A comprehensive determination method for compressive strength of soft rocks

Abstract

The invention discloses a method for comprehensively determining the compressive strength of soft rocks, which relates to the technical field of rock mechanics. The method adopts three methods, namely, a uniaxial compressive strength test of rocks, a point load strength test of rocks and a rebound strength test of rocks. The compressive strength of soft rocks is comprehensively determined by analyzing the correlation between the results of different rock strength test methods and combining the actual conditions of the rocks. The invention is suitable for determining the compressive strength of soft rocks, can effectively improve the accuracy of determining the strength of soft rocks, and can reflect the strength characteristics of soft rocks to a greater extent.

Description

Technical Field

[0001] The invention relates to the technical field of rock mechanics, and in particular to a comprehensive determination method for the compressive strength of soft rocks. Background Art

[0002] The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.

[0003] Compressive strength refers to the ability of rock to resist crushing under unidirectional pressure. Rock compressive strength refers to the maximum stress that rock can withstand under pressure perpendicular to its surface. It is usually expressed as force per unit area, in megapascals (MPa) or kilopascals (kPa). The purposes of measuring rock compressive strength are as follows: 1) Civil engineering design: In civil engineering, rock compressive strength is an important parameter for evaluating the bearing capacity of foundations. By measuring rock compressive strength, the stability and safety of engineering construction can be ensured. 2) Rock mining and resource utilization: For the development and utilization of rock resources such as mining and quarrying, understanding rock compressive strength is an important basis for determining mining methods and equipment. 3) Geological disaster assessment: Measuring rock compressive strength helps to evaluate the stability of rock mass, predict and prevent geological disasters such as rock collapse and landslides. 4) Research on rock engineering properties: For the study of the mechanical behavior and characteristics of rocks, compressive strength is a basic indicator of rock mechanics, which is of great significance for a deep understanding of the mechanical behavior of rocks. 5) Earth Science Research: In earth science research, measuring the compressive strength of rocks helps to understand issues such as the evolution of the earth's crust and geological history.

[0004] In short, the purpose of measuring the compressive strength of rock is to evaluate the bearing capacity of rock, ensure engineering safety, guide resource development and utilization, and conduct in-depth research on rock mechanics, etc., and it has a wide range of application value. Commonly used test methods for rock compressive strength include direct method and indirect method. The direct method refers to applying pressure to the rock specimen until the specimen is destroyed and measuring the maximum pressure. The uniaxial compressive strength test of rock and the point load strength test of rock are often used. The indirect method refers to calculating the maximum pressure by measuring the deformation or strain of the rock specimen. The rock rebound strength test is often used. Although the technology for measuring the compressive strength of rock has been quite perfect, the current measurement methods for weak rocks are very limited, and their credibility is still questionable. Weak rock refers to rocks with low compressive strength and easy to deform or destroy. The compressive strength of weak rocks is not easy to determine, mainly because the compressive strength of weak rocks is relatively difficult to determine due to their low compressive strength, easy deformation, and cracks. The main reasons include: 1) Sampling difficulties: weak rocks are often broken or loose, and it is difficult to obtain representative samples. 2) Limitations of the test method: Traditional compressive strength tests have certain requirements for sample integrity and size, and weak rocks may not meet these requirements. 3) Large deformation: Weak rocks will deform significantly when under pressure, making it difficult to accurately measure strength parameters during the test. 4) Heterogeneity: The heterogeneity of weak rocks may lead to local damage during the test, making it difficult to obtain the overall compressive strength value. Summary of the invention

[0005] The purpose of the present invention is to provide a comprehensive determination method for the compressive strength of soft rock in response to the problems existing in the prior art. The method adopts three methods, namely, rock uniaxial compressive strength test, rock point load strength test and rock rebound strength test. By analyzing the correlation between the results of different rock strength test methods and combining the actual conditions of the rock, the compressive strength of the soft rock is comprehensively determined. The method is suitable for determining the compressive strength of soft rock, can effectively improve the accuracy of determining the strength of soft rock, and can reflect the strength characteristics of soft rock to a greater extent, thereby solving the above-mentioned problems.

[0006] The technical solution of the present invention is as follows:

[0007] A comprehensive determination method for the compressive strength of soft rock is provided. The uniaxial compressive strength test, point load strength test and rebound strength test of soft rock are respectively carried out on the soft rock. The compressive strength of the soft rock is comprehensively determined by analyzing the correlation between the results of the three rock strength test methods and combining the actual conditions of the rock.

[0008] Further, the following steps are included:

[0009] Step S1: performing multiple groups of rock uniaxial compressive strength tests on soft rocks;

[0010] Step S2: performing multiple groups of rock point load strength tests on the soft rock;

[0011] Step S3: performing multiple groups of rock rebound strength tests on the soft rock;

[0012] Step S4: analyzing the correlation of different rock strength test results by fitting multiple groups of uniaxial compressive strength test results, rock point load strength test results and rock rebound strength test results;

[0013] Step S5: By analyzing the correlation between the three rock strength test results and combining the actual situation of the soft rock, the compressive strength of the soft rock is comprehensively determined.

[0014] Furthermore, the step S1 comprises:

[0015] Step S11: specimen preparation, taking samples from the soft rock mass and preparing them into multiple cylindrical or cubic specimens according to the test requirements; the diameter and height of the specimens should be determined according to the maximum particle size of the soft rock and the test requirements;

[0016] Step S12: processing the specimen, processing the specimen into a smooth surface and ensuring that the geometric shape and size of the specimen meet the test requirements;

[0017] Step S13: test preparation, placing the test piece on the pressure plate of the testing machine, and adjusting the height and position of the testing machine to ensure that the test piece is subjected to pressure perpendicular to its axis;

[0018] Step S14: Load application: the testing machine starts to apply a load perpendicular to the axis of the specimen, and gradually increases the load until the specimen breaks; during the test, the deformation and strain data under different loads are recorded;

[0019] Step S15: Test data processing, drawing a stress-strain curve based on the test data; finding the peak load of the soft rock, that is, the maximum load before the specimen breaks; and calculating the uniaxial compressive strength of the soft rock based on the peak load and the geometric parameters of the specimen.

[0020] Furthermore, the step S2 comprises:

[0021] Step S21: specimen preparation, taking samples from the soft rock mass and preparing them into standard cylindrical specimens or directly selecting them; the thickness of the specimens should be determined according to the test requirements;

[0022] Step S22: processing the specimen, processing the specimen into a smooth surface and ensuring that the geometric shape and size of the specimen meet the test requirements;

[0023] Step S23: Test preparation, placing the specimen between the two ball-end cones of the point load instrument, and adjusting the height and position of the testing machine to ensure that the specimen is subjected to a pressure perpendicular to its axis;

[0024] Step S24: applying a load, applying a vertical concentrated load on the testing machine, increasing it at a certain speed until the specimen is destroyed; when the specimen is destroyed, recording the load value at the time of destruction;

[0025] Step S25: Result calculation: the rock point load strength index is calculated by placing the rock sample between the two ball-end cones of the point load meter, applying a vertical concentrated load until the sample fails, and then calculating it based on the size of the sample and the load value at the time of failure; based on the point load strength index and the physical and mechanical properties of the rock, the point load strength of the weak rock is estimated using an empirical formula or statistical method.

[0026] Furthermore, the step S3 includes:

[0027] Step S31: Sample preparation: taking samples from soft rock bodies, requiring the sample to have an aspect ratio between 1:1 and 1:2 and a thickness of not less than 50 mm; the sample surface is flat and has no obvious cracks or defects;

[0028] Step S32: Test equipment, placing the sample on a rock rebound strength tester; the rock rebound strength tester includes a heavy hammer and an elastic collision surface, the mass of the heavy hammer is greater than the weight of the sample, so as to ensure that the sample is subjected to sufficient impact load during collision;

[0029] Step S33: During the test, slowly lift the heavy hammer and make it collide with the sample at a certain speed; repeat the collision multiple times, and observe whether the sample has cracks or damage after each collision;

[0030] Step S34: data recording, during each collision process, record the falling height, collision speed, and collision energy parameters of the weight; at the same time, observe the deformation and damage of the sample, and record the residual height and residual width of the sample after each collision;

[0031] Step S35: Data processing, by analyzing the test data, the rebound strength of the soft rock is calculated.

[0032] Furthermore, the rebound strength is represented by the ratio of the collision energy to the residual height or residual width.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] A comprehensive determination method for the compressive strength of soft rock, which adopts three methods: rock uniaxial compressive strength test, rock point load strength test and rock rebound strength test. By analyzing the correlation of the results of different rock strength test methods and combining the actual situation of the rock, the compressive strength of soft rock is comprehensively determined. The three methods of rock uniaxial compressive strength test, rock point load strength test and rock rebound strength test have their own defects for soft rock. The difficulty of coring soft rock in the rock uniaxial compressive strength test leads to a large rock compressive strength. In the rock point load strength test, the rock sample is locally stressed, and there may be differences in different parts, which may not fully reflect the compressive strength of the whole rock body. In the rock rebound strength test, the porosity, cracks and structure of the soft rock affect the determination results, and there may be certain errors. Therefore, the three methods of rock uniaxial compressive strength test, rock point load strength test and rock rebound strength test are used to comprehensively determine the compressive strength of soft rock, which can effectively improve the accuracy and reliability of the determination results of the compressive strength of soft rock. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 This is a flow chart of a comprehensive determination method for compressive strength of soft rock;

[0036] Figure 2 Schematic diagram of rock test preparation and loading process;

[0037] Figure 3 It is a schematic diagram of the point load tester and the rock loading process;

[0038] Figure 4 Schematic diagram of rock test preparation and loading process;

[0039] Figure 5 Corrected point load index diagram for rock;

[0040] Figure 6a is the relationship diagram between rock point load strength and uniaxial compressive strength;

[0041] Figure 6b This is the relationship diagram between rock rebound strength and uniaxial compressive strength. DETAILED DESCRIPTION

[0042] It should be noted that relational terms such as "first" and "second" are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the existence of other identical elements in the process, method, article or device including the elements.

[0043] The features and performance of the present invention are further described in detail below in conjunction with the embodiments.

[0044] Embodiment 1

[0045] Accurate determination of the compressive strength of weak rocks requires a combination of different test methods and techniques, and special attention should be paid to sample preparation and test condition control during the experiment to improve the reliability of the test results. For the engineering application and research of weak rocks, it is usually necessary to comprehensively consider other mechanical properties and actual conditions on site. The uniaxial compressive strength test of rock is one of the most commonly used test methods in rock mechanics, which is used to determine the compressive strength of rock in a single direction. The uniaxial compressive strength test of rock has strict requirements on the size and accuracy of the specimen. The test process is cumbersome, time-consuming and costly. The biggest difficulty for weak rocks is the difficulty in coring. The experimental study on the calculation of the uniaxial compressive strength of rock based on different point load tests has practical significance and engineering application value. The rock point load strength test is a commonly used rock mechanics test method used to determine the compressive strength of rock under point load. This test is relatively simple, with low equipment requirements, and is suitable for smaller rock samples, such as core samples, which can be obtained on site. However, due to the local force, differences may occur in different parts, and may not fully reflect the compressive strength of the entire rock body. Rock rebound strength test is a commonly used non-destructive test method for evaluating the elastic properties of rocks. This test method evaluates the rebound performance of rocks by measuring the deformation recovered after being loaded. Rock rebound strength test refers to a simple test method that uses a rebound hammer to impact the surface of the rock mass, and determines the rock rebound strength according to the rebound value, and then obtains the rock compressive strength. The results of the rock rebound strength test are affected by the surface conditions of the rock, the test equipment and the operating technology. At the same time, the results are affected by factors such as the porosity, cracks and structure of the rock, and there may be certain errors. For weak rocks, rocks below a certain strength value cannot accurately measure the rock rebound strength, because the rebound hammer has a certain impact energy, which may crush the rock.

[0046] In summary, to determine the compressive strength of soft rock, three methods are needed: rock uniaxial compressive strength test, rock point load strength test and rock rebound strength test. By analyzing the correlation between the results of different rock strength test methods and combining the actual situation of the rock, the compressive strength of soft rock can be comprehensively determined.

[0047] For details, please refer to Figure 1 This embodiment proposes a comprehensive determination method for the compressive strength of soft rocks, which is as follows:

[0048] (1) Rock uniaxial compressive strength test: This test usually uses a cylindrical or cubic specimen and loads it under standard conditions until the specimen fails. The following is the general process of this test:

[0049] ① Specimen preparation: Take enough samples from the rock and prepare them into cylindrical or cubic specimens according to the test requirements. The diameter and height of the specimen should be determined according to the maximum particle size of the rock and the test requirements.

[0050] ② Specimen processing: Process the specimen into a smooth surface and ensure that the specimen’s geometry and size meet the test requirements.

[0051] ③Test preparation: Place the specimen on the pressure plate of the testing machine and adjust the height and position of the testing machine to ensure that the specimen is subjected to pressure perpendicular to its axis.

[0052] ④ Load application: The testing machine starts to apply a load perpendicular to the axis of the sample, gradually increasing the load until the sample breaks. During the test, the deformation and strain data under different loads are recorded.

[0053] ⑤Test data processing: Draw the stress-strain curve based on the test data. Find the peak load of the rock, that is, the maximum load before the sample breaks. Calculate the compressive strength of the rock based on the peak load and the geometric parameters of the sample.

[0054] ⑥Result analysis: Analyze the test results and evaluate the compressive properties and strength characteristics of the rock.

[0055] It should be noted that the size and processing accuracy of the specimen have a great influence on the test results, so the quality and dimensional accuracy of the specimen should be ensured when preparing the specimen. In addition, the test results also need to be corrected according to the size of the specimen and the test conditions to obtain the true compressive strength of the rock.

[0056] (2) Rock point load strength test: This method can directly select drilled cores and irregular rock blocks and prepare standard cylindrical specimens to conduct tests on a point load instrument. The following is the general process of this test:

[0057] ① Specimen preparation: Take enough samples from the rock and prepare them into standard cylindrical specimens or directly select them. The thickness of the specimen should be determined according to the test requirements.

[0058] ② Specimen processing: Process the specimen into a smooth surface and ensure that the specimen’s geometry and size meet the test requirements.

[0059] ③Test preparation: Place the specimen between the two ball-end cones of the point load instrument, and adjust the height and position of the testing machine to ensure that the specimen is subjected to pressure perpendicular to its axis.

[0060] ④ Load application: Apply a vertical concentrated load to the testing machine and increase it at a certain speed until the specimen fails. When the specimen fails, record the load value at failure.

[0061] ⑤ Result calculation: The rock point load strength index is calculated by placing the rock sample between the two ball-end cones of the point load instrument, applying a vertical concentrated load until the specimen fails, and then calculating it based on the size of the specimen and the load value at failure. Based on the point load strength index and the physical and mechanical properties of the rock, the compressive strength of the rock can be estimated using empirical formulas or statistical methods.

[0062] It should be noted that the size and processing accuracy of the specimen have a great influence on the test results, so the quality and dimensional accuracy of the specimen should be ensured when preparing the specimen. In addition, the test results also need to be corrected according to the size of the specimen and the test conditions to obtain the true compressive strength of the rock.

[0063] (3) Rock rebound strength test: The rock rebound strength test is a test method used to measure the recovery strength of rocks under impact or dynamic load. The following is the rock rebound strength test process:

[0064] ① Sample preparation: Take a sample of suitable size from the rock mass. The sample’s length-to-width ratio is usually required to be between 1:1 and 1:2, and the thickness should not be less than 50 mm. The sample surface should be flat, without obvious cracks and defects.

[0065] ②Test equipment: Place the sample on a rock rebound strength tester. The tester includes a heavy hammer and an elastic collision surface. The mass of the heavy hammer should be greater than the weight of the sample to ensure that the sample is subjected to sufficient impact load during collision.

[0066] ③Test process: Slowly lift the heavy hammer and make it collide with the sample at a certain speed. Repeat the collision several times and observe whether the sample has cracks or damage after each collision.

[0067] ④Data recording: During each collision, record the falling height, collision speed, collision energy and other parameters of the heavy hammer. At the same time, observe the deformation and damage of the sample, and record the residual height and residual width of the sample after each collision.

[0068] ⑤Data processing: Calculate the rock rebound strength by analyzing the test data. The rebound strength is usually expressed as the ratio of collision energy to residual height or residual width.

[0069] It should be noted that the results of the rock rebound strength test are affected by factors such as the size, shape, and material properties of the specimen, so the test results should be analyzed and evaluated based on the actual situation. At the same time, the safety of the specimen should be ensured during the test to avoid damage or loss of stability.

[0070] (4) Correlation analysis of different rock strength test results: The correlation of the results of different rock strength test methods was analyzed by fitting multiple sets of rock uniaxial compressive strength test data, rock point load strength test data, and rock rebound strength test data.

[0071] (5) Determine the test results: By analyzing the correlation between the three rock strength test results and combining them with the actual situation of the soft rock, the compressive strength of the soft rock is comprehensively determined.

[0072] Embodiment 2

[0073] Embodiment 2 is a specific application of a comprehensive determination method for compressive strength of soft rocks proposed in Embodiment 1.

[0074] Project Overview: Haba Snow Mountain is located on the southeastern edge of the Qinghai-Tibet Plateau, in the middle section of the Hengduan Mountains, on the left bank of the Jinsha River, and belongs to the plateau tectonic erosion landform area. The mountain is nearly north-south oriented, with low terrain on the left and high terrain on the right. It is located in the erosion platform of the Chongjiang River and the Jinsha River. The ground elevation is 2050-3400m, the terrain is undulating, the natural cross slope is 15°-40°, and some parts are steep cliffs. The tunnel is a mountain-crossing tunnel, and the slope vegetation is well developed, mostly pine forests. The total length of the tunnel is 9523m, and the maximum buried depth (1155m) is at about DK58+900 of the tunnel mileage. The overall orientation of a tunnel in the southwest is east-west. The total length of the tunnel is about 18km. It is designed as two single-hole single-slope tunnels. The entire line is planned to be constructed by drilling and blasting. The entrance and exit elevations are 3272m and 3700m respectively. The tunnel structure is buried at a depth of 500-1100m, and the general burial depth is 500-800m. The entrance and exit sections are relatively small, with a minimum burial depth of about 11m. The traffic conditions at the entrance of the tunnel are acceptable, and the slope of the exit section is high and narrow, without any roads, and traffic is extremely difficult. The cross-section of the tunnel is a horseshoe shape of "five-center circle + inverted arch", with a height of 10.87m and a width of 9.43m. It is excavated by the "three steps + inverted arch" method. The height of the upper step is about 2.6m, the height of the middle step is about 3.3m, the height of the lower step is about 2.6m, and the height of the inverted arch is about 2.5m. The total length of the tunnel is 17,803.3 meters, with a total of 50 meters of Grade III surrounding rock section, accounting for 0.28% of the entire line, with a total of one section; the total length of Grade IV surrounding rock section is 15,143.3 meters, accounting for 85.06% of the entire line, with a total of 12 sections; the total length of Grade V surrounding rock section is 2,610 meters, accounting for 14.66% of the entire line, with a total of 12 sections.

[0075] S1. Rock uniaxial compressive strength test: Rock uniaxial compressive strength test rock sample preparation and loading process as follows Figure 2 As shown, a DYE-2000 electro-hydraulic pressure testing machine was used for uniaxial compression test, and its technical indicators are: maximum test force 2000kN; test force accuracy ±1kN; maximum spacing between upper and lower pressure plates 320mm; pressure plate size 205×250mm; maximum piston stroke 50mm.

[0076] The uniaxial compressive test of rock was carried out by drilling cores inside and outside the tunnel, with a total of 60 groups. The minimum uniaxial compressive strength of the rock was 18.26MPa, the maximum uniaxial compressive strength was 79.59MPa, and it obeyed the normal distribution. The average uniaxial compressive strength was about 33.33MPa. Compared with the surrounding rock strength of the previous large deformation tunnel, the average uniaxial compressive strength was slightly larger, mainly because harder rocks were easier to coring successfully during the coring process. The drilling rig used in this test was a water drill. During the coring process, water was used to reduce the friction between the drill bit and the rock, reduce the temperature of the drill bit, and improve the quality of the drill core. However, during the coring process, it was found that the drilling speed of harder rocks was slower (0.3-0.6cm / min), the drilling speed of softer rocks was faster (more than 1.0cm / min), and it was difficult to coring extremely broken rocks. When the uniaxial compressive strength of rock is less than 18MPa, the core is easily broken during the core drilling process, mainly because of the development of internal cracks in the rock, the friction of the drill bit during the drilling process, and the effect of water, which eventually leads to the core breaking. However, through statistical analysis of the uniaxial compressive strength of rock, it is found that the rock in the tunnel area is relatively soft. In addition, the surrounding rock of the tunnel is not all soft rock, but mainly soft rock, with soft rock and hard rock coexisting. Most of the cores taken come from harder rocks.

[0077] S2. Rock point load strength test: Point load tester and rock loading process are as follows Figure 3 As shown. The point load tester mainly includes: ① Loading system, which consists of a jack, a pressure frame and a ball-end conical pressure plate. The maximum output of the jack is about 100kN, the piston stroke is 140mm, the diameter is 32mm, and the maximum spacing between loading points is 90mm. The loading frame has sufficient rigidity to ensure that no permanent distortion or deformation occurs under the repeated action of the maximum destructive load; the spherical curvature radius of the ball-end conical pressure plate is 5mm and it is made of hard material; ② Data recorder, the rock point load test data recorder uses a liquid crystal display with a pressure accuracy of 0.01kN. It uses a fast-charging battery and can record and store the peak value during rock loading. Point load rock specimens such as Figure 4 shown.

[0078] By statistically analyzing 100 sets of rock point load data, the point load index after size correction is as follows: Figure 5 The rock sample failure height ranges from 0.9 to 6.8 cm, and has a linear correlation with the peak load: y = 1.4x, with a correlation coefficient of R 2 is 0.74; the damage width range is 2.4 to 16.5 cm, and has a linear correlation with the peak load: y = 0.81x, and the correlation coefficient R 2 =0.72; damage area range 3.77~89.10cm 2 , has a linear correlation with the peak load: y = 0.18x, correlation coefficient R2 =0.71; the equivalent failure diameter ranges from 2.19 to 10.65 cm, and the failure load ranges from 0.6 to 16.9 kN; the rock point load index ranges from 0.16 to 9.32 MPa, with an average value of 2.16 MPa, showing a typical normal distribution. Most of the rock failure in the point load test occurs from the penetrating joint surface or crack surface.

[0079] S3. Rock rebound strength test: On-site rebound test should select representative complete rock mass (stone), different types of weathered rock (except fully weathered) and structural rock. During the test, the rebound hammer should be perpendicular to the rock surface, and angle correction should be made when it is at other angles. The number of hammer strikes at each point should be no less than 16 times, and the maximum and minimum values ​​should be discarded 3 times each. The average value is calculated from the remaining 10 times. Technical indicators of HT225-B integrated digital rebound hammer: nominal kinetic energy 2.207J, spring stiffness 785±30N / m, spring stretch length 75±0.3mm.

[0080] There are 82 groups of rock rebound strength, with rock rebound strength ranging from 12.12 to 58.99 MPa, and an average of 28.42 MPa. Generally speaking, the rebound strength of C30 concrete is above 34.2 MPa, which shows that the rock rebound strength is relatively low. However, the minimum rebound strength is 12.12 MPa, which may also be determined by the strength test method. Rocks below this value cannot accurately measure the rock rebound strength because the rebound hammer has a certain impact energy, which may crush the rock. Of course, the above results include test results inside and outside the cave. When testing inside the cave, the rebound strength of the unexcavated rock can be directly measured. Since the constraints of the unexcavated rock mass are strong, it is easier to conduct rebound strength tests. Tests outside the cave are more targeted at relatively intact large rocks.

[0081] S4. Correlation analysis of different rock strength test results: By fitting 100 sets of point loads, 82 sets of rebound and 60 sets of uniaxial compression test data, such as Figure 6a and Figure 6bAs described above, the correlation of the results of different rock strength test methods was analyzed. The uniaxial compressive strength of rock has a linear correlation with the rebound strength and point load strength. The relationship between the point load index and the uniaxial compressive strength of rock is: y = 10.97x, the correlation coefficient is 0.93, and the correlation is high; it can be seen that the uniaxial compressive strength of rock measured by the point load test is between 1.76 and 102.24MPa, with an average value of 23.7MPa; the relationship between the rebound strength and the uniaxial compressive strength of rock is: y = 1.26x-7.39, the correlation coefficient is 0.76, and the correlation is lower than the point load; the blue area is the 95% confidence band. As the rock point load index increases, the confidence area of ​​the relationship between the point load index and the uniaxial compressive strength increases; as the rebound strength increases, the confidence area of ​​the relationship between the rebound and the uniaxial compressive strength decreases first and then increases. Therefore, for the determination of the strength of weak surrounding rock, considering the characteristics of rock rebound strength, it is recommended to use the method of point load and uniaxial compressive strength for comprehensive determination.

[0082] The relationship between the uniaxial compressive strength of rock and the point load index includes two cases where the intercept is 0 and non-0. However, the loading methods of the point load and uniaxial compression test are similar, both of which gradually increase the load at the upper and lower ends, but the loading form is different. Based on this, it is recommended that the relationship between the uniaxial compressive strength of rock and the point load index be fitted using a linear formula with an intercept of 0. In comparison, the loading method of the rebound hammer is different from the above two methods. It mainly obtains the surface strength of the rock through instantaneous energy impact. When the rock is soft, this loading method is not applicable. The above studies show that the rebound hammer is only suitable for the rebound strength test of concrete or rock not less than 10MPa.

[0083] (5) Determination of the test results: The minimum uniaxial compressive strength of the rock is 18.26 MPa, the maximum uniaxial compressive strength is 79.59 MPa, which obeys the normal distribution, and the average uniaxial compressive strength is about 33.33 MPa; the rock point load index (I s(50) ) ranges from 0.16 to 9.32 MPa, with an average value of 2.16 MPa; the rock rebound strength is 12.12 to 58.99 MPa, with an average value of 28.42 MPa; the relationship between the point load index and the uniaxial compressive strength of rock is: y = 10.97x, with a correlation coefficient of 0.93; the relationship between the rebound strength and the uniaxial compressive strength of rock is: y = 1.26x-7.39, with a correlation coefficient of 0.76.

[0084] The above-mentioned embodiments only express the specific implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the protection scope of the present application. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the technical solution concept of the present application, and these all belong to the protection scope of the present application.

[0085] This background section is provided to generally present the context of the invention, and the work of the presently named inventors, the work to the extent described in this background section, and aspects of this section that did not constitute prior art at the time of application are neither explicitly nor implicitly admitted to be prior art to the present invention.

Claims

1. A comprehensive determination method for compressive strength of soft rock, characterized in that: The soft rock is subjected to rock uniaxial compressive strength test, rock point load strength test and rock rebound strength test respectively. By analyzing the correlation of the results of the three rock strength test methods and combining the actual conditions of the rock, the compressive strength of the soft rock is comprehensively determined. The specific steps include: Step S1: performing multiple groups of rock uniaxial compressive strength tests on soft rocks; Step S2: performing multiple groups of rock point load strength tests on the soft rock; Step S3: performing multiple groups of rock rebound strength tests on the soft rock; Step S4: analyzing the correlation of different rock strength test results by fitting multiple groups of uniaxial compressive strength test results, rock point load strength test results and rock rebound strength test results; Step S5: By analyzing the correlation between the three rock strength test results and combining the actual situation of the soft rock, the compressive strength of the soft rock is comprehensively determined; The step S3 comprises: Step S31: Sample preparation: taking samples from soft rock bodies, requiring the sample to have an aspect ratio between 1:1 and 1:2 and a thickness of not less than 50 mm; the sample surface is flat and has no obvious cracks or defects; Step S32: Test equipment, placing the sample on a rock rebound strength tester; the rock rebound strength tester includes a heavy hammer and an elastic collision surface, the mass of the heavy hammer is greater than the weight of the sample, so as to ensure that the sample is subjected to sufficient impact load during collision; Step S33: During the test, slowly lift the heavy hammer and make it collide with the sample at a certain speed; repeat the collision multiple times, and observe whether the sample has cracks or damage after each collision; Step S34: data recording, during each collision process, record the falling height, collision speed, and collision energy parameters of the weight; at the same time, observe the deformation and damage of the sample, and record the residual height and residual width of the sample after each collision; Step S35: data processing, calculating the rebound strength of the soft rock by analyzing the test data; The rebound strength is expressed as a ratio of collision energy to residual height or residual width.

2. A method for comprehensively determining the compressive strength of soft rock according to claim 1, characterized in that: The step S1 comprises: Step S11: specimen preparation, taking samples from the soft rock mass and preparing them into multiple cylindrical or cubic specimens according to the test requirements; the diameter and height of the specimens should be determined according to the maximum particle size of the soft rock and the test requirements; Step S12: processing the specimen, processing the specimen into a smooth surface and ensuring that the geometric shape and size of the specimen meet the test requirements; Step S13: test preparation, placing the test piece on the pressure plate of the testing machine, and adjusting the height and position of the testing machine to ensure that the test piece is subjected to pressure perpendicular to its axis; Step S14: Load application: the testing machine starts to apply a load perpendicular to the axis of the specimen, and gradually increases the load until the specimen breaks; during the test, the deformation and strain data under different loads are recorded; Step S15: Test data processing, drawing a stress-strain curve based on the test data; finding the peak load of the soft rock, that is, the maximum load before the specimen breaks; and calculating the uniaxial compressive strength of the soft rock based on the peak load and the geometric parameters of the specimen.

3. A method for comprehensively determining the compressive strength of soft rocks according to claim 2, characterized in that: The step S2 comprises: Step S21: specimen preparation, taking samples from the soft rock mass and preparing them into standard cylindrical specimens or directly selecting them; the thickness of the specimens should be determined according to the test requirements; Step S22: processing the specimen, processing the specimen into a smooth surface and ensuring that the geometric shape and size of the specimen meet the test requirements; Step S23: Test preparation, placing the specimen between the two ball-end cones of the point load instrument, and adjusting the height and position of the testing machine to ensure that the specimen is subjected to a pressure perpendicular to its axis; Step S24: applying a load, applying a vertical concentrated load on the testing machine, increasing it at a certain speed until the specimen is destroyed; when the specimen is destroyed, recording the load value at the time of destruction; Step S25: Result calculation: the rock point load strength index is calculated by placing the rock sample between the two ball-end cones of the point load meter, applying a vertical concentrated load until the sample fails, and then calculating it based on the size of the sample and the load value at the time of failure; based on the point load strength index and the physical and mechanical properties of the rock, the point load strength of the weak rock is estimated using an empirical formula or statistical method.

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