Volcanic ash stratum large-diameter large-gradient ultra-shallow-buried shield launching control method

Abstract

The invention discloses a volcanic ash stratum large-diameter large-gradient ultra-shallow-buried shield launching control method which comprises the following steps that S1, the stratum reinforcement range is calculated based on geological parameters, and a launching end stratum is reinforced through directional grouting; s2, a multi-stage sealing device is installed at the shield launching hole, and sealing performance verification is carried out before the hole portal is broken; s3, thrust, torque and grouting parameters are dynamically adjusted during shield tunneling, and ground surface settlement is controlled to be smaller than or equal to 3 mm; and S4, the shield attitude and stratum deformation are monitored in real time, and construction parameters are adjusted through a data feedback closed loop. According to the technical scheme, the reliability of the volcanic ash stratum component when the large-diameter, large-gradient and shallow-buried tunnel is constructed is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of shield tunnel engineering, in particular to a method for controlling the starting of a large-diameter, large-slope, and ultra-shallow buried shield machine in a volcanic ash stratum. Background Art

[0002] With the rapid development of urban underground space, the demand for large-diameter shield tunnels in complex strata is growing. Volcanic ash strata, a typical example of unfavorable geological conditions, are characterized by loose structure, high porosity, and strong permeability. The initial construction of large-diameter (diameter > 8 m), steep slopes (slope > 5%), and ultra-shallow (burial depth < 1 tunnel diameter) shield tunnels in these strata presents numerous technical challenges. First, the poor self-stability of the stratum leads to a significant increase in the incidence of collapse accidents. Second, controlling surface subsidence in ultra-shallow conditions is challenging. Third, controlling the shield's attitude is difficult in steep slope conditions.

[0003] Therefore, it is urgent to develop a set of control methods for the launch of large-diameter, large-slope and ultra-shallow buried shield tunnels in volcanic ash strata to ensure construction safety. Summary of the Invention

[0004] The main purpose of the present invention is to propose a method for starting control of a large-diameter, large-slope and ultra-shallow shield machine in volcanic ash strata, aiming to improve the reliability of volcanic ash strata components with large diameter, large slope and shallow burial tunnels.

[0005] To achieve the above-mentioned object, the present invention proposes a method for controlling the start of a large-diameter, large-slope, and ultra-shallow shield machine in a volcanic ash stratum. The method comprises the following steps: Step S1: Calculate the stratum reinforcement range based on geological parameters and reinforce the starting stratum by directional grouting; Step S2: Install a multi-stage sealing device at the shield tunneling portal and verify the sealing performance before breaking the portal; Step S3: Dynamically adjust thrust, torque and grouting parameters during shield tunneling to control surface settlement to ≤3mm; Step S4: monitor the shield attitude and ground deformation in real time, and adjust the construction parameters through a closed-loop data feedback loop.

[0006] In some embodiments, the formation reinforcement range is calculated using the following formula: Among them, L str is the length of the reinforcement area, D is the shield diameter, β is the starting slope angle, H is the tunnel depth, C u is the undrained shear strength of volcanic ash, S r is the porosity correction factor of volcanic ash, and k is the safety factor.

[0007] In some embodiments, the directional grouting uses cement slurry and / or water glass, and the grouting pressure is controlled according to the following formula: Among them, P inj is the maximum grouting pressure, σ v is the vertical earth pressure, σ h is the horizontal earth pressure, K0 is the static earth pressure coefficient, μ is the slurry viscosity, v is the grouting rate, d p is the equivalent diameter of the grouting hole, and α is the correction coefficient for the volcanic ash formation.

[0008] In some embodiments, the sealing device includes a wire brush sealing ring, an expandable rubber sealing ring and an emergency airbag sealing layer arranged in sequence from the outside to the inside.

[0009] In some embodiments, a gap in a forward sealing device such as bentonite slurry is broken at the portal to form a pressure balance zone, wherein the pressure value of the pressure balance zone is 1.05 to 1.15 times the static earth pressure.

[0010] In some embodiments, the thrust of the shield tunneling is dynamically adjusted according to the following formula: Among them, F t is the real-time thrust, γ is the effective bulk density of volcanic ash, K p is the passive earth pressure coefficient, F add Add resistance to the slope, L con is the contact length between the shield and the formation.

[0011] In some embodiments, the slope additional resistance F add Calculate according to the following formula: Where W is the weight of the shield machine, θ is the real-time excavation slope angle, and fr is the volcanic ash friction coefficient.

[0012] In some embodiments, the real-time monitoring of shield posture and stratum deformation is achieved by cooperating with at least two of a fiber grating sensor matrix, a distributed strain sensing fiber, and a three-dimensional laser scanner.

[0013] In some embodiments, when monitoring the shield machine posture in real time, when the shield machine pitch angle deviation is detected to be greater than 0.3°, a posture correction program is started, and the posture correction program includes the following steps: Adjust the thrust difference between different zones to 120%~150% of the design value; Inject high molecular weight polymer drag reducer at the low side cutterhead position; Use fast-setting slurry for simultaneous grouting.

[0014] In some embodiments, the synchronous grouting in the initial stage adopts an intermittent pulse grouting mode, and the grouting frequency f and the advancing speed v satisfy the following formula: Among them, S t is the density coefficient of volcanic ash, and e is a natural constant.

[0015] The technical solution of the present invention systematically optimizes the entire shield starting process through geological parameterized stratum reinforcement, multi-stage sealing device configuration, dynamic adjustment of tunneling parameters and real-time monitoring closed-loop control, effectively solving the problems of collapse, sand gushing, settlement and axis instability when the shield is started in volcanic ash strata with large slopes. It has the advantages of significantly reducing the risk of stratum collapse, completely suppressing water and sand gushing, accurately controlling surface settlement, and ensuring stable and reliable shield posture. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying any creative work.

[0017] Figure 1 This is a flowchart of a method for controlling the start of a large-diameter, large-slope, and ultra-shallow shield machine in volcanic ash strata according to one embodiment of the present invention.

[0018] The purpose, features and advantages of the present invention will be further described with reference to the accompanying drawings and in conjunction with the embodiments. DETAILED DESCRIPTION

[0019] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0020] It should be noted that if the embodiments of the present invention involve directional indications (such as up, down, left, right, front, back, etc.), the directional indications are only used to explain the relative position relationship, movement status, etc. between the various components under a certain specific posture. If the specific posture changes, the directional indications will also change accordingly.

[0021] In addition, if there are descriptions involving "first", "second", etc. in the embodiments of the present invention, the descriptions of "first", "second", etc. are only for descriptive purposes and cannot be understood as indicating or suggesting their relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features limited to "first" and "second" may explicitly or implicitly include at least one of such features. In addition, if "and / or" or "and / or" appears in the full text, its meaning includes three parallel solutions. Taking "A and / or B" as an example, it includes solution A, solution B, or solutions that satisfy both A and B. In addition, the technical solutions between the various embodiments can be combined with each other, but it must be based on the ability of ordinary technicians in this field to implement. When the combination of technical solutions is mutually contradictory or cannot be implemented, it should be deemed that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0022] See also Figure 1 The present invention proposes a method for controlling the start of a large-diameter, large-slope, and ultra-shallow shield machine in a volcanic ash stratum. The method comprises the following steps: step S1, calculating the stratum reinforcement range based on geological parameters, and using directional grouting to reinforce the starting stratum; step S2, installing a multi-stage sealing device at the starting entrance of the shield machine, and verifying the sealing before breaking the tunnel door; step S3, dynamically adjusting the thrust, torque and grouting parameters during shield excavation to control the surface settlement to ≤3mm; step S4, monitoring the shield machine posture and stratum deformation in real time, and adjusting the construction parameters through a data feedback closed loop.

[0023] In existing technologies, urban underground space development faces special challenges brought by volcanic ash strata. The stratum structure is loose and has high porosity, and traditional shield starting technology is difficult to meet the needs of large-diameter tunnel construction. Conventional stratum reinforcement methods have calculation deviations of the reinforcement range, resulting in local collapse in the starting stage. The portal sealing device is prone to leakage failure under high pressure difference conditions, and conventional grouting technology is difficult to adapt to the highly permeable geological characteristics. The control of construction parameters relies on experience and judgment, and lacks a real-time feedback mechanism, resulting in a significant increase in the risk of posture instability during large-slope excavation.

[0024] To address these issues and address the lack of accuracy in calculating the extent of stratum reinforcement, the research team discovered that traditional empirical formulas fail to account for the impact of volcanic ash pore structure on the ductility of the reinforced zone. Analysis of sealing device failure revealed that a single-stage sealing structure struggles to adapt to sudden pressure changes under ultra-shallow burial conditions. Analyzing the coupling relationship between shield thrust and stratum deformation, the team realized that static parameter settings cannot meet the dynamic balance requirements of steep excavation. Based on multi-source monitoring data fusion technology, they proposed the need for a real-time feedback and adjustment mechanism for construction parameters.

[0025] Therefore, the present application proposes a technical solution comprising the following steps: Step S1, calculating the stratum reinforcement range based on geological parameters, and using directional grouting to reinforce the starting stratum; Step S2, installing a multi-stage sealing device at the starting entrance of the shield, and verifying the sealing before the tunnel door is broken; Step S3, dynamically adjusting the thrust, torque and grouting parameters during shield excavation to control surface settlement; Step S4, real-time monitoring of the shield posture and stratum deformation, and adjusting the construction parameters through a data feedback closed loop.

[0026] Among them, the calculation of the stratum reinforcement range refers to determining the grouting reinforcement area based on the physical characteristics of the volcanic ash stratum. It can be achieved by combining geological exploration data with numerical simulation methods. This step ensures that the reinforcement area matches the mechanical characteristics of the stratum. The installation of a multi-stage sealing device refers to setting up multiple sealing structure layers. For example, the combination of sealing rings made of different materials can be installed. This structure can absorb pressure fluctuations in a graded manner. Dynamic parameter adjustment refers to correcting construction parameters according to real-time working condition changes. It can be achieved through an automatic control system. This measure maintains the mechanical balance of the excavation process. Data feedback closed-loop adjustment refers to establishing a real-time association between monitoring data and construction parameters. For example, a sensor network is used to collect data. This mechanism realizes precise control of the construction process.

[0027] Specifically, by collecting the porosity and shear strength parameters of the volcanic ash stratum, a reinforcement range calculation model was established to determine the optimal grouting area. Different sealing components were installed in sequence at the portal structure, and the pressure-bearing capacity of the sealing system was verified through pressure testing. During the shield tunneling process, the propulsion system output parameters were corrected in real time based on the earth pressure balance state. Distributed monitoring equipment was deployed to collect stratum deformation data, and the settlement amount was fed back to the grouting control system to adjust the slurry ratio. When the monitoring data exceeded the set threshold, the parameter correction program was automatically triggered to redistribute the cutterhead torque.

[0028] Compared with existing technologies, traditional reinforcement methods using constant-thickness grouting are prone to material waste. This solution achieves precise reinforcement through geological parameter calculation. Conventional single-stage sealing structures are prone to failure due to pressure fluctuations. This solution's multi-stage sealing device creates a progressive sealing effect. Empirical parameter settings are difficult to adapt to complex working conditions. This solution's dynamic adjustment mechanism improves the controllability of the construction process. Manual monitoring suffers from data lag. This solution's closed-loop feedback system achieves millimeter-level settlement control.

[0029] Through the above technical solutions, this application effectively prevents collapse accidents in the initial stage of volcanic ash formations and ensures the reliability of the portal sealing system under high-pressure differential conditions. The earth pressure balance of shield tunneling is maintained through dynamic parameter adjustment, reducing the risk of posture deviation during large-slope advancement. The real-time data feedback mechanism realizes active control of surface settlement and avoids damage to the ground structure during ultra-shallow tunnel construction. The synergistic effect of multiple technologies significantly improves the safety and construction efficiency of shield tunneling in complex geological conditions.

[0030] In some embodiments, the formation reinforcement range is calculated using the following formula: Among them, L str is the length of the reinforcement area, D is the shield diameter, β is the starting slope angle, H is the tunnel depth, C u is the undrained shear strength of volcanic ash, S r is the porosity correction factor of volcanic ash, and k is the safety factor.

[0031] Reinforcement area length L str It refers to the longitudinal extension range that needs to be reinforced at the starting end of the shield machine. It can be determined through geological exploration data and numerical simulation analysis to ensure that the reinforcement range covers the potential unstable area.

[0032] The shield diameter D refers to the outer diameter of the shield machine cutterhead, which can be obtained through a laser rangefinder or a mechanical measuring device and directly affects the lateral dimensions of the reinforcement range.

[0033] The starting slope angle β refers to the angle between the axis of the starting section of the shield and the horizontal plane. It can be measured by a total station or an inclination sensor to reflect the impact of large slope conditions on stratum stability.

[0034] Tunnel burial depth H refers to the vertical distance from the tunnel top to the ground surface. It can be determined through geological radar or borehole data and is used to evaluate the soil pressure distribution under ultra-shallow burial conditions.

[0035] Undrained shear strength of volcanic ash C u It refers to the shear resistance of volcanic ash strata under rapid loading conditions, which can be measured through indoor direct shear tests or in-situ cross-plate shear tests to characterize the strength characteristics of the strata.

[0036] Volcanic ash porosity correction factor S r It refers to the adjustment parameter introduced based on the effect of volcanic ash porosity on permeability and compressibility. It can be determined through porosity testing and regression analysis of historical engineering data, and is used to correct the calculation error of the reinforcement range.

[0037] The safety factor k refers to a redundancy factor that takes into account construction uncertainty and formation variability. It can be selected based on the project risk level and geological complexity. For example, the value range is 1.2 to 1.5.

[0038] Specifically, by substituting key parameters such as shield diameter, starting slope angle, and tunnel depth into the formula, the reinforcement requirements for volcanic ash formations can be quantified. For example, as the shield diameter increases, the length of the reinforcement zone expands according to the cube root relationship, preventing formation collapse due to insufficient reinforcement. As the porosity correction factor increases, the formula automatically increases the reinforcement range to offset the risks posed by volcanic ash permeability. Thus, this method, through multi-parameter coupled calculations, accurately matches reinforcement requirements under complex geological conditions, resolving the problem of insufficient or excessive reinforcement in volcanic ash formations often encountered with traditional empirical methods.

[0039] Compared to existing technologies, traditional reinforcement range calculation methods typically use linear estimates based on a single parameter (such as burial depth or shield diameter), failing to consider the combined effects of steep slopes, porosity, and shear strength. This approach, by introducing a cube root function and a multi-parameter product relationship, incorporates formation strength, geometric conditions, and geological characteristics into a unified model. This significantly improves the scientific nature and adaptability of reinforcement range calculations, making it particularly suitable for addressing nonlinear instability issues caused by high parameter sensitivity in volcanic ash formations.

[0040] Through the above-mentioned technical solution, this application can precisely control the scope of ground reinforcement, avoiding surface subsidence or collapse accidents caused by insufficient reinforcement in ultra-shallow buried conditions, while also preventing the waste of resources caused by excessive reinforcement. By dynamically adapting to the characteristics of volcanic ash formations, this method effectively balances construction safety and economic efficiency, providing reliable support for the initiation of large-diameter and large-slope shield tunneling in complex geology.

[0041] In some embodiments, the directional grouting uses cement slurry and / or water glass, and the grouting pressure is controlled according to the following formula: Among them, P inj is the maximum grouting pressure, σ v is the vertical earth pressure, σ h is the horizontal earth pressure, K0 is the static earth pressure coefficient, μ is the slurry viscosity, v is the grouting rate, d p is the equivalent diameter of the grouting hole, and α is the correction coefficient for the volcanic ash formation.

[0042] Cement slurry refers to a grouting material with silicate cement as the main agent. Specifically, ordinary silicate cement and water can be mixed in proportion to form a slurry, which forms a rigid reinforcement after solidification. Water glass refers to a sodium silicate solution. Specifically, a water glass solution with a modulus of 2.4-3.0 can be used, which forms a gel by reacting with an acidic substance. The equivalent diameter of the grouting hole refers to the equivalent pore size converted according to the arrangement of the grouting pipes. Specifically, it can be calculated by the fluid mechanics equivalent formula when the porous grouting pipes are arranged in parallel, and is used to characterize the equivalent size of the slurry diffusion channel. The volcanic ash formation correction coefficient refers to a parameter that reflects the influence of the volcanic ash pore structure on the permeability of the slurry. Specifically, it can be determined by fitting the laboratory permeability test combined with the field pumping test data.

[0043] Specifically, when implementing directional grouting in volcanic ash formations, cement slurry and water glass are injected alternately through a dual-liquid grouting system, where cement slurry is used to fill large pore structures and water glass is used to block small seepage channels. The grouting pressure is calculated by collecting formation stress data in real time, substituting the vertical and horizontal soil pressures into the formula to calculate the baseline pressure value, and then superimposing the slurry flow resistance component to form a dynamic control threshold. When the grouting equipment detects that the pressure is close to the calculated value, it automatically adjusts the displacement parameters of the grouting pump to ensure that the actual grouting pressure is always lower than the critical value of the formation splitting. For example, in areas with high porosity, the flow resistance component can be reduced by increasing the equivalent diameter of the grouting hole to avoid pressure accumulation and formation disturbance.

[0044] Compared with existing technologies, traditional grouting pressure control methods only consider the static earth pressure component and fail to account for the effects of slurry rheological properties and grouting rate. This can easily lead to excessive pressure causing formation fractures or insufficient grouting leading to reinforcement failure. This solution introduces a viscosity-velocity coupling term to establish a dynamic pressure control model that can adapt to the grouting needs of formations with different pore structures. In existing technologies, a single slurry material cannot meet the dual requirements of pore filling and fracture plugging. However, this solution utilizes a composite grouting system of cement slurry and water glass, which can achieve a multi-scale reinforcement effect.

[0045] Through the above technical solution, this application can accurately control the grouting pressure within a safe range, ensuring that the slurry effectively fills the pores of the volcanic ash formation while avoiding damage to the formation structure caused by excessive pressure. The dual-liquid grouting system can simultaneously achieve macro-reinforcement and micro-blocking, significantly improving the overall stability of the starting formation and creating safe operating conditions for subsequent shield starting. The rheological parameter term introduced in the pressure control formula can effectively compensate for the flow loss of the slurry in complex pore channels, ensuring a uniform and reliable grouting effect.

[0046] In some embodiments, the sealing device includes a wire brush sealing ring, an expandable rubber sealing ring and an emergency airbag sealing layer arranged in sequence from the outside to the inside.

[0047] A wire brush sealing ring refers to an annular sealing structure formed by weaving metal wires, which can be specifically achieved by a cross-weaving process of stainless steel wires. The diameter of the metal wires can be, for example, 0.3 mm to 0.5 mm. By stacking multiple layers, a dense barrier is formed to block the invasion of formation particles. An expandable rubber sealing ring refers to a rubber component with the property of swelling when exposed to water, which can be specifically made of a composite of butyl rubber and a water-absorbing resin. It can expand in volume when in contact with groundwater and is used to compensate for the sealing gap. An emergency airbag sealing layer refers to a polymer sealing component with a built-in inflatable cavity, which can be specifically made of a polyurethane composite material. Dynamic sealing is achieved through air pressure regulation to cope with sudden pressure fluctuations.

[0048] Specifically, before the tunnel portal is breached, a wire brush seal forms a first physical barrier through mechanical engagement, preventing loose particles from the volcanic ash formation from entering the launch area. During shield tunneling, the expandable rubber seal absorbs leaking water, expanding in volume and filling any sealing gaps caused by shield displacement. The emergency airbag seal activates inflation upon detecting abnormal pressure, expanding the airbag to form an emergency seal and prevent mud and water seepage from causing ground instability.

[0049] Compared to existing technologies, traditional shield launch seals typically use a single-layer rubber curtain fabric, which is prone to slurry leakage in the high permeability of volcanic ash formations. This solution uses a triple-seal structure to create a gradient protection. The wire brush seal ring intercepts large particles, the expandable rubber seal achieves dynamic adaptive sealing, and the emergency airbag seal layer provides emergency protection. The three work together to adapt to the complex formation pressure changes in ultra-shallow burial conditions.

[0050] Through the above technical solution, this application can effectively prevent mud and water leakage caused by tunnel gate sealing failure during the initial stage of shield tunneling, maintain the pressure balance of the excavation surface, and reduce the risk of surface subsidence caused by sealing failure. It is especially suitable for volcanic ash strata with high porosity and strong permeability.

[0051] In some embodiments, a gap in a forward sealing device such as bentonite slurry is broken at the portal to form a pressure balance zone, wherein the pressure value of the pressure balance zone is 1.05 to 1.15 times the static earth pressure.

[0052] Bentonite slurry refers to a thixotropic slurry with sodium bentonite as the main component. It can be achieved by using a water to bentonite mass ratio of 1:8 to 1:12. Its water-expanding properties can fill the gap between the sealing device and the shield machine shell. The pressure balance zone refers to an annular closed area with a specific pressure threshold formed by grouting. It can be achieved by interlocking the pressure sensor and the grouting pump to offset the impact of the formation pressure fluctuation on the sealing structure when the shield is started. The pressure value range of 1.05 times to 1.15 times refers to the dynamic control range based on the measured value of the static earth pressure. It can be achieved by real-time collection of formation pressure data and feedback to the grouting system. This range can prevent slurry leakage and avoid overload of the sealing structure.

[0053] Specifically, before the concrete removal of the portal, bentonite slurry is injected into the annular gap of the multi-stage sealing device through pre-buried grouting pipes. The slurry forms a pressure-maintaining gel layer between the sealing wire brush and the rubber ring. The pressure of this layer is maintained between 1.05 and 1.15 times the static earth pressure by a closed-loop control system. When the shield machine begins to advance, the thixotropic properties of the bentonite slurry transform it into a dense aquiclude under mechanical compression. Simultaneously, the pressure balance zone offsets changes in ground pressure by adjusting the grouting volume in real time, preventing external water and soil from seeping through the gap between the shield shell and the sealing device.

[0054] Compared to existing technologies, traditional shield initial sealing relies solely on the static compression force of the mechanical seal structure, which is prone to slurry leakage in conditions such as volcanic ash formations with high permeability and fluctuating pore pressure. This solution creates an adjustable pressure balance zone to ensure that the sealing interface pressure is always higher than the external formation pressure, forming a dynamic pressure barrier.

[0055] Through the above technical solution, this application effectively solves the problem of high leakage risk of the shield starting sealing interface in volcanic ash strata. The pressure adaptive characteristics of the bentonite slurry and the multi-stage sealing device form a synergistic effect to ensure the reliability of the tunnel portal sealing system in the shield starting stage.

[0056] In some embodiments, the thrust of the shield tunneling is dynamically adjusted according to the following formula: Among them, F t is the real-time thrust, γ is the effective bulk density of volcanic ash, K p is the passive earth pressure coefficient, F add Add resistance to the slope, L con is the contact length between the shield and the formation.

[0057] Real-time thrust refers to the shield thrust calculated in real time based on geological conditions. This can be achieved through the linkage of pressure sensors and the thrust cylinder control system, and its function is to match changes in ground resistance. The effective bulk density of volcanic ash refers to the weight of soil per unit volume after deducting pore water pressure. This can be determined through field sampling combined with indoor triaxial testing to accurately calculate the lateral pressure generated by the soil's own weight. The passive earth pressure coefficient refers to the lateral pressure coefficient when the soil is in a passive limit equilibrium state. It can be calculated using Rankine's earth pressure theory combined with the internal friction angle of volcanic ash and is used to characterize the compressive effect of the soil on the shield during shield advancement. Slope added resistance refers to the additional frictional resistance generated by the shield machine's own weight during inclined advancement. This can be achieved through real-time measurement of the tunneling inclination angle using attitude sensors and calculation of the component to compensate for thrust deviations under steep slope conditions. The shield-ground contact length refers to the actual contact area between the shield shell and the reinforced soil. This can be determined using distributed strain sensing fiber optics to monitor the stress distribution in the shield shell and reflects the interaction area between the shield and the ground.

[0058] Specifically, during the shield tunneling process, by collecting stratum parameters and equipment status data in real time, parameters such as the effective bulk density of volcanic ash and the passive earth pressure coefficient are substituted into the thrust calculation formula. Combined with dynamic compensation for the added resistance of the slope, a closed-loop control circuit is formed. For example, when the shield machine's climbing angle is monitored to increase, the control system automatically increases the calculation weight of Fadd and synchronously adjusts the total thrust output. At the same time, based on the real-time changes in contact length, the impact of soil shear strength on thrust is dynamically corrected to avoid thrust calculation errors caused by changes in the contact surface.

[0059] Compared with existing technologies, traditional shield thrust control often relies on fixed empirical coefficients or single parameter adjustments, failing to comprehensively consider the impact of deadweight under steep slope conditions and the dynamic changes in the contact characteristics of volcanic ash formations. This solution, by establishing a multi-parameter coupled thrust calculation model, achieves coordinated feedback of geological conditions, equipment posture, and construction parameters, significantly improving thrust control accuracy under complex conditions.

[0060] Through the above technical solution, this application effectively solves the risk of machine jamming caused by insufficient thrust during shield tunneling on a large slope and the problem of stratum disturbance caused by excessive thrust. By dynamically compensating for the slope additional resistance and real-time correction of the contact length parameters, it ensures that the propulsion force of the shield machine in the volcanic ash stratum is always balanced with the stratum resistance, providing precise mechanical guarantee for controlling surface subsidence and posture deviation.

[0061] In some embodiments, the slope additional resistance F add Calculate according to the following formula: Where W is the weight of the shield machine, θ is the real-time excavation slope angle, and fr is the volcanic ash friction coefficient.

[0062] The weight of a shield machine refers to the overall mass of the shield equipment. This can be calibrated using a weighing sensor or factory parameters to quantify the impact of the equipment's own weight on ramp construction. The real-time excavation slope angle refers to the instantaneous angle between the shield axis and the horizontal plane. This can be dynamically monitored using a high-precision inclinometer to reflect actual slope changes during excavation. The volcanic ash friction coefficient refers to the friction characteristic parameter of the contact surface between the shield shell and the volcanic ash stratum. This can be obtained through on-site direct shear tests or geological survey data and is used to characterize the frictional resistance of the stratum to the shield movement.

[0063] Specifically, when a shield machine advances along a steep slope, the machine's own weight creates additional resistance along the slope. By collecting real-time data from the machine weight, inclinometer angle, and ground friction coefficient, the system dynamically calculates the slope's additional resistance. This resistance value is added to the basic thrust formula to form a real-time total thrust control target. For example, when the slope angle increases to 7%, the system automatically increases thrust output to overcome the increased downward force component and prevent the shield machine from sliding downhill due to insufficient thrust. As the slope angle decreases, thrust output is reduced accordingly to prevent ground disturbance caused by overthrusting.

[0064] Compared to existing technologies, traditional methods typically use fixed empirical coefficients to estimate slope added resistance, failing to consider the dynamic coupling between real-time slope changes and formation friction characteristics. This solution achieves precise calculation of added resistance by establishing a mechanical model to quantify the product relationship between slope angle, equipment weight, and friction coefficient. For example, when porosity fluctuations in volcanic ash formations cause changes in the friction coefficient, the system automatically adjusts the calculation parameters to avoid thrust control errors caused by deviations in the friction coefficient value.

[0065] Through the above technical solution, this application effectively solves the problem of insufficient thrust control accuracy in large-slope shield tunneling. By dynamically calculating the slope additional resistance, it ensures that the thrust output accurately matches the actual working conditions of the stratum, avoiding equipment slippage caused by insufficient thrust or stratum extrusion damage caused by excessive thrust, thereby improving the shield attitude control stability and surface settlement control effect.

[0066] In some embodiments, the real-time monitoring of shield posture and stratum deformation is achieved by cooperating with at least two of a fiber grating sensor matrix, a distributed strain sensing fiber, and a three-dimensional laser scanner.

[0067] A fiber Bragg grating sensor matrix refers to a monitoring system formed by multiple fiber Bragg grating sensors arranged in a spatial array. Specifically, wavelength modulation technology can be used to achieve continuous measurement of stratum strain distribution, and its high sensitivity can capture millimeter-level deformations. A distributed strain sensing fiber refers to a continuous distributed measurement device based on the principle of optical time-domain reflectometry. Specifically, it can reconstruct the full-section strain field by detecting optical fiber microbend losses. Its spatial resolution advantage is suitable for large-scale stratum monitoring. A three-dimensional laser scanner refers to a spatial coordinate acquisition device based on the principle of laser ranging. Specifically, multi-site cloud splicing technology can be used to achieve stereoscopic measurement of the shield machine's position. Its non-contact measurement characteristics are suitable for dynamic construction environments.

[0068] Specifically, during the tunneling process, a fiber Bragg grating (FBG) sensor matrix is ​​deployed along the tunnel axis, providing real-time feedback on ground compression and deformation. A distributed strain sensing fiber is wrapped circumferentially around the shield, simultaneously monitoring circumferential stress distribution. A 3D laser scanner, mounted behind the launch shaft, periodically acquires the 3D coordinates of the shield machine. These three systems use a data fusion algorithm to establish a coupled model of the shield's attitude and ground deformation. When a pitch angle deviation exceeding a threshold is detected, they automatically trigger zoned thrust adjustment and synchronized grouting parameter optimization.

[0069] Compared with existing technologies, traditional shield monitoring often relies on a single type of sensor, such as total stations for point measurements. This fails to capture continuous strain field data and is significantly affected by construction vibrations. This solution leverages the collaborative work of multiple heterogeneous sensors to ensure the spatial integrity of attitude measurements while enabling distributed sensing of stratum deformation, effectively addressing the issue of delayed identification of sudden deformation changes in volcanic ash formations.

[0070] Through the above technical solution, this application realizes the synchronous and precise monitoring of shield posture and stratum deformation, can timely identify the mismatch of construction parameters under complex geological conditions, and suppress the surface subsidence risk within a controllable range through a closed-loop control mechanism, thereby ensuring the safety of shield starting under large slope and ultra-shallow buried conditions.

[0071] In some embodiments, when monitoring the shield machine posture in real time, when the shield machine pitch angle deviation is detected to be greater than 0.3°, a posture correction program is started, and the posture correction program includes the following steps: Adjust the thrust difference between different zones to 120%~150% of the design value; Inject high molecular weight polymer drag reducer at the low side cutterhead position; Use fast-setting slurry for simultaneous grouting.

[0072] The pitch angle deviation refers to the angular offset between the shield machine axis and the design axis in the vertical plane. It can be achieved by measuring the strain distribution of the shield machine shell through the fiber optic Bragg grating sensor matrix to determine whether the shield machine is rising or falling.

[0073] Among them, the posture correction program refers to the control process of restoring the shield posture through the coordinated adjustment of multiple parameters. It can be implemented by a hierarchical response mechanism, which is automatically triggered when the deviation exceeds the threshold.

[0074] Among them, the zone thrust difference refers to the thrust difference generated by each hydraulic zone of the shield propulsion system, which can be achieved by adjusting the pressure distribution of the hydraulic pump station to generate a corrective torque.

[0075] Among them, the high molecular polymer drag reducer refers to a non-Newtonian fluid material with shear thinning properties, which can be specifically realized by using a polyacrylamide aqueous solution to reduce the friction resistance at the contact surface between the cutter head and the formation.

[0076] Among them, fast-setting slurry refers to a cement-based material with an initial setting time of less than 30 minutes. It can be achieved by using a composite formula of sulphoaluminate cement and a quick-setting agent to quickly fill the shield tail gap.

[0077] Specifically, when the fiber grating sensor detects that the strain difference between the front and rear of the shield machine reaches a preset threshold, the control system determines that the pitch angle deviation exceeds the allowable range. At this point, the thrust difference between the propulsion system zones is automatically increased to 1.2-1.5 times the original design value. This increased thrust difference between the front and rear generates a corrective torque. Simultaneously, a high-molecular polymer material is injected in front of the cutterhead on the sinking side. This material's viscosity decreases under shear, penetrating the contact surface between the cutterhead and the formation to form a lubricating layer. Synchronous grouting is performed using a fast-setting slurry, which quickly solidifies after the shield tail is detached, forming a support structure.

[0078] In some embodiments, the injection rate of the polymer drag reducer can be adjusted in real time based on changes in cutterhead torque, with injection stopped when the torque drops by 15%. The setting time of the rapid-setting slurry can be controlled within a range of 5-15 minutes by adjusting the amount of coagulant, while the grouting pressure is maintained at 0.8-1.0 times the static earth pressure of the formation.

[0079] Compared to existing technologies, current shield machine posture correction methods often rely solely on thrust adjustment, which can easily lead to increased ground disturbance. This solution utilizes a triple mechanism of thrust differential adjustment, drag reducer lubrication, and rapid support to correct posture while maintaining ground stability. While existing slurry typically takes over an hour to set, this solution utilizes fast-setting materials to shorten support response time by over 60%.

[0080] Through the above-mentioned technical solution, this application can quickly implement active corrections at the initial stage of pitch angle anomalies, preventing shield jams caused by accumulated deviations. Drag-reducing agent injection effectively reduces additional ground disturbances during the correction process, and the rapid-setting slurry promptly forms a support structure to prevent soil collapse. The synergistic effect of these three measures improves shield attitude recovery efficiency while simultaneously controlling incremental surface settlement to less than 1mm.

[0081] In some embodiments, the synchronous grouting in the initial stage adopts an intermittent pulse grouting mode, and the grouting frequency f and the advancing speed v satisfy the following formula: Among them, S t is the density coefficient of volcanic ash, and e is a natural constant.

[0082] Intermittent pulse grouting mode refers to a non-continuous grouting method achieved by periodically opening and closing the grouting valve. This can be achieved by linking a solenoid valve group with a PLC control system. This mode controls the interval between slurry injections, allowing the slurry to fully fill the formation pores under the action of high-pressure pulses. The grouting frequency refers to the number of grouting pulses per unit time, which can be achieved by adjusting the solenoid valve operation cycle. This parameter forms a dynamic matching relationship with the shield propulsion speed. The volcanic ash density coefficient is a dimensionless parameter that reflects the degree of cementation between volcanic ash particles. It can be determined through indoor triaxial testing. This coefficient is used to correct the adaptability of the grouting frequency to the formation permeability.

[0083] Specifically, during the initial advancement of the shield, the grouting system dynamically calculates the optimal grouting frequency based on real-time collected advancement speed data using the formula f=2v / D e^(-0.02S_t). As the advancement speed increases, the grouting frequency increases linearly to ensure the grouting volume per unit excavation distance, while compensating for the permeability characteristics of the volcanic ash formation using an exponential function. For example, in a volcanic ash formation with a density coefficient St=50, when the shield advances at a speed of 20mm / min, the grouting frequency can be controlled to 3-4 pulses per minute, with each pulse lasting 8-10 seconds. This mode uses the pressure fluctuation effect to encourage the slurry to form a root-like diffusion path in the loose formation, while avoiding excessive slurry diffusion caused by continuous grouting.

[0084] Compared to existing technologies, traditional synchronous grouting often uses a constant-rate continuous grouting method. This method is susceptible to grouting pressure decay in volcanic ash formations due to continuous slurry penetration, resulting in a limited effective slurry diffusion radius. Intermittent pulse grouting, on the other hand, maintains slurry penetration dynamics through periodic pressure shocks. The pulse intervals also provide a time window for the dissipation of pore water pressure in the formation, facilitating the formation of a dense reinforcement layer. While existing grouting parameters are often set empirically, the frequency-velocity mathematical model developed in this approach enables dynamic coupled control of grouting and tunneling parameters.

[0085] Through the above-mentioned technical solution, this application effectively resolves the technical contradiction between excessive slurry penetration and grouting pressure decay during grouting of volcanic ash formations. The periodic pressure shocks generated by pulse grouting both ensure the effective diffusion range of the slurry and prevent the loss of large amounts of slurry to non-reinforced areas. This control method precisely matches the grouting volume with the excavation progress, forming a continuous and uniform reinforcement ring under ultra-shallow burial conditions, providing reliable protection for controlling surface subsidence.

[0086] The above description is only a preferred embodiment of the present invention and does not limit the patent scope of the present invention. All equivalent structural transformations made by using the contents of the present invention description and drawings under the inventive concept of the present invention, or direct / indirect application in other related technical fields are included in the patent protection scope of the present invention.

Claims

1. A method for controlling the launch of a large-diameter, large-slope, and ultra-shallow shield tunnel in a volcanic ash stratum, characterized in that: The steps include: The scope of stratum reinforcement is calculated based on geological parameters, and directional grouting is used to reinforce the starting stratum; Install a multi-stage sealing device at the shield tunneling portal and verify the sealing performance before breaking the portal; Dynamically adjust thrust, torque and grouting parameters during shield tunneling to control surface settlement to ≤3mm; Monitor shield posture and ground deformation in real time, and adjust construction parameters through a closed-loop data feedback loop.

2. The method for controlling the start of a large-diameter, large-slope, ultra-shallow shield tunnel in volcanic ash strata according to claim 1 is characterized in that: The stratum reinforcement range is calculated by the following formula: Among them, L str is the length of the reinforcement area, D is the shield diameter, β is the starting slope angle, H is the tunnel depth, C u is the undrained shear strength of volcanic ash, S r is the porosity correction factor of volcanic ash, and k is the safety factor.

3. The method for controlling the start of a large-diameter, large-slope, ultra-shallow shield tunnel in volcanic ash strata according to claim 2, characterized in that: The directional grouting uses cement slurry and / or water glass, and the grouting pressure is controlled according to the following formula: Among them, P inj is the maximum grouting pressure, σ v is the vertical earth pressure, σ h is the horizontal earth pressure, K0 is the static earth pressure coefficient, μ is the slurry viscosity, v is the grouting rate, d p is the equivalent diameter of the grouting hole, and α is the correction coefficient for the volcanic ash formation.

4. The method for controlling the start of a large-diameter, large-slope, ultra-shallow shield tunnel in volcanic ash strata according to claim 1 is characterized in that: The sealing device comprises a wire brush sealing ring, an expandable rubber sealing ring and an emergency airbag sealing layer which are arranged in sequence from the outside to the inside.

5. The method for controlling the start of a large-diameter, large-slope, and ultra-shallow shield tunnel in volcanic ash strata according to claim 4 is characterized in that: A gap in a forward sealing device such as bentonite slurry is broken at the portal to form a pressure balance zone, wherein the pressure value of the pressure balance zone is 1.05 to 1.15 times the static earth pressure.

6. The method for controlling the start of a large-diameter, large-slope, and ultra-shallow shield tunnel in volcanic ash strata according to claim 2, characterized in that: The thrust of the shield machine is dynamically adjusted during tunneling according to the following formula: Among them, F t is the real-time thrust, γ is the effective bulk density of volcanic ash, K p is the passive earth pressure coefficient, F add Add resistance to the slope, L con is the contact length between the shield and the formation.

7. The method for controlling the start of a large-diameter, large-slope, ultra-shallow shield tunnel in volcanic ash strata according to claim 6, characterized in that: Slope additional resistance F add Calculate according to the following formula: Where W is the weight of the shield machine, θ is the real-time excavation slope angle, and fr is the volcanic ash friction coefficient.

8. The method for controlling the start of a large-diameter, large-slope, and ultra-shallow shield tunnel in volcanic ash strata according to claim 1 is characterized in that: The real-time monitoring of shield posture and stratum deformation is achieved by cooperating with at least two of a fiber grating sensor matrix, a distributed strain sensing optical fiber, and a three-dimensional laser scanner.

9. The method for controlling the start of a large-diameter, large-slope, ultra-shallow shield tunnel in volcanic ash strata according to claim 8, characterized in that: When monitoring the shield machine's attitude in real time, if the shield machine's pitch angle deviation is detected to be greater than 0.3°, the attitude correction program is started. The attitude correction program includes the following steps: Adjust the thrust difference between different zones to 120%~150% of the design value; Inject high molecular weight polymer drag reducer at the low side cutterhead position; Use fast-setting slurry for simultaneous grouting.

10. The method for controlling the start of a large-diameter, large-slope, and ultra-shallow shield tunnel in volcanic ash strata according to claim 2, characterized in that: The synchronous grouting in the initial stage adopts the intermittent pulse grouting mode, and the grouting frequency f and the propulsion speed v satisfy the following formula: Among them, S t is the density coefficient of volcanic ash, and e is a natural constant.

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