Batch one-time sample preparation method for columnar jointed rock mass similar material model test

Abstract

The invention provides a batch one-time sample preparation method for a columnar jointed rock mass similar material model test. The batch one-time sample preparation method comprises the following steps: S1) geological survey, S2) 3D printing of a columnar jointed network, S3) primary pouring, S4) secondary pouring, S5) sample maintenance and S6) loading test. The method has the advantages that the preparation method is simple, the yield of the sample is high, damage to the sample by a joint network adding mode is small, the consistency of physical and mechanical properties of the sample in the same batch is high, the occurrence characteristics of the natural columnar jointed rock mass in a to-be-researched area can be reduced to a high degree, and the test conclusion is more targeted.

Description

Technical Field

[0001] This invention relates to the field of rock mechanics and rock physical mechanics testing technology, specifically to a method for batch one-time sample preparation for similar material model tests of columnar jointed rock masses. Background Technology

[0002] Jointed rock masses, as representative engineering geological bodies, refer to rock masses that have developed specific structural characteristics due to long-term geological tectonic activity within a particular geological environment. They are primarily composed of bedrock and structural planes, exhibiting discontinuous, heterogeneous, anisotropic, and complex initial damage states. In their natural state, the joints within the rock mass are initially interlocked. However, with increasing engineering disturbance, the weak structural planes within the rock mass, exhibiting varying degrees of stress distribution and development scale, displaying mechanical behaviors far exceeding those of isotropic materials. Extensive geotechnical engineering practice demonstrates that the deterioration, instability, and failure of engineering rock masses are closely related to the expansion and interconnection of their internal joint planes. Neglecting in-depth research into this type of geological environment, especially with the increasingly close relationship between humans and mega-projects, can sometimes lead to catastrophic casualties and property damage.

[0003] The Baihetan Hydropower Station is the second cascade hydropower station on the lower reaches of the Jinsha River. As another giant hydropower project with a total installed capacity exceeding 10 million kW, following the Three Gorges and Xiluodu hydropower stations, its dam site area is characterized by widely developed primary tension-fractured columnar jointed basalt with generally low RQD values, poor integrity, and significant discontinuities, easy cracking, strong anisotropy, and strong interfacial permeability. In hydraulic engineering practice, the deterioration and instability of the engineering rock mass are closely related to the expansion and penetration of its internal joint surfaces. As the dam foundation rock mass, under complex geostress and high water pressure conditions, the nonlinear mechanics and permeability characteristics of the columnar jointed rock mass have a significant impact on the deformation of the dam body, the dam abutments, slopes, and the surrounding rock stability of the hydraulic cavern group. Therefore, research on the permeability evolution characteristics and failure mechanism of columnar jointed rock mass under stress-seepage coupling, given the complex occurrence conditions and special structural features of the columnar jointed rock mass in the Baihetan Dam foundation, is of great significance to the safety and stability of the Baihetan Hydropower Station during construction and operation, and can also provide valuable experience for subsequent related hydropower projects.

[0004] Domestic and international scholars have conducted extensive and in-depth research on the physical, mechanical, and seepage characteristics of columnar jointed rock masses. However, considering the large cross-sections of columnar jointed rock masses, the difficulty and cost of on-site sampling, and the difficulty in meeting REV size requirements, it is difficult to accurately reflect the physical and mechanical properties of columnar jointed rock masses. Therefore, conducting indoor physical model tests using similar materials is currently an effective research method for columnar jointed rock masses. At present, domestic and international scholars widely use similar materials to simulate columns, and then prepare similar material samples of columnar jointed rock through a series of processes such as curing, bonding, grinding, and polishing. Since both the column and the joint network need to be cured in batches until the final setting stage, the preparation cycle is extremely long. Furthermore, because bonding and grinding are all manual operations, the consistency of samples within the same batch is poor, and cracks are easily generated during grinding and polishing, resulting in a low overall sample preparation success rate.

[0005] Regarding the sample preparation method and process of similar material model of columnar jointed rock mass, Chinese invention patent with publication number CN 112345334 A discloses "a method for preparing rock samples containing anisotropic joints based on 3D printing", and Chinese invention patent with publication number CN 111157322 A discloses "a method for preparing irregular columnar jointed rock mass samples with nested interlayer fault zones". Both of the above patents propose the preparation of similar material model of columnar jointed rock mass and the corresponding test method. Through the methods described in the above two patents, cylindrical columnar jointed rock mass similar model materials with regular cross-sectional shapes (quadrilateral, pentagon and hexagon) can be obtained. However, there are the following shortcomings: (1) The above sample preparation methods have not achieved batch one-time sample preparation of similar material model of columnar jointed rock mass. The sample preparation process requires high technical proficiency of scientific research personnel and lacks effective vibration compaction methods, which easily leads to damage units such as voids and honeycomb pitting in the sample; (2) (3) The effective triaxial stress loading method that can be performed on cylindrical specimens is only conventional triaxial loading, that is, the first principal stress σ1 > the second principal stress σ2 = the third principal stress σ2. It is difficult to reflect the rock deterioration behavior under triaxial unequal pressure conditions in actual engineering. It is necessary to prepare cubic specimens and perform true triaxial loading (first principal stress σ1 > second principal stress σ2 > third principal stress σ2) to reflect the influence of circumferential stress. (4) The above specimen preparation methods do not fully consider the natural geometric cross-sectional shape of columnar jointed rock bodies. They only simulate the columnar shape of columnar jointed rock bodies by using square prisms, pentagonal prisms and hexagonal prisms.

[0006] Therefore, a method, equipment, and process for batch one-time preparation of cubic specimens of similar material models that can effectively reflect the natural geometry of columnar jointed rock masses and describe the actual stress conditions in the field has become a scientific problem that urgently needs to be solved in the field of rock mechanics. Summary of the Invention

[0007] The purpose of this invention is to provide a method for batch preparation of similar materials for columnar jointed rock masses that can effectively reflect the natural geometric morphology of columnar jointed rock masses, describe the actual stress conditions in the field, and complete the batch preparation of similar materials for columnar jointed rock masses from one-time batch preparation and subsequent deterioration mode exploration through true triaxial tests combined with discrete element software numerical simulation results, thus realizing the whole process of columnar jointed rock mass similar material model test.

[0008] To achieve the above objectives, the present invention is implemented through the following technical solution: A method for batch, one-time sample preparation for similar material model tests of columnar jointed rock masses, characterized by the following steps: S1) Geological Survey Considering that columnar jointed rock masses are primarily irregular polygons in engineering practice, mathematical statistics were performed on the columnar jointed sections in the study area to construct cross-sectional diagrams of columnar jointed rock masses with different cross-sectional shapes. Geological survey methods were used to investigate the cross-sectional shapes and rock occurrences of the columnar jointed rock masses in the study area to determine the proportion of different cross-sectional shapes and further obtain the coefficient of variation C for cross-sectional shapes. VQ The average area A of a single cross section Q and the average side length A of the prism L Using the aforementioned characterization parameters, the REV (representational unit volume) of the columnar jointed rock mass in the study area is determined. Irregular polygonal units are constructed using Delaunay triangulation, generating n seed points, each numbered V. i Further according to the formula (1) Find the seed point corresponding to the minimum distance, and the distance D between the seed points. i It can be expressed as a formula (2) Connect all the seed point boundaries to obtain the cross-sectional diagram of columnar jointed rock mass with different cross-sectional shapes, and number the polygons in sequence.

[0009] S2) 3D printed columnar jointed network A three-dimensional joint network was constructed from the obtained cross-sectional image of the columnar jointed rock mass, and then columnar joint networks with different dip angles were 3D printed using 3D printing technology. Based on the geological survey results, the axial dip angle β of the columnar joint network was set to 45°, 60°, 75° and 90°. The columnar joint network was made of soluble polyvinyl acetate material (PVA material). Rhino 7.0 3D printing software was used for high-precision modeling.

[0010] S3) First pouring Install a disposable sample preparation mold, uniformly spray petroleum jelly inside the mold, and place the 3D-printed columnar joint network inside the mold; then pour a columnar similar material solution into the columnar joint network, and use an appropriate vibration frequency and vibration time. After vibration, let it stand until the columnar sample initially sets; preferably, select a medium-low vibration frequency and vibrate for 10 minutes. Stop vibration when no floating slurry or air bubbles are observed on the upper surface of the sample. After vibration, let it stand for 30 minutes until the column initially sets and has a certain strength.

[0011] The column-like material cement mortar is composed of cement, gypsum, river sand, and water, with a weight ratio of 5:0.5:2.5:5; a naphthalene-based early-strength water-reducing agent is added, with an addition amount of 0.2% of the total mass.

[0012] The disposable sample preparation mold includes an upper casting cavity, a lower base plate, and a vibration section. The upper casting cavity consists of two main back plates and two auxiliary back plates arranged opposite each other. The main back plates and auxiliary back plates are interlocked and further secured by several tie bolts to ensure the airtightness and watertightness of the casting cavity. The main back plates and auxiliary back plates are respectively connected to the lower base plate through lower insert plates. The vibration section is located at the four corners of the lower base plate. Both the upper casting cavity and the lower base plate are made of polymethyl methacrylate (plexiglass). Plexiglass not only has excellent optical properties but also good weather resistance, acid and alkali resistance, dimensional stability, insulation, and mechanical strength, thus it can be effectively recycled.

[0013] S4) Secondary pouring The soluble joint network within the sample is dissolved in a water bath, while the drain outlet at the bottom of the mold is opened to discharge the waste liquid. Then, a joint-like material solution is poured into the sample, vibrated to compact it, and left to stand until the joint-like material initially sets. The tie bolts are removed, the sample is taken out, and the next step of sample curing is carried out.

[0014] The joint-like material gypsum mortar is composed of high-strength white cement and water in a weight ratio of 1:0.5; a naphthalene-based early-strength water-reducing agent is added at a dosage of 0.2% of the total mass.

[0015] S5) Sample curing The columnar sample was placed in a constant temperature curing chamber with a temperature of 20±1℃ and a humidity of ≥90% for no less than 28 days to prepare a columnar jointed rock mass similar material sample.

[0016] S6) Loading Test True triaxial loading tests and true triaxial stress-seepage coupled loading tests were conducted on similar material specimens of columnar jointed rock mass to obtain the physical model test structure. Meanwhile, the columnar jointed specimens were modeled in three dimensions using Rhino software, and the test conditions were imported into the discrete element software for numerical simulation. By comparing numerical simulation results with physical model test results, the failure mode of columnar jointed rock mass under macro-micro conditions is revealed.

[0017] Compared with the prior art, the present invention has the following advantages: This invention provides a batch one-time sample preparation method for similar material model tests of columnar jointed rock masses. The preparation method is simple, the sample yield is high, the joint network addition method causes less damage to the sample, the physical and mechanical properties of samples within the same batch are highly consistent, and it can also reproduce the occurrence characteristics of natural columnar jointed rock masses in the area under study to a high extent, making the test conclusions more targeted.

[0018] Specifically, this invention considers the geometric cross-sectional characteristics of columnar jointed rock masses in their natural state. Through geological surveys combined with a seed generation algorithm, irregular polygonal units are constructed and further stretched into three-dimensional columnar joint networks with different inclinations. This can recreate the occurrence characteristics of natural columnar jointed rock masses in the study area to a high degree, making the experimental conclusions more targeted. The proposed method and equipment for one-time preparation of columnar jointed similar material samples are simple to use, have a high sample yield, and exhibit strong consistency in physical and mechanical properties within the same batch. The cubic samples prepared by this invention can undergo true triaxial loading tests, effectively simulating rock mass deterioration modes under real triaxial unequal pressure conditions. The method of adding the joint network in this invention minimizes the impact on the sample, and the joint network has good uniformity. This invention greatly enriches the sample methods in the field of physical, mechanical, and seepage mechanics testing of columnar jointed rock masses. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the method flow of the present invention.

[0020] Figure 2 This is a polygonal cross-sectional view of columnar jointed rock mass with different cross-sectional shapes according to the present invention.

[0021] Figure 3 This is a physical image of a 3D printed columnar joint network with different inclination angles containing an irregular cross section, according to the present invention.

[0022] Figure 4 This is a schematic diagram of the structure of the disposable sample preparation mold of the present invention.

[0023] Figure 5 This is a schematic diagram of the upper casting cavity of the disposable sample preparation mold of the present invention.

[0024] Figure 6 This is a schematic diagram of the structure of the lower base plate and the vibration section of the disposable sample preparation mold of the present invention.

[0025] Figure 7This is a schematic diagram of a columnar jointed rock mass similar material sample of the present invention.

[0026] Figure 8 This is a schematic diagram of the compression failure of a columnar jointed specimen imported into discrete element software according to the present invention.

[0027] Reference numerals: 1. Upper casting cavity; 11. Main back plate; 12. Auxiliary back plate; 13. Tie bolt; 14. Lower insert plate; 2. Lower base plate; 21. Drainage hole; 22. Drainage channel; 23. Slot; 3. Vibration section; 31. Vibration control switch. Detailed Implementation

[0028] The embodiments of the present invention will now be described in further detail with reference to the accompanying drawings.

[0029] Columnar jointed rock mass similar material samples were prepared using the method and process of this invention, such as... Figure 1 As shown, this can be achieved through the following steps: Step S1) Geological survey Mathematical statistics were performed on the columnar joint sections of the study area, and in-situ column cross-sectional diagrams were generated based on the engineering structural characteristics, such as... Figure 2 As shown.

[0030] Step S2) 3D printing columnar joint network Four joint networks with tilt angles β of 45°, 60°, 75°, and 90° were generated in Rhino 7.0 software. The external dimensions of each joint network were 100mm × 100mm × 100mm cubes, and the network thickness was 1mm. A soluble material, polyvinyl acetate (PVA), was added to the Sermoon D3 3D printer. After printing, the joint networks were stored in a dark place at low temperature. The joint networks are shown below. Figure 3 As shown.

[0031] Step S3) First pouring A mold for preparing one-time specimens of columnar jointed rock mass, such as... Figure 4 , Figure 5 , Figure 6As shown, the disposable sample preparation mold includes an upper casting cavity 1, a lower base plate 2, and a vibrating section 3. The upper casting cavity 1 consists of two main back plates 11 and two auxiliary back plates 12 arranged opposite each other. The main back plates 11 and auxiliary back plates 12 are fitted together and further fixed by several tie bolts 13 to ensure the airtightness and watertightness of the upper casting cavity 1. The main back plates 11 and auxiliary back plates 12 are respectively connected to the slots 23 of the lower base plate 2 through lower insert plates 14. The vibrating section 3 is located at the four corners of the lower base plate 2 and is controlled to open and close by a vibration control switch 31. The lower base plate 2 is provided with several drainage holes 21 that all lead to a drainage channel 22 of the lower base plate 2. The drainage channel 22 is controlled to open and close by a switch.

[0032] The cement mortar mix proportion for the column is similar to that of cement, gypsum, river sand and water, with a weight ratio of 5:0.5:2.5:5. The amount of naphthalene-based early strength water-reducing agent added is 0.2% of the total mass.

[0033] The 3D-printed soluble columnar joint network prepared in step S2) is vertically placed into the columnar joint rock mass disposable sample preparation mold prepared in step S3). Vaseline is uniformly sprayed inside the mold. A well-stirred similar material solution with suitable workability is poured into the joint network. The sample is vibrated at a medium-low frequency for 10 minutes. Vibration is stopped when no floating slurry or air bubbles are observed on the upper surface of the sample. After vibration, the sample is left to stand for 30 minutes until the column has initially set and has a certain strength.

[0034] Step S4) Secondary pouring The 3D printed joint network was dissolved using a water bath method, while the drainage channel 22 at the bottom of the upper casting cavity 1 was opened to discharge the waste liquid.

[0035] The gypsum mortar mix proportion for preparing the joint network similar material was determined. The components were high-strength white cement and water, with a weight ratio of 1:0.5. A naphthalene-based early-strength water-reducing agent was added at 0.2% of the total mass. The joint network similar material solution was poured, vibrated to compact, and allowed to stand until the similar material achieved initial setting and strength. The tie bolts were removed, and the samples were taken out for further sample curing.

[0036] Step S5) Sample curing The cubic monolithic specimen is placed in a constant temperature curing chamber at a temperature of 20±1℃ and a humidity of ≥90% for no less than 28 days. The cubic monolithic specimen after curing is the prepared columnar jointed rock mass similar material specimen, which can be used for the next loading test.

[0037] Step S6) True triaxial loading test and numerical simulation of columnar jointed rock mass A true triaxial seepage test system was used to conduct similar material model tests on columnar jointed basalt samples. By applying triaxial unequal pressure loading and seepage pressure loading to the columnar jointed samples, the anisotropic deformation and seepage characteristics of the samples under different loading paths were studied. At the same time, the failure mode of columnar jointed rock mass was analyzed, so as to explore the deterioration and failure characteristics of bedrock and tunnel surrounding rock.

[0038] Numerical simulation images of a three-dimensional columnar jointed rock mass sample with a dip angle of 90° generated using Rhino software are shown below. Figure 7 As shown in the figure. After the experiment, numerical simulation was performed using the three-dimensional discrete element analysis software 3DEC. The joint and columnar mechanical parameters of the columnar jointed rock mass sample were fitted using inverse analysis. Further true triaxial stress-seepage coupling tests under different working conditions were then conducted. The numerical simulation process is as follows: Figure 8 As shown, different colored areas represent different axial displacements. Finally, the numerical simulation results are compared with the sample failure images captured by a high-definition camera to reveal the failure mode of columnar jointed rock masses under macro- and micro-scale conditions.

[0039] The above description is only a preferred embodiment of the present invention. It should be noted that those skilled in the art can make several improvements and modifications without departing from the concept of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for batch, one-time sample preparation for similar material model tests of columnar jointed rock masses, characterized in that... Includes the following steps: S1) Geological Survey Mathematical statistics were performed on columnar joint sections in the study area to construct cross-sectional diagrams of columnar jointed rock masses with different cross-sectional shapes; S2) 3D printed columnar jointed network A three-dimensional joint network was constructed from the obtained cross-sectional image of the columnar jointed rock mass, and then columnar joint networks with different dip angles were printed using 3D printing technology. S3) First pouring Install a disposable sample preparation mold, uniformly spray petroleum jelly inside the mold, place the 3D printed columnar joint network inside the mold; then pour a columnar similar material solution into the columnar joint network, use an appropriate vibration frequency and vibration time, and after vibration, let it stand until the columnar sample initially sets; S4) Secondary pouring The soluble joint network in the sample is dissolved by water bath, and the drain outlet at the bottom of the mold is opened to drain the waste liquid. Then, a joint-like material solution is poured into the sample, vibrated to compact it, and left to stand until the joint-like material initially sets. S5) Sample curing The columnar sample was placed in a constant temperature curing chamber with a temperature of 20±1℃ and a humidity of ≥90% for no less than 28 days to prepare a columnar jointed rock mass similar material sample. S6) Loading Test True triaxial loading tests and true triaxial stress-seepage coupled loading tests were conducted on similar material specimens of columnar jointed rock mass to obtain the physical model test structure. Meanwhile, the columnar jointed specimens were modeled in three dimensions using Rhino software, and the test conditions were imported into the discrete element software for numerical simulation. By comparing numerical simulation results with physical model test results, the failure mode of columnar jointed rock mass under macro-micro conditions is revealed.

2. The method for batch one-time sample preparation for similar material model tests of columnar jointed rock masses according to claim 1, characterized in that: In step S1), geological survey methods are used to investigate information such as the cross-sectional shape and rock occurrence of columnar jointed rock masses in the study area, determine the proportion of different cross-sectional shapes of columnar jointed rock masses, and further obtain the cross-sectional shape variation coefficient C. VQ The average area A of a single cross section Q and the average side length A of the prism L Using the aforementioned characterization parameters, the REV (representational unit volume) of the columnar jointed rock mass in the study area is determined. Irregular polygonal units are constructed using Delaunay triangulation, generating n seed points, each numbered V. i Further according to the formula (1) Find the seed point corresponding to the minimum distance, and the distance D between the seed points. i It can be expressed as a formula (2) Connect all the seed point boundaries to obtain the cross-sectional diagram of columnar jointed rock mass with different cross-sectional shapes, and number the polygons in sequence.

3. The method for batch one-time sample preparation for similar material model tests of columnar jointed rock masses according to claim 1, characterized in that: In step S2), based on the geological survey results, the axial dip angle of the columnar joint network is determined. β The columnar joint network is made of soluble polyvinyl acetate material and is set to 45°, 60°, 75° and 90°.

4. The method for batch one-time sample preparation for similar material model tests of columnar jointed rock masses according to claim 1, characterized in that: The disposable sample preparation mold includes an upper casting cavity, a lower base plate, and a vibration section. The upper casting cavity consists of two main back plates and two auxiliary back plates arranged opposite each other. The main back plates and auxiliary back plates are interlocked and further fixed by several tie bolts. The main back plates and auxiliary back plates are respectively connected to the lower base plate through lower insert plates. The vibration section is located at the four corners of the lower base plate.

5. The method for batch one-time sample preparation for similar material model tests of columnar jointed rock masses according to claim 1, characterized in that: In step S3), the cement mortar of the column-like material consists of cement, gypsum, river sand and water, with a weight ratio of 5:0.5:2.5:5; and a naphthalene-based early strength water-reducing agent is added, with an addition amount of 0.2% of the total mass.

6. The method for batch one-time sample preparation for similar material model tests of columnar jointed rock masses according to claim 1, characterized in that: In step S3), select a medium-low vibration frequency and vibrate for 10 minutes. Stop vibrating when no floating slurry or air bubbles are observed on the upper surface of the sample. After vibration, let stand for 30 minutes until the column has initially set and has a certain strength.

7. The method for batch one-time sample preparation for similar material model tests of columnar jointed rock masses according to claim 1, characterized in that: In step S4), the joint-similar material gypsum mortar is composed of high-strength white cement and water, with a weight ratio of 1:0.5; a naphthalene-based early-strength water-reducing agent is added, with an addition amount of 0.2% of the total mass.

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