Preparation method of soft rock standard cylinder sample

Abstract

According to the preparation method of the soft rock standard cylinder sample provided by the invention, the soft rock test block is wrapped by the fast-hardening gypsum, and after the gypsum is cured, the bond stress on the soft rock test block is provided, and the overall stability of the soft rock test block is enhanced, so that the soft rock test block can bear the impact force of direct turning of a lathe. Then turning the soft rock test block wrapped by the gypsum by using a lathe to form a standard cylinder sample in one step, and obtaining the standard cylinder sample of which the diameter tolerance is less than 0.05 mm only through one-time rough turning without re-grinding; meanwhile, one end face of the standard cylinder sample is directly turned and flattened, and the flatness is high; and the other end face is cut off by linear cutting, and the non-parallelism of the two end faces is less than 0.05 mm. According to the method, the standard sample meeting the national standard can be efficiently and stably prepared, the preparation success rate can reach 90% or above, and the problems that an existing soft rock sample is low in preparation efficiency and low in preparation success rate are well solved.

Description

Technical Field

[0001] The invention belongs to the field of rock mechanics tests, and in particular relates to a method for preparing a standard cylindrical sample of soft rock. Background Art

[0002] In the construction of tunnels, it is inevitable to encounter soft rock. Soft rock generally refers to rock with weak rock quality, low bearing capacity, developed joints and fissures, and broken structure. If the tunnel is not properly handled when passing through the soft surrounding rock, it is very easy to cause large deformation and collapse. In order to master the mechanical parameter properties of soft rock, indoor tests are still the main means to study the various properties of rock and the deformation and failure laws under different stress conditions. In particular, triaxial tests require the production of standard cylindrical specimens of specific sizes according to the requirements of the specifications. The production of rock specimens is a crucial step. According to the requirements of the Engineering Rock Test Method Standard (GB / T50266-2013), the diameter of the standard cylindrical specimen is (50) mm, the height-to-diameter ratio is (2±0.2), the upper and lower diameter deviation should not be greater than 0.3 mm, the maximum and minimum height deviations should be controlled within 0.05 mm, and the non-parallelism of the two end faces of the specimen should not be greater than 0.05 mm. If the specimen size does not meet the standard requirements, there will be many errors in the experimental results, affecting the accuracy of the test results. If general cutting tools are used for manual cutting, it is difficult to control the size of the cut cylinder to obtain a standard cylindrical specimen, and thus it is impossible to carry out relevant indoor test research, or the sample preparation success rate is very low and it is impossible to obtain sufficient specimens to conduct a large number of tests to draw reliable conclusions.

[0003] Chinese patent publication number CN111482852A discloses an integrated device for cutting and grinding layered soft rock standard test blocks and a method for using the device. The device has a three-layer structure, including a base arranged on the first layer, a mobile cutting mechanism and a horizontal grinding mechanism arranged on the second layer, and a turntable mechanism arranged on the third layer. After the rock test block is fixed, the test block is first cut into a hexahedron by the mobile cutting mechanism on the second layer, and then the six planes of the hexahedron test block are respectively ground using the horizontal grinding mechanism on the second layer to form a cubic standard rock test block, and then a grinding rod is inserted to grind the cubic standard test block into a standard cylindrical test block. However, the preparation steps of the standard cylindrical test block are relatively complicated. It needs to be first polished to form a hexahedron and then polished to form a standard cylinder. In addition, soft rock is relatively weak and has a low bearing capacity. Direct multiple polishing can easily cause the soft rock test block to crack and cause the test block preparation to fail. In addition, to prepare a cylindrical sample, a cubic test block must be prepared first, and then polished to form a cylindrical test block. The combination of two cutting methods and two polishing methods has a long preparation cycle and requires reliance on specific equipment. It is still difficult to meet the preparation needs of standard samples for indoor soft rock tests. Summary of the invention

[0004] In order to solve the above technical problems, the present invention provides a method for preparing a standard cylindrical specimen of soft rock, and its purpose is to provide a method for preparing a standard cylindrical specimen with high preparation efficiency and stable test block quality.

[0005] To achieve the above object, the present invention provides a method for preparing a standard cylindrical sample of soft rock, comprising the following steps:

[0006] S1. Sampling of soft rock specimens: Soft rock specimens are produced by tunnel excavation or obtained by wire cutting;

[0007] S2. Rock sample pretreatment: Use compressed air to blow away the surface scum of the soft rock specimens, and wrap the rock samples with plastic wrap several times to ensure that external water cannot contact the rock samples;

[0008] S3, preparing the sample to be cut: placing the rock sample wrapped in the plastic wrap in step S2 at the center of the bottom of a sample preparation barrel with an inner diameter of D mm, and making the bottom of the rock sample parallel to the bottom of the sample preparation barrel or at a preset inclination angle as required, and then adding the prepared rapid hardening gypsum liquid into the sample preparation barrel, the rapid hardening gypsum liquid must cover the top of the rock sample, and taking it out after the rapid hardening gypsum liquid is solidified as a whole, so as to obtain a cylindrical sample to be cut;

[0009] S4, turning: fix the first end of the sample to be cut obtained in step S3 on the three-jaw chuck of a lathe, with a clamping length greater than 20 mm, first turn the end face of the second end until the end face is flat; then control the cutting tool to turn the cylinder from the second end of the sample to be cut to the first end, with a turning depth of (Dd) / 2 mm, a lathe spindle speed of 350-600 r / min, a feed rate of 70-120 mm / min, and no turning is performed on the clamping part of the first end of the sample to be cut, and the sample that has been turned is removed to obtain a semi-finished soft rock standard cylindrical specimen;

[0010] S5, truncation: accurately measuring and truncating the semi-finished soft rock standard cylindrical sample processed in step S4 from the second end to the first end by a preset length to obtain a standard soft rock cylindrical sample;

[0011] Wherein, d is the diameter of the standard cylindrical specimen of soft rock, Dd≥20 mm, and the truncation method in step S5 is wire cutting.

[0012] Preferably, the method for obtaining rock samples by wire cutting in step S1 comprises the following steps:

[0013] S11, select a sampling location for a soft rock specimen, demarcate a square area, and drill holes with a diameter of 0.1 m at the four corners of the square area;

[0014] S12, inserting wire cutting machines into two parallel sides of the square area in sequence, and cutting out large rock samples from the four sides of the positive direction area;

[0015] S13, cutting off the bottom of the square area with a wire cutting machine to extract a large square rock sample;

[0016] S14. Cut the large square rock sample into soft rock specimens with a square cross-section and a side length of ≥60 mm using a wire cutting machine, and the height of the soft rock specimens is ≥130 mm.

[0017] Preferably, the inner wall of the sample preparation barrel is provided with angle auxiliary marking lines to quickly confirm the pre-cutting angle of the soft rock specimen sample; two length auxiliary marking lines are provided along the diameter direction at the bottom of the sample preparation barrel, and the two length auxiliary marking lines are perpendicular to each other to quickly adjust and confirm that the soft rock specimen sample is in the center position of the sample preparation barrel.

[0018] Preferably, the method for controlling the preset inclination angle between the bottom of the rock sample and the bottom of the sample preparation barrel in step S3 is: first, add an appropriate amount of rapid hardening gypsum to the sample preparation barrel to form an inclined surface with a preset inclination angle with the bottom of the sample preparation barrel, and then place the rock sample vertically on the center of the inclined surface to control the preset inclination angle between the bottom of the rock sample and the bottom of the sample preparation barrel.

[0019] Preferably, the mass ratio of gypsum to water in the rapid hardening gypsum liquid is 1:2.

[0020] Preferably, the diameter d of the soft rock standard cylindrical sample is 50 mm, and the preset length of the truncation in step S5 is 100 mm.

[0021] Preferably, the preset inclination angle in step S3 is greater than 0° and less than or equal to 10°.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] (1) The present invention creatively uses rapid hardening gypsum to wrap the soft rock test block. After the gypsum is cured, it provides a gripping force for the soft rock test block, greatly enhancing the overall stability of the soft rock test block, thereby ensuring that the soft rock test block can withstand the impact force of direct turning processing on a lathe.

[0024] (2) The present invention directly uses conventional lathe tools to turn the soft rock test block to form a standard cylindrical specimen in one step, and only one rough turning is required to obtain a diameter tolerance of the standard cylindrical specimen of less than 0.05 mm, which is much higher than the national standard GB / T 50266-2013 that the diameter deviation of the upper and lower ends should not be greater than 0.3 mm, and no further grinding is required; at the same time, one end face of the standard cylindrical specimen is directly turned flat with high flatness; the other end face is cut by wire cutting. Since the diameter tolerance of the standard cylinder itself is extremely small after turning, the second end face obtained by wire cutting is also basically strictly perpendicular to the axis of the standard cylinder, and the non-parallelism of the two end faces is less than 0.05 without further grinding, which meets the national standard GB / T 50266-2013 on end face parallelism.

[0025] (3) The present invention uses gypsum to wrap the soft rock test block. The plasticity of the gypsum can be used to conveniently adjust the pre-tilt angle of the soft rock test block. Combined with turning processing, standard cylindrical soft rock specimens with different inclination angles can be directly and quickly obtained. The angle auxiliary marking line in the sample preparation barrel can accurately locate the inclination angle, which is simple and reliable.

[0026] (4) The method for preparing the soft rock standard cylindrical sample of the present invention only requires conventional equipment to efficiently and stably prepare standard samples that meet national standards with a high preparation success rate, which effectively solves the current problem of low preparation efficiency and low preparation success rate of soft rock samples. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0028] Figure 1 This is a schematic diagram of the overall structure of the sample preparation barrel of the present invention;

[0029] Figure 2 This is a top view of the overall structure of the sample preparation barrel of the present invention;

[0030] Figure 3 This is a structural cross-sectional view of the bottom of the soft rock sample in Example 1, which is parallel to the bottom of the sample preparation barrel;

[0031] Figure 4 It is a structural cross-sectional view of the bottom of the soft rock sample in Example 2, in which the bottom of the sample preparation barrel is at a preset inclination angle;

[0032] Figure 5 This is a product picture of a standard cylindrical sample of soft rock prepared in Example 1 of the present invention.

[0033] Description of Reference Numerals

[0034] 1- sample preparation bucket; 2- angle auxiliary marking line; 3- length auxiliary marking line; 4- soft rock specimen rock sample; 5- gypsum layer. DETAILED DESCRIPTION

[0035] In order to make the technical problems, technical solutions and advantages to be solved by the present invention more clear, a detailed description will be given below with reference to the accompanying drawings and specific embodiments.

[0036] The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention. Without departing from the spirit and substance of the present invention, modifications or substitutions made to the methods, steps or conditions of the present invention are within the scope of the present invention.

[0037] Unless otherwise specified, the technical means used in the examples are conventional means well known to those skilled in the art; unless otherwise specified, the reagents used in the examples are commercially available.

[0038] Example 1

[0039] Prepare the standard cylindrical specimen of soft rock according to the following steps:

[0040] S1. Sampling of soft rock specimens: Soft rock specimens were obtained by wire cutting. The sampling location of soft rock specimens was selected, and a 1.2m*1.2m square area was demarcated. First, holes with a diameter of 0.1m and a depth of 1m were drilled at the four corners. Then, the wire cutting machine was inserted into the two parallel sides of the square area in turn, and large rock samples were cut out from the four sides of the positive direction area. Then, the wire cutting machine was used to cut off the bottom of the square area, and the large square rock samples were taken out. The large square rock samples were cut at a suitable height without any fracture marks, and the wire cutting machine was used to cut into 12 rectangular soft rock specimens with a length, width and height of 60mm, 60mm and 130mm respectively.

[0041] The diameter d of the standard soft rock cylindrical specimen processed in this embodiment is 50 mm, the height is 100 mm, and the height-to-diameter ratio is 2. Therefore, the cross section of the rectangular soft rock specimen formed is a square with a side length of 60 mm, which can ensure that a cylinder with a diameter of 50 mm can be processed and the turning allowance can be reduced, thereby improving the processing efficiency and quality.

[0042] S2. Rock sample pretreatment: Blow the surface scum of the 60mm*60mm*130mm soft rock sample obtained above with compressed air, and wrap the rock sample with plastic wrap for many times to ensure that external water cannot contact the rock sample, so as to prevent water from contacting the soft rock sample when gypsum liquid is added later, causing the soft rock to collapse. In this embodiment, wrapping the rock sample with plastic wrap is more suitable than conventionally applying waterproof coating, because the waterproof coating will penetrate into the rock surface, thereby affecting the strength of the soft rock.

[0043] S3, preparing the sample to be cut: placing the rock sample wrapped with plastic wrap in step S2 at the bottom center of the sample preparation barrel 1.

[0044] The sample preparation barrel 1 is cylindrical with an inner diameter of 80 mm, the top is open, and two length auxiliary marking lines 3 are set along the diameter direction at the bottom. The two length auxiliary marking lines 3 are perpendicular to each other, and the focus of the two length auxiliary marking lines 3 is the center of the bottom circle. When the rock sample is placed at the bottom, the distance between the four sides of the rock sample and the center of the bottom circle is adjusted by the length auxiliary marking lines 3 to be basically consistent, and the rock sample can be quickly confirmed to be at the center of the bottom of the sample preparation barrel.

[0045] After the rock sample is placed in the sample preparation barrel 1, the prepared quick-hardening gypsum liquid is added to the sample preparation barrel 1. The quick-hardening gypsum liquid needs to cover the top of the rock sample by 10 to 20 mm. After the quick-hardening gypsum liquid is solidified and formed as a whole, it is taken out from the sample preparation barrel 1 as a whole to obtain a cylindrical sample to be cut. In order to more conveniently take out the cylindrical sample to be cut from the sample preparation barrel 1, the sample preparation barrel 1 can be designed to be a combination of two symmetrical semi-cylinders. After the gypsum hardens, the two semi-cylinders can be disassembled to directly obtain the cylindrical sample to be cut. Of course, the specific opening and closing structure of the sample preparation barrel 1 can also be other structures that are convenient for combination and sample removal, which will not be repeated here.

[0046] In addition, the inner diameter of the sample preparation barrel 1 determines the diameter of the cylindrical sample to be cut. The larger the diameter of the cylindrical sample to be cut, the thicker the wrapped gypsum layer, and the stronger the gripping force provided to the soft rock sample. However, the machining allowance of the turning process will also increase. Technical personnel in this field can select other suitable inner diameters of the sample preparation barrel according to the specific conditions of the rock sample.

[0047] S4, turning: fix the first end of the cylindrical sample to be cut obtained in step S3 on the three-jaw chuck of the lathe, with a clamping length greater than 20mm, and first turn the end face of the second end until the end face is flat; then control the cutting tool to turn the cylinder from the second end of the sample to be cut to the first end, with a turning depth of (80-60) / 2=10mm, a lathe spindle speed of 600r / min, and a feed rate of 120mm / min. The clamping part of the first end of the sample to be cut is no longer turned, and the sample that has been turned is removed to obtain a semi-finished soft rock standard cylindrical sample. In this embodiment, since the sample to be cut is reinforced with gypsum, the processed part has lost the gypsum wrapping and cannot provide stable support. If the first end and the second end need to be swapped according to the conventional turning steps, the first end is turned again, but in this application, the first end (clamping end) that has not been turned cannot be directly turned.

[0048] S5, cutting: the semi-finished soft rock standard cylindrical sample processed in step S4 is cut by wire cutting at a length of 100 mm accurately measured from the second end to the first end to obtain a standard soft rock cylindrical sample with a diameter of 50 mm and a height of 100 mm.

[0049] The cross-sectional view of the cylindrical sample to be cut obtained in this embodiment is as follows: Figure 3 As shown, the gypsum layer 5 is wrapped around the outer periphery of the soft rock specimen sample 4. The cylindrical sample to be cut is formed by lathe cutting. Figure 3 The cylindrical standard specimen is shown within the dotted line.

[0050] The standard soft rock cylindrical sample products are as follows: Figure 5 As shown, after testing with a vernier caliper, the diameter tolerance of the standard soft rock cylindrical specimen is less than 0.05mm, the non-parallelism of the two end faces is less than 0.05mm, and the surface is relatively smooth, which fully meets the requirements of GB / T50266-2013 for standard soft rock cylindrical specimens.

[0051] In this embodiment, a total of 12 cuboid soft rock specimens were obtained, and after turning, 11 of them were successfully processed into standard soft rock cylindrical specimens that meet the standard requirements, and only one failed due to cracking during turning, and the processing success rate reached 91.7%. The preparation method of the present application well solves a series of problems such as the current standard soft rock cylindrical specimen processing steps are cumbersome, the specimens do not meet the standards, the processing efficiency is low, and the processing success rate is low.

[0052] Example 2

[0053] Prepare the standard cylindrical specimen of soft rock with pre-tilt angle according to the following steps:

[0054] S1. Sampling of soft rock specimens: Soft rock specimens were obtained by wire cutting. The sampling location of soft rock specimens was selected, and a 1.2m*1.2m square area was demarcated. First, holes with a diameter of 0.1m and a depth of 1m were drilled at the four corners. Then, the wire cutting machine was inserted into the two parallel sides of the square area in turn, and large rock samples were cut out from the four sides of the positive direction area. Then, the wire cutting machine was used to cut off the bottom of the square area, and the large square rock samples were taken out. The large square rock samples were cut at a suitable height without any fracture marks, and the wire cutting machine was used to cut to form multiple rectangular soft rock specimens with a length, width and height of 80mm, 80mm and 150mm respectively.

[0055] S2. Rock sample pretreatment: Use compressed air to blow off the scum on the surface of the soft rock specimen of 80mm*80mm*150mm obtained above, and wrap the rock sample with plastic wrap for several times.

[0056] S3. Prepare the sample to be cut: Figure 4As shown, first add an appropriate amount of quick-hardening gypsum liquid to the sample preparation barrel 1 to form a slope with a preset inclination angle α with the bottom of the sample preparation barrel, and quickly adjust the preset inclination angle α of the slope according to the angle auxiliary marking line on the inner wall of the sample preparation barrel 1. Then place the rock sample at the center of the slope with the preset inclination angle α, and the rock sample is perpendicular to the slope to control the preset inclination angle α between the bottom of the rock sample and the bottom of the sample preparation barrel. Where 0°<α≤10°, by Figure 4 It can be seen that if the preset inclination angle is too large, the length and width of the rectangular soft rock specimen placed in the sample preparation barrel are required to be larger to ensure that the standard cylinder formed by cutting meets the requirements of 50mm in diameter and 100mm in height. However, the larger the length and width of the rectangular soft rock specimen, the larger the diameter of the sample to be cut, which makes the turning process more difficult and is not suitable for processing by this method. The preset inclination angle α in this embodiment is 8°, and a rectangular soft rock specimen with a cross section of 80mm*80mm can be selected, and the inner diameter of the corresponding sample preparation barrel 1 is adjusted to 100mm.

[0057] After the rock sample is placed in the sample preparation barrel 1, continue to add the prepared quick-hardening gypsum liquid into the sample preparation barrel 1. The quick-hardening gypsum liquid needs to cover the top of the rock sample by 10 to 20 mm. After the quick-hardening gypsum liquid is solidified as a whole, it is taken out of the sample preparation barrel 1 as a whole to obtain a cylindrical sample to be cut.

[0058] S4, turning: fix the first end of the cylindrical sample to be cut obtained in step S3 on the three-jaw chuck of a lathe, with a clamping length greater than 20 mm, first turn the end face of the second end until the end face is flat; then control the cutting tool to turn the cylinder from the second end of the sample to be cut to the first end, with a turning depth of (100-60) / 2=20 mm, a lathe spindle speed of 400 r / min, a feed rate of 70 mm / min, and no longer turn the clamping part of the first end of the sample to be cut, remove the sample after turning to obtain a semi-finished soft rock standard cylindrical specimen.

[0059] S5, cutting: the semi-finished soft rock standard cylindrical sample processed in step S4 is cut by wire cutting at a length of 100 mm accurately measured from the second end to the first end to obtain a standard soft rock cylindrical sample with a diameter of 50 mm and a height of 100 mm.

[0060] The standard soft rock cylindrical sample product prepared in this embodiment is tested by a vernier caliper, and the diameter tolerance is less than 0.05 mm, the non-parallelism of the two end faces is less than 0.05 mm, and the surface is relatively smooth, which fully meets the requirements of GB / T 50266-2013 for standard soft rock cylindrical samples.

[0061] The above descriptions are merely embodiments of the present invention and are not intended to limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made using the contents of the invention specification, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A method for preparing a standard cylindrical specimen of soft rock, characterized in that: The following steps are involved: S1. Sampling of soft rock specimens: Soft rock specimens are produced by tunnel excavation or obtained by wire cutting; S2. Rock sample pretreatment: Use compressed air to blow away the scum on the surface of the soft rock sample, and wrap the rock sample with plastic wrap several times to ensure that external water cannot contact the rock sample; S3, preparing the sample to be cut: placing the rock sample wrapped with the plastic wrap in step S2 at the center of the bottom of a sample preparation barrel (1) with an inner diameter of D mm, and making the bottom of the rock sample parallel to the bottom of the sample preparation barrel (1) or at a preset angle as required, and then adding the prepared rapid hardening gypsum liquid into the sample preparation barrel (1), the rapid hardening gypsum liquid must cover the top of the rock sample, and taking it out after the rapid hardening gypsum liquid is solidified and formed as a whole, so as to obtain a cylindrical sample to be cut; S4, turning: fix the first end of the sample to be cut obtained in step S3 on the three-jaw chuck of a lathe, with a clamping length greater than 20 mm, first turn the end face of the second end until the end face is flat; then control the cutting tool to turn the cylinder from the second end of the sample to be cut to the first end, with a turning depth of (Dd) / 2 mm, a lathe spindle speed of 350-600 r / min, a feed rate of 70-120 mm / min, and no turning is performed on the clamping part of the first end of the sample to be cut, and the sample that has been turned is removed to obtain a semi-finished soft rock standard cylindrical specimen; S5, truncation: accurately measuring and truncating the semi-finished soft rock standard cylindrical sample processed in step S4 from the second end to the first end by a preset length to obtain a standard soft rock cylindrical sample; Wherein, d is the diameter of the standard cylindrical specimen of soft rock, Dd≥20 mm, and the truncation method in step S5 is wire cutting.

2. The method for preparing a standard cylindrical specimen of soft rock according to claim 1, characterized in that: The method for obtaining rock samples by wire cutting in step S1 comprises the following steps: S11, select a sampling location for a soft rock specimen, demarcate a square area, and drill holes with a diameter of 0.1 m at the four corners of the square area; S12, inserting wire cutting machines into two parallel sides of the square area in sequence, and cutting out large rock samples from the four sides of the positive direction area; S13, cutting off the bottom of the square area with a wire cutting machine to extract a large square rock sample; S14. Cut the large square rock sample into soft rock specimens with a square cross-section and a side length of ≥60 mm using a wire cutting machine, and the height of the soft rock specimens is ≥130 mm.

3. The method for preparing a standard cylindrical specimen of soft rock according to claim 1, characterized in that: Angle auxiliary marking lines (2) are arranged on the inner wall of the sample preparation barrel (1) to quickly confirm the pre-cutting angle of the soft rock specimen rock sample; two length auxiliary marking lines (3) are arranged on the bottom of the sample preparation barrel (1) along the diameter direction, and the two length auxiliary marking lines (3) are perpendicular to each other to quickly adjust and confirm that the soft rock specimen rock sample is at the center position of the sample preparation barrel (1).

4. The method for preparing a standard cylindrical specimen of soft rock according to claim 1, characterized in that: The method for controlling the preset inclination angle between the bottom of the rock sample and the bottom of the sample preparation barrel (1) in step S3 is as follows: first, a proper amount of rapid hardening gypsum is added to the sample preparation barrel (1) to form an inclined surface with a preset inclination angle with the bottom of the sample preparation barrel (1), and then the rock sample is vertically placed on the center of the inclined surface to control the preset inclination angle between the bottom of the rock sample and the bottom of the sample preparation barrel (1).

5. The method for preparing a standard cylindrical specimen of soft rock according to claim 1, characterized in that: The mass ratio of gypsum to water in the rapid hardening gypsum liquid is 1:

2.

6. The method for preparing a standard cylindrical specimen of soft rock according to claim 1, characterized in that: The diameter d of the soft rock standard cylindrical sample is 50 mm, and the preset length of the cutoff in step S5 is 100 mm.

7. The method for preparing a standard cylindrical specimen of soft rock according to claim 1, characterized in that: In the step S3, the preset inclination angle is greater than 0° and less than or equal to 10°.

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