A method for preparing a soft rock standard cylinder sample

Abstract

The application provides a preparation method of a soft rock standard cylinder sample, which adopts fast hard gypsum to wrap a soft rock sample, and the gypsum provides a holding force for the soft rock sample after solidification, enhances the overall stability of the soft rock sample, and thus ensures that the soft rock sample can bear the impact force of direct lathe turning processing. Then, the soft rock sample wrapped by the gypsum is subjected to lathe turning processing by using a lathe, and a standard cylinder sample is formed in one step. The diameter tolerance of the standard cylinder sample obtained by one rough turning processing is less than 0.05 mm, and there is no need to polish again. Meanwhile, one end surface of the standard cylinder sample is directly flattened by using lathe turning processing, and the flatness is high. The other end surface is cut by using wire cutting, and the non-parallelism of the two end surfaces is less than 0.05 mm. The application can efficiently and stably prepare a standard sample meeting the national standard, and the preparation success rate can reach more than 90%, and thus the problems of low preparation efficiency and low preparation success rate of the soft rock sample are solved.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of rock mechanics test, and particularly relates to a preparation method of a soft rock standard cylindrical sample. BACKGROUND

[0002] In the construction of a tunnel, soft rock will inevitably be encountered. Soft rock generally refers to rock mass with weak rock quality, low bearing capacity, developed joint fissure and broken structure. If the tunnel passes through soft surrounding rock and is not properly treated, large deformation and collapse and other dangers are likely to occur. In order to master the mechanical parameter properties of soft rock, at present, indoor test is still the main means to study various properties of rock and deformation and failure law under different stress conditions, especially triaxial test needs to produce standard cylindrical samples of specific size according to the specification. The production of rock samples is a crucial step. According to the requirements of the Standard Test Method for Engineering Rock Mass (GB / T 50266-2013), the diameter of the standard cylindrical sample is (50) mm, the height-diameter ratio is (2±0.2), the upper and lower end diameter deviation should not be greater than 0.3 mm, the maximum and minimum value deviation of the height should be controlled within 0.05 mm, and the non-parallelism of the two end faces of the sample should not be greater than 0.05 mm. If the size of the sample does not meet the standard requirements, many errors will occur in the experimental results, affecting the accuracy of the test results. If general cutters are used for manual cutting, it is difficult to control the size of the cut cylindrical body to obtain a standard cylindrical sample, and thus it is impossible to carry out related indoor test research, or the success rate of sample production is very low and sufficient samples cannot be obtained for a large number of tests to obtain reliable conclusions.

[0003] Chinese Patent Publication No. CN111482852A discloses a layered soft rock standard test block cutting and polishing integrated device and a use method. The device has a three-layer structure, including a base provided on the first layer, a moving cutting mechanism and a horizontal polishing mechanism provided on the second layer, and a turntable mechanism provided on the third layer. After the rock test block is fixed, the test block is first cut into a hexahedron by the moving cutting mechanism of the second layer, and then the horizontal polishing mechanism of the second layer is used to polish the six planes of the hexahedron test block to form a cubic standard rock test block. Then the polishing rod is inserted, and the cubic standard test block is polished by the polishing rod to form a standard cylindrical test block. However, the preparation steps of the standard cylindrical test block are relatively complex, and the soft rock needs to be polished to form a hexahedron first, and then polished to form a standard cylindrical body. Moreover, the soft rock is relatively weak and has low bearing capacity, and direct multiple polishing is likely to cause the collapse of the soft rock test block and cause the test block preparation to fail. In addition, the preparation of the cylindrical test sample must first prepare the cubic test sample, and then polish the cylindrical test sample. The fusion of the two cutting methods and the two polishing methods has a long preparation period and needs to rely on specific equipment, and still cannot meet the preparation requirements of the standard sample for the indoor test of soft rock. SUMMARY

[0004] In order to solve the above technical problems, the application provides a preparation method of a soft rock standard cylindrical sample, which aims to provide a preparation method of a standard cylindrical sample with high preparation efficiency and stable sample quality.

[0005] In order to achieve the above-mentioned purpose, the application provides a preparation method of a soft rock standard cylindrical sample, which comprises the following steps:

[0006] S1, soft rock sample sampling: the soft rock sample is obtained by tunnel excavation or linear cutting;

[0007] S2, rock sample pretreatment: the obtained soft rock sample is blown with compressed air to remove surface dregs, and the rock sample is wrapped with plastic wrap multiple times to ensure that external water cannot contact the rock sample;

[0008] S3, preparation of a to-be-cut sample: the rock sample wrapped with plastic wrap in step S2 is placed at the center position of the bottom of a sample preparation barrel with an inner diameter of D mm, and the bottom of the rock sample is parallel to the bottom of the sample preparation barrel or at a preset inclination angle according to the needs, then the prepared quick-hardening gypsum liquid is added into the sample preparation barrel, and the quick-hardening gypsum liquid needs to cover the top of the rock sample, and after the quick-hardening gypsum liquid is completely solidified and formed, the cylindrical to-be-cut sample is obtained;

[0009] S4, turning processing: the first end of the to-be-cut sample prepared in step S3 is fixed on a lathe three-jaw chuck, the clamping length is greater than 20 mm, and the second end face is first turned to be flat; then the turning processing of the cylindrical body is started from the second end to the first end of the to-be-cut sample, the turning depth is (D-d) / 2 mm, the turning speed of the lathe spindle is 350-600 r / min, the feed rate is 70-120 mm / min, the first end clamping part of the to-be-cut sample is not subjected to turning processing any more, and the sample subjected to turning processing is taken off to obtain a soft rock standard cylindrical sample semi-finished product;

[0010] S5, cutting: the soft rock standard cylindrical sample semi-finished product processed in step S4 is accurately cut to a preset length from the second end to the first end, and a standard soft rock cylindrical sample is obtained;

[0011] Wherein, d is the diameter of the soft rock standard cylindrical sample, D-d≥20 mm, and the cutting method in step S5 is linear cutting.

[0012] As a preferred, the method of linear cutting of the rock sample in step S1 comprises the following steps:

[0013] S11, selecting a soft rock sample sampling position, and marking a square region, and drilling holes with a diameter of 0.1 m at four corner positions of the square region;

[0014] S12, inserting a wire cutting machine in two parallel edges of the square region in sequence, cutting out the four edges of the square region to obtain large rock samples;

[0015] S13, cutting the bottom of the square region by using the wire cutting machine to obtain a large square rock sample;

[0016] S14, cutting the large square rock sample into a soft rock sample with a square cross section and a side length greater than or equal to 60mm by using the wire cutting machine, and the height of the soft rock sample is greater than or equal to 130mm.

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

[0018] Preferably, the control method that the bottom of the rock sample and the bottom of the sample preparation barrel form a preset inclination angle in step S3 is that: first, add an appropriate amount of fast hard 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 vertically place the rock sample on the center of the inclined surface to control the bottom of the rock sample and the bottom of the sample preparation barrel to form a preset inclination angle.

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

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

[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 application has the following beneficial effects:

[0023] (1) The present application creatively uses fast hard gypsum to wrap the soft rock test block, and the gypsum provides a gripping force for the soft rock test block after solidification, 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 lathe turning machining.

[0024] (2) This invention directly uses conventional lathe tools to machine soft rock specimens, forming standard cylindrical specimens in one step. Moreover, only one rough machining is required to obtain a standard cylindrical specimen with a diameter tolerance of less than 0.05 mm, which is far higher than the national standard GB / T 50266-2013, which stipulates that the diameter deviation of the upper and lower ends should not exceed 0.3 mm. No further grinding is required. At the same time, one end face of the standard cylindrical specimen is directly machined to be flat with high flatness. The other end face is cut off by wire cutting. Since the diameter tolerance of the machined standard cylinder itself is extremely small, the second end face obtained by wire cutting is also basically strictly perpendicular to the axis of the standard cylinder. No further grinding is required. The non-parallelism of the two end faces is less than 0.05, which meets the national standard GB / T 50266-2013 regarding the parallelism of end faces.

[0025] (3) The present invention uses gypsum to wrap soft rock test blocks. The plasticity of gypsum can be used to easily adjust the pre-tilt angle of the soft rock test blocks. Combined with turning, standard cylindrical soft rock test blocks with different inclination angles can be obtained directly and quickly. In addition, the sample preparation barrel has built-in angle auxiliary markings to accurately position the inclination angle, which is simple and reliable.

[0026] (4) The method for preparing standard cylindrical soft rock samples of the present invention only requires conventional equipment to efficiently and stably prepare standard samples that meet national standards, with a high success rate, and effectively solves the current problems of low efficiency and low success rate in soft rock sample preparation. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

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

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

[0030] Figure 3 This is a cross-sectional view of the soft rock sample bottom in Example 1, with the bottom of the sample preparation container parallel to the bottom of the sample.

[0031] Figure 4 This is a cross-sectional view of the soft rock sample bottom and the sample preparation barrel bottom in Example 2, which are at a predetermined angle.

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

[0033] Reference Signs List

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

[0035] In order to make the technical problems, technical solutions and advantages of the present application clearer, the following will be described in detail with reference to the drawings and specific embodiments.

[0036] The following examples are used to illustrate the present application, but not to limit the scope of the present application. Modifications or replacements of the methods, steps or conditions of the present application, without departing from the spirit and essence of the present application, all belong to the scope of the present application.

[0037] If not specifically indicated, the technical means used in the examples are conventional means known to those skilled in the art; if not specifically indicated, the reagents used in the examples are commercially available.

[0038] Example 1

[0039] The soft rock standard cylindrical sample was prepared according to the following steps:

[0040] S1, soft rock sample taking: the soft rock sample was obtained by wire cutting. The soft rock sample taking position was selected, 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 corner positions, then the wire cutting machine was inserted in turn at two parallel edges of the square area, the four edges of the square area were cut out to form large rock samples, then the wire cutting machine was used to cut off at the bottom of the square area, and the large square rock sample was taken out; the wire cutting machine was used to cut off the large square rock sample at a suitable height and without fracture marks to form 12 cuboid soft rock samples with a length of 60mm, a width of 60mm and a height of 130mm.

[0041] In this embodiment, the diameter d of the soft rock standard cylindrical sample processed is 50mm, the height is 100mm, and the height to diameter ratio is 2. Therefore, the cross section of the cuboid soft rock sample is a square with a side length of 60mm, which can not only ensure that a cylindrical sample with a diameter of 50mm can be processed, but also reduce the turning processing allowance, thereby improving the processing efficiency and quality.

[0042] S2, rock sample pretreatment: the 60mm*60mm*130mm soft rock sample obtained above was blown with compressed air to remove surface dregs, and the rock sample was wrapped with plastic wrap multiple times to ensure that the external water cannot contact the rock sample, so as to avoid the water contacting the soft rock sample when the gypsum liquid is added subsequently, which may cause the soft rock to disintegrate. In this embodiment, wrapping the rock sample with plastic wrap is more suitable than conventional waterproof coating, because the waterproof coating may 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 the preservative film in step S2 to the center position of the bottom of the sample preparation barrel 1.

[0044] The sample preparation barrel 1 is a cylinder with an inner diameter of 80 mm, the top is open, and two length auxiliary lines 3 are arranged on the bottom along the diameter direction, the two length auxiliary lines 3 are perpendicular to each other, and the focal point of the two length auxiliary lines 3 is the center position of the bottom circle. When the rock sample is placed at the bottom, the distance between the four edges of the rock sample and the center of the bottom is adjusted to be basically consistent through the length auxiliary lines 3, 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, and the quick-hardening gypsum liquid needs to cover the top of the rock sample by 10-20 mm. After the quick-hardening gypsum liquid is completely solidified and formed, it is taken out from the sample preparation barrel 1, and a cylindrical sample to be cut is prepared. 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 as two symmetrical half-cylinders combined and fixed. After the gypsum is hardened, the two half-cylinders are 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 to combine and convenient to take out the sample, which will not be described 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 for turning processing will also increase. Those skilled in the art can select other appropriate inner diameters of the sample preparation barrel according to the specific conditions of the rock sample.

[0047] S4, turning processing: fixing the first end of the cylindrical sample to be cut prepared in step S3 to the lathe three-jaw chuck, clamping a length greater than 20 mm, and turning processing the second end face to be flat; then controlling the cutting tool to start turning processing the cylinder from the second end to the first end of the sample to be cut, the turning depth is (80-60) / 2=10 mm, the turning speed of the lathe spindle is 600 r / min, the feed rate is 120 mm / min, the first end of the sample to be cut is not clamped. The clamped part is no longer turned, and the sample after turning processing is taken off to obtain a soft rock standard cylindrical sample semi-finished product. In this embodiment, since the sample to be cut is reinforced by gypsum, the processed part has lost the wrapping of the gypsum and cannot provide stable support. If the conventional turning processing steps are followed, the first end and the second end need to be exchanged, and the first end needs to be turned again. However, in this application, the first end (clamped end) that has not been turned cannot be directly turned.

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

[0049] A cross-sectional view of the cylindrical sample to be cut prepared in this embodiment is shown in Figure 3 , in which the gypsum layer 5 is wrapped around the outer periphery of the soft rock sample 4. After turning machining of the cylindrical sample to be cut, a cylinder standard sample shown in Figure 3 is formed.

[0050] The prepared standard soft rock cylinder sample product is shown in Figure 5 . The standard soft rock cylinder sample has a diameter tolerance of less than 0.05mm, a non-parallelism of less than 0.05mm between the two end faces, and a smooth surface, completely meeting the requirements of GB / T 50266-2013 for the standard soft rock cylinder sample.

[0051] In this embodiment, a total of 12 cuboid soft rock samples were obtained, and after turning machining, finally 11 were successfully machined into standard soft rock cylinder samples meeting the standard requirements, and only one failed due to cracking during turning machining, with a machining success rate of 91.7%. The preparation method of the present application solves a series of problems such as complicated machining steps, unqualified samples, low machining efficiency, and low machining success rate of the current standard soft rock cylinder sample.

[0052] Example 2

[0053] A pre-inclination soft rock standard cylinder sample was prepared according to the following steps:

[0054] S1, soft rock sample sampling: a soft rock sample was obtained by wire cutting. A 1.2m*1.2m square area was selected, four holes with a diameter of 0.1m and a depth of 1m were drilled at the four corners, then a wire cutting machine was inserted into two parallel sides of the square area in turn, and the four sides of the square area were cut out to form a large rock sample, then the large square rock sample was cut off at the bottom using the wire cutting machine. A plurality of cuboid soft rock samples with a length of 80mm, a width of 80mm and a height of 150mm were obtained by cutting the large square rock sample at a suitable height and without any cracking marks.

[0055] S2, rock sample pretreatment: the 80mm*80mm*150mm soft rock sample obtained above was blown with compressed air to remove surface dregs, and the rock sample was wrapped with plastic wrap multiple times.

[0056] S3, preparation of sample to be cut: as Figure 4As shown, first add a proper amount of quick-hardening gypsum liquid to the sample preparation barrel 1 to form an inclined plane with a preset inclination angle a with the bottom of the sample preparation barrel, and quickly adjust the size of the preset inclination angle a according to the angle auxiliary mark line on the inner wall of the sample preparation barrel 1. Then place the rock sample on the center of the inclined plane with the preset inclination angle a, and the rock sample is perpendicular to the inclined plane to control the rock sample bottom to have the preset inclination angle a with the bottom of the sample preparation barrel. Wherein 0° < a ≤ 10°, and the rock sample is placed on the center of the inclined plane with the preset inclination angle a. Figure 4 It can be known that if the preset inclination angle is too large, the length and width of the cuboid soft rock test piece placed in the sample preparation barrel need to be large to ensure that the standard cylinder formed by cutting processing meets the requirements of 50 mm in diameter and 100 mm in height, but the larger the length and width of the cuboid soft rock test piece, the larger the diameter of the prepared sample to be cut, and the cutting processing is difficult, which is not suitable for the method. The preset inclination angle a in the embodiment is 8°, and a cuboid soft rock test piece with a cross section of 80 mm*80 mm can be selected, and the inner diameter of the sample preparation barrel 1 is adjusted to 100 mm.

[0057] After the rock sample is placed in place in the sample preparation barrel 1, the prepared quick-hardening gypsum liquid is continuously added to the sample preparation barrel 1, and the quick-hardening gypsum liquid needs to be 10-20 mm higher than the top of the rock sample. After the quick-hardening gypsum liquid is completely solidified and formed, it is taken out from the sample preparation barrel 1 to obtain a cylindrical sample to be cut.

[0058] S4, turning processing: the first end of the cylindrical sample to be cut prepared in step S3 is fixed on the lathe three-jaw chuck, the clamping length is greater than 20 mm, and the second end face is first turned to be flat; then the cutting tool is controlled to start turning the cylinder from the second end to the first end of the sample to be cut, the turning depth is (100-60) / 2=20 mm, the turning speed of the lathe spindle is 400 r / min, the feed rate is 70 mm / min, and the first end clamping part of the sample to be cut is not turned any more. The sample after turning processing is taken down to obtain a soft rock standard cylinder test sample semi-finished product.

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

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

[0061] The above merely illustrates the embodiments of the present application, and is not intended to limit the patent scope of the present application. Any equivalent structure or equivalent process conversion, or direct or indirect application in other related technical fields, made by using the content of the present application, are also included in the patent protection scope of the present application.

Claims

1. A method for preparing a standard cylindrical specimen of soft rock, characterized in that, Includes the following steps: S1. Sampling of soft rock specimens: Soft rock specimens are obtained from tunnel excavation or by wire cutting. S2. Rock sample pretreatment: The obtained soft rock sample is blown off the surface scum with compressed air, and the rock sample is wrapped with plastic wrap multiple times to ensure that external water cannot come into contact with the rock sample. S3. Preparation of the sample to be cut: Place the rock sample wrapped in plastic wrap in step S2 at the bottom center of the sample preparation barrel (1) with an inner diameter of D mm. As needed, the bottom of the rock sample is parallel to the bottom of the sample preparation barrel (1) or at a preset angle. Then add the prepared quick-hardening gypsum liquid to the sample preparation barrel (1). The quick-hardening gypsum liquid should cover the top of the rock sample. After the quick-hardening gypsum liquid has solidified and formed, take it out 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 the lathe with a clamping length greater than 20mm. First, turn the second end face until it is flat. Then, control the cutting tool to turn the cylinder from the second end to the first end of the sample to be cut. The turning depth is (Dd) / 2mm, the lathe spindle speed is 350-600r / min, and the feed rate is 70-120mm / min. The clamping part of the first end of the sample to be cut is no longer turned. Remove the turned sample to obtain the semi-finished soft rock standard cylindrical sample. S5. Cutting: The semi-finished soft rock standard cylindrical sample obtained in step S4 is accurately cut from the second end to the first end by a preset length to obtain a standard soft rock cylindrical sample. Where d is the diameter of the standard cylindrical sample of soft rock, Dd≥20mm, and the cutting 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 line cutting in step S1 includes the following steps: S11. Select the sampling location for the soft rock specimen, delineate a square area, and drill holes with a diameter of 0.1m at the four corners of the square area; S12. Insert wire cutting machines into the two parallel sides of the square area in sequence to cut out large rock samples from the four sides of the square area. S13. Cut the bottom of the square area with a wire cutter 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 ≥ 60 mm using a wire cutting machine. 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 markings (2) are provided on the inner wall of the sample preparation barrel (1) to quickly confirm the pre-cut angle of the soft rock specimen; two length auxiliary markings (3) are provided at the bottom of the sample preparation barrel (1) along the diameter direction, and the two length auxiliary markings (3) are perpendicular to each other to quickly adjust and confirm that the soft rock specimen is in 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 bottom of the rock sample and the bottom of the sample preparation bucket (1) to form a preset angle in step S3 is as follows: First, add an appropriate amount of quick-hardening gypsum to the sample preparation bucket (1) to form a slope with a preset angle to the bottom of the sample preparation bucket (1), and then place the rock sample vertically on the center of the slope to control the bottom of the rock sample and the bottom of the sample preparation bucket (1) to form a preset angle.

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 quick-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 cut 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 step S3, the preset tilt angle is greater than 0° and less than or equal to 10°.

Images