Lake bottom shallow layer small-diameter shield underneath crossing construction method

Abstract

The invention discloses a small-diameter shield underneath pass construction method for a shallow layer at the bottom of a lake, and relates to the field of shield construction methods. According to the lake bottom shallow layer small-diameter shield underneath pass construction method, an efficient construction method system capable of conducting parameter feedback according to the construction process is formed by integrating the five steps of trial tunneling parameter determination, dynamic muddy water pressure and mud film control, synchronous grouting, slurry performance feedback adjustment based on muck properties and secondary grouting compensation based on monitoring; according to the method, accurate dynamic balance of water and soil pressure of the excavation face can be achieved, the stability of the excavation face is guaranteed, the mud performance is optimized through a real-time feedback mechanism, it is guaranteed that a mud film is effectively sealed, the water blocking effect is good, and refined control over stratum deformation is achieved by combining dual grouting control; therefore, the technical problems that the excavation face is unstable and settlement is difficult to control when the shallow layer penetrates through the water body are solved.

Description

Technical Field

[0001] This invention relates to the technical field of shield tunneling methods, specifically a method for constructing shallow, small-diameter shield tunnels under lake bottoms. Background Technology

[0002] With the continuous expansion of urban underground space development, shield tunneling is increasingly widely used in projects crossing sensitive water bodies such as rivers, lakes, and reservoirs. For water-rich strata, the existing technology mainly adopts the slurry balance shield tunneling method, which balances water and soil pressure by applying slurry pressure to the excavation face and uses slurry to form a mud film in the stratum pores to stabilize the excavation face. At the same time, synchronous grouting technology is used to control stratum deformation. This technology system constitutes the mainstream process basis for current construction of tunnels under water bodies.

[0003] However, under the specific conditions of shallow-buried, small-diameter tunnels at the bottom of lakes, existing technologies still have the following problems. First, the strata have poor self-stability under shallow overburden conditions and are extremely sensitive to pressure fluctuations in the slurry chamber. Conventional pressure control strategies are difficult to achieve dynamic balance within a predetermined range, which can easily lead to instability of the excavation face or surface slurry seepage. Second, facing the complex and variable strata at the bottom of lakes, the water-blocking effect is poor during construction, and the risk of groundwater seepage is high. Third, settlement control mainly relies on synchronous grouting. For delayed settlement caused by soil creep or insufficient grouting in the later stages, there is a lack of compensation mechanism, making it difficult to control the total settlement within the target range. In view of the shortcomings of existing technologies, this invention provides a method for constructing shallow, small-diameter shield tunnels at the bottom of lakes to solve the above problems. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a method for constructing shallow, small-diameter shield tunnels under lake bottoms. This method integrates five steps: determining trial excavation parameters, controlling dynamic slurry pressure and mud film, synchronous grouting, adjusting mud performance based on soil properties, and secondary grouting compensation based on monitoring. This forms a highly efficient construction method system capable of responding to feedback from construction process parameters. This method achieves precise dynamic balance of water and soil pressure at the excavation face, ensuring its stability. Furthermore, it optimizes mud performance through a real-time feedback mechanism, ensuring effective mud film sealing and good water-blocking effect. Combined with dual grouting control, it achieves refined management of ground deformation, thereby solving the technical problems of excavation face instability and settlement control when tunneling under shallow water bodies.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a method for constructing a shallow, small-diameter shield tunnel under a lake bottom, the method comprising the following steps: Step S1: Before the tunnel boring machine enters the lake bottom influence zone, a trial tunneling section is set up to obtain and determine the tunnel boring parameter set that matches the engineering strata through the trial tunneling. In step S2, the tunnel boring machine enters the lake bottom influence area to carry out underpass excavation. The pressure of the slurry chamber is dynamically adjusted to balance the water and soil pressure at the excavation face. At the same time, a specific ratio of slurry is injected into the strata at the excavation face to form a sealing mud film. Step S3: Simultaneous grouting is performed during the tunneling process to fill the gaps in the tail shield structure; Step S4: Based on real-time monitoring of the properties of the excavated soil during the tunneling process, dynamically adjust the performance parameters of the mud. Step S5: Based on real-time monitoring data of lakebed strata settlement, determine whether secondary grouting compensation should be carried out after tunnel lining.

[0006] Preferably, in the process of dynamically adjusting the pressure of the slurry tank in step S2, the flow rates of slurry inlet and outlet are dynamically adjusted according to the real-time monitored soil and water pressure of the formation, so that the pressure of the slurry tank is maintained within 1.1 to 1.3 times the calculated value of the static soil and water pressure of the formation, and the pressure fluctuation is controlled within a preset threshold.

[0007] Preferably, in the process of forming a closed mud film in step S2, the mud slurry with a specific ratio contains fine particles and polymer additives, which form a low-permeability dense mud film in the pores of the formation through infiltration to block the seepage of groundwater to the excavation face.

[0008] Preferably, in step S4, the excavated soil output from the sludge discharge pipeline is continuously sampled and observed. When the properties of the excavated soil deviate from the preset ideal plastic state, at least one of the clay content, polymer additive ratio and water volume in the mud is adjusted to change the viscosity, water loss or sludge carrying capacity of the mud, so that the mud can be restored to a state that meets the requirements of excavation face stability and mud film formation.

[0009] Preferably, before step S1, the tunnel boring machine is subjected to graded initial excavation. The graded initial excavation is divided into at least two stages. From the previous stage to the next stage, the pressure setting value of the slurry chamber is gradually increased, and the tunneling speed is gradually increased until the normal tunneling parameters determined in step S1 are reached.

[0010] Preferably, between steps S1 and S2, the cutterhead of the tunnel boring machine is inspected. During the inspection, the wear of the cutter is first checked to be less than a preset threshold, and finally the torque of all cutter fixing bolts is checked.

[0011] Preferably, in the synchronous grouting process described in step S3, a fast-setting grout is used and implemented through a multi-point grouting system at the shield tail. The grouting process adopts a dual control mode of flow rate and pressure, and the total grouting volume is greater than the theoretical building gap volume.

[0012] Preferably, during the secondary grouting compensation process in step S5, when the lake bottom settlement rate or cumulative settlement in a specific area exceeds the preset alarm value, compensation grout is injected into the stratum behind the lining through the grouting holes on the tunnel lining segments. The grouting adopts an intermittent, low-pressure grouting process, and the stabilization of the settlement curve in the area is used as the control standard for stopping the grouting.

[0013] Preferably, the method further includes establishing a precise correspondence between lakebed settlement monitoring points and tunnel lining ring numbers, and in step S5, when a monitoring point alarms, the secondary grouting compensation is initiated for the specific lining ring area corresponding to that monitoring point.

[0014] Preferably, the method further includes a mud recycling treatment step, in which the waste mud generated during tunneling is subjected to multi-stage separation and dewatering treatment, the separated water is reused in the mud preparation system, and the separated slag is dewatered until the moisture content is lower than the environmental protection requirements before being transported off-site.

[0015] The technical effects and advantages of this invention are as follows: 1. The method for constructing shallow, small-diameter shield tunnels under the lake bottom integrates five steps: determining trial excavation parameters, controlling dynamic slurry pressure and mud film, synchronous grouting, adjusting mud performance based on soil properties, and secondary grouting compensation based on monitoring. This forms a highly efficient construction method system that can respond to feedback from construction process parameters. This method can achieve precise dynamic balance of water and soil pressure at the excavation face, ensuring the stability of the excavation face. Through a real-time feedback mechanism, it optimizes mud performance, ensuring effective mud film sealing and good water-blocking effect. Combined with dual grouting control, it achieves refined management of stratum deformation, thereby solving the technical problems of excavation face instability and settlement control when tunneling under shallow water bodies.

[0016] 2. The method of using a small-diameter shield tunnel to pass under the shallow bottom of the lake improves construction speed and reliability through an automated control system and refined construction management, reduces manual intervention and troubleshooting time, and reduces resource consumption by recycling materials, thus lowering the overall construction cost compared to traditional methods.

[0017] 3. The shallow, small-diameter shield tunneling method at the bottom of the lake, through the supporting multi-stage mud separation and dewatering recycling system, achieves near-zero discharge of construction waste mud and efficient reuse of water resources. The separated slag has a low moisture content, meeting the requirements for environmentally friendly transportation, minimizing the risk of pollution to the water body crossing the lake, achieving environmental protection, and meeting the requirements of green construction technology. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a schematic diagram of the overall method flow of the present invention; Figure 2 This is a flowchart of the secondary grouting compensation process of the present invention; Figure 3 This is a flowchart of the mud circulation treatment process of the present invention. 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 some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] This embodiment discloses a method for constructing a shallow, small-diameter shield tunnel under a lake bottom, according to the attached... Figure 1 To be continued Figure 3 As shown, a complete and reliable shallow water crossing construction system has been formed by integrating trial tunneling parameter optimization, dynamic slurry pressure balance and mud film sealing, synchronous and secondary grouting settlement control, mud performance adjustment based on soil property feedback, and green mud recycling technology.

[0022] According to the appendix Figure 1 The schematic diagram of the overall method flow of the present invention shown below illustrates that the method includes the following steps: Step S1: Before the tunnel boring machine enters the lake bottom influence zone, a trial tunneling section is set up to obtain and determine the tunnel boring parameter set that matches the engineering strata through the trial tunneling. Step S2: The tunnel boring machine enters the lake bottom influence area to carry out underpass tunneling. The pressure of the slurry chamber is dynamically adjusted to balance the water and soil pressure at the excavation face. At the same time, a specific ratio of slurry is injected into the strata at the excavation face to form a sealing mud film. Step S3: Simultaneous grouting is carried out during the tunneling process to fill the gaps in the tail shield structure; Step S4: Based on real-time monitoring of the properties of the excavated soil during the tunneling process, dynamically adjust the performance parameters of the mud. Step S5: Based on real-time monitoring data of lakebed strata settlement, determine whether secondary grouting compensation should be carried out after tunnel lining.

[0023] In addition, the method may include auxiliary steps such as graded initiation, cutter inspection, and mud circulation treatment.

[0024] Furthermore, the dynamic control of the slurry chamber pressure relies on a closed-loop control system. This system includes soil and water pressure sensors deployed in the strata ahead of the excavation face and inside the slurry chamber, a PLC programmable logic controller, and a variable frequency speed control device connecting the slurry inlet pump and the slurry outlet pump. The PLC calculates the stratum pressure P based on the real-time monitoring of the static soil and water pressure from the sensors. According to the formula Pslurry = K × Pslurry, the target pressure value of the slurry chamber is dynamically set, where K is a safety factor, typically set to 1.1 to 1.3. Pslurry = Pstatic water + Psoil, dynamically adjusted based on the stratum permeability. Pstatic water = γw × h, Psoil = K0 × γ × z, where γw is the water unit weight, h is the water depth, K0 is the static earth pressure coefficient, γ is the soil unit weight, and z is the burial depth. By using a PID proportional-integral-derivative control algorithm, the PLC compares the target pressure with the actual pressure and outputs control signals to dynamically adjust the flow rates of the slurry inlet and outlet pumps, keeping the pressure in the slurry chamber within the set range and controlling pressure fluctuations within a preset threshold of ±0.02MPa. This achieves precise dynamic balance of water and soil pressure at the excavation face, effectively preventing collapse or roof fall at the excavation face.

[0025] Furthermore, the formation of a closed mud film depends on a mud system with a specific formulation. This mud uses bentonite as a base and incorporates 0.1%-0.3% polymer additives, such as carboxymethyl cellulose (CMC) or polyanionic cellulose (PAC). The prepared mud is injected into the excavation face under pressure using a mud pump. Under the pressure difference, fine particles with a diameter d ≤ 0.075 mm are forced into the formation pores through infiltration, gradually accumulating to form a dense, continuous, low-permeability mud film. This mud film is typically 0.5-1.0 mm thick, and its permeability coefficient can be as low as ≤ The viscosity of the mud (cm / s) effectively blocks groundwater seepage to the excavation face, enhancing the self-stability of the excavation face and the effective transmission of slurry pressure. Key performance control indicators for the mud include: Marsh funnel viscosity 20-25 seconds, specific gravity 1.1-1.3 g / cm³. 3 The sand content is ≤5%.

[0026] In particular, step S4, adjusting mud properties based on excavated soil characteristics, establishes an important process feedback mechanism. Continuous excavated soil sampling and observation points are set up at the outlet of the sludge discharge pipeline. Construction personnel sample the discharged excavated soil every hour, judging its properties visually and tactilely. Ideally, the excavated soil should be soft, viscous, and have good plasticity—a "viscous" state—indicating strong sludge carrying capacity, good mud film formation, and a stable excavation face. When the excavated soil appears like a "dry cake," it is too dry, indicating insufficient water loss in the mud or a possible malfunction in the water injection system, requiring increased water content or adjustments to additives to improve fluidity. When the excavated soil appears like a "thin soup," it is too thin and has excessive water content, indicating excessive water loss in the mud or abnormal formation moisture content, requiring increased mud viscosity and inspection of the mud film sealing effect, such as increasing the content of bentonite or polymer additives. Through this real-time feedback, the clay content, polymer additive ratio, and water volume in the mud can be dynamically adjusted, and the mud performance can be quickly restored to a state that meets the requirements for excavation face stability and mud film formation.

[0027] Prior to step S1, it is preferable to perform staged excavation of the tunnel boring machine. The staged excavation is divided into at least three stages, for example, three stages.

[0028] The first stage is the low-parameter adaptation period, such as the first 10 rings. The pressure in the mud chamber is set to the lower limit, such as 1.1 times the formation pressure, and the propulsion speed is controlled at a low level, such as ≤20mm / min.

[0029] The second stage is the parameter improvement and optimization period. For example, if the range is set to 10-30 rings, the pressure is gradually increased to the intermediate value, such as 1.2 times the formation pressure, and the velocity is appropriately increased, such as 30 mm / min. The parameters are then fine-tuned by comparing the monitoring data.

[0030] The third stage involves entering the normal tunneling period, with pressure stabilizing at 1.2-1.3 times the normal pressure and speed reaching normal values, such as 40 mm / min. Through staged initiation, the various systems of the tunnel boring machine smoothly enter their optimal working state, laying the foundation for the accurate determination of parameters for subsequent trial tunneling sections.

[0031] Between step S1 (trial excavation) and step S2 (formal underwater tunneling), a comprehensive inspection of the tunnel boring machine's (TBM) cutterhead and cutting tools must be conducted. This inspection is carried out at atmospheric pressure during the initial shaft or a safe area. The inspection process includes: First, using measuring tools, checking the wear of all cutting tools, including the lead-in tearing cutter, heavy-duty scraper, and peripheral scraper, to ensure it is below the preset safety threshold. Cutters with excessive wear must be replaced immediately. Second, after inspecting or replacing the cutting tools, using a torque wrench, the torque of all cutting tool fixing bolts must be checked to ensure they all reach the design torque value, and detailed records must be kept. This step aims to ensure the TBM enters the high-risk tunneling section with optimal cutting performance, minimizing the significant risk of underwater pressurized opening due to cutting tool damage.

[0032] Synchronous grouting in step S3 is crucial for controlling early-stage formation deformation. This system uses a fast-setting cement-based grout, for example, with an initial setting time ≤30 seconds and a 28-day compressive strength ≥15 MPa, pumped through six or more grouting holes evenly distributed on the shield tail shell and corresponding grouting pipelines. The grouting process employs a dual-control mode of flow rate and pressure: on the one hand, a flow meter ensures the total grout volume is greater than 120%-150% of the theoretical construction gap volume to achieve full filling; on the other hand, a pressure sensor controls the grouting pressure within the range of 0.3-0.5 MPa to prevent excessive pressure from puncturing the shield tail seal or damaging the tunnel segments. Simultaneous or alternating grouting at multiple points helps the grout to distribute evenly in the shield tail gap, achieving a filling rate of over 95%.

[0033] The secondary grouting compensation in step S5 is an active control measure to address potential subsequent settlement after simultaneous grouting. The secondary grouting procedure is triggered when data from the surface settlement monitoring system deployed on the lakebed shows that the settlement rate in a specific area exceeds the preset alarm value or the cumulative settlement exceeds the allowable value. Grouting is carried out through pre-reserved lifting holes on the assembled tunnel segments. The compensation grout is prepared using materials such as ultrafine cement, and the grouting process follows the principle of "intermittent, low pressure, slow injection": a small amount of grout is slowly injected at a low pressure, then paused for a period of time to observe changes in the settlement monitoring curve. This process can be repeated. The control standard for stopping grouting is not a fixed grouting volume, but rather when the settlement curve at that monitoring point tends to stabilize or shows a slight rebound, indicating that the stratum has been effectively replenished and reinforced.

[0034] Specifically, to accurately implement secondary grouting, a precise spatial correspondence between lakebed settlement monitoring points and tunnel lining segment ring numbers must be established in advance. Through measurement and calculation, the range of segment ring numbers corresponding to the projected position of each lakebed monitoring point on the tunnel axis is determined. In step S5, when a monitoring point alarms, the control system or construction personnel can immediately locate the specific lining ring area requiring compensation grouting, typically directly below the monitoring point and several adjacent rings, thereby initiating targeted secondary grouting compensation and improving the accuracy and speed of settlement control.

[0035] The method also includes a mud circulation treatment step throughout the entire construction process to achieve green construction. For the waste mud discharged from the excavation face and carrying muck, it is first pumped to a mud separation station for treatment. The treatment process usually has three levels: the first-level treatment uses a hydrocyclone to remove large muck particles with a particle size greater than 2 mm; the second-level treatment uses a centrifuge or a finer hydrocyclone to separate fine sand particles with a size of 0.075 - 2 mm; the third-level treatment uses a filter press to dehydrate the remaining fine-particle mud into mud cakes. Through this system, more than 95% of the water in the mud is separated and recycled, and is transported back to the mud preparation tank to be reused for preparing fresh mud, realizing the recycling of water resources. After the separated muck is dehydrated, its moisture content can be less than 20%, and it is transported out as general waste soil for disposal, achieving zero discharge of mud, reducing the pollution of lake water bodies and the pressure of construction waste disposal.

[0036] According to the attached Figure 1 to the attached Figure 3 As shown, it needs to be particularly emphasized that step S1 provides optimized basic parameters for the formal underpass; step S2 of dynamic mud pressure balance and mud film sealing is the core to maintain the stability of the excavation face; step S3 of synchronous grouting is the main measure to control the immediate deformation of the formation; step S4 of mud adjustment based on the properties of muck is the real-time optimization and guarantee of the core process step S2; step S5 of secondary grouting based on monitoring is the late-stage fine compensation for settlement. And the mud circulation treatment constitutes the environmental protection foundation. The whole method forms an intelligent construction method adaptable to complex formations by real-time monitoring of state data such as pressure, settlement, and muck, using real-time data to form feedback regulation of multiple shield processes, and driving the dynamic adjustment of construction parameters.

[0037] According to the attached Figure 1 to the attached Figure 3 As shown, it needs to be particularly emphasized that this method also puts forward other basic inspection requirements for equipment status management. In addition to a comprehensive tool inspection before the underpass, during the staged launch and normal tunneling stages, it is necessary to regularly maintain the key components of the shield machine, especially the main bearing seal, tail seal, hinge seal, etc. The tail tail of the tail seal needs to be regularly pressure-tested. Inject high-pressure grease into the seal cavity, and maintain the pressure at 1.2 times the design value for at least 30 minutes. If the pressure drop does not exceed 10%, it is qualified, ensuring the reliability of the seal in a high-pressure mud water environment and preventing slurry and groundwater from flowing into the tunnel.

[0038]

[0038] Example 1. In this example, taking the second bid section of the main section of the raw water pipeline project from Lianhuashan to Luhuakeng Water Plant, the L4 - L5 shield interval underpassing Luhuakeng Reservoir as an example, combined with the attached Figure 1 to the attached Figure 3 The working process of this method is described in detail.

[0039] The tunnel section is 1.518km long and was constructed using a single Φ4480mm slurry shield tunneling machine. The minimum overburden thickness at the tunnel top is approximately 11.2 meters, typical of shallow-buried conditions. The strata it traverses are primarily weakly to slightly weathered granite gneiss, with localized areas of composite strata consisting of soft upper layers and hard lower layers. These strata are highly permeable and rich in groundwater. The section passing under the Luhuakeng Reservoir is a major source of construction risk. The workflow is as follows: The tunnel boring machine (TBM) was assembled in the working shaft, and the slurry circulation system, synchronous grouting system, guiding system, and sealing system were fully debugged. The system was equipped with an HSDS-200 slurry separation system, a SYB-50 / 10 synchronous grouting pump, and an HJ-200 secondary grouting equipment.

[0040] The tunnel boring machine (TBM) began excavation from the launching shaft. For the first 10 rings, conservative parameters were used: slurry pressure was set at 1.1 times the theoretical calculation value, and the advance speed was ≤20 mm / min. After completing 10 rings, the machine was stopped to check cutter wear. From rings 11 to 30, the pressure was gradually increased to 1.2 times the theoretical value, and the speed was increased to 30 mm / min, with close monitoring of the parameters and settlement relationship. After ring 30, the third stage of normal initial excavation began, and the parameters remained basically stable.

[0041] Approximately 50 meters before entering the reservoir's influence zone, a test tunnel section was designated. Within this section, based on geological changes, the tunnel transitioned from terrestrial strata to the strata beneath the reservoir, systematically adjusting parameters such as slurry pressure, advance speed, cutterhead rotation speed, torque, grouting pressure, and flow rate. Simultaneously, surface settlement and internal displacement monitoring were intensified in this section. Through data analysis, a set of optimal tunneling parameters was determined for the strata beneath the reservoir to be entered: slurry pressure setpoint K=1.25, advance speed 35mm / min, synchronous grouting pressure 0.35MPa, and grouting volume 130% of the theoretical gap.

[0042] When the tunnel boring machine (TBM) cutterhead is approximately 20 meters from the reservoir boundary, a final atmospheric pressure cutter inspection is conducted. It is confirmed that all cutter wear is less than 3mm, the advanced tearing cutter and heavy-duty scraper are properly matched, and all bolt torques meet specifications. Simultaneously, a pressure test is performed on the tail seal; only after passing this test can the machine proceed.

[0043] The tunnel boring machine officially entered the area affected by the reservoir. Based on the soil and water pressure monitoring values ​​of the strata ahead, the PLC system calculated the pressure of the stratum P in real time and automatically controlled the pressure in the slurry chamber at P_slurry = 1.25 × P_stratum, with fluctuations strictly controlled within ±0.02 MPa. Simultaneously, a 22s viscosity and a specific gravity of 1.2 g / cm³ were continuously injected into the excavation face. 3 The mud containing CMC additives ensures the rapid formation of an effective mud film in permeable formations.

[0044] Six grouting holes at the shield tail were simultaneously injected with quick-setting grout. The initial setting time was 25 seconds. Flow rate and pressure were controlled simultaneously. The grouting pressure was 0.35±0.05MPa, and the grouting volume per ring was approximately 6.5m. 3 The theoretical gap is about 5m. 3 The fill rate is approximately 130%.

[0045] A designated person takes samples at the sludge discharge point every hour. In the initial stage of the excavation, the excavated soil contains some lumpy rocks, so the mud viscosity is adjusted to 24s to enhance the excavated soil carrying capacity. In the middle stage, the excavated soil properties are ideal, exhibiting a viscous plastic state. In the later stage, it is found that the excavated soil is too thin, so the bentonite content in the mud is immediately increased to restore the viscosity and ensure the quality of the mud film.

[0046] Dense automated settlement monitoring points were deployed on the lakebed, and their precise correspondence with the segment ring numbers inside the tunnel was calculated.

[0047] During the underpass, the settlement at most monitoring points was within 2-3 mm. However, when traversing a certain area in the middle, a group of monitoring points showed a daily settlement rate of 1.2 mm / d, with a cumulative value approaching 4 mm, triggering an alarm.

[0048] Based on the corresponding relationships, secondary compensation grouting was immediately carried out on the five rings of segments directly below and before and after them. Using an HJ-200 grouting machine through the segment hoisting holes, 0.3m of grout was injected at a low pressure of 0.3MPa each time. 3 Three rounds of grouting were performed using ultrafine cement grout, with observations every 4 hours. The settlement curve in this area stabilized 10 hours after grouting, and the final cumulative settlement was controlled at 3.8 mm.

[0049] All discharged sludge enters the sludge-water separation system. After three stages of treatment, 96% of the water is recycled, and the separated sludge, after being filtered, has a moisture content of 18% and is transported to a designated spoil disposal site.

[0050] After the tunnel boring machine completely passed through the reservoir's affected area, it continued normal tunneling to the receiving shaft. Analysis and summary of monitoring data for the entire section crossing the reservoir showed a maximum settlement of 3.8 mm, far below the control standard of 5 mm, verifying the effectiveness of this method.

[0051] Example 2: This example uses a subway tunnel passing under an urban landscape lake in a certain city as an example, combined with the attached... Figure 1 To be continued Figure 3 This document details the workflow of this method in more complex composite formations with soft upper layers and hard lower layers.

[0052] The tunnel has an outer diameter of 6.2 meters and a soil overburden thickness of 18-25 meters. The lakebed strata beneath the tunnel are typical of a "soft upper layer and hard lower layer" composite strata: the upper layer is 5-8 meters thick silty clay, and the lower layer is moderately weathered mudstone. The groundwater and lake water are hydraulically connected; the working process is as follows: For formations with a soft upper layer and a hard lower layer, the cutterhead configuration is optimized, employing a combination of pre-cutting cutters, heavy-duty scrapers, and peripheral scrapers. Two mud formulations are prepared to address the varying mud performance requirements of different formations.

[0053] The same three-stage, graded launch method was adopted. In step S1 of the trial excavation section, the focus was on testing the effectiveness of the cutterhead assembly and the parameter switching logic at different geological interfaces. It was determined that a slightly lower torque and speed would be used in soft soil layers, while the cutterhead torque would be increased when entering hard rock. At the same time, the slurry pressure needed to be calculated and determined based on the combined pressure of the upper and lower strata.

[0054] When entering the soft soil layer of the lake area, the slurry pressure setting mainly considers the water and soil pressure of the upper soft soil, adopting a lower limit coefficient of 1.15. The slurry focuses on its ability to protect the wall and form a mud film, and the content of polymer additives is appropriately increased.

[0055] When the lower part of the cutterhead cuts into moderately weathered mudstone, the risk of pressure imbalance between the upper and lower surfaces of the excavation face increases. At this time, the slurry pressure setting needs to be a balance value between soft soil pressure and hard rock pressure, or pressure compartment control technology can be adopted to indirectly affect the excavation face through fine-tuning of the tunneling posture. In this embodiment, the pressure coefficient is increased to 1.25 and the stability of the excavation face is closely monitored.

[0056] Simultaneous grouting was carried out in the soft soil strata, with the grouting volume set at the upper limit of 150%, in order to support the upper soft soil as quickly as possible.

[0057] At the interface between soft and hard rock, the discharged excavated material should be a mixture of soft soil and rock fragments. If there is too much or too large rock fragments, it indicates that the tearing cutter is not breaking the rock effectively or the scraper is not cleaning it in time, and the cutterhead speed or torque needs to be adjusted. If it is all soft mud with no rock fragments, the cutterhead may not be effectively cutting the hard rock, posing a risk of head-up, and the shield attitude needs to be adjusted.

[0058] Because the soft soil above is sensitive to settlement, monitoring points on the lakebed were deployed more densely. During the crossing, despite proper parameter control, there was still a possibility that some locations might experience settlement rates exceeding the limit due to soft soil creep. Secondary compensation grouting was immediately initiated, using a slower intermittent grouting process. Over two days, multiple rounds of grout were injected, ultimately stabilizing the settlement at 4.5 mm.

[0059] Given the ecological sensitivity of the scenic lake, the mud-water separation system incorporates a wastewater purification process to ensure higher quality reclaimed water and effluent. Construction was scheduled to avoid peak lake viewing season, and sound barriers were installed.

[0060] This embodiment demonstrates that the method can achieve safe and controllable tunneling in complex strata through tool combination optimization, dynamic parameter adaptation, and refined settlement compensation.

[0061] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for constructing a shallow, small-diameter shield tunnel under a lake bottom, characterized in that... The method includes the following steps: Step S1: Before the tunnel boring machine enters the lake bottom influence zone, a trial tunneling section is set up to obtain and determine the tunnel boring parameter set that matches the engineering strata through the trial tunneling. In step S2, the tunnel boring machine enters the lake bottom influence area to carry out underpass excavation. The pressure of the slurry chamber is dynamically adjusted to balance the water and soil pressure at the excavation face. At the same time, a specific ratio of slurry is injected into the strata at the excavation face to form a sealing mud film. Step S3: Simultaneous grouting is performed during the tunneling process to fill the gaps in the tail shield structure; Step S4: Based on real-time monitoring of the properties of the excavated soil during the tunneling process, dynamically adjust the performance parameters of the mud. Step S5: Based on real-time monitoring data of lakebed strata settlement, determine whether secondary grouting compensation should be carried out after tunnel lining.

2. The method for constructing a shallow, small-diameter shield tunnel under a lake bottom according to claim 1, characterized in that, In step S2, during the dynamic control of the slurry tank pressure, the flow rates of slurry inlet and outlet are dynamically adjusted according to the real-time monitored formation water and soil pressure, so that the slurry tank pressure is maintained within 1.1 to 1.3 times the calculated value of the static formation water and soil pressure, and the pressure fluctuation is controlled within the preset threshold.

3. The method for constructing a shallow, small-diameter shield tunnel under a lake bottom according to claim 2, characterized in that, In step S2, during the formation of the sealed mud film, the mud slurry with a specific ratio contains fine particles and polymer additives. Through filtration, it forms a dense mud film with low permeability in the pores of the formation, blocking the seepage of groundwater to the excavation face.

4. The method for constructing a shallow, small-diameter shield tunnel under a lake bottom according to claim 3, characterized in that, In step S4, the excavated soil output from the sludge discharge pipeline is continuously sampled and observed. When the properties of the excavated soil deviate from the preset ideal plastic state, the viscosity, water loss or sludge carrying capacity of the sludge is changed by adjusting at least one of the clay content, polymer additive ratio and water volume in the sludge, so that the sludge can be restored to a state that meets the requirements of excavation face stability and mud film formation.

5. The method for constructing a shallow, small-diameter shield tunnel under a lake bottom according to claim 1, characterized in that, Before step S1, the tunnel boring machine is subjected to graded initial excavation. The graded initial excavation is divided into at least two stages. From the previous stage to the next stage, the pressure setting value of the slurry chamber is gradually increased, and the tunneling speed is gradually increased until the normal tunneling parameters determined in step S1 are reached.

6. The method for constructing a shallow, small-diameter shield tunnel under a lake bottom according to claim 5, characterized in that, Between steps S1 and S2, the cutterhead of the tunnel boring machine is inspected. During the inspection, the wear of the cutter is first checked to be less than a preset threshold, and finally the torque of all cutter fixing bolts is checked.

7. The method for constructing a shallow, small-diameter shield tunnel under a lake bottom according to claim 1, characterized in that, In the synchronous grouting process described in step S3, a fast-setting grout is used and implemented through a multi-point grouting system at the shield tail. The grouting process adopts a dual control mode of flow rate and pressure, and the total grouting volume is greater than the theoretical building gap volume.

8. The method for constructing a shallow, small-diameter shield tunnel under a lake bottom according to claim 1, characterized in that, In the secondary grouting compensation process described in step S5, when the lake bottom settlement rate or cumulative settlement in a specific area exceeds the preset alarm value, compensation grout is injected into the stratum behind the lining through the grouting holes on the tunnel lining segments. The grouting adopts an intermittent, low-pressure grouting process, and the stabilization of the settlement curve in the area is used as the control standard for stopping the grouting.

9. A method for constructing a shallow, small-diameter shield tunnel under a lake bottom according to claim 8, characterized in that, The method also includes establishing a precise correspondence between lakebed settlement monitoring points and tunnel lining ring numbers, and in step S5, when a monitoring point alarms, the secondary grouting compensation is initiated for the specific lining ring area corresponding to that monitoring point.

10. The method for constructing a shallow, small-diameter shield tunnel under a lake bottom according to claim 1, characterized in that, The method also includes a mud recycling process, in which the waste mud generated during tunneling is subjected to multi-stage separation and dewatering treatment. The separated water is reused in the mud preparation system, and the separated slag is dewatered until its moisture content is lower than the environmental protection requirements before being transported off-site.

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