Study on experimental method of dynamic mechanical properties of jointed rock mass under multi-stress state

Abstract

The present application belongs to the field of jointed rock mass dynamics and engineering technology, and particularly relates to an experimental method for studying dynamic mechanical properties of jointed rock mass under multi-stress state. The method is carried out by using a split Hopkinson pressure bar system combined with a loading system, and a coordinate system is established with the length direction of the split Hopkinson pressure bar as the X axis, the width direction of the split Hopkinson pressure bar as the Y axis, and the height direction of the split Hopkinson pressure bar as the Z axis. The loading system can load the loading chamber from the X axis, Y axis and Z axis directions respectively. The method specifically comprises the following steps: 1. preparing a cubic full-penetrating cross jointed rock mass sample; 2. selecting a corresponding test mode according to the site working condition; 3. biaxial test; 4. triaxial test; and 5. data analysis. The present application simulates the working conditions of the excavated area and the unexcavated area, thereby studying the dynamic mechanical properties of the rock mass under high strain rate and triaxial stress, and thus providing a basis for the design of underground engineering such as tunnels.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of jointed rock mass dynamics and engineering technology, and particularly relates to an experimental method for studying dynamic mechanical properties of jointed rock mass under multi-stress state. BACKGROUND

[0002] A large number of jointed rock masses are formed in the process of geological structure evolution, which are confined in a certain geostress environment of the crust and upper mantle. The typical tectonic stress is not uniaxial, and rarely is axisymmetric. The geostress of rock increases with the increase of depth. When the vertical geostress caused by the burial depth is not equal to the horizontal geostress around the rock mass, the rock mass at this position can be regarded as being under the condition of true triaxial (σ1>σ2>σ3) prestress. The rock mass near the tunnel wall can be regarded as being under the condition of biaxial (σ1>σ2=σ3=0) prestress load. In addition to the multi-axial stress constraint, these jointed rock masses may be subjected to various dynamic disturbances, such as drilling, blasting and earthquakes. Under the action of dynamic load, the initiation, development, coalescence and penetration of new cracks in the rock mass are jointly affected by the strain rate and the existing joints, thereby leading to different failure modes of the rock mass. These joints significantly reduce the strength of the rock mass, and seriously affect the dynamic mechanical properties and failure mechanism of the rock mass. However, due to the limitations of loading equipment and methods, the existing research objects are mostly based on complete rock samples. The research on full-penetration cross-jointed rock mass is relatively less. Therefore, mastering the dynamic mechanical properties and failure mechanism of full-penetration cross-jointed rock mass under biaxial or triaxial stress state provides a basis for the stability analysis of underground engineering such as tunnels.

[0003] The existing researches show that different stress conditions affect the properties of rock mass, including strength, deformation and failure mode. Therefore, under the high strain rate level consistent with blasting, impact and earthquake, more complex researches on rock under multi-axial confining pressure are needed. Split Hopkinson Pressure Bar (SHPB) has been widely used to determine the dynamic mechanical properties of rock materials at high strain rates. However, under different confining pressures, the strain rate dependence of mechanical properties may be different. In the past few decades, the SHPB system has been developed to some extent in order to apply static confining pressure to rock samples before dynamic loading. Generally speaking, the improved SHPB system can realize the multi-axial static prestress loading of the sample through pressure or displacement boundary conditions. The pressure boundary condition is realized by the hydrostatic pressure of the hydraulic chamber. The displacement boundary condition uses the heat shrinkage technology and the metal sleeve to wrap the cylindrical surface of the sample. So far, there is still a lack of experimental data on the dynamic mechanical properties of rock mass under triaxial stress at high strain rate (>10 / s), which is urgently needed to be solved in the design of underground engineering such as tunnels. SUMMARY

[0004] The present application provides an experimental method for studying dynamic mechanical properties of jointed rock mass under multi-stress state,

[0005] The technical solution adopted by this invention to solve its technical problem is: an experimental method for studying the dynamic mechanical properties of jointed rock mass under multi-stress state. This experimental method uses a split Hopkinson bar system combined with a loading system. The experimental method takes the loading chamber of the split Hopkinson bar system as the origin, the length direction of the split Hopkinson bar as the X-axis, the width direction of the split Hopkinson bar as the Y-axis, and the height direction of the split Hopkinson bar as the Z-axis to establish a three-dimensional coordinate system.

[0006] The loading system can load indoor objects from the X-axis, Y-axis, and Z-axis respectively;

[0007] This experimental method specifically includes the following steps:

[0008] Step S1: Prepare cubic fully-connected interjointed rock mass samples

[0009] Rock materials were selected on site, cut vertically and horizontally, and then core samples were taken. The rock mass containing vertical and horizontal cuts was used as a cubic fully-connected cross-jointed rock mass sample.

[0010] Step S2: Select the appropriate test method based on the field conditions to conduct experiments on the dynamic mechanical properties of jointed rock mass under multiple stress states.

[0011] There are two types of on-site working conditions: the first type is the area after excavation, and the second type is the area before excavation.

[0012] There are two testing methods: the first is the biaxial test, and the second is the triaxial test.

[0013] If the current working condition is the first type, adopt the first test method and proceed to step S3;

[0014] If the current working condition is the second type, the second test method shall be adopted and step S4 shall be performed;

[0015] Step S3: Perform biaxial testing

[0016] Biaxial testing includes biaxial dynamic and static combined loading tests and biaxial unloading impact tests;

[0017] If the current working condition is tunnel face blasting, and there is a vibration effect on the tunnel sidewall behind the face, then step S3-1, biaxial dynamic and static combined loading test, is carried out to obtain the required degree of damage and strain rate of the fully penetrated cross-jointed rock mass.

[0018] If the current working condition is tunnel face blasting, the position of the tunnel sidewall near the face rear due to rock block falling or damage caused by blasting, then proceed to step S3-2 biaxial unloading impact test, obtain the required full-through cross joint rock mass failure degree and strain rate;

[0019] Step S4, triaxial test

[0020] The triaxial test includes triaxial dynamic-static combined loading test and triaxial unloading impact test;

[0021] If the current working condition is tunnel face blasting, the position of the tunnel sidewall near the face rear due to rock block falling or damage caused by blasting, then proceed to step S3-2 biaxial unloading impact test, obtain the required full-through cross joint rock mass failure degree and strain rate;

[0022] If the current working condition is tunnel face blasting, the position of the tunnel sidewall near the face rear due to rock block falling or damage caused by blasting, then proceed to step S3-2 biaxial unloading impact test, obtain the required full-through cross joint rock mass failure degree and strain rate;

[0023] Step S5, data analysis

[0024] According to the required full-through cross joint rock mass failure degree and strain rate obtained in steps S3-1, S3-2, S4-1 and S4-2, the corresponding incident wave, reflected wave and transmitted wave of the split Hopkinson pressure bar system are obtained, and then the compressive strength, elastic modulus and peak strain of the full-through cross joint rock mass are analyzed, so as to study the dynamic mechanical properties of the full-through cross joint rock mass under biaxial dynamic-static combined loading test, biaxial unloading impact test, triaxial dynamic-static combined loading test and triaxial unloading impact test, respectively.

[0025] As a further preferred embodiment of the present application, step S1 comprises the following preparation steps:

[0026] Step S1-1, preparing rock mass sample:

[0027] Step S1-1-1, selecting rock material on site;

[0028] Step S1-1-2, cutting the rock material selected in step S1-1-1 into a cubic rock mass sample;

[0029] Step S1-2, preparing bonded sample:

[0030] Step S1-2-1, cutting at least one sub-vertical joint with an angle to the vertical direction from the rock mass sample in step S1-1-2, and all the sub-vertical joints form a sub-vertical joint group;

[0031] Step S1-2-2, coring in the vertical direction from a position containing a vertical joint group;

[0032] Step S1-2-3, using transparent adhesive tape, bonding the cores taken out in step S1-2-2 together to form a bonded sample;

[0033] Step S1-3, preparing a cubic full-penetration cross-joint rock mass sample:

[0034] Step S1-3-1, cutting in the horizontal direction from a position close to the top surface of the bonded sample prepared in step S1-2-3 to form an upper end surface 16;

[0035] Step S1-3-2, cutting at least one sub-horizontal joint 17 at an angle to the horizontal direction, and all the sub-horizontal joints 17 form a sub-horizontal joint 17 group;

[0036] Step S1-3-3, cutting in the horizontal direction from a position close to the bottom surface of the bonded sample after step S1-3-2 to form a lower end surface 18, and forming a cubic full-penetration cross-joint rock mass sample;

[0037] Step S1-4, processing the cubic full-penetration cross-joint rock mass sample:

[0038] Step S1-4-1, using transparent adhesive tape, bonding the peripheral part of the cubic full-penetration cross-joint rock mass sample prepared in step S1-3-3 to form a wrapped sample;

[0039] Step S1-4-2, polishing the wrapped sample in step S1-4-1.

[0040] As a further preferred embodiment of the present application, the non-perpendicularity and non-parallelism of each face of the cubic full-penetration cross-joint rock mass sample after polishing in step S1-4-2 are less than 0.02 mm.

[0041] As a further preferred embodiment of the present application, the biaxial dynamic-static combined loading test in step S3-1 specifically includes the following test steps:

[0042] Step S3-1-1, making DIC speckles on the surface of the cubic full-penetration cross-joint rock mass sample prepared in step S1, and then placing it in a loading chamber;

[0043] Step S3-1-2, setting the constant loading rate and the target value of the axial static pre-stress of the X-axis and Y-axis of the split Hopkinson pressure bar system;

[0044] Step S3-1-3, loading according to the constant loading rate set in step S3-1-2 until the target value set in step S3-1-2 is reached;

[0045] Step S3-1-4, monitoring the surface speckle of the cubic full-penetration cross-jointed rock mass sample during the failure process;

[0046] Step S3-1-5, setting the impact air pressure of the launching device of the split Hopkinson pressure bar system and the position of the bullet in the barrel;

[0047] Step S3-1-6, performing dynamic-static combined loading test on the cubic full-penetration cross-jointed rock mass sample by using the launching device, recording the bullet speed of each impact, and changing the impact air pressure or the position of the bullet in the barrel to obtain the required full-penetration cross-jointed rock mass failure degree and strain rate.

[0048] As a further preferred embodiment of the present application, the step S3-2 biaxial unloading impact test specifically comprises the following test steps:

[0049] Step S3-2-1, making DIC speckle on the surface of the cubic full-penetration cross-jointed rock mass sample prepared in step S1, and then placing it into the loading chamber;

[0050] Step S3-2-2, setting the constant unloading rate of the X-axis and Y-axis of the split Hopkinson pressure bar system, and the target value of the axial static pre-stress;

[0051] Step S3-2-3, unloading according to the constant unloading rate set in step S3-2-2;

[0052] Step S3-2-4, monitoring the surface speckle of the cubic full-penetration cross-jointed rock mass sample during the failure process;

[0053] Step S3-2-5, setting the impact air pressure of the launching device of the split Hopkinson pressure bar system and the position of the bullet in the barrel;

[0054] Step S3-2-6, performing biaxial unloading impact test on the cubic full-penetration cross-jointed rock mass sample by using the launching device before the unloading target value reaches zero, recording the bullet speed of each impact, and changing the impact air pressure or the position of the bullet in the barrel to obtain the required full-penetration cross-jointed rock mass failure degree and strain rate.

[0055] As a further preferred embodiment of the present application, the step S4-1 triaxial dynamic-static combined loading test specifically comprises the following test steps:

[0056] Step S4-1-1, placing the cubic full-penetration cross-jointed rock mass sample prepared in step S1 into the loading chamber;

[0057] Step S4-1-2, setting the constant loading rate of the X-axis, Y-axis and Z-axis of the split Hopkinson pressure bar system, and the target value of the axial static pre-stress;

[0058] Step S4-1-3, loading is carried out according to the constant loading rate set in step S4-1-2 until the target value set in step S4-1-2 is reached.

[0059] Step S4-1-4, the impact air pressure of the launching device of the split Hopkinson pressure bar system and the position of the bullet in the barrel are set.

[0060] Step S4-1-5, triaxial dynamic-static combined loading test is carried out on the cubic full-penetrating cross-joint rock mass sample by using the launching device, the bullet speed of each impact is recorded, and the required full-penetrating cross-joint rock mass damage degree and strain rate are obtained by changing the size of the impact air pressure or the position of the bullet in the barrel.

[0061] As a further preferred embodiment of the application, the triaxial unloading impact test of step S4-2 specifically comprises the following test steps:

[0062] Step S4-2-1, the cubic full-penetrating cross-joint rock mass sample prepared in step S1 is placed in the loading chamber.

[0063] Step S4-2-2, the constant unloading rate of the X-axis, Y-axis and Z-axis of the split Hopkinson pressure bar system, and the target value of the axial static prestress are set.

[0064] Step S4-2-3, unloading is carried out according to the constant unloading rate set in step S3-2-2.

[0065] Step S4-2-4, the impact air pressure of the launching device of the split Hopkinson pressure bar system and the position of the bullet in the barrel are set.

[0066] Step S4-2-5, before the unloading target value reaches zero, biaxial unloading impact test is carried out on the cubic full-penetrating cross-joint rock mass sample by using the launching device, the bullet speed of each impact is recorded, and the required full-penetrating cross-joint rock mass damage degree and strain rate are obtained by changing the size of the impact air pressure or the position of the bullet in the barrel.

[0067] Through the above technical scheme, compared with the prior art, the application has the following beneficial effects:

[0068] 1. The application simulates the excavated area (biaxial test) and the unexcavated area (triaxial test), thereby studying the dynamic mechanical properties of rock mass under triaxial stress at high strain rate (>10 / s), and thus providing a basis for the design of underground engineering such as tunnels.

[0069] Specifically in order to meet the various stress conditions of deep buried rock mass, the biaxial (X and Y direction) dynamic and static combined loading experiment, biaxial unloading impact experiment, triaxial (X, Y and Z direction) dynamic and static combined loading experiment and triaxial unloading impact experiment are considered respectively. In order to meet the loading of full-penetration cross joint rock mass, the joint does not dislocation in the loading process and meets the experimental sample requirements. The loading rate and initial positioning force of X direction, Y direction (and Z direction) SHPB rod are set respectively, and the DIC data acquisition system and SHPB data acquisition system are set. The static pre-stress target value of X direction, Y direction (and Z direction) is set, and slowly loaded to the target value. At this time, if the unloading impact experiment is studied, the bullet needs to be fired in the slow unloading process to start the experiment. If the dynamic and static combined loading experiment is studied, the bullet only needs to be fired directly to start the experiment. By recording the impact air pressure and bullet position of each experiment, the numerical value meeting the joint rock mass breaking degree or strain rate is obtained. The dynamic mechanical properties such as compressive strength of joint rock mass under different strain rates and axial pressure combination conditions are obtained.

[0070] 2, In order to avoid the dislocation of rock joint in the loading process, the control system is used to apply slow and constant axial pressure to the joint rock mass, which is first loaded to a small positioning force, and then continues to load to the target value. If the impact test in the unloading process is carried out, a slow unloading force is set, and the bullet is fired in the process to carry out the impact test. If the dynamic and static combined loading experiment is carried out, the bullet is directly fired to carry out the impact experiment. In this way, the various complex geological environments of the actual engineering rock mass can be realized.

[0071] 3, In the sample preparation aspect of the present application, the preparation of cubic full-penetration cross joint rock mass is studied to avoid the problem of cross section reduction of the cut sample, and the joint structure of the rock dynamics research object is expanded. The research object in the past is mostly cylindrical non-penetrating joint rock mass, and this kind of sample cannot be subjected to multi-axial pre-stress.

[0072] 4, The cubic full-penetration joint rock mass preparation method and impact experiment under multi-stress state designed in the present application considers the deficiency of rock dynamics experimental object and the dynamic mechanical property test method of joint rock mass under different stress loading modes, better meets the dynamic failure conditions of actual engineering rock mass, such as deep buried tunnel surrounding rock of blasting excavation, the sample preparation method is simple, the experimental operation mode is convenient, and it has important significance for revealing the dynamic instability mechanism of tunnel engineering surrounding rock under different stress environment. BRIEF DESCRIPTION OF DRAWINGS

[0073] The present application will be further described below in combination with the drawings and examples.

[0074] Figure 1 It is a simple flow chart of the experimental method of the present application;

[0075] Figure 2is a schematic diagram of a sub-vertical joint of the present application;

[0076] Figure 3 is a schematic diagram of a coring position of a rock sample coring device of the present application;

[0077] Figure 4 is a schematic diagram of a sub-horizontal joint group, upper end face and lower end face position of the present application;

[0078] Figure 5 is a schematic diagram of triaxial stress of a loaded indoor object of the present application;

[0079] Figure 6 is a schematic diagram of an overall structure of the present application.

[0080] In the figure: 1, nitrogen cylinder; 2, barrel; 3, bullet; 4, laser speedometer; 5, fixed plug; 6, SHPB loading control device; 7, SHPB data acquisition system; 8, DIC data acquisition system; 9-1, first high-speed camera; 9-2, second high-speed camera; 10-1, X-axis direction hydraulic loading device; 10-2, Y-axis direction hydraulic loading device; 10-3, Z-axis direction hydraulic loading device; 11-1, X-axis direction incident rod; 11-2, X-axis direction transmission rod; 11-3, Y-axis direction first transmission rod; 11-4, Y-axis direction second transmission rod; 11-5, Z-axis direction first transmission rod; 11-6, Z-axis direction second transmission rod; 12-1, X-axis direction incident rod strain gauge; 12-2, X-axis direction transmission rod strain gauge; 12-3, Y-axis direction first transmission rod strain gauge; 12-4, Y-axis direction second transmission rod strain gauge; 12-5, Z-axis direction first transmission rod strain gauge; 12-6, Z-axis direction second transmission rod strain gauge; 13, sub-vertical joint; 14, rock sample coring device; 15, rock fixing clamp; 16, upper end face; 17, sub-horizontal joint; 18, lower end face. DETAILED DESCRIPTION

[0081] The present application will now be further described in detail by reference to the drawings. These drawings show only the essential features of the present application and are not to be construed as limiting the scope of the application.

[0082] In the description of the present application, it should be understood that the terms "left side", "right side", "upper portion", "lower portion" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and "first", "second" and the like do not represent the importance of the parts, and therefore cannot be understood as limiting the present application. The specific dimensions used in this embodiment are only for the purpose of illustrating the technical solutions and do not limit the protection scope of the present application.

[0083] Embodiment 1

[0084] The embodiment provides an experimental method for researching dynamic mechanical properties of jointed rock mass under a multi-stress state, as shown in the following formula (I): Figures 1 to 6 The experimental method is performed by using a split Hopkinson pressure bar system combined with a loading system, and a three-dimensional coordinate system is established with the loading chamber of the split Hopkinson pressure bar system as an origin, the length direction of the split Hopkinson pressure bar as an X axis, the width direction of the split Hopkinson pressure bar as a Y axis, and the height direction of the split Hopkinson pressure bar as a Z axis.

[0085] Specifically, the split Hopkinson pressure bar system comprises a nitrogen cylinder 1, a barrel 2, a bullet 3, a laser speedometer 4, a fixed plug 5, and a loading chamber. The loading system comprises two SHPB loading control devices 6, three SHPB data acquisition systems 7, a DIC data acquisition device, a first high-speed camera 9-1, a second high-speed camera 9-2, an X-axis direction hydraulic loading device, a Y-axis direction hydraulic loading device, a Z-axis direction hydraulic loading device, an X-axis direction incident rod 11-1, an X-axis direction transmission rod 11-2, a Y-axis direction first transmission rod 12-3, a Y-axis direction second transmission rod 12-4, a Z-axis direction first transmission rod 12-5, a Z-axis direction second transmission rod, an X-axis direction incident rod strain gauge 12-1, an X-axis direction transmission rod strain gauge 12-2, a Y-axis direction first transmission rod strain gauge 12-3, a Y-axis direction second transmission rod strain gauge 12-4, a Z-axis direction first transmission rod strain gauge 12-5, and a Z-axis direction second transmission rod strain gauge 12-6.

[0086] Further, the nitrogen cylinder 1 is connected with the barrel 2, the barrel 2 has the bullet 3 therein, the fixed plug 5 is arranged at the outlet of the barrel 2, and the laser speedometer 4 is arranged between the barrel 2 and the fixed plug 5. The loading chamber is arranged on the side, away from the barrel 2, of the fixed plug 5.

[0087] A three-dimensional coordinate system is established with the loading chamber of the split Hopkinson pressure bar system as an origin, the length direction of the split Hopkinson pressure bar as an X axis, the width direction of the split Hopkinson pressure bar as a Y axis, and the height direction of the split Hopkinson pressure bar as a Z axis.

[0088] An X-axis direction incident rod 11-1 is arranged between the loading chamber and the fixed plug 5 along the X-axis direction, and an X-axis direction transmission rod 11-2 is arranged on the side opposite to the X-axis direction incident rod 11-1 along the X-axis direction. A Y-axis direction first transmission rod 11-3 and a Y-axis direction second transmission rod 12-411-4 are arranged on both sides of the loading chamber along the Y-axis direction. A Z-axis direction first transmission rod 11-5 and a Z-axis direction second transmission rod 11-6 are arranged on both sides of the loading chamber along the Z-axis direction. A first high-speed camera 9-1 and a second high-speed camera 9-2 are arranged above the loading chamber to monitor the state in the loading chamber; a DIC data acquisition system 8 acquires the information monitored by the first high-speed camera 9-1 and the second high-speed camera 9-2, and the DIC data acquisition system 8 is connected with a computer. An X-axis direction hydraulic loading device 10-1 is arranged at the tail of the X-axis direction transmission rod 11-2; a Y-axis direction hydraulic loading device 10-2 is arranged at the tail of the Y-axis direction first transmission rod 11-3; and a Z-axis direction hydraulic loading device 10-3 is arranged at the tail of the Z-axis direction first transmission rod 11-5. An X-axis direction incident rod 11-1 strain gauge is arranged on the X-axis direction incident rod 11-1; an X-axis direction transmission rod 11-2 strain gauge is arranged on the X-axis direction transmission rod 11-2; a Y-axis direction first transmission rod 11-3 strain gauge is arranged on the Y-axis direction first transmission rod 11-3; a Y-axis direction second transmission rod 12-411-4 strain gauge is arranged on the Y-axis direction first transmission rod 11-3; a Z-axis direction first transmission rod 11-5 strain gauge is arranged on the Z-axis direction first transmission rod 11-5; and a Z-axis direction second transmission rod 11-6 strain gauge is arranged on the Z-axis direction second transmission rod 11-6. One SHPB loading control device 6 is connected with the Z-axis direction hydraulic loading device 10-3 at one end and connected with the X-axis direction hydraulic loading device 10-1 at the other end; and the other SHPB loading control device 6 is connected with the nitrogen cylinder 1 at one end and connected with the Y-axis direction hydraulic loading device 10-2 at the other end. One SHPB data acquisition system 7 is connected with the laser speedometer 4, and this SHPB data acquisition system 7 acquires the information of the X-axis direction incident rod strain gauge 12-1 and the Y-axis direction first transmission rod strain gauge 12-3; one SHPB data acquisition system 7 acquires the information of the Y-axis direction second transmission rod strain gauge 12-4 and the Z-axis direction first transmission rod strain gauge 12-5; and one SHPB data acquisition system 7 acquires the information of the X-axis direction transmission rod strain gauge 12-2 and the Z-axis direction second transmission rod strain gauge 12-6.

[0089] The experimental method specifically includes the following steps:

[0090] Step S1, preparing a cubic full-penetrating cross-joint rock mass sample (as shown in Figures 2 to 5

[0091] ​The rock material is selected on site, cutting in the vertical direction and the horizontal direction, and then coring, and the rock mass obtained containing the vertical direction and the horizontal direction cutting joints is taken as a cubic full-penetration cross joint rock mass sample; the preparation steps include the following:

[0092] Step S1-1, preparing a rock mass sample:

[0093] Step S1-1-1, selecting a rock material with good homogeneity on site;

[0094] Step S1-1-2, cutting the rock material selected in step S1-1-1 into a cubic rock mass sample using a DQ-4 rock cutting machine (the model of the rock cutting machine is only for reference here), and preferably, the edge length of the cubic rock mass sample is 10 cm;

[0095] Step S1-2, preparing a bonded sample:

[0096] Step S1-2-1, cutting a sub-vertical joint 13 with an angle α (α is 5°) to the vertical direction from the rock mass sample in step S1-1-2, and the cut sub-vertical joint 13 forms a sub-vertical joint group;

[0097] Step S1-2-2, using a rock fixing clamp 15 to combine and clamp the rock sample cut in step S1-2-1, and cutting a cuboid joint sample containing the sub-vertical joint 13 cut in step S1-2-1 using a cutting machine, and preferably, the cross section of the cuboid is a square with an edge length of 50 mm, at which time the cut core is composed of two halves of rock as shown in Figure 4 ;

[0098] Step S1-2-3, using transparent adhesive tape to bond and combine the core cut in step S1-2-2 to form a bonded sample;

[0099] Step S1-3, preparing a cubic full-penetration cross joint rock mass sample:

[0100] Step S1-3-1, cutting from a position close to the top surface of the bonded sample prepared in step S1-2-3 to form an upper end surface 16 in the horizontal direction;

[0101] Step S1-3-2, cutting a sub-horizontal joint 17 with an angle β (β is 5°) to the horizontal direction, and the cut sub-horizontal joint 17 forms a sub-horizontal joint group 17;

[0102] Step S1-3-3, cutting from the position close to the bottom surface of the bonded sample after cutting in step S1-3-2 to form a lower end surface 18, to form a cubic full-penetrating cross-joint rock mass sample with a length * width * height = 50 mm * 50 mm * 50 mm;

[0103] Step S1-4, processing the cubic full-penetrating cross-joint rock mass sample:

[0104] Step S1-4-1, using transparent adhesive tape to wrap the cubic full-penetrating cross-joint rock mass sample prepared in step S1-3-3 periphery to prevent the joints of the rock sample from being dislocated during loading;

[0105] Step S1-4-2, using a SHM-200 double-end grinder (the model of the double-end grinder here is only for reference) to polish the wrapped cubic full-penetrating cross-joint rock mass sample in step S1-4-1, to ensure that the non-perpendicularity and non-parallelism of each face of the cubic full-penetrating cross-joint rock mass sample are less than 0.02 mm.

[0106] The number of the sub-horizontal joints 17, the number of the sub-vertical joints 13 and the inclination 5° are only a reference example. In fact, the angle and number of the sub-vertical joints 13 and the sub-horizontal joints 17 can be flexibly selected according to the design. For example, if the sub-vertical joint 13α is 30°, only need to cut 15 cm of the cube to make the cutter head inclined by 30°, that is Figure 2 The angle between the sub-vertical joint 13 and the vertical direction is 30°. Similarly, if the angle of the sub-horizontal joint 17 is to be changed, only need to change Figure 4 The angle between the sub-horizontal joint 17 and the horizontal direction is 30°. In addition, if the number of the sub-vertical joint 13 or the sub-horizontal joint 17 is to be changed, such as two sub-vertical joints 13 and two sub-horizontal joints 17, first need to reduce the Figure 2 The spacing of the sub-vertical joint 13, so that Figure 3 The drilling and coring device can contain two sub-vertical joints 13, and secondly, when cutting the sub-horizontal joint 17, two Figure 4 The sub-horizontal joints 17 in the 50 cm cube need to be cut. In this way, within the limit of the sample size, different angles and numbers of joints can be made according to the needs, greatly meeting the requirements of complex joints in rock mass engineering.

[0107] Step S2, selecting the corresponding test mode according to the site conditions to test the dynamic mechanical properties of the jointed rock mass under multiple stress states

[0108] The site conditions are divided into two types: the first type is the area after excavation, such as the tunnel sidewall; the second type is the area that has not been excavated, such as the area in front of the tunnel that has not been excavated;

[0109] The test mode is divided into two modes: the first test mode is a biaxial test, and the second test mode is a triaxial test;

[0110] If the current working condition is the first working condition, the first test mode is adopted, and step S3 is performed;

[0111] If the current working condition is the second working condition, the second test mode is adopted, and step S4 is performed.

[0112] Step S3, performing a biaxial test

[0113] The biaxial test includes a biaxial dynamic-static combined loading test and a biaxial unloading impact test;

[0114] If the current working condition is the tunnel face blasting, and the position of the tunnel sidewall behind the face has a vibration effect, step S3-1, the biaxial dynamic-static combined loading test, is performed to obtain the required full-penetration cross-joint rock mass failure degree and strain rate;

[0115] If the current working condition is the tunnel face blasting, and the position of the tunnel sidewall near the face has rock block falling or damage due to blasting, step S3-2, the biaxial unloading impact test, is performed to obtain the required full-penetration cross-joint rock mass failure degree and strain rate.

[0116] Step S3-1, the biaxial dynamic-static combined loading test, specifically includes the following test steps:

[0117] Step S3-1-1, install the first high-speed camera 9-1 and the second high-speed camera 9-2 above the loading chamber, and set up the DIC data acquisition system 8 to collect information of the first high-speed camera 9-1 and the second high-speed camera 9-2; and make DIC speckles on the surface of the cubic full-penetration cross-joint rock mass sample prepared in step S1, and then put it into the loading chamber;

[0118] Specifically, before putting the prepared cubic full-penetration cross-joint rock mass sample into the loading chamber, first adjust the height of the first transmission rod 11-5 in the Z-axis direction to avoid blocking the lenses of the first high-speed camera 9-1 and the second high-speed camera 9-2.

[0119] Regarding the DIC speckle making method: first make DIC speckles on the surface of the cubic full-penetration cross-joint rock mass sample, spray uniform matte white paint on the surface of the cubic full-penetration cross-joint rock mass sample about 50 cm above the sample, and after the white paint is dry, spray speckled black matte paint in the same way.

[0120] Step S3-1-2, turn on the first high-speed camera 9-1 and the second high-speed camera 9-2, set the focal length of the first high-speed camera 9-1 and the second high-speed camera 9-2 so that they can clearly capture the speckle on the surface of the cubic full-penetrating cross-joint rock mass sample, turn on the DIC data acquisition system 8, and turn on the trigger mode of the split Hopkinson pressure bar system and wait for triggering;

[0121] The loading rate of the X-axis direction hydraulic loading device 10-1 and the Y-axis direction hydraulic loading device 10-2 is set by using the SHPB loading control device 6, and the X-axis direction transmission rod 11-2 and the Y-axis direction first transmission rod 11-3 are slowly loaded. Specifically, the SHPB loading control device 6 is started to first load to an initial positioning force, which is a small force generally controlled within 2 MPa, so as to ensure that the cubic full-penetrating cross-joint rock mass sample is tightly attached to the rod, and to check whether the position of the joint is dislocated at this time.

[0122] Step S3-1-3, load according to the constant loading rate set in step S3-1-2 until the target value set in step S3-1-2 is reached;

[0123] Specifically, the target value of the static prestress in the X-axis direction and the Y-axis direction is set by using the SHPB loading control device 6, and the SHPB loading control device 6 is continued to be started to load to the target value, i.e. the holding pressure. At this time, the static prestress on the cubic full-penetrating cross-joint rock mass sample will always remain at the target value, providing a stable axial pressure.

[0124] And the SHPB data acquisition system 7 is turned on and appropriate parameters are set. The SHPB data acquisition system 7 mainly includes the laser speedometer 4, the X-axis direction incident rod strain gauge 12-1, the X-axis direction transmission rod strain gauge 12-2, the Y-axis direction first transmission rod strain gauge 12-3, the Y-axis direction second transmission rod strain gauge 12-4, the Z-axis direction first transmission rod strain gauge 12-5, and the Z-axis direction second transmission rod strain gauge 12-6.

[0125] Step S3-1-4, use the high-speed camera in the DIC data acquisition system 8 to monitor the surface speckle of the cubic full-penetrating cross-joint rock mass sample during the failure process;

[0126] Step S3-1-5, set the impact gas pressure of the launching device of the split Hopkinson pressure bar system and the position of the bullet 3 in the barrel 2;

[0127] Step S3-1-6, dynamic-static combined loading test is carried out on the cubic full-penetration cross-joint rock mass sample by using the launching device. Specifically, the bullet 3 is pushed to a suitable position of the barrel 2, and the muzzle of the barrel 2 is close to the fixed plug 5. The SHPB loading control device 6 is used to set the launching gas pressure of the nitrogen cylinder 1 and start the inflation. After the gas is filled, the launching is clicked.

[0128] The speed of the bullet 3 in each impact is recorded, and the required full-penetration cross-joint rock mass damage degree and strain rate are obtained by changing the size of the impact gas pressure or the position of the bullet 3 in the barrel 2.

[0129] Step S3-2, biaxial unloading impact test, specifically including the following test steps:

[0130] Step S3-2-1, the first high-speed camera 9-1 and the second high-speed camera 9-2 are installed above the loading chamber, and the DIC data acquisition system 8 is set to collect information of the first high-speed camera 9-1 and the second high-speed camera 9-2; and the DIC speckle is made on the surface of the cubic full-penetration cross-joint rock mass sample prepared in step S1, and then put into the loading chamber.

[0131] Specifically, before putting the prepared cubic full-penetration cross-joint rock mass sample into the loading chamber, the height of the first transmission rod 11-5 in the Z-axis direction is adjusted to avoid blocking the lens of the first high-speed camera 9-1 and the second high-speed camera 9-2.

[0132] Regarding the DIC speckle making method: first, make DIC speckle on the surface of the cubic full-penetration cross-joint rock mass sample, spray uniform matte white paint on the surface of the cubic full-penetration cross-joint rock mass sample at about 50 cm above the cubic full-penetration cross-joint rock mass sample, and then spray speckled black matte paint in the same way after the white paint is dry.

[0133] Step S3-2-2, the first high-speed camera 9-1 and the second high-speed camera 9-2 are opened, the focal length of the first high-speed camera 9-1 and the second high-speed camera 9-2 is set to clearly capture the speckle on the surface of the cubic full-penetration cross-joint rock mass sample, the DIC data acquisition system 8 is opened, and the trigger mode of the split Hopkinson pressure bar system is opened to wait for triggering;

[0134] The loading rate of the X-axis direction hydraulic loading device 10-1 and the Y-axis direction hydraulic loading device 10-2 is set by using the SHPB loading control device 6, and the X-axis direction transmission rod 11-2 and the Y-axis direction first transmission rod 11-3 are slowly loaded. Specifically, the SHPB loading control device 6 is started to load to an initial positioning force first, and the positioning force is a small force, generally controlled within 2 MPa, so as to ensure that the cubic full-penetration cross-joint rock mass sample is tightly attached to the rod, and whether the position of the joint at this time is dislocated is checked.

[0135] Step S3-2-3, unloading is performed according to the constant unloading rate set in step S3-2-2;

[0136] Step S3-2-4, the surface speckle of the cubic full-penetration cross-joint rock mass sample in the failure process is monitored by using the high-speed camera in the DIC data acquisition system 8;

[0137] Step S3-2-5, the impact air pressure of the launching device of the split Hopkinson pressure bar system and the position of the bullet 3 in the barrel 2 are set.

[0138] Step S3-2-6, before the unloading target value reaches zero, the biaxial unloading impact test of the cubic full-penetration cross-joint rock mass sample is carried out by using the launching device, the speed of the bullet 3 in each impact is recorded, and the required full-penetration cross-joint rock mass failure degree and strain rate are obtained by changing the size of the impact air pressure or the position of the bullet 3 in the barrel 2.

[0139] Specifically, the unloading rates of the X-axis direction hydraulic loading device 10-1 and the Y-axis direction hydraulic loading device 10-2 are set by using the SHPB loading control device 6, and the X-axis direction transmission rod 11-2 and the Y-axis direction first transmission rod 11-3 are slowly unloaded. During the slow unloading process (i.e. before the sample and the rod are separated), the bullet 3 is launched.

[0140] Step S4, triaxial test (the triaxial test cannot use the first high-speed camera 9-1 and the second high-speed camera 9-2 and the DIC data acquisition system 8, so there is no need to make DIC speckles)

[0141] The triaxial test includes triaxial dynamic-static combined loading test and triaxial unloading impact test.

[0142] If the current working condition is tunnel face blasting, the unexcavated rock mass in front of the face has a vibration effect but the rock mass is not damaged, the triaxial dynamic-static combined loading test in step S4-1 is performed to obtain the required full-penetration cross-joint rock mass failure degree and strain rate.

[0143] If the current working condition is tunnel face blasting, the front of the face has a vibration effect and produces rock blasting or damaged rock, then step S4-2 triaxial unloading impact test is performed to obtain the required full-through cross joint rock failure degree and strain rate.

[0144] Step S4-1, triaxial dynamic-static combined loading test, specifically includes the following test steps:

[0145] Step S4-1-1, place the cubic full-through cross joint rock sample prepared in step S1 into the loading chamber;

[0146] Step S4-1-2, set the loading rate of the X-axis direction hydraulic loading device 10-1, the Y-axis direction hydraulic loading device 10-2, and the Z-axis direction hydraulic loading device 10-3 using the SHPB loading control device 6, slowly load the X-axis direction transmission rod 11-2, the Y-axis direction first transmission rod 11-3, and the Z-axis direction first transmission rod 11-5. Specifically, start the SHPB loading control device 6 to first load to the initial positioning force, which is a small force generally controlled within 2MPa, to ensure that the sample is tightly attached to the rod.

[0147] Step S4-1-3, load according to the constant loading rate set in step S4-1-2 until the target value set in step S4-1-2 is reached;

[0148] Specifically, set the static prestress target value of the X-axis direction, Y-axis direction, and Z-axis direction using the SHPB loading control device 6, and continue to start the SHPB loading control device 6 to load to the target value, i.e. the holding pressure. At this time, the static prestress on the cubic full-through cross joint rock sample will always remain at the target value, providing a stable axial pressure. Also, open the SHPB data acquisition system 7 and set appropriate parameters.

[0149] Step S4-1-4, set the impact gas pressure of the launching device of the split Hopkinson pressure bar system and the position of the bullet 3 in the barrel 2; advance the bullet 3 to the appropriate position of the barrel 2, and place the muzzle of the barrel 2 close to the fixed plug 5. Set the launch gas pressure of the nitrogen cylinder 1 using the SHPB loading control device and start charging. After the gas is filled, click to launch.

[0150] Step S4-1-5, use the launching device to perform triaxial dynamic-static combined loading test on the cubic full-through cross joint rock sample, specifically, advance the bullet 3 to the appropriate position of the barrel 2, and place the muzzle of the barrel 2 close to the fixed plug 5. Record the speed of the bullet 3 for each impact, and change the size of the impact gas pressure or the position of the bullet 3 in the barrel 2 to obtain the required full-through cross joint rock failure degree and strain rate.

[0151] Step S4-2, triaxial unloading impact test, specifically comprising the following test steps:

[0152] Step S4-2-1, placing the cubic full-penetration cross-joint rock mass sample prepared in step S1 into the loading chamber;

[0153] Step S4-2-2, setting the loading rate of the X-axis direction hydraulic loading device 10-1, the Y-axis direction hydraulic loading device 10-2, and the Z-axis direction hydraulic loading device 10-3 by using the SHPB loading control device 6, slowly loading the X-axis direction transmission rod 11-2, the Y-axis direction first transmission rod 11-3, and the Z-axis direction first transmission rod 11-5, specifically, starting the SHPB loading control device 6 to first load to the initial positioning force, which is a small force, generally controlled within 2 MPa, to ensure that the sample is tightly attached to the rod.

[0154] Step S4-2-3, unloading according to the constant unloading rate set in step S3-2-2;

[0155] Open the SHPB data acquisition system 7 and set appropriate parameters. Push the bullet 3 to the appropriate position of the barrel 2, and place the muzzle of the barrel 2 close to the fixed plug 5. Set the launch gas pressure of the nitrogen cylinder 1 by using the SHPB loading control device 6 and start charging until the impact gas pressure is reached.

[0156] Step S4-2-4, setting the impact gas pressure of the launch device of the split Hopkinson pressure bar system and the position of the bullet 3 in the barrel 2;

[0157] Set the unloading rate of the X-axis direction hydraulic loading device 10-1, the Y-axis direction hydraulic loading device 10-2, and the Z-axis direction hydraulic loading device 10-3 by using the SHPB loading control device 6, slowly unload the X-axis direction transmission rod 11-2, the Y-axis direction first transmission rod 11-3, and the Z-axis direction first transmission rod 11-5, and click the bullet 3 to launch during the slow unloading process (i.e. before the full-penetration cross-joint rock mass sample is separated from the rod).

[0158] Step S4-2-5, before the unloading target value reaches zero, conducting biaxial unloading impact test on the cubic full-penetration cross-joint rock mass sample by using the launch device, recording the speed of the bullet 3 for each impact, and obtaining the required full-penetration cross-joint rock mass damage degree and strain rate by changing the size of the impact gas pressure or the position of the bullet 3 in the barrel 2.

[0159] Step S5, data analysis

[0160] According to the required full-through cross-joint rock mass failure degree and strain rate obtained in the step S3-1, the step S3-2, the step S4-1 and the step S4-2, the corresponding incident wave, reflected wave and transmitted wave of the split Hopkinson pressure bar system are obtained, and then the compressive strength, the elastic modulus and the peak strain of the full-through cross-joint rock mass are analyzed, so as to study the dynamic mechanical properties of the full-through cross-joint rock mass under the biaxial dynamic-static combined loading test, the biaxial unloading impact test, the triaxial dynamic-static combined loading test and the triaxial unloading impact test.

[0161] Specifically, the strain field and the displacement field in the sample surface damage process are analyzed by combining the information collected by the first high-speed camera 9-1 and the second high-speed camera 9-2 with the DIC data acquisition system 8, the incident wave, the reflected wave and the transmitted wave of each rod are monitored and recorded by the DIC data acquisition system 8, and the compressive strength, the elastic modulus, the peak strain and other mechanical properties of the full-through cross-joint rock mass are analyzed.

[0162] Those skilled in the art can understand that, unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. It should also be understood that terms such as those defined in general dictionaries should be understood to have meanings consistent with those in the context of the prior art, and should not be interpreted in an idealized or overly formal sense unless defined as such.

[0163] The meaning of "and / or" described in the present application means that each single existence or both existences are included.

[0164] The meaning of "connection" described in the present application can be a direct connection between components or an indirect connection between components through other components.

[0165] Based on the above ideal embodiments according to the present application, the relevant personnel can make various changes and modifications without deviating from the technical idea of the present application. The technical scope of the present application is not limited to the contents of the specification, and must be determined by the scope of the claims.

Claims

1. An experimental method for studying the dynamic mechanical properties of jointed rock masses under multiple stress states, characterized in that: This experimental method utilizes a split Hopkinson bar system combined with a loading system. The experimental method establishes a three-dimensional coordinate system with the loading chamber of the split Hopkinson bar system as the origin, the length direction of the split Hopkinson bar as the X-axis, the width direction of the split Hopkinson bar as the Y-axis, and the height direction of the split Hopkinson bar as the Z-axis. The loading system can load indoor objects from the X-axis, Y-axis, and Z-axis respectively; This experimental method specifically includes the following steps: Step S1: Prepare cubic fully-connected interjointed rock mass samples Rock materials were selected on site, cut vertically and horizontally, and then core samples were taken. The rock mass containing vertical and horizontal cuts was used as a cubic fully-connected cross-jointed rock mass sample. Step S2: Select the appropriate test method according to the field conditions to conduct the test on the dynamic mechanical properties of jointed rock mass under multiple stress conditions. There are two types of field conditions: the first is the area after excavation, and the second is the area before excavation. There are two testing methods: the first is the biaxial test, and the second is the triaxial test. If the current working condition is the first type, adopt the first test method and proceed to step S3; If the current working condition is the second type, the second test method shall be adopted and step S4 shall be performed; Step S3: Perform biaxial testing Biaxial testing includes biaxial dynamic and static combined loading tests and biaxial unloading impact tests; If the current working condition is tunnel face blasting, and there is a vibration effect on the tunnel sidewall behind the face, then step S3-1, biaxial dynamic and static combined loading test, is carried out to obtain the required degree of damage and strain rate of the fully penetrated cross-jointed rock mass. If the current working condition is tunnel face blasting, and the tunnel sidewall near the rear of the face is damaged or broken due to rock fragments caused by the blasting, then step S3-2, biaxial unloading impact test, is performed to obtain the required degree of damage and strain rate of the fully connected cross-jointed rock mass. Step S4: Perform triaxial test Triaxial testing includes triaxial dynamic and static combined loading test and triaxial unloading impact test; If the current working condition is tunnel face blasting, and there is vibration effect in front of the tunnel face but the rock mass is not damaged, then the triaxial dynamic and static combined loading test in step S4-1 is carried out to obtain the required degree of damage and strain rate of the fully penetrated cross-jointed rock mass. If the current working condition is tunnel face blasting, and there is vibration effect in front of the tunnel face and rock mass is blasted or damaged, then step S4-2 triaxial unloading impact test is carried out to obtain the required degree of damage and strain rate of fully penetrated cross-jointed rock mass. Step S5: Data Analysis Based on the required degree of failure and strain rate of the fully penetrated cross-jointed rock mass obtained in steps S3-1, S3-2, S4-1, and S4-2, the incident wave, reflected wave, and transmitted wave of the corresponding split Hopkinson pressure bar system are obtained. Then, the compressive strength, elastic modulus, and peak strain of the fully penetrated cross-jointed rock mass are analyzed. Thus, the dynamic mechanical properties of the fully penetrated cross-jointed rock mass under biaxial dynamic-static combined loading test, biaxial unloading impact test, triaxial dynamic-static combined loading test, and triaxial unloading impact test are studied.

2. The experimental method for studying the dynamic mechanical properties of jointed rock masses under multiple stress states according to claim 1, characterized in that: Step S1 includes the following preparation steps: Step S1-1, preparing rock mass samples: Step S1-1-1: Select rock materials on site; Step S1-1-2: Cut the rock material selected in step S1-1-1 into a cubic rock sample; Step S1-2: Prepare the bonding sample: Step S1-2-1: Cut at least one sub-vertical joint with an angle α to the vertical direction from the rock mass sample in step S1-1-2. All the cut sub-vertical joints form a sub-vertical joint group. Step S1-2-2: Core sampling is performed from the location containing the vertical joint group along the vertical direction; Step S1-2-3: Use transparent tape to bond the rock cores taken out in step S1-2-2 together to form a bonded sample; Step S1-3: Prepare a cubic fully-penetrating cross-jointed rock mass sample: Step S1-3-1: Cut along the horizontal direction from a position close to the top surface of the bonded sample prepared in step S1-2-3 to form the upper end face. Step S1-3-2: Cut out at least one sub-horizontal joint that forms an angle β with the horizontal direction. All the cut sub-horizontal joints form a sub-horizontal joint group. Step S1-3-3: Cut along the horizontal direction from the position near the bottom surface of the bonded sample cut in step S1-3-2 to form the lower end face, forming a cubic fully penetrating cross-jointed rock mass sample; Step S1-4: Process the cubic fully-connected interjointed rock mass sample: Step S1-4-1: Use transparent tape to bond and wrap the periphery of the cubic fully-penetrating interjointed rock mass sample prepared in step S1-3-3. Step S1-4-2: Grind the cube-shaped fully-penetrating interjointed rock mass sample wrapped in step S1-4-1.

3. The experimental method for studying the dynamic mechanical properties of jointed rock masses under multiple stress states according to claim 2, characterized in that: In step S1-4-2, the non-perpendicularity and non-parallelism of each face of the polished cubic fully interconnected jointed rock mass sample are less than 0.02 mm.

4. The experimental method for studying the dynamic mechanical properties of jointed rock masses under multiple stress states according to claim 3, characterized in that: Step S3-1 Biaxial dynamic and static combined loading test, specifically includes the following test steps: Step S3-1-1, DIC speckle is made on the surface of the cubic fully penetrated cross-jointed rock mass sample prepared in step S1, and then it is placed in the loading chamber; Step S3-1-2: Set the constant loading rate and target value of axial static prestress for the X-axis and Y-axis of the split Hopkinson bar system; Step S3-1-3: Load according to the constant loading rate set in step S3-1-2 until the target value set in step S3-1-2 is reached; Step S3-1-4: Monitor the surface speckle pattern during the failure process of the cubic fully-penetrating interjointed rock mass sample; Step S3-1-5: Set the impact air pressure of the launching device of the split Hopkinson pressure bar system and the position of the bullet in the barrel; Step S3-1-6: Use the launching device to carry out dynamic and static combined loading tests on the cubic fully penetrated cross-jointed rock mass sample, record the bullet velocity of each impact, and obtain the required degree of damage and strain rate of the fully penetrated cross-jointed rock mass by changing the magnitude of the impact air pressure or the position of the bullet in the barrel.

5. The experimental method for studying the dynamic mechanical properties of jointed rock masses under multiple stress states according to claim 4, characterized in that: Step S3-2 Biaxial unloading impact test, specifically includes the following test steps: Step S3-2-1, DIC speckle pattern is made on the surface of the cubic fully penetrated cross-jointed rock mass sample prepared in step S1, and then it is placed in the loading chamber; Step S3-2-2: Set the constant unloading rate and target value of axial static prestress for the X-axis and Y-axis of the split Hopkinson bar system; Step S3-2-3: Unload according to the constant unloading rate set in step S3-2-2; Step S3-2-4: Monitor the surface speckle pattern during the failure process of the cubic fully-connected interjointed rock mass sample; Step S3-2-5: Set the impact air pressure of the launching device of the split Hopkinson pressure bar system and the position of the bullet in the barrel; Step S3-2-6: Before unloading the target value to zero, use the launching device to carry out a biaxial unloading impact test on the cubic fully penetrated cross-jointed rock mass sample, record the bullet velocity of each impact, and obtain the required degree of damage and strain rate of the fully penetrated cross-jointed rock mass by changing the magnitude of the impact air pressure or the position of the bullet in the barrel.

6. The experimental method for studying the dynamic mechanical properties of jointed rock masses under multiple stress states according to claim 5, characterized in that: Step S4-1 Triaxial dynamic and static combined loading test, specifically includes the following test steps: Step S4-1-1, Place the cubic fully interconnected cross-jointed rock mass sample prepared in step S1 into the loading chamber; Step S4-1-2: Set the constant loading rate and target value of axial static prestress for the X-axis, Y-axis and Z-axis of the split Hopkinson bar system; Step S4-1-3: Load according to the constant loading rate set in step S4-1-2 until the target value set in step S4-1-2 is reached; Step S4-1-4: Set the impact air pressure of the launching device of the split Hopkinson pressure bar system and the position of the bullet in the barrel; Step S4-1-5: Use the launching device to carry out a triaxial dynamic and static combined loading test on the cubic fully penetrated cross-jointed rock mass sample, record the bullet velocity of each impact, and obtain the required degree of damage and strain rate of the fully penetrated cross-jointed rock mass by changing the magnitude of the impact air pressure or the position of the bullet in the barrel.

7. The experimental method for studying the dynamic mechanical properties of jointed rock masses under multiple stress states according to claim 6, characterized in that: Step S4-2 Triaxial Unloading Impact Test, specifically includes the following test steps: Step S4-2-1, Place the cubic fully interconnected cross-jointed rock mass sample prepared in step S1 into the loading chamber; Step S4-2-2: Set the constant unloading rate and target value of axial static prestress for the X-axis, Y-axis and Z-axis of the split Hopkinson bar system; Step S4-2-3: Unload according to the constant unloading rate set in step S3-2-2; Step S4-2-4: Set the impact air pressure of the launching device of the split Hopkinson pressure bar system and the position of the bullet in the barrel; Step S4-2-5: Before unloading the target value to zero, use the launching device to conduct a triaxial unloading impact test on the cubic fully penetrated cross-jointed rock mass sample, record the bullet velocity of each impact, and obtain the required degree of damage and strain rate of the fully penetrated cross-jointed rock mass by changing the magnitude of the impact air pressure or the position of the bullet in the barrel.

Images