A refined simulation method considering fault mechanics similarity and deformation similarity

Abstract

The application provides a fine simulation method considering fault mechanics similarity and deformation similarity, and utilizes rock block masonry structure surface lower rock mass and upper rock mass to set a simulated fault structure between the lower rock mass and the upper rock mass as a test model, and utilizes the test model to carry out a geomechanics model test, wherein the simulated fault structure is composed of plastic soft material and film material, the plastic soft material is made of barite powder, machine oil and high polymer material, and the thickness can be accurately 1mm, and the film material is aluminum foil paper, polyethylene, polyester and polyvinyl alcohol coating and the like. The application overcomes the shortcomings of the prior art, the simulated fault can be accurately 1mm, i.e. in the range of 100-300 scale, the application can realize the simulation of the fault with a width of 0.1m-0.3m in the engineering, thereby realizing the fine simulation of the engineering geological structure, improving the accuracy of the model test, and making the model test results more real and reliable.

Description

Technical Field

[0001] This invention belongs to the field of geomechanical model testing technology, and specifically relates to a refined simulation method that comprehensively considers fault mechanical similarity and deformation similarity. Background Technology

[0002] Theoretical analysis and numerical calculations have certain limitations when analyzing complex geological conditions. However, geomechanical model tests based on similarity theory can systematically simulate unfavorable structural planes such as faults, fracture zones, and weak interlayers, studying their impact on engineering deformation and stability. This allows for a direct, accurate, and comprehensive reflection of the spatiotemporal evolution of rock and soil masses under complex geological conditions and reveals their failure characteristics. Therefore, geomechanical model tests are an important tool for studying complex geological engineering and are widely used in major projects such as water conservancy, tunnels, and mining projects with complex geological conditions.

[0003] In geotechnical engineering, faults are widely developed fracture structures in the shallow crust that disrupt the continuity and integrity of rock masses. Faulted rock masses are characterized by low strength, large deformation, and high permeability, exhibiting significant differences in physical and mechanical properties compared to the surrounding rock masses. The presence of faults poses significant safety hazards to large-scale engineering projects such as water conservancy, tunneling, and mining. Therefore, faults are important simulation objects in geomechanical model tests, and refined simulation of fault structural surfaces is a key technology for ensuring the reliability of experimental results.

[0004] The current research status of experimental devices and operating methods for fault simulation in geomechanical model tests, both domestically and internationally, is as follows:

[0005] 1. Cui Guangyao et al. (Cui Guangyao, Wang Mingnian, Yu Li, Lin Guojin. Model test study on vibration reduction technology of damping layer for tunnels crossing stick-slip faults [J]. Chinese Journal of Geotechnical Engineering, 2013, 35(09): 1753-1758.) introduced a test technique for preparing stick-slip faults in model tests. The technique uses two layers of PVC plastic boards with grease in between to simulate stick-slip faults. The paper does not mention how to achieve geometric and mechanical similarity of the fault simulation, and the use of PVC boards will have a certain impact on the mechanical properties of the model materials near the fault.

[0006] 2. Xu Qianwei et al. (Xu Qianwei, Cheng Panpan, Zhu Hehua et al. Progressive failure model test and numerical simulation of surrounding rock of cross-fault tunnel [J]. Chinese Journal of Rock Mechanics and Engineering, 2016, 35(03):433-445.) introduced a test method using talc powder to simulate inclined faults and used a self-made shear box to determine the friction coefficient of the simulated fault. This technique does not consider the deformation characteristics of the fault, and in order to meet the shear strength characteristics of the fault, the required fault thickness is often large, which cannot meet the geometric similarity conditions of the model and may lead to dangerous test results.

[0007] 3. Liu Yaoru et al. (application number: 201310113054.4) introduced a method of pasting paper on both sides of dehydrated gypsum sheets to simulate discontinuous structural surfaces. However, dehydrated gypsum cannot meet the requirement of similar bulk density of model materials, and the cohesion of the fault is not considered, which makes the shear strength of the fault in the model too high or too low, which is inconsistent with the actual engineering.

[0008] 4. Ding Zelin et al. (Ding Zelin, Xue Jianghan, Wang Jing, Bao Chuang. Catastrophic failure criterion for model test of cemented gravel dam [J]. Journal of Hydroelectric Engineering, 2022, 41(09): 98-107.) introduced a method to simulate faults using soft materials, waxed paper, or polytetrafluoroethylene film. In the experiment, only the frictional force of the fault was considered, while the cohesion of the fault was ignored. The mechanical properties of the fault were considered according to the shear strength. This often leads to the cohesion of the model material being too high or too low, which does not meet the mechanical similarity requirements of the model test. In addition, for high arch dams of 200-300 meters, the method of considering the mechanical properties of the fault only by the shear strength is not suitable for the stability study of the abutments of high arch dams, and its practicality is low.

[0009] 5. In foreign countries, when simulating the friction coefficient, a mixture of varnish, lubricating grease and talc is often used as a coating between the layers. This method can obtain a wide range of different friction coefficients (f=0.1~1.0). However, the material properties are unstable and easily affected by temperature or spraying process, resulting in high dispersion and poor stability of the results.

[0010] In summary, traditional techniques often fail to simultaneously meet the conditions of geometric similarity, unit weight similarity, mechanical similarity, and deformation similarity in fault simulation, resulting in simulation results that often deviate from engineering reality and cannot truly reflect the deformation and stress characteristics of the engineering project. Summary of the Invention

[0011] To address the problems existing in the current research on experimental devices and operating methods for fault simulation in geomechanical model tests, this invention provides a refined simulation method that comprehensively considers fault mechanical similarity and deformation similarity.

[0012] The solution adopted by this invention to solve its technical problem is: a refined simulation method that comprehensively considers fault mechanical similarity and deformation similarity, using rock blocks to construct the footwall and hanging wall rock mass, setting up a simulated fault structure between the footwall and hanging wall rock mass as an experimental model, and using the experimental model to conduct geomechanical model tests.

[0013] The simulated fault structure includes a plastic soft material and a thin film material, and the preparation of the simulated fault structure includes the following steps:

[0014] S1. Preparation of plastic soft materials and thin film materials

[0015] The plastic soft material is made by mixing barite powder, machine oil and polymer materials in a certain proportion. Multiple sets of plastic soft material specimens with different machine oil contents are made, and each set contains multiple plastic soft material specimens.

[0016] The thin film material is initially selected based on the interlayer friction coefficient f in the experiment, and the material is cut into a predetermined shape and size.

[0017] S2. Calculate the deformation modulus E and shear strength.

[0018] The film material is attached to the upper surface of the plastic soft material specimen. Uniaxial compression and shear tests are performed on the combined block of the plastic soft material specimen and the film material, respectively. The average deformation modulus E and average shear strength of the combined block are obtained. If the parameters are similar to the prototype parameters, the film material is used. If they are not similar to the prototype parameters, a new film material or plastic soft material is selected for the test.

[0019] S3, a combination of soft plastic material and thin film to simulate fault structure.

[0020] The model is constructed from the downstream area to the upstream area. When constructing the fault, plastic soft material is first rammed or laid on the side of the lower rock mass. The film material is then pasted in a staggered manner on the contact surface between the plastic soft material and the upper rock mass. After pasting, the upper rock mass is constructed.

[0021] In step S2, when conducting the shear test, the friction coefficient and cohesion of the fault material are first calculated. The normal stress on the fault in the model is calculated using similarity relationships. The calculation results are then substituted into the Mohr-Coulomb formula to calculate the shear strength of the fault material.

[0022] Uniaxial compression and shear tests were conducted on multiple sets of composite blocks to select the composite blocks that could simultaneously meet the requirements of fault deformation similarity and shear strength similarity. When deformation similarity and shear strength similarity could not be met simultaneously, the requirement of shear strength similarity of the model was prioritized.

[0023] In step S3, for faults with a width > 1 cm in the masonry model, the plastic soft material is pressed into small blocks and masonry is carried out using the ramming method. For faults with a width between 1 mm and 1 cm, the filling method is used for masonry.

[0024] Furthermore, when the simulated fault width is >1cm, the plastic soft material is stirred evenly and poured into a mold to form small blocks; when the simulated fault width is in the range of 1mm to 1cm, the plastic soft material is mixed evenly and wrapped in a plastic bag made of plastic film, left to stand for 48 hours, and then laid on the footwall rock mass.

[0025] The dimensions of the rock blocks in the lower and upper rock masses of the masonry structure are 10cm×10cm×10cm.

[0026] In step S2, six sets of composite blocks are made. Three sets are subjected to uniaxial compression tests, and the other three sets are subjected to shear tests. The average deformation modulus E and average shear strength of the composite blocks are obtained through multiple tests.

[0027] The film material is aluminum foil, polyethylene, polyester, or polyvinyl alcohol coating, etc.

[0028] The beneficial effects of this invention are as follows: The faults simulated by this invention can be accurate to 1 mm. That is, within the scale range of 100 to 300, this invention can simulate faults with a bandwidth of 0.1 m to 0.3 m in engineering projects, realize the fine simulation of engineering prototypes, and thus improve the accuracy of model test results.

[0029] This invention solves the problem of density similarity of fault materials in model tests. This invention uses a plastic soft material + film material to simulate the structural surface. The plastic soft material is composed of barite powder, machine oil and polymer materials. The material properties are relatively stable. Barite powder has the advantages of high density, low strength, low modulus of elasticity and low cost. It can meet the density similarity requirements of fault structure while achieving low modulus of elasticity.

[0030] This invention comprehensively considers the shear strength of the fault to meet the mechanical similarity requirements of the model. It also comprehensively considers the friction coefficient and cohesion of the material. By satisfying the shear strength similarity, the mechanical similarity between the model and the prototype is achieved, which is more in line with engineering practice and the test results are highly reliable.

[0031] This invention achieves the deformation similarity requirement for fault simulation. It uses barite powder, engine oil, and polymer materials to simulate fault materials. For specific faults in specific engineering projects, a uniaxial compression test is conducted on a combined block of plastic soft material and thin film material according to its inherent material parameters. The plastic soft material that meets the requirements of fault deformation parameters is selected, thereby satisfying the deformation similarity requirement of the material. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of a fault simulation structure.

[0033] Figure 2 This is a table of data from arch dam prototype and model tests.

[0034] Figure 3 These are the calculation results from uniaxial compression and shear tests.

[0035] The diagram is labeled as follows: 1. Plastic soft material; 2. Thin film material; 3. Lower footwall rock mass; 4. Upper footwall rock mass. Implementation

[0036] Example 1: The purpose of this invention is to overcome the shortcomings of existing technologies and provide a method for simulating fault structures in geomechanical model tests, thereby achieving refined simulation of engineering geological structures, improving the accuracy of model tests, and making the results of model tests more realistic and reliable.

[0037] like Figure 1 As shown, this invention utilizes the rock block masonry structure to construct the footwall rock mass 3 and the footwall rock mass 4, and sets up a simulated fault structure between the footwall rock mass 3 and the footwall rock mass 4 as an experimental model, and uses the experimental model to conduct geomechanical model tests.

[0038] The simulated fault structure consists of a plastic soft material 1 and a thin film material 2. The plastic soft material is made of barite powder, machine oil and polymer materials in a specific ratio, and the thickness can be accurate to 1 mm. The thin film material is made of aluminum foil, polyethylene, polyester and polyvinyl alcohol coating, etc.

[0039] The specific preparation method of the fault structure includes: ① preparation of plastic soft material 1 and film material 2; ② determination of the plastic soft material 1 and film material 2 according to the deformation modulus E and shear strength; ③ simulation of the fault structure by combining plastic soft material and film.

[0040] The specific process is as follows:

[0041] The first step is the preparation of plastic soft materials and thin film materials: referring to previous engineering experience and combining the deformation and mechanical parameters of the specific project, multiple test schemes are initially formulated for each fault, and 6 specimens are made for each scheme.

[0042] The plastic soft material was prepared using barite powder, machine oil, and polymer materials. Multiple sets of plastic soft material specimens with varying machine oil contents were fabricated, with multiple specimens prepared for each set. The simulated fault bandwidth was >1cm (this is the model value; the prototype value is based on the geometric scale C). L =100~300, approximately 1m~3m), mix barite powder, machine oil and polymer materials according to the pre-set ratio, stir evenly and pour into a mold to make small blocks (the area of ​​the small blocks is 10cm×10cm, and the thickness is the fault bandwidth); when the simulated fault bandwidth is in the range of 1mm to 1cm (the model value), after the materials are mixed evenly, wrap them in a plastic bag and let them stand for 48h.

[0043] In the experiment, the corresponding film material was initially selected based on the fault friction coefficient f, and the material was cut into a predetermined shape and size. During the experiment, the fault will be subjected to arching thrust compression and shearing. If the entire film material is pasted onto the surface of the soft plastic material, the film is prone to wrinkling under shear force, thereby changing the stress state of the fault and deviating from the actual engineering situation. Therefore, the film material needs to be processed. Since the size of the soil and rock modules in the model is 10cm×10cm×10cm, corresponding to the rock joints, the film material is also cut to a size of 10cm×10cm.

[0044] Step two involves calculating the deformation modulus E and shear strength: The film material 2 is adhered to the upper surface of the soft plastic specimen. Uniaxial compression tests (3 groups) and shear tests (3 groups) are then conducted on the assembled block to obtain the average deformation modulus E and average shear strength. These parameters need to be similar to the prototype parameters based on similarity relationships. If they are not similar, a new film material or soft plastic specimen needs to be selected for the test.

[0045] When conducting shear tests, the friction coefficient and cohesion of the fault material are first calculated. The normal stress on the fault in the model is calculated using similarity relationships. The calculation results are then substituted into the Mohr-Coulomb formula to calculate the shear strength of the fault material.

[0046] Multiple test schemes were subjected to uniaxial compression and shear tests, and the scheme that could simultaneously meet the requirements of fault deformation similarity and shear strength similarity was selected. When deformation similarity and shear strength similarity could not be simultaneously met, the scheme that met the shear strength similarity requirement of the model was prioritized.

[0047] Step three involves simulating fault structures using a combination of plastic soft material and film: the model is constructed from the downstream far zone to the upstream. When constructing the fault, plastic soft material is first compacted or laid on the footwall side. Films measuring 10cm x 10cm are then staggered and pasted onto the contact surface between the plastic soft material and the footwall. After pasting, the footwall rock material is continued to be constructed. For faults with a width > 1cm in the model, the plastic soft material is compressed into small blocks and constructed using the compaction method. For faults with a width between 1mm and 1cm, the laying method is used.

[0048] Example 2: Taking a model test of an arch dam as an example, the present invention is illustrated. The geometric similarity coefficient, deformation modulus similarity coefficient, and shear strength similarity coefficient of the arch dam model test are as follows: The fault simulation method of this example includes three parts: preparation of plastic soft material and film material, calculation of deformation modulus E and shear strength, and simulation of fault structure by combining plastic soft material and film.

[0049] The prototype and model test data of the arch dam in this embodiment are as follows: Figure 2 As shown:

[0050] This embodiment specifically includes the following steps:

[0051] 1. Preparation of plastic soft materials and thin film materials

[0052] In the model test of this embodiment, the geometric similarity coefficient is 250, the deformation model similarity coefficient is 250, and the shear strength similarity coefficient is 250. Taking the left bank fault f124 as an example, its average bandwidth is 350 mm, its deformation modulus is less than 1 GPa, its average shear strength is 1.64 MPa, and its friction coefficient is 0.45; then the corresponding model fault has a bandwidth of 1.40 mm, a deformation modulus of less than 4 MPa, a shear strength of 6.6 kPa, and a friction coefficient of 0.45.

[0053] In this project, the fault deformation modulus in the model tests was less than 4 MPa. Therefore, three groups of soft plastic material specimens with oil contents of 8.0%, 9.0%, and 10.0% were prepared, with multiple specimens prepared for each group. For the film material, different combinations of materials such as aluminum foil, polyethylene, polyester, and polyvinyl alcohol coating were selected according to their friction coefficients. The friction coefficient of the simulated fault in this embodiment is 0.45. Based on previous engineering experience, the tentative simulation schemes are two layers of wax paper, aluminum foil + wax paper + aluminum foil, and two layers of polyethylene.

[0054] There are a total of 9 experimental schemes for the above combination of plastic soft material and film material, and 6 specimens are made for each scheme for testing.

[0055] 2. Calculate the deformation modulus E and shear strength.

[0056] The film material needs to be adhered to the contact surface between the plastic soft material and the hanging wall rock to provide shear strength. In the test, the film material is adhered to the upper surface of the plastic soft material for uniaxial compression and shear tests. Three specimens are taken from each group for uniaxial compression tests, the deformation modulus of these three specimens is measured, and the average deformation modulus is calculated.

[0057] Three specimens from each design were subjected to shear tests, and their average shear strength was calculated. During the shear test, the friction coefficient and cohesion of the fault material were first calculated. The normal stress on the fault in the model was then calculated using similarity relationships, and the results were substituted into the Mohr-Coulomb formula to calculate the shear strength of the fault material. The deformation modulus and shear strength corresponding to the above designs are as follows: Figure 3 As shown.

[0058] Based on the calculation results, in this embodiment, the fault f124 is simulated using a plastic soft material with an oil content of 10.0% and two layers of polyethylene film material.

[0059] 3. Simulation of fault structure by combining soft plastic material and thin film

[0060] In the model test of this embodiment, the geometric similarity coefficient is 250, the fault f124 bandwidth is 350mm, and after conversion, its model bandwidth is 1.40mm<1cm. The masonry is constructed using the filling method.

[0061] The model is constructed from the downstream far zone to the upstream. When constructing the fault, plastic soft material is first laid on the side of the lower rock mass. A 10cm×10cm film material is then pasted in a staggered manner on the contact surface between the plastic soft material and the upper rock mass. After pasting, the upper rock mass material is continued to be constructed.

Claims

1. A fine simulation method considering fault mechanics similarity and deformation similarity, comprising the following steps: preparing a test model by using a rock block masonry structure surface lower rock mass (3) and upper rock mass (4) and setting a simulated fault structure between the lower rock mass (3) and the upper rock mass (4); and performing a geomechanical model test by using the test model. characterized in that The simulated fault structure comprises plastic soft material (1) and film material (2), and the preparation of the simulated fault structure comprises the following steps: S1, preparing plastic soft material (1) and film material (2) The plastic soft material (1) is prepared by proportioning barite powder, machine oil and high molecular material, and a plurality of plastic soft material test pieces with different machine oil contents are prepared, and each group contains a plurality of plastic soft material test pieces; The film material (2) is preliminarily selected according to the fault friction coefficient f in the test, and the material is cut into a predetermined shape and size; S2, calculating the deformation modulus E and the shear strength The film material (2) is pasted on the upper surface of the plastic soft material test piece, and the uniaxial compression test and the shear test are performed on the combined block of the plastic soft material test piece and the film material (2), so as to obtain the average deformation modulus E and the average shear strength of the combined block, and if the average deformation modulus E and the average shear strength are similar to the prototype parameters, the film material is adopted, and if the average deformation modulus E and the average shear strength are not similar to the prototype parameters, the film material or the plastic soft material is reselected for test; S3, plastic soft material and film combined simulation fault structure The model masonry sequence is from the downstream far zone to the upstream, and when the fault is masonry, the plastic soft material (1) is first rammed or laid on the lower rock mass (3) side, the film material (2) is staggered and pasted on the contact surface between the plastic soft material (1) and the upper rock mass (4), and after pasting, the upper rock mass (4) is masonry.

2. The refined simulation method considering fault mechanics similarity and deformation similarity according to claim 1, characterized in that, In step S2, the friction coefficient and the cohesion of the fault material are calculated first, the normal stress of the fault in the model is calculated by using the similarity relationship, and the shear strength of the fault material is calculated by bringing the calculation result into the Mohr-Coulomb formula; A plurality of combined blocks are subjected to uniaxial compression and shear test, and a combined block which can simultaneously satisfy the fault deformation similarity and the shear strength similarity is selected from the combined blocks, and when the deformation similarity and the shear strength similarity cannot be simultaneously satisfied, the shear strength similarity of the model is mainly satisfied.

3. The refined simulation method with consideration of fault mechanics similarity and deformation similarity according to claim 1, characterized in that, In step S3, the fault with a width of more than 1 cm in the masonry model is pressed into small blocks by using the plastic soft material, and is masonry by using the ramming method, and for the fault with a width of 1 mm to 1 cm, the laying method is used for masonry.

4. The refined simulation method with consideration of fault mechanics similarity and deformation similarity according to claim 3, characterized in that, When the simulated fault width is more than 1 cm, the plastic soft material (1) is stirred uniformly and then poured into a mold to form small blocks; when the simulated fault width is in the range of 1 mm to 1 cm, the plastic soft material (1) is mixed uniformly and then wrapped in a plastic bag made of film material (2), and after standing for 48 h, the plastic soft material is laid on the lower rock mass (3).

5. The refined simulation method with consideration of fault mechanics similarity and deformation similarity according to claim 1, characterized in that, The size of the rock block is 10 cm x 10 cm x 10 cm.

6. The refined simulation method with consideration of fault mechanics similarity and deformation similarity according to claim 1, characterized in that, In step S2, six groups of combined blocks are prepared, three of which are subjected to uniaxial compression test, and the other three are subjected to shear test.

7. The refined simulation method with consideration of fault mechanics similarity and deformation similarity according to claim 1, characterized in that, The film material (2) is aluminum foil paper, polyethylene, polyester and polyvinyl alcohol coating.

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