Model test method for shield parallel crossing of existing tunnel in sandy gravel stratum

Abstract

The invention discloses a model test method suitable for a shield to parallelly pass through an existing tunnel in a sandy gravel stratum, which comprises the following steps of: researching the characteristics of the sandy gravel stratum, and calculating and determining a model test material and a proportion according to a similarity ratio; on the basis, an existing tunnel model is prepared, and similar soil bodies are filled; measuring points such as traditional strain gauges, displacement meters and soil pressure boxes are arranged in the model, and meanwhile, an intelligent sensing technology (such as distributed optical fiber sensing and digital image related technologies) is introduced for multi-dimensional monitoring; and then simulating a shield parallel crossing process and carrying out an excavation test. Through a series of innovative measures and process iteration, the soil body similarity, the monitoring precision and the test result credibility are remarkably improved, and a more scientific decision basis is provided for engineering design and safety control of parallel penetration of the shield through the existing tunnel in the sandy gravel stratum.

Description

Technical Field

[0001] The present invention relates to the technical field of model tests, and more particularly, to a model test method for a shield tunneling parallelly crossing an existing tunnel in a sandy cobble stratum. Background Art

[0002] Under the background of the rapid development of urbanization, the development and utilization of urban underground space are increasing day by day. As a key part of the urban transportation network, subway and other tunnel projects play an important role in urban infrastructure construction. With the increasing tension of urban underground space resources, new tunnel projects often need to cross or be adjacent to existing tunnel structures, which brings great challenges in engineering technology, especially when constructing in complex strata such as sandy cobbles.

[0003] Due to the characteristics of uneven particle structure, looseness and high permeability of the sandy cobble stratum, the risk of shield tunneling construction is increased, such as problems like possible ground settlement and tunnel structure damage. During the shield tunneling construction process, especially when the tunnel needs to cross an existing tunnel in parallel, ensuring construction safety, controlling ground displacement and protecting the existing tunnel structure from being affected become the key points of technical research.

[0004] It is difficult to meet the accuracy and stability of shield tests under complex working conditions in indoor model test technology. Therefore, in the traditional test process, the test process is unidirectional and linear, from test design - test implementation - data acquisition - conclusion drawing, without a feedback link, and the test reliability is poor. Therefore, we make improvements in this regard and propose a model test method for a shield tunneling parallelly crossing an existing tunnel in a sandy cobble stratum. Summary of the Invention

[0005] The purpose of the present invention is to address the problem that the current test process is unidirectional and linear, from test design - test implementation - data acquisition - conclusion drawing, without a feedback link, and the test reliability is poor.

[0006] To achieve the above-mentioned invention purpose, the present invention provides a model test method for a shield tunneling parallelly crossing an existing tunnel in a sandy cobble stratum to improve the above problems.

[0007] Specifically, this application is as follows:

[0008] A model test method for a shield tunneling parallelly crossing an existing tunnel in a sandy cobble stratum includes the following steps:

[0009] S1. Study on sandy and gravel strata: Obtain sandy and gravel soil samples from the strata that the shield mainly passes through from the project site, conduct screening tests on a vibrating screener to obtain the particle gradation of sandy and gravel, and scale down the particle size of the soil sample particles according to the geometric similarity ratio to obtain the ideal particle gradation of the test sandy and gravel soil. Use three different gradings of sandy and gravel soil and conduct multiple proportioning tests to determine the appropriate optimal proportion of similar sandy and gravel soil. Under the optimal proportion, the particle gradation of the soil obtained should be similar to the particle gradation of the ideal test sandy and gravel soil obtained after scaling down.

[0010] S2. Calculation of geometric similarity ratio: Determine the cutter head diameter D according to the project site s The cutter head diameter D in the test m The geometric similarity ratio C of the test is determined by the ratio l ; Obtain all similarity ratios of the scaled test; Based on the geometric similarity ratio, the gradation of the sand and gravel after scaled and the size of the existing tunnel model can be determined. The gravity acceleration similarity ratio is determined to be 1, and the material for simulating the existing tunnel is determined. The stiffness similarity ratio can be calculated by the ratio of the on-site segment stiffness to the stiffness of the existing tunnel. Since the stiffness is EI and the elastic modulus is E, the moment of inertia of the I section can be calculated from the size section, and the elastic modulus similarity ratio is also obtained;

[0011] S3. Determination of similar materials for existing tunnels: Ensure that the geometric dimensions and bending stiffness between the existing tunnel and the existing tunnel model meet the similarity principle, determine the similarity constant values ​​and theoretical values ​​of the physical quantities of length, weight, gravitational acceleration and stiffness based on the similarity ratio; determine a material in reality based on the theoretical value, and measure the physical properties of the existing tunnel model made of the determined material to ensure that it meets the theoretical value;

[0012] S4. Filling of the test model: Paste smooth wallpaper on the inner wall of the model box to reduce friction, and mark the scale on the wallpaper. Use a laser leveler to ensure the flatness of the layer when filling similar sand and gravel soil in layers. When filling to a predetermined height, place the existing tunnel model equipped with monitoring elements horizontally, and use elastic ropes to accurately control its position, and then continue to fill in layers until it reaches the surface.

[0013] S5. Arrange displacement monitoring points: According to the test purpose, displacement meters are arranged at preset points to measure surface displacement and underground displacement;

[0014] S6. Arrangement of additional earth pressure monitoring points for existing tunnels: According to the test purpose, earth pressure boxes are arranged at preset points to measure the additional earth pressure of the existing tunnel during the shield tunneling process;

[0015] S7. Arrange additional strain monitoring points for existing tunnels: According to the test purpose, strain gauges are attached to the preset points to measure the additional strain of the existing tunnel during the shield tunneling process;

[0016] S8. Intelligent sensing and fiber optic sensing deployment: Distributed fiber optic sensors are embedded in the tunnel model and surrounding soil, and digital image correlation (DIC) technology is used to identify points to monitor the continuous strain and deformation field distribution of the tunnel and surrounding soil.

[0017] S9, excavation and shield simulation test: simulate the excavation process of the shield machine parallel to the existing tunnel in a similar model;

[0018] S10, data acquisition and preliminary processing: synchronous acquisition and preliminary filtering of strain gauges, displacement meters, earth pressure boxes, distributed optical fiber sensor data and DIC image data;

[0019] S11. Data inversion and intelligent analysis: The preliminarily processed data is input into the numerical simulation model and deep learning model for parameter inversion and pattern recognition, so as to determine the precise values ​​of key parameters of the soil and tunnel model and identify signs of nonlinear failure or abnormal strain distribution;

[0020] S12, iterative optimization and result verification: According to the data inversion and intelligent analysis results, the test conditions, similar material ratios, sensor layout locations and excavation conditions are optimized and adjusted in a targeted manner to form a closed-loop iterative process of test-analysis-optimization;

[0021] S13. Comprehensive analysis of test data and output of conclusions: After multiple rounds of iterative verification and optimization, the final data is comprehensively analyzed and summarized to draw test conclusions, which provide technical references for the engineering design and safety control of shield tunneling parallel to existing tunnels in sandy and gravel strata.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] In the scheme of this application:

[0024] 1. This application can accurately simulate the mechanical properties of tunnel excavation through accurate similarity ratio calculation, reasonable selection and optimization of model materials and parameters, provide important physical parameters for simulation tests, and improve test reliability;

[0025] 2. This application not only arranges traditional strain gauges, displacement meters, earth pressure boxes and other measuring points in the model, but also introduces intelligent sensing technology for multi-dimensional monitoring, which can realize non-contact, multi-dimensional monitoring of the continuous strain field and displacement field of the tunnel and surrounding soil, and obtain more comprehensive data;

[0026] 3. The present application introduces a data inversion and intelligent analysis module, and feeds the analysis results back into the test process to adjust the test conditions, model parameters, and measuring point layout, forming a closed-loop iterative process of test - analysis - optimization, which significantly improves the soil similarity, monitoring accuracy, and reliability of test results, providing a more scientific decision-making basis for engineering design and safety control;

[0027] 4. The present application makes targeted optimizations and adjustments to the test conditions, similar material ratios, sensor layout positions, and excavation conditions according to the data inversion and intelligent analysis results, and can continuously approach test results closer to the actual engineering situation. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 is the model test flow chart of the shield tunneling parallel crossing existing tunnel model test method in sandy pebble stratum provided by the present application;

[0029] Figure 2 is the model test monitoring plane layout drawing of the shield tunneling parallel crossing existing tunnel model test method in sandy pebble stratum provided by the present application;

[0030] Figure 3 is the layout drawing of the monitoring points of the existing tunnel of the shield tunneling parallel crossing existing tunnel model test method in sandy pebble stratum provided by the present application;

[0031] Figure 4 is the cross-sectional layout drawing of the monitoring points of the existing tunnel of the shield tunneling parallel crossing existing tunnel model test method in sandy pebble stratum provided by the present application. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0032] In order to enable those skilled in the art to better understand the solution of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0033] It should be noted that, without conflict, the embodiments in the present invention and the features and technical solutions in the embodiments can be combined with each other.

[0034] It should be noted that similar reference numerals and letters denote similar items in the following drawings. Therefore, once an item is defined in one drawing, it does not need to be further defined and explained in subsequent drawings.

[0035] Embodiment, please refer to Figures 1 - 4 , a shield tunneling parallel crossing existing tunnel model test method in sandy pebble stratum, comprising the following steps:

[0036] S1. Research on sandy cobble stratum: Obtain sandy cobble soil samples from the main stratum traversed by the shield at the construction site, conduct sieving tests on a vibrating sieve shaker to obtain the particle size distribution of the sandy cobbles, scale down the particle size of the soil samples according to the geometric similarity ratio to obtain the particle size distribution of the ideal test sandy cobble soil mass, use three different gradations of sandy soil and determine the optimal ratio of the suitable similar sandy cobble soil mass through multiple proportioning tests. At the optimal ratio, the particle size distribution of the prepared soil mass should be similar to that of the ideal test sandy cobble soil mass obtained after scaling down;

[0037] By obtaining sandy cobble soil samples from the construction site and conducting sieving tests, the particle size distribution of the sandy cobbles in the main stratum traversed by the shield can be accurately grasped, which provides basic data for subsequent tests, enables the soil mass used in the tests to be as close as possible to the particle distribution characteristics of the actual stratum, and thus improves the reliability and representativeness of the test results;

[0038] Scale down the particle size of the soil samples according to the geometric similarity ratio to obtain the particle size distribution of the ideal test sandy cobble soil mass, which further ensures the similarity of the test model and the actual project in terms of particle size distribution. This similarity is crucial for simulating the mechanical properties of the actual stratum because the particle size distribution directly affects the strength, deformation characteristics, etc. of the soil mass;

[0039] Use three different gradations of sandy soil to conduct multiple proportioning tests to determine the optimal ratio of the suitable similar sandy cobble soil mass, and make the particle size distribution of the prepared soil mass similar to that of the ideal test sandy cobble soil mass obtained after scaling down. This process not only considers the similarity of the particle size distribution but also the interaction and combined effect between different sandy soils, making the soil mass used in the tests closer to the actual stratum in terms of mechanical properties and providing a strong guarantee for the accuracy of subsequent tests;

[0040] Accurate soil proportioning helps reduce the uncertainty and errors in the test process and improve the repeatability of the test results. Different soil proportions may lead to significant differences in the test results, and by determining the optimal ratio, the test can be carried out under relatively stable and controllable conditions, thus obtaining more reliable and accurate test results;

[0041] S2. Calculation of geometric similarity ratio: Determine the geometric similarity ratio C of the test according to the ratio of the cutterhead diameter D at the construction site s to the cutterhead diameter D in the test m l ​; Obtain all the similarity ratios of the scaled-down test; Based on the geometric similarity ratio, the gradation of the scaled-down sand and gravel and the dimensions of the existing tunnel model can be determined. The similarity ratio of gravitational acceleration is determined to be 1. Determine the material for simulating the existing tunnel (such as polyethylene). The similarity ratio of stiffness can be deduced from the ratio of the stiffness of the on-site segment to that of the existing tunnel. Since the stiffness is EI, the elastic modulus is E, and the cross-sectional moment of inertia I can be calculated from the cross-sectional dimensions, thus the similarity ratio of the elastic modulus is also obtained; The similarity ratio is the basis and core of the model test. In the model test, due to the large scale of the actual project, it is difficult to directly conduct a comprehensive experimental study. Therefore, it is necessary to establish a similarity model to simulate the actual project situation. Accurate calculation of the similarity ratio can ensure that the test model is similar to the actual project in terms of geometric dimensions, mechanical properties, etc., so that the test results can reasonably infer the actual project situation. By analyzing and calculating key parameters such as the cutter head diameter and segment stiffness, each similarity ratio can be determined, thus constructing a scientific and reasonable test model;

[0042] S3. Determination of the similar material for the existing tunnel: Ensure that the geometric dimensions and flexural stiffness between the existing tunnel and the existing tunnel model both satisfy the similarity principle. Determine the similarity constant values and theoretical values of physical quantities such as length, specific weight, gravitational acceleration, and stiffness according to the similarity ratio; Determine a material in reality according to the theoretical value, and measure the physical properties of the existing tunnel model made of the determined material to ensure that it meets the theoretical value; The existing tunnel mainly bears flexural action during the shield tunneling process. Its geometric dimensions and flexural stiffness are the key factors affecting its mechanical properties. By ensuring the similarity between the model and the actual existing tunnel in these aspects, the mechanical response of the model in the test can be similar to that of the actual existing tunnel, thus more accurately simulating the actual project situation. The determination of the similarity constant values of physical quantities and the measurement and verification of material properties can ensure that the design and production of the model conform to the similarity principle, improving the accuracy and reliability of the test results. The three-point bending test is a direct and effective verification method, which can intuitively test whether the flexural stiffness of the model meets the requirements;

[0043] S4. Filling of the test model: Paste smooth wallpaper on the inner wall of the model box to reduce friction, and calibrate the scale on the wallpaper. Use a laser level to ensure the flatness of the layer surface when filling the similar sand and gravel soil in layers; When filling to the predetermined height, horizontally place the existing tunnel model equipped with monitoring elements, and precisely control its position using elastic ropes, and then continue to fill in layers until the ground surface;

[0044] Pasting smooth wallpaper on the inner wall of the model box to reduce friction can reduce the influence of the friction force of the model box wall on the soil body, making the mechanical properties of the soil body closer to the actual stratum situation during the filling and test process. The existence of friction force may lead to uneven stress distribution of the soil body, affecting the accuracy of the test results, and reducing friction can effectively reduce this influence;

[0045] Calibrate the scale on the wallpaper to facilitate accurate control of the height of each layer of soil and the filling quality during the filling process, ensuring the filling accuracy of the test model. Accurate filling height and quality are crucial for ensuring the mechanical properties and simulation effect of the test model. Calibrating the scale can provide a clear reference standard for the filling process;

[0046] Use a laser leveler to ensure the levelness of the layer surface, enabling each layer of soil to be evenly distributed in the horizontal direction, avoiding stress concentration and uneven deformation of the soil caused by uneven layer surfaces. Improving the levelness helps ensure the uniformity of the mechanical properties of the test model and enhances the reliability of the test results;

[0047] When filling to the predetermined height, horizontally place the existing tunnel model equipped with monitoring elements and precisely control its position using elastic ropes. This can ensure the accurate position of the existing tunnel model in the test model, avoiding errors in the test results caused by position deviations. Precise position control helps accurately simulate the interaction between the existing tunnel and the surrounding soil during the shield tunneling process;

[0048] Continue to fill in layers until the ground surface is reached, enabling the test model to fully simulate the actual stratum conditions, including the interaction between the existing tunnel and the surrounding soil. The complete filling process can ensure that the test model is similar to the actual project in terms of mechanical properties and structure, enhancing the representativeness of the test results;

[0049] Strictly controlling the model filling process helps improve the quality and stability of the test model, reducing uncertainties and errors during the test process, thereby obtaining more accurate and reliable test results;

[0050] S5. Arrange displacement monitoring points: According to the test purpose requirements, install displacement gauges at the preset points to measure surface displacement and in - ground displacement; Displacement is an important indicator reflecting the mechanical response of the stratum and the existing tunnel. During the shield tunneling process, the stratum will be disturbed by the shield machine and deform, and the existing tunnel will also displace due to the stratum deformation. By monitoring surface displacement and in - ground displacement, the impact degree and scope of shield construction on the surrounding environment can be comprehensively understood. Displacement monitoring data can intuitively reflect the deformation of the stratum and the existing tunnel, providing an important basis for engineering safety assessment and construction parameter optimization. At the same time, the long - term accumulation of displacement monitoring data helps summarize experience and laws, improving the level of engineering design and construction;

[0051] S6. Arrangement of additional earth pressure monitoring points for the existing tunnel: According to the test purpose requirements, soil pressure cells are arranged at the preset positions to measure the additional earth pressure on the existing tunnel during the shield tunneling process. The additional earth pressure is one of the important loads borne by the existing tunnel during the shield construction process, and its magnitude and distribution will directly affect the structural safety of the existing tunnel. During the shield tunneling process, the propulsion of the shield machine and the disturbance of the soil will cause the soil pressure around the existing tunnel to change, generating additional earth pressure. By arranging soil pressure cells for monitoring, the change information of the additional earth pressure can be obtained in real time, providing a basis for the safety assessment and design optimization of the existing tunnel. At the same time, the comparative analysis of the monitoring data and the numerical simulation results can improve the accuracy of the numerical simulation and provide more scientific guidance for the shield construction.

[0052] S7. Arrangement of additional strain monitoring points for the existing tunnel: According to the test purpose requirements, strain gauges are pasted at the preset positions to measure the additional strain on the existing tunnel during the shield tunneling process. The existing tunnel will be subjected to complex mechanical actions during the shield tunneling process, resulting in structural strain. Strain is a direct manifestation of the structural force deformation. By pasting strain gauges to monitor the additional strain, the force state information of the tunnel structure can be obtained most directly and accurately. Different force conditions will produce different strain characteristics. By analyzing the strain data, the mechanical response mechanism of the tunnel structure can be deeply understood. And timely grasping the strain situation of the tunnel structure can provide key basis for the safety assessment, maintenance decision-making and design optimization of the structure, thus ensuring the safe and stable operation of the existing tunnel during the shield tunneling process.

[0053] S8. Intelligent perception and fiber optic sensing deployment: Embedded distributed fiber optic sensors and markers applying digital image correlation (DIC) technology in the tunnel model and the surrounding soil to monitor the continuous strain field and deformation field distribution of the tunnel and the surrounding soil. The influence of shield construction on the tunnel and the surrounding soil is a complex three-dimensional mechanical process, and the traditional single-point monitoring method is difficult to comprehensively and accurately reflect its mechanical response characteristics. Distributed fiber optic sensing technology and DIC technology have their own advantages. Distributed fiber optic sensors can continuously measure strain, while DIC technology can achieve full-field deformation measurement. Combining the two can realize multi-dimensional and non-contact monitoring of the tunnel and the surrounding soil, and comprehensively and real-time obtain the mechanical information of the tunnel and the soil. The continuous monitoring data can capture the dynamic changes of the tunnel and the soil during the shield construction process, helping to timely discover potential safety hazards. At the same time, the mutual verification of the monitoring data and the numerical simulation can improve the understanding and comprehension of the mechanical process of shield construction, providing more scientific basis for engineering design and construction.

[0054] S9. Excavation and Shield Simulation Test: Simulate the excavation process of the shield machine passing parallel to the existing tunnel in a similarity model. The actual shield construction process is complex and affected by various factors such as formation conditions and construction parameters. Simulating the shield construction process in a model test can study the impact of shield construction on the existing tunnel and the surrounding formation under controllable conditions.

[0055] S10. Data Acquisition and Preliminary Processing: Synchronously collect and perform preliminary filtering on the data of strain gauges, displacement gauges, earth pressure cells, distributed optical fiber sensing data, and DIC image data. In shield construction monitoring, data collected by different types of sensors have different physical meanings and time characteristics. Synchronous collection can ensure the temporal correspondence of these data, enabling the correct manifestation of the correlation between data. Filtering is a common method to remove data noise and interference. It can improve the signal-to-noise ratio of the data, making the data better reflect real physical phenomena. High-quality data is the premise for accurate data analysis and decision-making. Only by ensuring the accuracy and reliability of the data can valuable information be extracted from the data to provide effective support for engineering design and construction. At the same time, good data management and storage help improve the utilization efficiency of the data, and timely detection of problems in the monitoring system can ensure the continuity and reliability of the monitoring data.

[0056] S11. Data Inversion and Intelligent Analysis: Input the preliminarily processed data into numerical simulation models and deep learning models for parameter inversion and pattern recognition, so as to determine the accurate values of the key parameters of the soil and tunnel models and identify non-linear failure signs or abnormal strain distributions. The soil and tunnel structures in actual engineering have complex mechanical properties, and the determination of their parameters often has a certain degree of uncertainty. Finite element inversion calculations can establish models based on mechanical theories, but the accuracy of the model parameters needs to be calibrated through measured data. Deep learning algorithms can learn the internal laws of the data from a large amount of measured data and optimize the model parameters.

[0057] S12. Iterative Optimization and Result Verification: Based on the data inversion and intelligent analysis results, the test conditions, similar material ratios, sensor layout positions, and excavation conditions are optimized and adjusted specifically. When necessary, some test steps are repeated to form a closed-loop iterative process of test - analysis - optimization. The complexity and uncertainty of actual projects make it difficult for a one-time test to fully and accurately simulate the actual situation. Through the process of iterative optimization and result verification, the data and experience obtained from each test can be fully utilized, continuously adjusting and improving the test model and parameters, gradually eliminating the differences between the test and the actual situation. Data inversion and intelligent analysis provide a scientific basis for optimization, accurately pointing out the problems in the test and the directions for improvement. The iterative method ensures the sustainability and effectiveness of the optimization process, enabling the test results to continuously approach the real engineering situation, thus providing reliable technical support for actual projects.

[0058] S13. Comprehensive Analysis of Test Data and Output of Conclusions: After multiple rounds of iterative verification and optimization, the final data is comprehensively analyzed and summarized to draw test conclusions, providing technical references for the engineering design and safety control of shield tunneling parallel to existing tunnels in sandy cobble strata.

[0059] Furthermore, in step S1, the similar sandy cobble soil mixture materials are fine sand, medium sand, and coarse sand, with a mass ratio of 1.1:1.1:1.0. The particle size distribution of the actual sandy cobble strata is determined by its geological origin and sedimentary environment, showing certain regularity. Through the analysis and experimental research of actual strata soil samples, the specific mass ratio of 1.1:1.1:1.0 of fine sand, medium sand, and coarse sand is determined, enabling the particle size distribution of the test soil to be similar to that of the actual strata. This similarity is the key to ensuring that the test results can reflect the actual engineering situation. Improving the repeatability of the test, reducing test errors, and optimizing test costs and efficiency are all based on the fact that a clear and reasonable ratio scheme can ensure the consistency and stability of the test soil, thereby enhancing the scientific nature and reliability of the entire test process.

[0060] Furthermore, in step S3, the similarity constant values of each physical quantity in the determination of similar materials include:

[0061] Geometric similarity constant: C l = D s / D m ;

[0062] Unit weight similarity constant: C γ = γ s / γ m ;

[0063] Gravity similarity constant: C g = 1;

[0064] Elastic modulus similarity constant:

[0065] Flexural rigidity similarity constant:

[0066] Wherein, D s is the diameter of the shield cutter head at the project site, D m is the diameter of the shield cutter head in the test, γ s is the unit weight of the existing tunnel material at the project site, γ m is the unit weight of the test soil mass; these similarity constants provide accurate parameter basis for the design and production of the existing tunnel model, ensuring the similarity of the model with the actual existing tunnel in terms of various key physical quantities.

[0067] Furthermore, step S3 also includes: the production and rationality verification of the existing tunnel model. According to the determined similar materials and dimensions, the existing tunnel model is manufactured and processed. During the test, the main force on the existing tunnel is flexural. In order to verify that the flexural rigidity of the model meets the requirements, a three-point bending test is carried out on it, and its flexural rigidity is obtained and verified with the theoretical value. In the actual project of shield tunneling through an existing tunnel, the existing tunnel mainly bears flexural action. The flexural rigidity of the model is directly related to the mechanical properties of the actual tunnel. Only when the flexural rigidity of the model is consistent with the theoretical value can it be ensured that the model can accurately simulate the mechanical response of the actual tunnel during shield construction in the test, thus providing a reliable basis for subsequent tests.

[0068] Furthermore, in step S8, the distributed fiber optic sensing technology (FBG grating) and DIC technology are used as monitoring means to realize non-contact and multi-dimensional monitoring of the continuous strain field and displacement field of the tunnel and the surrounding soil mass; the distributed fiber optic sensing technology (FBG grating) has the characteristics of high precision and high resolution, and can accurately measure the tiny strain changes of the tunnel and the surrounding soil mass. During the shield construction process, the strain changes of the soil mass and the tunnel structure are often very subtle, but these subtle changes may be early signals of structural damage or potential dangers. Through the high-precision monitoring of the FBG grating, these tiny strains can be captured in time, providing strong support for engineering safety warning. The DIC technology can realize high-precision measurement of the displacement field and accurately obtain the displacement information on the surface of the tunnel and the soil mass, further improving the monitoring accuracy of the structural deformation; by combining these two technologies, non-contact and multi-dimensional monitoring of the continuous strain field and displacement field of the tunnel and the surrounding soil mass can be realized.

[0069] Further, in step S11, data inversion and intelligent analysis adopt a method combining finite element inversion calculation and deep learning algorithm to perform multiple rounds of iterative fitting on the measured data and numerical model, so as to accurately identify the formation parameters and structural response characteristics. The method of combining finite element inversion calculation and deep learning algorithm can give full play to the advantages of the two methods and improve the identification accuracy of formation parameters and structural response characteristics. The finite element inversion calculation establishes a numerical model based on mechanical principles, which can simulate and analyze the mechanical behavior of soil and tunnel structures. However, when dealing with complex practical problems, the determination of model parameters often has certain uncertainties. The deep learning algorithm has powerful data processing and pattern recognition capabilities and can extract potential laws and characteristics from a large amount of measured data. By combining the two, the parameters of the numerical model can be continuously optimized through multiple rounds of iterative fitting, making the model calculation results closer to the measured data, so as to accurately identify the formation parameters and structural response characteristics.

[0070] Further, in step S12, through the implementation and re-testing of the optimization results, the loop iteration of the test process is realized. When the analysis results show parameter errors or mismatches, the test conditions and ratios are re-fined, and then simulated excavation and data collection are carried out again to continuously approach the test results closer to the actual engineering situation. By implementing and re-testing the optimization results to realize the loop iteration of the test process, the test model and parameters can be continuously corrected and gradually approach the real situation of the actual project. In each iteration, according to the analysis results, the problems and deficiencies in the test are found, and the test conditions, similar material ratios, sensor layout positions, etc. are slightly adjusted, and then simulated excavation and data collection are carried out again. Through multiple iterations, the gap between the test results and the actual engineering situation is continuously reduced, making the test results more accurately reflect the mechanical phenomena and laws in the actual project.

[0071] Further, the simulated excavation adopts the method of simulating shield excavation, and the jacking speed and cutter head rotation speed parameters are controlled by an electric control method to achieve continuous and automatic forward excavation. The excavated soil enters the soil chamber after being cut by the cutter head and is discharged out of the chamber along with the screw conveyor, so as to realize the simulation of real three-dimensional tunnel excavation. By using the electric control method to control the jacking speed and cutter head rotation speed parameters to achieve continuous and automatic forward excavation, and through the way of cutting the soil by the cutter head, accommodating the soil in the soil chamber and discharging the soil by the screw conveyor, the three-dimensional excavation process of actual shield construction can be truly simulated. In actual projects, the excavation process of shield construction involves complex mechanical and physical phenomena, such as soil cutting, disturbance, stress release, etc. Through this real simulation, the influence of shield construction on existing tunnels and surrounding strata can be studied more accurately, providing a more real and reliable basis for engineering design and construction.

[0072] Furthermore, the scaled model test includes: after obtaining the sandy gravel soil mass at the engineering site, conducting a screening test to obtain the grading curve of the in-situ soil mass. In the grading curve, the abscissa represents the particle size, and the ordinate represents the percentage of the soil weight content smaller than a certain particle size. According to the geometric similarity ratio, the particle size on the abscissa is reduced to obtain the grading curve of the ideal test soil mass, and thus the scaling is completed. Then, soil masses with various different particle sizes are taken, and a proportioning test is designed to determine a proportion of the soil mass whose grading curve is most similar to the target grading curve. In shield tunneling construction, the particle grading of the soil mass affects the mechanical properties of the soil mass and the effect of shield tunneling construction. By accurately simulating the particle grading, the test results can better reflect the impact of shield tunneling construction on the stratum in actual engineering, improving the accuracy and reliability of the test.

[0073] Furthermore, in step S4, during the model filling, the filling quality of each layer of soil in the model test is controlled according to the compactness of the soil in the actual stratum. The required parameters are as follows:

[0074] The relative density D obtained from the geological exploration results r ;

[0075] The dry density ρ of the soil measured by physical experiments d ;

[0076] The height h of each layer of soil;

[0077] The length L of the model box;

[0078] The width W of the model box;

[0079] Calculate the porosity according to the relative density and dry density:

[0080] The filling quality of each layer of soil in the model test: m = L × W × h × ρ d ;

[0081] Calculating the filling quality of each layer of soil according to parameters such as the relative density, dry density, height of each layer of soil, length and width of the model box can ensure that the filling quality of each layer of soil is uniform. This helps to ensure the consistency of the mechanical properties of the test model at different positions and different layers, and avoid deviations in the test results caused by uneven filling quality. By precisely controlling the filling quality of each layer of soil, the test process has higher repeatability. In different tests, as long as the filling is carried out according to the same parameters and methods, similar test models can be obtained, which makes the results between different tests comparable, helps to compare and analyze different research schemes or design parameters, and improves the scientificity and reliability of the research.

[0082] In the present invention, unless otherwise clearly specified or limited, terms such as "installed", "connected", "coupled", "fixed", etc. shall be understood in a broad sense. For example, it may be a fixed connection, a detachable connection, or integrated; it may be a mechanical connection, an electrical connection, or communicable with each other; it may be directly connected, or indirectly connected through an intermediate medium, and it may be the internal communication of two components or the interaction relationship between two components, unless otherwise clearly defined. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0083] Obviously, the embodiments described above are only a part of the embodiments of the present invention, rather than all embodiments. The preferred embodiments of the present invention are given in the drawings, but do not limit the patent scope of the present invention. The present invention can be implemented in many different forms. On the contrary, the purpose of providing these embodiments is to make the understanding of the disclosed content of the present invention more thorough and comprehensive. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing specific embodiments, or perform equivalent replacements for some of the technical features. Any equivalent structure made by using the specification and drawings of the present invention, directly or indirectly applied to other related technical fields, is equally within the scope of the patent protection of the present invention.

Claims

1. A model test method for parallel crossing of an existing tunnel by a shield machine in sand and gravel strata, characterized in that: The steps include: S1. Study on sandy and gravel strata: Obtain sandy and gravel soil samples from the strata that the shield mainly passes through from the project site, conduct screening tests on a vibrating screener to obtain the particle gradation of sandy and gravel, and scale down the particle size of the soil sample particles according to the geometric similarity ratio to obtain the ideal particle gradation of the test sandy and gravel soil. Use three different gradings of sandy and gravel soil and conduct multiple proportioning tests to determine the appropriate optimal proportion of similar sandy and gravel soil. Under the optimal proportion, the particle gradation of the soil obtained should be similar to the particle gradation of the ideal test sandy and gravel soil obtained after scaling down. S2. Calculation of geometric similarity ratio: Determine the cutter head diameter D according to the project site s The cutter head diameter D in the test m The geometric similarity ratio C of the test is determined by the ratio l ; Obtain all similarity ratios of the scaled test; According to the geometric similarity ratio, the gradation of the sand and gravel after scale-down and the size of the existing tunnel model can be determined. The gravity acceleration similarity ratio is determined to be 1, and the material for simulating the existing tunnel is determined. The stiffness similarity ratio can be calculated by the ratio of the on-site segment stiffness to the stiffness of the existing tunnel. Since the stiffness is EI and the elastic modulus is E, the moment of inertia of the I section can be calculated from the size section, and the elastic modulus similarity ratio is also obtained. S3. Determination of similar materials for existing tunnels: Ensure that the geometric dimensions and bending stiffness between the existing tunnel and the existing tunnel model meet the similarity principle, and determine the similarity constant values ​​and theoretical values ​​of the physical quantities of length, weight, gravitational acceleration and stiffness based on the similarity ratio; Determine a material in reality based on the theoretical value, and measure the physical properties of the existing tunnel model made of the determined material to determine whether it meets the theoretical value; S4. Filling of the test model: Paste smooth wallpaper on the inner wall of the model box to reduce friction, and mark the scale on the wallpaper. Use a laser leveler to ensure the flatness of the layer when filling similar sand and gravel soil in layers. When filling to a predetermined height, place the existing tunnel model equipped with monitoring elements horizontally, and use elastic ropes to accurately control its position, and then continue to fill in layers until it reaches the surface. S5. Arrange displacement monitoring points: According to the test purpose, displacement meters are arranged at preset points to measure surface displacement and underground displacement; S6. Arrangement of additional earth pressure monitoring points for existing tunnels: According to the test purpose, earth pressure boxes are arranged at preset points to measure the additional earth pressure of the existing tunnel during the shield tunneling process; S7. Arrange additional strain monitoring points for existing tunnels: According to the test purpose, strain gauges are attached to the preset points to measure the additional strain of the existing tunnel during the shield tunneling process; S8. Intelligent sensing and fiber optic sensing deployment: Distributed fiber optic sensors are embedded in the tunnel model and surrounding soil, and digital image correlation (DIC) technology is used to identify points to monitor the continuous strain and deformation field distribution of the tunnel and surrounding soil. S9, excavation and shield simulation test: simulate the excavation process of the shield machine parallel to the existing tunnel in a similar model; S10, data acquisition and preliminary processing: synchronous acquisition and preliminary filtering of strain gauges, displacement meters, earth pressure boxes, distributed optical fiber sensor data and DIC image data; S11. Data inversion and intelligent analysis: The preliminarily processed data is input into the numerical simulation model and deep learning model for parameter inversion and pattern recognition, so as to determine the precise values ​​of key parameters of the soil and tunnel model and identify signs of nonlinear failure or abnormal strain distribution; S12, iterative optimization and result verification: According to the data inversion and intelligent analysis results, the test conditions, similar material ratios, sensor layout locations and excavation conditions are optimized and adjusted in a targeted manner to form a closed-loop iterative process of test-analysis-optimization; S13. Comprehensive analysis of test data and output of conclusions: After multiple rounds of iterative verification and optimization, the final data is comprehensively analyzed and summarized to draw test conclusions, which provide technical references for the engineering design and safety control of shield tunneling parallel to existing tunnels in sandy and gravel strata.

2. A model test method for parallel crossing of an existing tunnel by a shield machine in sand and gravel strata according to claim 1, characterized in that: In step S1, the similar sand-pebble soil mix material ratio is fine sand, medium sand and coarse sand, and the mass ratio is 1.1:1.1:1.

0.

3. The model test method for parallel crossing of an existing tunnel by a shield machine in sand and gravel strata according to claim 1 is characterized in that: The similar constant values ​​of various physical quantities in the similar material determination in step S3 include: Geometric similarity constant: C l =D s / D m ; Heavy similarity constant: C γ =γ s / γ m ; Gravitational similarity constant: C g =1; Similarity constant of elastic modulus: C E =C F *C l -2 ; Bending stiffness similarity constant: C EI =C F *C l 2 ; Among them, D s is the diameter of the shield cutterhead at the engineering site, D m is the cutterhead diameter of the shield in the test, γ s The existing tunnel material at the project site is heavy, γ m is the material density of the test soil.

4. A model test method for parallel passage of a shield tunnel through an existing tunnel in a sandy gravel stratum according to claim 1 or 3, characterized in that: Step S3 also includes: making and rationality verification of an existing tunnel model. According to the determined similar materials and dimensions, a model of an existing tunnel is made and processed. During the test, the existing tunnel is mainly subjected to bending. In order to verify that the bending stiffness of the model meets the requirements, a three-point bending test is performed on it to obtain its bending stiffness and theoretical value for verification.

5. The model test method for parallel crossing of an existing tunnel by a shield machine in sand and gravel strata according to claim 1 is characterized in that: In step S8, distributed fiber optic sensing technology (FBG grating) and DIC technology are used as monitoring means to achieve non-contact, multi-dimensional monitoring of the continuous strain field and displacement field of the tunnel and surrounding soil.

6. The model test method for parallel crossing of an existing tunnel by a shield machine in sand and gravel strata according to claim 1 is characterized in that: In step S11, data inversion and intelligent analysis adopt a combination of finite element inversion calculation and deep learning algorithm to perform multiple rounds of iterative fitting of measured data and numerical models to accurately identify formation parameters and structural response characteristics.

7. The model test method for parallel crossing of an existing tunnel by a shield machine in sand and gravel strata according to claim 1 is characterized in that: In step S12, the optimization results are implemented and retested to achieve a cyclic iteration of the test process. When the analysis results show parameter errors or mismatches, the test conditions and proportions are re-fine-tuned, and simulated excavation and data collection are performed again to continuously approach test results that are closer to actual engineering conditions.

8. A model test method for parallel crossing of an existing tunnel by a shield machine in sand and gravel strata according to claim 7, characterized in that: The simulated excavation adopts the method of simulating shield excavation, and uses electronic control to control the jacking speed and cutterhead speed parameters to achieve continuous and automatic forward excavation. The excavated soil enters the soil chamber after being cut by the cutterhead and is discharged out of the chamber along with the spiral excavator to achieve a real three-dimensional tunnel excavation simulation.

9. The model test method for parallel crossing of an existing tunnel by a shield machine in sand and gravel strata according to claim 1 is characterized in that: The scaled-down test includes: after obtaining the sand and gravel soil at the project site, a screening test is performed to obtain the grading curve of the on-site soil. The horizontal axis of the grading curve is the particle size, and the vertical axis is the percentage of soil weight less than a certain particle size. The particle size of the horizontal axis is reduced according to the geometric similarity ratio to obtain the grading curve of the ideal test soil. The scale-down is completed. Then, soils of various different particle sizes are taken, and a mix ratio test is designed to determine a soil grading curve obtained by a mix ratio that is most similar to the target grading curve.

10. The model test method of a sand-pebble stratum shield tunneling parallel to an existing tunnel according to claim 1, characterized in that: In step S4, the filling quality of each layer of soil in the model test is controlled according to the compactness of the soil in the actual stratum during the model filling, and the required parameters are as follows: The relative density D obtained based on the geological survey results r ; According to physical experiments, the dry density of soil is d ; The height of each soil layer h; Model box length L; Model box width W; Calculate the porosity based on relative density and dry density: The filling mass of each layer of soil in the model test: m = L × W × h × ρ d .

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