Deeply-buried tunnel hard rock TBM jamming escape method based on three-dimensional finite difference numerical simulation

Abstract

The invention discloses a deep tunnel hard rock TBM (tunnel boring machine) stuck-out method based on three-dimensional finite difference numerical simulation, which comprises the following steps: firstly, evaluating a stuck-out state, and determining a rock burst occurrence position and a rock mass crushing condition; secondly, establishing a three-dimensional finite difference numerical model, simulating a shield structure and a surrounding rock environment around the shield structure, performing blasting parameter inversion by adopting an equivalent loading method, and calculating a single-hole explosive load; then, a PVC wall protection pipe with a threaded connector and an axial groove is adopted to follow up while drilling, and charging, detonating and follow-up cleaning are carried out; and finally, after the TBM is successfully released, real-time monitoring of propulsion parameters is enhanced, and follow-up supporting and tunneling parameters are optimized. According to the method, accurate quantitative control of blasting parameters is achieved through numerical simulation and equivalent load inversion, and the damage risk of the shield is greatly reduced; a special PVC pipe is adopted to improve the pore-forming rate of the broken rock stratum; the overall detrapping efficiency is improved by more than 80%, the problem of TBM jamming of the deeply-buried hard rock tunnel can be effectively solved, and construction period delay and equipment damage are remarkably reduced.

Description

Technical Field

[0001] This invention relates to the field of tunnels and underground engineering, and particularly to a method for freeing a stuck TBM in deep-buried hard rock tunnels based on three-dimensional finite difference numerical simulation. The method combines three-dimensional finite difference numerical simulation to determine blasting parameters and employs special borehole wall protection measures, utilizing micro-blasting technology to release the stuck TBM. This invention is applicable to stuck conditions caused by minor or moderate rock bursts leading to the accumulation of rock fragments and loosening of the surrounding rock around the TBM shield. Background Technology

[0002] With the increasing number of deep-buried, long-distance, and large-section hard rock tunnel projects, such as deep-buried water conveyance tunnels, highway or railway tunnels, and pumped storage power station water diversion tunnels, tunnel boring machines (TBMs) have been increasingly widely used in these projects due to their advantages such as fast tunneling speed, minimal impact on the surface environment, high degree of automation, and ability to ensure tunnel alignment accuracy.

[0003] However, deeply buried hard rock strata are typically accompanied by geological characteristics such as high ground stress and high rock brittleness. Under high ground stress conditions, the surrounding rock stores enormous elastic strain energy. When the TBM disturbs the original stress equilibrium state of the rock mass during tunneling, this strain energy may be suddenly released, leading to rockburst disasters. Rockbursts are generally classified into four levels according to their degree of damage and energy release scale: minor, moderate, severe, and extremely severe. Severe and above-level rockbursts often cause a large number of rock fragments to be ejected, seriously threatening the safety of construction personnel and even potentially damaging the TBM equipment. While minor or moderate rockbursts are relatively less destructive, the resulting rock flakes or blocks may peel off and accumulate around the TBM shield, or cause the loosened zone of the surrounding rock to expand, hindering the TBM's progress during tunneling and causing it to jam. Jamming not only leads to construction stoppages, delays, and increased costs, but may also further damage the TBM equipment or surrounding rock structure due to prolonged downtime or forced pushing, resulting in greater economic losses and safety risks.

[0004] Currently, the main methods for handling TBM card readers include the following: 1. Mechanical jacking method: This method uses the TBM's own propulsion system or its auxiliary systems (such as trolley jacks) to push the jammed part. This method is suitable for situations with low jamming resistance, but if the jamming resistance is too high, forcibly pushing may cause TBM structural deformation, component damage, or even worsen the jamming situation.

[0005] 2. High-pressure water jet method: This method uses a high-pressure water jet to impact the rock or rock debris stuck in the machine, attempting to disperse or wash it away. This method requires sophisticated equipment and has limited effectiveness on dense, hard rocks or large rock masses. It also consumes a large amount of water and the cleaning process is relatively complex.

[0006] 3. Manual or mechanical removal method: If the jamming location allows personnel access, manual removal can be carried out under or around the shield, or small excavators, pneumatic drills, or other machinery can be used for clearing. This method is labor-intensive, inefficient, and poses significant safety risks in areas with frequent rock bursts or unstable rock formations.

[0007] 4. Chemical expanding agent method: A chemical expanding agent is injected into the borehole, and the pressure generated by its expansion upon contact with water is used to break the rock. This method is vibration-free and noise-free, with little environmental impact, but the breaking efficiency is relatively low, the cost is high, and the effect on dense and hard rocks is limited. It also takes a long time to deal with large-scale jamming problems.

[0008] 5. Loosening Blasting Method: Drill holes around the jammed area, insert a small amount of explosives for micro-blasting to loosen or break the rock in the jammed area, and then clear it. This method is relatively efficient, but the biggest challenge lies in the precise control of the amount of explosives. Too little explosives will not effectively loosen or break the rock, failing to achieve the goal of freeing the machine; too much explosives may damage the TBM shield structure, or even trigger more serious rock bursts or induce surrounding rock instability, bringing unpredictable risks. Especially under conditions of deep buried hard rock, the rock mechanics under high ground stress is complex, and the blasting effect is difficult to predict accurately.

[0009] The aforementioned existing technologies each have their limitations. In particular, how to safely, efficiently, and accurately carry out blasting to free a trapped TBM in the complex working conditions of a deeply buried hard rock is a technical problem that urgently needs to be solved.

[0010] While existing technologies have attempted to utilize numerical simulation to assist blasting design, they often focus on simulating the blasting process itself or optimizing the blasting network. They rarely integrate numerical simulation with the specific working condition of TBM jamming, particularly using simulation results to invert or equivalently determine the blasting load (i.e., explosive charge) that is difficult to measure precisely in actual engineering. Furthermore, for blocky or plate-cracked structures in the surrounding rock after rockburst, drilling is highly susceptible to jamming and borehole collapse. Existing technologies lack targeted, simple, and effective solutions, directly impacting the construction quality and blasting effect of the blast holes.

[0011] Therefore, there is an urgent need to develop a new method that can accurately calculate blasting parameters, effectively solve drilling problems, and ensure the safe escape of TBMs. This invention addresses the shortcomings of existing technologies by proposing a method for escaping stuck TBMs in hard rock deep-buried tunnels based on three-dimensional finite difference numerical simulation, aiming to improve the safety, reliability, and efficiency of escape operations. Summary of the Invention

[0012] The purpose of this invention is to address the shortcomings of existing technologies by proposing a method for freeing stuck TBMs in deep-buried hard rock tunnels based on three-dimensional finite difference numerical simulation. The main technical problem to be solved is: how to provide a method for accurately determining the amount of explosives required for micro-blasting, effectively preventing borehole jamming and collapse during drilling, and ensuring the safe freeing of the TBM in situations where TBMs in deep-buried hard rock tunnels are stuck due to minor or moderate rock bursts. This overcomes the shortcomings of existing technologies, such as difficulty in controlling blasting parameters, drilling difficulties, low freeing efficiency, and high risks.

[0013] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: a method for escaping a stuck TBM in a deep-buried tunnel in hard rock based on three-dimensional finite difference numerical simulation, comprising the following steps: Step 1: Assess the TBM jamming status, determine the location of the rock burst and the rock mass fracturing condition, and obtain the TBM shield size and surrounding geological parameters; Step 2: Based on the parameter data in Step 1, establish a TBM shield model and perform a three-dimensional finite difference numerical simulation of the post-rockburst state. Step 3: Set the blasting target and virtually arrange blasting holes in the TBM shield model. Set the equivalent load as the triangular pulse pressure acting on the blasting hole wall. Use the equivalent load method to calculate the blasting parameters and the amount of explosives. Step 4: Drill a hole using a drill rod with a PVC pipe. After drilling, leave the PVC pipe inside the hole, load explosives and detonate them. After cleaning up the rock fragments and rock powder from the rockburst, the TBM jamming condition is released. Further, Step 1 specifically includes: Step 101: Monitor the magnitude and changes in jamming resistance using the TBM's own sensors (such as thrust sensors and torque sensors) to initially determine the severity of the jamming.

[0014] Step 102: Simultaneously, organize geological engineers and safety personnel to enter the site (provided safety is ensured) to conduct a detailed investigation of the surrounding rock conditions in the jamming area. Record the extent of the rock burst, the size and shape of the rock fragments (whether they are clastic, massive, or plate-cracked structures), the accumulation, the degree of loosening and stability of the surrounding rock, etc.

[0015] Step 103: Record the extent of the rock burst, the size and shape of the rock fragments (whether they are clastic, massive, or plate-like), their accumulation, and the degree of loosening and stability of the surrounding rock. Further investigate the development of fractures and the extent of the loosened zone within the surrounding rock using non-destructive testing methods such as ground-penetrating radar and acoustic wave testing.

[0016] Further, step 102 specifically includes: Step 102: Obtain key geomechanical parameters of the surrounding rock in the Kaji area. These parameters form the basis for subsequent numerical simulations and directly affect the accuracy of the simulation results. They mainly include: rock physical and mechanical parameters: density, elastic modulus, Poisson's ratio, uniaxial compressive strength (UCS), tensile strength, cohesion (c), internal friction angle (φ), and elastic strain energy indices (such as storage index). These parameters can be obtained through indoor rock mechanics tests (such as uniaxial compression tests, triaxial compression tests, Brazilian splitting tests, etc.) and corrected based on field core observations and experience.

[0017] Furthermore, the geostress parameters: horizontal principal stress (σ H σ h ) and vertical principal stress (σ v The magnitude and direction of rock bursts. Ground stress is the fundamental cause of rock bursts and a key factor affecting blasting effectiveness. Ground stress data can be obtained through on-site ground stress testing or estimated based on regional geological data, burial depth, and the weight of overlying strata. Surrounding rock structural characteristic parameters include: the degree of development, occurrence, spacing, and filling of joints and fissures.

[0018] Furthermore, the above parameters can be obtained through geological logging, core observation, and geophysical exploration to more realistically reflect the mechanical properties of the surrounding rock in the numerical model. TBM shield structural parameters include the shield's external dimensions, thickness, and material properties (elastic modulus, Poisson's ratio, etc.). These parameters are used to establish an accurate TBM shield model in the numerical model.

[0019] Furthermore, step 2 specifically includes: Step 201: Based on the jamming status and geological parameters obtained in Step 1, use FLAC3D three-dimensional finite difference numerical simulation software to establish a refined three-dimensional model that can reflect the actual geomechanical conditions of the jamming area. Step 202: Determining the Model Scope: The model should be large enough to encompass the TBM shield and the surrounding rock area potentially affected by the blasting. Typically, the model's length along the TBM axis (tunneling direction) should cover a certain range before and after the shield (extending 3-5 times the shield diameter both front and back), and its radial width (perpendicular to the tunneling direction) should also cover a sufficiently large area around the shield (extending 3-5 times the shield diameter outwards) to ensure that boundary effects do not affect the main analysis area. The top and bottom boundaries of the model should exceed the main stress influence range.

[0020] Step 203: Model Meshing: Mesh the model using primarily hexahedral elements. Refine the mesh in the TBM shield and surrounding area to be blasted to improve computational accuracy; in areas far from this zone, the mesh size can be appropriately widened to reduce computational load. Ensure good mesh matching between the TBM shield model and the surrounding rock model.

[0021] Step 204: Selection of Constitutive Model: Based on the brittleness of the rock and the characteristics of rockburst, select a suitable constitutive model. For brittle hard rock, the Mohr-Coulomb elastoplastic model can be considered, taking into account the material's strain softening or damage characteristics to more realistically simulate the surrounding rock mechanical behavior after a rockburst. TBM shields typically use a linear elastic model.

[0022] Step 205: Boundary Condition Setting: The lateral boundaries of the model are typically subject to a boundary condition with zero velocity in the horizontal direction (i.e., normal displacement constraint) to simulate the lateral confinement effect of an infinite domain. The bottom boundary of the model is subject to a boundary condition with zero velocity in the vertical direction. The top boundary of the model is subject to a stress boundary condition based on the actual situation, usually by applying the actual measured or estimated geostress field to this boundary.

[0023] Step 206: Applying the initial stress field: The acquired geostress parameters (magnitude and direction of principal stresses) are applied to the model to generate the initial geostress field. This is crucial for simulating rock mass behavior under high geostress conditions.

[0024] Step 207: TBM Shield Model Creation: Accurately create a three-dimensional geometric model of the TBM shield in the model and assign it corresponding material properties.

[0025] Step 208: Simulation of Surrounding Rock Condition After Rockburst: In the model, based on the results of the on-site investigation, the areas that have already scabbed over after the rockburst are simulated. The loosened areas and scabbed rock blocks after the rockburst can be simulated by pre-setting a certain range of damaged or partially removed elements in the model. For areas exhibiting blocky or plate-cracked structures, corresponding joints or weak surfaces can be pre-set in the model.

[0026] Furthermore, if the ground stress data is incomplete, gravity loading can also be used, but it needs to be adjusted in conjunction with the lateral pressure coefficient.

[0027] Furthermore, step 3 specifically includes: This step is one of the core innovations of this invention. Since it is neither feasible nor safe to conduct blasting tests directly at the jamming location to determine the optimal explosive quantity in actual engineering, this invention proposes using a numerical simulation-based equivalent load method to back-calculate or determine the required explosive quantity.

[0028] Step 301, Set the blasting target: Define the main target of the blasting, namely, loosen or break the rock mass (especially the stuck rock blocks) within a certain range around the TBM shield to create a clearable space, while ensuring that the damage to the TBM shield is minimized.

[0029] Step 302, Equivalent Load Concept: In FLAC3D, directly simulating the complex physical processes of explosive explosions (detonation, shock wave, stress wave propagation) involves a large amount of computation and a complex model. This invention uses the equivalent load method to simplify the dynamic stress effect generated by the explosion into an equivalent dynamic load (stress or pressure time history curve) acting on a specific location (simulated blast hole wall).

[0030] Step 303: Simulated blasting hole layout: In the numerical model, blasting holes are virtually arranged based on the jamming area and rockburst distribution determined by the field survey. The location, number, depth, inclination angle, and spacing of the holes are determined. The blasting holes will be placed in the close contact area between the shield and the jammed rock, as well as in areas where loosening is expected to provide space for escape. The hole depth should ensure that the blasting action can affect the root of the jammed rock or the deep part of the loosened zone.

[0031] Step 304: Apply equivalent load and perform simulation: Apply the initially set equivalent dynamic load to the blast hole wall in the model. Run the FLAC3D simulation, observe the calculation results, and pay special attention to the following: a) Stress distribution and stress concentration in the surrounding rock under blasting load.

[0032] b) Displacement field and deformation of the surrounding rock.

[0033] c) Whether new cracks are generated inside the surrounding rock, and the extent and pattern of crack propagation.

[0034] d) Stress, strain and displacement experienced by the TBM shield.

[0035] Step 305, Parameter Adjustment and Iteration: Based on the comparison between the simulation results and the blasting target, adjust the parameters of the equivalent load (such as peak pressure, pressurization time, duration, and range of action), or adjust the layout parameters of the blasting holes (such as hole spacing and hole depth), and then rerun the simulation. Repeat this process until the simulation results show that the surrounding rock has reached the expected loosening or micro-crack state within the desired blasting influence range. The maximum stress borne by the TBM shield is lower than the yield strength of its material, and the maximum deformation is within the safe allowable range, ensuring the safety of the shield structure.

[0036] Step 306: Determine equivalent load parameters: Through the above iterative process, the equivalent load parameters that can achieve the goal of getting out of trouble and ensure the safety of the TBM are finally determined.

[0037] Step 307: Back-calculate the actual explosive usage: This step is crucial in connecting numerical simulation with actual engineering. It requires establishing a quantitative relationship between the equivalent load and the actual explosive usage. This is typically based on empirical formulas, similarity theories, or simplified theoretical models used in blasting engineering. Referencing the empirical formulas for unit explosive usage in rock blasting from the standard "Blasting Safety Regulations" or relevant literature, and considering rock properties and blasting hole parameters (hole diameter, hole depth, minimum resistance line, hole spacing, etc.), the calculation is performed. By adjusting the intensity of the equivalent load to ensure the simulation results meet the requirements, this adjusted equivalent load intensity is used as a basis, combined with the actual hole network parameters, to finally calculate the amount of explosive required for each blasting hole.

[0038] Furthermore, the propagation process of the detonation wave is extremely complex. To determine the maximum equivalent borehole wall pressure formed by the explosive explosion, this study employs the Gaussian function method proposed by Henrych et al. This method simplifies the calculation of the instantaneous peak pressure of a cylindrical explosive charge explosion based on the ideal gas law. The expression for the equivalent peak pressure acting on the borehole wall is as follows: In the formula, P b The pressure at the borehole wall is Pa. ρ e Density of explosive, kg / m³ 3 ; V d The propagation speed of the detonation wave is expressed in m / s; d c The diameter of the propellant charge; d h The diameter of the borehole; γ The average adiabatic index of the explosion gas expansion.

[0039] On the other hand, the blasting pressure acting on the borehole wall exhibits a dynamic decay characteristic over time, rather than being a constant value. To accurately simulate this dynamic decay process, this invention uses an exponential decay time history function to equivalently characterize the borehole wall pressure change law, the general mathematical expression of which is as follows: In the formula, P t The equivalent borehole wall pressure is expressed in Pa. δ S is the attenuation coefficient. -1 ; t For time, s.

[0040] Furthermore, in view of the blocky or plate-cracked structure of the surrounding rock after a rockburst, which makes it easy for the borehole to get stuck or collapse during drilling, this invention proposes to use PVC pipes with threaded and slotted designs as a borehole wall protection measure.

[0041] PVC Pipe Selection and Design: Further, material selection: Choose PVC pipes with sufficient strength, pressure resistance, and bending resistance, while also possessing a certain degree of flexibility. The pipe wall thickness needs to be calculated and selected based on the expected borehole pressure and surrounding rock conditions. It must be able to withstand the pressure of borehole wall collapse without being too heavy and affecting drilling efficiency. High-density, engineering-grade PVC pipes are typically selected.

[0042] Threaded Design: The PVC pipe uses an external thread design. During drilling, the PVC pipe sections with external threads are sequentially screwed onto the front end of the drill rod or a special connector. As the drilling depth increases, the PVC pipe is continuously extended to ensure it fits tightly against the hole wall. The threaded connection must ensure sufficient connection strength and sealing to withstand the axial tensile force and torque transmission during drilling. The thread design should facilitate quick connection and disassembly.

[0043] Grooving design: Grooving involves creating a certain number, shape, and size of grooves on the outer wall of a PVC pipe. The main purposes of grooving are twofold: 1. Allowing rock powder to be discharged: A large amount of rock powder will be generated during the drilling of blasting holes. The slotting provides a channel for the rock powder to be discharged out of the hole, avoiding the rock powder from clogging the bottom of the hole and affecting the continued drilling.

[0044] 2. Controlling the Direction of Blasting Load: During blasting, the gas and stress waves generated by the explosion propagate outwards from the borehole wall. The presence of slots alters the continuity of the borehole wall, reducing stress concentration near the slot openings while maintaining relatively high stress concentration in the pipe wall region between slots. This helps guide the blast energy to act more concentratedly in the inter-slot region, i.e., the part closer to the actual rock borehole wall, thereby improving the effective utilization rate of blasting energy and potentially controlling the initial direction of crack propagation to some extent, making it more inclined to develop into the rock mass rather than along the interface between the PVC pipe and the rock wall.

[0045] The shape, spacing, and depth of the grooves are as follows: The shape of the grooves can be straight, curved, or wavy; the spacing of the grooves should be reasonably set according to the diameter of the PVC pipe and the diameter of the drill hole, so as to ensure sufficient powder discharge channels and sufficient support strength of the pipe wall; the depth of the grooves should reach a certain proportion of the pipe wall thickness (such as 1 / 3 to 1 / 2) to ensure the powder discharge effect, but should not be too deep so as to affect the overall strength of the pipe.

[0046] Drilling Implementation: Based on the blasting hole layout plan determined in step 3, drill holes using a suitable drilling machine (such as a handheld rock drill, a TBM-equipped drilling machine with guide rails, etc.).

[0047] At the start of drilling, first lower the drill rod with the PVC pipe fitting (usually the end that connects to the drill pipe) into the hole. When the drill has penetrated 85-90% of the PVC pipe length, stop drilling, remove the drill rod from the drilling rig, and then screw on the next PVC pipe section with external threads, ensuring a secure connection. Lower the connected drill rod and PVC pipe together into the hole and continue drilling. Repeat this process until the designed drilling depth is reached.

[0048] During drilling, maintain appropriate drilling parameters (rotation speed, impact frequency, thrust) and pay attention to the dust removal. Due to the grooved design of the PVC pipe, the rock dust should be able to be discharged smoothly.

[0049] After drilling is completed, the PVC pipe is kept inside the hole as a channel for subsequent charging and detonation, and also plays a continuous protective role in preventing the hole wall from collapsing during charging and waiting for detonation.

[0050] Furthermore, the specific process of loading and detonating the explosives includes: Charge Preparation: Based on the calculated precise amount of explosive, select the appropriate type of explosive (such as emulsion explosives, water-gel explosives, etc., considering their water resistance, detonation velocity, and yield) and charge structure (such as coupled charges or differential charges). Carefully load the calculated explosive into the drilled hole with a PVC pipe. Usually, use a tamping rod to gently compact the charge, ensuring it is tightly packed. A certain length of detonating cord or detonator can be left at the hole opening for initiation.

[0051] Plugging: Appropriate plugging is applied between the top of the explosive charge and the orifice, according to the blasting design requirements, to improve blasting effectiveness and safety. The slotted design of the PVC pipe may also aid in securing the plugging material here.

[0052] Detonation: A reliable detonation network shall be used, and detonation shall be carried out in accordance with the designed detonation sequence (such as simultaneous detonation or micro-delay detonation). Before detonation, it must be ensured that TBM operators and related personnel have been evacuated to a safe area and warning signs shall be set up.

[0053] Ventilation and Inspection: After blasting, wait for the prescribed ventilation time to remove the blasting fumes. Then, a safety inspection should be conducted by professionals to confirm that there are no residual explosives and no dangerous rock fragments suspended in the air before proceeding to the next step.

[0054] Cleanup: Use high-pressure water guns, small excavators, or manual labor to remove loosened rock fragments and rock dust from the blasting. Pay special attention to clearing obstructions around and under the TBM shield. Handle with care during the cleanup process to avoid causing secondary damage to the TBM equipment. Continue cleanup until there is sufficient space around the TBM shield and the jamming is completely released.

[0055] Furthermore, after the jam is cleared, the TBM resumes tunneling and implements the following measures: Attempt to start: After clearing, attempt to start the TBM propulsion system and observe whether it can move forward normally.

[0056] Monitoring: After the TBM resumes tunneling, intensify monitoring of its thrust, torque, vibration, and other parameters, as well as observation of the surrounding rock stability. If any abnormalities are detected, tunneling should be stopped immediately for analysis and handling.

[0057] Subsequent support: Depending on the rockburst situation and the stability of the surrounding rock, it may be necessary to strengthen the initial support or advanced support measures in the area after the TBM is freed, such as increasing the anchor bolts, the thickness of the shotcrete, and setting up advanced small guide pipes, to prevent rockbursts from causing the machine to get stuck again.

[0058] Adjusting tunneling parameters: Based on the cause of the machine jam and the process of getting out of trouble, it may be necessary to adjust the subsequent TBM tunneling parameters, such as reducing the advance speed, reducing the cutterhead pressure, and strengthening advanced geological forecasting, in order to adapt to the current geological conditions.

[0059] Compared with the prior art, the present invention has the following advantages and beneficial effects: 1. Precise control of blasting parameters: This invention uses FLAC3D three-dimensional finite difference numerical simulation and equivalent load method to more scientifically and accurately calculate or determine the amount of explosives required to release the stuck machine, avoiding the uncertainty brought about by traditional empirical methods or test blasting methods, greatly reducing the risk of damage to the TBM shield due to improper explosive quantity, and improving the safety of the escape operation.

[0060] 2. Improved extrication efficiency: Precise blasting parameters and reasonable hole mesh layout ensure that blasting energy can effectively act on the stuck rock mass, quickly forming a clearable space, shortening the extrication time and reducing downtime losses.

[0061] 3. Effectively solves drilling challenges: Using threaded and slotted PVC pipes as borehole casing effectively prevents common problems such as stuck holes and hole collapses when drilling in blocky or cracked rock formations, ensuring drilling quality and efficiency and laying the foundation for subsequent blasting. Considers surrounding rock stability: Numerical simulations can predict the impact of blasting on surrounding rock stability, allowing for the selection of blasting schemes that both extricate trapped materials and minimize disturbance to the surrounding rock. This helps maintain relative stability of the surrounding rock and reduces the risk of secondary disasters.

[0062] 4. Relatively simple operation: Compared to complex physical model tests or field test explosions, numerical simulation methods are lower in cost, shorter in cycle, and easier to adjust parameters. PVC pipe wall protection measures are also relatively simple and easy to implement, making them easy to promote on construction sites.

[0063] 5. Strong adaptability: The method of this invention is applicable to TBM jamming conditions in deep-buried hard rock with different scales and jamming degrees, and has strong adaptability and universality. Attached Figure Description

[0064] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0065] Figure 1 A schematic diagram of a PVC pipe structure with threaded and slotted designs; Figure 2 This is a schematic diagram of the cross-section of the TBM truck tunnel; Figure 3 The equivalent load time history curve of the borehole wall during the drilling and blasting process in the equivalent load method; Figure 4 This is a schematic diagram showing the distribution of micro-blasting boreholes in a TBM (Turbine Machine Tool) system. Figure 5 Top view of the micro-blasting borehole of the TBM blasting machine; Figure 6 This is a front view of the FLAC3d model of the TBM micro-explosive machine; Figure 7 This is a schematic diagram of the FLAC3d model of the TBM card machine micro-explosion.

[0066] In the diagram, 1-drill rod; 2-PVC pipe; 3-PVC pipe external thread; 4-PVC pipe groove; 5-drill bit; 6-TBM shield; 7-fractured surrounding rock; 8-fractured surrounding rock boundary; 9-surrounding rock; 10-blast hole; 11-circle at the center of the blast hole; 12-main crack around the blast hole; 13-secondary crack around the blast hole; 14-time axis; 15-equivalent borehole wall pressure; 16-excavated tunnel. Detailed Implementation

[0067] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

[0068] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicating orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0069] This invention provides a method for freeing a stuck TBM (Tunnel Boring Machine) in hard rock deep-buried tunnels based on three-dimensional finite difference numerical simulation. To make the technical solution of this invention clearer, specific embodiments are described in detail below. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0070] Example: TBM jamming escape in a deep-buried water conveyance tunnel Project Background: A deep-buried water conveyance tunnel, approximately 800 meters deep, is located in a section of granite with a uniaxial compressive strength of about 120 MPa. The tunnel exhibits significant brittleness and high ground stress. During tunneling, the TBM encountered a moderate rockburst, causing a large amount of rock to flake off and accumulate around the shield, hindering TBM advance. The thrust sensor readings indicated that the resistance reached over 80% of the design maximum, indicating a machine jam.

[0071] The method of the present invention specifically includes the following steps: Step 1: Machine status assessment and geological parameter acquisition On-site investigation revealed that, Figure 2 As shown, rockbursts mainly occurred near the sidewalls and crown of TBM shield 6. The detached fragmented surrounding rock 7 was mostly plate-like, with a maximum size of approximately 50cm × 30cm. Some rock fragments were stuck between TBM shield 6 and the boundary 8 of the fragmented surrounding rock. Ground-penetrating radar detection showed that the rock mass within a 1-1.5 meter radius around TBM shield 6 was relatively fragmented, with a loose zone present.

[0072] Geological parameters obtained: Granite density 2650 kg / m³ 3 Elastic modulus 40 GPa, Poisson's ratio 0.25, UCS = 120 MPa, tensile strength 10 MPa, cohesion c = 5 MPa, internal friction angle φ = 45°. Ground stress test results: Vertical principal stress... σv =20 MPa, horizontal principal stress σ H =18.5 MPa σ h =16.5 MPa, with the direction of the maximum principal stress approximately horizontal.

[0073] The TBM shield has an outer diameter of 8.5 m and a thickness of 0.3 m. It is made of steel with an elastic modulus of 210 GPa and a Poisson's ratio of 0.3.

[0074] Step 2: Establish a three-dimensional finite difference numerical model The model was built using FLAC3D (Fast Lagrangian Analysis of Continua in 3 Dimensions). Model dimensions: 25 m axial length and 30 m radial width (covering the shield and a sufficiently large surrounding area). Mesh generation: The mesh was fined within 2 m of the shield and surrounding area, with a cell size of approximately 0.1 m; the cell size gradually increased to 0.5 m in the outer area, generating approximately 200,000 cells in total.

[0075] Material model: The surrounding rock adopts the Mohr-Coulomb elastoplastic model, with an elastic modulus of 55 GPa, Poisson's ratio of 0.27, cohesion of 25 MPa, internal friction angle of 48°, and tensile strength of 4.20 MPa. The TBM shield adopts the linear elastic model.

[0076] Boundary conditions: Apply normal velocity constraints to the sides and bottom, and apply ground stress boundary conditions to the top.

[0077] Initial stress field: The measured geostress field applied.

[0078] TBM shield model: A shield model with a diameter of 8.5 m and a thickness of 0.3 m was accurately constructed.

[0079] Post-rockburst state simulation: In the TBM shield model, some units within a range of 1-1.5 m around the shield are pre-set to a damaged state to simulate the loosened area after a rockburst.

[0080] Step 3: Calculate blasting parameters using the equivalent load method. Explosion target: Loosen the rock mass within 1 m around the shield to create a clearable space of at least 0.5 m thickness, ensuring that the TBM can push through smoothly; the maximum stress of the TBM shield is lower than the yield strength, and the maximum deformation is less than 5 mm.

[0081] Blasting hole layout: Blasting holes are virtually arranged in the TBM shield model. Considering that rockbursts mainly occur on the sidewalls and crown, such as... Figure 4As shown, circle 11 is used to determine the center position of the blasting holes, and blasting holes 10 are arranged near the sidewalls and dome of the shield. A total of 8 holes are arranged, with a depth of 1.0 m, a diameter of 42 mm, and the hole openings are about 0.5 m away from the shield surface.

[0082] Equivalent load application and simulation: The initial equivalent load is set as a triangular pulse pressure acting on the borehole wall. The time history curve of the equivalent load on the borehole wall during the drilling and blasting process is as follows: Figure 3 As shown, the horizontal axis represents time, and the vertical axis represents the equivalent borehole wall pressure. The peak pressure is 50 MPa, the pressure rise time is 0.1 ms, and the duration is 2 ms. This load is applied to the corresponding location in the TBM shield model.

[0083] Simulation results analysis: such as Figure 6 and Figure 7 As shown, running FLAC3D reveals that within the blasting influence range, the surrounding rock stress is somewhat released, and some elements enter a plastic state or develop microcracks (such as...). Figure 5 As shown, the loosening effect was achieved, including the main crack 12 and secondary crack 13 around the blast hole. However, in the area where the shield is in close contact with the rock wall of the excavated tunnel 16, the stress concentration is more severe, with the maximum stress of the shield reaching 280 MPa, close to the yield strength; the maximum deformation is about 4 mm, close to the safety limit. Parameter adjustment and iteration: In order to reduce the impact on the shield while ensuring the loosening effect, it was decided to reduce the peak value of the equivalent load to 40 MPa and slightly reduce the range of action to be closer to the rock wall of the excavated tunnel 16. After resimulation, the results showed that the maximum stress of the shield was reduced to 250 MPa and the deformation was reduced to 3 mm, which met the safety requirements; the loosening effect of the surrounding rock was slightly weakened, but still within the acceptable range. Determination of equivalent load parameters: Finally, the equivalent load was determined to be a triangular pulse pressure with a peak value of 40 MPa, a pressure rise time of 0.1 ms, and a duration of 2 ms, acting on a virtual hole wall about 5 mm away from the rock hole wall.

[0084] Calculating the actual explosive dosage: Referring to empirical formulas and considering the characteristics of high rock strength and shallow hole depth, a preliminary unit explosive dosage of 0.15 kg / m³ is selected. 3 Emulsion explosive cartridges with a diameter of 32 mm are selected, with a single cartridge weighing approximately 0.2 kg. Therefore, 0.75 cartridges can be loaded into each hole to meet the requirements.

[0085] Step 4: Special Drilling and Wall Protection Measures PVC pipe selection and design: such as Figure 1 As shown, the outer side of drill pipe 1 is made of high-density PVC pipe 2 with an outer diameter of 50 mm, an inner diameter of 40 mm, and a wall thickness of 5 mm, which meets the requirements for strength and flexibility.

[0086] PVC pipe 2 features an internal and external thread design. The external thread 3 is used to connect to the drill rod or a special connector, while the internal thread is used to connect to the next PVC pipe segment. Standard pipe threads should be selected.

[0087] Three longitudinal straight PVC pipe grooves 4 are made on the outer wall of the PVC pipe, each groove being 15 mm wide and evenly spaced. The grooves are oriented towards the drill bit 5, consistent with the drilling direction.

[0088] The total length of PVC pipe 2 is determined based on the drilling depth. If the hole depth exceeds the length of a single PVC pipe, multiple PVC pipe sections may need to be connected by threads.

[0089] Drilling implementation: Drilling is performed using a rock drill with guide rails that comes with the TBM. At the start of drilling, the first PVC pipe with a PVC fitting (external thread end) is connected to the drill rod and lowered into the borehole.

[0090] After drilling 0.8 m, stop drilling and remove drill rod 1 from the drilling rig. Then, connect the second PVC pipe to the external thread of the first PVC pipe using its internal thread, ensuring a tight connection. Lower the connected drill rod and PVC pipe into the hole as a whole and continue drilling to the remaining depth.

[0091] During drilling, maintain an appropriate rotation speed and impact frequency, and pay attention to powder removal. Due to the grooved design of the PVC pipe, rock powder can be discharged from the groove opening, making drilling relatively smooth, without any jamming or serious hole collapse.

[0092] After drilling is completed, the PVC pipe remains inside the hole, providing good wall protection.

[0093] Step 5: Loading, Detonation, and Cleanup Loading: Carefully load 0.75 rolls of emulsion explosive into the PVC pipe and gently tamp it down with a tamping rod. Leave about 10cm of detonating cord at the opening.

[0094] Blocking: Use a mixture of clay and rock powder to block a section of about 20 cm from the orifice. The grooves in the PVC pipe allow the blockage to be well fixed to the outside of the pipe.

[0095] Detonation: Connect the detonating cord network, set up a warning line, and detonate after confirming safety.

[0096] Cleanup: After the blast, ventilate for approximately 15 minutes. After confirming safety, use a high-pressure water gun in conjunction with manual labor to clean up the rock blocks and rock dust around and under the shield. During the cleanup process, it was found that most of the rock blocks had been loosened or broken, and the jamming was released.

[0097] Step Six: TBM Resumption of Tunneling and Follow-up Measures After clearing was completed, the TBM propulsion system was started, and the tunnel advanced smoothly. Geological forecasting and parameter monitoring were strengthened during subsequent tunneling, and the cutterhead pressure and propulsion speed were appropriately reduced. In the escape zone, reinforced support was implemented, such as increasing the density of anchor bolts and the thickness of shotcrete.

[0098] The entire process of getting out of the predicament, from discovering the jam to resuming tunneling, took approximately 24 hours (including assessment, simulation, drilling, blasting, and clearing), which was more efficient than the planned mechanical jacking attempt or high-pressure water jetting.

[0099] The above embodiments are used to explain and illustrate the present invention, but not to limit the present invention. Any modifications and changes made to the present invention within the spirit and scope of the claims shall fall within the protection scope of the present invention.

Claims

1. A method for escaping a stuck TBM (Tunnel Boring Machine) in hard rock deep-buried tunnels based on three-dimensional finite difference numerical simulation, characterized in that: Includes the following steps: Step 1: Assess the TBM jamming status, determine the location of the rock burst and the rock mass fracturing condition, and obtain the TBM shield size and surrounding geological parameters; Step 2: Based on the parameter data in Step 1, establish a TBM shield model and perform a three-dimensional finite difference numerical simulation of the post-rockburst state. Step 3: Set the blasting target and virtually arrange blasting holes in the TBM shield model. Set the equivalent load as the triangular pulse pressure acting on the blasting hole wall. Use the equivalent load method to calculate the blasting parameters and the amount of explosives. Step 4: Drill holes using drill rods with PVC pipes. After drilling, leave the PVC pipes in the hole, load explosives and detonate them. After cleaning up the rock fragments and rock powder after the rock burst, release the TBM jamming status.

2. The method for escaping a stuck TBM (Tunnel Boring Machine) in hard rock deep tunnels based on three-dimensional finite difference numerical simulation according to claim 1, characterized in that, Step 1 specifically includes: Step 101: When the TBM jams, stop tunneling and monitor the magnitude and changes of the jamming resistance using the TBM's own sensors to make a preliminary judgment on the severity of the jam. Step 102: At the same time, conduct a detailed on-site investigation of the surrounding rock conditions in the jamming area to determine the location of the rock burst, the degree of rock fragmentation, and the loosening and stability of the surrounding rock. Step 103: Using non-destructive testing methods, further investigate the development of fractures and the extent of loosening zones within the surrounding rock.

3. The method for escaping a stuck TBM in hard rock deep-buried tunnels based on three-dimensional finite difference numerical simulation according to claim 1, characterized in that, Step 2 specifically includes: Step 201: Using the FLAC3D three-dimensional finite difference numerical simulation software, the jamming status and geological parameters obtained in Step 1 are used to establish a refined three-dimensional model that can reflect the actual geomechanical conditions of the jamming area. Step 202, Model Scope Determination: The dimensions of the TBM shield model include the TBM shield and the surrounding rock area that may be affected by the blasting; and ensure that boundary effects do not affect the analysis area; the top and bottom boundaries of the TBM shield model should exceed the range of influence of ground stress; Step 203, Model Mesh Generation: The model is meshed using hexahedral mesh elements; and the mesh is further refined in the TBM shield and the surrounding area to be blasted, according to the required computational accuracy. Step 204, Material Constitutive Model Selection: Based on the brittleness of the rock and the characteristics of rockburst, the Mohr-Coulomb elastoplastic constitutive model is selected for hard rock, and the strain softening or damage characteristics of the material are considered. The TBM shield adopts a linear elastic model. Step 205: Boundary condition setting: Apply a boundary condition with zero velocity in the horizontal direction to the side boundary of the model to simulate the lateral confinement effect of the infinite domain; apply a boundary condition with zero velocity in the vertical direction to the bottom boundary of the model; apply an actual measured or estimated geostress field to the top boundary of the model. Step 206: Applying the initial stress field: Applying the geostress parameters to the model to generate the initial geostress field; Step 207: TBM Shield Model Creation: Accurately create a three-dimensional geometric model of the TBM shield in the model and assign it corresponding material properties; Step 208: Simulation of surrounding rock condition after rockburst: In the established TBM shield model, the area that has been spalled after the rockburst is simulated based on the field survey results; the loosened area and spalled rock blocks after the rockburst are simulated by setting a certain range of damage or removing some units in the model in advance; for areas with blocky or plate-cracked structures, the corresponding joints or weak surfaces are preset in the model.

4. The method for escaping a stuck TBM in a hard rock tunnel based on three-dimensional finite difference numerical simulation according to claim 1, characterized in that, In step 205, if the ground stress data is incomplete, gravity loading is used, and adjustments are made in conjunction with the lateral pressure coefficient.

5. The method for escaping a stuck TBM in hard rock deep-buried tunnels based on three-dimensional finite difference numerical simulation according to claim 1, characterized in that, In step 3, the equivalent load method of numerical simulation is used to back-calculate or determine the required amount of explosives, specifically including: Step 301: Set the blasting target: The blasting target is to loosen or break the rock mass that forms a blockage within a certain range around the TBM shield, creating a space that can be cleared, while ensuring that the damage to the TBM shield is minimized. Step 302, Equivalent Load Concept: In FLAC3D, the dynamic stress effect generated by the explosion is simplified into an equivalent dynamic load acting on the simulated blast hole wall, and stress or pressure time history curves are established. Step 303, Simulated blasting hole layout: In the numerical model, based on the jamming area and rockburst distribution determined by the field survey, blasting holes are virtually arranged in the close contact area between the shield and the jammed rock block, as well as in the area where it is expected to need to be loosened to provide space for escape; the hole depth should be sufficient to ensure that the blasting action can affect the root of the jammed rock block or the deep part of the loosening zone. Step 304: Apply equivalent load and perform simulation: Apply the initially set equivalent dynamic load to the blast hole wall in the model; run the FLAC3D simulation, observe the calculation results, and pay special attention to the following: a) Stress distribution and stress concentration in the surrounding rock under blasting load; b) Displacement field and deformation of the surrounding rock; c) Whether new cracks are generated inside the surrounding rock, and the extent and pattern of crack propagation; d) The stress, strain, and displacement experienced by the TBM shield; Step 305, Parameter Adjustment and Iteration: Based on the comparison between the simulation results and the blasting target, adjust the parameters of the equivalent load or the arrangement parameters of the blasting holes, and then rerun the simulation; repeat this process until the simulation results show that the surrounding rock has reached the expected loosening or micro-crack state within the expected blasting influence range. Step 306: Determine equivalent load parameters: Through the iterative process in step 305, the equivalent load parameters that can achieve the goal of getting out of trouble and ensure the safety of the TBM are finally determined. Step 307: Back-calculate the actual explosive usage: Based on empirical formulas, similarity theories, or simplified theoretical models for blasting engineering, and combined with rock properties and blast hole parameters, establish a quantitative relationship between the equivalent load and the actual explosive usage; by adjusting the strength of the equivalent load to ensure that the simulation results meet the requirements, and then using the adjusted equivalent load strength as a basis, combined with the actual hole network parameters, finally calculate the amount of explosive required to be loaded into each blast hole.

6. The method for escaping a stuck TBM in hard rock deep-buried tunnels based on three-dimensional finite difference numerical simulation according to claim 5, characterized in that, In step 302, the Gaussian function method is used to simplify the calculation of the instantaneous peak pressure of the cylindrical explosive charge explosion based on the ideal gas law. The equivalent peak pressure acting on the borehole wall is expressed as follows: In the formula, P b The pressure at the borehole wall is Pa. ρ e Density of explosive, kg / m³ 3 ; V d The propagation speed of the detonation wave is expressed in m / s; d c The diameter of the propellant charge; d h The diameter of the borehole; γ The average adiabatic index of the explosion gas expansion; On the other hand, the blasting pressure acting on the borehole wall exhibits a dynamic decay characteristic over time, rather than being a constant value. To accurately simulate this dynamic decay process, an exponential decay time history function is used to equivalently characterize the borehole wall pressure change law, and its mathematical expression is as follows: In the formula, P t The equivalent borehole wall pressure is expressed in Pa. δ S is the attenuation coefficient. -1 ; t For time, s.

7. A method for escaping a stuck TBM in a deep-buried tunnel in hard rock based on three-dimensional finite difference numerical simulation, as described in claim 1, is characterized in that... In step 4, for the blocky or plate-cracked structure of the surrounding rock after a rockburst, PVC pipes with threaded and slotted designs are used as borehole wall protection measures. The drilling process specifically includes: PVC pipe selection and design: Material selection: Select PVC pipes that meet the requirements of strength, pressure resistance, bending resistance, and flexibility; the pipe wall thickness is selected based on the expected pressure inside the borehole and the surrounding rock conditions. Threaded design: The PVC pipe adopts an external thread design. During drilling, the PVC pipe sections with external threads are screwed sequentially onto the front end of the drill rod or a special connector. As the drilling depth increases, the PVC pipe is continuously extended to make it fit tightly against the hole wall. Grooving design: A certain number, shape and size of grooves are opened on the outer wall of the PVC pipe to discharge rock powder and change the continuity of the hole wall, reduce stress concentration near the groove opening, increase stress concentration in the pipe wall area between grooves, control the initial propagation direction of cracks, and make them more inclined to develop into the rock mass. The groove shape, spacing, and depth are as follows: The groove can be straight, curved, or wavy; the groove spacing is set according to the PVC pipe diameter and the drilling diameter to ensure sufficient powder discharge channels while meeting the requirements of pipe wall support strength; the groove depth is 1 / 3 to 1 / 2 of the pipe wall thickness. Drilling implementation: Based on the blast hole layout plan determined in step 3, select a drilling rig to perform drilling; When drilling begins, first lower the drill rod with the PVC pipe fitting into the hole. When the drill rod has reached 85-90% of the length of the PVC pipe, stop drilling, remove the drill rod from the drilling machine, and then screw on a PVC pipe section with external threads, ensuring a secure connection. Lower the connected drill rod and PVC pipe into the hole together and continue drilling. Repeat this process until the designed drilling depth is reached. During drilling, maintain the required drilling parameters and remove drilling dust. After drilling is completed, the PVC pipe is kept inside the hole as a channel for subsequent charging and detonation, and also as a wall protection measure to prevent the hole wall from collapsing during charging and waiting for detonation.

8. The method for escaping a stuck TBM in a hard rock tunnel based on three-dimensional finite difference numerical simulation according to claim 1, characterized in that, The specific process of loading and detonating the explosives in step 4 includes: Loading: Based on the amount of explosives, select the appropriate type of explosives and loading structure, load them into the drill hole with the PVC pipe, and tamp them down. Blocking: According to the blasting design requirements, the blockage is performed between the top of the charge and the orifice to improve the blasting effect and safety, and the blockage material is fixed based on the groove of the PVC pipe; Initiation: Initiation is carried out using an initiation network according to the designed initiation sequence; Ventilation and Inspection: After blasting, ventilation and smoke removal are carried out. Then, after completing a safety inspection and confirming that there are no residual explosives and no dangerous rock blocks hanging in the air, cleanup is carried out. Cleanup: Remove the blasted rock and rock dust, as well as any obstructions around and at the bottom of the TBM shield; avoid causing secondary damage to the TBM equipment during the cleanup process, and completely release the jammed state after the cleanup is completed.

9. A method for escaping a stuck TBM in hard rock deep-buried tunnels based on three-dimensional finite difference numerical simulation according to claim 1, characterized in that, After the machine is released from jamming, the TBM resumes tunneling and implements subsequent measures: Attempt to start: After cleaning, try starting the TBM propulsion system and observe whether it can move forward normally; Monitoring: After the TBM restarts tunneling, monitor the TBM thrust, torque and vibration parameters, as well as observe the stability of the surrounding rock; If any abnormality is detected, tunneling should be stopped immediately for analysis and handling. Subsequent support: Based on the rockburst situation and the stability of the surrounding rock, after the TBM is freed, strengthen the initial support or advanced support measures in the rockburst area to prevent rockbursts from occurring again and causing the machine to get stuck. Adjusting tunneling parameters: Based on the cause of the TBM jamming and the extrication process, it is necessary to adjust the subsequent TBM tunneling parameters to adapt to the current geological conditions.

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