Device and method for preparing indoor large-size fractured rock test piece

Abstract

The invention provides a device and a method for preparing an indoor large-size fractured rock test piece. The device comprises a fractured rock sample, a cuboid plastic net, a cuboid mold and a cement paste layer, the fractured rock sample is obtained by manually chiseling at a representative position; the cuboid plastic net bags the fractured rock sample and then is placed in the middle of the cuboid mold; the cuboid mold is a hollow cuboid; and the cement paste layer is formed by pouring cement paste into a gap between the fractured rock sample and the cuboid mold. According to the invention, the integrity of the fractured rock can be ensured, the large-scale fractured rock test piece can be effectively prepared, the large-scale fractured rock indoor test is realized, and the current situation that only on-site rock mechanical test can be carried out is changed.

Description

Technical Field

[0001] The invention relates to the field of rock mechanics testing, and in particular to an indoor large-size fractured rock specimen preparation device and method. Background Art

[0002] Rock mechanics parameters are important parameters for stability analysis and design of rock projects such as rock slope engineering and rock tunnel engineering. Rock mechanics parameters are mainly obtained through indoor rock mechanics tests and field rock mechanics tests. When conducting field rock mechanics tests, different types of rock mechanics test equipment must be transported to the site, and space is also required for installation and commissioning. Therefore, the cost of field rock mechanics tests is high. In order to control the test cost, simple projects that do not require large test equipment are generally carried out on site, and complex projects that require large test equipment are carried out indoors.

[0003] In order to conduct rock mechanics tests indoors, it is necessary to transport rock samples from the site back to the room. For intact rocks, they can be directly transported to the indoor test room after simple processing on site, and rock specimens are not easily damaged. In recent years, in order to truly reflect the properties of rocks, the size of rock samples has become larger and larger, from the traditional few centimeters to tens of centimeters, and even to the meter level. In this way, large-sized rock samples will inevitably contain varying numbers of criss-crossing structural surfaces or cracks (referred to as fragile rocks). The external forces generated by handling and transportation will damage the internal structure of the rock, and the test results will seriously deviate from the true value. What is more serious is that some fractured rock samples cannot be made into rock specimens required by the test, and it is impossible to effectively carry out indoor rock mechanics tests. This is also the difficulty and gap in conducting indoor rock mechanics tests on fractured rocks in China.

[0004] At present, in order to obtain the mechanical parameters of fractured rocks, experimental researchers use experience to discount the obtained complete rock mechanical parameter values. Due to the complexity of fractured rock structures, the artificially converted estimates are often quite different from the actual situation. If the conversion is too small, it will leave safety hazards for the project. This is also the main reason why some rock projects still have engineering accidents despite reinforcement. If the conversion is too large, it will increase the cost of rock project management.

[0005] At present, rock mechanics tests generally include tensile strength tests, compressive strength tests, shear strength tests and compression strength tests of rocks under different water content states. Whether various mechanical tests can be carried out smoothly depends mainly on whether the rock specimens can be successfully made. According to the clear requirements of international and domestic rock test regulations: rock specimens should be representative; the surface of the specimens should be flat, without obvious cracks and defects; when making samples of different specifications and shapes, rock specimens should try to use consistent methods and tools, cut, polish and process according to test requirements, and ensure that the internal structure of the rock specimens is not affected. For small-sized intact rocks, rock specimens can easily meet the above requirements, but for large-sized fractured rocks, if they are not properly handled, on-site sampling, transportation, indoor processing and other activities will cause serious damage to their internal structure, resulting in serious deviations from the true value of the test results. What is more serious is that the samples cannot be successfully prepared, resulting in the inability to carry out the test smoothly.

[0006] In view of the difficulties encountered in conducting rock mechanics tests on large-sized fractured rocks, the key problem to be solved is to effectively produce fractured rock specimens while ensuring that the internal properties of the fractured rock are not seriously damaged. The test results of the successfully produced fractured rock specimens are less affected and can reflect the mechanical properties of the fractured rock itself. Summary of the invention

[0007] The purpose of the present invention is to provide an indoor large-size fractured rock specimen preparation device and method, which solves the problem of effectively making fractured rock specimens of large-size fractured rocks with little damage to their original mechanical properties, thereby realizing indoor replacement of field rock mechanics tests; through indoor tests, not only can the mechanical parameters of fractured rocks under different water content states be obtained, but also the test cost is greatly reduced.

[0008] An indoor large-size fractured rock specimen preparation device, including a large-size fractured rock specimen preparation device and method, including a fractured rock sample, a rectangular plastic net, a rectangular mold and a cement slurry layer;

[0009] The fractured rock sample is a cuboid, which is obtained by manually chiseling at a representative position according to the requirements of rock mechanics test;

[0010] The rectangular plastic net has a lower strength than the fractured rock sample and is open at one end along the length direction. The rectangular plastic net holds the fractured rock sample and is placed in the middle of the rectangular mold.

[0011] The rectangular parallelepiped mold is in the shape of a hollow rectangular parallelepiped. One rectangular alloy plate of the rectangular parallelepiped mold is freely removable as a free alloy plate. A small hole is left at the end along the length direction of the free alloy plate for grouting, exhaust and drainage. The other three rectangular alloy plates are a whole. One of the two square surfaces perpendicular to the rectangular surface is open and has no alloy cover plate, and the other square alloy plate and the three rectangular alloy plates form a whole.

[0012] The cement slurry layer is formed by pouring cement slurry into the gap between the fractured rock sample and the rectangular parallelepiped mold.

[0013] Furthermore, the specifications of the fractured rock sample are height×width×length=30cm×30cm×60cm.

[0014] Furthermore, the inner dimensions of the rectangular plastic net are height×width×length=32cm×32cm×62cm, the wall thickness is 0.2cm, and the mesh size is 1-2cm.

[0015] Furthermore, the inner dimensions of the rectangular parallelepiped mold are: height×width×length

[0016] =34cm×34cm×64cm, the material is alloy material, and the wall thickness is 1~2cm.

[0017] Furthermore, the free alloy plate can be freely disassembled from other adjacent surfaces of the rectangular parallelepiped mold through locking buckles.

[0018] Furthermore, a cylinder with a height of 1 cm and a radius of 2 cm is left at the four inner corners of another square alloy plate of the two square faces perpendicular to the rectangular face.

[0019] Furthermore, the water-cement ratio of the cement slurry is 0.6:1, the cement grade is 325#, and the consistency is 70mm.

[0020] A method for preparing indoor large-size fractured rock specimens, which is carried out using the device, and the method comprises the following steps:

[0021] Step 1: Conduct field investigation on site to determine the location where the fractured rock samples are to be taken and mark them;

[0022] Step 2: According to the test requirements, artificially chisel at the designated location to obtain a fractured rock sample, and measure the size of the fractured rock sample;

[0023] Step 3: Use a plastic net to cover the fractured rock sample;

[0024] Step 4: Remove the free alloy plate from the rectangular parallelepiped mold and place it steadily on a flat ground. Then place the fractured rock sample covered with a plastic net steadily on the free alloy plate. Cover the rest of the rectangular parallelepiped mold, fasten the free and detachable free alloy plate, and then flip it over so that the side of the rectangular parallelepiped mold without the alloy plate faces upward and the end of the free alloy plate with the small hole faces downward. Adjust the position of the fractured rock sample (1) so that the fractured rock sample (1) is centered in the rectangular parallelepiped mold.

[0025] Step 5: Mix the cement slurry according to the mix ratio and consistency obtained in the test, stir evenly, open the small holes of the free alloy plate, slowly pour the mixed cement slurry into the gap between the fractured rock sample and the rectangular mold, and shake and stir to form; at the same time, use the conventional concrete pouring method to make a pure cement slurry specimen;

[0026] Step 6: After the age reaches 7 days, the composite structure consisting of the fractured rock, the plastic mesh and the cement slurry layer is taken out from the rectangular mold, and the composite structure and the pure cement specimen are transported back to the indoor test room.

[0027] Furthermore, it also includes:

[0028] Step 7: Without any grinding or processing, the composite structure and pure cement specimens are directly cured according to the test method conditions, and different indoor rock mechanics tests are carried out; the pure cement specimens and the composite structure are subjected to the same type of mechanical tests, and the pressure and deformation curves of the slurry layer after cement curing are obtained through the mechanical tests of the pure cement specimens;

[0029] Step 8: According to the change characteristics of the pressure and deformation curves obtained from the composite structure test, the pressure F and the corresponding deformation μ when the fractured rock is broken are read from the curve. According to the obtained deformation μ, the pressure value corresponding to the deformation μ is found in the pressure and deformation curve of the pure cement specimen, and the strength of the cement slurry layer σ0 is calculated. The fractured rock strength is set to σ, the bottom area or side area of ​​the mold is S1, and the bottom area or side area of ​​the fractured rock specimen is S2. According to the limit equilibrium theory and the comparative analysis of the test results, the fractured rock strength σ is calculated according to the rock strength correction formula:

[0030]

[0031] The calculated rock mechanical parameter values ​​can accurately reflect the mechanical properties of the rock.

[0032] Aiming at the problem that large-sized fractured rocks are difficult to shape indoors, the present invention develops a low-strength, high-permeability slurry material, and utilizes the developed cement slurry layer and highly flexible plastic mesh composite structure with certain compressive and tensile properties to seal, protect and reinforce fractured rock samples, so that fractured rocks are not easily damaged and destroyed during transportation and preparation, thereby ensuring the integrity of fractured rocks, and effectively preparing large-scale fractured rock specimens, thereby realizing indoor testing of large-scale fractured rocks and changing the current situation where only on-site rock mechanics testing can be performed; the uniaxial compressive strength of the cement slurry layer composite structure is much lower than the uniaxial compressive strength of the rock, which is conducive to effectively identifying the fracture pressure of the slurry layer and the fracture pressure of the rock specimen from the test pressure and deformation curve, thereby ensuring the accuracy of the rock strength parameters obtained from the test; the high permeability of the cement slurry layer composite structure is conducive to achieving hydraulic connectivity between the rock specimen and the outside world, and can realize the preparation of rock specimens in different water states such as dry, natural and saturated. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 1 is a schematic diagram of the structure of an indoor large-size fractured rock specimen preparation device according to an embodiment of the present invention, wherein (a) is a top plan view, and (b) is a front elevation view;

[0034] Figure 2 It is a force diagram of the indoor rock mechanics test in the present invention.

[0035] In the figure: 1 - rock sample, 2 - plastic net, 3 - rectangular mold, 4 - forming cement slurry layer DETAILED DESCRIPTION

[0036] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0037] See also Figure 1 and Figure 2 An embodiment of the present invention provides an indoor large-size fractured rock specimen preparation device, comprising a fractured rock sample 1, a rectangular plastic net 2, a rectangular mold 3 and a cement slurry layer 4.

[0038] The rock sample 1 is obtained by artificial chiseling at a representative location according to the requirements of rock mechanics tests, and its size is about 30cm×30cm×60cm.

[0039] The rectangular plastic net 2 has low material strength, good flexibility, and is not easy to break. The inner size is about 32cm×32cm×62cm, the wall thickness is about 0.2cm, the mesh size is 1-2cm, and one end is open along the length direction. It is installed between the fractured rock sample 1 and the rectangular mold 3. Its function is to play a reinforcing role when pouring cement slurry. The cement slurry is not easy to disperse, which increases the bonding force.

[0040] The inner dimensions of the rectangular mold 3 are 34 cm × 34 cm × 64 cm, and the wall thickness is about 1 to 2 cm. An alloy plate with a rectangular surface in the rectangular mold 3 can be removed as a free alloy plate, and a small hole is left at the center position near the end of the alloy plate along its length. In this embodiment, a hole is left at 1.5 cm from the edge of the free alloy plate. The small holes are used for exhaust and drainage during grouting; one of the two square faces is open and has no alloy plate, and the other square face has cylinders with a height of 2 cm and a radius of 1-2 cm at the four corners inside the alloy plate; the three rectangular alloy plates and one square alloy plate form a whole, and the free alloy plate and the whole formed by other faces are connected by locks, and the rectangular mold 3 plays a role in forming and protecting the cement slurry.

[0041] In order to satisfy the effect that the cement slurry layer 4 has low strength and good permeability after molding, the following mixing ratio is obtained through experiments: the water-cement ratio is 0.6:1, and the consistency is about 70mm.

[0042] The embodiment of the present invention further provides a method for preparing a large-size fractured rock specimen indoors, which is performed using the above-mentioned device, and the method comprises the following steps:

[0043] Step 1: Conduct a field investigation on site to determine the locations where fractured rock samples are to be taken and mark them clearly.

[0044] Step 2: Manually chisel a fractured rock sample 1 at a designated location and measure the sample size.

[0045] Step 3: Remove the free alloy plate from the rectangular mold 3, place the free alloy plate flat on a flat ground, then place the rectangular plastic net 2 with the fractured rock sample 1 on the free alloy plate steadily, put on the other parts of the rectangular mold 3, connect the end of the free alloy plate with the small hole to the end with the square alloy plate, fasten the lock and turn it over so that the side of the rectangular mold 3 without the alloy plate opening faces upward, adjust the position of the rectangular plastic net 2 and the fractured rock sample 1 so that the fractured rock sample 1 is centered in the rectangular mold 3.

[0046] Step 4: Mix cement slurry according to the mix ratio and consistency, stir evenly, open the small holes on the free alloy plate, slowly pour the mixed cement slurry into the gap between the fractured rock sample 1 and the rectangular mold 3, oscillate and stir to form, and at the same time cast a pure cement slurry specimen in the conventional concrete pouring method.

[0047] Step 5: After the age reaches 7 days, the composite structure consisting of the fractured rock sample 1, the plastic mesh 2 and the cement slurry layer 4 is taken out from the rectangular parallelepiped mold 3 and transported back to the indoor test room.

[0048] Step 6: Without any processing or polishing, the returned composite structure is cured according to the test method requirements, and then the indoor rock mechanics test can be carried out. The pure cement specimen and the composite structure are subjected to the same type of mechanical test. Through the mechanical test of the pure cement specimen, the pressure and deformation curve of the cement slurry layer 4 after cement solidification can be obtained.

[0049] Step 7: According to the change characteristics of the pressure and deformation curves obtained from the mechanical test of the composite structure, the pressure F and the corresponding deformation μ when the rock breaks are read from the curve, and then the pressure value corresponding to the deformation μ is found from the pressure-deformation curve of the pure cement specimen, and the cement slurry layer strength σ0 corresponding to the deformation μ is calculated. Assuming that the strength of the fractured rock is σ, S2 is the bottom area or side area of ​​the fractured rock sample, and S1 is the bottom area or side area of ​​the empty space in the rectangular mold 3, the limit equilibrium theory and the test results are compared and analyzed, and the rock strength correction formula is as follows:

[0050]

[0051] The calculated fractured rock strength has eliminated the influence of the cement slurry layer, and the obtained rock mechanical parameter values ​​directly reflect the mechanical properties of the rock itself.

[0052] Indoor tests replace field tests. First, they reduce test costs. Second, they can obtain rock mechanical parameters under different water content states, breaking through the dilemma that field tests can only obtain rock mechanical parameters under a certain water content state. In the past, the compressive strength parameters of fractured rock specimens were calculated directly using the uniaxial compressive load-displacement curve, ignoring the influence of the protective mortar strength, and the calculated parameter values ​​were approximate values. The calculation formula proposed in the present invention eliminates the load portion borne by the mortar in the mortar-protected fractured rock specimen. The calculated uniaxial compressive strength of the fractured rock specimen is the true strength value of the fractured rock, and the calculation result is more accurate.

[0053] The present invention develops a cement slurry layer material with low strength and good permeability, and uses it to protect and reinforce fractured rocks to prevent them from being damaged or destroyed during handling or transportation, solves the problem that large-scale fractured rocks cannot be prepared and formed indoors, and realizes indoor rock mechanics testing of large-scale fractured rocks; the large-scale fractured rock specimens made by the device are not easy to break under the action of external forces, and the formed composite structure does not need any treatment except for curing according to the test conditions specified in the test method; the indoor rock mechanics test replaces the on-site rock mechanics test, firstly, it reduces the test cost, and secondly, it can obtain rock mechanics parameters under different water content states, breaking through the dilemma that on-site tests can only obtain rock mechanics parameters under a certain water content state; the proposed fractured rock strength calculation formula eliminates the influence of the cement slurry layer strength, and the calculation result can reflect the mechanical properties of the rock itself.

[0054] The contents not described in detail in this specification belong to the prior art known to professional and technical personnel in this field.

[0055] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. An indoor large-size fractured rock specimen preparation device, characterized in that: It comprises a fractured rock sample (1), a rectangular plastic net (2), a rectangular mold (3) and a cement slurry layer (4); The fractured rock sample (1) is a rectangular parallelepiped, which is obtained by manually chiseling at a representative position according to the requirements of rock mechanics test; The rectangular parallelepiped plastic net (2) has a lower strength than the fractured rock sample (1) and is open at one end along the length direction. The rectangular parallelepiped plastic net (2) holds the fractured rock sample (1) and is placed in the middle of the rectangular parallelepiped mold (3); The rectangular parallelepiped mold (3) is in the shape of a hollow rectangular parallelepiped. One rectangular alloy plate of the rectangular parallelepiped mold (3) is freely removable as a free alloy plate. A small hole is left at the end of the free alloy plate along the length direction for grouting, exhaust and drainage. The other three rectangular alloy plates are an integral whole. One of the two square faces perpendicular to the rectangular face is open and has no alloy cover plate. The other square alloy plate and the three rectangular alloy plates form an integral whole. The cement slurry layer (4) is formed by pouring cement slurry into the gap between the fractured rock sample (1) and the rectangular parallelepiped mold (3).

2. An indoor large-size fractured rock specimen preparation device as claimed in claim 1, characterized in that: The specifications of the fractured rock sample (1) are height×width×length=30cm×30cm×60cm.

3. An indoor large-size fractured rock specimen preparation device as claimed in claim 2, characterized in that: The inner dimensions of the rectangular plastic net (2) are height×width×length=32cm×32cm×62cm, the wall thickness is 0.2cm, and the mesh size is 1-2cm.

4. The indoor large-size fractured rock specimen preparation device according to claim 3, characterized in that: The inner dimensions of the rectangular parallelepiped mold (3) are height×width×length=34cm×34cm×64cm, and the material is alloy material with a wall thickness of 1 to 2cm.

5. The indoor large-size fractured rock specimen preparation device according to claim 1, characterized in that: The free alloy plate can be freely disassembled from other adjacent surfaces of the rectangular parallelepiped mold (3) by means of locking buckles.

6. The indoor large-size fractured rock specimen preparation device according to claim 1, characterized in that: The other square alloy plate of the two square faces perpendicular to the rectangular face has cylinders with a height of 1 cm and a radius of 2 cm at the four inner corners.

7. The indoor large-size fractured rock specimen preparation device according to claim 1, characterized in that: The water-cement ratio of the cement slurry is 0.6:1, the cement grade is 325#, and the consistency is 70mm.

8. A method for preparing indoor large-size fractured rock specimens, characterized in that The method is carried out using the device according to any one of claims 1 to 7, and comprises the following steps: Step 1: Conduct a field survey on site to determine the location where the fractured rock samples are to be taken and mark them; Step 2: According to the test requirements, a fractured rock sample (1) is obtained by artificially chiseling at a designated location, and the size of the fractured rock sample (1) is measured; Step 3: Cover the fractured rock sample (1) with a plastic net (2); Step 4: Remove the free alloy plate from the rectangular parallelepiped mold (3) and place it steadily on a flat ground. Then place the fractured rock sample (1) covered by the plastic net (2) steadily on the free alloy plate. Cover the rest of the rectangular parallelepiped mold (3), fasten the free and detachable free alloy plate, and then flip it over so that the side of the rectangular parallelepiped mold (3) without the alloy plate faces upward and the end of the free alloy plate with the small hole faces downward. Adjust the position of the fractured rock sample (1) so that the fractured rock sample (1) is centered in the rectangular parallelepiped mold (3). Step 5: Mix cement slurry according to the mix ratio and consistency obtained in the test, stir evenly, open the small holes of the free alloy plate, slowly pour the mixed cement slurry into the gap between the fractured rock sample (1) and the rectangular parallelepiped mold (3), and shake and stir to form; at the same time, use a conventional concrete pouring method to make pure cement slurry specimens of the same specifications; Step 6: After the age reaches 7 days, the composite structure consisting of the fractured rock (1), the plastic mesh (2) and the cement slurry layer (4) is taken out from the rectangular parallelepiped mold (3), and the composite structure and the pure cement specimen are transported back to the indoor laboratory.

9. The method for preparing a large-size fractured rock specimen indoor according to claim 8, characterized in that: Also includes: Step 7: without any grinding or processing, the composite structure and the pure cement specimens are directly cured according to the test method conditions, and then different indoor rock mechanics tests are carried out; the pure cement specimens and the composite structure are subjected to the same type of mechanical tests, and the pressure and deformation curves of the slurry layer (4) after cement curing are obtained through the mechanical tests of the pure cement specimens; Step 8: According to the change characteristics of the pressure and deformation curve obtained from the composite structure test, the pressure F and the corresponding deformation μ when the fractured rock is broken are read from the curve. According to the obtained deformation μ, the pressure value corresponding to the deformation μ is found in the pressure and deformation curve of the pure cement specimen, and the strength σ0 of the cement slurry layer (4) is calculated. The fractured rock strength is set to σ, the bottom area or side area of ​​the mold (3) is S1, and the bottom area or side area of ​​the fractured rock specimen (1) is S2. According to the limit equilibrium theory and the comparative analysis of the test results, the fractured rock strength σ is calculated according to the rock strength correction formula: The calculated rock mechanical parameter values ​​can accurately reflect the mechanical properties of the rock.

Images