Rock-like triaxial seepage test method for simulating fracture extension and cavern excavation

Abstract

The invention relates to the technical field of rock mechanics and underground engineering, in particular to a rock-like triaxial seepage test method for simulating fracture extension and cavern excavation. Comprising the steps that a soluble prefabricated structure of a soluble crack framework and a soluble cavern framework is arranged in a mold; a rock-like material is poured into the mold, the soluble sheet body is doped in the pouring process, and a rock-like test block is obtained after the rock-like material is cured and formed; confining pressure and seepage boundary conditions are applied to the rock-like test block, meanwhile, a seepage medium is introduced, so that the soluble fissure skeleton, the soluble cavern skeleton and the soluble sheet body are gradually dissolved under the combined action of triaxial stress and the seepage conditions, and fissure extension and cavern cavities are formed in the test block in the loading process. According to the method, the crack expansion process from microcosmic to macroscopic and the excavation forming process of the cavern are dynamically simulated in situ, so that the mechanical and seepage response characteristics of the surrounding rock of the complex underground engineering are more truly reflected.

Description

Technical Field

[0001] This invention relates to the fields of rock mechanics and underground engineering, and in particular to a triaxial seepage test method for simulating fracture propagation and cavern excavation in rock-like materials. Background Technology

[0002] In the fields of rock mechanics and underground engineering research, triaxial seepage tests on rock-like specimens are an important means of revealing the evolution of the mechanical and permeability characteristics of rock masses under complex stress and seepage coupling. These tests typically use artificially prepared rock-like specimens to simulate natural rock masses, and apply confining pressure, axial pressure, and seepage pressure in a triaxial pressure chamber to study fracture development and propagation and their impact on the seepage path. This is crucial for evaluating the stability of engineering structures such as underground caverns, slopes, and dam foundations.

[0003] In existing technologies, a single or multiple fracture structure is prefabricated using a soluble material, and this fracture structure is cast into the interior of the test block. Before the test, the soluble material is dissolved through pre-soaking, thus forming a pre-set fracture network before the test begins, followed by seepage or mechanical testing. However, the above method has the following technical problems encountered during testing: First, the formation of cracks in this method is completely disconnected from the experimental loading process. Since the soluble structure has been completely dissolved through pre-soaking before the test, the cracks already exist statically before the specimen bears any mechanical load. This makes it impossible to simulate the dynamic initiation and gradual expansion of cracks in real rock masses under the combined drive of stress and seepage. Consequently, the experimental conditions do not match the temporal coupling mechanism of excavation-stress release-crack development in actual engineering.

[0004] Secondly, this method typically only simulates macroscopic fractures at a single scale, making it difficult to integrate multi-scale structural features such as microfractures and macroscopic fractures within the same test block. Microfractures have a significant impact on the initiation and development of seepage in rock masses, but current technologies lack effective means to simultaneously introduce and observe the coordinated evolution of multi-scale fractures under loading conditions.

[0005] Furthermore, this technical solution has a relatively limited function, primarily focusing on fracture simulation, making it difficult to simultaneously achieve equivalent simulation of the underground cavern excavation process in the same experiment. To study the coupling effect between cavern excavation and fracture propagation, separate experiments are required, making it impossible to reveal the interaction mechanism between the two under the same stress and seepage conditions. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the purpose of this invention is to provide a triaxial seepage test method for simulating fracture propagation and cavern excavation in rock-like materials. This method involves prefabricating a soluble fracture framework, a soluble cavern framework, and multi-scale soluble sheets within a rock-like specimen. During triaxial stress and seepage tests, these structures are gradually dissolved, thereby forming fracture propagation and cavern cavities in situ under loading conditions. This allows for the controllable simulation of fracture propagation and cavern excavation processes. Specifically, under triaxial loading and seepage conditions, the method can dynamically simulate the fracture propagation process from microscopic to macroscopic levels, as well as the cavern excavation and formation process, thus more realistically reflecting the mechanical and seepage response characteristics of surrounding rock in complex underground engineering projects.

[0007] To achieve the above objectives, the embodiments of the present invention provide the following technical solutions: A triaxial seepage test method for simulating fracture propagation and cavern excavation in rock-like materials includes: A soluble prefabricated structure containing at least one soluble fissure skeleton and at least one soluble cavity skeleton is laid out in the mold. A rock-like material is poured into the mold, and soluble flakes are added during the pouring process. After the rock-like material solidifies and forms, a rock-like test block is obtained. Confining pressure and seepage boundary conditions are applied to the rock-like specimen, and a seepage medium is introduced at the same time. Under the combined action of triaxial force and seepage conditions, the soluble fracture skeleton, the soluble cavity skeleton and the soluble sheet gradually dissolve. During the loading process, fracture expansion and cavity cavities are formed inside the specimen.

[0008] Optionally, the soluble fissure skeleton and the soluble cavity skeleton are prepared by additive manufacturing or mold forming, and the shape, size, inclination angle and spatial position of the soluble fissure skeleton and the soluble cavity skeleton are predetermined before casting.

[0009] Optionally, the soluble sheet has a sheet-like structure, and the equivalent size of the soluble sheet is smaller than the characteristic size of the soluble fracture skeleton.

[0010] Optionally, the equivalent size of the soluble sheet is 0.1 mm to 1 mm, and the volume fraction within the rock-like specimen is 1% to 20%.

[0011] Optionally, the soluble sheets are arranged in predetermined spatial regions, so that the interior of the rock-like specimen forms a partitioned structure with different microcrack densities.

[0012] Optionally, the soluble cavity skeleton gradually dissolves under triaxial stress and seepage conditions, causing the cavity to form under load.

[0013] Optionally, the crack propagation process and the cavern excavation process occur continuously during the same triaxial seepage test.

[0014] Optionally, the soluble fissure skeleton, the soluble cavity skeleton, and the soluble sheet are made of water-soluble materials.

[0015] Optionally, the rock-like material uses cement mortar, gypsum, or a mixture of the two as a binder, and incorporates sand, fine aggregate, or metal powder to adjust its mechanical and permeability properties.

[0016] Optionally, the rock-like specimen is a cylinder or a cube.

[0017] One or more technical solutions provided in the embodiments of the present invention have at least the following technical effects or advantages: 1. The experimental method of this invention involves pre-placing three types of soluble prefabricated structures—soluble fracture skeleton, soluble cavity skeleton, and soluble sheet—into a mold, and then encasing them with a rock-like material to form a specimen that is initially intact and contains the entity to be dissolved. After the specimen is installed in the triaxial seepage test device, it is not first dissolved to form a cavity before loading, nor is it loaded under seepage-free conditions. Instead, confining pressure and seepage boundary conditions are applied simultaneously, and a seepage medium is introduced, so that the dissolution process of the soluble structure is fully coupled with the triaxial stress state and seepage field of the specimen. The gradual dissolution of the soluble fracture skeleton and soluble sheet simulates the process of fracture expansion along a predetermined macroscopic path and the gradual initiation and connection of microscopic fractures starting from a predetermined location and driven by stress and seepage. At the same time, the dissolution process of the soluble cavity skeleton is equivalent to excavating a cavity under the existing surrounding rock stress and seepage environment, with the formation of the cavity accompanied by real-time adjustment of the surrounding stress field. This method allows the processes of fracture propagation and cavern excavation to proceed in parallel in time, overlap in space, and influence each other in terms of mechanical and seepage effects. As a result, it enables a more realistic physical simulation of the surrounding rock response in complex underground engineering in a continuous experimental process, and more realistically reflects the mechanical and seepage response characteristics of the surrounding rock in complex underground engineering.

[0018] 2. Improved test accuracy: The fissures and cavities form in situ during the seepage loading process, avoiding the randomness introduced by manual cutting and pre-soaking before the test, making the location, size and formation process of the fissures more controllable and repeatable; 3. Improved testing efficiency: Without the need for multiple pretreatments or high-stress-induced crack propagation, crack propagation and cavern excavation simulation can be achieved under conventional triaxial seepage conditions, significantly shortening the testing cycle; 4. Improved data quality: Permeability coefficient, deformation parameters and failure characteristics data can be continuously acquired throughout the entire process of crack formation, avoiding the limitation of traditional tests that can only obtain comparative data before and after crack formation; 5. Enhanced engineering applicability: By adjusting the size, dosage, and spatial zoning of the microstructure sheets, the fracture development and cavern excavation process under different engineering surrounding rock conditions can be simulated, making it suitable for various application scenarios such as underground engineering, water conservancy engineering, and energy engineering.

[0019] Advantages of additional aspects of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. The drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. In addition, the dimensions or spacing between the components are exaggerated to show the position of each component, and the schematic diagrams are for illustrative purposes only.

[0021] Figure 1 This is a schematic diagram of several exemplary prefabricated caverns and macroscopic fissure combinations of soluble skeletons according to the present invention; Figure 2 This is a schematic diagram of several prefabricated microcrack sheets of the present invention; Figure 3 This is a schematic diagram of several cylindrical rock-like specimens containing a multi-scale soluble fracture framework according to the present invention. Figure 4 This is a schematic diagram showing the arrangement of the cylindrical rock specimens of the present invention in a triaxial seepage test system; Figure 5 This is a schematic diagram illustrating the gradual formation of multi-scale fractures in a cylindrical rock specimen during a triaxial flow test according to the present invention. Figure 6 This is a schematic diagram of several cubic rock specimens containing caverns and a multi-scale soluble fracture framework according to the present invention. Figure 7 This is a schematic diagram showing the arrangement of the cubic rock specimens of the present invention in a triaxial seepage test system; Figure 8 This is a schematic diagram of the equivalent excavation of soluble structure dissolution chambers and the gradual generation of multi-scale fractures in cubic rock specimens during triaxial seepage tests according to the present invention. In the figure: 1. Soluble macroscopic fracture skeleton; 2. Soluble cavity skeleton; 3. Soluble microstructure sheet; 4. Combination of soluble macroscopic fracture skeleton and rock-like material; 5. Cylindrical rock-like specimen; 6. Cylindrical triaxial seepage test equipment; 7. Water pipe; 8. Test line pipeline; 9. Direction of seepage pressure loading; 10. Fracture network; 11. Combination of soluble macroscopic fracture skeleton, cavity skeleton and rock-like material; 12. Cubic rock-like specimen; 13. Cubic triaxial seepage test equipment; 14. Seepage pipeline; 15. Fracture network and cavity cavity. Detailed Implementation

[0022] It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0023] Terminology Explanation: Rock-like test blocks: These are artificial test blocks made from base materials such as sand and metal powder, combined with cement, mortar, gypsum, or other binding materials, and used to simulate the mechanical and seepage characteristics of natural rocks.

[0024] Soluble prefabricated structures refer to solid structures made of soluble materials that can gradually dissolve when exposed to water or seepage media, including soluble fracture skeletons, soluble cavity skeletons, and soluble sheets.

[0025] Soluble fracture skeleton: refers to a soluble material entity used to simulate macroscopic fractures or structural surfaces. Its shape, size, tilt angle and spatial position are pre-set before the specimen is formed.

[0026] Soluble cavern skeleton: refers to a solid soluble material used to simulate the geometry of underground caverns, which gradually dissolves during the experiment to form cavern cavities.

[0027] Soluble sheets: refer to sheet-like or thin-sheet soluble materials with dimensions smaller than the soluble fracture skeleton, used to simulate microscale fractures inside rock-like specimens.

[0028] Equivalent excavation: refers to the process of forming a cavity by gradually dissolving a soluble structure under the conditions of confining pressure, axial pressure and seepage on the test block, in order to simulate the stress release and structural response process caused by cavity excavation in engineering.

[0029] Triaxial flow test: refers to a test method that applies flow boundary conditions to a specimen under triaxial stress to test its permeability and mechanical response.

[0030] As described in the background section, the existing technology has at least the following shortcomings and technical problems: 1. The formation and evolution of cracks are uncontrollable. Existing methods that induce crack propagation by increasing axial pressure result in highly random crack propagation paths and the generation of secondary cracks, making it difficult to achieve precise control over crack geometry and evolution.

[0031] 2. The single scale of the fracture makes it difficult to reflect the multi-scale structural characteristics. Existing technologies are mostly focused on the study of single fractures or a small number of macroscopic fractures, making it difficult to simultaneously simulate micro-fractures, macroscopic fractures and their coupling effects, and thus failing to truly reflect the multi-scale fracture structural characteristics of natural rock masses.

[0032] 3. Soluble fracture technology often uses pre-soaking methods, which cannot simulate the evolution of fractures under load. Existing fracture tests based on soluble materials usually involve pre-soaking to form fractures before the test. The fractures are already present before loading, making it difficult to reflect the process of gradual formation and expansion of fractures under the combined action of confining pressure and seepage conditions.

[0033] 4. The simulation of caverns is too simplistic and cannot accurately simulate the actual excavation process. The caverns in existing rock-like test blocks are mostly formed by pre-reserved holes or prefabricated cavities. The caverns are already fully present before the test begins, making it impossible to simulate the excavation process of the cavern under load conditions and the resulting stress changes and seepage redistribution.

[0034] 5. There is a lack of research methods for the coupling effect between fractures and caverns. Existing technologies usually conduct fracture tests and cavern tests separately. There is a lack of a test method that can simultaneously simulate the multi-scale fracture evolution and cavern excavation process in the same test block, which limits the research on complex underground engineering problems.

[0035] This invention aims to solve the problems of the single fracture formation mode, uncontrollable fracture evolution, and difficulty in simulating the excavation process of the cavern under load in existing rock seepage tests. It provides a reasonable, efficient and repeatable test method for studying the seepage-mechanical response under multi-scale fracture-cavity coupling.

[0036] A triaxial seepage test method for rock-like structures based on soluble prefabricated structures to simulate fracture propagation and cavern excavation includes: A soluble prefabricated structure is arranged in the test mold. The soluble prefabricated structure includes at least one soluble fissure skeleton and at least one soluble cavity skeleton. The soluble fissure skeleton is used to simulate macroscopic fissure structures, and the soluble cavity skeleton is used to simulate cavity structures. After the soluble fracture skeleton and the cavity skeleton are laid out, rock-like material is poured into the test mold, and soluble flakes are sprinkled into the rock-like material during the pouring process, so that potential fractures of different scales and densities are formed inside the rock-like material. After the rock-like material has solidified and formed, a rock-like test block containing undissolved soluble pre-fabricated fissures and cavity structures and soluble sheets is obtained. The rock-like specimen was placed entirely into a triaxial seepage test apparatus, and confining pressure and seepage boundary conditions were applied to the specimen. While applying confining pressure, a seepage medium is introduced, causing the soluble fracture skeleton, soluble cavity skeleton, and soluble sheet to gradually dissolve under the combined action of triaxial force and seepage conditions, forming internal fractures and cavity cavities in the test block, thereby achieving an equivalent simulation of the fracture propagation and cavity excavation process.

[0037] The synergistic effect of the soluble fracture framework and soluble sheets enables the simultaneous simulation of the formation and evolution of both macroscopic and micro-fractures, overcoming the limitation of single fracture scale in existing technologies. The soluble structure gradually dissolves under the combined effects of triaxial stress and seepage conditions, rather than being pre-formed before the experiment. This allows fracture propagation and cavern excavation to synchronize with the evolution of the stress and seepage fields, solving the problems of uncontrollable fracture evolution and difficulty in simulating cavern excavation under load. The combination of soluble prefabricated structures, soluble sheets, and rock-like materials enables the synergistic simulation of fractures and caverns within the same specimen, addressing the lack of sufficient methods for studying their coupling effects.

[0038] The soluble fissure skeleton and soluble cavity skeleton are solid structures of soluble materials prepared by additive manufacturing or mold forming. Their shape, size, inclination angle and spatial position are predetermined before the test block is cast.

[0039] Using additive manufacturing or molding methods, soluble fracture and cavity skeletons with complex three-dimensional shapes, specific dimensions, inclination angles, and spatial locations can be precisely fabricated. Pre-design ensures that the fracture network morphology and cavity geometry formed by subsequent dissolution are controllable, rather than randomly generated, providing a repeatable experimental basis for studying the influence of fractures with specific orientations and the stability of shaped cavities.

[0040] The soluble sheets are plate-like or sheet-like structures with an equivalent size smaller than the characteristic size of the soluble fracture skeleton, used to simulate microscale fracture structures. Furthermore, the equivalent size of the soluble sheets is 0.1–1 mm, the volume fraction is 1%–20%, and they are uniformly or non-uniformly distributed within the rock-like specimen.

[0041] Soluble sheets were prepared into a sheet-like structure with an equivalent size smaller than the macroscopic soluble fracture framework. This simulated microfractures or potential weak points with different scales than macroscopic fractures within the specimen. The size range was limited to 0.1–1 mm. The volume fraction was limited to 1%–20%, providing a reasonable parameter range for controlling the overall density of microscale defects within the specimen. By adjusting the size and incorporation amount of the sheets, the differences in the degree of microfracture development within different rock masses, i.e., different initial damage states, could be simulated. The microscale soluble sheets dissolved under seepage, forming distributed microfractures in the rock-like matrix. These microfractures connected with the main fractures formed by the dissolution of the macroscopic fracture framework, creating a multi-level seepage channel network that more realistically reflects the seepage characteristics of the multi-scale pore-fracture system of natural rock masses.

[0042] The soluble flakes are arranged in predetermined spatial zones, creating a partitioned structure with varying microfracture densities within the rock-like specimen. For example, higher-density microfracture flakes can be arranged in stress concentration zones around the simulated cavern, while lower-density flakes can be arranged in areas far from the cavern. This allows the experimental method to simulate the uneven damage or defect distribution commonly found in actual engineering rock masses, study the impact of locally weakened zones on overall mechanical stability and seepage path evolution, and improve the simulation fidelity of complex geological conditions.

[0043] The soluble cavern skeleton gradually dissolves under triaxial stress and seepage conditions, causing the cavern cavity to form under load, thereby achieving equivalent excavation simulation of the cavern under seepage conditions.

[0044] In traditional methods, the cavern cavity exists before the application of load, failing to reflect the stress redistribution and unloading effects experienced by the surrounding rock during the actual excavation process, from its intact state to the moment the free face is formed. In this method, however, under confining pressure and axial pressure, the cavern skeleton exists as a temporary support structure. As it gradually dissolves, the load originally borne by the skeleton is gradually transferred to the surrounding rock-like material. This process dynamically simulates the stress release, migration, and establishment of a new equilibrium state in the surrounding rock caused by excavation, making the obtained data on surrounding rock deformation, failure, and seepage more closely reflect actual engineering conditions.

[0045] The crack propagation process and the tunnel excavation process occur continuously in the same triaxial seepage test, realizing the seepage-mechanical response test under the coupling effect of multi-scale cracks and tunnels.

[0046] Under the conditions of continuous seepage and sustained triaxial stress, the dissolution processes of the soluble fracture framework, soluble lamellae, and soluble cavern framework overlap on the time axis. For example, during cavern formation, surrounding fractures simultaneously initiate and expand, or the expansion of existing fractures is accelerated or changes direction due to stress disturbances caused by cavern formation. This continuous, coupled evolutionary process is key to simulating the development of surrounding rock fractures induced by excavation disturbance in real underground engineering, making it possible to study the interaction mechanism between fractures and caverns, and avoiding the errors caused by studying the two processes separately.

[0047] The soluble fracture framework, the soluble cavity framework, and the soluble sheet are made of water-soluble materials. Common water-soluble materials, such as polyvinyl alcohol or its modified forms, have good controllable dissolution characteristics, and the dissolution rate can be adjusted by factors such as material formulation and water temperature. The selection of water-soluble materials ensures that under the action of seepage water at room temperature or moderately heated, the soluble structure can gradually dissolve at a certain rate, rather than collapsing instantly or remaining completely undissolved. This guarantees the gradual and controllable nature of fracture expansion and cavity formation, allowing researchers to observe and record the dynamic evolution process.

[0048] The rock-like material uses cement mortar, gypsum, or a mixture of both as a binder, providing basic mechanical strength and formability, and incorporates sand, fine aggregate, or metal powder to adjust its mechanical properties and permeability.

[0049] The rock-like specimens are either cylindrical or cubic. Cylindrical specimens are a common standard shape in triaxial rock mechanics testing, well-suited to conventional triaxial pressure chambers, providing uniform stress boundary conditions and facilitating comparative experiments and data standardization. Cubic specimens, on the other hand, offer larger dimensions and more flexible boundary condition settings, and are also more suitable for arranging complex spatial orientation combinations of fractures and cavities within them. The choice of either shape provides a suitable platform for different experimental research focuses.

[0050] In summary, this invention is based on the fundamental principle of "gradual dissolution of soluble prefabricated structures under confining pressure and seepage conditions." By prefabricating soluble macroscopic fracture skeletons, cavern skeletons, and soluble microstructure sheets of different sizes and distribution densities inside a rock-like specimen, the invention utilizes the continuous action of the seepage medium during triaxial seepage tests to cause the aforementioned soluble structures to dissolve in situ under loading conditions. This achieves the gradual expansion of fractures from microscopic to macroscopic and simulates the equivalent excavation process of caverns.

[0051] Compared with the existing technology of "forming cracks in one go through pre-soaking before the test", this test method shifts the timing of crack and cavity formation from before the test to during the triaxial seepage loading process. This couples the appearance of cracks and cavities with the evolution of stress field and seepage field, solving the problem of static and non-evolvable crack state in the existing technology. It truly reflects the crack-stress-seepage interaction mechanism during the loading process.

[0052] By incorporating soluble microstructure sheets of different sizes and dosages during the casting process of the test block, a potential microfracture zone with spatial heterogeneity can be constructed inside the test body. During the seepage process, it gradually transforms into an actual microfracture structure, realizing the simulation of multi-scale collaborative formation and evolution of microfractures, macrofractures, and cavities. This makes up for the shortcomings of existing rock-like test methods that are difficult to reflect multi-scale fracture characteristics at the same time.

[0053] By introducing a soluble prefabricated cavern structure, rock-like specimens can simultaneously simulate caverns and multi-scale fractures while maintaining overall integrity. By pre-embedding a soluble cavern framework during the specimen casting stage and gradually dissolving this framework using the seepage medium during triaxial seepage tests, in-situ formation of the cavern cavity under loading and seepage conditions is achieved, thus simulating the equivalent excavation of the cavern under seepage conditions. Compared to existing cavern simulation methods that use prefabricated cavities, post-exposure, or strong loading to induce failure, this experimental method avoids stress redistribution problems caused by pre-exposed or prematurely unloaded caverns. It couples the cavern excavation process with the evolution of the surrounding rock stress field and seepage field, more realistically reflecting the surrounding rock response characteristics at the moment of cavern excavation and its subsequent stages in actual engineering projects.

[0054] This invention, through the combination of prefabricated caverns, macroscopic fracture skeletons, and microscale soluble structural sheets, achieves for the first time multi-scale collaborative simulation of caverns, macroscopic fractures, and microfractures in a single type of rock specimen. This allows the cavern excavation process and the fracture propagation process to influence each other in space and time, overcoming the problem of the cavern simulation and fracture simulation being isolated and difficult to couple in existing experimental methods.

[0055] Example 1 A typical implementation method, such as Figures 1-5 As shown. Triaxial flow test of a cylindrical rock specimen containing multi-scale soluble pre-fabricated fractures. This embodiment provides a method for triaxial flow test of a cylindrical rock specimen containing multi-scale soluble pre-fabricated fractures. A cylindrical rock specimen with a diameter of 50 mm and a height of 100 mm is used.

[0056] A soluble macroscopic fracture skeleton 1 is prepared by additive manufacturing or molding using polyvinyl alcohol (PVA) or modified PVA as the soluble material. In this embodiment, the macroscopic fracture skeleton is configured as a single, double, or triple dispersed fracture structure with three fracture thicknesses of 0.2 mm, 0.5 mm, and 1.0 mm, respectively. The fracture length and width are both 30 mm, and the fracture inclination angles are 0°, 45°, and 90°, respectively.

[0057] The rock-like material is a cement-based composite material, which can use cement, gypsum, or a mixture thereof as the binder, and incorporate sand, fine aggregate, or metal powder to adjust its mechanical and permeability properties. In this embodiment, the mass ratio of the rock-like material is: "Silicate cement: Quartz sand: Iron concentrate: Fly ash: Water = 18:32:35:7:8". The quartz sand uses a common continuous gradation, with a particle size distribution of: 0.1–0.25 mm 30%, 0.25–0.5 mm 40%, and 0.5–1.0 mm 30%, to ensure good compactness and stable permeability characteristics.

[0058] Add soluble microstructured sheets 3 (such as...) to the well-stirred rock-like material. Figure 2 As shown), to simulate microscale fracture structures. Figure 3 As shown, a soluble macroscopic fracture framework and a rock-like material combination 4 are formed inside the specimen. The soluble sheets are made of sheet-like PVA material with a thickness of 0.1 mm and a length and width of 10 mm. In this embodiment, 25, 50, and 100 soluble sheets are added respectively to form different microfracture distribution densities, thereby simulating different initial damage levels of the rock mass. Microscale fractures and macroscopic fractures can form continuous or non-continuous structures to study the influence of multi-scale fractures on seepage parameters.

[0059] A prefabricated macroscopic fracture skeleton was fixed in a cylindrical mold, and rock-like material was filled in using a layered casting method. After each layer was cast, it was vibrated to eliminate air bubbles and ensure the compactness of the specimen. After demolding and curing, a cylindrical rock-like specimen 5 was finally formed, which was wrapped with rock-like material on the outside and contained macroscopic fractures of different numbers (single, double, and triple), different inclination angles (0°, 45°, and 90°), different thicknesses (0.2 mm, 0.5 mm, and 1.0 mm), as well as microscale fractures of different distribution densities.

[0060] like Figure 4 As shown, the test block is installed in the cylindrical triaxial seepage test apparatus 6, and the water pipe 7 and test line pipe 8 are connected. The confining pressure is set to 5 MPa, and a constant pressure difference of 3 MPa is applied to the upper and lower ends of the test block for seepage. The direction of seepage pressure loading 9 is as shown. Figure 5As shown, the permeation medium water is heated to about 50 °C to accelerate the dissolution process of the PVA material.

[0061] During the experiment, real-time data were recorded on seepage flow, inlet and outlet pressures, axial displacement of the specimen, and stress changes. As time progressed, the internal fracture skeleton of the cylindrical specimen gradually dissolved due to seepage pressure, forming a fracture network 10. The gradual formation and expansion of fractures during the dissolution of the soluble material were observed and recorded (e.g., Figure 5 As shown in the figure, the permeability coefficient as a function of time k(t) was obtained, and the evolution image of the internal cross-sectional structure of the test block was obtained by taking pictures or CT scans.

[0062] Example 2 A typical implementation method, such as Figure 1 , Figures 6-8 As shown in the figure. This embodiment provides a triaxial seepage test method for a cubic rock specimen that simultaneously incorporates multi-scale fractures and cavern structures. A cubic rock specimen 12 is used, with a specimen size of 150 mm × 150 mm × 150 mm.

[0063] Following the method of Example 1, a soluble macroscopic fracture framework 1 and a soluble cavity framework 2 were prepared using soluble PVA or modified PVA. The soluble macroscopic fracture framework and cavity framework-like rock material combination 11 inside the specimen is as follows: Figure 6 As shown, the cavern skeleton is an arched cavern structure with a sidewall thickness of 1.5 mm, a total height of 40 mm, a cavern width of 20 mm, a sidewall height of 30 mm, and an arch height of 10 mm. The cavern skeleton is connected to a macroscopic fissure skeleton, with macroscopic fissures evenly distributed around the cavern perimeter. The fissure skeleton thickness is set in three specifications: 0.2 mm, 0.5 mm, and 1.0 mm; the fissure length is set in two specifications: 10 mm and 15 mm; and the angle between the fissures and the cavern wall is set in two specifications: 90° and 45°.

[0064] The specimen fabrication process is basically the same as in Example 1, except that the mold is a cubic mold. A prefabricated fracture-cavity composite skeleton structure is embedded in the mold at the designed locations. Before casting, 100, 200, and 400 soluble sheets are added to the rock-like material, respectively, to simulate different micro-fracture distribution densities. This method allows for the combined simulation of cavities, macroscopic fractures, and microscale fractures within the same specimen.

[0065] like Figure 7 As shown, the cured cubic specimen is placed into the cubic triaxial seepage test device 13, and the seepage pipe 14 is connected. Based on the applied confining pressure, seepage pressure is applied around the specimen, causing the seepage medium to form a multi-directional seepage field inside the specimen. Figure 8As shown, during the experiment, as the soluble fracture skeleton, soluble cavity skeleton and soluble sheet gradually dissolve, a fracture network and cavity 15 are formed in sequence inside the test block, realizing the equivalent excavation process of the cavity under seepage conditions, and the changes in seepage parameters and mechanical parameters can be recorded in real time throughout the entire process of fracture expansion and cavity excavation.

[0066] Compared with cylindrical test blocks, cubic rock test blocks have larger dimensions and more flexible boundary condition settings, enabling multi-directional seepage loading, which is more conducive to simulating the complex three-dimensional seepage and stress states in actual underground engineering. At the same time, more complex fracture-cavity combination structures can be arranged inside the cubic test block, which is suitable for conducting comparative tests and parameter sensitivity analyses on the coupling effect of fracture propagation and cavity excavation.

[0067] While the specific embodiments of the present invention have been described above, they are not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art without creative effort based on the technical solutions of the present invention are still within the scope of protection of the present invention.

Claims

1. A triaxial seepage test method for simulating fracture propagation and cavern excavation in rock-like materials, characterized in that, include: A soluble prefabricated structure containing at least one soluble fissure skeleton and at least one soluble cavity skeleton is laid out in the mold. A rock-like material is poured into the mold, and soluble flakes are added during the pouring process. After the rock-like material solidifies and forms, a rock-like test block is obtained. Confining pressure and seepage boundary conditions are applied to the rock-like specimen, and seepage medium is introduced to cause the soluble fracture skeleton, the soluble cavity skeleton and the soluble sheet to gradually dissolve under the combined action of triaxial force and seepage conditions. During the loading process, fractures and cavities are formed inside the specimen.

2. The triaxial seepage test method for simulating fracture propagation and cavern excavation in rock-like materials as described in claim 1, characterized in that, The soluble fissure skeleton and the soluble cavity skeleton are prepared by additive manufacturing or mold forming. The shape, size, inclination angle and spatial position of the soluble fissure skeleton and the soluble cavity skeleton are determined in advance before casting.

3. The triaxial seepage test method for simulating fracture propagation and cavern excavation in rock-like materials as described in claim 1, characterized in that, The soluble sheet has a sheet-like structure, and the equivalent size of the soluble sheet is smaller than the characteristic size of the soluble fracture skeleton.

4. The triaxial seepage test method for simulating fracture propagation and cavern excavation in rock-like materials as described in claim 3, characterized in that, The equivalent size of the soluble sheet is 0.1 mm to 1 mm, and its volume fraction within the rock-like specimen is 1% to 20%.

5. The triaxial seepage test method for simulating fracture propagation and cavern excavation in rock-like materials as described in claim 3, characterized in that, The soluble flakes are arranged in predetermined spatial regions, resulting in a partitioned structure with different microcrack densities inside the rock-like specimen.

6. The triaxial seepage test method for simulating fracture propagation and cavern excavation in rock-like materials as described in claim 1, characterized in that, The soluble cavern skeleton gradually dissolves under triaxial stress and seepage conditions, causing the cavern cavity to form under load.

7. The triaxial seepage test method for simulating fracture propagation and cavern excavation in rock-like materials as described in claim 1, characterized in that, The crack propagation process and the cavern excavation process occurred consecutively during the same triaxial seepage test.

8. The triaxial seepage test method for simulating fracture propagation and cavern excavation in rock-like materials as described in claim 1, characterized in that, The soluble fissure skeleton, the soluble cavity skeleton, and the soluble sheet are made of water-soluble materials.

9. The triaxial seepage test method for simulating fracture propagation and cavern excavation in rock-like materials as described in claim 1, characterized in that, The rock-like material uses cement mortar, gypsum, or a mixture of the two as a binder, and incorporates sand, fine aggregate, or metal powder to adjust its mechanical and permeability properties.

10. The triaxial seepage test method for simulating fracture propagation and cavern excavation in rock-like materials as described in claim 1, characterized in that, The rock-like test blocks are cylindrical or cubic.

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