Experimental method of dynamic mechanical properties of jointed rock mass under combined static and dynamic loading in three dimensions

Abstract

The present application belongs to the field of jointed rock mass dynamics and engineering technology, and particularly relates to a method for testing dynamic mechanical properties of jointed rock mass under three-dimensional dynamic and static combined loading, which comprises the following steps: 1. preparing a cylindrical full-penetrating jointed rock mass sample; 2. pre-experimenting an empty rod; 3. pre-experimenting the empty rod impact, so that the incident stress wave + reflected stress wave ≈ transmitted stress wave to carry out formal experiment; 4. loading and impact testing by placing the sample into a confining pressure device; 5. setting the impact air pressure of the launching device and the position of the bullet, and testing the required working conditions; and 6. calculating the dynamic compressive strength, elastic modulus and peak strain of the jointed rock mass sample based on the collected incident stress wave, reflected stress wave and transmitted stress wave, and then calculating the incident energy, reflected energy, transmitted energy and cracking energy of the cylindrical full-penetrating jointed rock mass sample. The present application can well analyze the dynamic mechanical properties of deep-buried jointed rock mass, and has important significance for revealing the instability mechanism of surrounding rock of tunnels and other projects under dynamic and static combined loading.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of jointed rock mass dynamics and engineering technology, and particularly relates to a method for testing dynamic mechanical properties of jointed rock mass under three-dimensional dynamic and static combined loading. BACKGROUND

[0002] During the evolution of geological structure, a large number of intersecting jointed rock masses are formed, which may be subjected to various dynamic disturbances such as earthquakes, engineering blasting and mechanical vibration. Moreover, these rock masses are already under certain static stress or ground stress before being subjected to dynamic load, such as the stability problem of deep surrounding rock, which is a typical rock mass dynamic and static combined loading problem. When the vertical ground stress caused by the burial depth is equal to the horizontal ground stress around the rock mass, the rock mass at this position can be regarded as being under three-dimensional confining pressure loading, and one of the horizontal ground stresses can be regarded as an axial pre-stress. Compared with the characterization unit of engineering rock mass, part of the large joint can be regarded as a full-penetration joint, which has different effects on the rock mass than non-penetrating joints. Due to the limitations of loading equipment and methods, the study of full-penetration intersecting jointed rock mass is relatively less. Therefore, understanding the mechanical properties of full-penetration intersecting jointed rock mass under dynamic and static combined loading provides a basis for the failure mechanism and control of surrounding rock instability of engineering rock mass.

[0003] At present, some scholars have used new dynamic load equipment to study the dynamic mechanical response of rock mass with different joint structures. The split Hopkinson pressure bar (SHPB) system has been widely used for the study of dynamic mechanical behavior of rock materials under 10 1 -10 3 / s-1 strain rate range due to its ease of operation and accuracy. Using the improved SHPB system, people have done a lot of research to understand the influence of joint geometry on the dynamic mechanical properties of rock mass. However, the previous research objects are mostly prismatic rocks containing non-penetrating joints, because the manufacturing method of non-penetrating intersecting joints is simpler compared with cylindrical samples, and the loading method is more related to uniaxial dynamic compression experiments. The study of cylindrical full-penetration intersecting jointed rock mass under three-dimensional dynamic and static combined loading is very limited. SUMMARY

[0004] The present application provides a method for testing the dynamic mechanical properties of jointed rock mass under three-dimensional dynamic and static combined loading. The preparation of cylindrical jointed rock mass samples avoids the potential reduction in diameter of the cross section of the cut sample, meets the sample mass problem and the dynamic stress balance assumption in the SHPB method, and the dynamic and static combined loading method includes axial static load, circumferential static load and axial dynamic load. It can meet the deep burial and blasting excavation environment of actual engineering rock mass, and the dynamic mechanical properties of full-penetration jointed rock mass obtained are more consistent with the engineering practice.

[0005] The technical solution adopted by the present invention to solve the technical problem is: an experimental method for the dynamic mechanical properties of jointed rock mass under three-dimensional dynamic and static combined loading. The experimental method is carried out by using a split Hopkinson pressure bar system in combination with a three-dimensional dynamic and static combined loading system. The three-dimensional dynamic and static combined loading system includes a launching device, an axial pressure loading device, a confining pressure loading device, and a data acquisition system. The experimental method specifically includes the following steps:

[0006] Step S1: preparing rock samples:

[0007] Step S1-1, selecting homogeneous rock materials on site;

[0008] Step S1-2, cutting the rock material selected in step S1-1 into a cubic rock sample;

[0009] Step S2: preparing a bonding sample:

[0010] Step S2-1, cutting the rock sample in step S1-2 to obtain at least one secondary vertical joint with an angle α with the vertical direction, and all the secondary vertical joints cut to form a secondary vertical joint group;

[0011] Step S2-2, coring along the vertical direction from a location containing a vertical joint group;

[0012] Step S2-3: Using transparent tape, the cores taken out in step S2-2 are bonded together to form a bonded sample;

[0013] Step S3: preparing a cylindrical fully through cross-jointed rock mass sample:

[0014] Step S3-1, cutting in a horizontal direction from a position close to the top surface of the bonding sample prepared in step S2 to form an upper end surface;

[0015] Step S3-2, cutting out at least one sub-horizontal joint having an angle β with the horizontal direction, and all the sub-horizontal joints cut out form a sub-horizontal joint group;

[0016] Step S3-3: cutting the bottom end surface of the bonded sample after steps S3-1 and S3-2 in a horizontal direction to form a cylindrical fully-through cross-jointed rock mass sample;

[0017] Step S4: Processing the cylindrical fully-through cross-jointed rock mass sample:

[0018] Step S4-1: Use transparent tape to wrap the outer periphery of the cylindrical fully through cross-jointed rock mass specimen prepared in step S3-3;

[0019] Step S4-2, polishing the cylindrical fully-through cross-jointed rock mass sample wrapped in step S4-1 to ensure that the non-perpendicularity and non-parallelism of the cylindrical fully-through cross-jointed rock mass sample are both less than 0.02 mm;

[0020] Step S5: Determine the target values ​​of the required axial loading rate, circumferential loading rate, and axial pressure according to the confining pressure and axial pressure parameters of the current working condition and the static load application rate;

[0021] Step S6: Conduct formal experiment:

[0022] Step S6-1, setting the set values ​​of the axial loading rate, the hoop loading rate, and the axial pressure to the target values ​​of the axial loading rate, the hoop loading rate, and the axial pressure required in step S5;

[0023] Step S6-2: placing the cylindrical fully-through cross-jointed rock mass specimen processed in step S4 into a confining pressure loading device; then applying axial pressure to the fully-through cross-jointed rock mass specimen using the axial pressure loading device at a slow and constant loading rate until the target value is reached, and waiting to ensure that the axial pressure remains at a stable value;

[0024] At the same time, a confining pressure loading device is used to apply circumferential pressure to the fully penetrated cross-jointed rock mass specimen at a slow and constant loading rate until the target value is reached, and then the circumferential pressure is kept at a stable value.

[0025] Step S6-3: setting the impact pressure value of the launch device and the position of the bullet in the barrel, using the launch device to conduct a dynamic and static combined impact test on a fully penetrated cross-jointed rock mass specimen, and recording the bullet velocity at each impact;

[0026] Step S7, analyzing the dynamic mechanical properties of the fully-penetrating cross-jointed rock mass specimen under the current three-dimensional dynamic and static combined loading: analyzing the dynamic mechanical properties of the fully-penetrating cross-jointed rock mass specimen under the current three-dimensional dynamic and static combined loading based on the incident stress wave, reflected stress wave, and transmitted stress wave signals in step S6 monitored by the data acquisition system.

[0027] As a further preference of the present invention, before performing step S6, it is necessary to first perform the empty rod pre-experiment of step a:

[0028] Step Sa-1, setting the set values ​​of the axial loading rate, the hoop loading rate, and the axial pressure to the target values ​​of the axial loading rate, the hoop loading rate, and the axial pressure required in step S5;

[0029] Step Sa-2: Adjusting the flatness and fit of the incident rod and the transmission rod in the split Hopkinson pressure rod system;

[0030] Step Sa-3: Apply an axial load at a slow and constant loading rate using an axial load loading device until the set value of the axial load rate is reached, and wait until the axial load is stable;

[0031] At the same time, the confining pressure loading device is used to apply the hoop load at a slow and constant loading rate until the set value of the hoop loading rate is reached, and then the hoop load is ensured to be at a stable value.

[0032] Step Sa-4: Conduct a preliminary empty rod impact test using a launch device, and record incident stress wave, reflected stress wave, and transmitted stress wave signals using a data acquisition system;

[0033] Step Sa-5: Analyze the flatness and fit of the incident rod and the transmitted rod based on the incident stress wave, reflected stress wave, and transmitted stress wave signals monitored by the data acquisition system to determine whether the ratio (incident stress wave - transmitted stress wave) / incident stress wave is less than 0.1 and the reflected stress wave is less than 10 MPa.

[0034] If the requirements are met, proceed to the next step. If not, repeat steps S6-2 to S6-5 until (incident stress wave - transmitted stress wave) / incident stress wave is less than 0.1 and the reflected stress wave size is <10 MPa.

[0035] As a further preferred embodiment of the present invention, the angle α in step S2-1 and the angle β in step S3-2 are both between 0-90°.

[0036] As a further preferred embodiment of the present invention, when the secondary vertical joint group has two secondary vertical joints and the secondary horizontal joint group has two secondary horizontal joints, the cutting order in step S3 is the lower end face, the first secondary horizontal joint, the second secondary horizontal joint, and the upper end face.

[0037] As a further preferred embodiment of the present invention, in step S3-3, the distance between the lower end surface and the upper end surface is in the range of 51 mm to 53 mm.

[0038] As a further preferred embodiment of the present invention, the step S6-3 and the step S6-2 are both performed by waiting for 5 minutes.

[0039] As a further preference of the present invention, step S7 specifically includes the following steps:

[0040] Step S7-1: Obtain the incident stress wave ε according to the incident stress wave, reflected stress wave and transmitted stress wave signals in step S6 monitored by the data acquisition system. I (t), reflected stress wave ε R (t) and the transmitted stress wave ε T (t);

[0041] Step S7-2, the normal stress σ, the normal strain ε and the strain rate of the full-penetration cross-joint rock mass sample in the impact test process under the three-dimensional dynamic-static combined loading are calculated according to the three-wave method The curve changing with time t, that is, σ t , ε(t) and

[0042] Step S7-3, the dynamic compressive strength, the elastic modulus and the peak strain of the jointed rock mass are calculated according to σ t , ε(t) and

[0043] Step S7-4, the incident energy, the reflected energy, the transmitted energy and the cracking energy of the sample are calculated by using the one-dimensional stress wave theory and the impact dynamics method, so as to analyze the dynamic mechanical properties of the compressive strength, the elastic modulus, the peak strain and the cracking energy of the full-penetration cross-joint rock mass sample under the current three-dimensional dynamic-static combined loading.

[0044] By means of the above technical scheme, the present application has the following beneficial effects relative to the prior art:

[0045] 1. The present application can study the preparation of the full-penetration cross-joint rock mass in the form of a cylinder to avoid the non-circular cross section of the cut sample, and can change the number of joints and the joint inclination angle of the full-penetration cross-joint rock mass sample in the form of a jointed cylinder, thus expanding the joint structure of the rock dynamics research object.

[0046] 2. The previous research object is mostly a prismatic non-penetrating jointed rock mass, and such a sample cannot be loaded with confining pressure; in the experiment aspect, in order to avoid the joint dislocation of the rock mass sample during loading, the loading rates of the axial stress and the hoop stress are set respectively, and are slowly loaded at the same time to reach the respective target values. In addition, different strain rate loadings can be realized by changing the impact air pressure value in the launching device and the position of the bullet in the barrel. At the same time, the dynamic mechanical properties of the jointed rock mass under different loading conditions can be analyzed by changing the axial pressure target value, the hoop pressure target value and the impact air pressure value.

[0047] 3. The preparation method of the full-penetration jointed rock mass in the form of a cylinder and the three-dimensional dynamic-static combined loading experiment mode designed by the present application consider the deficiency of the joint structure in the rock dynamics experiment object, that is, the rock mass sample containing different numbers and different inclination angles of joints, and avoid the problem of the non-circular cross section of the cut rock mass sample. At the same time, the mechanical property test method of the jointed rock mass under different dynamic-static combined loading modes is considered, which can better meet the dynamic failure conditions of the actual engineering rock mass, such as the tunnel surrounding rock in deep-buried blasting excavation, the sample preparation method is simple, the experiment operation mode is convenient, and it has important significance for revealing the instability mechanism of the tunnel and other engineering surrounding rock under the dynamic-static combined load. BRIEF DESCRIPTION OF DRAWINGS​

[0048] The present invention will be further described below with reference to the accompanying drawings and examples.

[0049] Figure 1 This is a simple schematic diagram of step S2-1 in Example 1 of the present invention;

[0050] Figure 2 This is a simple schematic diagram of step S2-2 in Example 1 of the present invention;

[0051] Figure 3 Schematic diagram of the structure of a cylindrical fully-through cross-jointed rock mass specimen in Example 1 of the present invention;

[0052] Figure 4 This is a schematic diagram of the stress on a cylindrical fully-through cross-jointed rock mass specimen in Example 1 of the present invention;

[0053] Figure 5 This is a simple schematic diagram of step S2-1 in Example 2 of the present invention;

[0054] Figure 6 This is a simple schematic diagram of step S2-2 in Example 2 of the present invention;

[0055] Figure 7 Schematic diagram of the structure of a cylindrical fully-through cross-jointed rock mass specimen in Example 2 of the present invention;

[0056] Figure 8 This is a schematic diagram of the stress on a cylindrical fully-through cross-jointed rock mass specimen in Example 2 of the present invention;

[0057] Figure 9 It is a structural schematic diagram of the three-dimensional dynamic and static combined loading system of the present invention;

[0058] Figure 10 It is a curve diagram of the strain rate variation over time of a cylindrical fully through cross-jointed rock mass specimen of the present invention;

[0059] Figure 11 It is the dynamic stress-strain curve of the present invention.

[0060] In the figure: 1. Subvertical joint; 2. Rock sample coring device; 3. Rock mass fixing fixture; 4. Upper end face; 5. Subhorizontal joint; 6. Lower end face; 7. Nitrogen bottle; 8. Launch control system; 9. Bullet; 10. Wheatstone bridge; 11. Strain amplifier; 12. Oscilloscope; 13. Axial pressure hydraulic loading instrument; 14. Axial pressure and confining pressure control system; 15. Confining pressure device; 16. Gun barrel; 17. Incident rod strain gauge; 18. Cylindrical full-through cross-jointed rock mass specimen; 19. Transmission rod strain gauge; 20. Axial pressure loading and fixing system; 21. Velocity monitor; 22. Incident rod; 23. Transmission rod; 24. Plug. DETAILED DESCRIPTION

[0061] The present invention will now be described in further detail with reference to the accompanying drawings, which are simplified schematic diagrams that illustrate the basic structure of the present invention in a schematic manner.

[0062] In the description of the present invention, it should be understood that the terms "left side," "right side," "upper," "lower," etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings and are intended solely to facilitate the description of the present invention and simplify the description. They do not indicate or imply that the devices or components referred to must have a specific orientation, be constructed, or operate in a specific orientation. Terms such as "first" and "second" do not indicate the importance of components and therefore should not be construed as limitations on the present invention. The specific dimensions used in this embodiment are intended only to illustrate the technical solution and do not limit the scope of protection of the present invention.

[0063] This application provides an experimental method for the dynamic mechanical properties of jointed rock mass under three-dimensional dynamic and static combined loading, such as Figures 1 to 11 As shown in the figure, this experimental method is carried out by using a split Hopkinson pressure bar system combined with a three-dimensional dynamic and static combined loading system. The three-dimensional dynamic and static combined loading system includes a launch device, an axial pressure loading device, a confining pressure loading device, and a data acquisition system, wherein:

[0064] like Figure 9 As shown, the launching device includes a nitrogen cylinder, a launching control system, a bullet, a barrel, and a speed monitor; the axial pressure loading device includes an axial pressure hydraulic loading instrument, an axial pressure loading fixing system, and a plug for the axial pressure device; the confining pressure loading device and the axial pressure loading device are controlled by the axial pressure and confining pressure control systems; the data acquisition system includes a Wheatstone bridge, a strain amplifier, an oscilloscope, an incident rod strain gauge, and a transmission rod strain gauge.

[0065] The above experimental method specifically includes the following steps:

[0066] Step S1: preparing rock samples:

[0067] Step S1-1, selecting rock materials on site;

[0068] Step S1-2: Cut the rock material selected in step S1-1 into a cubic rock sample.

[0069] Step S2: preparing a bonding sample:

[0070] Step S2-1, cutting the rock sample in step S1-2 to obtain at least one secondary vertical joint having an angle α with the vertical direction, wherein all the secondary vertical joints cut form a secondary vertical joint group; preferably, the angle α is between 0° and 90°;

[0071] Step S2-2, coring along the vertical direction from a location containing a vertical joint group;

[0072] Step S2-3: Use transparent tape to bond the cores taken out in step S2-2 together to form a bonded sample.

[0073] Step S3: preparing a cylindrical fully through cross-jointed rock mass sample:

[0074] Step S3-1, cutting in a horizontal direction from a position close to the top surface of the bonding sample prepared in step S2 to form an upper end surface;

[0075] Step S3-2, cutting out at least one sub-horizontal joint having an angle β with the horizontal direction, and all the sub-horizontal joints cut out form a sub-horizontal joint group; preferably, the angle β is between 0° and 90°;

[0076] Step S3-3: cutting the bottom end surface of the bonded sample after steps S3-1 and S3-2 in a horizontal direction to form a cylindrical fully-through cross-jointed rock mass sample;

[0077] Specifically, the distance between the lower end surface and the upper end surface is in the range of 50 mm to 100 mm; preferably, the distance between the upper end surface and the lower end surface is 50 mm.

[0078] Step S4: Processing the cylindrical fully-through cross-jointed rock mass sample:

[0079] Step S4-1: Use transparent tape to wrap the outer periphery of the cylindrical fully through cross-jointed rock mass specimen prepared in step S3-3;

[0080] Step S4-2: Grind the cylindrical fully-through cross-jointed rock mass specimen wrapped in step S4-1 to ensure that the non-perpendicularity and non-parallelism of the cylindrical fully-through cross-jointed rock mass specimen are both less than 0.02 mm.

[0081] Step S5: Determine the target values ​​of the required axial loading rate, circumferential loading rate, and axial pressure according to the confining pressure and axial pressure parameters of the current working condition and the application rate of the static load.

[0082] Step a: Empty rod pre-experiment:

[0083] Step Sa-1, setting the set values ​​of the axial loading rate, the hoop loading rate, and the axial pressure to the target values ​​of the axial loading rate, the hoop loading rate, and the axial pressure required in step S5;

[0084] Step Sa-2: Adjusting the flatness and fit of the incident rod and the transmission rod in the split Hopkinson pressure rod system;

[0085] Step Sa-3: Use the axial load device to apply an axial load at a slow and constant loading rate until the set value of the axial loading rate is reached, and wait for 5 minutes to ensure that the axial load is at a stable value;

[0086] At the same time, use the confining pressure loading device to apply the hoop load at a slow and constant loading rate until the set value of the hoop loading rate is reached, and wait for 5 minutes to ensure that the hoop load is at a stable value;

[0087] Step Sa-4: Conduct a preliminary empty rod impact test using a launch device, and record incident stress wave, reflected stress wave, and transmitted stress wave signals using a data acquisition system;

[0088] Step Sa-5: Analyze the flatness and fit of the incident rod and the transmitted rod based on the incident stress wave, reflected stress wave, and transmitted stress wave signals monitored by the data acquisition system to determine whether the ratio (incident stress wave - transmitted stress wave) / incident stress wave is less than 0.1 and the reflected stress wave is less than 10 MPa.

[0089] If the requirements are met, proceed to the next step. If not, repeat steps S6-2 to S6-5 until (incident stress wave - transmitted stress wave) / incident stress wave is less than 0.1 and the reflected stress wave size is <10 MPa.

[0090] Step S6: Conduct formal experiment:

[0091] Step S6-1, setting the set values ​​of the axial loading rate, the hoop loading rate, and the axial pressure to the target values ​​of the axial loading rate, the hoop loading rate, and the axial pressure required in step S5;

[0092] Step S6-2: Place the cylindrical fully-through cross-jointed rock mass specimen processed in step S4 into a confining pressure loading device; then use the axial pressure loading device to apply axial pressure to the fully-through cross-jointed rock mass specimen at a slow and constant loading rate until the target value is reached, and wait for 5 minutes to ensure that the axial pressure remains at a stable value;

[0093] At the same time, a confining pressure loading device is used to apply circumferential pressure to the fully penetrated cross-jointed rock mass specimen at a slow and constant loading rate until the target value is reached. Wait for 5 minutes to ensure that the circumferential pressure remains at a stable value.

[0094] Step S6-3: Set the impact pressure value of the launch device and the position of the bullet in the barrel, use the launch device to carry out a dynamic and static combined impact test on the fully penetrated cross-jointed rock mass sample, and record the bullet velocity of each impact.

[0095] Step S7: Analyze the dynamic mechanical properties of the fully through cross-jointed rock mass specimen under the current three-dimensional dynamic and static combined loading:

[0096] Step S7-1, according to the data acquisition system monitoring the incident stress wave, reflected stress wave and transmitted stress wave signal in step S6, the incident stress wave ε I (t), reflected stress wave ε R (t) and transmitted stress wave ε T (t);

[0097] Step S7-2, according to the three-wave method, the stress σ, strain ε and strain rate of the full-penetration cross-joint rock mass sample under three-dimensional dynamic and static combined loading are calculated The curve changes with time t, that is, σ t , ε(t) and

[0098] Step S7-3, according to σ t , ε(t) and in step S7-2, the dynamic compressive strength, elastic modulus and peak strain of the jointed rock mass are calculated.

[0099] Step S7-4, using one-dimensional stress wave theory and impact dynamics method, the incident energy, reflected energy, transmitted energy and cracking energy of the sample are calculated, so as to analyze the dynamic mechanical properties of the compressive strength, elastic modulus, peak strain and cracking energy of the full-penetration cross-joint rock mass sample under the current three-dimensional dynamic and static combined loading.

[0100] When the sub-vertical joint group has two sub-vertical joints, and the sub-horizontal joint group has two sub-horizontal joints, the cutting order in step S3 is the lower end surface, the first sub-horizontal joint, the second sub-horizontal joint, and the upper end surface.

[0101] Example 1

[0102] In this embodiment, the above experimental method is used when the cylindrical full-penetration cross-joint rock mass sample has one sub-vertical joint and one sub-horizontal joint, and the angle α between the sub-vertical joint and the vertical direction and the angle β between the sub-horizontal joint and the horizontal direction are both 5°, as shown in Figures 1 to 4 , specifically as follows:

[0103] Step S1, preparing the rock mass sample:

[0104] Step S1-1, selecting rock materials with good integrity and uniformity on site;

[0105] Step S1-2, using a DQ-4 rock cutting machine to cut the rock material selected in step S1-1 into a cubic rock mass sample with a side length of 15 cm, and the surface of the rock mass sample is not subjected to special polishing treatment at this time;

[0106] Step S2, preparing the bonded sample:

[0107] Step S2-1, as Figure 1 As shown, the rock sample in step S1-2 is cut to form a secondary vertical joint with an angle α (α=5°) with the vertical direction, and the cut secondary vertical joint forms a secondary vertical joint group;

[0108] Then, use the rock fixing fixture 3 to combine and clamp the rocks cut in step S2-1;

[0109] Step S2-2, as Figure 2 As shown, the core was taken from the position containing the vertical joint group in the vertical direction. Figure 3 The figure shown consists of two halves of rock;

[0110] Step S2-3: Use transparent tape to bond the cores taken out in step S2-2 together to form a bonded sample (such as Figure 3 shown);

[0111] Step S3, as Figure 3 As shown, a cylindrical fully through cross-jointed rock mass specimen was prepared:

[0112] Step S3-1: Cut the top surface of the bonding sample prepared in step S2 in a horizontal direction using a DQ-4 rock cutter from a position close to the top surface thereof to form an upper end surface;

[0113] Step S3-2: Using a rock cutter, cut out a sub-horizontal joint with an angle β (β=20°) with the horizontal direction, and the cut sub-horizontal joint forms a sub-horizontal joint group;

[0114] Step S3-3: Taking into account the thickness of the cutter head of the rock cutter, cut horizontally from a position close to the bottom surface of the bonded sample after steps S3-1 and S3-2 to form a lower end surface, so that the distance between the upper end surface and the lower end surface is 50 mm, thereby forming a cylindrical fully-through cross-jointed rock mass specimen;

[0115] Step S4: Processing the cylindrical fully-through cross-jointed rock mass sample:

[0116] Step S4-1: Using transparent tape, wrap the outer periphery of the cylindrical fully through cross-jointed rock mass specimen prepared in step S3-3. The thickness of the transparent tape does not affect the deformation of the jointed rock mass.

[0117] Step S4-2: Grind the cylindrical fully-through cross-jointed rock mass sample wrapped in step S4-1. Preferably, use an SHM-200 double-end surface grinding machine to grind it to ensure that the non-perpendicularity and non-parallelism of the cylindrical fully-through cross-jointed rock mass sample are both less than 0.02 mm.

[0118] Example 2

[0119] This embodiment uses the above experimental method. When two sub-vertical joints and two sub-horizontal joints are prepared, and the sub-vertical joints are

[0120] For a cylindrical fully penetrating cross-jointed rock mass specimen, the angle h with the vertical direction and the angle g between the sub-horizontal joint and the horizontal direction are both 20°, as Figures 5 to 8 As shown, the details are as follows:

[0121] Step S1: preparing rock samples:

[0122] Step S1-1: Select rock materials with good integrity and uniformity on site;

[0123] Step S1-2: Using a DQ-4 rock cutter, cut the rock material selected in step S1-1 into a cubic rock sample with a side length of 15 cm. The surface of the rock sample does not require special grinding treatment.

[0124] Step S2: preparing a bonding sample:

[0125] Step S2-1: Figure 5 As shown, the rock sample in step S1-2 is cut to obtain two sub-vertical joints with an angle h (h=20°) with the vertical direction, and the two sub-vertical joints formed a sub-vertical joint group;

[0126] Then, use the rock fixing fixture 3 to combine and clamp the rocks cut in step S2-1;

[0127] Step S2-2, as Figure 2 As shown, a rock sample coring device 2 is used to coring from a position containing a vertical joint group in a vertical direction. The core taken out is as shown in FIG. Figure 6 The one shown consists of three rocks;

[0128] Step S2-3: Use transparent tape to bond the cores taken out in step S2-2 together to form a bonded sample (such as Figure 7 shown);

[0129] Step S3, as Figure 7 As shown, a cylindrical fully through cross-jointed rock mass specimen was prepared:

[0130] Step S3-1: Cut the top surface of the bonding sample prepared in step S2 in a horizontal direction using a DQ-4 rock cutter from a position close to the top surface thereof to form an upper end surface;

[0131] Step S3-2: Using a rock cutter, cut out two sub-horizontal joints at an angle g to the horizontal direction, and the two sub-horizontal joints formed a sub-horizontal joint group;

[0132] Step S3-3: Taking into account the thickness of the cutter head of the rock cutter, cut horizontally from a position close to the bottom surface of the bonded sample after steps S3-1 and S3-2 to form a lower end surface, so that the distance between the upper end surface and the lower end surface is 50 mm, thereby forming a cylindrical fully-through cross-jointed rock mass specimen;

[0133] Step S4: Processing the cylindrical fully-through cross-jointed rock mass sample:

[0134] Step S4-1: Using transparent tape, wrap the outer periphery of the cylindrical fully through-cross-jointed rock mass specimen prepared in step S3-3. The thickness of the transparent tape does not affect the deformation of the jointed rock mass.

[0135] Step S4-2: Grind the cylindrical fully-through cross-jointed rock mass sample wrapped in step S4-1. Preferably, use an SHM-200 double-end surface grinding machine to grind it to ensure that the non-perpendicularity and non-parallelism of the cylindrical fully-through cross-jointed rock mass sample are both less than 0.02 mm.

[0136] Researchers can use the methods of making cylindrical fully-through cross-jointed rock samples of the above two embodiments to make cylindrical fully-through cross-jointed rock samples with different numbers of joints and joint inclinations.

[0137] After preparing cylindrical fully through cross-jointed rock mass specimens, the mechanical properties experiment of fully through cross-jointed rock mass under three-dimensional dynamic and static combined loading was carried out. At present, there are two main problems with the experiments on cross-jointed rocks. One is that the previous joint types were mostly non-through joints, and the other is that the loading method of cross-joints is almost only uniaxial loading. There are very few studies on fully through cross-jointed rock mass under three-dimensional dynamic and static combined loading. However, compared with underground projects such as tunnels, the large jointed rock mass existing in actual projects can be regarded as fully through cross-joints, which are very prone to disasters such as surrounding rock instability under dynamic loads such as blasting excavation or earthquakes. However, research in this area is still insufficient. In order to solve this problem, the following method steps are proposed:

[0138] Step S5: Determine the target values ​​of the required axial loading rate, circumferential loading rate, and axial pressure according to the confining pressure and axial pressure parameters of the current working condition and the static load application rate;

[0139] Specifically, the axial loading rate and the circumferential loading rate as well as the axial pressure target value and the confining pressure target value are set using the control system of the axial pressure and the confining pressure.

[0140] Step a: To eliminate the error of the SHPB system, conduct an empty rod pre-experiment:

[0141] Step Sa-1, setting the set values ​​of the axial loading rate, the hoop loading rate, and the axial pressure to the target values ​​of the axial loading rate, the hoop loading rate, and the axial pressure required in step S5;

[0142] Specifically, the axial pressure and the annular pressure are loaded respectively by the axial pressure hydraulic loading instrument and the confining pressure device until the target values ​​of the required axial loading rate, annular loading rate and axial pressure are reached.

[0143] Step Sa-2: Preliminarily adjust the flatness and fit of the incident rod and the transmission rod in the split-Hopkinson pressure bar system so that the axes of the split-Hopkinson pressure bar system coincide and the incident rod and the transmission rod fit tightly together, i.e., there is no cylinder in the middle that fully penetrates the cross-jointed rock mass sample;

[0144] Step Sa-3: Apply an axial load at a slow and constant loading rate using an axial load loading device until the set value of the axial load rate is reached, and wait until the axial load is stable;

[0145] At the same time, the confining pressure loading device is used to apply the hoop load at a slow and constant loading rate until the set value of the hoop loading rate is reached, and then the hoop load is ensured to be at a stable value.

[0146] Step Sa-4: Conduct a preliminary empty rod impact test using a launch device, and record incident stress wave, reflected stress wave, and transmitted stress wave signals using a data acquisition system;

[0147] Specifically, the data acquisition system is turned on and waits for triggering. Its working mode is to use the incident rod strain gauge and the transmission rod strain gauge to monitor the impact signals on the incident rod and the transmission rod, including the incident stress wave, the transmission stress wave and the reflected stress wave, which are transmitted to the strain amplifier through the Wheatstone bridge and displayed through the oscilloscope. The incident stress wave ε I (t), reflected stress wave ε R (t) and the transmitted stress wave ε T (t) is exported to an Excel spreadsheet for subsequent calculations. The bullet velocimeter measures the velocity of the bullet during each experiment, allowing for more precise control of the strain rate of the specimen.

[0148] Step Sa-5: Analyze the flatness and fit of the incident rod and the transmitted rod based on the incident stress wave, reflected stress wave, and transmitted stress wave signals monitored by the data acquisition system to determine whether the ratio (incident stress wave - transmitted stress wave) / incident stress wave is less than 0.1 and the reflected stress wave is less than 10 MPa.

[0149] If the requirements are met, proceed to the next step. If not, repeat steps S6-2 to S6-5 until (incident stress wave - transmitted stress wave) / incident stress wave is less than 0.1 and the reflected stress wave size is <10 MPa.

[0150] Step S6: Conduct formal experiment:

[0151] Step S6-1, setting the set values ​​of the axial loading rate, the hoop loading rate, and the axial pressure to the target values ​​of the axial loading rate, the hoop loading rate, and the axial pressure required in step S5;

[0152] Specifically, the axial pressure and the annular pressure are loaded respectively by the axial pressure hydraulic loading instrument and the confining pressure device until the target values ​​of the required axial loading rate, annular loading rate and axial pressure are reached.

[0153] Step S6-2: Apply a small amount of lubricating oil to both ends of the cylindrical fully-through cross-jointed rock mass specimen processed in step S4 to reduce friction between the specimen and the SHPB rod, and then place it in the confining pressure loading device; then use the axial pressure loading device to apply axial pressure to the fully-through cross-jointed rock mass specimen at a slow and constant loading rate until the target value is reached, and wait to ensure that the axial pressure remains at a stable value;

[0154] At the same time, the confining pressure loading device is used to apply circumferential pressure to the fully penetrated cross-jointed rock mass specimen at a slow and constant loading rate until the target value is reached, and the circumferential pressure is kept stable. If different axial pressure and confining pressure conditions are to be studied, the axial pressure target value and the confining pressure target value can be modified.

[0155] Step S6-3: Turn on the data acquisition system and wait for a trigger. Use the launch control system to set the launcher's impact pressure and the bullet's position in the barrel. Once the impact pressure reaches the target value, click Launch to begin the experiment. Use the launcher to conduct a combined static and dynamic impact test on a fully penetrated, cross-jointed rock mass specimen, recording the bullet velocity at each impact. To study operating conditions with different strain rates, modify the impact pressure or the bullet's position in the barrel.

[0156] Step S7: Analyze the dynamic mechanical properties of the fully through cross-jointed rock mass specimen under the current three-dimensional dynamic and static combined loading:

[0157] According to the incident stress wave, reflected stress wave and transmitted stress wave signals in step S6 monitored by the data acquisition system, the dynamic mechanical properties of the fully through cross-jointed rock mass specimen under the current three-dimensional dynamic and static combined loading are analyzed.

[0158] Specifically, according to the incident stress wave ε monitored by the data acquisition system I (t), reflected stress wave ε R (t) and the transmitted stress wave ε T (t), the normal stress σ, normal strain ε and strain rate of the fully through cross-jointed rock specimen during the impact test can be calculated according to the three-wave method (Formulas (1)-(3)) The curve that changes with time t, that is, σ t , ε(t) and The curve of strain rate changing with time The average value of the top horizontal segment is the true strain rate of the specimen, such as Figure 10 The peak value of the stress-strain curve (i.e., the σ-ε curve) is the dynamic compressive strength of the specimen, the slope of the straight rising section of the σ-ε curve is the elastic modulus, and the abscissa corresponding to the dynamic compressive strength is the peak strain, as shown in the figure. Figure 11 shown.

[0159] According to the incident stress wave ε monitored by the data acquisition system I (t), reflected stress wave ε R (t) and the transmitted stress wave ε T (t), the incident energy E of the jointed rock sample is calculated using the one-dimensional stress wave theory and the impact dynamics method (Formula (4)) I , reflected energy E R , transmission energy E T and cracking energy E A .

[0160]

[0161]

[0162]

[0163]

[0164] Where A e 、C e and E e are the cross-sectional area of ​​the incident rod, the longitudinal wave velocity and Young’s modulus. s and L s are the cross-sectional area and length of the cylindrical fully through-cross-jointed rock mass specimen, respectively.

[0165] This implementation scheme avoids the problem of non-circular cross-section of cylindrical fully-through cross-jointed rock mass specimens, and for this type of jointed rock mass, a three-dimensional dynamic and static combined loading experimental method is designed to study the dynamic mechanical properties of jointed rock mass. For the preparation of cylindrical fully-through cross-jointed rock mass specimens, rock mass specimens with different numbers of joints and joint inclinations can be flexibly produced. Designing different numbers of joints can analyze the effects of the number and spacing of joints on the dynamic mechanical properties of rock mass, and designing different angles can analyze the effects of joint inclination (i.e., anisotropy) on the dynamic mechanical properties of rock mass. Based on this, within the range allowed by the specimen size, we can design jointed rock mass specimens with a variety of inclinations or numbers of joints, which greatly meets the requirements of complex joints in actual engineering rock mass.

[0166] For loading conditions, refer to the attached Figure 9 To prevent joint dislocation during loading, a control system for axial and confining pressures applies slow but constant axial and circumferential loading rates to the jointed rock mass. Target values ​​for the axial and confining pressures are set. Finally, varying the impact pressure and the bullet's position in the barrel are used to achieve different strain rates. This approach addresses the complex geological environments found in actual engineering rock masses.

[0167] It will be understood by those skilled in the art that, unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by those skilled in the art to which this application belongs. It should also be understood that terms such as those defined in common dictionaries should be understood to have meanings consistent with their meanings in the context of the prior art and, unless defined as such herein, will not be interpreted in an idealized or overly formal sense.

[0168] The meaning of "and / or" in this application means that both situations where each exists alone or both exist at the same time are included.

[0169] The term “connection” as used in this application may mean a direct connection between components or an indirect connection between components via other components.

[0170] With the above-described preferred embodiments of the present invention as a guide, and with reference to the above description, relevant personnel are fully capable of making various changes and modifications without departing from the technical scope of this invention. The technical scope of this invention is not limited to the contents of the specification and must be determined according to the scope of the claims.

Claims

1. An experimental method for dynamic mechanical properties of jointed rock mass under three-dimensional dynamic and static combined loading, characterized in that: This experimental method is carried out using a split Hopkinson pressure bar system combined with a three-dimensional dynamic and static combined loading system. The three-dimensional dynamic and static combined loading system includes a launch device, an axial pressure loading device, a confining pressure loading device, and a data acquisition system. This experimental method specifically includes the following steps: Step S1: preparing rock samples: Step S1-1, selecting rock materials on site; Step S1-2, cutting the rock material selected in step S1-1 into a cubic rock sample; Step S2: preparing a bonding sample: Step S2-1, cutting the rock sample in step S1-2 to obtain at least one secondary vertical joint with an angle α with the vertical direction, and all the secondary vertical joints cut to form a secondary vertical joint group; Step S2-2, coring along the vertical direction from a location containing a vertical joint group; Step S2-3: Using transparent tape, the cores taken out in step S2-2 are bonded together to form a bonded sample; Step S3: preparing a cylindrical fully through cross-jointed rock mass sample: Step S3-1, cutting in a horizontal direction from a position close to the top surface of the bonding sample prepared in step S2 to form an upper end surface; Step S3-2, cutting out at least one sub-horizontal joint having an angle β with the horizontal direction, and all the sub-horizontal joints cut out form a sub-horizontal joint group; Step S3-3: cutting the bottom end surface of the bonded sample after steps S3-1 and S3-2 in a horizontal direction to form a cylindrical fully-through cross-jointed rock mass sample; Step S4: Processing the cylindrical fully-through cross-jointed rock mass sample: Step S4-1: Use transparent tape to wrap the outer periphery of the cylindrical fully through cross-jointed rock mass specimen prepared in step S3-3; Step S4-2, polishing the cylindrical fully-through cross-jointed rock mass sample wrapped in step S4-1 to ensure that the non-perpendicularity and non-parallelism of the cylindrical fully-through cross-jointed rock mass sample are both less than 0.02 mm; Step S5: Determine the required axial loading rate, circumferential loading rate, and target values ​​of the axial pressure and confining pressure according to the confining pressure and axial pressure parameters of the current working condition and the static load application rate; Step S6: Conduct formal experiment: Step S6-1, setting the set values ​​of the axial loading rate, the hoop loading rate, and the axial pressure to the target values ​​of the axial loading rate, the hoop loading rate, and the axial pressure required in step S5; Step S6-2: placing the cylindrical fully-through cross-jointed rock mass specimen processed in step S4 into a confining pressure loading device; then applying axial pressure to the fully-through cross-jointed rock mass specimen using the axial pressure loading device at a slow and constant loading rate until the target value is reached, and waiting to ensure that the axial pressure remains at a stable value; At the same time, a confining pressure loading device is used to apply circumferential pressure to the fully penetrated cross-jointed rock mass specimen at a slow and constant loading rate until the target value is reached, and then the circumferential pressure is kept at a stable value. Step S6-3: setting the impact pressure value of the launch device and the position of the bullet in the barrel, using the launch device to conduct a dynamic and static combined impact test on a fully penetrated cross-jointed rock mass specimen, and recording the bullet velocity at each impact; Step S7: Analyze the dynamic mechanical properties of the fully through cross-jointed rock mass specimen under the current three-dimensional dynamic and static combined loading: According to the incident stress wave, reflected stress wave and transmitted stress wave signals in step S6 monitored by the data acquisition system, the dynamic mechanical properties of the fully through cross-jointed rock mass specimen under the current three-dimensional dynamic and static combined loading are analyzed.

2. The method for testing the dynamic mechanical properties of jointed rock mass under three-dimensional combined dynamic and static loading according to claim 1, characterized in that: Before proceeding to step S6, it is necessary to first perform the empty rod pre-experiment in step a: Step Sa-1, setting the set values ​​of the axial loading rate, the hoop loading rate, and the axial pressure to the target values ​​of the axial loading rate, the hoop loading rate, and the axial pressure required in step S5; Step Sa-2: Adjusting the flatness and fit of the incident rod and the transmission rod in the split Hopkinson pressure rod system; Step Sa-3: Apply an axial load at a slow and constant loading rate using an axial load loading device until the set value of the axial load rate is reached, and wait until the axial load is stable; At the same time, the confining pressure loading device is used to apply the hoop load at a slow and constant loading rate until the set value of the hoop loading rate is reached, and then the hoop load is ensured to be at a stable value. Step Sa-4: Conduct a preliminary empty rod impact test using a launch device, and record incident stress wave, reflected stress wave, and transmitted stress wave signals using a data acquisition system; Step Sa-5: Analyze the flatness and fit of the incident rod and the transmitted rod based on the incident stress wave, reflected stress wave, and transmitted stress wave signals monitored by the data acquisition system to determine whether the ratio (incident stress wave - transmitted stress wave) / incident stress wave is less than 0.1 and the reflected stress wave is less than 10 MPa. If the requirements in step Sa-5 are met, proceed to the next step. If not, repeat steps S6-2 to S6-5 until (incident stress wave - transmitted stress wave) / incident stress wave is less than 0.1 and the reflected stress wave size is <10MPa.

3. The method for testing the dynamic mechanical properties of jointed rock mass under three-dimensional combined dynamic and static loading according to claim 2, characterized in that: The angle α in step S2-1 and the angle β in step S3-2 are both between 0-90°.

4. The method for testing the dynamic mechanical properties of jointed rock mass under three-dimensional combined dynamic and static loading according to claim 2, characterized in that: When the secondary vertical joint group has two secondary vertical joints and the secondary horizontal joint group has two secondary horizontal joints, the cutting order in step S3 is the lower end face, the first secondary horizontal joint, the second secondary horizontal joint, and the upper end face.

5. The method for testing the dynamic mechanical properties of jointed rock mass under three-dimensional combined dynamic and static loading according to claim 2, characterized in that: In step S3-3, the distance between the lower end surface and the upper end surface is in the range of 51 mm to 53 mm.

6. The method for testing the dynamic mechanical properties of jointed rock mass under three-dimensional combined dynamic and static loading according to claim 2, characterized in that: In both step S6-3 and step S6-2, the waiting time is 5 minutes.

7. The method for testing the dynamic mechanical properties of jointed rock mass under three-dimensional combined dynamic and static loading according to claim 2, characterized in that: Step S7 specifically includes the following steps: Step S7-1: Obtain the incident stress wave ε according to the incident stress wave, reflected stress wave and transmitted stress wave signals in step S6 monitored by the data acquisition system. I (t), reflected stress wave ε R (t) and the transmitted stress wave ε T (t); Step S7-2: Calculate the normal stress σ, normal strain ε and strain rate of the fully through cross-jointed rock mass specimen under three-dimensional dynamic and static combined loading during the impact test according to the three-wave method. The curve that changes with time t, that is, σ t , ε(t) and Step S7-3: According to σ in step S7-2 t , ε(t) and Calculate the dynamic compressive strength, elastic modulus, and peak strain of jointed rock masses; Step S7-4: Use one-dimensional stress wave theory and impact dynamics method to calculate the incident energy, reflected energy, transmitted energy and fracture energy of the sample, so as to analyze the dynamic mechanical characteristics of the compressive strength, elastic modulus, peak strain and fracture energy of the fully through cross-jointed rock sample under the current three-dimensional dynamic and static combined loading.

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