A tunnel structure high water pressure and ground stress coupling damage simulation and monitoring test device

Abstract

The application discloses a tunnel structure high water pressure and ground stress coupling damage simulation and monitoring test device, which integrates high water pressure closed loop loading and air bag type multi-directional ground stress loading, realizes synchronous, stable and controllable reproduction of the engineering coupling loading process, and improves the consistency between the test working condition and the actual condition. The device adopts a visual window, and combined with the joint monitoring and mutual verification of DIC and seepage pressure, displacement, strain and other sensors, the full-field and key point response of surrounding rock and lining from initial stress to the whole process of damage evolution can be obtained. The matching data acquisition and processing system supports multi-dimensional result analysis, and ensures the accuracy of data. Overall, the platform has obvious advantages in specific working condition reproduction, monitoring integrity, data analysis and evaluation, can be used for mechanism research, design optimization and protection and reinforcement scheme verification, and has good engineering applicability and popularization prospect.

Description

Technical Field

[0001] This invention relates to the field of tunnel structure modeling technology, and in particular to a test device for simulating and monitoring the coupled failure of tunnel structures under high water pressure and ground stress. Background Technology

[0002] As tunnel engineering progresses into deeper and more complex geological and high-water-pressure environments, the failure mechanism of tunnel structures under high water pressure has attracted increasing attention. Particularly in island and reef areas such as the South China Sea, tunnels often traverse coral reef limestone strata. These rock masses have complex structures, well-developed pores and fractures, and strong hydraulic connectivity, making the simulation of their failure mechanism under the combined effects of high ground stress and high water pressure particularly difficult. Existing experimental devices lack the ability to realistically simulate such complex conditions. Furthermore, most existing model devices can only apply ground stress or hydrostatic pressure independently, failing to achieve simultaneous loading and control of water pressure and ground stress. While some systems have water supply capabilities, they cannot meet the demands of high water pressure loading, and their loading stability and control precision are limited, making it difficult to maintain a stable high-water-pressure environment over long periods. Simultaneously, traditional monitoring methods rely heavily on point sensors such as strain gauges and displacement meters, with limited sampling ranges, making it impossible to continuously track and identify the failure process across the entire field, especially lacking direct recording of the expansion and collapse processes of surface cracks in the surrounding rock. Reef limestone: refers to carbonate rocks formed by the accumulation of biological remains such as corals, shells, and algae in a marine environment and through diagenesis. It is often distributed in island and reef areas and is characterized by well-developed pores and fissures, high permeability, and heterogeneous structure. Under high water pressure and geostress, its mechanical response and failure behavior are significantly different from those of ordinary intact limestone or conventional soil.

[0003] To address the aforementioned technical issues, patent application CN202211137351.8 proposes a water inrush and burst test system for water-rich tunnels, comprising, for example, a model box 3, a water tank, a water tank height adjustment device, and a seepage simulation device, to simulate water inrush and burst conditions in tunnels under different hydraulic conditions. Another patent application, CN202411195875.1, provides a multi-directional ground stress loading test system, including a rigid loading frame, hydraulic loading components, and a seepage supply device, which can apply water pressure to the model in a laboratory. While these patents can achieve combined loading of water pressure and ground stress, they employ a gravity-supply method with an upper-mounted water tank, which can only create low-head seepage conditions and is insufficient to achieve the high-water-pressure environment common in deeply buried tunnels. Furthermore, the water pressure depends on the height of the water tank, with a limited adjustment range, making it difficult to precisely control and maintain long-term stability, and even more difficult to achieve precise coordinated control with ground stress loading. In addition, the monitoring methods of these devices mainly rely on local measurements such as strain gauges and pressure sensors, lacking multimodal visualization monitoring capabilities, and are unable to fully capture the entire process of deformation and failure of tunnel structures under the coupling of high water pressure and ground stress.

[0004] In summary, existing technologies can only simulate low-head seepage conditions, cannot achieve precise coupling loading of high water pressure and ground stress, and have limited monitoring methods. Summary of the Invention

[0005] The purpose of this invention is to provide a test device for simulating and monitoring the coupled failure of tunnel structures under high water pressure and ground stress, which solves the problem that existing technologies cannot achieve accurate coupled loading of high water pressure and ground stress and have limited monitoring methods.

[0006] This invention is implemented as follows: This invention provides a test device for simulating and monitoring the coupled failure of tunnel structures under high water pressure and ground stress, characterized in that it comprises:

[0007] A model box, the model box having a space for accommodating materials similar to the surrounding rock, and transparent observation windows at the front and back of the model box;

[0008] The tunnel model is housed in a rock-like material inside the model box;

[0009] The loading system includes a ground stress loading unit and a high water pressure loading unit. The ground stress loading unit includes at least one flexible airbag arranged on the top and / or sidewall of the model box, and an air pressure control component connected to the flexible airbag for providing and regulating air pressure. The high water pressure loading unit includes a high-pressure water pump, a high-pressure water storage tank connected to the high-pressure water pump, and a high-pressure pipeline connecting the high-pressure water storage tank to the inside of the model box. The high water pressure loading unit is used to apply controllable pore water pressure to the surrounding rock similar material.

[0010] The monitoring system includes an optical monitoring unit, a sensor unit, and a data acquisition and processing unit. The optical monitoring unit includes at least one high-precision camera facing the transparent observation window, used to acquire image sequences of the surface of the surrounding rock similar material and the surface of the tunnel model. The sensor unit includes a displacement sensor, a seepage pressure sensor, and a pressure sensor embedded in the surrounding rock similar material. The data acquisition and processing unit is communicatively connected to the optical monitoring unit and the sensor unit, used to synchronously acquire and process image data and sensor data.

[0011] The experimental device for simulating and visually monitoring the failure process of tunnels under high water pressure-ground stress coupling provided by this invention integrates high water pressure closed-loop loading with airbag-type multi-directional ground stress loading to achieve synchronous, stable, and controllable reproduction of the engineering coupled loading process, improving the consistency between experimental conditions and actual conditions. The device uses a viewing window, combined with DIC and sensors for joint monitoring and mutual verification of seepage pressure, displacement, and strain, to acquire the full-field and key-point responses of the surrounding rock and lining from initial stress to failure evolution. The supporting data acquisition and processing system supports multi-dimensional result analysis, ensuring data accuracy. Overall, the platform has significant advantages in specific condition reproduction, monitoring completeness, and data analysis and evaluation, and can be used for mechanism research, design optimization, and verification of protection and reinforcement schemes, possessing good engineering applicability and promising prospects for widespread application.

[0012] A further technical solution of the present invention is: the side plates and the outer periphery of the top plate of the model box are flexibly sealed, and the ground stress loading unit can drive the side plates and / or the top plate to move.

[0013] A further technical solution of the present invention is: the air pressure regulation component includes an air compressor, a pressure regulating valve and a sub-control system, used to realize precise regulation and multi-level loading control of the air pressure inside the flexible airbag.

[0014] A further technical solution of the present invention is: the high water pressure loading unit further includes a water pressure control console, which is connected to a pressure sensor for real-time monitoring of the water pressure in the model box and feedback control of the output of the high-pressure water pump, forming a closed-loop control.

[0015] A further technical solution of the present invention is: a permeation distribution plate is provided inside the model box, and a water pressure cavity is formed between the side plate of the model box and the permeation distribution plate; the high-pressure pipeline is connected to the water pressure cavity and is used to uniformly apply water pressure to the surrounding rock similar material in the form of surface load.

[0016] A further technical solution of the present invention is: multiple monitoring holes are arranged radially along the arch top, arch waist and arch bottom of the tunnel model, and the sensor unit is arranged in the monitoring hole, and the sensor unit is buried in stages at different burial depths.

[0017] A further technical solution of the present invention is: the displacement sensor is a multi-point displacement meter, used to obtain the stratified displacement and convergence development characteristics of the surrounding rock from near the tunnel wall to the depth; the pressure sensor is a pressure cell, used to record the stress redistribution and local unloading / concentration changes of the surrounding rock; the permeability sensor is a piezometer, used to monitor the transmission, dissipation and abnormal fluctuations of pore water pressure.

[0018] A further technical solution of the present invention is: the optical monitoring unit further includes a speckle pattern set on the observation surface of the surrounding rock, and an illumination source is set around the model box to provide uniform illumination for image acquisition.

[0019] A further technical solution of the present invention is: the tunnel model is a scaled-down model made of a material similar to the surrounding rock, and its outer surface is coated with a waterproof sealing layer.

[0020] A further technical solution of the present invention is: the data acquisition and processing unit comprises a multi-channel data acquisition instrument, a signal conditioning module, a computer terminal and a synchronous triggering unit, and is used for synchronous acquisition, storage and processing of sensor unit monitoring signals and optical image data.

[0021] The beneficial effects of this invention: This invention aims to solve the problem of difficulty in simulating the failure mechanism in deep reef limestone strata tunnel excavation in island and reef areas due to the high permeability of the surrounding rock, strong fissure development, and high water pressure conditions. In existing technologies, most tunnel physical model test devices struggle to simultaneously achieve stable and coordinated loading of high water pressure and geostress, leading to deviations between simulated working conditions and actual engineering environments. Furthermore, monitoring methods often rely on single sensors or local measuring points, lacking the ability to identify deformation and failure across the entire field in real time, thus failing to fully reveal the stress and failure mechanism of tunnels under the combined action of high water pressure and geostress. To address these problems, this invention provides a test device for simulating and visually monitoring the failure process of tunnels under the coupled action of high water pressure and geostress. The core technical solution of this device includes: an integrated loading system: combining a high-precision closed-loop water pressure loading system with an airbag-type bidirectional (or multidirectional) geostress loading device, achieving synchronous, stable, and controllable coupled loading of high water pressure and complex geostress fields, significantly improving the consistency between test conditions and actual geological conditions. Multimodal Monitoring System: A digital image correlation (DIC) system is deployed through the device's viewing window to conduct full-field, real-time observation of the fracture propagation process on the surrounding rock surface. Multiple sensors, including those for seepage pressure, displacement, and strain, are pre-embedded within the tunnel and surrounding rock to monitor internal mechanical response and failure evolution. These monitoring methods can mutually verify each other, forming a complete monitoring network from surface to interior, and from the entire field to key points. Data Acquisition and Analysis System: Equipped with a supporting data acquisition and processing system, it supports the simultaneous acquisition, processing, and multi-dimensional analysis of multi-source monitoring information, ensuring data accuracy and analytical depth.

[0022] Through the above scheme, this invention can accurately simulate the entire process of tunnel stress, deformation, and even collapse under high water pressure and high ground stress conditions, and achieve visualized monitoring and data analysis of the failure mechanism. Its technical effects and advantages are reflected in: realistically reproducing complex working conditions: through the synergistic loading of water pressure and ground stress, the stress state and failure process of the tunnel under complex stress and seepage coupling conditions are realistically reproduced. Achieving full-process visualized and precise monitoring: combining DIC full-field observation and internal sensor network, full-process, multi-dimensional monitoring from initial stress to final failure is achieved, overcoming the limitations of traditional local monitoring. Enhancing data reliability and application value: multi-modal data mutual verification and supporting systems for in-depth analysis ensure the reliability of experimental results. This device provides an efficient platform for the study of tunnel failure mechanisms, engineering design optimization, and verification of protection and reinforcement measures under extreme hydrogeological conditions, and has significant engineering applicability and promotion prospects. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of a test device for simulating and monitoring the coupled failure of tunnel structures under high water pressure and ground stress, provided by the present invention.

[0024] Figure 2 This is a side view of the model box provided by the present invention;

[0025] Figure 3 This is a cross-sectional view of the arrangement of the multi-point displacement gauge provided by the present invention;

[0026] Figure 4 This is a cross-sectional view of the arrangement of the miniature pressure cell provided by the present invention;

[0027] Figure 5 This is a cross-sectional view of the arrangement of the micro piezometer provided by the present invention;

[0028] Figure 6 This is a schematic diagram of the strain gauge arrangement provided by the present invention;

[0029] Figure 7 This is a schematic diagram of the speckle pattern provided by the present invention;

[0030] Figure 8 This is a schematic diagram of the airbag control component provided by the present invention;

[0031] Figure 9 This is a schematic diagram of the high water pressure loading unit provided by the present invention;

[0032] Figure 10 This is a schematic diagram of the internal structure of the model box on the right side provided by the present invention.

[0033] Reference numerals: 1. Reaction frame; 2. Flexible airbag; 3. Model box; 4. Tunnel model; 5. Transparent observation window; 6. High-pressure pump box; 7. High-pressure water storage tank; 8. Water pressure control console; 9. Light source; 10. Camera; 11. High-pressure pipeline; 12. Surrounding rock similar material; 13. Multi-point displacement gauge arrangement section; 14. Miniature pressure cell arrangement section; 15. Miniature piezometer arrangement section; 16. Strain gauge; 17. Pressure stabilizing valve; 18. Air compressor; 19. Water pressure gauge; 20. High-pressure water pump; 21. Water pressure chamber; 22. Permeability distribution plate. Detailed Implementation

[0034] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0035] Example 1:

[0036] like Figure 1-10 The experimental device for simulating and monitoring the coupled failure of tunnel structures under high water pressure and ground stress, as shown, includes:

[0037] Model box 3, the model box 3 is provided with a space for accommodating surrounding rock similar material 12, and the model box 3 is provided with transparent observation windows 5 at the front and back;

[0038] Tunnel model 4 is placed in the surrounding rock similar material 12 inside the model box 3;

[0039] The loading system includes a ground stress loading unit and a high water pressure loading unit. The ground stress loading unit includes at least one flexible airbag 2 arranged on the top and / or side wall of the model box 3, and an air pressure control component connected to the flexible airbag 2 for providing and regulating air pressure. The high water pressure loading unit includes a high pressure water pump 20, a high pressure water storage tank 7 connected to the high pressure water pump 20, and a high pressure pipeline 11 connecting the high pressure water storage tank 7 to the inside of the model box 3. The high water pressure loading unit is used to apply controllable pore water pressure to the surrounding rock similar material 12.

[0040] The monitoring system includes an optical monitoring unit, a sensor unit, and a data acquisition and processing unit. The optical monitoring unit includes at least one high-precision camera 10 facing the transparent observation window 5, used to acquire image sequences of the surface of the surrounding rock similar material 12 and the surface of the tunnel model 4. The sensor unit includes a displacement sensor, a seepage pressure sensor, and a pressure sensor embedded in the surrounding rock similar material 12. The data acquisition and processing unit is communicatively connected to the optical monitoring unit and the sensor unit, used to synchronously acquire and process image data and sensor data.

[0041] In this embodiment, the model box adopts a steel plate reinforced frame structure, consisting of a bottom plate, four side sealing plates, and front and rear visual observation windows. Transparent observation windows are provided on the front and rear sides to facilitate direct observation of the tunnel structure and the entire process of surrounding rock damage. The remaining side walls are enclosed with thickened steel plates, and the connection points are sealed to ensure the overall rigidity and watertightness of the model box. Drainage holes and fixing bracket interfaces are provided at the bottom of the model box for adjusting the experimental environment and ensuring structural stability.

[0042] In this embodiment, surrounding rock refers to the rock or soil mass surrounding the tunnel or underground cavern. The surrounding rock bears and transmits loads such as in-situ stress and groundwater pressure, and its mechanical properties have a significant impact on the stability of the tunnel structure. In model tests, the surrounding rock is typically simulated by filling it with similar materials to reproduce the supporting role and deformation characteristics of the surrounding rock under actual geological conditions.

[0043] In this embodiment, the surrounding rock simulation material is selected based on the actual working conditions simulated in the experiment. This material is then layered and compacted into the model box to simulate the mechanical properties of different types of surrounding rock. During the filling process of the similar material, permeability sensors and multi-point displacement sensors are pre-embedded according to the design to synchronously monitor changes in pore water pressure and radial deformation response of the surrounding rock during loading.

[0044] In this embodiment, "similar material" refers to materials selected in the model test that are similar to the prototype soil and rock in terms of mechanical and seepage properties, and are used to simulate actual engineering media based on similarity theory. By adjusting parameters such as the material's proportion, density, and moisture content, the density, strength, permeability coefficient, and other indicators of the similar material can be made to meet the requirements of the similarity criteria, thereby ensuring that the deformation and failure behavior of the surrounding rock and tunnel in the scaled-down model matches the actual situation.

[0045] In this embodiment, the model box 3 and the ground stress loading unit are mounted on the reaction frame 1.

[0046] In this embodiment, the side plates and top plate of the model box 3 are flexibly sealed, and the ground stress loading unit can drive the side plates and / or the top plate to move.

[0047] In this embodiment, the surrounding rock similar material 12 and the monitoring hole system are as follows: the surrounding rock is filled and compacted in layers according to the similar material, and monitoring holes are arranged near the tunnel and at different depths. A seepage pressure sensor and a multi-point displacement sensor are embedded to simultaneously reflect the pore water pressure transmission and the radial deformation evolution of the surrounding rock. Strain gauges 16 are configured at key parts of the lining to obtain the strain response of the structural components, which is used to verify the results with the visual measurement results.

[0048] In this embodiment, pore water pressure refers to the pressure exerted by water existing in the pores of rock and soil on the surrounding medium. High pore water pressure weakens the strength of rock and soil and causes buoyancy and seepage damage to tunnel linings. In the model test of this invention, a predetermined pore water pressure environment is applied through a high water pressure loading system to study its impact on the stability of the surrounding rock and tunnel.

[0049] In this embodiment, tunnel lining refers to the structure installed or cast around the tunnel to support the pressure of the surrounding soil or rock mass. The tunnel lining in the scaled-down model is typically made of hard plastic, plaster, or other engineering materials to simulate the lining formed during actual construction.

[0050] In this embodiment, the loading system includes a ground stress loading system: flexible airbag loading devices are arranged on the top and sides of the model box 3. The loading air pressure is adjusted by an air compressor 18, a pressure stabilizing valve 17, and a sub-control system to achieve controllable application of ground stress in different directions. Flexible airbag loading can effectively simulate the constraint and counter-pressure effect of surrounding rock on the tunnel, providing uniform loading, high adjustability, and control over multi-stage loading and unloading processes. Flexible airbag loading effectively avoids stress concentration caused by rigid loading, ensuring uniform pressure application and dynamic adjustment as needed for the experiment. The placement, number, and shape of the airbags can be flexibly adjusted according to the size of the tunnel model 4, loading requirements, and experimental objectives under different working conditions. The pressure adjustment of each airbag is precisely controlled by a pressure stabilizing and regulating unit to ensure stable and continuous pressure output. Furthermore, the system supports multi-stage loading and unloading processes, enabling multiple loading and releasing at different stages as needed for the experiment, providing dynamic loading control, and is particularly suitable for simulating the gradual loading process of surrounding rock during tunnel excavation. Furthermore, by adjusting the number and size of the airbags and combining them with loading beam assemblies of different specifications, the system can meet various testing needs, from small-scale experiments to large-scale tunnel structures.

[0051] As another embodiment, the ground stress loading device can employ either a hydraulic jack loading method or a mechanical servo lever loading method. Both methods can be combined with pressure feedback or displacement feedback to achieve graded loading, constant velocity loading, steady-state holding, and controlled unloading, meeting the experimental requirements for different stiffness boundaries and control precision.

[0052] In this embodiment, airbag-type in-situ stress loading refers to a loading method that uses inflatable airbags to simulate the in-situ stress on a tunnel. By arranging flexible airbags on the top and side walls of the model box and adjusting their internal pressure, uniform vertical and lateral pressures can be applied to similar surrounding rock materials, thus reproducing the confining pressure effect of multi-directional in-situ stress on the tunnel in the underground environment.

[0053] In this embodiment, geostress refers to the stress field inherent in underground rock and soil masses, formed by the combined effects of the overlying rock strata's self-weight and geological tectonic activity; that is, the triaxial pressure borne by the rock mass in an undisturbed state. Geostress has a profound impact on the design and safety of underground structures such as tunnels. In model tests, external pressure is applied using a specialized loading device to simulate the real geostress environment.

[0054] In this embodiment, the loading system also includes a high-pressure water loading system, consisting of a high-pressure water storage tank 7, a high-pressure water pump 20, a water pressure loading device, a water pressure control console 8, and a high-pressure pipeline 11. The high-pressure water pump 20 is placed inside the high-pressure pump box 6. The output pressure of the high-pressure water pump 20 is not directly applied to the surrounding rock similar material 12 through point-type water inlet, but rather the water pressure is first injected into the water pressure chamber 21 around the model box 3 through the high-pressure pipeline 11 to increase the pressure, so that the pressure is homogenized within the box. Subsequently, the water pressure is uniformly transmitted to the bottom of the surrounding rock or the preset seepage boundary in the form of a surface load through the pressure equalization structure, i.e., the permeation distribution plate 22 and the filter layer, thereby forming a stable, controllable, and more spatially uniform pore water pressure field inside the surrounding rock, which can be transmitted to the tunnel perimeter along the preset seepage channel. This "pump pressure - model box water pressure chamber equalization - surface pressure application" loading method can effectively avoid the problems of local jet scouring, pore pressure field distortion, and non-repetitive loading caused by traditional point-type high-pressure water inlet, and significantly improve the uniformity, stability, and test repeatability of high-pressure loading. The system is connected to the model box 3 via high-pressure pipeline 11, enabling water pressure loading of 3 MPa. The water pressure loading device adopts a closed-loop control method, automatically adjusting the pump speed and valve opening based on real-time feedback from the water pressure gauge 19 to ensure the stability and accuracy of the water pressure loading process. The water pressure gauge 19 is installed on the high-pressure pipeline 11. The water pressure control console 8 integrates data acquisition and display functions, displaying the system water pressure, flow rate, and loading rate in real time, achieving continuous, controllable, and precise water pressure loading.

[0055] In this embodiment, high water pressure loading refers to a loading method that applies high horizontal static water pressure to the model to simulate the action of groundwater. This provides a stable and adjustable water pressure environment of up to tens of megapascals to the surrounding rock and tunnel of the model. The system controls the rise and fall of water pressure in real time through pressure sensors and maintains it constant over a long period to reproduce the high pore water pressure conditions in deeply buried tunnels.

[0056] High water pressure-ground stress synergistic loading system: The high water pressure loading system consists of a high-pressure water storage tank 7, a high-pressure water pump 20 and a closed-loop control unit, which can stably load to a high pressure level; the ground stress loading adopts airbag-type multi-directional loading, which is precisely controlled by an air compressor 18 and a pressure stabilization / distribution control unit to achieve two-field coupling, programmable graded loading and unloading.

[0057] As another embodiment, the water pressure loading device can be a gravity water tower combined with a pressure stabilizing device, or an electric booster pump combined with a pressure stabilizing container, to obtain stable hydrostatic pressure and constant pressure water supply for a longer period of time.

[0058] In this embodiment, the optical monitoring and digital image correlation (DIC) system

[0059] Scattered speckle pattern: Random speckle patterns are uniformly sprayed onto the observation surface of the surrounding rock and lining as optical feature markers to meet the surface texture requirements of DIC technology.

[0060] High-precision camera deployment: A high-frame-rate, high-resolution camera 10 is selected and mounted on the outside of the model box 3 via a fixed bracket. It can capture and record the deformation process of key parts from different perspectives. Depending on the experimental requirements, one or more cameras 10 can be deployed to simultaneously collect deformation data of the surrounding rock and tunnel lining structure to achieve three-dimensional deformation analysis.

[0061] Light source system: Set up uniform and stable lighting sources 9 (LED or ring light source) around the model box 3 to avoid image noise and DIC error caused by uneven lighting.

[0062] The integration of high-precision optical observation and digital image correlation (DIC) technology: speckle patterns are sprayed on the tunnel structure, surrounding rock, and key interfaces, and captured by a high-precision camera 10 to provide high-resolution image data for DIC analysis. DIC technology enables accurate measurement of displacement and deformation across the entire surface of the structure, and combined with data from strain gauges 16 and displacement sensors, it forms a comprehensive monitoring system with multiple dimensions and scales.

[0063] In this embodiment, Digital Image Correlation (DIC) is an image processing-based measurement technique that uses correlation analysis of continuously captured surface images with speckle patterns to obtain the surface displacement and strain fields. Compared to traditional point-measurement strain gauges, DIC can achieve full-field (i.e., the entire surface of the measurement area) displacement and strain measurement.

[0064] In this embodiment, the high-precision camera is a camera device designed specifically for scientific research or industrial inspection, featuring high resolution and high frame rate. In conjunction with the speckle observation surface, it can record sequential images during vibration loading or stress deformation, providing data for DIC analysis.

[0065] In this embodiment, the tunnel structure uses a scaled-down model. Tunnel model 4 is made of plaster of a similar material and is cast in scale. The outer wall of the model is coated with an epoxy or silicone rubber waterproof material to ensure the internal sealing and pressure-bearing performance of the model. Tunnel model 4 can be designed as a monolithic cast-in-place or modular structure according to the test requirements. The monolithic structure is cast in one piece, while the modular structure is connected by circumferential splicing and high-strength adhesive or bolts to ensure integrity. Strain gauges 16 are arranged on the inner wall of the tunnel, distributed in the circumferential, longitudinal, and joint areas where strain changes are likely to occur. The strain gauges 16 are fixed by non-destructive adhesives or special bonding methods, and are properly shielded and insulated.

[0066] In this embodiment, the experimental acquisition and data processing system comprises a multi-channel data acquisition instrument, a signal conditioning module, a computer terminal, and a synchronous triggering unit. It is used to synchronously acquire, store, and process monitoring signals and optical image data from displacement gauges, pressure cells, and piezometers. To achieve full-process identification of the loosened rock zone, this invention arranges several monitoring holes radially at typical locations such as the tunnel arch crown, arch waist, and arch bottom. Multiple displacement gauges, pressure cells, and piezometers are installed at different burial depths. The positional relationship of the multi-point displacement gauge arrangement section 13, the miniature pressure cell arrangement section 14, and the miniature piezometer arrangement section 15 is referenced. Figure 2-5 Multi-point displacement gauges are used to obtain the stratified displacement and convergence development characteristics of the surrounding rock from near the tunnel wall to the depths; pressure cells are used to record the stress redistribution and local unloading / concentration changes in the surrounding rock; and piezometers are used to monitor the transmission, dissipation, and abnormal fluctuations of pore water pressure. During loading, by comparing the spatial attenuation patterns of "displacement-pressure-permeability" at each buried depth measuring point, when the response of the near-tunnel wall measuring point is significant while the response of the deep measuring point is significantly weakened and tends to stabilize, the boundary of the loosened zone can be comprehensively determined based on the displacement gradient abrupt change point, pressure recovery point, and permeability influence range. Furthermore, by combining data from multi-directional monitoring wells for spatial interpolation and evolution tracking, the range of the loosened zone and its spatiotemporal distribution with changes in water pressure and geostress are formed, providing data support for the analysis of surrounding rock failure mechanisms and structural evaluation.

[0067] Synchronous sensor acquisition and unified data processing: The test acquisition system consists of a pressure sensor, a displacement sensor, a strain acquisition instrument, a dynamic signal acquisition instrument, and a high-precision camera 10. It realizes the synchronous recording of multi-source data such as pressure, displacement, strain, and optical images under the same time base. It can jointly calibrate and fuse the full-field measurement results of DIC with point sensor data, identify key characteristics of failure evolution in real time, and evaluate the stress and deformation mechanism of tunnel and surrounding rock under coupled working conditions more comprehensively and accurately.

[0068] In this embodiment, a pressure sensor refers to a sensor used to measure the pore water pressure inside a rock or soil mass. It is embedded in a similar material to the surrounding rock to monitor changes in water pressure within the soil in real time during the test. Data collected by the pressure sensor can be used to assess the impact of seepage on the stability of the tunnel's surrounding rock.

[0069] In this embodiment, a displacement sensor refers to a sensor used to measure the amount of displacement of a component or medium relative to its initial position. It can be used to detect the deformation of the surrounding rock or tunnel structure in the model. In model tests, multiple displacement sensors are typically deployed at different locations around the tunnel to record the displacement response of the surrounding rock and lining during loading, thereby obtaining the deformation distribution of the structure under stress.

[0070] In this embodiment, strain gauges are specialized data acquisition devices for strain measurement, capable of simultaneously acquiring strain changes from multiple strain gauges. Combined with high-frequency sampling, they can accurately record the entire process of structural stress changes.

[0071] As another embodiment, edge computing devices are integrated at the data acquisition end to perform preliminary data processing, reduce data transmission volume, and improve real-time performance.

[0072] As another embodiment, data processing is migrated to the cloud using a cloud computing platform, and large-scale data analysis and storage are performed using cloud computing resources to improve data processing capabilities.

[0073] As another embodiment, fiber Bragg grating (FBG) sensors are used to replace traditional strain gauges to achieve strain monitoring with higher sensitivity; laser displacement sensors replace some displacement sensors to provide higher precision non-contact displacement measurement.

[0074] This invention provides a physical model test device for simulating the failure process of deep tunnel surrounding rock under the combined action of high water pressure and ground stress and for visual monitoring. The device mainly consists of a model box 3, a tunnel structure, a loading system, an optical monitoring and digital image correlation (DIC) system, and a test acquisition and data processing system.

[0075] In this embodiment, the overall model construction includes model box preparation:

[0076] A rectangular model box 3 with dimensions of approximately 1.0m in length, 1.0m in width, and 1.0m in height was selected. The box body adopts a steel frame structure, with transparent plexiglass observation windows 5 on the front and rear sides. The other side walls are enclosed with thickened steel plates, and the joints are sealed to ensure the overall rigidity and watertightness of the model box 3. Reinforcing ribs are added to the side walls and bottom plate of the box body to ensure that it does not undergo significant deformation or leakage during the filling of the surrounding rock similar material 12 and the application of loads. Drainage holes and fixed support interfaces are reserved at the bottom of the model box 3 for adjusting the test environment (such as controlling the groundwater level) and ensuring the stable support of the model box 3.

[0077] The overall model construction also includes surrounding rock filling:

[0078] Based on the simulated real-world conditions, similar materials of surrounding rock or soil that meet the requirements of mechanical similarity (such as strength, deformation modulus, etc.) and seepage similarity (such as permeability coefficient, seepage pressure response, pore structure, etc.) are selected and filled into model box 3 through layered laying and compaction to simulate the physical and mechanical properties and seepage characteristics of actual surrounding rock and soil layers. During the filling process of the similar materials, seepage pressure sensors and multi-point displacement sensors are pre-embedded according to the design to simultaneously monitor the changes in pore water pressure and radial deformation response of the surrounding rock under seepage-stress coupled loading conditions. After the surrounding rock is filled to the predetermined height, excavation space of corresponding size is reserved at the tunnel design location for subsequent placement of tunnel model 4.

[0079] Tunnel model installation:

[0080] Tunnel model 4 is cast in scale using a similar material (such as plaster). The outer surface of tunnel model 4 is coated with a waterproof sealant such as epoxy resin or silicone rubber to ensure good internal sealing and pressure resistance. Tunnel model 4 can be made into a monolithic cast-in-place structure or a structure composed of several annular tunnel segments, secured with high-strength adhesives or bolts to ensure overall strength. According to design requirements, resistance strain gauges 16 are applied to the circumferential, longitudinal, and joint locations on the inner wall of tunnel model 4, and fixed with non-destructive adhesives, ensuring waterproofing and insulation protection. The completed tunnel model 4 is placed in the pre-reserved installation space in the surrounding rock, ensuring close contact between the top and sidewalls of tunnel model 4 and the surrounding filled rock-like material 12. After tunnel model 4 is in place, if gaps exist, they can be filled with the same similar material and compacted appropriately to ensure uniform stress and good contact around tunnel model 4.

[0081] In this embodiment, the geostress and hydraulic pressure loading system includes geostress loading:

[0082] At the beginning of the experiment, the in-situ stress field of the surrounding rock was first applied. Flexible airbag loading devices 2 were arranged on the top and inner walls of the model box 3. Pressure was supplied by an air compressor 18, and the pressure inside the airbags was precisely adjusted by a pressure regulating valve 17 and a sub-control system to achieve controllable application of in-situ stress in both vertical and horizontal directions. During loading, the airbag pressure was increased gradually in stages until the predetermined in-situ stress level was reached. At each pressure level, the pressure could be maintained for a suitable period to simulate the gradual increase and stabilization of actual stratum stress. The airbag loading method applied uniform pressure with a wide adjustable range, effectively simulating the constraint and counter-pressure effect of the surrounding rock on the tunnel structure. If necessary, multi-stage cyclic loading or unloading could be performed according to the experimental plan to study the tunnel's response characteristics under different stress paths.

[0083] Water pressure loading:

[0084] After the surrounding rock stress field is applied and stabilized, the high-pressure loading system is activated to gradually introduce water pressure into the model box 3 to simulate the increase in groundwater pressure. The high-pressure loading system consists of a high-pressure water storage tank 7, a high-pressure water pump 20, and a water pressure control console 8. The device is connected to the model box 3 via a high-pressure pipeline 11. A closed-loop control mode is used during loading: pressure sensors monitor the water pressure in the model box 3 in real time and feed it back to the control unit, automatically adjusting the pump output and valve opening to ensure a stable and controllable increase in water pressure and avoid instantaneous pressure shocks. The water pressure application process also adopts a phased and gradual approach: the pump output pressure is slowly increased, causing the pore water pressure to rise step by step, and maintained at each stage pressure for a period of time, allowing the surrounding rock seepage field to gradually reach equilibrium and stability. The water pressure control console 8 can monitor parameters such as the current water pressure value, flow rate, and loading rate in real time, and adjust the loading process as needed. The entire water pressure loading process is coordinated with the ground stress loading process to ensure that the test conditions reflect the true evolution of the stress state of the tunnel structure under the coupling of high water pressure and ground stress.

[0085] In this embodiment, the monitoring setup and data acquisition process is as follows:

[0086] Sensor deployment:

[0087] During model assembly, various sensors were installed at key locations according to the design to achieve comprehensive monitoring of the tunnel and surrounding rock conditions. Pressure sensors embedded at different depths within the surrounding rock are used to measure changes in pore water pressure in real time; multi-point displacement sensors record the deformation of the surrounding rock towards the tunnel; and miniature pressure cells monitor changes in internal pressure within the surrounding rock or soil. Strain gauges 16 attached to the inner surface of tunnel model 4 monitor the strain response of the lining structure during loading. All sensors are connected to the corresponding channels of the data acquisition system via lead wires and are checked and calibrated before loading to ensure accurate and synchronous recording of signals from each measuring point during testing.

[0088] Speckle spraying and optical monitoring setup:

[0089] Random black and white speckle patterns are sprayed onto the exposed rock surface corresponding to the transparent observation window 5 of model box 3 and the visible surface of tunnel model 4. The speckle size is generally controlled within the range of 1 to 3 mm, with uniform distribution and obvious contrast, so as to facilitate subsequent calculations using the digital image correlation (DIC) method.

[0090] A high-frame-rate, high-resolution industrial camera 10 (e.g., tens of millions of pixels, with a frame rate of 50-100fps as needed) is mounted externally on the model box 3 via a fixed bracket. The camera's optical axis is positioned as perpendicular to the observation window plane as possible or tilted at a small angle. Depending on the experimental requirements, one or more cameras 10 can be deployed to simultaneously capture deformation images of key parts of the tunnel and surrounding rock from different perspectives. Simultaneously, uniform and stable lighting sources 9 (such as LED panel lights or ring lights) are arranged around the model box 3 to avoid image noise and DIC measurement errors caused by uneven lighting, ensuring the acquisition of high-quality image data.

[0091] Data acquisition process:

[0092] During the experiment, all monitoring data were synchronously acquired and recorded by a multi-channel data acquisition system. Before the loading began, the data acquisition device and the triggering system of the industrial camera 10 were linked and set to operate under a unified time base. When the ground stress and water pressure loading were carried out, the signals of each sensor were continuously acquired at a preset high sampling rate (e.g., 1kHz), and the industrial camera 10 synchronously captured speckle image sequences in real time to ensure that the sensor data and image frames corresponded one-to-one in time.

[0093] The system can automatically save data and image information of each channel at each loading stage, providing complete original evidence for subsequent data processing and analysis.

[0094] In this embodiment, the excavation process steps are as follows:

[0095] After completing the surrounding rock filling, tunnel structure installation, monitoring device deployment, and the application and stabilization of the ground stress field, a simulation of the tunnel excavation stage was conducted. To ensure that the excavation process is controllable and consistent with the actual construction stage, the excavation was carried out by removing the filling material.

[0096] Excavation path determination and segmentation:

[0097] Before excavation, the ground stress loading is maintained at a set stable value, and the high water pressure loading system is in a state of waiting to be loaded or low pressure holding. According to the designed tunnel excavation method, the tunnel is divided into several excavation sections along the axial direction (or into upper step / middle step / lower step along the cross section), and the location and excavation sequence of the excavation sections are marked on the outside of the model box 3 to ensure the repeatability and comparability of each excavation.

[0098] Step-by-step excavation - stability monitoring:

[0099] The tunnel is pre-filled with controllable strength materials (such as low-strength gypsum / foam materials / soluble materials). During excavation, these materials are removed or cut away section by section from the tunnel entrance using special tools to form the excavation face advancement process, realizing the sequential process of "excavation face advancement - surrounding rock unloading - structural response".

[0100] After each stage of excavation, the ground stress is kept constant, and high water pressure is applied or increased to the target value for that stage according to the test plan. This constant loading condition is maintained for a period of time to allow the surrounding rock deformation and seepage field to reach a stage of stability. Simultaneously, the DIC system continuously acquires the evolution of the surrounding rock surface displacement and strain field, and sensors synchronously record changes in displacement, pressure, and seepage pressure. This process is repeated until the predetermined excavation length is completed or the entire cross-section excavation is finished.

[0101] In this embodiment, data analysis and post-processing:

[0102] Signals such as seepage pressure, displacement, and strain are processed in the time and frequency domains respectively. Methods such as fast Fourier transform or wavelet analysis are used to identify the characteristic frequency bands, peak value changes, and response laws during the linkage loading process of high water pressure and geostress, and to extract the evolution characteristics of surrounding rock convergence and lining strain.

[0103] The full-field displacement cloud map, principal strain cloud map, and displacement vector field obtained by digital image correlation can intuitively display the interaction between the surrounding rock and the lining, the crack initiation and propagation path, and the local instability process.

[0104] By combining sensor data and digital image correlation results, the weak areas, key damage sites and potential failure modes of the structure under coupled working conditions are determined, forming criteria and parameter indicators for engineering selection design and safety assessment.

[0105] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A test device for simulating and monitoring the coupled failure of tunnel structures under high water pressure and ground stress, characterized in that, include: Model box (3), the model box (3) is provided with a space for accommodating surrounding rock similar material (12), and the model box (3) is provided with transparent observation windows (5) at the front and back. The tunnel model (4) is placed in the surrounding rock similar material (12) inside the model box (3); The loading system includes a ground stress loading unit and a high water pressure loading unit. The ground stress loading unit includes a flexible airbag (2) arranged on the top and side walls of the model box (3) and a pressure control component connected to the flexible airbag (2) for providing and regulating air pressure. The high water pressure loading unit includes a high pressure water pump (20), a high pressure water storage tank (7) connected to the high pressure water pump (20), and a high pressure pipeline (11) connecting the high pressure water storage tank (7) to the inside of the model box (3). The high water pressure loading unit is used to apply controllable pore water pressure to the surrounding rock similar material (12). The monitoring system includes an optical monitoring unit, a sensor unit, and a data acquisition and processing unit. The optical monitoring unit includes at least one camera (10) facing the transparent observation window (5) for acquiring image sequences of the surface of the surrounding rock similar material (12) and the surface of the tunnel model (4). The sensor unit includes a displacement sensor, a seepage pressure sensor, and a pressure sensor embedded in the surrounding rock similar material (12). The data acquisition and processing unit is communicatively connected to the optical monitoring unit and the sensor unit for synchronously acquiring and processing image data and sensor data.

2. The experimental device for simulating and monitoring the coupled failure of tunnel structures under high water pressure and ground stress according to claim 1, characterized in that: The side plates and top plate of the model box (3) are flexibly sealed, and the ground stress loading unit can drive the side plates and top plate to move.

3. The experimental device for simulating and monitoring the coupled failure of tunnel structures under high water pressure and ground stress according to claim 1, characterized in that: The air pressure regulation component includes an air compressor (18), a pressure regulating valve (17), and a sub-control system, which are used to achieve precise adjustment and multi-level loading control of the air pressure inside the flexible airbag (2).

4. The experimental device for simulating and monitoring the coupled failure of tunnel structures under high water pressure and ground stress according to claim 1, characterized in that: The high water pressure loading unit also includes a water pressure control console (8), which is connected to a pressure sensor to monitor the water pressure in the model box (3) in real time and control the output of the high pressure water pump (20) to form a closed-loop control.

5. The experimental device for simulating and monitoring the coupled failure of tunnel structures under high water pressure and ground stress according to claim 4, characterized in that: The model box (3) is provided with a permeation distribution plate (22) on the inside, and a water pressure cavity (21) is formed between the side plate of the model box (3) and the permeation distribution plate (22); the high pressure pipeline (11) is connected to the water pressure cavity (21) and is used to apply water pressure uniformly to the surrounding rock similar material (12) in the form of surface load.

6. The experimental device for simulating and monitoring the coupled failure of tunnel structures under high water pressure and ground stress according to claim 1, characterized in that: Multiple monitoring holes are arranged radially along the arch top, arch waist and arch bottom of the tunnel model (4), and the sensor unit is installed in the monitoring hole. The sensor unit is buried in stages at different burial depths.

7. The experimental device for simulating and monitoring the coupled failure of tunnel structures under high water pressure and ground stress according to claim 6, characterized in that: The displacement sensor is a multi-point displacement meter, used to obtain the stratified displacement and convergence development characteristics of the surrounding rock from near the tunnel wall to the depths; The pressure sensor is a pressure cell used to record the redistribution of stress in the surrounding rock and changes in local unloading / concentration; the pore pressure sensor is a piezometer used to monitor the transmission, dissipation, and abnormal fluctuations of pore water pressure.

8. The experimental device for simulating and monitoring the coupled failure of tunnel structures under high water pressure and ground stress according to claim 1, characterized in that: The optical monitoring unit also includes a speckle pattern set on the observation surface of the surrounding rock, and an illumination source (9) is set around the model box (3) to provide uniform illumination for image acquisition.

9. The experimental device for simulating and monitoring the coupled failure of tunnel structures under high water pressure and ground stress according to claim 1, characterized in that: The tunnel model (4) is a scaled-down model made of materials similar to the surrounding rock, and its outer surface is coated with a waterproof sealing layer.

10. The experimental device for simulating and monitoring the coupled failure of tunnel structures under high water pressure and ground stress according to claim 1, characterized in that: The data acquisition and processing unit consists of a multi-channel data acquisition instrument, a signal conditioning module, a computer terminal, and a synchronous triggering unit, and is used for synchronous acquisition, storage, and processing of sensor unit monitoring signals and optical image data.

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