A laboratory measurement method for the impact shear strength of rock mass structural surfaces

Abstract

A laboratory measurement method for the impact shear strength of a rock mass structural surface comprises the following steps: S1: selecting a target rock mass, obtaining the rock mass compressive strength, preparing mortar and making the strength of the specimen cast by the mortar consistent with the rock mass strength; S2: selecting a target structural surface, obtaining the exposed contour line of the structural surface, and casting a one-dimensional cylindrical specimen with the mortar in S1; S3: manually comparing the contour line with the standard contour line of the joint roughness coefficient to obtain the roughness coefficient of the structural surface; S4: performing a modified split Hopkinson bar test on the cylindrical specimen to obtain the shear strength of the rock; S5: on the basis of steps S3 and S4, calculating the shear strength of the specimen and the corresponding confining pressure size under different impact shear rates according to the known data such as the elastic modulus of the rod and the sleeve; S6: evaluating the impact shear strength of the rock mass structural surface. The present invention provides a reliable laboratory measurement method for the impact shear strength of the rock mass structural surface, filling the blank in this field.

Description

Technical Field

[0001] The invention relates to a laboratory measurement method for the impact shear strength of a rock mass structural surface, and belongs to the field of rock mechanics experiments. Background Art

[0002] Rock mass is composed of rock blocks and structural surfaces, and has obvious structural characteristics. Structural surfaces are affected by the combined effects of geological stresses inside and outside the earth, and their mechanical properties are very different from those of rock blocks. Under the impact disturbance of explosions, they are prone to dislocation, slippage, and even secondary disasters, which poses great risks to people's production and life. The impact shear strength of structural surfaces guides the mechanical properties of rock masses containing structural surfaces, so the study of the impact shear strength of structural surfaces is of great significance.

[0003] The mechanical properties of the structural surface are controlled by the rock composition. People often cannot directly obtain the morphological characteristics of the structural surface in the rock mass. The current mainstream morphological acquisition method is to use the exposed contour line of the structural surface as the basis for judging the roughness of the straight structural surface. Obtaining the basic mechanical properties of the rock and the one-dimensional roughness of the structural surface is the primary task of measuring the impact shear strength of the rock mass structural surface. Summary of the invention

[0004] The present invention aims to provide a laboratory measurement method for the impact shear strength of rock mass structural surfaces. Through a modified split Hopkinson bar test, the impact shear strength of rock mass structural surfaces at different shear speeds is measured to judge the stability of the rock mass. Under the conditions of different impact speeds, shear speeds and roughness corresponding to the rock mass structural surfaces with different profiles, the stability of the rock mass containing structural surfaces under impact loads is evaluated, providing guidance for engineering protection and ensuring the safety of deep engineering construction.

[0005] To achieve the above object, the present invention adopts the following technical solution: a laboratory measurement method for the impact shear strength of a rock mass structural surface, comprising the following steps:

[0006] Step 1: Select the target rock mass structural surface, obtain the compressive strength of the rock mass by the Schmidt hammer method, prepare the mortar so that the strength of the specimen cast by the mortar is consistent with the rock mass strength, and obtain the mortar mix ratio.

[0007] When obtaining the compressive strength of rock mass, a relatively straight structural surface should be selected. When using the Schmidt hammer method, the selected position should be as close to the structural surface as possible to fully consider the influence of rock weathering.

[0008] Step 2: After selecting the target structural surface, the exposed contour line of the structural surface is obtained through the contour comb, and the one-dimensional cylindrical specimen is cast with the mortar prepared in step 1, which specifically includes the following sub-steps:

[0009] Sub-step 2-1: Use a contour comb to obtain the contour line of the structural surface, and digitize the contour line for machine tool processing;

[0010] Sub-step 2-2: prepare cylindrical specimens according to the mix ratio obtained in step 1 and fully cure them;

[0011] Sub-step 2-3: grinding the specimen obtained in sub-step 2-2 with reference to the contour line obtained in sub-step 2-1 to obtain a cylindrical specimen with a certain roughness;

[0012] Sub-step 2-4: The specimen obtained in sub-step 2-3 is cast for a second time using a steel sleeve as a mold and fully cured to obtain a discontinuous structural surface with the required roughness, and a steel sleeve is attached to the outside with a strain gauge to obtain the specimen confining pressure;

[0013] Sub-step 2-5: Perform standard curing on the cylindrical specimen obtained from sub-step 2-4 and prepare for testing.

[0014] Step 3: Manually compare the contour line obtained in step 2 with the joint roughness coefficient (JRC) standard contour line to obtain the roughness coefficient of the structural surface.

[0015] Step 4: Use the modified split Hopkinson bar to test the cylindrical sample processed in step 2 to obtain the one-dimensional shear strength of the rock, which specifically includes the following sub-steps:

[0016] Sub-step 4-1: Modify the split Hopkinson bar to prepare for the plugging test;

[0017] Sub-step 4-2: Install strain gauges on the incident rod and the transmission rod respectively;

[0018] Sub-step 4-3: testing whether the impact short rod receiving device is normal. If normal, adding the impact short rod to the gas gun;

[0019] Sub-step 4-4: testing whether the time interval meter works properly;

[0020] Sub-step 4-5: Setting parameters of the transient waveform storage instrument and initializing it;

[0021] Sub-step 4-6: Clamp the specimen and arrange the protective cover;

[0022] Sub-step 4-7: Select appropriate air pressure for impact according to the required impact velocity to obtain one-dimensional impact shear strength.

[0023] Step 5: Based on the comparison results of step 3, on the basis of the one-dimensional impact shear strength of the contour line used for the specimen obtained in step 4, the shear strength and corresponding confining pressure of the specimen under different impact shear rates are calculated according to the known data such as the elastic modulus of the rod and sleeve.

[0024] Step 6: Evaluate the impact shear strength of the rock mass structural surface based on the results in step 5.

[0025] Preferably, in step 1, admixtures may be added to the mortar to reduce the curing time, but the strength of the specimens prepared with the mortar containing the admixtures should be consistent with the rock strength at the rock mass structural surface.

[0026] Preferably, in step 2, the size of the specimen is φ75mm×100mm, the gap between the inner and outer parts does not exceed 0.5mm when the specimen is assembled, and the surface unevenness is less than 0.05mm. If the size of the specimen is adjusted, the shape of the contour line also needs to be adjusted accordingly.

[0027] Preferably, in step 3, when the joint roughness coefficient obtained by manual comparison is unreliable, a relatively accurate value of the joint roughness coefficient can be obtained by referring to an empirical formula obtained by methods such as fractal dimension.

[0028] Specifically, in step 4, the specimens should be tested at different impact velocities, and at least three sets of valid results should be obtained for each impact velocity to better evaluate the stability of the structural surface under different impact loads.

[0029] The impact shear strength of the rock mass structural surface refers to the maximum stress value reached during the first stress rise during the impact process, that is, the maximum stress value that the structural surface can withstand to remain stable, not the maximum stress value during the entire impact process.

[0030] Specifically, in step 5, the impact shear strength of the structural surface is the ratio of the impact load obtained in step 4 to the side area of ​​the cylindrical specimen.

[0031] Beneficial effects:

[0032] 1. The present invention uses a modified split-Hopkinson bar test to measure the shear strength of the rock structure surface and evaluate the stability of the rock mass, filling the current gap in the evaluation of the impact shear strength of the rock structure surface and providing a more reliable laboratory measurement method.

[0033] 2. The present invention comprehensively considers multiple factors, including rock strength, structural surface roughness, impact shear velocity, etc., and provides a theoretical basis for the evaluation of surrounding rock stability, project site selection, excavation and support design of deep engineering. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 A schematic diagram of a split Hopkinson bar device modified according to the present invention,

[0035] Figure 2 This is a side view of the cylindrical specimen of the present invention.

[0036] Figure 3 This is a front view of the cylindrical specimen of the present invention.

[0037] Figure 4 This is a side view of the incident rod of the present invention.

[0038] Figure 5 This is a front view of the incident rod of the present invention,

[0039] Figure 6 This is a side view of the transmission rod of the present invention.

[0040] Figure 7 This is a front view of the transmission rod of the present invention.

[0041] Figure 8 This is a schematic diagram of the relationship between shear load and shear time in an embodiment of the present invention.

[0042] Fig. 9 Schematic diagram of the relationship between shear load and shear displacement in an embodiment of the present invention. DETAILED DESCRIPTION

[0043] The present invention is described in detail below in conjunction with the accompanying drawings and embodiments. It is worth noting that the embodiments are only used to explain the present invention, but do not constitute any limitation to the present invention.

[0044] The present invention provides a laboratory measurement method for the impact shear strength of a rock mass structural surface, comprising the following steps:

[0045] Step 1: Select the target rock mass structural surface and obtain the rock mass compressive strength by Schmidt hammer method. When obtaining the rock mass compressive strength, select a relatively straight structural surface. The position selected by Schmidt hammer method should be as close to the structural surface as possible to fully consider the influence of rock weathering. Prepare mortar and make the strength of the specimen prepared by the mortar consistent with the rock mass strength to obtain the mortar mix ratio.

[0046] Step 2: Select the target structural surface, use the contour comb to obtain the exposed contour line of the structural surface, and use the mortar obtained in step 1 to cast a one-dimensional cylindrical specimen, which specifically includes the following sub-steps:

[0047] Sub-step 2-1: Obtain the contour line of the structural surface through the contour comb, and digitize the contour line for machine tool processing;

[0048] Sub-step 2-2: prepare cylindrical specimens according to the mix ratio obtained in step 1 and fully cure them;

[0049] Sub-step 2-3: grinding the specimen obtained in step 2-2 with reference to the contour line obtained in step 2-1 to obtain a cylindrical specimen with a certain roughness;

[0050] Sub-step 2-4: Using a steel sleeve as a mold, the specimen obtained in sub-step 2-3 is cast for a second time and fully cured to obtain a discontinuous structural surface with the required roughness, with a steel sleeve attached to the outside to obtain the specimen confining pressure;

[0051] Sub-step 2-5: Perform standard curing on the specimens obtained in sub-step 2-4 in preparation for testing.

[0052] Step 3: Manually compare the contour line obtained in step 2 with the joint roughness coefficient (JRC) standard contour line to obtain the roughness coefficient of the structural surface;

[0053] Step 4: Perform a modified split Hopkinson bar test on the cylindrical specimen processed in step 2 to obtain the shear strength of the rock, which specifically includes the following sub-steps:

[0054] Sub-step 4-1: Modify the split Hopkinson bar to prepare for the plugging test;

[0055] Sub-step 4-2: Install strain gauges on the incident rod, the transmission rod and the sleeve respectively;

[0056] Sub-step 4-3: Test whether the impact short rod receiving device is normal, and if normal, add the impact short rod into the gas gun;

[0057] Sub-step 4-4: testing whether the time interval meter works properly;

[0058] Sub-step 4-5: Setting parameters of the transient waveform storage instrument and initializing it;

[0059] Sub-step 4-6: Clamp the specimen and arrange the protective cover;

[0060] Sub-step 4-7: Select appropriate air pressure for impact according to the required impact speed.

[0061] Step 5: See the instructions for Figure 7 and 8 On the basis of the one-dimensional impact shear strength of the contour line used by the specimen obtained through steps 3 and 4, the shear strength and corresponding confining pressure of the specimen under different impact shear rates are calculated according to the known data such as the elastic modulus of the rod and the sleeve.

[0062] Step 6: Evaluate the impact shear strength of the rock mass structural surface based on step 5.

[0063] Example 1

[0064] According to step 1 of the implementation method, the rock mass strength is obtained, wherein, when preparing the mortar, an admixture is added to reduce the curing time, but the strength of the mortar after curing should be consistent with the rock strength at the rock mass structural surface; refer to the attached manual Figure 2 ,3 , 4, 5, 6 and 7, the specimen size is φ75mm×100mm, the interval between the inner and outer joints of the specimen shall not exceed 0.5mm, and the surface unevenness shall be less than 0.05mm; Figure 1 Configure the device, check the device and make it work properly; refer to the instructions attached Figure 1 Install strain gauges on the incident rod, transmission rod and sleeve respectively; test whether the impact short rod receiving device is normal, and add the impact short rod to the gas gun if it is normal; test the time interval meter to make it work normally, set and initialize the transient waveform storage instrument, clamp the test piece and arrange the protective cover; finally, select the appropriate air pressure according to the required impact speed for impact, and stop the test after obtaining three sets of valid data for each condition.

[0065] After the laboratory test, the data obtained were processed and the results were as follows: Figure 8 , Fig. 9 It should be noted that the selected data segments are only the first reflected wave and the transmitted wave. The shear strength obtained when evaluating the rock mass is the shear strength that the structural surface can withstand while maintaining stability, rather than the maximum shear strength that the structural surface can withstand after displacement.

[0066] The present invention is described in detail above through embodiments. It should be noted that the above embodiments are only preferred embodiments of the present invention, not all embodiments of the present invention, and do not constitute any limitation on the scope of protection of the present invention. The scope of protection of the present invention is determined by the claims of this application document. Under the premise of not departing from the spirit of the present invention, the technical solutions or embodiments obtained by equivalent replacement or other various transformations of the technical features of the present invention by ordinary technicians in this field all fall within the scope of protection of the present invention.

Claims

1. A laboratory measurement method for the impact shear strength of a rock mass structural surface, characterized in that: The laboratory measurement method The following steps are involved: S1: Select the target rock mass structural surface, obtain the rock mass compressive strength by Schmidt hammer method, prepare mortar and make the strength of the specimen cast by the mortar consistent with the rock mass strength, and obtain the mortar mix ratio. When obtaining the rock mass compressive strength, a relatively straight structural surface should be selected, and the position selected by the Schmidt hammer method should be as close to the structural surface as possible; S2: Obtain the exposed contour line of the structural surface by contour comb, and cast a one-dimensional cylindrical specimen with the mortar obtained from step S1; S3: Manually compare the contour line obtained from step S2 with the standard contour line of joint roughness coefficient to obtain the roughness coefficient of the structural surface; S4: Use the modified split Hopkinson bar to test the cylindrical specimen prepared in step 2 to obtain the shear strength of the rock; S5: Based on the comparison result of step 3, on the basis of the one-dimensional impact shear strength of the contour line used for the specimen obtained in step 4, the shear strength of the specimen and the corresponding confining pressure at different impact shear rates are calculated according to the known data such as the elastic modulus of the rod and the sleeve; S6: Evaluate the impact shear strength of the rock mass structural surface based on the result in step S5.

2. A laboratory measurement method for the impact shear strength of a rock mass structure surface according to claim 1, characterized in that: In the step S1, admixtures may be added to the mortar to reduce the curing time, but the strength of the specimens prepared from the mortar with admixtures added should be consistent with the rock strength at the rock mass structural surface.

3. A laboratory measurement method for the impact shear strength of a rock mass structure surface according to claim 2, characterized in that: The step S2 specifically includes the following sub-steps: S2-1: using a contour comb to obtain the contour line of the structural surface, and digitizing the contour line for machine tool processing; S2-2: preparing a cylindrical specimen according to the mix ratio obtained in the step S1 and fully curing it; S2-3: grinding the specimen obtained from the sub-step S2-2 with reference to the contour line obtained in the sub-step S2-1 to obtain a cylindrical specimen with a certain roughness; S2-4: using a steel sleeve as a mold to cast the cylindrical specimen for a second time and fully curing it to obtain a discontinuous structural surface with a required roughness, and a steel sleeve with a strain gauge attached to the outside to obtain the specimen confining pressure; S2-5: performing standard curing on the cylindrical specimen obtained from the step S2-4, and preparing for testing.

4. A laboratory measurement method for the impact shear strength of a rock mass structure surface according to claim 3, characterized in that: The step S4 specifically includes the following sub-steps: S4-1: modifying the split Hopkinson bar to prepare for the impact test; S4-2: installing strain gauges on the incident bar, the transmission bar and the sleeve respectively; S4-3: testing whether the impact short rod receiving device is normal, and adding the impact short rod to the gas gun after it is normal; S4-4: testing whether the time interval meter works normally; S4-5: setting the parameters of the transient waveform storage instrument and initializing it; S4-6: clamping the test piece and arranging the protective cover; S4-7: selecting the appropriate air pressure for impact according to the required impact speed.

5. A laboratory measurement method for the impact shear strength of a rock mass structural surface according to claim 1, characterized in that: In step S2, the specimen size is φ75mm×100mm, the gap between the inner and outer parts of the specimen does not exceed 0.5mm when the specimen is assembled, and the surface roughness is less than 0.05mm. If the specimen size is adjusted, the contour shape also needs to be adjusted accordingly; in step S3, when the joint roughness coefficient obtained by manual comparison is unreliable, a relatively accurate joint roughness coefficient value can be obtained by referring to the empirical formula obtained from methods such as fractal dimension.

6. A laboratory measurement method for the impact shear strength of a rock mass structure surface according to claim 5, characterized in that: In step S4, the specimen should be tested at different impact speeds, and at least three groups of valid results should be obtained for each impact speed to better evaluate the stability of the structural surface under different impact loads.

7. A laboratory measurement method for the impact shear strength of a rock mass structure surface according to claim 6, characterized in that: In step S5, the impact shear strength of the structural surface is the ratio of the impact load obtained in step 4 to the side area of ​​the cylindrical specimen.

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