Underpass construction method for karst-related area

Abstract

The invention discloses a karst-related area interval underpass construction method, and relates to the technical field of tunnel engineering, and the karst-related area interval underpass construction method comprises the following steps: carrying out field classification and improvement treatment on soft rock muck discharged by shield tunneling to obtain aggregate muck which can be directly used for backfilling and fine-grain muck which can be used for preparing grouting slurry; muck improvement slurry is prepared from fine muck, karst cavities on the construction path are pre-filled, and advanced grouting reinforcement is conducted on the stratum of the underpass section; during the period that shield tunneling penetrates through a karst area or penetrates through an existing structure under the karst area, synchronous grouting is conducted through muck improvement grout, and grouting parameters and tunneling parameters are dynamically adjusted according to real-time monitoring data; and after segmental lining is completed, compensation grouting is conducted through muck improved grout, and a stacked grouting supporting system is formed in the surrounding rock. According to the method, the shield muck can be recycled, the grouting material cost is reduced, and the safety and reliability of shield underneath pass construction are ensured.

Description

Technical Field

[0001] This invention relates to the field of tunnel engineering technology, and in particular to a method for constructing tunnels through karst areas. Background Technology

[0002] With the continuous expansion of urban rail transit construction, shield tunneling has become a core technology for subway tunnel engineering due to its high efficiency and safety. In karst geological areas, especially in typical karst distribution zones such as southwestern China, the geological structure is complex and variable. Shield tunnel construction frequently faces challenges such as traversing karst caves, fractured strata, and passing under existing buildings, operating railways, or underground pipelines. In such construction environments, the unpredictability of karst cavities, the difficulty in controlling stratum stability, and the requirements for protecting existing structures significantly increase construction safety risks. Meanwhile, with the increasing popularity of green construction concepts, the resource utilization of the large amount of soft rock excavation generated during shield tunneling has attracted much attention, and how to achieve efficient recycling of excavation has become a focus of the industry.

[0003] In current shield tunneling practices in karst areas, a combined approach of advanced geological exploration and grouting reinforcement is commonly adopted. For karst cavities, the conventional method is to fill them by drilling and injecting cement-based or chemical grouts. For sections passing under existing structures, a combination of synchronous grouting and secondary compensation grouting is used to suppress ground deformation. Grouting materials mainly consist of traditional formulas such as purchased cement grout and cement-water glass dual-liquid grout, which are costly and their supply chain is easily constrained by external factors. Meanwhile, soft rock excavation waste is typically treated as waste and disposed of through off-site landfill or temporary stockpiling. This not only significantly increases project costs but also causes land occupation and environmental pollution. While some projects have attempted to use the excavated soil for simple backfilling, the lack of a systematic on-site classification mechanism and targeted improvement technologies has resulted in the ineffective separation of usable components in the excavated soil, leading to unstable backfilling results and significant resource waste.

[0004] The existing technological system suffers from several shortcomings: First, traditional grouting materials rely on external procurement, placing a heavy economic burden on long-distance tunnel construction and large-scale karst treatment. Second, the potential resource of tunnel boring machine (TBM) excavated soil has not been fully exploited, resulting in the waste of a large amount of usable materials, which not only increases the cost of excavated soil disposal but also violates the principles of sustainable development. Third, adjustments to grouting parameters during tunneling are often based on experience-based judgments, failing to establish a dynamic correlation with the real-time status of the excavated soil and structural monitoring data during TBM tunneling, making precise control difficult. Finally, existing grouting support structures often exhibit single-layer characteristics, resulting in significant deficiencies in adaptability and long-term stability when dealing with complex geological conditions in karst areas. These technological bottlenecks collectively lead to a comprehensive predicament for TBM construction in karst regions, characterized by poor economic efficiency, high safety risks, and significant environmental pressures. Summary of the Invention

[0005] The main objective of this invention is to propose a method for tunneling under karst areas, which aims to recycle tunnel excavated soil, reduce the cost of grouting materials, and ensure the safety and reliability of tunneling under construction.

[0006] To achieve the above objectives, the present invention proposes a method for tunneling under karst-inhabited areas, used with a tunnel boring machine. The method includes: The soft rock slag discharged from the tunnel boring machine is classified and improved on-site to obtain aggregate slag that can be directly used for backfilling and fine slag that can be used to prepare grouting slurry. The fine-grained slag was used to prepare a slag improvement grout, which was used to pre-fill karst cavities along the construction path and to reinforce the strata in the underpass section with advanced grouting. During shield tunneling through karst areas or under existing structures, the aforementioned modified slag grout is used for synchronous grouting, and the grouting parameters and tunneling parameters are dynamically adjusted based on real-time monitoring data. After the segment lining is completed, the improved slag grout is used for compensation grouting, forming a layered grouting support system in the surrounding rock.

[0007] In one embodiment, the steps of classifying and improving the soft rock excavation soil discharged from the tunnel boring machine to obtain aggregate excavation soil that can be directly used for backfilling and fine-grained excavation soil that can be used to prepare grouting slurry include: The excavated soil discharged from the tunnel boring machine is screened and classified according to particle size into Class A aggregate excavated soil with a particle size greater than 10mm, Class B fine-grained excavated soil with a particle size less than 10mm, and Class C excavated soil with high moisture content. The type B fine-grained slag and cementitious materials are mixed in a set ratio to form a slag improvement slurry with pumpability and a set setting time. The Class A aggregate slag is stored separately for backfilling the skeleton of karst cavities.

[0008] In one embodiment, the cementitious material includes cement and bentonite, and the mixing mass ratio of the Class B fine-grained slag, cement and bentonite is (6~8):(1~2):(0.5~1), and the initial fluidity of the mixed slurry is not less than 180mm.

[0009] In one embodiment, the steps of using the fine-grained slag to prepare a slag-improved grout for pre-filling karst cavities along the construction path and for pre-grouting reinforcement of the strata in the underpass section include: Detect and locate karst cavities along the construction path to determine their location, size, and filling status; For cavities with a volume greater than a set threshold, first, the Class A aggregate and slag are poured into the cavity to form a skeleton, and then the slag improvement slurry is injected until the cavities are filled. For cavities with a volume smaller than a set threshold, high-concentration soil amendment slurry can be directly injected, and a quick-setting agent can be selectively added.

[0010] In one embodiment, the steps of using the fine-grained slag to prepare a slag-improved grout for pre-filling karst cavities along the construction path and for pre-grouting reinforcement of the strata in the underpass section further include: In front of the shield cutterhead in the underpass section, grouting holes are arranged in a quincunx pattern along the tunnel axis, with a hole spacing of 1.5 to 2.5 m. The grouting is carried out using the aforementioned modified slag grout, and the grouting range covers an area of ​​at least 3 m outside the tunnel outline to form a continuous reinforced shell.

[0011] In one embodiment, during shield tunneling through karst areas or under existing structures, the steps of simultaneously grouting with the aforementioned modified slag grout and dynamically adjusting the grouting parameters and tunneling parameters based on real-time monitoring data include: During the tunneling process, the injection ratio of foam or bentonite is adjusted in real time according to the state of the slag sample discharged by the screw conveyor in order to maintain the fluidity of the slag. The aforementioned slag-modified grout is used for synchronous grouting. The grouting pressure is dynamically controlled according to the distance to the object being grouted. When the object being grouted is an existing tunnel, the grouting pressure does not exceed 0.3 MPa, and a multiple, low-pressure grouting mode is adopted. Automated monitoring points are deployed to monitor the settlement and displacement of existing structures at a frequency of no less than once every 2 hours, and the grouting volume and tunneling speed are adjusted in real time based on the monitoring data.

[0012] In one embodiment, the step of using the prepared slag grout for compensation grouting after the segment lining is completed, and forming a layered grouting support system in the surrounding rock, includes: After the tunnel segments are assembled and the grouting has set, compensation grouting is performed through the grouting holes reserved in the segments. The grouting sequence starts from the bottom of the tunnel and proceeds ring by ring towards the top to ensure that the grout fills the shield tail gap and the surrounding disturbance zone.

[0013] In one embodiment, the step of using the prepared slag grout for compensation grouting after the segment lining is completed, and forming a layered grouting support system in the surrounding rock, further includes: The first layer of grouting is carried out through the grouting holes of the pipe segments, and the modified slag grout of conventional consistency is injected to fill the gap between the pipe segments and the surrounding rock. A second layer of grouting is performed through radial deep holes, injecting the slag-modified grout mixed with fibers or toughening agents to form a tough transition layer in the surrounding rock. A third layer of grouting is performed outside the second layer of grouting body, injecting high-strength slag-modified grout to form a load-bearing arch shell deep within the surrounding rock.

[0014] In one embodiment, before the step of classifying and improving the soft rock excavation soil discharged from the tunnel boring machine to obtain aggregate soil that can be directly used for backfilling and fine-grained soil that can be used to prepare grouting slurry, the method for tunneling under karst areas further includes: Based on geological survey data, karst development areas, sand layer distribution areas, and sensitive areas to be traversed along the construction route were identified, and corresponding standards for waste soil classification, grout mixing ratios, and grouting reinforcement parameters were formulated.

[0015] In one embodiment, the steps of using the fine-grained slag to prepare a slag-improved grout for pre-filling karst cavities along the construction path and for pre-grouting reinforcement of the strata in the underpass section further include: The formation reinforcement is carried out by using a two-component slurry, wherein the two-component slurry is formed by instant mixing the soil improvement slurry and water glass solution at a volume ratio of (3~5):1; During the tunneling process, the slag outlet of the screw conveyor was sealed and modified by installing baffles and slag collection boxes to prevent gushing.

[0016] The technical solution of this invention involves on-site classification and improvement of soft rock excavation waste soil discharged from tunnel boring machines, transforming it into aggregate waste soil suitable for backfilling and fine-grained waste soil suitable for preparing grouting slurry. This achieves the resource utilization of waste soil. Since it avoids the large-scale transportation and disposal of waste soil as in traditional solutions, it effectively reduces engineering costs and environmental impact, prevents secondary pollution to the surrounding environment, and reduces dependence on external material supplies. Furthermore, the waste soil improvement slurry prepared using the improved fine-grained waste soil can be precisely controlled in terms of proportions and flow... Its mobility gives it excellent pumpability, stability, and controllable setting time, enabling it to adapt to various construction stages such as karst cavity pre-filling, advanced grouting reinforcement of strata, synchronous grouting, and compensating grouting. This eliminates the need for frequent material changes or mix adjustments, significantly improving construction continuity and efficiency. Furthermore, it employs differentiated treatment strategies for karst cavities of different volumes: for large cavities, aggregates are first added to form a framework before grout injection; for small cavities, high-concentration grout is directly injected, and quick-setting agents can be added, effectively reducing grout usage and improving filling efficiency. The underpass section forms a continuous reinforced shell through a quincunx arrangement of grouting holes. Grouting and tunneling parameters are dynamically adjusted based on real-time monitoring data. A multi-stage, low-pressure grouting method is employed, avoiding the problems of delayed parameter adjustments and insufficient control precision in traditional methods, thus minimizing disturbance to existing structures. After the segment lining is completed, a layered grouting support system with progressively increasing strength and toughness from the inside out is constructed. This overcomes the limitations of traditional single-layer grouting support in adaptability and long-term stability under complex geological conditions, effectively absorbing and dispersing ground stress, providing more reliable and durable structural support for the tunnel. In summary, this invention comprehensively solves the technical challenges of high grouting material costs, waste of soil resources, insufficient control precision in underpass construction, and a single support system in karst areas through systematic utilization of excavated soil resources, differentiated treatment of karst cavities, refined pre-reinforcement, real-time dynamic adjustment of synchronous grouting, and a layered compensating grouting support system. This significantly improves the economy, safety, environmental friendliness, and long-term stability of the construction. 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 flowchart illustrating an embodiment of the construction method for tunneling through 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 existing shield tunneling construction in karst areas, grouting materials are expensive and reliant on external purchases, resulting in poor economic efficiency. The excavated soil generated during shield tunneling is not effectively utilized, increasing project costs and environmental pressure. When tunneling under existing structures, the adjustment of grouting parameters lacks a linkage mechanism with the condition of the excavated soil and real-time monitoring data, making precise control difficult. Furthermore, existing grouting support systems are mostly single-layered, lacking adaptability and long-term stability under complex geological conditions.

[0024] To address this technical problem, this invention proposes a method for constructing underpasses in karst areas.

[0025] Please see Figure 1 In one embodiment of the present invention, the method for constructing tunnels through karst areas is used with a tunnel boring machine, and the method includes: S10 involves on-site classification and improvement of soft rock slag discharged from shield tunneling to obtain aggregate slag that can be directly used for backfilling and fine-grained slag that can be used to prepare grouting slurry. S20, using the fine-grained slag to prepare slag improvement grout, pre-filling karst cavities along the construction path, and pre-grouting reinforcement of the strata in the underpass section; S30, During shield tunneling through karst areas or under existing structures, the aforementioned modified slag grout is used for synchronous grouting, and the grouting parameters and tunneling parameters are dynamically adjusted according to real-time monitoring data; S40, after the segment lining is completed, the improved slag grout is used for compensation grouting, and a layered grouting support system is formed in the surrounding rock.

[0026] For ease of understanding, the following explains some key terms in this embodiment: The construction method for tunneling under karst areas refers to the construction technology of using a tunnel boring machine to excavate tunnels in areas containing karst geological structures, and passing through or adjacent to sensitive structures such as existing buildings and operating lines during the excavation process.

[0027] A tunnel boring machine (TBM) is a mechanical device used for tunnel excavation. It has a cutterhead at the front end that rotates to cut soil or rock and assembles tunnel segments to form the tunnel lining while excavating.

[0028] Soft rock slag refers to a mixture discharged by a tunnel boring machine during the tunneling process, mainly composed of broken soft rock or soil, and usually has a high water content and plasticity.

[0029] Slag improvement slurry is a slurry with specific rheological and setting properties formed by modifying the fine-grained slag discharged from shield tunneling through the addition of cementing materials. It can be used for grouting reinforcement and filling.

[0030] Karst cavities are underground spaces formed in karst strata by the dissolution of groundwater. Their shapes, sizes and filling conditions vary, posing a challenge to tunnel construction.

[0031] Pre-grouting reinforcement refers to the process of injecting grout into the strata in front of the tunnel boring machine to reinforce the strata in advance, thereby improving strata stability, reducing strata deformation, and controlling groundwater.

[0032] Synchronous grouting refers to the process of injecting grout into the annular gap between the tunnel segments and the surrounding rock through the grouting holes at the tail of the shield during tunneling, in order to fill the gap, balance the ground pressure, and control the deformation of the ground.

[0033] Compensation grouting refers to the injection of grout into the surrounding rock or stratum through pre-reserved grouting holes or boreholes after the tunnel segment lining is completed, in order to further fill voids, adjust stratum stress, and control stratum settlement or uplift.

[0034] Layered grouting support system refers to a grouting system that provides comprehensive support by injecting grouts with different properties in layers and in stages to form a multi-layered structure inside the surrounding rock.

[0035] The method for constructing tunnels in karst areas as described in this application first involves on-site classification and improvement of the soft rock excavation waste soil discharged from the tunnel boring machine (TBM) to obtain aggregate waste soil that can be directly used for backfilling and fine-grained waste soil that can be used to prepare grouting slurry. For example, the waste soil can be classified using physical separation methods, separating large particles from small particles manually or mechanically. The separated fine-grained waste soil can be mixed with one or more solidifying agents (such as cement or lime) to change its rheological properties or strength. The classified aggregate waste soil and fine-grained waste soil can be stored separately for subsequent use.

[0036] Subsequently, the fine-grained slag was used to prepare a slag-improved grout, which was used to pre-fill karst cavities along the construction path and to reinforce the strata in the section under tunnel. For example, karst cavities along the construction path can be identified using conventional geological survey methods. Identified cavities can be filled using a single type of grout. Pre-grouting reinforcement of the strata involves setting grouting holes ahead of the tunnel boring machine and injecting conventional grout to pre-reinforce the strata and improve its bearing capacity.

[0037] During shield tunneling through karst areas or under existing structures, this modified slag grout is used for synchronous grouting, and grouting parameters are dynamically adjusted based on real-time monitoring data. For example, during tunneling, conventional synchronous grouting equipment can be used to inject grout into the tail section of the shield. Grouting parameters (such as grouting pressure and grouting volume) can be adjusted based on construction experience or a pre-set construction plan. Tunneling parameters (such as tunneling speed and cutterhead rotation speed) can also be manually adjusted based on on-site observations.

[0038] After the tunnel lining is completed, the modified slag grout is used for compensation grouting, forming a layered grouting support system within the surrounding rock. For example, after the tunnel lining is completed, compensation grouting can be performed through the pre-drilled grouting holes on the tunnel segments, injecting a single-formula grout to fill the gaps between the tunnel segments and the surrounding rock. This grouting process can create a reinforced zone within the surrounding rock, providing foundation support.

[0039] The method for tunneling under karst areas described in this application achieves resource utilization of the soft rock excavated during shield tunneling by classifying and improving the excavated soil on-site, effectively reducing the external procurement costs of grouting materials and the expenses for excavated soil disposal. The improved excavated soil grout is used for pre-filling karst cavities, pre-reinforcing the strata, simultaneous grouting, and compensating grouting, forming a multi-layered grouting support system that improves the strata reinforcement effect and the stability of the tunnel structure. Simultaneously, by dynamically adjusting grouting and tunneling parameters based on real-time monitoring data, the construction safety and ground deformation control accuracy under sensitive structures are ensured.

[0040] In embodiments of the present invention, the steps of classifying and improving the soft rock excavated soil discharged from shield tunneling to obtain aggregate excavated soil that can be directly used for backfilling and fine-grained excavated soil that can be used to prepare grouting slurry include: S11, the slag discharged from the tunnel boring machine is screened and classified into Class A aggregate slag with a particle size greater than 10mm, Class B fine slag with a particle size less than 10mm, and Class C slag with high moisture content according to particle size. S12, the B-type fine-grained slag and cementitious materials are mixed in a set ratio to form a slag improvement slurry with pumpability and a set setting time. S13, the Class A aggregate slag is stored separately for backfilling the skeleton of karst cavities.

[0041] Specifically, the excavated soil from the tunnel boring machine (TBM) is screened and classified according to particle size into three categories: Category A aggregate soil (greater than 10mm), Category B fine-grained soil (less than 10mm), and Category C high-moisture soil. This step aims to physically separate the raw excavated soil from the TBM tunneling process into materials with different engineering uses based on their particle size and moisture content. Mechanical screening can be performed using equipment such as vibrating screens, drum screens, or hydrocyclones. Category A aggregate soil (greater than 10mm) is identified as suitable as structural backfill material due to its good skeletal support capacity. Category B fine-grained soil (less than 10mm) is more suitable for mixing with cementitious materials to prepare slurry due to its smaller particle size and larger specific surface area. Category C high-moisture soil may require further dewatering treatment or be disposed of as waste to avoid adverse effects on subsequent construction. This refined classification is fundamental to achieving the resource utilization of excavated soil and ensuring the stable performance of subsequent grouting materials.

[0042] Based on this, the Class B fine-grained slag and cementing materials are mixed in a set ratio to form a slag-improved slurry with pumpability and a set setting time. This step involves precisely proportioning and thoroughly mixing the sieved Class B fine-grained slag with cementing materials (such as cement, bentonite, fly ash, slag powder, etc.) to prepare a grouting slurry that meets specific engineering requirements. The "set ratio" is determined experimentally based on the physicochemical properties of the Class B fine-grained slag, the type of cementing material, and the required slurry performance indicators (such as strength, fluidity, setting time, etc.). The mixing process typically uses high-speed mixing equipment to ensure uniform dispersion of the cementing materials and fine-grained slag, forming a stable suspension system. The "pumpability" of the slurry is a key performance characteristic that ensures its smooth delivery to the grouting site via grouting pumps and pipelines, while the "set setting time" ensures that the slurry hardens within a predetermined time after injection, playing a reinforcing or filling role, and avoiding premature setting that blocks pipelines or delayed setting that affects construction progress.

[0043] Simultaneously, the Class A aggregate slag is stored separately for backfilling the skeleton of karst cavities. This step clarifies the specific use and management method of the Class A aggregate slag. Separating the larger-particle-size Class A aggregate slag from other slag and storing it separately facilitates its subsequent use as a skeleton filling material for karst cavities. In large karst cavities, directly injecting grout may result in a huge amount of grout used and difficulty in forming a stable support structure. By first adding Class A aggregate slag to form a coarse skeleton, the amount of grout used can be effectively reduced, engineering costs can be lowered, and a stable support foundation can be provided for subsequent injection of slag-modified grout, thereby improving the filling effect and the overall stability of the structure. Separate storage ensures the purity and usability of the material.

[0044] Through the detailed steps described above for on-site classification and improvement of soft rock excavation waste soil discharged from tunnel boring machines (TBMs), this application effectively transforms the complex waste soil generated during TBM excavation into materials with specific engineering applications. Specifically, by finely screening the waste soil, Class A aggregate waste soil with a particle size greater than 10mm is separated and used specifically for backfilling the skeleton of karst cavities. This not only significantly reduces grout consumption but also provides solid initial support for filling large cavities, improving the stability and economy of the filling process. Simultaneously, Class B fine-grained waste soil with a particle size less than 10mm is precisely mixed with cementitious materials in a set ratio to prepare a waste soil improvement grout with pumpability and a set setting time. This ensures that the grout functions stably and efficiently in all stages, including pre-filling, pre-grouting, synchronous grouting, and compensation grouting, avoiding construction difficulties caused by unstable material properties. This systematic method of waste soil classification and improvement ensures the material quality and performance of subsequent grouting and backfilling operations from the source, thereby significantly improving the overall reliability, efficiency and economy of underpass construction in karst areas and effectively addressing the complex challenges of construction under karst geological conditions.

[0045] In an embodiment of the present invention, the cementitious material includes cement and bentonite, and the mixing mass ratio of the B-type fine-grained slag, cement and bentonite is (6~8):(1~2):(0.5~1), and the initial fluidity of the mixed slurry is not less than 180mm.

[0046] Specifically, the composition of the cementitious material is crucial to the performance of the slag-modified grout. Cement, as the main cementitious component, undergoes a hydration reaction after mixing with water, forming a solidified body with certain strength and stability. This provides the necessary early and later strength to the grout, ensuring the grout can effectively withstand ground pressure and reinforce the surrounding rock. The type of cement can be selected according to project requirements, such as ordinary Portland cement or slag Portland cement, to meet different requirements for setting time, strength development, and durability. Bentonite, as an important rheology modifier, with its unique layered structure and water-absorbing swelling characteristics, can significantly improve the viscosity, thixotropy, and water retention of the grout, enhancing its anti-segregation performance and pumpability. This makes it less prone to settling and stratification during long-distance transportation and filling of complex cavities, while also facilitating better penetration and diffusion of the grout during injection.

[0047] The mixing ratio of the Class B fine-grained slag, cement, and bentonite is (6~8):(1~2):(0.5~1). This ratio range has been optimized to balance the cost, performance, and construction feasibility of the grout. The Class B fine-grained slag serves as the main filler aggregate, with a dosage of 6-8 parts. This effectively utilizes the waste slag generated during tunnel boring, reducing project costs, while providing sufficient solids content to form a dense grout body. The cement dosage is between 1-2 parts, ensuring sufficient strength after solidification to effectively reinforce the strata and fill voids. The bentonite dosage is between 0.5-1 parts, used to precisely adjust the rheological properties of the grout, ensuring good pumpability, stability, and filling capacity, while avoiding excessively high grout viscosity that would hinder pumping or penetration.

[0048] The initial fluidity of the mixed grout should be no less than 180 mm, which is a key indicator for measuring the pumpability and filling capacity of the grout. An initial fluidity of no less than 180 mm means that the grout has good initial fluidity, can be smoothly transported over long distances through grouting pumps and pipelines, and can effectively penetrate and fill karst cavities, geological fissures, and loose areas, ensuring the uniformity and compactness of the grouting and avoiding blockages or incomplete filling due to insufficient fluidity.

[0049] Through the above technical solution, cement and bentonite are used as cementing materials, and the mixing mass ratio of Class B fine-grained slag, cement, and bentonite is precisely controlled within the range of (6~8):(1~2):(0.5~1). Simultaneously, the initial fluidity of the mixed grout is ensured to be no less than 180mm, resulting in a slag-modified grout with excellent rheological properties, stability, and solidification strength. This grout not only effectively utilizes the waste slag generated during shield tunneling, reducing engineering costs, but also ensures the pumpability, permeability, and filling density of the grout in complex karst strata, effectively solving problems such as unstable grout performance and insufficient filling. The good fluidity of the grout ensures its smooth injection and filling of various karst cavities and stratum voids, while the appropriate setting time and solidification strength ensure rapid formation of the grout body and provide reliable support and reinforcement effects, thereby significantly improving the safety, efficiency, and quality of tunneling construction in karst areas.

[0050] In an embodiment of the present invention, the steps of using the fine-grained slag to prepare a slag-improved grout for pre-filling karst cavities along the construction path and for pre-grouting reinforcement of the strata in the underpass section include: S21, to detect and locate karst cavities along the construction path, and determine their location, size and filling status; S22, For cavities with a volume greater than a set threshold, first, the Class A aggregate slag is poured into the cavity to form a skeleton, and then the slag improvement slurry is injected until the cavities are filled. S23, for cavities with a volume smaller than a set threshold, directly inject the high-concentration slag improvement slurry, and optionally add a quick-setting agent.

[0051] Specifically, the steps of detecting and locating karst cavities along the construction path to determine their position, size, and filling state aim to accurately grasp the distribution characteristics of karst cavities and provide a basis for subsequent differentiated treatment. In practice, various geological exploration techniques can be employed. For example, ground-penetrating radar (GPR) can be used to detect the planar location and approximate depth of underground cavities; high-density electrical resistivity tomography (ERT) or transient electromagnetic method (TEM) can be used to obtain resistivity anomalies in the cavities to help determine their extent and filling medium; or core drilling and in-hole television imaging can be used to directly observe the actual size, shape, and internal filling material (such as water, silt, gravel, etc.) of the cavities. The comprehensive application of these detection methods ensures accurate assessment of the location coordinates, three-dimensional dimensions (such as length, width, height, or volume), and filling state (whether it is filled with water, mud, or is hollow), thus providing reliable data support for subsequent grouting scheme design.

[0052] Based on this, for cavities with a volume exceeding a set threshold, the Class A aggregate slag is first poured into the cavity to form a skeleton, and then the slag-improving grout is injected until the voids are filled. This step is designed for large karst cavities and aims to optimize material usage and improve filling efficiency through a step-by-step filling method. The Class A aggregate slag refers to aggregate slag with a particle size greater than 10mm, which, as a skeleton material, has good permeability and a certain bearing capacity. In implementation, the Class A aggregate slag can be poured into the cavity through drilling, gravity flow, pneumatic conveying, or mechanical pumping, allowing it to accumulate and form a coarse aggregate skeleton. Subsequently, the slag-improving grout (made by mixing the Class B fine-grained slag and cementing materials in a set ratio) is injected into the voids of the formed skeleton. The slag-improving grout can penetrate and fill the tiny pores between the aggregates, solidifying the skeleton into a whole, thereby achieving effective filling and reinforcement of large cavities. The “set threshold” here can be set according to engineering experience, cavitary geological conditions and economic considerations, for example, it can be set to 1 cubic meter or 5 cubic meters.

[0053] Simultaneously, for cavities with a volume smaller than a set threshold, a high-concentration modified slag grout is directly injected, with optional addition of a quick-setting agent. This step targets small karst cavities, aiming for rapid and thorough filling and reinforcement. Unlike large cavities, small cavities do not require pre-filling with aggregate. The "high-concentration modified slag grout" directly injected refers to grout prepared by adjusting the ratio of fine-grained slag, cementitious materials (such as cement and bentonite), and water to achieve a higher solids content and faster early strength development. This high-concentration grout better resists hydraulic erosion and sets and solidifies quickly, effectively filling small cavities. Furthermore, to further accelerate the setting speed of the grout, especially in areas requiring rapid sealing or reinforcement, an "optional quick-setting agent" can be added. Accelerating agents (such as water glass, calcium chloride, sodium aluminate, etc.) can significantly shorten the initial and final setting time of the grout, ensuring that the grout quickly forms a stable solidified body in the cavity, preventing the grout from being lost or diluted by groundwater, thereby improving the reinforcement effect and construction efficiency.

[0054] Through the above technical solutions, this application can adopt differentiated pre-filling and advanced grouting reinforcement strategies for karst cavities with different characteristics along the construction path. Firstly, precise detection and location of karst cavities allows for a comprehensive understanding of their location, size, and filling state, providing accurate data for subsequent refined treatment and avoiding blind or excessive grouting, thus improving the targeting and effectiveness of grouting. Secondly, for cavities with larger volumes, the aforementioned Class A aggregate and slag are first placed to form a skeleton, followed by the injection of the slag-modified grout. This significantly reduces the amount of grout used, lowers project costs, and effectively utilizes the waste slag generated during shield tunneling, reflecting the environmentally friendly concept of resource recycling. Simultaneously, the combination of the aggregate skeleton and the grout enhances the overall stability and load-bearing capacity of the filling body. Furthermore, for smaller cavities, high-concentration modified slag grout can be directly injected, with optional addition of a quick-setting agent. This ensures the grout can quickly and thoroughly fill the cavities and rapidly solidify, effectively preventing grout loss and accelerating the formation reinforcement process. This is particularly suitable for areas with high timeliness requirements. In summary, this application, through the combination of refined detection and differentiated grouting strategies, achieves precise, efficient, economical, and environmentally friendly advanced reinforcement of complex karst formations, significantly improving the safety and stability of shield tunneling through karst areas.

[0055] In an embodiment of the present invention, the steps of using the fine-grained slag to prepare a slag-improved grout for pre-filling karst cavities along the construction path and for pre-grouting reinforcement of the strata in the underpass section further include: S24. In front of the shield cutterhead of the underpass section, grouting holes are arranged in a quincunx pattern along the tunnel axis, with a hole spacing of 1.5 to 2.5 m. The grouting is carried out using the aforementioned modified slag grout, and the grouting range covers an area of ​​at least 3 m outside the tunnel outline to form a continuous reinforced shell.

[0056] It should be noted that grouting is performed before the tunnel boring machine (TBM) cutterhead reaches the target area, constituting a form of pre-reinforcement. This proactive approach ensures that the strata have acquired sufficient strength and stability before TBM excavation, effectively reducing potential risks during the excavation process, such as sudden water inrush, mudslides, or ground subsidence. A staggered arrangement of grout holes is an efficient and uniform method. This pattern typically includes a central hole and multiple peripheral holes distributed around it, or an alternating arrangement, designed to ensure maximum diffusion and penetration of the grout within the target area, avoiding grouting blind spots or weak points. Compared to simple straight or grid arrangements, a staggered arrangement creates a denser and more uniform reinforced layer, particularly suitable for karst strata with complex geological conditions and uneven permeability. The spacing of the grout holes is a key parameter affecting the grouting effect. A hole spacing of 1.5–2.5 m is an optimized choice that balances construction efficiency and economy while ensuring effective grout diffusion and uniform reinforcement. Appropriate hole spacing ensures effective overlap and penetration of grout between adjacent holes, forming a continuous and sufficiently strong reinforced zone, avoiding discontinuous reinforcement or insufficient strength due to excessive hole spacing. The slag-modified grout used for injection is prepared from fine-grained slag discharged during shield tunneling and cementitious materials. This grout has good pumpability, controllable setting time, and sufficient early strength, effectively filling fissures, pores, and loose areas in the strata. Its environmental friendliness and economy also make this approach more advantageous. Extending the grouting range to at least 3m outside the tunnel outline aims to form a sufficiently wide and thick reinforced zone. This reinforced zone not only provides direct support for the tunnel structure, but more importantly, it effectively constrains the deformation of the surrounding strata, reduces stress concentration, and thus provides a stable and safe enclosure environment for the tunnel during shield tunneling, reducing the impact on the surrounding environment and existing structures. Through the above series of measures, a continuous and integral reinforced shell is ultimately formed in the strata. This shell, acting like a pre-constructed "tunnel shell," effectively resists ground pressure, stabilizes the excavation face, and provides a uniform and stable tunneling medium for the tunnel boring machine. This continuous reinforced shell significantly improves the safety, stability, and efficiency of tunnel boring, especially when traversing high-risk karst formations.

[0057] The aforementioned technical solution creates a pre-reinforced continuous shell in front of the tunnel boring machine (TBM), effectively solving the problem of ensuring overall ground stability under complex karst geological conditions. The quincunx-shaped arrangement of grouting holes, combined with a reasonable hole spacing, ensures the uniform diffusion and penetration of the slag-modified grout in the surrounding strata, thus constructing a reinforced area of ​​sufficient thickness and uniform strength. This continuous reinforced shell effectively constrains ground deformation, reduces the risk of ground instability during tunneling, and provides a stable and controllable tunneling environment for the TBM. Simultaneously, using the slag discharged from the TBM to prepare the grout for reinforcement reflects the environmentally friendly concept of resource recycling and reduces project costs.

[0058] In an embodiment of the present invention, during shield tunneling through karst areas or under existing structures, the steps of simultaneously grouting with the aforementioned modified slag grout and dynamically adjusting the grouting parameters and tunneling parameters based on real-time monitoring data include: S31, during the tunneling process, the injection ratio of foam or bentonite is adjusted in real time according to the state of the slag sample discharged by the screw conveyor in order to maintain the fluidity of the slag. S32, synchronous grouting is performed using the aforementioned slag-modified grout. The grouting pressure is dynamically controlled according to the distance to the underpass. When the underpass is an existing tunnel, the grouting pressure does not exceed 0.3 MPa, and a multiple, low-pressure grouting mode is adopted. S33 involves deploying automated monitoring points to monitor the settlement and displacement of existing structures at a frequency of no less than once every 2 hours, and adjusting the grouting volume and tunneling speed in real time based on the monitoring data.

[0059] Specifically, during tunnel boring machine (TBM) excavation, the state of the excavated material discharged by the screw conveyor is a crucial indicator reflecting the stability of the excavation face and the plasticity of the excavated soil. The state of the excavated material is typically determined by observing its moisture content, plasticity index, particle size distribution, and flowability. For example, excessively dry excavated soil may lead to increased cutterhead torque and tunneling resistance, while excessively wet soil may cause instability and blowouts at the excavation face. To maintain the plasticity of the excavated soil, the injection ratio of foam or bentonite can be adjusted in real time. Foam injection improves the plasticity of the excavated soil, reduces its cohesion, and makes it easier to transport; bentonite increases the thixotropy of the excavated soil, improving its water retention capacity and plasticity. Through real-time feedback on the state of the excavated material, operators can precisely control the injection volume of foam or bentonite to ensure that the excavated soil remains in a suitable plastic state, thereby ensuring smooth excavation, effectively controlling the stability of the excavation face, and reducing disturbance to the surrounding strata.

[0060] Simultaneous grouting using the aforementioned modified slag grout is a crucial step in controlling ground deformation during shield tunneling. Simultaneous grouting typically occurs at the tail of the tunnel boring machine (TBM). After the tunnel segments are assembled, the grout is injected through grouting holes on the segments into the annular gap between the segments and the surrounding rock. Controlling the grouting pressure is critical, especially when tunneling under existing structures. The grouting pressure needs to be dynamically controlled based on the distance to the tunnel object. The closer to the object, the more strictly the grouting pressure should be controlled. Lower grouting pressures are typically used to avoid uplift or compression effects on existing structures. For example, when tunneling under an existing tunnel, the grouting pressure is strictly controlled to no more than 0.3 MPa, which helps minimize the impact on the existing tunnel structure. Furthermore, employing a multi-stage, low-pressure grouting method—injecting small amounts of grout multiple times with each injection at a low pressure—avoids the impact of instantaneous high pressure on the ground and structures. This allows the grout sufficient time to diffuse fully and evenly fill the gaps, thus more effectively supporting the ground and controlling ground deformation.

[0061] To ensure construction safety and the stability of existing structures, automated monitoring points need to be deployed to monitor the settlement and displacement of existing structures in real time. These automated monitoring points can include settlement observation points, displacement sensors, inclinometers, etc., and are deployed at key locations on existing structures, such as tunnel roofs, sidewalls, and bridge piers. Monitoring frequency is no less than once every two hours to ensure timely detection of even minor deformation trends. Based on the monitoring data, construction personnel can assess the impact of construction on existing structures in real time. Once monitoring data shows that settlement or displacement exceeds preset warning values, the grouting volume and tunneling speed can be adjusted immediately based on the monitoring data. For example, when settlement is detected, the grouting volume can be increased to raise the ground; when displacement is detected, the tunneling speed can be adjusted to reduce disturbance to the ground, thereby achieving refined control and risk management of the construction process.

[0062] Through the above technical solutions, refined and dynamic management of the construction process can be achieved during shield tunneling through karst areas or under existing structures. Real-time adjustment of the excavation soil's fluidity and plasticity ensures the stability of the excavation face and smooth muck removal, effectively controlling ground disturbance. Dynamically controlled synchronous grouting, especially the low-pressure, multi-stage grouting mode for existing structures, minimizes the impact on existing structures and effectively controls ground deformation. Combined with real-time feedback from automated monitoring points, the construction team can promptly identify and correct potential problems. By adjusting the grouting volume and tunneling speed, construction safety is ensured, significantly improving the risk control capabilities and project quality of shield tunneling in karst areas and under sensitive structures.

[0063] In an embodiment of the present invention, the steps of performing compensation grouting using the slag-modified grout after the segment lining is completed, and forming a layered grouting support system within the surrounding rock, include: S41 After the tunnel segments are assembled and the grouting has initially set, compensation grouting is carried out through the grouting holes reserved in the tunnel segments. The grouting sequence starts from the bottom of the tunnel and proceeds ring by ring towards the top to ensure that the grout fills the shield tail gap and the surrounding disturbance zone.

[0064] Specifically, compensation grouting is performed after the tunnel segments are assembled and the synchronous grouting has initially set. This timing is crucial, as it ensures the tunnel segment lining structure is fully formed, providing stable boundary conditions for subsequent compensation grouting. Simultaneously, the synchronous grouting slurry has reached its initial setting state and possesses a certain strength, preventing interference or dilution between the compensation grouting slurry and the synchronous grouting slurry, thus guaranteeing the independence and effectiveness of the two grouting effects. This approach helps to precisely control the scope and effect of compensation grouting, avoiding grout loss or uneven filling.

[0065] Compensation grouting is performed through pre-drilled grouting holes in the tunnel lining segments. These pre-drilled holes are channels specifically designed for later grouting or inspection and are typically installed during segment manufacturing, equipped with grout stop valves or grout nozzles. Using these pre-drilled holes for compensation grouting allows for the direct and precise injection of modified soil grout into the annular gap between the tunnel lining segments and the surrounding rock, particularly the shield tail gap and disturbed areas. This method avoids secondary damage to the installed segments, simplifies the construction process, and ensures targeted grouting.

[0066] The grouting sequence begins at the bottom of the tunnel and proceeds ring by ring towards the top. This grouting sequence is optimized based on gravity and the flow characteristics of the grout. Starting grouting from the bottom of the tunnel allows the grout to better fill the voids at the bottom under gravity and gradually advance upwards, effectively expelling water or air from the voids and preventing the formation of air pockets or unfilled areas. The ring-by-ring upward grouting strategy ensures that the grout can uniformly and continuously fill the entire annular space, thereby forming a dense and complete support layer, effectively transmitting ground pressure and preventing localized stress concentration.

[0067] The aforementioned compensatory grouting aims to ensure that the grout fills the shield tail void and the surrounding disturbed area. The shield tail void refers to the annular gap formed between the shield tail and the assembled tunnel segments, as well as between the outer side of the tunnel segments and the surrounding rock, after the tunnel boring machine (TBM) advances. The surrounding disturbed area refers to the area of ​​loosening or stress release caused to the surrounding soil during TBM excavation. The main purpose of compensatory grouting is to accurately and thoroughly fill these critical areas. By filling the shield tail void, immediate support can be provided for the tunnel segments, preventing them from sinking or deforming; by filling the surrounding disturbed area, the compactness and bearing capacity of the strata can be restored, reducing surface settlement and effectively preventing groundwater infiltration into the tunnel, thereby significantly improving the overall stability and durability of the tunnel.

[0068] Through the aforementioned technical solution, after the tunnel segments are assembled and the initial grouting has set, compensatory grouting is performed using the pre-reserved grouting holes in the segments. Adopting a grouting sequence from bottom to top, this method can accurately and thoroughly fill the shield tail voids and surrounding disturbance zones formed during tunnel boring. This effectively compensates for potential shortcomings of synchronous grouting, avoiding problems such as segment deformation, ground settlement, and water leakage caused by residual voids, and significantly improving the overall stability and durability of the tunnel lining structure. In particular, under complex geological conditions involving karst areas or passing under existing structures, this compensatory grouting measure can further strengthen the bond between the surrounding rock and the lining, forming a denser support system and ensuring the long-term safety and reliability of the tunnel operation.

[0069] In an embodiment of the present invention, after the segment lining is completed, the step of using the slag-modified grout for compensation grouting and forming a layered grouting support system in the surrounding rock further includes: S42, the first layer of grouting is carried out through the grouting holes of the pipe segments, and the slag-modified grout of conventional consistency is injected to fill the gap between the pipe segments and the surrounding rock; S43, a second layer of grouting is performed through radial deep holes, injecting the slag-improved grout mixed with fibers or toughening agents to form a tough transition layer in the surrounding rock; S44, a third layer of grouting is performed outside the second layer of grouting body, injecting high-strength slag-modified grout to form a load-bearing arch shell deep in the surrounding rock.

[0070] Specifically, the first layer of grouting is carried out through the grouting holes reserved in the tunnel lining segments, aiming to fill the initial voids between the segments and the surrounding rock. During this process, a slag-modified grout of conventional consistency is injected. Its moderate fluidity ensures that the grout spreads evenly and effectively to the outside of the segments, thereby providing immediate support, reducing uneven stress on the segments, and laying the foundation for subsequent deep reinforcement.

[0071] Furthermore, a second layer of grouting is performed through radial deep holes, extending deep into the surrounding rock. The arrangement of these radial deep holes can be determined based on geological conditions and stress analysis, typically in a radial or spiral pattern. The injected slag-modified grout contains fibers or toughening agents, such as polypropylene fibers, glass fibers, or polymer toughening agents. These additives significantly improve the tensile strength, crack resistance, and toughness of the grout-consolidated body. In this way, a tough transition layer with a certain degree of elasticity and plasticity is formed in the surrounding rock. This layer effectively absorbs and disperses formation stress, reduces stress concentration, prevents brittle failure of the surrounding rock, and adapts to a certain degree of formation deformation, thereby improving the overall deformation resistance of the support system.

[0072] Building upon this foundation, a third layer of grouting is performed outside the second layer. The purpose is to construct a high-strength load-bearing arch shell deep within the surrounding rock, serving as the primary support structure for the tunnel's long-term stability. The injected modified slag grout possesses higher strength, which can be achieved by adjusting the proportions of the cementitious materials (e.g., increasing cement content), optimizing the water-cement ratio, or adding high-efficiency water-reducing agents. Once solidified, this high-strength grout forms a robust and dense ring structure, effectively bearing the stress of the overlying soil and strata, transferring the tunnel load to deeper, more stable strata, thereby significantly improving the tunnel's long-term stability and safety.

[0073] The aforementioned layered grouting support system significantly improves the long-term stability and bearing capacity of the tunnel surrounding rock. The first layer of grouting effectively fills the initial voids between the tunnel segments and the surrounding rock, providing immediate support. Building upon this, the second layer of grouting, using a modified slag grout mixed with fibers or toughening agents, constructs a tough transition layer within the surrounding rock. This layer absorbs and disperses ground stress, effectively resisting ground deformation and preventing brittle failure caused by stress concentration. Furthermore, the third layer of grouting forms a high-strength load-bearing arch shell deep within the surrounding rock, serving as the tunnel's primary long-term support structure and transferring loads to more stable strata. This composite support structure, with its progressively increasing strength and toughness from the inside out, overcomes the limitations of a single grouting layer in complex karst geological conditions, effectively addressing issues such as surrounding rock disturbance and uneven settlement, thereby ensuring the long-term safety and stable operation of the tunnel during construction under karst areas.

[0074] In an embodiment of the present invention, before the step of classifying and improving the soft rock excavation soil discharged from the tunnel boring machine to obtain aggregate excavation soil that can be directly used for backfilling and fine-grained excavation soil that can be used to prepare grouting slurry, the method for tunneling under karst areas further includes: S101, based on geological survey data, identifies karst development areas, sand layer distribution areas, and sensitive areas to be traversed along the construction path, and formulates corresponding slag classification standards, grout mixing schemes, and grouting reinforcement parameters.

[0075] Specifically, identifying karst development zones, sand layer distribution zones, and sensitive areas to be traversed along the construction route, based on geological survey data, involves a comprehensive and in-depth analysis and assessment of the geological conditions of the construction area by reviewing engineering geological survey reports, borehole columnar sections, geophysical exploration results (such as high-density electrical resistivity tomography, transient electromagnetic methods, and ground-penetrating radar), and hydrogeological reports. Karst development zones typically manifest as caves, solution channels, and fissures, while sand layer distribution zones refer to strata rich in sand. Sensitive areas to be traversed may include areas sensitive to settlement and deformation, such as existing buildings, important pipelines, and rivers. The identification process requires professional geological engineers to interpret and analyze the data, and to draw detailed geological profiles and planar distribution maps to clarify the spatial distribution, scale, and engineering characteristics of various geological bodies.

[0076] Based on this, establishing corresponding waste soil classification standards involves meticulously classifying the waste soil discharged from tunnel boring machines, taking into account the characteristics of identified karst development areas, sand layer distribution areas, and other factors. Because the properties of waste soil discharged from different geological regions vary significantly—for example, karst areas may discharge large amounts of gravel and marl waste soil, while sandy areas may discharge sandy waste soil with high water content—it is necessary to refine the particle size classification thresholds, water content control ranges, and uses of different categories of waste soil based on these geological characteristics. For instance, considering the high gravel content in karst areas, the lower limit of the particle size for Class A aggregate waste soil can be adjusted, or treatment requirements for Class C high-moisture-content waste soil can be increased to ensure the maximum utilization of waste soil resources and the effectiveness of subsequent treatment.

[0077] Simultaneously, developing corresponding grout mixing schemes refers to optimizing the proportions of various components (such as fine-grained slag, cementitious materials, water, and admixtures) in the slag-modified grout used for grouting, tailored to different geological conditions and grouting purposes. For example, when pre-filling karst cavities, large cavities may require grouts with high consistency and high strength; for fractured areas, grouts with good permeability and controllable setting time are needed. In sandy areas, the seepage prevention performance of the grout may need to be considered. Therefore, the grout mixing scheme should be finely adjusted based on the identified geological conditions, adjusting the mixing ratio of fine-grained slag, cement, and bentonite, and considering whether to add admixtures such as accelerators, retarders, and water-reducing agents to meet the requirements of different grouting purposes and geological conditions, ensuring that the grout performance is highly matched with actual needs.

[0078] Furthermore, establishing corresponding grouting reinforcement parameters involves determining key parameters such as grouting pressure, grouting volume, grouting rate, grouting hole spacing, and grouting sequence based on the identified karst development areas, sand layer distribution areas, and areas prone to penetration. For example, in karst cavity areas, a high-flow-rate, high-pressure grouting method may be necessary to ensure the grout fully fills the cavities; in sand layer areas, a low-pressure, multiple-stage grouting method may be required to prevent ground uplift or grout loss. In areas prone to penetration, grouting pressure and volume need to be strictly controlled and dynamically adjusted based on real-time monitoring data to minimize the impact on existing structures. The arrangement and spacing of grouting holes should also be optimized according to geological conditions and the reinforcement range to achieve precise and efficient grouting reinforcement.

[0079] By employing the aforementioned technical solutions, karst development zones, sand layer distribution zones, and sensitive areas along the construction path are identified based on geological survey data before construction. Targeted standards for waste soil classification, grout mixing ratios, and grouting reinforcement parameters are then developed. This allows for more targeted and scientific implementation of subsequent construction phases, such as waste soil handling, karst cavity pre-filling, pre-grouting reinforcement of strata, synchronous grouting, and compensatory grouting. This avoids the risks associated with blind construction and improper parameter settings, ensures the compatibility of grout properties with geological conditions, and improves the effectiveness of grouting reinforcement. Consequently, it significantly enhances the overall safety and efficiency of underpass construction in karst areas and effectively controls the impact on the surrounding environment and existing structures.

[0080] In an embodiment of the present invention, the steps of using the fine-grained slag to prepare a slag-improved grout for pre-filling karst cavities along the construction path and for pre-grouting reinforcement of the strata in the underpass section further include: S210, a two-component slurry is used for ground reinforcement, wherein the two-component slurry is formed by instant mixing the slag improvement slurry and water glass solution at a volume ratio of (3~5):1; S220, and during the tunneling process, the slag outlet of the screw conveyor was sealed and modified by installing baffles and slag collection boxes to prevent gushing.

[0081] Specifically, water glass solution, acting as a quick-setting agent, rapidly coagulates with the soil amendment grout, forming a solidified body. This immediate mixing is typically achieved using a dual-pump grouting system, delivering the two grouts separately to the grouting orifice or in-hole mixer to prevent premature coagulation in the delivery pipeline. This volume ratio aims to balance the grout's setting time, strength, and pumpability, ensuring the rapid formation of a high-strength, low-permeability solidified body after injection into the formation.

[0082] Furthermore, this application also involves sealing modifications to the slag discharge port of the screw conveyor during tunneling, including the installation of baffles and a slag collection box to prevent gushing. The sealing modification can involve installing a flexible sealing device, such as a rubber sealing ring or brush seal, between the slag discharge port and the slag collection box to reduce the leakage of slag and water from the gaps. Baffles are typically installed inside or outside the slag discharge port and can be adjusted according to the flow rate and pressure of the slag, acting as a throttling and buffer to slow the discharge speed and prevent instantaneous gushing. The slag collection box is located below or at the end of the screw conveyor slag discharge port to collect the discharged slag and guide it to subsequent processing equipment or transport vehicles. Its design should consider volume, sealing performance, and connection method with the screw conveyor to ensure smooth and continuous discharge of slag.

[0083] The above technical solution employs a two-component slurry, a mixture of slag-modified slurry and water glass solution, for ground reinforcement. Utilizing the rapid-setting properties of water glass, it quickly fills fissures and voids in the strata, forming a rapidly solidified, high-strength, and low-permeability reinforced body. This effectively solves the problems of slow setting speed, easy loss, and poor reinforcement effect of single slag-modified slurry when facing highly permeable strata or areas with high water pressure. It significantly improves the stability of the strata and the water-stopping effect, providing a solid guarantee for the safe tunneling of the shield. Simultaneously, during tunneling, the slag outlet of the screw conveyor is sealed and equipped with baffles and a slag collection box, effectively controlling the discharge flow and pressure of the slag and preventing slag gushing under water and soil pressure. This not only reduces slag loss and environmental pollution but also ensures the safety of construction personnel and helps maintain the stability of the shield tunneling face, ensuring the continuity and efficiency of construction.

[0084] The following example will provide a more detailed explanation of the above technical solution: In a certain urban rail transit project, a shield tunnel needs to be constructed to traverse a karst development area and pass under an existing, operational subway tunnel. The geological conditions in this area are complex, with numerous karst cavities and weak strata, and the requirement for controlling ground deformation is extremely high when passing under existing structures.

[0085] In the early stages of construction, the project team identified karst development areas, sand layer distribution areas, and sensitive areas along the construction path, including those passing under existing subway tunnels, based on detailed geological survey data. Based on this information, the team developed detailed standards for waste soil classification, mix proportions for waste soil amendment grout, and grouting reinforcement parameters. For example, for karst areas, the grouting pressure and range for pre-filling and advanced reinforcement were determined; for sections passing under existing tunnels, strict parameters for synchronous grouting and compensating grouting were set.

[0086] During tunnel boring machine (TBM) excavation, the soft rock excavated by the TBM is first classified and improved on-site. Using screening equipment, the excavated soil is divided into three categories based on particle size: Category A aggregate excavated soil with a particle size greater than 10mm, Category B fine-grained excavated soil with a particle size less than 10mm, and Category C excavated soil with high moisture content. Category A aggregate excavated soil is stored separately for subsequent backfilling of karst cavities. Category B fine-grained soil is mixed with cementitious materials (including cement and bentonite) at a preset mass ratio. For example, the mixing mass ratio of Category B fine-grained soil, cement, and bentonite is set at 7:1.5:0.8 to ensure that the initial fluidity of the mixed slurry is not less than 180mm, forming an improved slurry with good pumpability and a set setting time. This method effectively utilizes the excavated soil generated during TBM excavation, avoiding the cost and environmental problems of off-site disposal of excavated soil in traditional methods, while also reducing the procurement cost of grouting materials.

[0087] Before the tunnel boring machine (TBM) reaches the karst area, prepared slag-modified grout is used to pre-fill karst cavities along the construction path, and the strata in the section to be tunneled are reinforced by pre-grouting. First, advanced geological exploration technology is used to accurately detect and locate the position, size, and filling status of karst cavities. For cavities with a volume greater than a set threshold (e.g., 5 cubic meters), pre-stored Class A aggregate slag is first poured into the cavity to form a stable framework structure, followed by slag-modified grout until the voids are filled. For cavities with a volume less than the set threshold, a high-concentration slag-modified grout is directly injected, with accelerators added selectively as needed to speed up the grout's setting. Simultaneously, grouting holes are arranged in a quincunx pattern along the tunnel axis in front of the TBM cutterhead, with a spacing of approximately 2 meters between holes. Through these grouting holes, modified slag grout is injected, covering an area at least 3 meters outside the tunnel outline. This forms a continuous reinforced shell before shield tunneling, effectively improving the stability and bearing capacity of the surrounding rock and reducing the risk of sudden geological disasters during tunneling. Compared with traditional single cement grout, using modified slag grout for pre-filling and advanced reinforcement not only saves material costs but also improves the reinforcement effect due to its good permeability and filling properties.

[0088] During shield tunneling through karst areas or under existing subway tunnels, synchronous grouting is performed using a modified slag grout. During tunneling, construction personnel adjust the injection ratio of foam or bentonite in real time based on the state of the slag sample discharged from the screw conveyor to maintain the fluidity of the slag, ensuring smooth slag removal and effectively balancing the pressure at the tunnel face. The synchronous grouting uses a modified slag grout, and the grouting pressure is dynamically controlled according to the distance to the object being tunneled. When tunneling under an existing subway tunnel, the grouting pressure is strictly controlled below 0.3 MPa, and a multiple, low-pressure grouting mode is adopted to minimize disturbance to existing structures. Simultaneously, automated monitoring points are deployed in and around the existing subway tunnel to monitor its settlement and displacement in real time, with a monitoring frequency of no less than once every two hours. Based on the monitoring data, the construction team adjusts the synchronous grouting volume and shield tunneling speed in real time to achieve precise control and ensure the safety of existing structures. This linkage mechanism overcomes the problems of delayed grouting parameter adjustment and insufficient control precision in traditional methods. In addition, during the tunneling process, the slag outlet of the screw conveyor was sealed and modified, and baffles and slag collection boxes were installed to effectively prevent the gushing phenomenon that may occur in complex strata and ensure construction safety.

[0089] After the tunnel lining is completed, compensation grouting is performed using slag-modified grout to form a layered grouting support system within the surrounding rock. After the tunnel segments are assembled and the initial setting of the synchronous grouting, compensation grouting is performed through the pre-reserved grouting holes in the segments. The grouting sequence starts from the bottom of the tunnel and proceeds ring by ring towards the top, ensuring that the grout fully fills the shield tail voids and surrounding disturbed areas, further controlling ground deformation. To form a more stable and adaptable support system, this method also includes: First, the first layer of grouting is carried out through the grouting holes of the pipe segments, injecting slag-modified grout of conventional consistency to fill the gaps between the pipe segments and the surrounding rock, forming the basic filling layer.

[0090] Subsequently, a second layer of grouting was carried out through radial deep holes, injecting slag-modified grout mixed with fibers or toughening agents to form a tough transition layer in the surrounding rock, thereby enhancing the deformation resistance and overall stability of the surrounding rock.

[0091] Finally, a third layer of grouting is carried out outside the second layer of grouting body, injecting high-strength slag-modified grout to form a load-bearing arch shell deep in the surrounding rock, providing long-term structural support for the tunnel.

[0092] Through the aforementioned series of steps, this construction method not only effectively utilizes the excavated soil generated during shield tunneling, reducing project costs and environmental impact, but also successfully solves technical challenges such as karst cavity treatment, ground settlement control, and ensuring the safety of existing structures through multi-layered, refined grouting reinforcement and real-time dynamic adjustments. Compared with existing single-layer grouting support systems, the layered grouting support system formed by this method significantly improves adaptability and long-term stability under complex geological conditions.

[0093] The above description is merely an exemplary embodiment of the present invention and is not intended to 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 method for constructing tunnels through karst areas, used with a tunnel boring machine, characterized in that, The construction method for tunneling through karst areas includes: The soft rock slag discharged from the tunnel boring machine is classified and improved on-site to obtain aggregate slag that can be directly used for backfilling and fine slag that can be used to prepare grouting slurry. The fine-grained slag was used to prepare a slag improvement grout, which was used to pre-fill karst cavities along the construction path and to reinforce the strata in the underpass section with advanced grouting. During shield tunneling through karst areas or under existing structures, the aforementioned modified slag grout is used for synchronous grouting, and the grouting parameters and tunneling parameters are dynamically adjusted based on real-time monitoring data. After the segment lining is completed, the improved slag grout is used for compensation grouting, forming a layered grouting support system in the surrounding rock.

2. The construction method for tunneling through karst areas as described in claim 1, characterized in that, The steps for on-site classification and improvement of soft rock excavation waste soil discharged from tunnel boring machines to obtain aggregate waste soil that can be directly used for backfilling and fine-grained waste soil that can be used to prepare grouting slurry include: The excavated soil discharged from the tunnel boring machine is screened and classified according to particle size into Class A aggregate excavated soil with a particle size greater than 10mm, Class B fine-grained excavated soil with a particle size less than 10mm, and Class C excavated soil with high moisture content. The type B fine-grained slag and cementitious materials are mixed in a set ratio to form a slag improvement slurry with pumpability and a set setting time. The Class A aggregate slag is stored separately for backfilling the skeleton of karst cavities.

3. The construction method for tunneling through karst areas as described in claim 2, characterized in that, The cementitious material includes cement and bentonite. The mixing mass ratio of the B-type fine-grained slag, cement and bentonite is (6~8):(1~2):(0.5~1). The initial fluidity of the mixed slurry is not less than 180mm.

4. The construction method for tunneling through karst areas as described in claim 2 or 3, characterized in that, The steps of using the fine-grained slag to prepare a slag-improved grout for pre-filling karst cavities along the construction path and for pre-grouting reinforcement of the strata in the underpass section include: Detect and locate karst cavities along the construction path to determine their location, size, and filling status; For cavities with a volume greater than a set threshold, first, the Class A aggregate and slag are poured into the cavity to form a skeleton, and then the slag improvement slurry is injected until the cavities are filled. For cavities with a volume smaller than a set threshold, high-concentration soil amendment slurry can be directly injected, and a quick-setting agent can be selectively added.

5. The construction method for tunneling through karst areas as described in claim 4, characterized in that, The steps of using the fine-grained slag to prepare slag-improved grout for pre-filling karst cavities along the construction path and for pre-grouting reinforcement of the strata in the underpass section also include: In front of the shield cutterhead in the underpass section, grouting holes are arranged in a quincunx pattern along the tunnel axis, with a hole spacing of 1.5 to 2.5 m. The grouting is carried out using the aforementioned modified slag grout, and the grouting range covers an area of ​​at least 3 m outside the tunnel outline to form a continuous reinforced shell.

6. The construction method for tunneling through karst areas as described in claim 5, characterized in that, During shield tunneling through karst areas or under existing structures, the steps of simultaneously grouting with the aforementioned modified slag grout and dynamically adjusting grouting and tunneling parameters based on real-time monitoring data include: During the tunneling process, the injection ratio of foam or bentonite is adjusted in real time according to the state of the slag sample discharged by the screw conveyor in order to maintain the fluidity of the slag. The aforementioned slag-modified grout is used for synchronous grouting. The grouting pressure is dynamically controlled according to the distance to the object being grouted. When the object being grouted is an existing tunnel, the grouting pressure does not exceed 0.3 MPa, and a multiple, low-pressure grouting mode is adopted. Automated monitoring points are deployed to monitor the settlement and displacement of existing structures at a frequency of no less than once every 2 hours, and the grouting volume and tunneling speed are adjusted in real time based on the monitoring data.

7. The construction method for tunneling through karst areas as described in claim 6, characterized in that, After the segment lining is completed, the steps of using the aforementioned slag-modified grout for compensation grouting and forming a layered grouting support system within the surrounding rock include: After the tunnel segments are assembled and the grouting has set, compensation grouting is performed through the grouting holes reserved in the segments. The grouting sequence starts from the bottom of the tunnel and proceeds ring by ring towards the top to ensure that the grout fills the shield tail gap and the surrounding disturbance zone.

8. The construction method for tunneling through karst areas as described in claim 7, characterized in that, After the segment lining is completed, the steps of using the aforementioned slag-modified grout for compensation grouting and forming a layered grouting support system within the surrounding rock also include: The first layer of grouting is carried out through the grouting holes of the pipe segments, and the modified slag grout of conventional consistency is injected to fill the gap between the pipe segments and the surrounding rock. A second layer of grouting is performed through radial deep holes, injecting the slag-modified grout mixed with fibers or toughening agents to form a tough transition layer in the surrounding rock. A third layer of grouting is performed outside the second layer of grouting body, injecting high-strength slag-modified grout to form a load-bearing arch shell deep within the surrounding rock.

9. The construction method for tunneling through karst areas as described in claim 1, characterized in that, Before the steps of on-site classification and improvement of the soft rock excavation soil discharged from the tunnel boring machine to obtain aggregate soil that can be directly used for backfilling and fine-grained soil that can be used to prepare grouting slurry, the method for tunneling under karst areas also includes: Based on geological survey data, karst development areas, sand layer distribution areas, and sensitive areas to be traversed along the construction route were identified, and corresponding standards for waste soil classification, grout mixing ratios, and grouting reinforcement parameters were formulated.

10. The construction method for tunneling through karst areas as described in claim 9, characterized in that, The steps of using the fine-grained slag to prepare slag-improved grout for pre-filling karst cavities along the construction path and for pre-grouting reinforcement of the strata in the underpass section also include: The formation reinforcement is carried out by using a two-component slurry, wherein the two-component slurry is formed by instant mixing the soil improvement slurry and water glass solution at a volume ratio of (3~5):1; During the tunneling process, the slag outlet of the screw conveyor was sealed and modified by installing baffles and slag collection boxes to prevent gushing.

Images