the heating chamber to ensure the stability of the model during heating. Through the displacement loading system, the loading end is closely contacted with the four peripheral end faces of the fault model to ensure that the model is subjected to uniform stress. Heat the fault model from room temperature of 20°C to 200°C to simulate the thermal stress state deep in the crust. Then apply a fixed-size quasi-static load to the fault model. For example, through displacement loading, the loading end is closely contacted with the four peripheral end faces of the fault model, change the loading method to force loading, apply a pressure of 1 MPa to both sides of the fault model, keep the axial pressure unchanged, and gradually increase the vertical pressure to the set value of 2 MPa to simulate the fault tectonic stress state. After reaching the set vertical pressure, observe the fracture behavior of the fault model, record the fracture mode and fracture speed, and use high-precision sensors to record the strain and stress of the fault model throughout the process.

[0029] The foregoing has shown and described the basic principles, main features and advantages of the present invention. For those skilled in the art, it is obvious that the present invention is not limited to the details of the above-mentioned exemplary embodiments, and without departing from the spirit or basic features of the present invention, the present invention can be implemented in other specific forms. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-limiting. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, it is intended to embrace all changes that fall within the meaning and scope of the equivalent elements of the claims in the present invention, and any reference signs in the claims should not be regarded as limiting the claims involved.

[0030] Although the embodiments of the present invention have been shown and described, for those of ordinary skill in the art, it can be understood that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing and testing a triaxial compression seismic test sample, characterized in that: The triaxial compression seismic test sample includes the following fault models, and the fault models are composed of two identically shaped beveled models obtained by obliquely cutting a cube with a square cross-section of acm * acm along its cross-sectional diagonal. The contact surface of the two beveled models, that is, the opposite surface formed after obliquely cutting along the diagonal, is the fault surface, and the size of the fault surface is 1.414acm * acm; The testing method specifically includes: The first step is to obtain a preliminarily processed fault model: the cross-sections of the two beveled models in the fault model form a square with a side length of acm * acm, the model thickness is acm, the size of the fault surface is 1.414acm * acm, and the four corners are all triangular chamfers of 15mm * 15mm * amm; The second step is to perform water content treatment on the sample: pre-treat the beveled model to reach the target water content; The third step is to set up the experimental device: The experimental device includes: a fault model, a static loading system, a control system, a data measurement and acquisition system, and auxiliary testing instruments. The static loading system is composed of a loading frame and three subsystems in each principal stress direction; the loading frame adopts a high-rigidity integrated structure design; the designed stiffness of the loading frame is 15 GN / m, and each subsystem includes two loading units, two hydraulic pistons, two oil cylinders, two force sensors, two linear variable differential transformers, two MOOG servo controllers, and four accumulators; among them, the piston push rods in the X and Y directions provide a load of 4000 KN, while the load in the Z direction is 2700 KN; the size of the sample used in the true triaxial loading experiment is 100 mm x 100 mm x 100 mm, and correspondingly, stresses of 400 MPa, 400 MPa, and 270 MPa are generated in the X, Y, and Z directions of the sample respectively; the data measurement and acquisition system relies on the displacement of each indenter, pressure sensors, and a multi-channel acquisition card; during the test loading process, each loading unit is equipped with a force sensor, so each loading unit performs independent servo control through the computer with the data of the force sensor as the feedback signal. Two LVDTs are used to measure the displacement of the two hydraulic pistons in the oil cylinder. The stroke of the LVDT for the hydraulic piston in the X and Y directions is 0 - 80.0 mm, while the stroke in the Z direction is 0 - 50.0 mm, and the measurement error is less than 0.5%; in addition, each oil cylinder is equipped with a high-precision MOOG servo controller and a pair of accumulators to improve the stability, accuracy, and response speed during the loading process; the data is monitored by sensors and then transmitted to the data acquisition card through signals, and finally displayed and stored by the TTA software, realizing the automation of data acquisition and ensuring the reliability of data acquisition; Fourth step, apply prestress loading to the fault model: Fix the fault model at the center position of the heating chamber, place the fault model in the triaxial heating chamber for heating, and then apply a fixed-size quasi-static load to the fault model. For example, through displacement loading, make the loading end in close contact with the peripheral end faces of the fault model. Change the loading method to force loading, apply pressure to both sides of the fault model to a fixed load, keep the axial pressure unchanged, and increase the vertical pressure to the set value to simulate the stress state of the fault structure.

2. The method for preparing and testing a triaxial compression seismic test sample according to claim 1, wherein: The fault model is prepared from sandstone.

3. A method for preparing and testing a triaxial compression seismic test sample according to claim 1, characterized in that: The fault model has chamfers at its 12 edges, with a chamfer angle of 45° and a chamfer depth of 15 mm.

4. A method for preparing and testing a triaxial compression seismic test sample according to claim 1, characterized in that: In the first step to obtain the preliminarily processed fault model, the rock block is processed into a standard cubic rock specimen with dimensions of 100 mm x 100 mm x 100 mm. Each side length of the specimen is greater than the side length of the indenter by 3 mm. This length is reserved for the indenter to prevent the indenter from colliding in different directions during the loading process. Subsequently, the standard cubic rock specimen is chamfered to reduce the stress concentration problem during the loading process.

5. A method for preparing and testing a triaxial compression seismic test sample according to claim 1, characterized in that: The processing process of the fault model includes: making a 45° oblique cut along the diagonal of the square cross-section of the fault model to obtain two oblique cut models.

6. A method for preparing and testing a triaxial compression seismic test sample according to claim 1, characterized in that: In the second step of water content treatment for the specimen, the processing process of water content treatment includes: cleaning the rock specimen, removing the dust and loose particles on the surface, placing the specimen in an oven, drying it to a constant weight at a temperature of 105°C to 110°C; placing the dried specimen in a water container, first filling the water to 1 / 4 of the specimen height, and then filling the water to 1 / 2 and 3 / 4 of the specimen height every 2 hours respectively. After 6 hours, add water to 20 mm above the top surface of the specimen to facilitate the escape of air inside the specimen. After the specimen is completely submerged in water, let it freely absorb water for 48 hours; use the boiling method to forcibly saturate the specimen after free water absorption. Place the specimen in a water tank, fill the water to half of the specimen height, let it stand for 2 hours, then add more water to submerge it, boil for more than 6 hours, and keep the water depth unchanged; place the forcibly saturated specimen on a weighing device in water, weigh the mass of the specimen in water, and measure the water temperature; calculate the water absorption rate and saturated water absorption rate of the rock according to the dry mass, mass after immersion, and mass after forced saturation of the specimen.

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