A weak slate water-rich stratum tunnel construction parameter optimization and safety control method

Abstract

A weak slate water-rich stratum tunnel construction parameter optimization and safety control method, including construction method adaptability comparison and selection based on numerical simulation and field test; construction process parameter optimization research based on refined numerical analysis; identification and control of key factors of surrounding rock instability; integrated optimization parameter field construction implementation; effect verification and method standardization. The present application realizes the systematic breakthrough from method optimization, parameter quantitative optimization to key disaster-causing factor accurate control by deeply integrating numerical simulation, field test, real-time monitoring and process optimization, significantly improves the construction efficiency under the premise of ensuring the construction safety, forms a set of soft weak slate water-rich stratum tunnel rapid construction technology system which can be replicated and popularized, and solves the problem that the construction safety and efficiency are difficult to be considered in the existing technology under the geological condition of water-rich joint dense zone.

Description

Technical Field

[0001] This invention belongs to the field of tunnel and underground engineering construction technology, and specifically relates to a method for optimizing construction parameters and controlling safety in tunnels in water-rich strata of weak slate. Background Technology

[0002] In mountainous transportation infrastructure construction, tunnels traversing water-rich, densely jointed zones of weak slate (such as Devonian slate) face severe challenges, including low surrounding rock strength, poor self-stabilizing ability, easy softening upon contact with water, and difficulty in deformation control. Traditional construction methods often present a dilemma: while complex methods such as the three-stage method or the double-sidewall pilot tunnel method are relatively safe, they involve cumbersome procedures, narrow working spaces, extremely low construction efficiency, and high costs; on the other hand, the conventional two-stage method, due to blind parameter selection and insufficient targeted support, is prone to excessive deformation or even collapse risks.

[0003] Current technologies lack a systematic and comprehensive solution encompassing method selection, parameter optimization, and precise risk control. Construction relies heavily on experience, failing to organically integrate geological analysis, mechanical simulation, process monitoring, and construction techniques, thus hindering the optimal balance between safety and efficiency. Therefore, a rapid construction method based on systematic research, quantitative analysis, and replicability is urgently needed. Summary of the Invention

[0004] The purpose of this invention is to provide a method for optimizing construction parameters and controlling safety in tunnels in water-rich strata of weak slate, in order to solve the technical problem that existing technologies cannot simultaneously achieve both construction safety and efficiency under geological conditions of densely jointed water-rich zones.

[0005] To achieve the above objectives, the present invention adopts the following technical solution.

[0006] A method for optimizing construction parameters and controlling safety in tunnels located in water-rich, weak slate strata includes the following steps: Step 1: Comparison of construction methods based on numerical simulation and field tests: By establishing a three-dimensional numerical model, the construction process of the two-step method, the three-step method, and the double-sidewall pilot tunnel method in the water-rich soft slate strata is simulated respectively; Based on the surrounding rock deformation and support stress data obtained from the simulation, and combined with the construction efficiency, the construction method suitable for the water-rich soft slate strata is comprehensively compared and determined. Step two, the optimization study of construction process parameters based on refined numerical analysis, the specific process is as follows: Step 2.1: For the selected construction method, establish a refined numerical model that can be parameterized and adjusted; A three-dimensional numerical model was constructed based on the tunnel design cross section. The model size was set to eliminate boundary effects. Displacement constraints were applied to the bottom and sides of the model, and stress was applied to the top to simulate the initial in-situ stress field. An elastic-plastic constitutive model was adopted for the surrounding rock. An anchor support model was established using cable structural elements in flac3d. Step 2.2: Conduct deformation and stress analysis of the tunnel surrounding rock under multiple working conditions to quantitatively evaluate the impact of core construction parameters on tunnel stability; Step 2.3: Determine the safe construction parameters for the corresponding construction method; Step 3, Identification and control of key factors for surrounding rock instability: Based on numerical simulation results and field monitoring data, key disaster-causing factors leading to tunnel deformation are identified, and control measures are formulated accordingly; Step 4, On-site construction implementation of integrated optimization parameters: Based on the selected construction method, the tunnel excavation is carried out using the safe construction parameters determined in Step 2, and the control measures formulated in Step 3 are strictly implemented during construction. At the same time, the tunnel construction deformation and the stress of the surrounding rock-support structure system are monitored throughout the process. Step 5: Effect Verification and Construction Method Standardization: Compare the on-site monitoring data with the numerical simulation predictions, and verify the effectiveness of the safety construction parameters and control measures; Step six: Carry out construction based on the verified construction parameters and processes.

[0007] Preferably, in step one, the specific method for comparing the adaptability of construction methods is as follows: Step 1.1, Numerical Model Construction: Based on engineering geological data and design cross-sections, a three-dimensional numerical model of the tunnel is established using finite element software. The boundary conditions of the model are set as bottom and surrounding normal constraints, and the top is a free surface. The surrounding rock adopts an elastoplastic constitutive model, the initial support and secondary lining are simulated using elastic solid elements, the anchor bolts are simulated using truss elements, and the interaction between the structure and the surrounding rock is realized by embedding constraints or contact elements. Step 1.2, Determination of material parameters for the calculation model: Determine the physical and mechanical parameters and structural parameters of the slate in the densely jointed water-rich zone; Step 1.3: Comparative study of three construction methods: two-step method, three-step method and double-sidewall guide tunnel method. Simulate the construction process of the two-step method, three-step method and double-sidewall guide tunnel method respectively, and monitor the results. Step 1.4, Comprehensive Comparison and Analysis: Based on the numerical simulation results, compare and analyze the surrounding rock deformation analysis and initial support stress analysis under the three construction methods; combine the actual surrounding rock deformation data obtained from the field test section monitoring with the construction efficiency records; and comprehensively select the construction method based on the principles of controllable surrounding rock deformation, safe support stress, and simple and efficient construction procedures. Step 1.5, Setting up the field test section: In the actual tunnel construction, a water-rich jointed zone of weak and broken Devonian slate was selected for test excavation using the chosen construction method.

[0008] Preferably, the monitoring scheme in step 1.3 is as follows: Deformation monitoring points are set up at the tunnel arch crown, arch foot and invert arch; stress monitoring points are set up at the arch crown, arch shoulder, arch foot, wall foot and invert arch.

[0009] Preferably, in step 2.2, when the selected construction method is the two-step method, the height H of the upper step and the one-time excavation length L of the upper step are used as core variables to construct a multi-condition numerical calculation model to analyze the displacement field characteristics, stress field distribution, and the range and distribution of the plastic zone under different combinations of construction parameters (H, L). When the selected method is the three-step method, the height of the upper step H1, the height of the middle step H2, the height of the lower step H3, the length of the upper step L1 > the distance of the middle step lagging behind the upper step L2 > the distance of the lower step lagging behind the middle step L3 are taken as core variables to construct a multi-condition numerical calculation model and analyze the displacement field characteristics, stress field distribution and plastic zone development area under different combinations of construction parameters (H1, H2, H3, L1, L2, L3). When the selected method is the double-sided wall guide tunnel method, the guide tunnel width B, guide tunnel height h, central partition wall thickness D, and longitudinal offset ΔL of the left and right guide tunnels are used as core variables to construct a multi-condition numerical calculation model, and analyze the displacement field characteristics, stress field distribution and plastic zone development zone under different combinations of construction parameters (B, h, D, ΔL).

[0010] Preferably, the displacement field includes crown settlement, horizontal convergence, invert heave, and face extrusion deformation; the stress field includes stress concentration in the surrounding rock and support structure.

[0011] Preferably, in step three, the control measures specifically include proactive control and / or the use of high-strength rigid initial support and / or setting deformation management thresholds and / or strengthening key details, such as installing anchor bolts and temporary supports, strictly controlling the deformation of weak parts such as step joints, and / or strengthening the overall integrity of the support system.

[0012] Preferably, in step five, during on-site construction, inclinometers, total stations, and strain gauges are used to monitor the settlement of the tunnel arch and the horizontal convergence changes of the surrounding soil and rock in real time. The surrounding rock stress monitoring element adopts a vibrating wire element. The vibrating wire element is embedded between the tunnel surrounding rock and the initial lining, and eight measurement points are set at intervals on the same cross section.

[0013] Preferably, the specific process in step five is as follows: Step 5.1, Optimization of process effect verification: During and after the implementation of step four, deformation and stress monitoring will be continuously carried out. The measured final settlement value of the arch, horizontal convergence value, and maximum stress value of the support structure will be compared with the deformation and stress of the tunnel surrounding rock analyzed in the numerical model in step two to verify the effectiveness and accuracy of the safe construction parameters and control measures. Step 5.2, Comprehensive Efficiency Comparison Analysis: Record the construction efficiency indicators after adopting the optimization method, including average single-cycle operation time, average monthly advance, and average over-excavation value; compare and analyze the above construction efficiency indicators with the benchmark data.

[0014] Compared with the prior art, the present invention has the following features and beneficial effects.

[0015] 1. This invention transforms the complete scientific research chain into an executable construction process. Its core logic is "research guides construction, and construction verifies research." This method encompasses the entire process of method adaptability comparison, process parameter numerical optimization, disaster-causing factor significance analysis, optimized process implementation, and effect verification and evaluation. The process is closed-loop, facilitating quality control and integrating research, implementation, monitoring, and verification. The construction process is not only execution but also on-site verification and feedback of the adopted research conclusions. This forms a complete technical closed loop, ensuring the reliability and scalability of the method and providing a complete reference for similar projects, from methodology to specific parameters.

[0016] 2. This invention, through method comparison, abandons the selection of methods based solely on experience. It selects the two-step method based on quantitative data such as deformation values ​​and support stress, and determines the potential for efficiency improvement from the root. At the same time, combined with parameter optimization research and disaster-causing factor analysis, it provides specific and verified safety thresholds for step dimensions, controlling the risk of large deformation from the design source. The disaster-causing factor analysis enables support measures such as anchor pipe angle and longitudinal connection to be precisely targeted at the weakest link, achieving targeted safety control.

[0017] 3. The invention features a refined process and a significant breakthrough in construction efficiency. The optimized step height provides a spacious working surface for large-scale mechanized equipment, while the optimized blasting parameters reduce over-excavation and operation time. Efficiency comparison analysis quantifies the specific benefits of this method in shortening cycle time, increasing monthly advance, and reducing material consumption, proving its substantial "speed". Attached Figure Description

[0018] The present invention will now be described in further detail with reference to the accompanying drawings.

[0019] Figure 1 This is a schematic diagram of the tunnel lining cross-sectional structure of the present invention.

[0020] Figure 2 This is a schematic diagram of the monitoring point layout of the present invention.

[0021] Attached diagram labels: 1 - Initial support, 2 - Secondary lining, 3 - Deformation monitoring point, 4 - Stress monitoring point. Detailed Implementation

[0022] This method for optimizing tunnel construction parameters and controlling safety in water-rich strata of weak slate includes the following steps: Step 1: Comparison of construction methods based on numerical simulation and field tests: By establishing a three-dimensional numerical model, the construction process of the two-step method, the three-step method, and the double-sidewall pilot tunnel method in the water-rich soft slate strata is simulated respectively; Based on the surrounding rock deformation and support stress data obtained from the simulation, and combined with the construction efficiency, the construction method suitable for the water-rich soft slate strata is comprehensively compared and determined. The specific methods for comparing the adaptability of construction methods are as follows: Step 1.1, Numerical Model Construction: Based on engineering geological data and design cross-sections, a three-dimensional numerical model of the tunnel is established using finite element software. The model dimensions are determined according to Saint-Venant's principle. The model boundary conditions are set as bottom and surrounding normal constraints, with the top being a free surface. An elastoplastic constitutive model is used for the surrounding rock. The initial support 1 and secondary lining 2 are simulated using elastic solid elements, and the anchor bolts are simulated using truss elements. The interaction between the structure and the surrounding rock is realized through embedded constraints or contact elements. The excavation and support process is simulated through the "element birth and death" function. Step 1.2, Determination of material parameters for the calculation model: Based on field survey and engineering design data, combined with the geotechnical test results of slate samples, the physical and mechanical parameters and structural parameters of the slate in the water-rich, densely jointed area are determined. The physical and mechanical parameters and structural parameters of the slate include the unit weight γ (kN / m³), elastic modulus E (GPa), Poisson's ratio N, cohesion c (kPa), and internal friction angle φ (▫). The material unit weight γ (kN / m³), elastic modulus E (GPa), Poisson's ratio N, and thickness h (cm) of the initial support 1 are also determined. The material unit weight γ (kN / m³), elastic modulus E (GPa), Poisson's ratio N, and thickness h (cm) of the secondary lining 2 are also determined. Step 1.3 compares and selects three construction methods: the two-step method, the three-step method, and the double-sidewall pilot tunnel method. The construction process of each method is simulated and monitored. The principle of "excavation and support as needed" is strictly followed, with a step length of 6m. To quantify the mechanical response of each method, a unified benchmark condition is set when the first excavated face advances to the Y=45m section. The system statistically analyzes the surrounding rock deformation and support structure stress within a specific range before and after the face at this section. The monitoring scheme in this step involves setting deformation monitoring points 3 at the tunnel arch crown, arch foot, and invert; and stress monitoring points 4 at the arch crown, arch shoulder, arch foot, wall foot, and invert to comprehensively obtain key data for evaluating the merits of each method. The monitoring point layout cross-section diagram is shown below. Figure 2 .

[0023] Step 1.4, Comprehensive Comparison and Analysis: Based on the numerical simulation results, the rock deformation analysis under the three construction methods and the stress analysis of initial support 1 are compared and analyzed. Among them, the rock deformation analysis includes tunnel arch settlement and face extrusion deformation. Combined with the actual rock deformation data and construction efficiency records obtained from the field test section monitoring, and based on the principles of controllable rock deformation, safe support stress, and simple and efficient construction procedures, the two-step method is comprehensively selected as the construction method for water-rich jointed zones of weak slate. Step 1.5, Setting up the field test section: In the actual tunnel construction, a water-rich jointed zone of weak and broken Devonian slate was selected for test excavation using the chosen construction method; Step two, the optimization study of construction process parameters based on refined numerical analysis, the specific process is as follows: Step 2.1: For the selected construction method, establish a refined numerical model that can be parameterized and adjusted; Step 2.2: Conduct deformation and stress analysis of the tunnel surrounding rock under multiple working conditions to quantitatively evaluate the impact of core construction parameters on tunnel stability; Step 2.3: Determine the safe construction parameters for the corresponding construction method; Step 3, Identification and control of key factors for surrounding rock instability: Based on numerical simulation results and field monitoring data, key disaster-causing factors leading to tunnel deformation are identified, and control measures are formulated accordingly; The specific method for identifying key factors in surrounding rock instability is as follows: S3.1 Monitoring Data Acquisition and Analysis: The system collects multi-source monitoring data such as arch crown settlement, arch foot convergence, surrounding rock pressure, steel frame stress, and concrete strain; S3.2 Disaster-causing factor identification: Combining the time series and spatial distribution characteristics of the refined numerical simulation results and field monitoring data, comparative analysis and regression analysis are used to identify the key parts and key factors that lead to the deformation of the surrounding rock; it is determined that the horizontal displacement of the arch foot and wall foot area is the main factor that causes the overall convergence deformation, and the insufficient longitudinal stiffness of the support structure is an important factor that leads to local instability and crack development. S3.3 Targeted Control Measures: Based on the above analysis of disaster-causing factors, precise construction control measures are proposed. To control arch foot displacement, anchor pipes with optimized angles and lengths must be installed; to enhance the longitudinal stiffness of the support, the longitudinal connections between steel arch frames must be strengthened.

[0024] Step 4, On-site construction implementation of integrated optimization parameters: Based on the selected construction method, the tunnel excavation is carried out using the safe construction parameters determined in Step 2, and the control measures formulated in Step 3 are strictly implemented during construction. At the same time, the tunnel construction deformation and the stress of the surrounding rock-support structure system are monitored throughout the process. Step 5: Effect Verification and Construction Method Standardization: Compare the on-site monitoring data with the numerical simulation predictions, and verify the effectiveness of the safety construction parameters and control measures; Step six: Carry out construction based on the verified construction parameters and processes.

[0025] The field test verification of the technical solution of this invention was carried out in a specific geological section of a tunnel. The test strictly followed the principle of "short advance, strong support, and early closure" and implemented the optimized two-stage construction method and supporting support system. The specific implementation parameters were: stage height 4.5-6m, length 5-8m, single cycle advance ≤3m; Φ42×3.5mm pre-grouting support was adopted; the initial support 1 consisted of 25cm thick C25 shotcrete, I18 steel frame and system anchor bolts; and the initial support 1 was strictly closed at a distance of ≤35m from the tunnel face, and the secondary lining 2 was constructed at a distance of ≤90m from the tunnel face.

[0026] In this embodiment, in step 2.2, when the selected construction method is the two-step method, the height H of the upper step and the one-time excavation length L of the upper step are used as core variables to construct a multi-condition numerical calculation model to analyze the displacement field characteristics, stress field distribution, and range and distribution of the plastic zone under different combinations of construction parameters (H, L). Among them, H changes with a gradient of about 1.0m in the range of 5.4m to 8.4m, and L changes with a gradient of 4m or 8m in the range of 8m to 32m, thereby forming a series of (H, L) parameter combinations covering different working spaces and construction steps.

[0027] Specifically, this embodiment studies and analyzes the following three categories of response indicators for each set of parameter conditions: Variable design: The step height H and the step excavation length L in one go are used as the core variables.

[0028] H changes from 5.4m to 8.4m, with a gradient of approximately 1.0m.

[0029] L changes from 8m to 32m, with a gradient of 4m or 8m.

[0030] Analysis content: For each set of (H, L) parameter combinations, the following calculations and analyses are performed: Displacement field: crown settlement, horizontal convergence (focus on arch foot), invert heave, and extrusion deformation at the tunnel face.

[0031] Stress field: The stress concentration in the surrounding rock and support structure.

[0032] Plastic zone: The extent and distribution of yielding failure of the surrounding rock.

[0033] When the selected method is the three-step method, the height of the upper step H1, the height of the middle step H2, the height of the lower step H3, the length of the upper step L1 > the distance of the middle step lagging behind the upper step L2 > the distance of the lower step lagging behind the middle step L3 are taken as core variables to construct a multi-condition numerical calculation model and analyze the displacement field characteristics, stress field distribution and plastic zone development area under different combinations of construction parameters (H1, H2, H3, L1, L2, L3). When the selected method is the double-sided wall guide tunnel method, the guide tunnel width B, guide tunnel height h, central partition wall thickness D, and longitudinal offset ΔL of the left and right guide tunnels are used as core variables to construct a multi-condition numerical calculation model, and analyze the displacement field characteristics, stress field distribution and plastic zone development zone under different combinations of construction parameters (B, h, D, ΔL).

[0034] In this embodiment, after comprehensively comparing the two-step method, the double-sidewall guide tunnel method, and the three-step method, the selected construction method is the two-step method.

[0035] To accurately simulate the quantitative impact of different step heights and lengths (step excavation length in a single pass) on the stress, deformation, and plastic zone of the tunnel surrounding rock, this study employed a professional numerical modeling workflow. Based on the tunnel design cross-section, three-dimensional geometric modeling was performed using Rhino software. This model was then imported into HyperMesh software to generate a high-quality computational mesh, with local refinement applied to key areas around the tunnel to ensure computational accuracy. Subsequently, the mesh model was imported into the geotechnical engineering software flac3d to construct a three-dimensional numerical model. The model size was set to 100m × 100m × 100m to eliminate boundary effects. Displacement constraints were applied to the bottom and sides of the model, and an equivalent self-weight stress at a burial depth of 115m was applied to the top to simulate the initial geostress field. An elastoplastic constitutive model was used for the surrounding rock. An anchor bolt support model was established using cable structural elements in flac3d. Cable elements were modeled to reflect their nonlinear failure behavior, and the anchor bolt support was accurately characterized using cable elements specifically designed for simulating tension and compression members. This workflow constructed a reliable analysis platform, providing a foundation for systematically studying the mechanical response of the surrounding rock under varying construction parameters.

[0036] In this embodiment, the displacement field includes crown settlement, horizontal convergence (with a focus on the arch foot), invert heave, and extrusion deformation at the tunnel face; the stress field includes stress concentration in the surrounding rock and support structure, especially at the tunnel crown, arch waist, and the clearance area formed after tunnel excavation; the plastic zone includes the range and distribution of yield failure of the surrounding rock.

[0037] In this embodiment, the control measures in step three specifically include proactive control and / or the use of high-strength rigid initial support 1 and / or setting deformation management thresholds and / or strengthening key details, such as installing anchor bolts and temporary supports, strictly controlling deformation of weak parts such as step joints, and / or strengthening the overall integrity of the support system. Specifically, proactive control involves pre-reinforcing and pre-supporting the face and the core soil in front to suppress extrusion deformation and pre-convergence, and control harmful stress release. Using high-strength rigid initial support 1 specifically means: explicitly rejecting the use of flexible support to release stress, advocating for early suppression of the gradual failure process of the surrounding rock through high-rigidity support. Setting deformation management thresholds specifically means: not blindly relying on increasing the reserved deformation amount, but setting clear deformation limits for initial support 1, such as requiring reinforcement if the cumulative deformation exceeds 250mm, achieving quantitative early warning and proactive intervention. Strengthening key details specifically means timely implementation of... Using anchor bolts and temporary supports, deformation of weak points such as step joints is strictly controlled. Strengthening the overall integrity of the support system specifically involves enhancing the longitudinal connection stiffness between steel arch frames to ensure circumferential and longitudinal stiffness matching, preventing local instability from causing overall load-bearing capacity loss. Steel strain gauges are used to monitor the axial stress of the steel arch frames at the monitoring section. These strain gauges are welded to the steel frame, and the strain gauge deformation reflects the support force generated when the steel frame is subjected to surrounding rock pressure. Pressure boxes are placed in contact with the surrounding rock, and the pressure box base is welded to the steel frame to form an integrated force-bearing system. Pressure changes in the pressure box reflect the compression of the support system by the surrounding rock. Concrete strain gauges reflect the deformation of the support force-bearing system formed by shotcrete and the steel frame, thus reflecting the effect of surrounding rock disturbance on the support system during construction and excavation. These measures together constitute a proactive control system characterized by "advanced intervention, rigid constraints, quantitative control, and overall coordination."

[0038] In this embodiment, the stress change of the steel frame has three stages: rapid increase, slow increase, and stabilization. In the initial stage of the formation of the tunnel lining strength, the stress change on the inner and outer sides of the same steel frame fluctuates greatly. As the surrounding rock stress is released, the stress on the inner and outer sides gradually increases, and the fluctuation decreases. The strain change of the steel frame is large in the early stage, which leads to the change of the stress state. During the tunnel construction process, the monitoring data shows that: ① the steel frame responds quickly to the pressure of the surrounding rock and can quickly produce stress deformation after excavation; ② at the test section, the force generated at the arch is the largest. The maximum stress on the inner side of the steel frame, that is, the side closer to the surrounding rock, occurs at the arch at about 100 MPa. The maximum force on the outer side of the steel frame at the arch is about 64 MPa. Within the yield strength of the HRB400 grid steel frame, the structure is in a safe state; ③ the stress on the inner and outer sides of the steel frame in each section is basically stable for about 25-35 days after the entire section is excavated and supported.

[0039] In this embodiment, during on-site construction in step five, inclinometers, total stations, and strain gauges are used to monitor the settlement of the tunnel arch and the horizontal convergence changes of the surrounding rock and soil in real time. The surrounding rock stress monitoring element adopts a vibrating wire element. The vibrating wire element is embedded between the tunnel surrounding rock and the initial lining, and 8 measurement points are set at intervals in the same cross section. Among them, 1 is set at the arch crown, 2 are set at the two sides of the arch waist, 2 are set at the left and right side walls, and 3 are set at the invert arch position. Each point is equipped with 1 pressure box to measure the compressive stress of the surrounding rock on the initial support 1, 2 steel strain gauges to test the deformation caused by the stress on the steel frame, and 2 concrete strain gauges to measure the deformation of the concrete under stress. By monitoring the data changes of the stress and strain test elements, the spatiotemporal deformation law of the interaction between the initial lining and the slate surrounding rock is obtained. The steel and concrete strain gauges are installed on the same steel frame facing the tunnel face and both sides of the tunnel entrance.

[0040] In this embodiment, the specific process in step five is as follows: Step 5.1, Optimization of process effect verification: During and after the implementation of step four, deformation and stress monitoring will be continuously carried out. The measured final settlement value of the arch, horizontal convergence value, and maximum stress value of the support structure will be compared with the deformation and stress of the tunnel surrounding rock analyzed in the numerical model in step two to verify the effectiveness and accuracy of the safe construction parameters and control measures. Step 5.2, Comprehensive Efficiency Comparison Analysis: Record the construction efficiency indicators after adopting the optimization method, including average single-cycle operation time, average monthly advance and average over-excavation value, explosive consumption per unit area, and concrete spraying over-consumption coefficient; compare and analyze the above construction efficiency indicators with benchmark data (historical data under the conservative construction method parameters adopted in the original project design or traditional construction method data of similar projects in the same region). Quantitatively verify the comprehensive superiority of the optimization method in improving tunneling speed, reducing material consumption, and improving mechanization efficiency while ensuring construction safety.

[0041] In this embodiment, the weak slate is Devonian slate, and the water-rich jointed zone is a section with fractured rock mass, well-developed joints and fissures, and a daily water inflow exceeding 10,000 cubic meters.

[0042] The three-stage, seven-step pre-reserved core soil method was adopted for the water-rich fracture zone of the slate tunnel, which can effectively control settlement. During construction, drainage construction should be strengthened, and 42 Φ42×3.5mm advanced small pipe grouting was used with a hole length of 4.5m and a circumferential spacing of 3.2m per ring. This can improve the surrounding rock deformation control to a certain extent. In the thin carbonaceous slate lithology of the Haibaluo Tunnel of the Xiangli Expressway, scholars have found that by using 42mm diameter, 4.5m length anchor bolts, installed at 45°, and controlling the grouting range to 1m, the surrounding rock deformation can be well controlled. During the construction of the tunnel in the layered slate strata, the convergence of the left shoulder and two sides of the tunnel section is large. With the adoption of NPR anchor mesh cable support, the convergence deformation of the section is reduced. The optimal parameters determined in step three are: step height H = 7.2m-8.2m and step excavation length L = 25m-30m.

[0043] Increasing the step height linearly exacerbates face extrusion and significantly amplifies horizontal convergence and the plastic zone of the surrounding rock. When H exceeds 7.4m, the horizontal convergence and plastic zone expansion increase dramatically. Therefore, H should not exceed 7.4m, and the recommended optimization range is 7.2m-8.2m (with 7.4m as the equilibrium point). Increasing the step length significantly expands the plastic zone and stress concentration range. When L exceeds 28m-32m, the risk intensifies. Therefore, L should not exceed 32m, and a comprehensive construction efficiency of 25m-30m is recommended. In summary, controlling H≤7.4m and L≤32m are the key parameter boundaries to ensure safe construction in this stratum.

[0044] In this embodiment, the influence of the step height H is as follows: The settlement of the arch increases with increasing H, but the effect is relatively gradual.

[0045] Horizontal convergence is extremely sensitive to changes in H; when H exceeds 7.4m, the horizontal convergence value increases significantly (from 13.06mm to 14.68mm).

[0046] The extrusion deformation at the working face increases linearly with increasing H.

[0047] The plastic zone of the surrounding rock expands significantly after H exceeds 7.4m, and the stability risk increases sharply.

[0048] Conclusion: To control horizontal convergence and the plastic zone, H should not exceed 7.4m, and the recommended optimal height is 7.2m-8.2m, of which 7.4m is the key balance point between working space and safety.

[0049] Regarding the influence of step length L: The settlement of the arch increases slightly with the increase of L, but the rate of increase slows down after L exceeds 24m.

[0050] The extent of the plastic zone and the degree of stress concentration in the surrounding rock expand significantly with increasing L, and the growth intensifies after L exceeds 28m-32m.

[0051] A longer L is beneficial for controlling horizontal convergence and face extrusion during construction (not in the final state).

[0052] Conclusion: To control the development of the plastic zone and stress concentration, L should not exceed 32m; considering the continuity of construction, the recommended optimized length is 25m - 30m.

[0053] Step 4: Targeted Construction with Integrated Optimized Parameters: A test section (e.g., DK131+394) was selected on-site and construction was carried out using optimized parameters (step height H=7.4m, single excavation length L=28m). Verification showed that the optimized scheme was extremely effective in deformation control, with measured arch settlement of 13.3mm and horizontal convergence of 13.7mm, highly consistent with the numerical prediction values ​​(13.4mm, 14.0mm). Simultaneously, construction efficiency was significantly improved. Thanks to the increased step height creating a good free face, explosive consumption decreased from 0.88 kg / m³ to 0.63 kg / m³, and the average over-excavation decreased from 20-24cm to 10-12cm. Furthermore, the process flow was smoother, providing ample working space for large equipment and significantly shortening the single-cycle operation time, achieving the dual goals of safe and rapid construction.

[0054] On-site implementation: Select a test section on-site (such as DK131+394) and apply the optimized parameters (such as H=7.4m, L=28m) for construction.

[0055] Effect verification Deformation control: The measured arch settlement was 13.3 mm and the horizontal convergence was 13.7 mm, which are in high agreement with the numerical prediction values ​​(13.4 mm, 14.0 mm), proving that the parameter optimization is effective.

[0056] Optimization of blasting: By utilizing the increased step height to create a better free face, the explosive consumption per unit volume decreased from 0.88 kg / m³ to 0.63 kg / m³.

[0057] Over-excavation control: The average over-excavation amount was reduced from 20-24cm to 10-12cm.

[0058] Process speed improvement: The optimized process connections are smoother, providing space for large equipment and significantly shortening the single-cycle operation time.

[0059] The above embodiments are not exhaustive examples of specific implementation methods, and other embodiments are also possible. The purpose of the above embodiments is to illustrate the present invention, rather than to limit the scope of protection of the present invention. All applications derived from simple variations of the present invention fall within the scope of protection of the present invention.

Claims

1. A method for optimizing construction parameters and controlling safety in tunnels built in water-rich, weak slate strata, characterized in that: Includes the following steps, Step 1: Comparison of construction methods based on numerical simulation and field tests: By establishing a three-dimensional numerical model, the construction process of the two-step method, the three-step method, and the double-sidewall pilot tunnel method in the water-rich soft slate strata is simulated respectively; Based on the surrounding rock deformation and support stress data obtained from the simulation, and combined with the construction efficiency, the construction method suitable for the water-rich soft slate strata is comprehensively compared and determined. Step two, the optimization study of construction process parameters based on refined numerical analysis, the specific process is as follows: Step 2.1: For the selected construction method, establish a refined numerical model that can be parameterized and adjusted; A three-dimensional numerical model was constructed based on the tunnel design cross section. The model size was set to eliminate boundary effects. Displacement constraints were applied to the bottom and sides of the model, and stress was applied to the top to simulate the initial in-situ stress field. An elastic-plastic constitutive model was adopted for the surrounding rock. An anchor support model was established using cable structural elements in flac3d. Step 2.2: Conduct deformation and stress analysis of the tunnel surrounding rock under multiple working conditions to quantitatively evaluate the impact of core construction parameters on tunnel stability; Step 2.3: Determine the safe construction parameters for the corresponding construction method; Step 3, Identification and control of key factors for surrounding rock instability: Based on numerical simulation results and field monitoring data, key disaster-causing factors leading to tunnel deformation are identified, and control measures are formulated accordingly; Step 4, On-site construction implementation of integrated optimization parameters: Based on the selected construction method, the tunnel excavation is carried out using the safe construction parameters determined in Step 2, and the control measures formulated in Step 3 are strictly implemented during construction. At the same time, the tunnel construction deformation and the stress of the surrounding rock-support structure system are monitored throughout the process. Step 5: Effect Verification and Construction Method Standardization: Compare the on-site monitoring data with the numerical simulation predictions, and verify the effectiveness of the safety construction parameters and control measures; Step six: Carry out construction based on the verified construction parameters and processes.

2. The method for optimizing construction parameters and controlling safety in tunnels in water-rich strata of weak slate as described in claim 1, characterized in that: In step one, the specific method for comparing the adaptability of construction methods is as follows: Step 1.1, Numerical Model Construction: Based on engineering geological data and design cross-sections, a three-dimensional numerical model of the tunnel is established using finite element software. The boundary conditions of the model are set as bottom and surrounding normal constraints, and the top is a free surface. The surrounding rock adopts an elastoplastic constitutive model, the initial support and secondary lining are simulated using elastic solid elements, the anchor bolts are simulated using truss elements, and the interaction between the structure and the surrounding rock is realized by embedding constraints or contact elements. Step 1.2, Determination of material parameters for the calculation model: Determine the physical and mechanical parameters and structural parameters of the slate in the densely jointed water-rich zone; Step 1.3: Comparative study of three construction methods: the two-step method, the three-step method, and the double-sidewall guide tunnel method; construction process of the two-step method, the three-step method, and the double-sidewall guide tunnel method, and monitoring. Step 1.4, Comprehensive Comparison and Analysis: Based on the numerical simulation results, compare and analyze the surrounding rock deformation analysis and initial support stress analysis under the three construction methods; combine the actual surrounding rock deformation data obtained from the field test section monitoring with the construction efficiency records; and comprehensively select the construction method based on the principles of controllable surrounding rock deformation, safe support stress, and simple and efficient construction procedures. Step 1.5, Setting up the field test section: In the actual tunnel construction, a water-rich jointed zone of weak and broken Devonian slate was selected for test excavation using the chosen construction method.

3. The method for optimizing construction parameters and controlling safety in tunnels in water-rich strata of weak slate as described in claim 2, characterized in that: The monitoring plan for step 1.3 is as follows: Deformation monitoring points are set up at the tunnel arch crown, arch foot, and invert; stress monitoring points are set up at the arch crown, arch shoulder, arch foot, wall foot, and invert.

4. The method for optimizing construction parameters and controlling safety in tunnels in water-rich strata of weak slate as described in claim 1, characterized in that: In step 2.2, when the selected construction method is the two-step method, the height H of the upper step and the one-time excavation length L of the upper step are used as core variables to construct a multi-condition numerical calculation model to analyze the displacement field characteristics, stress field distribution, and the range and distribution of the plastic zone under different combinations of construction parameters (H, L). When the selected method is the three-step method, the height of the upper step H1, the height of the middle step H2, the height of the lower step H3, the length of the upper step L1 > the distance of the middle step lagging behind the upper step L2 > the distance of the lower step lagging behind the middle step L3 are taken as core variables to construct a multi-condition numerical calculation model and analyze the displacement field characteristics, stress field distribution and plastic zone development area under different combinations of construction parameters (H1, H2, H3, L1, L2, L3). When the selected method is the double-sided wall guide tunnel method, the guide tunnel width B, guide tunnel height h, central partition wall thickness D, and longitudinal offset ΔL of the left and right guide tunnels are used as core variables to construct a multi-condition numerical calculation model, and analyze the displacement field characteristics, stress field distribution and plastic zone development zone under different combinations of construction parameters (B, h, D, ΔL).

5. The method for optimizing construction parameters and controlling safety in tunnels in water-rich strata of weak slate as described in claim 4, characterized in that: The displacement field includes crown settlement, horizontal convergence, invert heave, and extrusion deformation at the tunnel face; the stress field includes stress concentration in the surrounding rock and support structure.

6. The method for optimizing construction parameters and controlling safety in tunnels in water-rich strata of weak slate as described in claim 1, characterized in that: In step three, the specific control measures include proactive control and / or the use of high-strength rigid initial support and / or setting deformation management thresholds and / or strengthening key details, such as installing anchor bolts and temporary supports, strictly controlling deformation of weak parts such as step joints, and / or strengthening the overall integrity of the support system.

7. The method for optimizing construction parameters and controlling safety in tunnels in water-rich strata of weak slate as described in claim 1, characterized in that: In step five, during on-site construction, inclinometers, total stations, and strain gauges are used to monitor the settlement of the tunnel arch and the horizontal convergence changes of the surrounding soil and rock in real time. The surrounding rock stress monitoring element adopts a vibrating wire element. The vibrating wire element is embedded between the tunnel surrounding rock and the initial lining, and eight measurement points are set at intervals on the same cross section.

8. The method for optimizing construction parameters and controlling safety in tunnels in water-rich strata of weak slate as described in claim 1, characterized in that: The specific process in step five is as follows: Step 5.1, Optimization of process effect verification: During and after the implementation of step four, deformation and stress monitoring will be continuously carried out. The measured final settlement value of the arch, horizontal convergence value, and maximum stress value of the support structure will be compared with the deformation and stress of the tunnel surrounding rock analyzed in the numerical model in step two to verify the effectiveness and accuracy of the safe construction parameters and control measures. Step 5.2, Comprehensive Efficiency Comparison Analysis: Record the construction efficiency indicators after adopting the optimization method, including average single-cycle operation time, average monthly advance, and average over-excavation value; compare and analyze the above construction efficiency indicators with the benchmark data.

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