Construction method for crossing karst groove in karst-related area

Abstract

The invention discloses a construction method for crossing a karst-related area, and relates to the technical field of tunnel construction.The construction method for crossing the karst-related area comprises the steps that before a shield tunneling machine reaches the area of the karst, the karst-related area reaches the area of the karst, the karst-related area reaches the karst-related area, and the karst-related area reaches the karst-related area; ground sleeve valve pipe grouting is carried out in a quincunx hole distribution mode, and the reinforcing depth is 0.5 m below the stable rock surface at the bottom of the dissolving tank; the method comprises the following steps: controlling a shield tunneling machine to tunnel in an earth pressure balance mode to penetrate through a solution tank, and continuously pumping thick slurry with the consistency of 90-120mm to a gap between the periphery of a shield body of the shield tunneling machine and a stratum through a radial grouting hole of the shield body of the shield tunneling machine in the tunneling process; and during the period of penetrating through the dissolving tank, a bentonite suspending agent solution with the concentration of 6%-8% is synchronously injected into the middle lower part of the spiral conveyor so as to penetrate through the dissolving tank. According to the method, the safety, controllability, engineering quality and construction efficiency of the construction of the shield penetrating through the karst groove in the karst-related area are improved.

Description

Technical Field

[0001] This invention relates to the field of tunnel construction technology, and in particular to a construction method for traversing solution channels in karst areas. Background Technology

[0002] In urban rail transit construction, shield tunneling technology has been widely applied in the field of underground engineering. Karst-developed areas commonly have complex geological structures such as underground caves and solution channels, and shield tunnel construction often needs to traverse such areas. Solution channels, as a typical feature of karst geology, are mostly filled with weak soil, groundwater, or a mixture of mud and sand, and their geological conditions are highly uncertain and prone to sudden changes.

[0003] During construction, when the tunnel boring machine (TBM) approaches or enters the karst basin's influence zone, it is highly susceptible to sudden outflows of excavated soil and groundwater, posing a serious threat to construction safety. Currently, the industry generally employs comprehensive measures such as ground pre-grouting reinforcement, synchronous grouting of the shield body, and excavated soil improvement to address the challenges of construction in karst areas. In practice, ground sleeve valve grouting is implemented after geological surveys determine the location of the karst basin before construction. During the tunneling phase, the shield body grouting system is used to fill the gaps at the shield tail, and a modifier is injected into the screw conveyor to improve the fluidity of the excavated soil. For tunnels passing under existing structures, additional pre-grouting and backfill grouting procedures are also added.

[0004] However, the existing technology system still has significant shortcomings: the hole layout scheme for ground grouting reinforcement lacks scientific basis, and improper control of reinforcement depth leads to discontinuity of the reinforced body, making it impossible to effectively seal the boundary of the karst trough; the synchronous grouting process of the shield body relies on fixed parameter settings and cannot respond in real time according to stratum deformation, especially when crossing under existing subway tunnels, the grouting operation and monitoring data are disconnected, making it difficult to dynamically control stratum settlement; the screw conveyor muck removal system is not equipped with a dedicated protective device when encountering sudden karst surges, and the high-speed jetting of muck and water can easily cause muck outlet blockage, equipment damage, and groundwater backflow accidents; in addition, if there are structural design deviations in the initial stage of shield tunneling, there is a lack of systematic correction strategies, which directly affects the accuracy of subsequent tunneling trajectory. The above problems together lead to the high risk of shield tunneling in karst areas, extended construction period, and significantly increased costs. Summary of the Invention

[0005] The main objective of this invention is to propose a construction method for crossing solution channels in karst areas, aiming to improve the safety and crossing efficiency of shield tunneling in karst areas.

[0006] To achieve the above objectives, the present invention proposes a construction method for traversing solution channels in karst areas, which is used for tunnel boring machines. Side baffles are installed on the left and right sides of the slag discharge port of the tunnel boring machine's screw conveyor, and a buffer baffle is installed at the front end of the slag discharge port. A slag receiving box is installed at the rear of the driven wheel of the screw conveyor through a sealing rubber sheet. The construction method for crossing the solution channel in the karst area includes: Before the tunnel boring machine reaches the area of ​​the karst trench, ground sleeve valve grouting is carried out in the karst trench influence area within 3 meters outside the tunnel design outline using a quincunx pattern, and the reinforcement depth extends to 0.5 meters below the bottom stable rock surface of the karst trench. The tunnel boring machine is controlled to tunnel through the karst trench in earth pressure balance mode. During the tunneling process, a thick grout with a consistency of 90mm to 120mm is continuously pumped into the gap between the outer periphery of the shield and the stratum through the radial grouting holes of the shield body. During the passage through the melting tank, a bentonite suspension solution with a concentration of 6% to 8% is simultaneously injected into the middle and lower part of the screw conveyor to pass through the melting tank.

[0007] In one embodiment, before the tunnel boring machine reaches the area of ​​the karst trench, ground sleeve valve grouting is performed in the karst trench influence area within 3 meters outside the tunnel design outline using a quincunx pattern, with the reinforcement depth extending to 0.5 meters below the bottom stable rock surface of the karst trench. This step includes: Within the influence zone of the molten pool, grouting holes are arranged in a plum blossom pattern with a horizontal spacing of 2 meters and a vertical spacing of 2 meters. Through the pre-embedded sleeve valve pipe, cement grout with a water-cement ratio of 0.8:1 to 1:1 is injected into the borehole in sections. The grout diffusion radius is controlled within 1 meter, and the adjacent diffusers maintain an interlocking distance of 0.2 meters until the designed solidified volume is completed.

[0008] In one embodiment, before the tunnel boring machine reaches the area of ​​the karst trench, in the karst trench influence area within 3 meters outside the tunnel design outline, ground sleeve valve grouting is performed using a quincunx pattern to reinforce the area to a depth of 0.5 meters below the bottom stable rock surface of the karst trench. Prior to this step, the construction method for crossing the karst trench in the karst-affected area includes: Ground-penetrating radar was used to scan along the tunnel axis to accurately determine the longitudinal range, transverse width, and type of filling material of the solution trough, and to assess its water-bearing capacity, thus obtaining the scanning results. Based on the scan results, key water inrush risk points that require special attention are marked.

[0009] In one embodiment, when the karst trench coincides with the section of the existing subway tunnel, the tunnel boring machine (TBM) is controlled to tunnel through the karst trench in earth pressure balance mode. Before the step of continuously pumping a thick grout with a consistency of 90mm to 120mm into the gap between the outer periphery of the TBM and the stratum through the radial grouting holes of the TBM's shield body during tunneling, the construction method for tunneling through the karst trench in the karst area further includes: Before the cutterhead of the tunnel boring machine enters the lower section, the soil within a 120° range of the arch crown is pre-grouted through the grouting holes reserved in the shield body. After the tunnel boring machine advances to the predetermined position inside the karst trench, a second advance grouting is carried out. The reinforcement zones of the two groutings maintain an overlap length of at least 3 meters along the tunneling direction, and the grouting pipe is installed at an angle of 15°.

[0010] In one embodiment, prior to the step of simultaneously injecting a 6%–8% bentonite suspension solution into the lower middle part of the screw conveyor during the crossing of the solution tank, the construction method for crossing the solution tank in the karst area further includes: During the tunnel boring machine's passage, after every three rings of segments are excavated, multiple low-pressure grouting methods are immediately employed to perform secondary compensation grouting on the wall through the lifting holes of the segments, with the grouting pressure controlled below 0.3 MPa.

[0011] In one embodiment, controlling the tunnel boring machine (TBM) to tunnel through the karst trench in earth pressure balance mode, and during the tunneling process, continuously pumping a thick grout with a consistency of 90mm to 120mm into the void between the outer periphery of the TBM and the stratum through the radial grouting holes of the TBM's shield body, includes the following steps: During the tunnel boring machine's passage, monitoring data was obtained by automatically collecting tunnel settlement and convergence data every 2 hours through static level and total station monitoring points installed on the inner wall of the existing subway tunnel. The monitoring data is transmitted to the tunnel boring machine operation control room in real time through a data transmission system. When the settlement rate at any monitoring point exceeds 2 mm / day twice consecutively, the control system will automatically alarm and, through a preset program, control the radial grouting holes of the shield body to perform point-to-point and quantitative compensation grouting in the stratum quadrant corresponding to the alarm point.

[0012] In one embodiment, the step of simultaneously injecting a bentonite suspension solution with a concentration of 6% to 8% into the lower middle part of the screw conveyor during the passage through the melting tank includes: Based on the real-time state of the slag in the screw conveyor, the injection flow rate of the bentonite suspension solution is dynamically adjusted to maintain the slump of the discharged slag within the range of 150 mm to 200 mm. During the tunneling process of the tunnel boring machine, the added side baffles are used to restrain the lateral scattering of the excavated soil at the muck outlet; the added buffer baffles are used to change the flow direction of the gushing excavated soil to consume some of its kinetic energy; the sealed muck receiving box is used to receive the buffered excavated soil, and the sealing rubber sheet is used to maintain the overall airtightness of the muck discharge system to prevent the continuous gushing of groundwater and mud.

[0013] In one embodiment, prior to the step of simultaneously injecting a 6%–8% bentonite suspension solution into the lower middle part of the screw conveyor during the crossing of the solution tank, the construction method for crossing the solution tank in the karst area further includes: A mobile, rapidly assembled enclosure should be set up on the ground surface within a range of 15 meters in front of and 15 meters behind the cutterhead of the tunnel boring machine, directly above the tunnel axis; and emergency grouting materials should be stored in fixed locations within this area. The materials include: a cement reserve of not less than 1.5 times the designed grouting volume of the melting tank; a water glass reserve at a mass ratio of 1:0.1 to the cement; and matching grouting pumps, mixers, and grouting pipelines.

[0014] In one embodiment, before controlling the tunnel boring machine to excavate through the karst trench in earth pressure balance mode, and before continuously pumping a thick grout with a consistency of 90mm to 120mm into the gap between the outer periphery of the shield and the stratum through the radial grouting holes of the shield body during the excavation process, the construction method for crossing the karst trench in the karst area further includes: If the centerline of the slag outlet is offset from the centerline of the tunnel due to the limitations of the launching shaft structure, the front end of the shield launching bracket will be pre-offset 100 mm towards the centerline of the tunnel and the tail end will be pre-offset 200 mm before installation. When assembling the negative ring segments, spacers are added between the segment circumferential joints to form a wedge-shaped ring that converges along the tunneling direction with a wedge shape of 300 mm. The tunnel boring machine advances along the pre-set secant excavation centerline until it has advanced a total of 9.699 meters, at which point its excavation centerline completely coincides with the tunnel design centerline. After that, it begins excavation of the main tunnel.

[0015] In one embodiment, after the step of simultaneously injecting a 6%–8% bentonite suspension solution into the lower middle part of the screw conveyor during the crossing of the solution tank, the construction method for crossing the solution tank in the karst area further includes: Ground-penetrating radar was used to scan the back wall of the assembled tunnel segments to check the grouting fullness; For identified voids or loose areas, additional grouting is performed through the grouting holes of the segments until the scanning results show that the filling is dense.

[0016] The technical solution of this invention employs a slag discharge protection system by adding side baffles, buffer baffles, and sealed slag receiving boxes to the slag discharge port of the tunnel boring machine's screw conveyor. This is combined with a series of technical measures, including ground-based sleeve valve pipe grooving reinforcement, phased pre-grouting, periodic secondary compensation grouting behind the wall, real-time monitoring and linkage control of grouting, dynamic adjustment of bentonite suspension solution injection flow rate, an emergency material reserve system, pre-offset of the launching bracket and wedge-shaped ring correction, and quality closed-loop verification of back-wall geological radar scanning and supplementary grouting. This constructs a complete, systematic, and refined technical system for shield tunneling through karst areas, effectively solving the technical problems of insufficient ground reinforcement, inaccurate grouting control, inadequate slag discharge system protection, difficulty in launching correction, and lack of quality verification in existing technologies. It significantly improves the safety, controllability, engineering quality, and construction efficiency of shield tunneling in karst areas, reduces construction risks, and ensures the structural safety and long-term stable operation of existing subway tunnels. Attached Figure Description

[0017] 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 the structures shown in these drawings without creative effort.

[0018] Figure 1 This is a schematic flowchart of an embodiment of the construction method for traversing solution channels in karst areas provided by the present invention.

[0019] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0021] It should be noted that if the embodiments of the present invention involve directional indicators (such as up, down, left, right, front, back, etc.), the directional indicators are only used to explain the relative positional relationship and movement of the components in a specific posture. If the specific posture changes, the directional indicators will also change accordingly.

[0022] Furthermore, if the embodiments of this invention involve descriptions such as "first" or "second," these descriptions are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined with "first" or "second" may explicitly or implicitly include at least one of those features. Additionally, the use of "and / or" or "and / or" throughout the text includes three parallel solutions. For example, "A and / or B" includes solution A, solution B, or a solution where both A and B are satisfied simultaneously. Furthermore, the technical solutions of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or impossible to implement, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed by this invention.

[0023] In urban rail transit construction, shield tunneling technology has been widely applied in the field of underground engineering. Karst-developed areas commonly have complex geological structures such as underground caves and solution channels, and shield tunnel construction often needs to traverse such areas. Solution channels, as a typical feature of karst geology, are mostly filled with weak soil, groundwater, or a mixture of mud and sand, and their geological conditions are highly uncertain and prone to sudden changes.

[0024] During construction, when the tunnel boring machine (TBM) approaches or enters the karst basin's influence zone, it is highly susceptible to sudden outflows of excavated soil and groundwater, posing a serious threat to construction safety. Currently, the industry generally employs comprehensive measures such as ground pre-grouting reinforcement, synchronous grouting of the shield body, and excavated soil improvement to address the challenges of construction in karst areas. In practice, ground sleeve valve grouting is implemented after geological surveys determine the location of the karst basin before construction. During the tunneling phase, the shield body grouting system is used to fill the gaps at the shield tail, and a modifier is injected into the screw conveyor to improve the fluidity of the excavated soil. For tunnels passing under existing structures, additional pre-grouting and backfill grouting procedures are also added.

[0025] However, the existing technology system still has significant shortcomings: the hole layout scheme for ground grouting reinforcement lacks scientific basis, and improper control of reinforcement depth leads to discontinuity of the reinforced body, making it impossible to effectively seal the boundary of the karst trough; the synchronous grouting process of the shield body relies on fixed parameter settings and cannot respond in real time according to stratum deformation, especially when crossing under existing subway tunnels, the grouting operation and monitoring data are disconnected, making it difficult to dynamically control stratum settlement; the screw conveyor muck removal system is not equipped with a dedicated protective device when encountering sudden karst surges, and the high-speed jetting of muck and water can easily cause muck outlet blockage, equipment damage, and groundwater backflow accidents; in addition, if there are structural design deviations in the initial stage of shield tunneling, there is a lack of systematic correction strategies, which directly affects the accuracy of subsequent tunneling trajectory. The above problems together lead to the high risk of shield tunneling in karst areas, extended construction period, and significantly increased costs.

[0026] To address this technical problem, this invention proposes a construction method for traversing solution channels in karst areas.

[0027] Please see Figure 1 In one embodiment of the present invention, the construction method for crossing the solution channel in the karst area is used for a tunnel boring machine. Side baffles are installed on the left and right sides of the slag outlet of the screw conveyor of the tunnel boring machine, a buffer baffle is installed at the front end of the slag outlet, and a slag receiving box is installed at the rear of the driven wheel of the screw conveyor by a sealing rubber sheet. The construction method for crossing the solution channel in the karst area includes: S10, before the tunnel boring machine reaches the area of ​​the karst groove, ground sleeve valve grouting is carried out in the karst groove influence area within 3 meters outside the tunnel design outline using a quincunx pattern, and the reinforcement depth extends to 0.5 meters below the bottom stable rock surface of the karst groove. S20, control the tunnel boring machine to tunnel through the karst trench in earth pressure balance mode. During the tunneling process, continuously pump a thick grout with a consistency of 90mm to 120mm into the gap between the outer periphery of the shield and the stratum through the radial grouting holes of the shield body of the tunnel boring machine. S30, during the passage through the melting tank, a bentonite suspension solution with a concentration of 6% to 8% is simultaneously injected into the middle and lower part of the screw conveyor to pass through the melting tank.

[0028] For ease of understanding, the following explains some key terms in this embodiment: A tunnel boring machine (TBM) is a mechanical device used for tunnel excavation. It has a cutterhead at the front for excavation and tunnel lining is formed by assembling segments at the rear.

[0029] A screw conveyor is a device inside a tunnel boring machine used to transport excavated soil from the excavation face to the muck removal system.

[0030] The slag outlet is the opening at the end of the screw conveyor used to discharge slag and soil.

[0031] Side baffles are plate-shaped structures installed on both sides of the slag outlet to limit the lateral scattering of slag.

[0032] A buffer baffle is a plate-shaped structure installed at the front end of the slag outlet to change the flow direction of the gushing slag and consume its kinetic energy.

[0033] Sealing rubber sheets are rubber materials with elasticity and sealing properties, used to form airtight or watertight seals at joints.

[0034] A slag receiving box is a container used to receive slag discharged from the slag outlet.

[0035] A solution channel is a groove-shaped depression formed by surface water dissolving along rock fissures in karst landforms. It is often filled with weak soil, groundwater, or a mixture of these elements.

[0036] Sleeve valve grouting is a method of reinforcing soil or blocking water by injecting grout into the stratum in sections and in a quantitative manner through pre-embedded grouting pipes with valves.

[0037] Earth pressure balance mode is a tunneling mode of tunnel boring machines that maintains the stability of the excavation face by adjusting the balance between earth pressure and groundwater pressure at the excavation face.

[0038] Radial grouting holes in the shield body are holes set on the outer shell of the shield machine, used to inject grout into the gap between the outer periphery of the shield body and the ground.

[0039] Thick slurry is a slurry with high viscosity, which is usually used to fill voids or reinforce formations.

[0040] Bentonite suspension solution is a suspension formed by mixing bentonite as the main component with water. It has good thixotropic and plastic properties and is often used to improve the fluidity of slag and soil.

[0041] This embodiment provides a construction method for traversing a solution channel in a karst area.

[0042] Specifically, this method improves the muck removal system of the tunnel boring machine. Side baffles can be installed on both sides of the muck discharge port of the screw conveyor. These side baffles, made of steel plates, are fixed to the edge of the discharge port by welding or bolting. Their main function is to prevent the muck from scattering to both sides during discharge. Simultaneously, a buffer baffle can be installed at the front of the discharge port. This buffer baffle, also made of steel plates, is fixed in front of the discharge port. Its function is to change the flow direction of the gushing muck and consume some of its kinetic energy. Furthermore, a muck receiving box can be installed behind the driven wheel of the screw conveyor. This receiving box can be a simple open container, fixed by mechanical connection, to receive the muck discharged from the discharge port. To maintain the airtightness of the muck removal system, sealing gaskets or sealant can be used to seal the connection between the receiving box and the screw conveyor.

[0043] Before the tunnel boring machine reaches the karst basin area, ground reinforcement of the basin's influence zone is necessary. This method involves ground-based sleeve valve grouting within the basin's influence zone, within 3 meters outside the tunnel's design outline, using a quincunx-shaped perforation pattern. During implementation, the planar location and depth of the grouting holes can be determined based on the preliminary geological survey report to ensure the grouting area covers the basin's influence zone. The grouting depth can be set to reach 0.5 meters below the bottom stable rock surface of the basin to form a stable reinforced body. Before grouting, conventional drilling sampling or geophysical exploration methods can be used to obtain basic geological information about the basin.

[0044] During the passage through the karst trench, the tunnel boring machine (TBM) is controlled to excavate in earth pressure balance mode. During excavation, operators can manually adjust the pressure within the earth chamber based on data from the pressure sensors, maintaining a rough balance with the soil and water pressure at the excavation face to ensure stability. Simultaneously, a thick grout with a consistency of 90mm–120mm is continuously pumped into the voids between the TBM's outer perimeter and the ground through the radial grouting holes in the shield body. The grouting pump can inject the thick grout into the outer perimeter of the shield body at a preset constant flow rate and pressure to fill the voids generated during excavation and reduce ground settlement.

[0045] In addition, during the passage through the karst trench, a bentonite suspension solution with a concentration of 6% to 8% is simultaneously injected into the lower middle part of the screw conveyor. This solution can be injected into the screw conveyor at a constant flow rate via an independent pumping system to mix with the excavated soil. The concentration of the solution can be pre-prepared before construction and maintained within a specified range. The injection timing can be set to begin after the tunnel boring machine cutterhead enters the karst trench area and continue until the cutterhead has completely left the karst trench area to improve the fluidity of the excavated soil and prevent it from gushing out.

[0046] This construction method effectively suppresses the risks of muck gushing and groundwater backflow by specifically improving the shield machine's muck removal system, adding side baffles, buffer baffles, and sealed muck collection boxes. Simultaneously, the use of quincunx-shaped perforated surface sleeve valves for grouting in front of the karst trench area enhances the targeted nature and effectiveness of the reinforcement. Combined with earth pressure balance tunneling, radial thick grouting of the shield body, and simultaneous injection of bentonite suspension solution via a screw conveyor, this method effectively addresses complex conditions such as muck gushing and ground instability during karst trench crossings, significantly improving construction safety and stability.

[0047] In an embodiment of the present invention, before the tunnel boring machine reaches the area of ​​the karst trench, ground sleeve valve grouting is performed in the karst trench influence area within 3 meters outside the tunnel design outline using a quincunx pattern, with the reinforcement depth extending to 0.5 meters below the bottom stable rock surface of the karst trench. This step includes: S11, within the influence zone of the molten pool, grouting holes are arranged in a plum blossom pattern with a horizontal spacing of 2 meters and a vertical spacing of 2 meters. S12, through the pre-embedded sleeve valve pipe, inject cement grout with a water-cement ratio of 0.8:1 to 1:1 into the borehole in sections, control the grout diffusion radius to 1 meter, and maintain a 0.2-meter interlock between adjacent diffusers until the designed solidified volume is completed.

[0048] Specifically, within the affected area of ​​the solution trough, grouting boreholes are arranged in a quincunx pattern with horizontal and vertical spacing of 2 meters. This aims to ensure that the grout forms a continuous and uniform reinforcement curtain within the affected area. The quincunx pattern is a grouting hole arrangement method that achieves good uniform coverage. Its characteristic is that adjacent holes are arranged alternately, forming a pattern similar to plum blossom petals, which minimizes grouting blind spots and ensures the reinforcement effect. The horizontal and vertical spacing of 2 meters are optimized parameters determined based on engineering experience and geological conditions, used to effectively fill karst caves and fissures, and improve the overall stability and bearing capacity of the strata.

[0049] Based on this, cement grout with a water-cement ratio of 0.8:1 to 1:1 is injected into the borehole in stages through pre-embedded sleeve valve pipes. The grout diffusion radius is controlled within 1 meter, and adjacent diffusers maintain a 0.2-meter interlocking distance until the designed solidified volume is completed. The sleeve valve pipe is a grouting pipe with multiple grout stop valves, allowing for staged grouting at different depths. This enables precise control of the grouting range and pressure, preventing grout loss or localized overpressure. Staged injection means that the grouting process is carried out step by step, according to the formation conditions and grouting effect, ensuring that the grout can fully penetrate and solidify. Cement grout with a water-cement ratio of 0.8:1 to 1:1 has good fluidity and setting properties, effectively filling cavities and fissures while ensuring the strength of the solidified body. Lower water-cement ratio grouts have higher consistency and are suitable for filling larger cavities; higher water-cement ratio grouts have better fluidity and are suitable for penetrating smaller fissures. The grouting diffusion radius is controlled at 1 meter, which is the target diffusion range set according to geological conditions and reinforcement requirements. This is achieved by controlling the grouting pressure and volume. A 0.2-meter interlocking distance is maintained between adjacent diffusers to ensure the continuity and integrity of the reinforced area, avoiding unreinforced weak areas and thus forming a strong, dense reinforced zone. Until the designed reinforced volume is completed, the ultimate goal of grouting is to achieve the expected reinforcement range and volume, which is typically determined by monitoring parameters such as grouting volume, grouting pressure, and surface deformation.

[0050] The above technical solution clarified the layout and spacing of grouting boreholes, as well as the control standards for grout mix ratio, grouting method, diffusion range, and solidification volume. This solved the problems of uneven reinforcement and poor results that might occur when using only a quincunx pattern for ground sleeve valve grouting. Precise borehole spacing and a quincunx pattern ensured uniform distribution and full penetration of the grout within the karst basin's influence zone, avoiding reinforcement blind spots. Segmented injection of cement grout with a suitable water-cement ratio, combined with precise control of the grout diffusion radius and the interlocking of adjacent diffusers, resulted in a continuous and dense solidification, effectively filling karst caves and fissures, and significantly improving the stability and bearing capacity of the strata. This provided a solid geological guarantee for the subsequent safe passage of the tunnel boring machine through the karst basin using earth pressure balance mode, reduced construction risks, and ensured the safety of the tunnel structure.

[0051] In an embodiment of the present invention, before the tunnel boring machine reaches the area of ​​the karst trench, in the karst trench influence area within 3 meters outside the tunnel design outline, ground sleeve valve grouting is performed using a quincunx pattern to reinforce the area to a depth of 0.5 meters below the bottom stable rock surface of the karst trench. Prior to this step, the construction method for crossing the karst trench in the karst-affected area includes: S101, a ground-penetrating radar is used to scan along the tunnel axis to accurately determine the longitudinal range, transverse width, and type of filling material of the solution trough, and to assess its water-bearing capacity, thereby obtaining the scanning results; S102, Based on the scan results, mark the water inrush risk points that need to be addressed.

[0052] The use of ground-penetrating radar (GPR) along the tunnel axis involves using GPR equipment to detect the electrical structure of the underground medium by transmitting and receiving high-frequency electromagnetic waves. This equipment conducts continuous or segmented detection along or near the tunnel's design axis to obtain detailed information about the solution channels in the tunnel's excavation direction. By analyzing the propagation, reflection, and scattering characteristics of electromagnetic waves in the underground medium, the boundaries of the solution channels can be accurately identified, and their length (longitudinal range) along the tunnel axis and their width perpendicular to the axis (lateral width) can be estimated. Furthermore, different filling materials (such as soil, sand, gravel, and water) respond differently to electromagnetic waves; waveform characteristics and attenuation can be used to infer the type of filling material within the solution channels. Additionally, by analyzing the rapid attenuation and significant reflection characteristics of GPR signals in aquifers, the presence of abundant groundwater or water-saturated areas within the solution channels can be assessed, indicating their water-bearing capacity. Finally, these detection data undergo professional processing and interpretation to generate radar profiles and other scanning results, visually demonstrating the underground structure and hydrogeological characteristics of the solution channels.

[0053] Based on the scan results, marking key water inrush risk points requires special attention. This involves professional engineers conducting in-depth analysis and interpretation of the data after obtaining the ground-penetrating radar scan results. Based on the water-rich areas, fracture zones, loose infill areas, or abnormal signals related to groundwater channels shown in the scan results, and combined with existing geological data and engineering experience, the locations and extents of potential water inrushes are clearly marked on plan or profile maps. These marked water inrush risk points are areas that require special attention and targeted measures during subsequent construction, such as increasing grouting density, adjusting grouting material ratios, or reserving drainage channels in these areas.

[0054] Using the aforementioned technical solution, ground-penetrating radar is employed to precisely survey the solution trench before surface sleeve valve grouting. This allows for a comprehensive understanding of the trench's geometry, the properties of its internal filling material, and its water-bearing status. Based on these detailed scanning results, potential water inrush risk points can be accurately identified and marked. This enables subsequent surface sleeve valve grouting to be carried out more effectively, such as adjusting the density of grouting holes, the ratio of grouting materials, and the grouting pressure. This ensures the reliability of the grouting reinforcement effect, effectively seals groundwater channels, and reduces the risk of sudden water and sand inrushes during tunneling. Simultaneously, accurate solution trench information also helps optimize the tunneling parameters and construction plan of the tunnel boring machine, improving construction safety and efficiency, and avoiding project delays and increased costs due to unclear geological conditions.

[0055] In an embodiment of the present invention, when the karst trench coincides with an existing subway tunnel section, the tunnel boring machine (TBM) is controlled to tunnel through the karst trench in earth pressure balance mode. Before the step of continuously pumping a thick grout with a consistency of 90mm to 120mm into the gap between the outer periphery of the TBM and the stratum through the radial grouting holes of the TBM's shield body during the tunneling process, the construction method for tunneling through the karst trench in the karst area section further includes: S201, before the cutterhead of the tunnel boring machine enters the lower section, the first pre-grouting is carried out in the soil within a 120° range of the arch crown through the grouting holes reserved in the shield body; S202, after the tunnel boring machine advances to the predetermined position inside the karst trench, a second advance grouting is carried out. The reinforcement zones of the two groutings maintain an overlap length of at least 3 meters along the tunneling direction, and the grouting pipe is installed at an angle of 15°.

[0056] Specifically, when the karst trench coincides with the section under an existing subway tunnel, the geological conditions are complex and sensitive, requiring extremely high control over ground deformation during construction to avoid adverse effects on the existing subway tunnel structure. Before the tunnel boring machine (TBM) cutterhead enters the underpass section, the first pre-grouting is performed on the soil within a 120° range of the tunnel crown through pre-reserved grouting holes in the shield body. This first pre-grouting is carried out before the TBM cutterhead enters the underpass section, and its purpose is to pre-reinforce the strata in the karst trench area to be excavated. The pre-reserved grouting holes in the shield body are channels on the TBM specifically used to inject grout into the strata ahead. Selecting a 120° range of the tunnel crown for grouting aims to focus on reinforcing the soil above the tunnel, forming a reinforced arch with a certain strength and stability to effectively resist possible changes in ground stress and settlement during excavation. Grouting materials such as cement-water glass grout or chemical grout can be used. By controlling the grouting pressure and flow rate, the grout can be fully diffused and consolidated into the soil. After the tunnel boring machine (TBM) advances to the predetermined position inside the karst trench, a second pre-grouting is performed. This second pre-grouting, conducted after the TBM has entered a specific location within the trench, aims to further and specifically reinforce the core area of ​​the trench. This compensates for any local deficiencies that may have occurred during the first grouting and addresses potential variations in geological conditions within the trench, ensuring the overall reinforcement effect of the entire trench crossing section. The reinforced areas of the two grouting sessions maintain an overlap of at least 3 meters along the tunneling direction. This overlap ensures the continuity and integrity of the reinforcement effect, preventing any unreinforced weak points between the two grouting areas, thus forming a continuous and stable reinforced zone that effectively transfers ground stress and prevents local instability. The grouting pipes are installed at a 15° angle. This 15° angle allows the grout to diffuse at a certain angle forward and upward, creating a wider and more uniform reinforced fan-shaped area in front of the TBM. This angle design helps the grout penetrate and consolidate the soil better, improving the integrity and stability of the reinforced body, and optimizing the diffusion range and reinforcement effect of the grout.

[0057] By performing two stages of pre-grouting before the tunnel boring machine (TBM) cutterhead enters the underpass section and after advancing to a predetermined position inside the karst trench, and ensuring that the reinforced area maintains an overlap length of at least 3 meters along the tunneling direction, and using a 15° grouting pipe installation angle, this application effectively pre-reinforces and continuously reinforces the strata in the karst trench area before and during TBM tunneling. This staged, overlapping pre-grouting strategy, especially in sensitive areas where the karst trench overlaps with the existing subway tunnel section, can significantly improve the overall stability and bearing capacity of the strata, forming a stronger, less permeable artificial reinforcement ring. This effectively suppresses potential ground settlement, uplift, or uneven deformation that may occur during TBM tunneling, maximizing the protection of the existing subway tunnel's structural safety and reducing construction risks. Simultaneously, pre-grouting also reduces the risk of face instability, providing a more stable environment for subsequent TBM tunneling.

[0058] In an embodiment of the present invention, prior to the step of simultaneously injecting a 6%–8% bentonite suspension solution into the lower part of the screw conveyor during the crossing of the karst trench, the construction method for crossing the karst trench in the karst area further includes: S301 During the tunnel boring machine's passage, after every three rings of segments are excavated, multiple low-pressure grouting methods are immediately used to perform secondary compensation grouting on the wall through the lifting holes of the segments, with the grouting pressure controlled below 0.3 MPa.

[0059] Specifically, the phrase "during the tunnel boring machine's passage" refers to the critical and sensitive construction phase where the tunnel boring machine passes beneath an existing subway tunnel. During this period, the ground is most disturbed, and the requirements for controlling surface settlement and deformation of existing structures are most stringent. To ensure the timeliness of grouting operations and avoid the widening of voids or accumulation of ground deformation due to excessively long intervals, this application stipulates that grouting should be carried out "after every three rings of tunnel segments are excavated." This periodic operation helps to intervene in the early stages of deformation and effectively control ground settlement.

[0060] Regarding the grouting method, this application adopts an "immediate, multiple, low-pressure grouting method." "Immediate" emphasizes the timeliness of grouting, meaning it is carried out rapidly after segment assembly to minimize the occurrence and development of formation deformation. "Multiple" refers to injecting the total grout volume in batches, rather than a single large-volume injection. This helps the grout spread more evenly, improving the fullness and density of the grout and avoiding local overpressure. "Low pressure" refers to the relatively low grouting pressure, which effectively avoids disturbing or damaging existing structures and surrounding formations. Especially when tunneling under sensitive structures, it reduces the risk of formation uplift or cracking, while promoting slow and sufficient grout penetration and diffusion.

[0061] This application describes "secondary compensation grouting behind the tunnel segment wall using the lifting holes of the tunnel segment." The "lifting holes of the tunnel segment" refer to the holes pre-drilled during the manufacturing and installation of the tunnel segment for lifting. After the tunnel segment is assembled, these holes can be cleverly utilized as grouting channels, eliminating the need for additional drilling, simplifying the construction process, and reducing secondary damage to the tunnel segment structure. "Behind the wall" specifically refers to the annular gap between the outer side of the tunnel segment and the ground. During shield tunneling, due to the shield's outer diameter being larger than the tunnel segment's outer diameter, and factors such as tunnel segment assembly errors, an annular gap of a certain thickness will form between the outer side of the tunnel segment and the ground. The purpose of secondary compensation grouting is to fill these gaps, ensuring close contact between the tunnel segment and the ground, and restoring the ground stress balance. "Secondary compensation grouting," relative to the initial grouting performed through the radial grouting holes of the shield body, is a supplementary grouting performed after tunnel segment assembly, primarily used to fill the gap behind the tunnel segment wall, compensate for ground losses, and further stabilize the ground.

[0062] To ensure the safety of the grouting process and prevent adverse effects such as ground uplift, deformation of existing structures, or rapid loss of grout along fissures due to excessive grouting pressure, this application specifies that the grouting pressure should be controlled below 0.3 MPa. This pressure value was determined based on engineering experience and geological conditions, aiming to achieve effective filling while maximizing the protection of the surrounding environment and structure.

[0063] By performing multiple, low-pressure secondary compensation groutings through the segment hoisting holes immediately after every three rings of tunnel segments are excavated during the tunnel boring machine's (TBM) tunneling process, and strictly controlling the grouting pressure below 0.3 MPa, this application can timely and effectively fill the voids behind the segment walls and compensate for ground losses. This refined grouting strategy combines the advantages of timeliness, batch injection, and low-pressure control, avoiding disturbances to the existing subway tunnel caused by untimely grouting or excessive pressure, thereby maximizing the control of ground settlement and deformation of the existing structure. Compared to the initial grouting relying solely on the radial grouting holes of the shield body, secondary compensation grouting can more thoroughly eliminate voids behind the segment walls, ensuring a tight bond between the segments and the ground, significantly improving the construction safety and stability of tunneling under existing subway tunnels through karst areas, and effectively guaranteeing the structural integrity and operational safety of existing subway tunnels.

[0064] In an embodiment of the present invention, controlling the tunnel boring machine to tunnel through the karst trench in earth pressure balance mode, and during the tunneling process, continuously pumping a thick grout with a consistency of 90mm to 120mm into the gap between the outer periphery of the shield and the stratum through the radial grouting holes of the shield body of the tunnel boring machine includes the following steps: S21. During the tunnel boring machine's passage, the tunnel settlement and convergence data are automatically collected every 2 hours through the static level and total station monitoring points installed on the inner wall of the existing subway tunnel to obtain monitoring data. S22, the monitoring data is sent to the tunnel boring machine operation control room in real time through the data transmission system; S23, when the settlement rate of any monitoring point exceeds 2 mm / day twice in a row, the control system will automatically alarm and control the radial grouting holes of the shield body through a preset program to perform fixed-point and quantitative compensation grouting in the stratum quadrant corresponding to the alarm point.

[0065] Specifically, during the tunnel boring machine's (TBM) passage through an existing subway tunnel, static leveling instruments and total stations are deployed on the tunnel walls to accurately monitor the tunnel's deformation. The static leveling instrument utilizes the principle of communicating vessels to precisely monitor the vertical displacement (settlement) of the tunnel structure through changes in the liquid level. The total station, an instrument integrating angle measurement, distance measurement, and data processing, can be used to monitor the horizontal displacement (convergence) and elevation changes of the tunnel structure. These monitoring points can directly and accurately acquire deformation data of the tunnel structure during the TBM's passage. To ensure data continuity and timeliness, the system automatically collects tunnel settlement and convergence data every two hours. This acquisition frequency aims to balance the real-time nature of monitoring with the data processing load, sufficiently capturing the dynamic trends of tunnel deformation and providing a basis for timely early warning and intervention.

[0066] The acquired tunnel settlement and convergence monitoring data are transmitted in real time to the tunnel boring machine (TBM) control room via a data transmission system. This data transmission system can use wired or wireless networks, such as fiber optics, Ethernet, or 4G / 5G wireless communication modules, to ensure that on-site monitoring data can be transmitted to the command center immediately. In the TBM control room, operators can correlate and analyze the tunnel deformation with the TBM's excavation parameters, grouting parameters, etc., to make more scientific adjustments.

[0067] To achieve intelligent response to tunnel deformation, this application establishes an early warning mechanism: when the settlement rate at any monitoring point exceeds 2 mm / day twice consecutively, the control system will automatically issue an alarm. Settlement rate is the change in settlement per unit time; compared to cumulative settlement, settlement rate better reflects the trend and urgency of deformation development. Two consecutive occurrences exceeding the threshold eliminate the possibility of single data fluctuations or measurement errors, indicating that the tunnel deformation trend has reached a level requiring immediate intervention. Once the alarm is triggered, the control system will, through a preset program, link and control the radial grouting holes in the shield body to perform targeted and quantitative compensation grouting in the stratum quadrant corresponding to the alarm point. The preset program is a grouting strategy pre-set based on engineering experience and geological conditions, including parameters such as grouting volume, grouting pressure, and grouting time. The radial grouting holes in the shield body can locally reinforce and compensate for the strata. By injecting grout into the strata, it fills the voids in the strata, increases the bearing capacity of the strata, and thus inhibits further development of tunnel settlement and deformation.

[0068] Through the aforementioned technical solution, this application achieves real-time, high-precision monitoring and closed-loop control of deformation in existing subway tunnels. During the tunnel boring machine's (TBM) passage, abnormal trends in tunnel settlement and convergence can be detected in a timely manner, and precise and quantitative compensation and reinforcement of the strata can be carried out through automatic alarms and linked grouting mechanisms. This proactive intervention method effectively suppresses the settlement and convergence of the existing tunnel caused by the TBM excavation, avoids structural damage caused by stratum disturbance, and thus significantly improves the safety of construction of existing subway tunnels in karst areas, ensures the stable operation of existing tunnels, and reduces construction risks.

[0069] In an embodiment of the present invention, the step of simultaneously injecting a bentonite suspension solution with a concentration of 6% to 8% into the lower middle part of the screw conveyor during the crossing of the melting tank includes: S31, Based on the real-time state of the slag in the screw conveyor, dynamically adjust the injection flow rate of the bentonite suspension solution to maintain the slump of the discharged slag within the range of 150 mm to 200 mm. S32, during the tunneling process of the tunnel boring machine, the added side baffles are used to restrain the lateral scattering of the slag at the slag outlet; the added buffer baffles are used to change the flow direction of the gushing slag to consume some of its kinetic energy; the sealed slag receiving box is used to receive the buffered slag, and the sealing rubber sheet is used to maintain the overall airtightness of the slag discharge system to prevent the continuous gushing of groundwater and mud.

[0070] Specifically, the injection flow rate of the bentonite suspension solution is dynamically adjusted based on the real-time state of the slag inside the screw conveyor to maintain the slump of the discharged slag within the range of 150 mm to 200 mm. This involves real-time monitoring of various parameters of the slag inside the screw conveyor, such as moisture content, density, and pressure, to determine the real-time state of the slag. Based on this monitoring data, the control system can intelligently adjust the injection volume of the bentonite suspension solution to ensure that the plasticity, fluidity, and stability of the discharged slag are within the optimal range, i.e., the slump is maintained between 150 mm and 200 mm. This helps prevent the slag from being too dry, leading to blockage, or too wet, leading to fluidization loss control, thereby ensuring the continuity and stability of slag discharge.

[0071] During the tunneling process of a tunnel boring machine (TBM), side baffles are installed to restrain the lateral scattering of excavated soil at the muck outlet. This refers to the installation of side baffles on both sides of the muck outlet of the screw conveyor. These side baffles act as physical barriers, effectively confining the excavated soil discharged from the screw conveyor within a predetermined discharge channel. This prevents the soil from splashing to both sides due to inertia or pressure during discharge, thereby maintaining the cleanliness of the construction site and reducing the impact on the surrounding environment.

[0072] The use of added buffer baffles to alter the flow direction of gushing construction waste, thereby consuming some of its kinetic energy, refers to the installation of buffer baffles at the front end of the screw conveyor's discharge port. When construction waste, especially when it gushes out at high speed or pressure, it first impacts these buffer baffles. The design of the buffer baffles allows them to change the direction of the construction waste's movement. Through this change in direction and the impact process, some of the construction waste's kinetic energy is converted into other forms of energy (such as heat energy and deformation energy), thus significantly reducing the gushing speed and impact force of the construction waste, making its subsequent processing safer and more controllable.

[0073] A sealed slag receiving box is used to collect buffered slag. This refers to a slag receiving box installed behind the driven wheel of the screw conveyor, sealed with a rubber sheet. The main function of this box is to collect and temporarily store the slag after it has been treated by the buffer baffle. Its sealed installation ensures that the slag will not overflow during the receiving process, and also helps maintain the pressure balance within the slag discharge system.

[0074] Maintaining the overall airtightness of the muck removal system by using sealing rubber sheets to prevent the continuous influx of groundwater and sediment refers to the coordinated operation of the sealing rubber sheets and the muck receiving box to create a sealed muck removal environment. These sealing rubber sheets are typically installed between the driven wheel of the screw conveyor and the muck receiving box, forming an effective sealing barrier. This airtightness is crucial for tunneling in water-rich strata or solution basins, effectively preventing external groundwater and sediment from continuously flowing into the tunnel boring machine under pressure differentials, thereby maintaining the stability of the tunnel face and ensuring construction safety.

[0075] Through the above technical solution, this application can dynamically adjust the injection flow rate of the bentonite suspension solution according to the real-time state of the slag in the screw conveyor, so that the slump of the discharged slag is always maintained within a suitable range of 150 mm to 200 mm. This effectively solves the problem of low slag discharge efficiency caused by unstable slag state, ensuring the continuity and stability of slag discharge. Simultaneously, by installing side baffles and buffer baffles at the slag outlet, the lateral dispersion of slag can be effectively restrained, and some of the kinetic energy of the gushing slag can be consumed, significantly reducing the risk and impact of slag gushing. Furthermore, the sealed slag receiving box and sealing rubber sheet work together to maintain the overall airtightness of the slag discharge system, fundamentally preventing the continuous inflow of groundwater and mud into the tunnel boring machine, greatly improving safety and environmental cleanliness during construction in karst areas crossing solution channels, and ensuring the smooth progress of tunneling operations.

[0076] In an embodiment of the present invention, prior to the step of simultaneously injecting a 6%–8% bentonite suspension solution into the lower part of the screw conveyor during the crossing of the karst trench, the construction method for crossing the karst trench in the karst area further includes: S310, within a ground area 15 meters in front of and 15 meters behind the cutterhead of the tunnel boring machine, a mobile barrier that can be quickly assembled shall be set up; and emergency grouting materials shall be stored in a fixed location within this area. The materials include: a cement reserve of not less than 1.5 times the designed grouting volume of the melting tank; a water glass reserve at a mass ratio of 1:0.1 to the cement; and matching grouting pumps, mixers, and grouting pipelines.

[0077] Specifically, setting up rapidly assembleable mobile barriers refers to pre-constructing or preparing a quickly deployable temporary barrier within the potential impact area of ​​the tunnel boring machine (TBM) traversing the karst trench—specifically, within a 15-meter radius above the tunnel axis and 15 meters in front of and behind the TBM cutterhead. These barriers typically employ a modular design, constructed from lightweight, high-strength materials such as steel plates and composite panels. They are assembled using pins, bolts, or quick-release clips to ensure rapid deployment in emergencies, minimizing delays in emergency response. Sealing strips or weights can be installed at the bottom of the barrier to enhance its stability and leak-proof capabilities, effectively isolating the construction area and preventing sudden water, mud, or grout inrushes from impacting the surrounding environment and personnel, thus providing a safety barrier for emergency response.

[0078] Meanwhile, emergency grouting materials are stored at fixed locations within the area to ensure rapid access and deployment in emergencies, avoiding delays in emergency response due to untimely material allocation. These emergency grouting materials include: cement reserves of no less than 1.5 times the designed grouting volume of the solution tank. Cement is a commonly used grouting material used to form a solidified body and stabilize the strata. The reserve quantity of 1.5 times the designed solidification volume provides sufficient redundancy to cope with complex situations where the grouting volume may exceed expectations during actual construction. Cement should be stored in a moisture-proof, well-ventilated warehouse or container to ensure its performance is not affected. Water glass reserves are matched with cement at a mass ratio of 1:0.1. Water glass (sodium silicate) is often used in conjunction with cement as a quick-setting agent or auxiliary grouting material, accelerating the setting of the cement slurry and improving grouting efficiency and sealing effect. The 1:0.1 mass ratio is a commonly used ratio determined based on engineering experience and material characteristics, ensuring synergistic effects between the two materials. Water glass should be stored in corrosion-resistant containers and protected from freezing. In addition, it is necessary to reserve matching grouting pumps, mixers and grouting pipelines. These are essential equipment for grouting operations and should be inspected and maintained regularly to ensure they are in good working order. Power and water supply interfaces should also be reserved near the reserve point for quick start-up.

[0079] By setting up a rapidly assembleable mobile barrier on the ground surface within 15 meters in front of and behind the tunnel boring machine (TBM) cutterhead directly above the tunnel axis, the construction area can be effectively isolated to prevent sudden water inrushes, mud inrushes, or grouting from impacting the surrounding environment and personnel, providing a safety barrier for emergency response. Simultaneously, sufficient emergency grouting materials, including cement, water glass, and supporting grouting pumps, mixers, and grouting pipelines, are stored at fixed locations within this area. This ensures that in the event of sudden water inrushes, mud inrushes, or ground instability during the TBM's passage through the karst trench, materials and equipment can be quickly mobilized to immediately initiate emergency grouting operations. This pre-deployed emergency measure, combined with conventional construction methods such as surface sleeve valve grouting reinforcement, earth pressure balance tunneling, and screw conveyor grouting, forms a more comprehensive risk control system. It significantly shortens emergency response time, improves emergency response efficiency, and effectively avoids secondary disasters and project delays caused by material shortages or untimely transportation, thereby ensuring the safety and continuity of TBM construction in karst areas.

[0080] In an embodiment of the present invention, prior to the step of controlling the tunnel boring machine to excavate through the karst trench in earth pressure balance mode, and during the excavation process, continuously pumping a thick grout with a consistency of 90mm to 120mm into the gap between the outer periphery of the shield body and the stratum through the radial grouting holes of the shield body, the construction method for crossing the karst trench in the karst area further includes: S210 If the centerline of the slag outlet is offset from the centerline of the tunnel design due to the limitations of the launching shaft structure, the front end of the shield launching bracket will be pre-offset 100 mm towards the centerline of the tunnel design, and the tail end will be pre-offset 200 mm before installation. S220: When assembling the negative ring segments, pads are added between the segment circumferential joints to form a wedge-shaped ring that converges along the tunneling direction with a wedge amount of 300 mm. S230, the tunnel boring machine advances along the preset secant excavation centerline until it has advanced a total of 9.699 meters, at which point its excavation centerline completely coincides with the tunnel design centerline, and then it enters the main tunnel excavation.

[0081] Specifically, when a tunnel boring machine (TBM) is assembled in the launching shaft, if the structural dimensions or spatial layout of the launching shaft prevents the centerline of the TBM's muck outlet from being directly aligned with the tunnel's design centerline, resulting in an initial design offset, a pre-offset installation of the TBM launching bracket is necessary. This pre-offset installation refers to adjusting the support position of the launching bracket during the TBM's assembly in the shaft, based on precise measurement and layout results. This pre-offsets the front end of the launching bracket by 100 mm towards the tunnel's design centerline, and the rear end by 200 mm. This pre-offset operation aims to create an initial small angle for the TBM to gradually return to the design centerline during subsequent tunneling, laying the foundation for curved tunneling. In practice, the precise pre-offset can be achieved by setting adjustable supports or pads between the bracket and the launching shaft structure, and a re-measurement is performed after installation to ensure the offset meets design requirements.

[0082] Based on this, during the assembly of the negative ring segments, spacers are added between the segment joints to form a wedge-shaped ring that converges along the tunneling direction with a wedge shape of 300 mm. The negative ring segment is a special segment ring assembled during the initial stage of the tunnel boring machine (TBM) launch, its function being to provide initial support and guidance for the TBM. By precisely adding spacers of a specific thickness between the segment joints, a wedge shape can be artificially created on the segment ring, causing a slight bend in the ring after assembly. This wedge-shaped ring has a wedge shape of 300 mm and converges along the tunneling direction, meaning it will guide the TBM to gradually approach the tunnel's designed centerline. During assembly, spacers of appropriate thickness (such as wooden wedges, steel plates, or special wedge-shaped spacers) must be selected according to the design drawings and calculation results, and precisely placed at specific joint positions on the segment ring. The thickness, quantity, and placement of the spacers must be strictly controlled to ensure that the formed wedge-shaped ring produces the expected steering effect. After assembly, the geometry of the segment ring needs to be measured to confirm that the wedge amount and convergence direction meet the requirements.

[0083] Subsequently, the tunnel boring machine (TBM) advanced along the pre-set secant excavation centerline until it had advanced a cumulative distance of 9.699 meters, at which point its excavation centerline completely coincided with the tunnel's design centerline. Afterward, it transitioned to the main tunnel excavation. The secant excavation centerline is a pre-set curved path that the TBM follows as it returns from its initial offset position to the tunnel's design centerline. This path is precisely calculated to ensure that the TBM smoothly completes attitude adjustments within a certain excavation distance. TBM operators must strictly control the excavation according to the pre-set secant excavation centerline, monitoring the TBM's attitude (pitch, roll, deviation) in real time, and adjusting parameters such as the thrust of the propulsion cylinders, the cutterhead speed, and the grouting volume based on the monitoring data to guide the TBM along the secant path. During the excavation process, continuous measurement and verification are required to ensure that the TBM's trajectory remains consistent with the secant excavation centerline. When the cumulative tunneling distance reached 9.699 meters, a precise measurement was taken again to confirm that the tunnel boring machine had completely returned to the tunnel design centerline. Then, the tunneling parameters were adjusted, and the machine was switched to the main tunnel excavation mode.

[0084] Through the above technical solution, this application effectively solves the initial offset problem caused by the structural limitations of the launching shaft of the tunnel boring machine (TBM). By pre-offsetting the launching bracket during the initial installation of the TBM and adding pads to form a wedge-shaped ring during the assembly of the negative ring segments, this application can actively guide the TBM to advance smoothly along the preset secant tunneling centerline. This gradual attitude adjustment method avoids large-scale and rapid correction operations by the TBM due to initial offset during the initial stage, thereby effectively reducing stress concentration on the TBM structure and segment rings and minimizing ground disturbance. After the TBM has advanced a predetermined distance, its tunneling centerline can accurately coincide with the tunnel design centerline, ensuring the accuracy of the TBM's attitude before entering complex strata such as karst caves. This provides a stable foundation for subsequent key steps such as earth pressure balance mode tunneling and thick slurry pumping, significantly improving tunnel forming quality and construction safety.

[0085] In an embodiment of the present invention, after the step of simultaneously injecting a bentonite suspension solution with a concentration of 6% to 8% into the lower part of the screw conveyor during the crossing of the karst trench, the construction method for crossing the karst trench in the karst area further includes: S40 uses ground-penetrating radar to scan the back wall of the assembled segments to detect the grouting fullness; S50, for the identified voids or loose areas, supplementary grouting is carried out through the grouting holes of the segments until the scanning results show that the filling is dense.

[0086] Specifically, ground-penetrating radar (GPR) is used to scan the back wall of the assembled tunnel segments to detect the fullness of the grouting. GPR is a geophysical exploration device that uses high-frequency electromagnetic waves to detect underground media. Its working principle is to emit high-frequency electromagnetic waves into the ground and receive the electromagnetic wave signals reflected back from the interfaces of different underground media. Because different media (such as dense grout, loose soil, water, or voids) have different dielectric constants and conductivity, GPR can identify the distribution of the grouting behind the tunnel segment wall and whether there are voids or loose areas by analyzing the amplitude, frequency, and phase characteristics of the reflected waves. This scanning process is usually carried out after the tunnel segments are assembled, aiming to comprehensively assess the grouting filling quality between the outer side of the tunnel segment and the strata, ensuring full grouting and no voids.

[0087] For identified voids or loose areas, supplementary grouting is performed through the segment grouting holes until the scanning results show that the filling is dense. Void areas refer to gaps behind the segment wall that are completely unfilled with grouting material, while loose areas refer to areas where the grouting material is unevenly filled, loose, or locally under-dense. These areas are potential weak points in the tunnel structure, potentially leading to ground settlement, uneven stress on the segments, or water leakage. Segment grouting holes are dedicated channels pre-installed on the tunnel segments for secondary or compensatory grouting after segment assembly. Once voids or loose areas are identified by ground-penetrating radar scanning, construction workers use these grouting holes to pump cement grout or other suitable grouting materials into these defective areas. The purpose of supplementary grouting is to fill voids, improve the density and uniformity of the soil behind the wall, thereby enhancing the overall stability and waterproofing performance of the tunnel lining. Low-pressure, multiple grouting methods are typically used during grouting to avoid excessive pressure on the assembled segments and to ensure that the grout can fully diffuse and fill the gaps. Supplementary grouting is not a one-time event, but a dynamic process of adjustment and verification. After each supplementary grouting, ground-penetrating radar is used again for scanning and detection to evaluate the grouting effect. Only when the ground-penetrating radar scan clearly shows that the previously voided or loose areas have been effectively filled and have reached the compaction required by the design is the grouting work in that area considered complete. This closed-loop control mechanism ensures the quality of grouting and avoids the problems of over-grouting or under-grouting.

[0088] Through the aforementioned technical solution, after simultaneously injecting bentonite suspension solution into the lower part of the screw conveyor during the karst trench crossing, ground-penetrating radar is used to scan the back wall of the assembled tunnel segments. This allows for precise and non-destructive detection of potential voids or incomplete grouting between the segments and the strata. Based on these scan results, targeted supplementary grouting can be performed on the identified defective areas through the segment grouting holes, with subsequent scan results used as feedback until the filling is confirmed to be dense. This refined post-processing effectively compensates for potential defects such as uneven or incomplete grouting during tunneling, significantly improving the overall density, waterproofing performance, and structural stability of the tunnel lining. It extends quality control in tunnel construction from the tunneling stage to the lining formation stage, forming a more comprehensive quality assurance system, thereby ensuring the long-term safe operation of tunnels in karst areas under complex geological conditions.

[0089] The following example will provide a more detailed explanation of the above technical solution: In the construction of an urban rail transit project, the tunnel boring machine (TBM) needed to traverse a water-rich karst area, which included a large sinkhole. Geological surveys revealed that the sinkhole was filled with weak soil and groundwater, posing a risk of sudden water inrush. To ensure the safe and efficient passage of the TBM through the sinkhole, the construction team adopted this technical solution.

[0090] First, before the tunnel boring machine (TBM) reached the karst trench area, the construction team made targeted modifications to the TBM's screw conveyor muck removal system. Specifically, side baffles were installed on both sides of the screw conveyor's muck outlet to effectively restrain the lateral scattering of muck. Simultaneously, a buffer baffle was installed at the front end of the muck outlet. This baffle alters the flow direction of the gushing muck, thereby absorbing some of its kinetic energy and reducing the impact on subsequent equipment. Furthermore, a muck receiving box was installed at the rear of the driven wheel of the screw conveyor, sealed with a rubber sheet, to receive the buffered muck. The sealing rubber sheet also maintains the overall airtightness of the muck removal system to prevent the continuous gushing of groundwater and silt that may occur when traversing the karst trench.

[0091] Before the tunnel boring machine entered the karst basin's influence zone, the construction team used ground-penetrating radar scans to accurately determine the basin's longitudinal extent, transverse width, and type of filling material, and assessed its water-bearing capacity, obtaining detailed scan results. Based on these results, the construction team marked key water inrush risk points requiring special attention. Subsequently, within 3 meters of the karst basin's influence zone outside the tunnel's design outline, a quincunx-shaped perforation pattern was used for ground-based sleeve valve grouting reinforcement. Specifically, grouting boreholes were laid out in a quincunx pattern with horizontal and vertical spacing of 2 meters within the karst basin's influence zone. Through pre-embedded sleeve valves, cement grout with a water-cement ratio of 0.8:1 was injected into the boreholes in stages, with the grout diffusion radius controlled at 1 meter and adjacent diffusers maintaining a 0.2-meter interlocking distance, until the designed solidified volume was completed. The reinforcement depth reached 0.5 meters below the bottom stable rock surface of the karst basin, thus forming a stable and dense solidified body around the basin, effectively reducing the risk of karst basin crossing. Compared with existing ground grouting methods that lack targeted design, this solution ensures the effectiveness and uniformity of the reinforced body through meticulous geological exploration, quincunx-shaped hole layout, and precise control of grouting parameters.

[0092] When the tunnel boring machine (TBM) begins excavating through the karst trench, it is controlled to operate in earth pressure balance mode. During excavation, a 100 mm thick grout is continuously pumped into the gap between the outer periphery of the TBM and the stratum through the radial grouting holes of the TBM's shield body. This synchronous grouting operation can promptly fill the gap between the shield body and the stratum, effectively controlling stratum deformation and preventing ground subsidence.

[0093] Simultaneously, during the passage through the karst trench, the construction team injected a 7% bentonite suspension solution into the lower and middle parts of the screw conveyor. The injection flow rate of this solution was dynamically adjusted according to the real-time condition of the excavated soil within the screw conveyor to ensure that the slump of the discharged excavated soil remained within 170 mm. This dynamic adjustment mechanism differs from the fixed-parameter injection method used in existing technologies, and can better adapt to the complex and variable excavated soil conditions within the karst trench, maintaining the stability of the tunnel face. During the tunnel boring machine's excavation, the added side baffles effectively constrained the lateral dispersion of excavated soil at the discharge port. The buffer baffles changed the flow direction of the gushing excavated soil, consuming some of its kinetic energy, while the sealed muck receiving box received the buffered excavated soil and maintained the overall airtightness of the muck discharge system through sealing rubber sheets. This effectively prevented the continuous gushing of groundwater and mud, significantly improving the safety and stability of the muck discharge system. This contrasts sharply with the existing screw conveyor muck discharge systems, which lack effective protection and buffering devices, making them prone to excavated soil gushing and groundwater backflow.

[0094] Through the synergistic effect of the above-mentioned series of technical features, including targeted modifications to the shield tunneling machine's muck removal system, refined ground pre-grouting reinforcement, synchronous grouting during tunneling, and dynamically adjusted bentonite suspension injection, this solution successfully enabled the shield tunneling machine to safely and stably traverse the water-rich karst trough. It effectively solved technical problems such as the lack of targeted ground grouting reinforcement and the slag removal system's tendency to surge during shield tunneling construction in karst areas, thus ensuring construction safety and project quality.

[0095] The above description is merely an exemplary embodiment of the present invention and does not limit the scope of protection of the present invention. Any equivalent structural transformations made based on the technical concept of the present invention and the contents of the specification and drawings of the present invention, or direct / indirect applications in other related technical fields, are included within the scope of protection of the present invention.

Claims

1. A construction method for traversing a sinkhole in a karst region, for a shield machine, characterized in that, The left and right sides of the screw conveyor discharge port of the shield machine are provided with side baffles, and the front end of the discharge port is provided with a buffer baffle, and a residue receiving box is sealingly installed behind the driven wheel of the screw conveyor through a sealing rubber sheet; The construction method for crossing the karst cave in the karst area section includes: Before the shield machine reaches the area of the karst cave, sleeve valve pipe grouting is performed in a quincunx hole arrangement manner in the karst cave influence area within 3 meters outside the tunnel design contour line, and the reinforcement depth reaches 0.5 meters below the stable rock mass surface of the bottom of the karst cave; The shield machine is controlled to excavate and cross the karst cave in a soil pressure balance mode, and in the process of excavation, thick slurry with a consistency of 90mm-120mm is continuously pumped to the gap between the periphery of the shield body of the shield machine and the stratum through the radial grouting holes of the shield body; During the crossing of the karst cave, a bentonite suspension agent solution with a concentration of 6%-8% is injected into the middle and lower parts of the screw conveyor simultaneously to cross the karst cave.

2. The method of claim 1, wherein the method further comprises: Before the shield machine reaches the area of the karst cave, sleeve valve pipe grouting is performed in a quincunx hole arrangement manner in the karst cave influence area within 3 meters outside the tunnel design contour line, and the reinforcement depth reaches 0.5 meters below the stable rock mass surface of the bottom of the karst cave. In the karst cave influence area, the grouting drill holes are arranged in a quincunx pattern with a horizontal spacing of 2 meters and a vertical spacing of 2 meters; Through the pre-buried sleeve valve pipe, cement slurry with a water-cement ratio of 0.8:1-1:1 is sectionally pressure injected into the drill holes, the grouting diffusion radius is controlled to be 1 meter, and an overlap of 0.2 meters is maintained between adjacent diffusion bodies until the designed reinforcement volume is completed.

3. The method of claim 2, wherein the method further comprises: Before the step of performing sleeve valve pipe grouting in a quincunx hole arrangement manner in the karst cave influence area within 3 meters outside the tunnel design contour line and to a reinforcement depth of 0.5 meters below the stable rock mass surface of the bottom of the karst cave before the shield machine reaches the area of the karst cave, the construction method for crossing the karst cave in the karst area section includes: Geological radar is used to scan along the tunnel axis to accurately determine the longitudinal range, transverse width, and filling type of the karst cave, and to evaluate its water enrichment property to obtain scanning results; Based on the scanning results, the water gushing risk points that need to be treated are marked.

4. The method of claim 1, wherein the method further comprises: When the karst cave coincides with the section of crossing the existing subway tunnel, before the step of controlling the shield machine to excavate and cross the karst cave in a soil pressure balance mode and continuously pumping thick slurry with a consistency of 90mm-120mm to the gap between the periphery of the shield body of the shield machine and the stratum through the radial grouting holes of the shield body in the process of excavation, the construction method for crossing the karst cave in the karst area section further includes: Before the cutter head of the shield machine enters the section of crossing, first advanced grouting is performed on the soil within a range of 120° of the vault through the shield body reserved grouting holes; After the shield machine advances to a predetermined position inside the karst cave, second advanced grouting is performed, and the reinforcement areas of the two grouting operations maintain an overlap length of at least 3 meters in the excavation direction, and the installation angle of the grouting pipe is 15°.

5. The method of claim 4, wherein the method further comprises: During the crossing of the solution trench, a bentonite suspension solution with a concentration of 6% to 8% is simultaneously injected into the middle and lower part of the screw conveyor. Prior to the step of crossing the solution trench in the karst area, the construction method for crossing the solution trench in the karst region further includes: During the tunnel boring machine's passage, after every three rings of segments are excavated, multiple low-pressure grouting methods are immediately employed to perform secondary compensation grouting on the wall through the lifting holes of the segments, with the grouting pressure controlled below 0.3 MPa.

6. The method of claim 5, wherein the method further comprises: The steps of controlling the tunnel boring machine to excavate through the karst trench in earth pressure balance mode, and continuously pumping a thick grout with a consistency of 90mm to 120mm into the gap between the outer periphery of the tunnel boring machine and the stratum through the radial grouting holes of the tunnel boring machine's shield body during the excavation process, include: During the tunnel boring machine's passage, monitoring data was obtained by automatically collecting tunnel settlement and convergence data every 2 hours through static level and total station monitoring points installed on the inner wall of the existing subway tunnel. The monitoring data is transmitted to the tunnel boring machine operation control room in real time through a data transmission system. When the settlement rate at any monitoring point exceeds 2 mm / day twice consecutively, the control system will automatically alarm and, through a preset program, control the radial grouting holes of the shield body to perform point-to-point and quantitative compensation grouting in the stratum quadrant corresponding to the alarm point.

7. The method of claim 1, wherein the method further comprises: drilling a first borehole in the karst region; drilling a second borehole in the karst region; and connecting the first borehole and the second borehole with a borehole connecting pipe. During the passage through the melting tank, a bentonite suspension solution with a concentration of 6% to 8% is simultaneously injected into the lower middle part of the screw conveyor to facilitate passage through the melting tank. Based on the real-time state of the slag in the screw conveyor, the injection flow rate of the bentonite suspension solution is dynamically adjusted to maintain the slump of the discharged slag within the range of 150 mm to 200 mm. During the tunneling process of the tunnel boring machine, the added side baffles are used to restrain the lateral scattering of the excavated soil at the muck outlet; the added buffer baffles are used to change the flow direction of the gushing excavated soil to consume some of its kinetic energy; the sealed muck receiving box is used to receive the buffered excavated soil, and the sealing rubber sheet is used to maintain the overall airtightness of the muck discharge system to prevent the continuous gushing of groundwater and mud.

8. The method of claim 1, wherein the method further comprises: drilling a first borehole in the karst region; drilling a second borehole in the karst region; and connecting the first borehole and the second borehole by drilling a third borehole in the karst region. During the crossing of the solution trench, a bentonite suspension solution with a concentration of 6% to 8% is simultaneously injected into the middle and lower part of the screw conveyor. Prior to the step of crossing the solution trench in the karst area, the construction method for crossing the solution trench in the karst region further includes: A mobile, rapidly assembled enclosure should be set up on the ground surface within a range of 15 meters in front of and 15 meters behind the cutterhead of the tunnel boring machine, directly above the tunnel axis; and emergency grouting materials should be stored in fixed locations within this area. The materials include: a cement reserve of not less than 1.5 times the designed grouting volume of the melting tank; a water glass reserve at a mass ratio of 1:0.1 to the cement; and matching grouting pumps, mixers, and grouting pipelines.

9. The method of claim 1 to 8, wherein, Before the step of continuously pumping thick slurry with a thickness of 90mm-120mm to the gap between the outer periphery of the shield body of the shield tunneling machine and the stratum through the radial grouting holes of the shield body of the shield tunneling machine during the tunneling process, the construction method for crossing the karst cave in the karst area section further comprises: If the center line of the slag outlet and the design center line of the tunnel exist a design offset due to the limitation of the structure of the starting well, the front end of the shield starting bracket is pre-offset by 100mm to the direction of the design center line of the tunnel, and the tail is pre-offset by 200mm for installation; When assembling the negative ring segment, a spacer is arranged between the segment ring joints to form a wedge-shaped ring with a convergence of 300mm in the tunneling direction; The shield tunneling machine advances along the preset cutting line tunneling center line until the cumulative advance is 9.699m, and the tunneling center line completely coincides with the design center line of the tunnel, and then the positive hole tunneling is started.

10. The method of claim 1, wherein the method further comprises: drilling a borehole through the karst region; and installing a pipe in the borehole. During the crossing of the karst cave, a bentonite suspension solution with a concentration of 6%-8% is injected into the middle and lower parts of the screw conveyor simultaneously to cross the karst cave, and after the step of crossing the karst cave, the construction method for crossing the karst cave in the karst area section further comprises: The wall behind the assembled segment is scanned by using a geological radar to detect the grouting fullness; For the identified void or non-dense area, supplementary grouting is performed through the segment grouting hole until the scanning result shows that the filling is dense.

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