Similar material sample preparation method suitable for lamellar physicochemical altered rock indoor test

Abstract

The invention provides a preparation method of a similar material sample suitable for a lamellar physico-chemical altered rock indoor test. The preparation method comprises the following steps: S1, determining types and proportions of similar materials; s2, after the similar materials are pretreated, accurate weighing is conducted according to a preset differentiation ratio; 5-10 layers of material ratio gradients are designed according to the differentiated ratio, and a strong alteration layer, a weak alteration layer and a transition layer are simulated; preparing the proportioned dry materials into a mixed material; s3, the mixture is placed in a mold; a layer-by-layer tamping method is adopted to cyclically tamp the mixture and the flaky similar material, and altered rock similar material samples with different dip angle flaky structures are prepared; s4, carrying out segmented solidification control and surface refining treatment on the altered rock similar material sample; and S5, carrying out internal structure characterization and mechanical property testing on the altered rock similar material sample. According to the method, the problems of rock mass primary structure damage, mineral component loss and the like caused by a traditional process are effectively solved, and the reliability of rock mass mechanical parameter testing and the accuracy of geological engineering evaluation can be remarkably improved.

Description

Technical Field

[0001] This invention relates to the field of rock mechanics and rock physical mechanics testing technology, specifically to a method for preparing similar material samples suitable for laboratory testing of foliated altered rocks. Background Technology

[0002] Foliar altered rocks are special rock masses formed by tectonic processes that create oriented foliation in primary rock masses, further modified by subsequent hydrothermal alteration. They are widely distributed in geologically active areas or regions frequently disturbed by engineering projects. Due to the directional development of foliation surfaces and the altered physicochemical properties of altered minerals, these rock masses exhibit significant heterogeneity, anisotropy, and softening characteristics upon contact with water. They are prone to progressive deformation and failure under engineering loads or environmental influences, and are a major contributing factor to geological disasters such as tunnel surrounding rock instability, slope slippage, and mine goaf collapse.

[0003] Due to their complex structural characteristics and mechanical behavior, traditional rock mechanics testing methods face significant bottlenecks in revealing their catastrophic mechanisms. Firstly, conventional similar materials are often designed based on homogeneous assumptions (such as cement-gypsum-based materials), making it difficult to reproduce the directional arrangement of foliation surfaces and the discontinuous weak surface structure of alteration zones. This results in experimental models failing to characterize the anisotropic mechanical response of real rock masses. Secondly, existing preparation processes lack targeted simulations of the water-softening effects of altered minerals (such as chlorite and kaolinite), leading to significant differences in material softening characteristics compared to the prototype rock mass. Consequently, experimental results are insufficient to support stability analysis under hydro-mechanical coupling. Furthermore, the strength parameters (such as shear strength and deformation modulus) of foliated altered rocks are synergistically influenced by the foliation dip angle, alteration degree, and confining pressure. Traditional proportioning methods struggle to achieve precise matching of multiple parameters through single-variable control, limiting the engineering applicability of experimental data. These issues lead to significant deviations between laboratory test results and actual rock mass behavior in engineering projects, directly impacting the reliability of engineering design parameters and potentially triggering engineering disasters. Therefore, developing a method for preparing similar materials that can accurately simulate the structural characteristics and mechanical properties of foliated altered rocks has become a key issue that urgently needs to be addressed in the field of geomechanical testing technology, and it has important scientific significance for improving the ability to predict engineering disasters in complex rock masses. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the present invention aims to provide a method for preparing similar material samples suitable for laboratory testing of foliated altered rocks. This invention effectively solves the problems of damage to the original rock structure and loss of mineral components caused by traditional processes, and can significantly improve the reliability of rock mass mechanical parameter testing and the accuracy of geological engineering evaluation.

[0005] This invention provides a method for preparing similar material samples suitable for laboratory testing of foliated altered rocks, comprising the following steps: S1: Based on the measured physical and mechanical parameters of the altered rocks in the engineering area, determine the types and proportions of similar materials, including: bentonite, plastic resin, quartz sand, and mica powder. S2: After pretreatment of similar materials, they are accurately weighed according to a preset differentiated ratio; the differentiated ratio is designed with 5 to 10 material ratio gradients based on the degree of rock alteration in the engineering area to simulate strong alteration layer, weak alteration layer and transition layer; then the proportioned dry materials are made into a mixture as the matrix through a wet material mixing process; S3: Install a detachable sample preparation mold, uniformly spray a release agent into the mold, place the mixture into the mold; use a layer-by-layer filling and pressing method to cyclically fill and press the mixture and foliated similar materials as the matrix to prepare altered rock similar material samples with different dip angles of foliation; S4: After segmented solidification control of the altered rock similar material sample, the surface of the altered rock similar material sample is finely treated. S5: Characterize the internal structure and test the mechanical properties of the prepared altered rock-like material samples.

[0006] As a preferred technical solution of the present invention: in step S1, the proportions of the similar materials are as follows: 30% to 50% of the total mass of bentonite simulates the clay mineral characteristics in altered rocks; 20% to 40% of the total mass of quartz sand and mica powder simulates the physicochemical mineral framework of altered rock schist; and 30% to 50% of the total mass of plastic resin simulates the cementing material in altered rocks.

[0007] As a preferred embodiment of the present invention: the pretreatment of the similar materials in step S2 includes: Bentonite activation: Industrial-grade sodium-based bentonite with a particle size ≤0.075mm was placed in an oven and dried at 105℃ for 4 hours to remove adsorbed water; Quartz sand and mica powder grading: Quartz sand with a particle size of 0.1~0.5mm is washed and screened, and mica powder with a particle size of 0.05~0.2mm is separated by electrostatic separation to ensure the integrity of the flaky particles.

[0008] As a preferred technical solution of the present invention: in step S2... The strongly altered layer is used to simulate highly clay-like areas. The composition of the strongly altered layer is: 50% bentonite, 20% quartz sand, 20% mica powder, and 10% plastic resin. The weakly altered layer is used to preserve the mineral framework characteristics. The composition of the weakly altered layer is: 30% bentonite, 30% quartz sand, 30% mica powder, and 10% plastic resin. The transition layer is used to avoid abrupt changes in mechanical properties, and 2 to 3 transition layers are set between adjacent layers.

[0009] As a preferred embodiment of the present invention: the wet material mixing process in step S2 includes the following steps: S21: Dry mixing stage: Pour the precisely weighed similar materials into a dry mixer and mix at low speed to ensure uniform dispersion; S22: Wet mixing stage: Premix glycerin and deionized water in a 1:3 ratio, then slowly pour the mixture into the mixer while simultaneously increasing the speed and stirring until a lump-free paste is formed; S23: Vacuum degassing: Transfer the mixture to a vacuum mixing tank and continue stirring to remove air bubbles and avoid internal pores in the sample.

[0010] As a preferred technical solution of the present invention: in step S3, the mold release agent is a silicone oil-based mold release agent uniformly sprayed on the inner wall of the mold or a polytetrafluoroethylene film applied thereon.

[0011] As a preferred embodiment of the present invention: In step S3, the layer-by-layer compaction process includes the following steps: S31: Substrate laying: Fill the bottom of the mold with the mixture, and control the thickness to be 2~3mm; S32: Matrix Oriented Pressing: Lightly press the surface of the mixture to form an oriented micro-protrusion structure; S33: Foliar-like material paving: Mica powder is evenly sprinkled on the surface of the mixture to simulate the foliation surface of altered rock using its flaky properties; the foliar-like material paving surface is at an angle to the horizontal plane. β By adjusting the laying angle, similar material samples of altered rocks with different foliation dip angles can be obtained; S34: Interface activation: Spray atomized water onto the surface of the cured layer to improve interlayer adhesion; S35: Cyclic compaction: Repeat steps S31~S34, with the total number of layers set according to test requirements; S36: Vibratory compaction: After the cyclic filling is completed, the sample of the altered rock similar material is compacted by using the sample preparation mold.

[0012] As a preferred embodiment of the present invention: the altered rock similar material sample, after being filled with a mold, is set into a cubic or cylindrical shape, and the foliation dip angle of the altered rock similar material sample is... β Set to 0°, 30°, 45°, 60°, or 90°.

[0013] As a preferred technical solution of the present invention: In step S4, the segmented solidification process of the altered rock-like material sample includes the following steps: S401: Initial setting and shaping: Before demolding, let it stand for a period of time at an ambient temperature of 25℃ and a humidity of 70% to allow the silicone rubber to initially crosslink and the gypsum to complete the hydration reaction. S402: Bentonite hydration enhancement: The sample was moved to a humidity curing chamber to promote full water absorption and expansion of bentonite, simulating the water content of natural altered rocks; S403: Gradient drying: First, dry at 40℃ for 6 hours, then raise the temperature to 50℃ and dry for 12 hours, with the final moisture content controlled at 8%~12%; S404: Balancing treatment: After drying, place in a desiccator and equilibrate with the test environment for 24 hours to eliminate internal stress.

[0014] As a preferred technical solution of the present invention: In step S4, the surface refinement process of the altered rock-like material sample includes the following steps: S411: Surface finishing: Grind unidirectionally along the bedding direction of the altered rock-like material sample to remove burrs and expose the internal structure. Grinding depth ≤ 0.2 mm. S412: Protective coating: For easily weathered samples, spray a 2%~5% concentration of polyvinyl alcohol solution or a transparent polyurethane coating to prevent debris from falling off during the test. S413: Marking and Numbering: Use a laser marking machine to mark the layer direction arrows and numbers on the non-stressed surface of the sample to ensure the consistency of the test loading direction.

[0015] The beneficial effects provided by this invention are as follows: This invention patent addresses the challenges in studying the mechanical properties of foliated altered rocks in geological engineering by innovatively proposing a precise method for preparing similar materials for indoor testing. By simulating the foliation structure, alteration characteristics, and mechanical parameters of real rock masses, it overcomes the bottleneck problem of traditional test materials' inability to effectively reproduce complex geological structures, significantly improving the reliability of research on rock mass deformation and failure mechanisms. Its results can be widely applied in fields such as tunnel surrounding rock stability analysis, geological disaster prevention and control, and mine engineering safety assessment. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the description of the embodiments or the prior art 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.

[0017] Figure 1 The main flowchart of the method for preparing similar material samples suitable for indoor testing of foliated altered rocks provided in the embodiments of the present invention; Figure 2 This is a three-dimensional structural schematic diagram of the apparatus for preparing cubic samples of foliated altered rock similar materials provided in an embodiment of the present invention; Figure 3A three-dimensional structural schematic diagram of the apparatus for preparing cylindrical samples of foliated altered rock similar materials provided in an embodiment of the present invention; Figure 4 A schematic diagram (front view) of cylindrical altered rock samples with different foliation dip angles provided in an embodiment of the present invention. Figure 5 A schematic diagram (front view) of cubic altered rock samples with different foliation dip angles provided in an embodiment of the present invention.

[0018] Reference numerals: 1. Hydraulic rod; 2. Axial preload plate for cubic specimen; 3. Tie bolt; 4. Back plate for cubic specimen preparation; 5. Vibration section; 6. Lower base plate; 7. Drainage channel; 8. Control panel for vibration table; 9. Axial preload plate for cylindrical specimen; 10. Back plate for cylindrical specimen preparation. Detailed Implementation

[0019] To enable those skilled in the art to better understand the technical solutions of the present invention, preferred embodiments of the present invention are described below in conjunction with specific examples. However, it should be understood that the accompanying drawings are for illustrative purposes only and should not be construed as limiting the present invention. For better illustration of this embodiment, some components in the drawings may be omitted, enlarged, or reduced, and do not represent the actual dimensions of the product. It is understandable that some well-known structures and their descriptions may be omitted in the drawings for those skilled in the art. The positional relationships described in the drawings are for illustrative purposes only and should not be construed as limiting the present invention.

[0020] The present invention will be further described below with reference to the accompanying drawings and embodiments, but this should not be construed as limiting the present invention.

[0021] like Figure 1 As shown, a method for preparing similar material samples suitable for laboratory testing of foliated altered rocks includes the following steps: S1: Material Selection and Proportioning Design. Based on the measured physical and mechanical parameters of the altered rocks in the engineering area, the types and proportions of similar materials were determined. The types of similar materials are: bentonite, plastic resin, quartz sand, and mica powder. Specifically, based on the on-site analysis of the mineral composition of the foliated altered rocks, the types and proportions of similar materials were determined.

[0022] In step S1, the proportions of the similar materials are as follows: 30% to 50% of the total mass of bentonite simulates the characteristics of clay minerals in altered rocks, providing high plasticity and water absorption and swelling properties; 20% to 40% of the total mass of quartz sand and mica powder simulates the physicochemical mineral framework of altered rocks, with mica powder used to enhance foliation orientation; and 30% to 50% of the total mass of plastic resin simulates the cementing substances in altered rocks, enhancing the material's ductility, preventing brittle fracture, and adjusting the curing time.

[0023] S2: Pretreatment and layered mixing of similar materials. After pretreatment, the similar materials are precisely weighed according to a preset differentiated ratio. The differentiated ratio is designed with a gradient of 5 to 10 material ratios based on the degree of rock alteration in the engineering area to simulate strong alteration layers, weak alteration layers, and transition layers. Subsequently, the proportioned dry materials are processed into a mixture as the matrix through a wet material mixing process. In step S2, the pretreatment of each similar material includes: Bentonite activation: Industrial grade sodium-based bentonite with a particle size ≤0.075mm is placed in an oven and dried at 105℃ for 4 hours to remove adsorbed water, and then passed through a 200-mesh sieve for later use. Quartz sand and mica powder grading: Quartz sand with a particle size of 0.1~0.5mm is washed and screened, and mica powder with a particle size of 0.05~0.2mm is separated by electrostatic separation to ensure the integrity of the flaky particles.

[0024] Weighing of similar materials: Weigh the dry materials layer by layer according to the preset ratio using an electronic balance (accuracy 0.01g), with the error controlled within ±0.5%.

[0025] In step S2 The strongly altered layer is used to simulate highly clay-like areas. The composition of the strongly altered layer is: 50% bentonite, 20% quartz sand, 20% mica powder, and 10% plastic resin. The weakly altered layer is used to preserve the mineral framework characteristics. The composition of the weakly altered layer is: 30% bentonite, 30% quartz sand, 30% mica powder, and 10% plastic resin. The transition layer is used to avoid abrupt changes in mechanical properties. Two to three transition layers are set between adjacent layers (the proportion of bentonite increases by 5% in each transition layer).

[0026] In step S2, the wet material mixing process includes the following steps: S21: Dry mixing stage: Pour the precisely weighed similar materials (bentonite, quartz sand, mica powder, plastic resin) into a dry mixer and mix at low speed (30 rpm) for 5 minutes to ensure uniform dispersion; S22: Wet mixing stage: Premix glycerin and deionized water in a 1:3 ratio (glycerin lubrication + water activation of bentonite), slowly pour into the mixer, and simultaneously increase the speed to 60 rpm, and mix for 15-20 minutes until a lump-free paste is formed; S23: Vacuum degassing: Transfer the mixture to a vacuum mixing tank and continue mixing for 5 minutes to remove air bubbles and avoid internal pores in the sample.

[0027] S3: Oriented bedding construction of foliated altered rock similar material specimens. A detachable specimen preparation mold is installed, and a release agent is uniformly sprayed inside the mold. The mixture is placed inside the mold, and the release agent is sprayed to ensure the integrity of the interface after demolding. The mixture and foliated similar material as the matrix are cyclically filled and compacted using a layer-by-layer filling and pressing method. A centrifuge is used to prepare altered rock similar material specimens with different dip angles of foliation by layer-by-layer centrifugation. In step S3, the release agent is a silicone oil-based release agent (approximately 10 μm thick) uniformly sprayed onto the inner wall of the mold or a polytetrafluoroethylene film, ensuring the integrity of the interlayer interface after demolding.

[0028] In step S3, the layer-by-layer compaction process includes the following steps: S31: Substrate laying: Fill the bottom of the cubic or cylindrical mold with the mixture, and control the thickness to 2~3mm (error ±0.1mm); use a laser thickness gauge to monitor the filling thickness in real time; S32: Matrix directional pressing: The axial pre-pressing sheet controlled by hydraulic pressure inside the mold is gently pressed onto the surface of the mixture along the long axis of the mold (preset layering direction) at a pressure of 0.05~0.1MPa. After holding the pressure for 10 seconds, the pressure is slowly released to form a directional micro-protrusion structure. S33: Laying of similar materials: Evenly sprinkle mica powder (0.5g / cm²) on the surface of the mixture through an 80-mesh sieve. 2 The foliated properties of the material are used to simulate the foliation surface of altered rocks; the foliation-similar material is laid at an angle to the horizontal plane. β When laying similar materials horizontally, the angle of inclination is... β =0°, by adjusting the laying angle, similar material samples of altered rocks with different foliation dip angles can be obtained; S34: Interface activation: Spray atomized water onto the surface of the cured layer to improve interlayer adhesion; S35: Cyclic compaction: Repeat steps S31~S34, with a 10-minute interval between each layer (initial setting time). The total number of layers is set according to the test requirements. The compaction process must be carried out under constant temperature and humidity conditions (temperature 20±2℃, humidity 60±5%).

[0029] S36: Vibration compaction: After the cyclic filling is completed, the sample is compacted by the vibration section at the bottom of the sample preparation mold, and then the sample is further compacted by the axial preload plate.

[0030] The altered rock-like material specimens, after being filled with molds, are set into cubic or cylindrical shapes. Figure 4 , Figure 5 The foliation dip angle of the altered rock similar material sample shown β Set to 0°, 30°, 45°, 60°, or 90°.

[0031] S4: Curing and post-treatment of foliated altered rock similar materials. After segmented curing control of the altered rock similar material samples, the surface of the altered rock similar material samples is refined. Specifically, in step S4, the segmented solidification process of the altered rock-like material sample includes the following steps: S401: Initial setting and shaping: Let stand for 12 hours before demolding, at an ambient temperature of 25℃ and a humidity of 70%, so that the silicone rubber can initially crosslink and the gypsum can complete the hydration reaction. S402: Bentonite hydration enhancement: The sample was moved to a humidity curing chamber (humidity 90%±3%, temperature 30℃) for 48 hours to promote full water absorption and expansion of bentonite, simulating the water content of natural altered rocks. S403: Gradient drying: First, dry at 40℃ for 6 hours, then raise the temperature to 50℃ and dry for 12 hours, with the final moisture content controlled at 8%~12% (monitored in real time by weighing method). S404: Balancing treatment: After drying, place in a desiccator and equilibrate with the test environment (e.g., 50% humidity) for 24 hours to eliminate internal stress.

[0032] Specifically, in step S4, the surface refinement process of the altered rock-like material sample includes the following steps: S411: Surface finishing: Use 400-grit sandpaper to grind the specimen along the bedding direction of the altered rock-like material in one direction to remove burrs and expose the internal structure. Grinding depth ≤ 0.2mm. S412: Protective coating: For easily weathered samples, spray a 2%~5% concentration of polyvinyl alcohol solution or a transparent polyurethane coating (thickness 20~50μm) to prevent debris from falling off during the test. S413: Marking and Numbering: Use a laser marking machine to mark the layer direction arrows and numbers on the non-stressed surface of the sample to ensure the consistency of the test loading direction.

[0033] S5: Quality control of foliated altered rock similar materials. The internal structure of the prepared altered rock similar material samples was characterized and their mechanical properties were tested.

[0034] Specifically, the internal foliation structure of the sample is monitored using methods such as industrial CT scanning and ultrasonic anisotropy testing; the mechanical properties of the sample are calibrated using methods such as uniaxial compression testing and direct shear testing.

[0035] Industrial CT scanning: Microfocus CT (10μm resolution) is used to perform tomographic scanning on the sample, reconstruct a three-dimensional model, and analyze the continuity of bedding and the mica dip angle distribution (the standard deviation of the dip angle is required to be ≤15°).

[0036] Ultrasonic anisotropy test: Using a longitudinal wave probe (frequency 1MHz), the wave velocity is measured along the parallel and perpendicular directions of the stratification, and the anisotropy coefficient is calculated (target value 1.5~2.5).

[0037] like Figure 2 and Figure 3 As shown, this invention provides two types of sample preparation molds, including an upper casting cavity, a lower base plate 6, an upper compaction section, and a vibrating section 5, and all components of the sample preparation mold are made of stainless steel. The upper casting cavity of the cubic sample preparation mold consists of four cubic sample preparation back plates 4. Similarly, the upper casting cavity of the altered rock similar material cylindrical sample preparation mold consists of two arc-shaped cylindrical sample preparation back plates 10. The sample preparation back plates are detachably connected by tie bolts 3. The sample preparation back plates are connected to slots in the lower base plate 6 via lower insert plates. The vibrating sections 5 are located at the four corners of the lower base plate 6. The vibration table control panel 8 can adjust the parameters of the vibrating sections 5 in real time to achieve compaction at different rates. The lower base plate 6 has several drainage holes with a diameter of 2mm, all leading to drainage channels 7 in the lower base plate 6. The drainage channels 7 are opened and closed by a switch. The upper compaction section consists of a hydraulic rod 1 and an axial preload plate 2 for a cubic specimen or an axial preload plate 9 for a cylindrical specimen. The hydraulic rod 1 is responsible for providing axial pressure to the axial preload plate, and the pressure is fed back to the control terminal in real time.

[0038] Based on the description and accompanying drawings of this invention, those skilled in the art can readily manufacture or use the method for preparing similar material samples suitable for laboratory testing of foliated altered rocks, and can achieve the positive effects described in this invention.

[0039] Unless otherwise specified, in this invention, terms such as "length," "width," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, the terms used to describe orientation or positional relationships in this invention are for illustrative purposes only and should not be construed as limiting this invention. For those skilled in the art, the specific meaning of the above terms can be understood in conjunction with the accompanying drawings and according to the specific circumstances.

[0040] Unless otherwise explicitly specified and limited, the terms "set up," "connected," and "linked" in this invention should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0041] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications or equivalent changes made to the above embodiments based on the technical essence of the present invention shall fall within the protection scope of the present invention.

Claims

1. A method for preparing a similar material sample suitable for indoor test of a schistosity-altered rock chamber, characterized in that: The method comprises the following steps: S1: according to the measured physical and mechanical parameters of the engineering area schistose altered rock, the type and proportion of the similar material are determined, wherein the type of the similar material is: bentonite, plastic resin, quartz sand and mica powder; S2: after the similar material is pretreated, it is accurately weighed according to the preset differential proportion; the differential proportion is designed according to the rock alteration degree of the engineering area, 5-10 layers of material proportion gradient are designed to simulate the strong alteration layer, the weak alteration layer and the transition layer; then the dry material after proportioning is made into a mixed material as a matrix through a wet material mixing process; S3: a detachable sample preparation mold is installed, the mold is uniformly sprayed with a release agent, and the mixed material is placed in the mold; the mixed material as a matrix and the schistose similar material are filled and pressed in cycles by using a layer-by-layer filling and pressing method to prepare an altered rock similar material sample containing different dip angle schistosity; S4: after the altered rock similar material sample is sectionally solidified and controlled, the surface of the altered rock similar material sample is finely treated; S5: the internal structure of the prepared altered rock similar material sample is characterized and the mechanical properties of the sample are tested.

2. The method for preparing similar material sample suitable for indoor test of schistosity-altered rock according to claim 1, characterized in that: In the step S1, the proportions of the similar materials are as follows: 30%-50% of the total mass of bentonite is used to simulate the clay mineral properties in the altered rock; 20%-40% of the total mass of quartz sand and mica powder is used to simulate the schistose mineral framework in the altered rock; and 30%-50% of the total mass of plastic resin is used to simulate the cementing material in the altered rock.

3. The method for preparing similar material sample suitable for indoor test of schistosity-altered rock according to claim 1, characterized in that: In the step S2, the pretreatment of the similar materials comprises: Bentonite activation: industrial grade sodium-based bentonite with a particle size of ≤0.075 mm is placed in an oven and dried at 105°C for 4 hours to remove adsorbed water; Quartz sand and mica powder classification: the 0.1-0.5 mm particle size quartz sand is washed and sieved, and the 0.05-0.2 mm particle size mica powder is electrostatically separated to ensure the integrity of the flaky particles.

4. The method for preparing similar material sample suitable for indoor test of schistosity-altered rock according to claim 1, characterized in that: In the step S2, The strong alteration layer is used to simulate the high clayification area, and the composition of the strong alteration layer is: 50% of bentonite, 20% of quartz sand, 20% of mica powder and 10% of plastic resin; The weak alteration layer is used to retain the mineral framework characteristics, and the composition of the weak alteration layer is: 30% of bentonite, 30% of quartz sand, 30% of mica powder and 10% of plastic resin; The transition layer is used to avoid mechanical property mutation, and 2-3 layers of transition proportion are arranged between adjacent layers.

5. The method for preparing similar material sample suitable for indoor test of schistosity-altered rock according to claim 1, characterized in that: In the step S2, the wet material mixing process comprises the following steps: S21: dry mixing stage: accurately weighed similar materials are poured into a dry mixer, and stirring is carried out at low speed to ensure uniform dispersion; S22: wet mixing stage: after glycerol and deionized water are premixed at a ratio of 1:3, they are slowly injected into the mixer, and the speed is simultaneously increased, and stirring is carried out until a lump-free paste is formed; S23: vacuum degassing: the mixed material is transferred to a vacuum stirring tank for continuous stirring to expel air bubbles and avoid internal pores of the sample.

6. The method for preparing a similar material sample suitable for indoor testing of a schistosity-altered rock chamber according to claim 1, characterized in that: In the step S3, the release agent is a silicon oil-based release agent uniformly sprayed on the inner wall of the mold or a polytetrafluoroethylene film attached.

7. The method for preparing similar material sample suitable for indoor test of schistosity-altered rock according to claim 1, characterized in that: In the step S3, the layer-by-layer filling and pressing method process comprises the following steps: S31: matrix laying: the mixed material is filled into the bottom of the mold, and the thickness is controlled to be 2-3 mm; ​ S32: Matrix directional pressing: Lightly press the surface of the mixture to form a directional micro-protrusion structure; S33: sheeting similar material laying: evenly spread mica powder on the surface of the mixture, and simulate the foliation surface of the altered rock by its sheeting characteristics; the angle between the sheeting similar material laying surface and the horizontal plane β By adjusting the laying angle, the altered rock similar material sample with different foliation angles can be obtained; S34: Interface activation: Spray atomized water on the surface of the solidified layer to improve the interlayer adhesion; S35: Recycle filling and pressing: Repeat steps S31-S34, and the total number of layers is set according to the test requirements; S36: Vibration compaction: After the cycle filling and pressing is completed, the compaction of the altered rock similar material sample is completed through the sample preparation mold.

8. The method for preparing a similar material sample suitable for indoor testing of a schistosity-altered rock chamber according to claim 1, characterized in that: The altered rock similar material specimens, after being filled with molds, are set into cubic or cylindrical shapes, and the foliation dip angle of the altered rock similar material specimens is... β Set to 0°, 30°, 45°, 60°, or 90°.

9. The method for preparing a similar material sample suitable for indoor testing of a schistosity-altered rock chamber according to claim 1, characterized in that: In the step S4, the segmented curing process of the altered rock similar material sample includes the following steps: S401: Initial setting and shaping: After demolding, the sample is placed for a period of time at an ambient temperature of 25°C and a humidity of 70%, so that the silicone rubber is preliminarily crosslinked and the gypsum completes the hydration reaction; S402: Bentonite hydration enhancement: The sample is moved to a humidity curing box to promote the full water absorption and swelling of the bentonite, simulating the water content state of natural altered rock; S403: Gradient drying: First, dry at 40°C for 6 hours, then increase the temperature to 50°C for 12 hours, and finally control the moisture content to 8%-12%; S404: Balance treatment: After drying, the sample is placed in a desiccator for 24 hours to balance with the test environment and eliminate internal stress.

10. The method for preparing a similar material sample suitable for indoor testing of a schistosity-altered rock chamber according to claim 1, characterized in that: In the step S4, the surface fine processing technology of the altered rock similar material sample includes the following steps: S411: Bedding surface finishing: Unidirectional polishing along the bedding direction of the altered rock similar material sample to remove burrs and expose the internal structure, with a polishing depth of ≤0.2mm; S412: Protective layer coating: For samples prone to weathering, spray 2%-5% concentration polyvinyl alcohol solution or transparent polyurethane coating to prevent debris from falling off during the test; S413: Marking and numbering: Use a laser marking machine to mark the bedding direction arrow and number on the non-stress surface of the sample to ensure the consistency of the test loading direction.

Images