Double-gate mechanism for controlling slag discharge spewing, shield tunneling machine and shield construction method

Abstract

The invention relates to a double-gate mechanism for controlling slag discharge spewing, a shield tunneling machine and a shield construction method. The method is suitable for the technical field of shield tunnel construction. The technical problem to be solved by the invention is to provide the double-gate mechanism for controlling slag discharge spewing, the shield tunneling machine and the shield construction method. According to the technical scheme, the double-gate mechanism for controlling the discharged slag gushing is arranged at an outlet of a spiral conveyor, the double-gate mechanism is provided with an inner gate and an outer gate which are opposite in opening and closing direction, and the distance between the inner gate and the outer gate is K2; the double-gate mechanism is used for controlling the opening degree of the inner gate to be K1 and the opening degree of the outer gate to be K3 and K2gt when slag is discharged and spewed; k1, K3gt; k2.

Description

Technical Field

[0001] This invention relates to a double-gate mechanism for controlling slag discharge gushing, a tunnel boring machine (TBM), and a TBM construction method. It is applicable to the field of shield tunneling technology. Background Technology

[0002] In the construction of modern urban rail transit, the earth pressure balance shield tunneling method faces significant technical challenges when tunneling through highly permeable, high-pressure, and water-rich strata. Engineering practice has verified that such strata are prone to engineering risks such as screw conveyor blowouts, face over-excavation and instability, excessive surface settlement, and abnormal cutter wear. These risks are essentially due to the incompatibility between the hydrogeological characteristics of the strata and the basic principles of the earth pressure balance method.

[0003] Highly permeable, high-pressure, and water-rich strata generally exhibit typical engineering characteristics such as significant porosity, low cementation, large internal friction angle, and weak self-stabilization capacity. When shield tunnels traverse such strata, pressure balance control is required to maintain rock stability due to the lack of self-stabilization. Given the highly interconnected nature of the strata pores, a "soil plug structure" with a pressure-blocking effect cannot be formed, causing the soil pressure to act directly on the slag discharge port of the screw conveyor through pore water, easily inducing fluid gushing during slag removal operations.

[0004] During the slag removal process, a sudden release of pressurized water within the earthen chamber will cause a sharp drop in chamber pressure. At this time, the screw conveyor, due to its delayed control response, will be unable to compensate for the pressure in time, and the screw conveyor gate must be shut down urgently to implement pressure compensation. Groundwater will rapidly replenish the earthen chamber pressure system through seepage channels, causing subsequent slag removal operations to repeatedly trigger the gushing mechanism, ultimately forming a periodic gushing cycle.

[0005] When the screw conveyor is in static operation, its compartment is mainly occupied by liquid water. The filling rate of the slag and soil inside the compartment is positively correlated with the fluid pressure loss. When the filling rate of the slag and soil decreases, the gushing pressure value dominated by the soil pressure system increases accordingly.

[0006] Because the slag discharge process involves a gushing flow, the amount of slag discharged becomes difficult to control precisely, leading to a sharp drop in the pressure of the soil chamber. Under these conditions, tunnel boring machine (TBM) operators often resort to the usual practice of immediately opening and closing the gates, but the screw conveyor remains stationary during this period, preventing the slag from being effectively discharged. As the slag continues to accumulate and its density increases, a "soil chamber" phenomenon eventually forms, completely filling the soil chamber. At this point, the cutterhead opening is blocked by dense slag, preventing newly cut slag from being smoothly introduced into the soil chamber. This causes a significant increase in the TBM's total thrust and cutterhead torque, while the tunneling rate exhibits a non-linear decreasing trend. This condition directly prolongs the single-ring tunneling cycle and exacerbates the mechanical disturbance effect of the cutterhead on the excavation face. According to engineering experience, in strata with poor self-stability, when the TBM's advance speed is below 40 mm / min, the risk of over-excavation increases as the speed decreases; when it is above 40 mm / min, the risk of over-excavation decreases significantly; when the actual slag discharge volume significantly exceeds the theoretical calculation value, it may induce engineering risks such as surface subsidence or collapse. The "accumulation" phenomenon will significantly increase the compaction of the slag in the soil bin, posing a risk that the equipment will not be able to operate normally because the starting torque of the cutterhead exceeds the load limit of the drive system.

[0007] During shield tunneling construction, the high-velocity, high-pressure transport characteristics of the slag discharge cause violent splashing. Large amounts of slag are scattered haphazardly across the tunnel face, resulting in significant problems such as high labor intensity, long processing times, and high labor costs for cleanup operations. This not only significantly reduces the efficiency of shield tunneling but also exacerbates the risk of slag exceeding volume limits.

[0008] Under ultra-high propulsion loads, high torque output, and low-speed conditions, tool wear exhibits an exponential growth trend, significantly shortening the tool replacement cycle. Performing tool replacement operations in unstable strata with strong geological disturbances significantly increases potential risks, and the implementation costs of corresponding safety measures rise accordingly. Simultaneously, the continuous accumulation of soil compaction within the cutterhead chamber triggers a surge in internal stress. Coupled with the high thrust and high torque, a localized high-temperature, high-pressure field forms at the cutterhead-face contact interface. Sintering reactions occur between soil particles, forming a hardened layer, ultimately inducing the consolidation of mud cake on the cutterhead panel. Summary of the Invention

[0009] The technical problem to be solved by the present invention is to provide a double gate mechanism for controlling slag discharge, a tunnel boring machine, and a tunnel boring construction method, in view of the above-mentioned problems.

[0010] The technical solution adopted in this invention is: a double gate mechanism for controlling slag discharge and gushing, which is set at the outlet of the screw conveyor. The double gate mechanism has an inner gate and an outer gate with opposite opening and closing directions, and the distance between the inner gate and the outer gate is K2. The double gate mechanism is used to control the slag discharge and gushing. The opening degree of the inner gate is K1, and the opening degree of the outer gate is K3, with K2>K1 and K3>K2.

[0011] The double gate mechanism is used to control the slag discharge and gushing, with the outer gate opening K3 being less than or equal to half of the rated opening.

[0012] The double gate mechanism adjusts the speed of the extruded slag as it passes through the double gate mechanism based on the inner gate opening K1 and the outer gate opening K3.

[0013] The double-gate mechanism adjusts the speed of the excavated soil as it is ejected through the mechanism based on the inner gate opening K1 and the outer gate opening K3, including: V1 and V3 describe the movement speed of the slag through the inner and outer gates, respectively.

[0014] The double gate mechanism adjusts the gushing pressure of the slag when it is ejected through the double gate mechanism based on the inner gate opening K1 and the outer gate opening K3.

[0015] The double-gate mechanism adjusts the gushing pressure of the excavated soil when it is ejected through the double-gate mechanism based on the inner gate opening K1 and the outer gate opening K3, including: P1 and P3 describe the gushing pressure of the slag when it is ejected through the inner and outer gates, respectively.

[0016] A tunnel boring machine (TBM) is provided with the aforementioned double gate mechanism at the outlet of its screw conveyor.

[0017] A method for shield tunneling in high-pressure, water-rich strata based on the aforementioned shield machine, comprising: Open the outer gate and control the opening degree K3 of the outer gate to be within half of the rated stroke of the outer gate, and K3>K2; Open the inner gate, gradually increase the opening degree K1 of the inner gate within a range less than K2, and monitor the slag discharge flow rate of the outer gate in real time until the slag discharge flow rate of the outer gate reaches the preset flow rate, then stop increasing the opening degree of the inner gate.

[0018] The beneficial effects of this invention are as follows: This invention controls the slag ejection through a double gate mechanism. By precisely adjusting the opening degree K1 of the inner gate and combining it with the distance between the inner and outer gates of K2, the first pressure regulation is achieved. By precisely adjusting the opening degree K3 of the outer gate and combining it with the distance between the inner and outer gates of K2, the second pressure regulation is achieved, thereby reducing the slag ejection pressure and speed, and effectively suppressing the ejection phenomenon.

[0019] Once the gushing pressure is stably controlled below the critical value, the screw conveyor immediately enters continuous operation, and the excavated soil inside the soil chamber exhibits dynamic renewal characteristics, effectively avoiding the risk of soil accumulation. Excavated soil stripped from the tunnel face is smoothly introduced into the soil chamber space, thus establishing a virtuous cycle of dynamic excavation. Under this condition, the total thrust parameters of the tunnel boring machine and the cutterhead torque value both tend to be stable and controllable, thereby significantly improving the tunnel excavation rate. The synchronously formed excavated soil filling layer in the screw cavity, working synergistically with the rotational force, effectively blocks the pressure transmission path and reduces the risk of gushing. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the double gate mechanism in the embodiment.

[0021] Figure 2 This is a geological profile of the section in Case 1 of the embodiments.

[0022] Figure 3 This is a geological profile of the section in Case 2 of the embodiment. Detailed Implementation

[0023] The main risks of shield tunneling in highly permeable, high-pressure, and water-rich strata stem from their unfavorable geological characteristics. Although engineering measures such as grouting and additive modification can theoretically alter these geological features, practice shows that these measures significantly increase construction costs. From an economic perspective, such solutions lack widespread applicability; and in terms of actual effectiveness, it is difficult to ensure that the expected improvement goals are achieved.

[0024] It is worth noting that the initial link in the risk transmission chain of tunnel boring machine (TBM) construction is the muck ejection phenomenon, which will trigger a chain reaction of subsequent risk events. If the muck ejection can be effectively controlled, the subsequent derivative risks can be simultaneously avoided through a risk source blocking mechanism. This provides a technical path with engineering practical value for risk prevention and control in water-rich strata construction.

[0025] This embodiment is a shield tunneling method for high-pressure water-rich strata. The shield tunneling method adopts a double gate mechanism at the outlet of the screw conveyor of the shield machine, which can be used to control the slag discharge and gushing.

[0026] In this example, the double-gate mechanism has an inner gate and an outer gate arranged sequentially along the slag discharge direction. The opening and closing directions of the inner and outer gates are opposite. If the inner gate opens from left to right, the outer gate opens from right to left. The distance between the inner and outer gates is K2, forming a gate cavity between them.

[0027] When the double gate mechanism is used to control the slag discharge gushing, the opening degree of the inner gate is controlled to be K1 (expressed by the gate displacement length), and the opening degree of the outer gate is controlled to be K3 (expressed by the gate displacement length). The distance between the inner and outer gates K2 is greater than the opening degree of the inner gate K1, and the opening degree of the outer gate K3 is greater than the distance between the inner and outer gates K2. The opening degree of the outer gate K3 is controlled to be less than or equal to half of its rated opening degree.

[0028] In this embodiment, a dual-gate mechanism is used to regulate the pressure gradient, reduce pressure and speed, and control the slag discharge flow. Figure 1 As shown, the specific working principle is as follows: During the operation of the double gate mechanism, the slag and soil pass through the inner gate at a flow rate of V1 under pressure. After entering the inter-gate cavity between the inner and outer gates, the flow rate decreases to V2, and finally it is discharged through the outer gate at a flow rate of V3.

[0029] The initial pressure regulation is applied to the inner gate region. Pressure gradient control is achieved by precisely adjusting the opening of the inner gate, which requires satisfying the constraint K2>K1. When the excavated soil breaks through the inner gate and enters the double-gate cavity, due to the expansion of the flow channel cross-sectional area, according to the law of conservation of flow, we can obtain: V1×D×K1=V2×D×K2 Secondary pressure regulation is implemented in the outer gate area. When the slag flows out through the outer gate, the flow channel expands secondaryly. Under the condition that K3>K2, a secondary gradient pressure reduction is carried out. According to the continuous flow equation, we can obtain: V2×D×K2=V3×D×K3 By combining the above equations, the velocity relationship can be derived: When the excavated soil is ejected from the inner gate, the gushing pressure is determined by the dynamic pressure (P1), and the density of the excavated soil is ρ, expressed as: When the excavated soil is ejected through the outer gate, the corresponding gushing pressure (P3) can be expressed as: The above parameters are defined as follows: K1 corresponds to the opening of the inner gate; K2 represents the distance between the inner and outer gates; K3 is the opening of the outer gate; V1, V2, and V3 describe the movement speed of the slag through the inner gate, the gate cavity, and the outer gate, respectively; D refers to the width parameters of the inner and outer gates and the gate cavity in the double gate mechanism; P1 can be read at the slag discharge port of the screw conveyor.

[0030] The formula derivation leads to the conclusion that the slag discharge gushing pressure of the screw conveyor is positively correlated with the square ratio of the inner and outer gate openings. Specifically, when the inner gate opening decreases and the outer gate opening increases, the slag discharge gushing pressure decreases quadratically. When the gushing pressure drops to the critical value of 0.5 bar, the gushing phenomenon can be effectively suppressed.

[0031] The shield tunneling method for high-pressure, water-rich strata in this embodiment specifically includes: The first step is to open the outer gate and control the opening degree K3 of the outer gate to within half of the rated stroke of the outer gate. It is strictly forbidden to open it completely, and K3>K2. If the opening is too large, the slag will directly form a jet flow through the inner gate, which will not form an effective pressure reduction barrier. If the opening is too small, it will affect the balance of the system.

[0032] The second step is to open the inner gate and gradually increase its opening degree K1 within a range less than K2, while monitoring the slag discharge velocity of the outer gate in real time. Continue increasing the inner gate opening until the slag discharge velocity of the outer gate reaches the preset velocity, thus eliminating the risk of gushing. It is crucial to ensure that the difference in opening degree between the inner and outer gates remains stable within the safe threshold range. It is particularly important to emphasize that the opening sequence of the inner gate must lag behind that of the outer gate; reversing this sequence will induce gushing.

[0033] The third step, after eliminating the risk of gushing, is to start the screw conveyor in continuous operation mode. By maintaining a dynamic replacement balance of excavated soil within the soil chamber, not only can the "soil accumulation" phenomenon be effectively avoided, but the potential energy of the gushing can also be reduced by enhancing the soil plugging effect. At this time, the opening of the inner gate can be increased to optimize the tunnel boring machine's propulsion efficiency while ensuring that gushing does not occur.

[0034] Fourth, when the operation is terminated, strictly adhere to the procedure of closing the inner gate first, followed by the outer gate. During subsequent tunneling operations in ordinary strata, the outer gate can remain open, and the operation process can be simplified and optimized simply by controlling the opening and closing of the inner gate.

[0035] For controlling water inrush in high-pressure, water-rich formations, current main anti-blowout measures include twin-helix machine systems, polymer additives, and bentonite conditioners. The following will provide a systematic comparative analysis from the perspectives of construction methods, efficiency, economy, and risks.

[0036] 1) The comparison of construction methods mainly covers the following technical elements: anti-gushing mechanism, geological adaptability range, and process complexity.

[0037] Table 1 Comparison of Construction Methods method principle Applicable strata Operational complexity Dual-gate pressure gradient control By adjusting the difference in opening between the inner and outer gates, the slag discharge cross-section is expanded, and the flow velocity is controlled by gradually reducing the pressure to prevent gushing. Highly confined water-rich sand layers, gravel strata, weathered rocks Simple (only gate opening needs to be adjusted) Twin-helix machine system The twin-screw conveyors connected in series create a "soil plug effect," reducing the slag discharge pressure. Extremely high pressure water-rich strata Complex (requires equipment modification and coordination of two machines) polymer Injecting polymer materials improves the flowability of slag and reduces permeability. Highly permeable sandy strata Medium (requires continuous addition and controlled mixing) Bentonite Improvement The mixture of bentonite and slag forms a viscous mud film, reducing water and sand separation. Sandy strata lacking cohesive soil Medium (requires precise proportions and mixing time) Comparative conclusion: The dual-gate pressure gradient control method is simple in principle, widely applicable to formations, and easy to operate.

[0038] 2) The construction efficiency assessment focuses on three aspects: tunneling speed, construction continuity, and the time consumed by auxiliary procedures, forming an evaluation system. Table 2 Comparison of Construction Efficiency method tunneling speed Construction continuity Auxiliary process time Dual-gate pressure gradient control 70-90 mm / min Continuous slag removal, no need to stop the machine No (directly operate the gate) Twin-helix machine system 40-60 mm / min The slag discharge rhythm of the two machines needs to be coordinated. Equipment debugging and maintenance time polymer 50-70 mm / min Waiting for the mixing reaction time is required Additive injection and mixing time Bentonite Improvement 30-50 mm / min Insufficient mixing can easily lead to interruption. Bentonite mixing and injection time Comparative conclusion: The dual-gate pressure gradient control method has the fastest tunneling speed, the best construction continuity, and requires no additional time-consuming procedures.

[0039] 3) The economic efficiency is mainly compared from the perspectives of equipment modification costs, material consumption costs, and overall costs: Table 3 Economic Comparison method Equipment modification costs Material consumption cost Comprehensive cost Dual-gate pressure gradient control None (only requires existing dual gates) No additives required. Low (labor operation costs only) Twin-helix machine system High (Dual-machine series conversion) Low High (high proportion of equipment upgrades) polymer Low High (continuously increasing unit price) Medium (continuous consumption) Bentonite Improvement Low China (large demand for bentonite) Medium (continuous consumption) Comparative conclusion: The dual-gate pressure gradient control method has the lowest overall cost and requires no investment in materials or equipment modifications.

[0040] 4) Construction risks are mainly compared from the perspectives of gushing risk, surface subsidence risk, and equipment failure risk: Table 4 Comparison of Construction Risks method Gust risk Surface subsidence risk Equipment failure risk Dual-gate pressure gradient control Low (controllable flow rate) Low (small disturbance during continuous slag discharge) Low (no complex equipment) Twin-helix machine system (Depends on soil plug effect) (Coordinating two machines is very difficult) High (high probability of dual-machine failure) polymer Insufficient mixing leads to failure. Medium (the improvement effect is unstable) Low Bentonite Improvement High (easily diluted by groundwater) High (Easy to over-excavate) Low Comparative conclusion: The dual-gate pressure gradient control method has the lowest overall risk and effectively controls gushing and surface subsidence.

[0041] In summary, the double-gate opening difference method is superior to existing methods in terms of construction efficiency, economy, and risk control. It is especially suitable for high-pressure water-rich sand layers, gravel strata, and rock strata with well-developed fissure water, and is a solution that combines innovation and practicality.

[0042] Case 1: A section of Metro Line 2 in a certain city is approximately 430.0m long, with a tunnel depth between 9.2m and 9.6m (e.g., Figure 2 The earth pressure balance shield tunneling method was used for construction.

[0043] 1) Left-line pressure-maintaining tunneling The dual-track tunnel boring machine (TBM) employed different techniques. During the pressure-maintaining tunneling of the left track, a malfunction in the auger gate caused a blowout, leading to ground subsidence. After the left track crossed the bridge area, the settlement rate at the XDC201-1 measuring point reached 57.6 mm / d (construction team) and 60.13 mm / d (third party). After discovering underground cavities, concrete backfilling was implemented, and traffic was restored.

[0044] The gushing in the left tunnel caused severe ground damage and abnormal tunneling parameters. Low advance rate prolonged cutterhead disturbance and increased muck discharge temperature. Bentonite grouting failed to control the gushing, resulting in excessive surface settlement and abnormal cutter wear, posing a high safety risk.

[0045] Cause of the gushing: Water from the water-rich strata continuously seeps into the soil chamber, creating a high-pressure water head. When the screw conveyor is opened, the water gushing occurs. After the gushing, the strata are replenished with water, creating a cycle of "gushing-depressurization-suffocation-pressurization," which ultimately leads to multiple collapses.

[0046] 2) Right-line under-pressure tunneling During shield tunneling, while the adoption of underpressure tunneling technology reduced gushing phenomena and increased tunneling speed, poor soil stability in coarse-to-medium sand strata led to earth pressure imbalance. For example, at the 178th ring, the torque surged to 6379 kN·m while the earth pressure dropped to 0.5 bar. The construction unit suspended maintenance and discovered foam leakage in the slewing joint, as well as broken and detached bolts. After surface reinforcement and multiple repairs, tunneling resumed, delaying the project by more than two months.

[0047] Inspection revealed that the soil chamber pressure was only 0.2 bar, which was mismatched with the cover thickness, causing the soil to sink as it was pushed. The construction unit reported that the excavated soil would compact after the machine was stopped, resulting in the cutterhead facing extremely high torque when restarted. Although the torque exceeded 4000 kN·m during normal operation, it did not cause a gushing, and the excavation process was smooth, with a speed of over 60 mm / min.

[0048] Over-excavation during under-pressure tunneling is mainly caused by the poor self-stability of coarse and medium sand strata. When the soil pressure in the tunnel chamber is lower than the active earth pressure at the tunnel face, surface subsidence occurs. During shutdown, the settling of excavated soil increases the risk of equipment damage; therefore, this method is not suitable for coarse and medium sand strata.

[0049] Case 2 The tunnel boring machine (TBM) is constructing a section approximately 1030 meters long. Over 70% of the strata it needs to traverse consist of coarse to medium sand and gravel, representing highly permeable ground (e.g.,...). Figure 3 ).

[0050] The construction of this section is highly challenging. The previous section was 636m long, with 200m of it consisting of medium-coarse sand and gravel strata, which took three months to complete. Abnormal parameters, such as cutterhead torque exceeding 4000kN·m, thrust exceeding 17000kN, and speed below 30mm / min, led to severe cutter wear and frequent surface subsidence. Therefore, it is planned to replace the cutterhead five times in this section.

[0051] This section employs dual-gate pressure gradient regulation to effectively control the screw compressor's gushing flow. During tunneling, the inner gate was maintained at an opening of 10-15 cm, the cutterhead torque was kept stable at 3000 kN·m, the thrust at 9000 kN, the speed reached 80 mm / min, and the earth pressure was 1.5 bar. The tunnel was completed in 4 months. Compared to the previous section, ground disturbance and cutter wear were significantly reduced. No cutter replacements were needed throughout the entire process, and there was no uneven wear of the cutterhead. Surface settlement remained under control. Practice has proven that the dual-gate, staged pressure reduction measure effectively curbed gushing. The earth pressure balance shield tunneling machine performed exceptionally well in water-rich sandy and gravelly strata, expanding the applicable range of this model.

Claims

1. A double-gate mechanism for controlling slag discharge gushing, characterized in that, Located at the outlet of the screw conveyor, the double gate mechanism has an inner gate and an outer gate with opposite opening and closing directions, and the distance between the inner gate and the outer gate is K2; The double gate mechanism is used to control the slag discharge and gushing. The opening degree of the inner gate is K1, and the opening degree of the outer gate is K3, with K2>K1 and K3>K2.

2. The double-gate mechanism for controlling slag discharge gushing according to claim 1, characterized in that, The double gate mechanism is used to control the slag discharge and gushing, with the outer gate opening K3 being less than or equal to half of the rated opening.

3. The double-gate mechanism for controlling slag discharge gushing according to claim 1, characterized in that, The double gate mechanism adjusts the speed of the extruded slag as it passes through the double gate mechanism based on the inner gate opening K1 and the outer gate opening K3.

4. The double-gate mechanism for controlling slag discharge gushing according to claim 3, characterized in that, The double-gate mechanism adjusts the speed of the excavated soil as it is ejected through the mechanism based on the inner gate opening K1 and the outer gate opening K3, including: V3= V1 and V3 describe the movement speed of the slag through the inner and outer gates, respectively.

5. The double-gate mechanism for controlling slag discharge gushing according to claim 1, characterized in that, The double gate mechanism adjusts the gushing pressure of the slag when it is ejected through the double gate mechanism based on the inner gate opening K1 and the outer gate opening K3.

6. The double-gate mechanism for controlling slag discharge gushing according to claim 5, characterized in that, The double-gate mechanism adjusts the gushing pressure of the excavated soil when it is ejected through the double-gate mechanism based on the inner gate opening K1 and the outer gate opening K3, including: P3 = P1 × P1 and P3 describe the gushing pressure of the slag when it is ejected through the inner and outer gates, respectively.

7. A tunnel boring machine, characterized in that, The tunnel boring machine is equipped with a double gate mechanism as described in any one of claims 1 to 6 at the outlet of the screw conveyor.

8. A method for shield tunneling in high-pressure, water-rich strata based on the shield machine described in claim 7, characterized in that, include: Open the outer gate and control the opening degree K3 of the outer gate to be within half of the rated stroke of the outer gate, and K3>K2; Open the inner gate, gradually increase the opening degree K1 of the inner gate within a range less than K2, and monitor the slag discharge flow rate of the outer gate in real time until the slag discharge flow rate of the outer gate reaches the preset flow rate, then stop increasing the opening degree of the inner gate.

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