Shield tunneling method based on large-diameter shield tunnel segment floating control

Abstract

The application discloses a shield construction method based on super-large-diameter shield tunnel segment floating control, and aims to solve the technical problem of how to guarantee the forming quality of the super-large-diameter shield tunnel. The application is targeted and comprehensive optimized from aspects of shield posture, tunneling pressure setting, improvement of grouting pipeline, segment back filling, advanced grouting, radial grouting of the shield tunneling machine, bolt re-tightening and the like, so that the super-large-diameter shield tunnel segment floating is effectively controlled, the forming of the shield tunnel is guaranteed to reach the standard, and meanwhile, the technical scheme has the advantages of low investment cost, strong implementability, wide application range and the like.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of super-large diameter shield tunnel construction, and particularly relates to a shield construction method based on super-large diameter shield tunnel segment floating control. BACKGROUND

[0002] In recent years, with the vigorous investment and construction of the state in urban infrastructure construction, urban underground tunnel engineering has developed rapidly, and has greatly promoted the development of shield construction technology. Super-large diameter shield tunnels are used in more and more fields, such as railways, highways, high-speed rails, and subways. Shield mechanical equipment and construction technology are also updated and iterated. The adaptability of shield construction to complex strata is greatly improved. Shield design and construction of super-large diameters of 10 m or more are increasing. The construction risks and uncertainty factors faced by large-section shield tunnels are also increasing. It is particularly important to ensure that the tunnel forming quality is within the specification requirements. Segment floating has the greatest impact on tunnel forming quality. Segment floating can easily cause segment leakage, segment misalignment, segment damage, and tunnel ovality exceeding the standard, which seriously threatens the overall performance and long-term stability of the tunnel.

[0003] The information disclosed in this BACKGROUND section is only for the purpose of enhancing the understanding of the background of the present disclosure and should not be taken as admitting that such information is prior art known to those of ordinary skill in the art. SUMMARY

[0004] The inventors have found that, in the process of super-large diameter shield construction, targeted and comprehensive optimization from the aspects of shield posture, tunneling pressure setting, improvement of grouting pipeline, filling behind the segment, advanced grouting, radial grouting of the shield machine, and bolt retightening can effectively control the segment floating of super-large diameter shield tunnels, so as to ensure that the shield tunnel forming meets the standards and thus solve the quality problems in shield construction.

[0005] Based on this, the present disclosure provides a shield construction method based on super-large diameter shield tunnel segment floating control, which comprises the following steps:

[0006] (1) Control the tunneling posture: control the vertical posture of the shield within -40 to -50 mm during shield tunneling to offset the segment floating amount, and control the vertical posture within -20 to -30 mm when tunneling in a full-section hard rock section of an upper-soft lower-hard segment; control the vertical deviation distance of the shield machine within -20 to 20 mm, and control the vertical deviation angle of the shield machine within -10 to 10 mm / m; control the stroke difference of the upper and lower jacks of the shield machine within -20 to 50 mm; and maintain the downward posture of the shield machine when the shield passes through the upper-soft lower-hard segment.

[0007] (2) Set the tunneling pressure: the theoretical value of the slurry tank pressure is determined by calculating the water and soil together, and the top pressure of the slurry tank during shield tunneling is between the upper and lower limits of the theoretical value of the slurry tank pressure; the deviation of the incision water pressure during the switching of the three states of shield machine propulsion, backwashing and bypassing is controlled between -20 and 20 kpa; the theoretical value of the slurry tank pressure is determined by the following formula: ,

[0008] In the formula, γ is the saturated unit weight of the stratum; H is the buried depth of the tunnel top; Ka is the active earth pressure coefficient; p is the ground load, which is taken as 20.

[0009] (3) Optimize the grouting management system: adopt an embedded tail shield grouting pipe, arrange 2-way piston type double-liquid grouting blocks at the top of the tail shield, and arrange 8 single-liquid grouting pipes for injecting mortar A liquid, while reserving synchronous grouting points for injecting B liquid.

[0010] The tail shield grouting pipe is embedded, which can effectively reduce the frictional resistance between the tail shield and the surrounding environment, thereby reducing the total thrust demand during shield tunneling, improving construction efficiency, and saving the power consumption of the shield machine; it can reduce the diameter of the cutterhead excavation face, thereby reducing the geological safety risks brought by large-area excavation, helping to reduce the uncertainty and potential risks in the construction process, and ensuring the smooth progress of the construction process; effectively avoid the phenomenon of jam caused by factors such as geological conditions and construction errors during use, thereby affecting the construction progress and quality, and successfully crossing the reinforced diaphragm wall.

[0011] The piston type double-liquid grouting block arranged at the top of the tail shield, combined with the single-liquid mortar grouting module, realizes the synchronous grouting of cement mortar and water glass double-liquid slurry, overcomes the disadvantages of single-liquid cement mortar such as long setting time and difficult control, and can solidify on the top of the segment in a very short time, fully filling the gap at the top of the segment and fixing the segment, not only improving the grouting efficiency, but also significantly improving the grouting quality, effectively controlling common construction defects such as ground subsidence, segment misalignment, and leakage.

[0012] (4) Synchronous grouting and secondary grouting behind the segment: synchronous grouting is carried out using cement mortar inert slurry, the grouting amount is 130% to 180% of the theoretical building void, and the grouting amount above the center of the segment is 55% to 65% of the total grouting amount, the grouting amount below the center of the segment is 35% to 45% of the total grouting amount, and the grouting pressure is greater than the outlet pressure by 0.1 to 0.3 Mpa; at least one grouting hole is added at the top of the segment, and when the segment is out of the shield tail by 3 rings during shield tunneling, double-liquid slurry is injected through the added grouting hole, and the grouting pressure is greater than the outlet pressure by 0.2 to 0.3 Mpa.

[0013] In the process of tunneling, the segment is subjected to lateral pressure and upward thrust applied by the hydraulic jack, and the gap formed after the upper part of the segment is excavated, which is easy to lead to the segment floating. The present application increases the upper synchronous grouting amount to generate downward pressure to offset part of the upward thrust; at the same time, in view of the problem that the flowability of the slurry easily leads to the grouting pressure at the bottom being too large and the grouting pressure at the top being too small, the present application further controls the proportion of the grouting amount above the center part to be greater than that below the center part of the segment, thereby optimizing the slurry distribution and ensuring that the slurry is evenly distributed along the segment, which not only effectively reduces the segment floating amount, but also improves the grouting density, the overall stability of the tunnel and the waterproof performance.

[0014] Increasing the grouting pressure can effectively control the ground settlement, prevent the water and soil pressure behind the segment from being too large to cause reverse flow, significantly improve the mortar fullness of the top of the segment, and reduce the segment floating amount caused by the gap at the top of the segment.

[0015] (5) Advanced grouting: presetting an inclined advanced grouting hole in the shield position of the shield machine, and performing advanced pre-grouting reinforcement on the stratum within 1.8-2.2 m outside the 180° arch of the working face in the abnormal section shown in the advanced geological prediction and survey data, the pressure of the advanced pre-grouting reinforcement being 0.5-1.0 Mpa, and the grouting range being 4 rings of segments in front of the cutter head.

[0016] (6) Radial grouting: presetting a radial grouting hole at the top of the shield machine, and injecting ≥4 m of slurry per ring during the shield tunneling process, the injection pressure being ≤7 bar. 3

[0017] (7) Bolt retightening: during the process of completing the segment assembly and proceeding with the next ring tunneling, checking and retightening the bolts of the segments within the range of 3 rings of adjacent completed rings every 450-550 mm of tunneling, to ensure the bolt fastening connection.

[0018] In some embodiments of the present disclosure, in the step (3), the columnar pump is used to deliver the slurry A liquid and the B liquid, wherein the columnar pump for delivering the B liquid is provided with 4 output channels.

[0019] In some embodiments of the present disclosure, in the step (4), the cement mortar inert slurry is composed of cement, fine sand, fly ash, water and additive in a density ratio of 23-27:1200-1300:290-310:290-310:75-85; and the additive is lime.

[0020] The lime as the additive can shorten the setting time of the mortar, accelerate the water discharge in the mortar, reduce the flowability of the mortar, reduce the loss of the synchronous grouting filling mortar, improve the filling density behind the segment, and the strength of the mortar after setting is high.

[0021] ​In some embodiments of the present disclosure, in the step (4), the double slurry is formed by mixing the cement slurry and the water glass at a volume ratio of 1:1-2, wherein the cement is P.O 42.5 ordinary cement; the water-cement ratio is 1:1-2; and the Be value is 30-35 be.

[0022] In some embodiments of the present disclosure, in the step (5), the advanced pre-grouting reinforcement uses the cement-water glass double slurry; the water-cement ratio of the cement slurry in the double slurry is 0.8-1:1; the Be value is 30-35 be; and the volume ratio of the cement to the water glass is 1:1-2.

[0023] In some embodiments of the present disclosure, in the step (6), the radial grouting uses the shield shell mud-water glass double slurry; the shield shell mud is composed of cement:bentonite:water at a mass ratio of 420-480:220-280:670-730; and the volume ratio of the shield shell mud to the water glass is 1:1-2.

[0024] In some embodiments of the present disclosure, in the step (2), the active earth pressure coefficient Ka is determined by the following formula:

[0025]

[0026] In the formula, φ is the internal friction angle of the stratum.

[0027] The one or more technical solutions provided in the embodiments of the present disclosure have at least any of the following technical effects or advantages:

[0028] 1. The method for controlling the pipe segment floating and the required equipment in the technical solutions of the present disclosure are performed at the initial stage of the shield design and the construction stage, the required time for the system training of the operating personnel is shortened, the controllability in the construction process is improved, the method is applicable to different strata, slurry or earth pressure balanced shields, or tunnels with a cross section diameter less than 10 m, has strong implementation and wide applicability, and the cost, manpower and equipment are less, the construction cost can be effectively reduced, and the pipe segment forming quality is improved.

[0029] 2. The grouting pressure and the grouting amount are double-controlled in the synchronous grouting, the secondary grouting, the advanced grouting and the radial grouting processes, the grouting sensor can upload the related parameters to the control page, and the visualization degree is high.

[0030] ​3. In order to ensure the safety and stability of the tunneling operation of the shield machine, firstly, the upward floating of the stratum is inhibited by reasonably setting the tunneling pressure, so as to avoid the upward floating of the segment; meanwhile, according to the results of geological exploration and advanced geological prediction, the advanced grouting and radial grouting reinforcement treatment are carried out on the adverse stratum in front of the shield, so as to enhance the stability of the stratum; on this basis, the optimized grouting pipeline is used to efficiently fill the gap at the top of the segment, so as to prevent the uneven stress and upward floating of the segment caused by the soft upper and hard lower stratum, and the reinforcement of the soil body also effectively resists the upward floating force of the segment, thereby comprehensively improving the safety and stability of the tunneling.

[0031] In addition, during the tunneling of the shield machine, the vertical attitude is controlled to be lower than the design axis by 40-50 mm, which effectively offsets the upward floating amount of the segment. During the adjustment process of the shield attitude, the gap behind the top of the segment will change; therefore, the optimized grouting pipeline can be further used to quickly fill these gaps by accurately regulating the synchronous grouting amount, secondary grouting amount and grouting pressure, so as to effectively inhibit the upward floating of the segment; meanwhile, the synchronous grouting is carried out by selecting the mortar with a short setting time, which reduces the influence of the upward floating of the segment caused by the buoyancy of the mortar with a long setting time, thereby further ensuring the safety and stability of the tunneling operation.

[0032] Finally, during the front, middle and rear three stages of the segment out of the shield tail, the segment is affected by multiple factors such as the pushing pressure, the mortar buoyancy and the filling density behind the segment, and the combined action of these factors may cause the gap in the indirect joint between the segments. In order to effectively reduce these gaps and reduce the upward floating amount of the segment, the three times of segment bolt retightening measures are adopted, which can significantly improve the connection tightness between the segments, thereby further ensuring the stability and safety of the tunnel structure. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 It is a mud pressure distribution schematic diagram in an embodiment of the present application.

[0034] Figure 2 It is a synchronous grouting pipeline layout schematic diagram in an embodiment of the present application; wherein, 1: double-liquid grouting block; 2: A-liquid common pipeline; 3: A-liquid standby pipeline; 4: B-liquid synchronous grouting point position.

[0035] Figure 3 It is a ground subsidence longitudinal section curve in the shield construction process in an embodiment of the present application; wherein, 1: shield machine; 2: excavation face; 3: shield tail; 4: shield tunnel and subsequent trailer.

[0036] Figure 4 It is a synchronous grouting schematic diagram in an embodiment of the present application; wherein, 1: grout stop plate; 2: synchronous mortar; 3: segment; 4: shield shell.

[0037] Figure 5It is a schematic diagram of a cross section of advanced reinforcement in an embodiment of the application; wherein 1: radial grouting hole contour; 2: reserved inclined grouting hole; 3: middle shield.

[0038] Figure 6 It is a schematic diagram of a longitudinal section of advanced reinforcement channel in an embodiment of the application; wherein 1: cutter head; 2: grouting reinforcement contour.

[0039] Figure 7 It is an enlarged view of a side surface of a radial guide hole channel in an embodiment of the application; wherein 1: radial grouting; 2: shield shell; 3: guide hole drilling machine.

[0040] Figure 8 It is a tunnel hole reinforcement cross and longitudinal section diagram in an embodiment of the application; wherein 1: hole grouting; 2: segment contour; 3: tunnel center line.

[0041] Figure 9 It is a schematic diagram of shield shell mud injection in an embodiment of the application; wherein 1: original soil body; 2: circulating mud; 3: advanced grouting hole; 4: shield shell outer quick-setting mud; 5: synchronous mortar. DETAILED DESCRIPTION

[0042] In order to better understand the technical scheme of the application, the above technical scheme will be described in detail below in combination with specific embodiments.

[0043] In order to effectively control the floating of the segments of the super-large diameter shield tunnel and ensure that the shield tunnel forming meets the standards, the present application optimizes the construction process or parameters from the aspects of shield posture, excavation pressure setting, improvement of grouting pipeline, filling behind the segment, advanced grouting, radial grouting of the shield machine, bolt retightening, etc. in the construction of the super-large diameter shield, and formulates targeted methods and measures to effectively solve the quality problems in shield construction.

[0044] Embodiment one, excavation posture control

[0045] 1. Reduce the vertical posture of the shield: according to the analysis of the construction conditions of multiple super-large diameter shield tunnels, the floating amount of the segments of the large-section shield tunnel is generally between 30-40mm, so the vertical posture of the shield can be controlled at-40- -50mm during shield excavation, which can effectively offset the segment floating amount, so as to ensure that the tunnel forming axis meets the design requirements.

[0046] 2. Strictly control the adjustment of the vertical posture of the shield:

[0047] (1) Generally, the vertical deviation of the shield machine should be controlled within -20~20 mm, and the inclination angle should be controlled within -5~5 mm / m. In special cases (i.e. when the pipe segment floats up and the vertical posture needs to be adjusted downward, or the shield posture appears uncontrollable and out of limits in the upper-soft and lower-hard stratum and the posture needs to be adjusted upward), the inclination angle range can be increased, and the inclination angle should not exceed -10~10 mm / m, otherwise, the shield machine will turn too sharply, causing the shield tail gap to be too small and the pipe segments to be misaligned and broken.

[0048] (2) When the shield machine passes through the upper-soft and lower-hard segment, the shield machine is appropriately kept in a downward posture to prevent the shield machine head from floating upward. When the shield machine excavates in the upper-soft and lower-hard segment and the full-face hard rock segment, the vertical posture is controlled within -20~-30 mm.

[0049] (3) When operating the shield machine, attention should be paid to the stroke difference between the upper jacks and the lower jacks, which should not differ too much, generally controlled within -20~20 mm, and in special cases, should not exceed 50 mm.

[0050] Example Two, Setting of Excavation Pressure

[0051] If the pressure setting during shield excavation cannot balance the soil pressure, it will easily cause changes in the stratum, causing the pipe segments to float up and deform. Figure 1 ).

[0052] Determination of slurry chamber pressure:

[0053] (1) Theoretical calculation: According to the geological survey results in the detailed exploration stage, the stratum is generally permeable, and the calculation is determined by using the water-soil combined calculation method: ,

[0054] In the formula: γ - stratum saturated unit weight (kN / m³); H - tunnel top buried depth (m); Ka - active soil pressure coefficient, Ka = tan 2 (45°-φ / 2); p - ground load, taken as 20 Kpa; φ - stratum internal friction angle.

[0055] (2) Determination of slurry chamber top pressure during excavation: The slurry chamber top pressure during shield machine excavation should be between the upper and lower limits of the theoretical calculation value, and should be adjusted appropriately according to the surface monitoring settlement and geological conditions (when the monitoring data in the working face range show that the ground is rising, the slurry chamber pressure can be reduced, and vice versa, the slurry chamber pressure can be increased, and the adjustment of the slurry chamber pressure should not exceed ±0.2 bar). During backwashing, the slurry discharge pipe in the slurry chamber or the shield machine is in a blocked state, so the slurry discharge flow should be increased during backwashing, but the incision slurry pressure should not be reduced. The incision slurry pressure deviation value during switching between shield machine advancement, backwashing and bypassing should be controlled within -20~20 kPa.

[0056] Example 3: Optimization of Grouting Management System

[0057] The tail shield grouting pipes are embedded, which reduces frictional resistance, reduces the cutterhead excavation diameter, and effectively avoids jamming issues compared to external grouting pipes. Two piston-type dual-liquid grouting blocks are installed at the top of the tail shield (sections 1 and 10), with reserved dual-liquid grout input channels. At other locations (sections 2-8), eight single-liquid (mortar A liquid) grouting pipes are installed, with reserved B liquid pipe channels. Figure 2 The A liquid pump (mortar) uses a plunger pump, and the B liquid pump (water glass) uses a plunger pump (4-way). The A liquid (mortar) is supplied by the storage tank on the trailer, and the B liquid (water glass) is supplied by the added B liquid storage tank. The A liquid and B liquid are mixed in the shield tail grouting pipeline.

[0058] During tunneling, sections 1 and 10 are injected with a dual-component grout (A+B liquid), while the remaining eight sections are injected with liquid A. Compared to single-component cement grout, the cement-water glass dual-component grout overcomes the disadvantages of single-component cement mortar, such as long setting time and difficulty in control. It can solidify extremely quickly at the top of the tunnel segments, fully filling the gaps at the top of the segments, fixing the segments, and thus controlling the amount of segment floating. It can also effectively control defects such as ground settlement, segment misalignment, and leakage. The gel time of the dual-component grout is related to the concentration of water glass, the concentration of cement grout (i.e., the water-cement ratio), the volume ratio of water glass to cement grout, and the temperature. Generally, a higher cement grout concentration results in a longer gel time; a higher water glass to cement grout volume ratio results in a shorter gel time; and a higher water glass concentration results in a shorter gel time. The concentration of water glass can be adjusted according to the geological conditions to regulate the characteristics of the synchronous grout, ensuring the filling of synchronous grouting, thereby effectively controlling segment floating and ensuring the quality of tunnel formation.

[0059] Example 4: Filling behind the segments

[0060] During tunnel boring machine (TBM) excavation, incomplete backfilling behind tunnel segments or prolonged setting time of the synchronous mortar can easily lead to ground settlement and segment uplift. Ground settlement mainly depends on the type of geological formation, the type of TBM, construction conditions, and the fullness of the mortar behind the tunnel segments. The settlement duration curve of TBM construction is divided into 5 stages (…). Figure 3 Generally, the displacement increases most rapidly when the tunnel boring machine (TBM) passes through the measurement section between 0 and 12 meters; after the TBM passes through the measurement section 30 meters, the settlement rate decreases significantly. The specific settlement process is as follows:

[0061] (1) Pre-settlement: refers to the settlement that occurs from when the tunnel excavation face is still a considerable distance (tens of meters) from the ground observation point until the excavation face reaches the observation point.

[0062] (2) Settlement and uplift in front of the excavation face: refers to the settlement or uplift phenomenon that occurs from when the excavation face is very close to the observation point (about a few meters) until the excavation face is directly below the observation point.

[0063] (3) Machine body through settlement: refers to the settlement generated after the machine body passes through the observation point, mainly due to the disturbance of the soil body.

[0064] (4) Shield tail gap settlement: refers to the settlement generated after the tail of the shield machine passes through the observation point, which is caused by the elastic-plastic deformation of the soil stress release of the shield tail gap.

[0065] (5) Subsequent settlement: refers to the consolidation and creep residual deformation settlement.

[0066] As can be seen from the above, adjusting the tunneling parameters of the shield machine (see Example 1 and Example 2) can reduce the settlement of the first to third stages; the fourth stage settlement can be reduced by synchronous grouting and secondary grouting; the fifth stage settlement is the subsequent settlement of the soil body, which generally accounts for 10% of the total settlement of the shield construction, and can be controlled by tracking grouting and system grouting as follows:

[0067] 1. Synchronous grouting behind the segment: synchronous grouting behind the segment during shield tunneling to fill the annular gap behind the segment, ensure that the grout is filled and the actual grouting amount is 130% to 180% of the theoretical construction gap, this example changes the traditional grouting method, according to the total amount of grouting above the center of the segment 60%, the lower part 40% is injected, the grouting pressure is greater than the outlet pressure 0.1-0.3Mpa. Since most of the shield tunnel passes through silty clay, combined with domestic large-section slurry shield construction cases, the synchronous grouting grout selects cement mortar inert grout, the setting time should be around 2-4h (add or subtract thickener CMC and anti-dispersant according to the geological conditions), the grout ratio is shown in Table 1, and the synchronous grouting is shown in Figure 4 , the inert grout has a short final setting time, a higher filling density than ordinary cement grout (low water bleeding rate), a solid body strength of not less than 0.2 Mpa for 1d (equivalent to the unconfined compressive strength of soft rock), and not less than 1 Mpa for 28d, wherein lime as an additive can shorten the setting time of the mortar, accelerate the water bleeding in the mortar, reduce the fluidity of the mortar, reduce the loss of synchronous filling, improve the filling density, and the strength of the mortar after setting is high.

[0068] Table 1 Synchronous grouting material reference ratio

[0069] .

[0070] 2. Secondary grouting: Add grouting holes in the segment manufacturing stage, add 3 grouting holes in each segment, when the segment is out of the shield tail 3 rings, inject cement-silicate double liquid slurry into the top of the segment using the added multiple grouting holes, wherein the cement uses P.O42.5 ordinary cement, the water-cement ratio is 1:1; the degree of polymerization is controlled between 30-35be; the volume ratio of cement slurry to water glass is 1:1, the setting time of double liquid slurry is about 40S, the grouting pressure is greater than the pressure at the outlet of the segment grouting hole by 0.2-0.3MPa. The grouting pressure and grouting amount are taken as double control indexes, and the grouting is stopped immediately when the calculated theoretical index is reached. Increasing the grouting pressure can control the ground settlement, prevent the backflow caused by excessive water and soil pressure behind the segment, significantly improve the segment top mortar fullness, shorten the setting time of synchronous mortar, and effectively reduce the segment floating amount.

[0071] Example five, advanced grouting and radial grouting

[0072] 1. Advanced grouting: The stratum to be excavated is improved and reinforced to improve the strength of the soil above the segment, thereby reducing the segment floating amount.

[0073] In the design stage of the shield machine, inclined advanced grouting holes are reserved at the position of the middle shield. Grouting reinforcement is carried out in the section of the abnormal area in the advanced geological prediction and survey data. Open the gate valve at the reserved hole position, install a drilling machine at the position to drill and grout, and reinforce the stratum in front of the cutter head. Figure 5 、 Figure 6 、 Figure 7 ).

[0074] The stratum within 2m outside the 180° arch of the tunnel face in the section requiring advanced grouting reinforcement is advanced and pre-grouted (. Figure 8 ). The reinforcement uses cement-silicate double liquid slurry, the grouting pressure is taken as 0.5-1.0Mpa, and the grouting should be carried out hole by hole, and the grouting range is 4 rings of segments in front of the cutter head each time. After excavating 4 rings, the next cycle of grouting is carried out. The pressure maintaining work of the shield machine should be done well during the grouting process, and the monitoring should be strengthened.

[0075] The grouting material uses ordinary cement-silicate double liquid slurry, and the material type and ratio selection adjustment is carried out according to the water inflow and stratum grouting conditions during the construction process, as shown in Table 2.

[0076] Table 2 Grouting material parameter table

[0077] .

[0078] 2. Radial grouting

[0079] During the excavation, shield mud is injected into the top of the shield shell. Figure 9), reduce the gap above the shield, fix the shield to reduce the amount of pipe piece floating after separating from the shield tail, according to the actual situation and monitoring data, consider injecting shield mud into the stratum through the radial grouting hole reserved in the middle shield to reduce the gap between the stratum and the shield, reduce the exposure time of the soil, and reduce the soil settlement; the shield mud injection position is the top three hole positions of the middle shield, which is carried out synchronously during shield tunneling, the injection amount of each ring is not less than 4 cubic meters, the injection pressure is not greater than 7 bar, 1 cubic meter of shield mud is prepared by mixing cement: bentonite: water in a mass ratio of 450:250:700 during construction, and the shield mud slurry: water glass slurry = 1:1.

[0080] Example six, bolt retightening

[0081] The shield segment bolt is an important component for connecting the segments. It has two main functions: one is to connect the segments and fix them together to form a whole tunnel structure; the other is to transfer loads, such as soil pressure, water pressure and other external forces, and transfer them to the segments and foundation. In order to ensure the quality of the formed tunnel, the adjacent ring segments are connected into a whole, the overall weight of the segments is increased to resist the stratum buoyancy, the slurry buoyancy behind the segments, and the shield machine force. During the process of assembling the segments and excavating the next ring, the segment bolts in the range of 3 rings of the adjacent formed ring are comprehensively checked and retightened every 500mm of excavation to ensure the tight connection of the bolts.

[0082] Although some preferred embodiments of the present application have been described, those skilled in the art can make further changes and modifications to these embodiments once they know the basic inventive concept. Therefore, the appended claims are intended to be interpreted as including all the preferred embodiments and all changes and modifications falling within the scope of the present application.

[0083] Obviously, those skilled in the art can make various modifications and variations to the present application without departing from the spirit and scope of the inventive concept. Thus, if these modifications and variations of the present application fall within the scope of the claims of the present application and their equivalent technologies, the present application also intends to include these modifications and variations.

Claims

1. A shield tunneling method based on the floating control of ultra-large diameter shield tunnel segments, characterized in that, Includes the following steps: (1) Controlling the tunneling attitude: During the tunneling process, the vertical attitude of the shield is controlled within -40 to -50 mm to offset the upward movement of the segments. When tunneling in the hard rock section with soft upper and hard lower sections, the vertical attitude is controlled between -20 and -30 mm. The vertical deviation distance of the shield machine is controlled between -20 and 20 mm, and its vertical deviation angle is controlled between -10 and 10 mm / m. The stroke difference between the upper and lower jacks of the shield machine is controlled between -20 and 50 mm. When the shield passes through the soft upper and hard lower sections, the shield machine is kept in a downward tilting attitude. (2) Setting the tunneling pressure: The theoretical value of the slurry chamber pressure Pa is determined using a water and soil combined calculation method. During shield tunneling, the pressure at the top of the slurry chamber is between the upper and lower limits of the theoretical value of the slurry chamber pressure. The deviation of the cut-off water pressure during the switching of the shield machine's three states—advancement, reverse washing, and bypass—is controlled between -20 and 20 kPa. The theoretical value of the slurry chamber pressure Pa is determined by the following formula: ， In the formula, γ is the saturated unit weight of the stratum; H is the burial depth of the tunnel top; Ka is the active earth pressure coefficient; p is the ground load, taken as 20 kPa; (3) Optimize the grouting management system: adopt embedded tail shield grouting pipes, arrange two piston-type double liquid grouting blocks at the top of the tail shield, and arrange eight single liquid grouting pipes for use and eight for standby at other positions for injecting mortar A liquid, while reserving synchronous grouting points for injecting B liquid. (4) Synchronous grouting and secondary grouting behind the tunnel segments: synchronous grouting is carried out using cement mortar inert grout, with the grouting volume being 130% to 180% of the theoretical building voids. The grouting volume above the center of the tunnel segment is 55% to 65% of the total grouting volume, and the grouting volume below the center of the tunnel segment is 35% to 45% of the total grouting volume. The grouting pressure is 0.1 to 0.3 MPa greater than the outlet pressure. At least one additional grouting hole is added to the top of the tunnel segment. During shield tunneling, when the tunnel segment exits the shield tail 3 rings, the additional grouting hole is used to inject double-liquid grout, with the grouting pressure being 0.2 to 0.3 MPa greater than the outlet pressure. (5) Pre-grouting: Inclined pre-grouting holes are pre-set at the shield position of the tunnel boring machine. In sections where abnormalities are shown in the advanced geological forecast and exploration data, the strata within 1.8 to 2.2 m outside the arch of the tunnel face are pre-grouted and reinforced hole by hole. The pressure of the pre-grouting reinforcement is 0.5 to 1.0 MPa. The grouting range is 4 rings of segments in front of the cutterhead. (6) Radial grouting: Radial grouting holes are pre-set at the top of the shield in the tunnel boring machine, and the amount of grout injected per ring during the tunneling process is ≥4 m³. 3 Injection pressure ≤ 7 bar; (7) Bolt re-tightening: During the process of tunneling the next ring after the segment assembly is completed, the bolts of the segments within the range of the three adjacent rings that have been formed are fully inspected and re-tightened every 450-550mm of tunneling to ensure the bolt connection is tight.

2. The shield tunneling method according to claim 1, characterized in that, In step (3), a plunger pump is used to transport mortar liquid A and liquid B, wherein the plunger pump used to transport liquid B is equipped with 4 output channels.

3. The shield tunneling method according to claim 1, characterized in that, In step (4), the cement mortar inert slurry is composed of cement, fine sand, fly ash, water, and admixture in a density ratio of 23~27:1200~1300:290~310:290~310:75~85; the admixture is lime.

4. The shield tunneling method according to claim 1, characterized in that, In step (4), the two-component slurry is made by mixing cement slurry and water glass in a volume ratio of 1:1 to 2, wherein the cement is P.O42.5 ordinary cement; the water-cement ratio is 1:1 to 2; and the glass degree is 30 to 35be.

5. The shield tunneling method according to claim 1, characterized in that, In step (5), the pre-grouting reinforcement uses a cement-water glass double grout; the water-cement ratio of the cement grout in the double grout is 0.8 to 1:1; the glass density is 30 to 35Be; and the volume ratio of cement to water glass is 1:1 to 2.

6. The shield tunneling method according to claim 1, characterized in that, In step (6), radial grouting uses a shield mud-water glass dual grout; the shield mud is composed of cement: bentonite: water in a mass ratio of 420-480:220-280:670-730; the volume ratio of the shield mud to the water glass is 1:1-2.

7. The shield tunneling method according to claim 1, characterized in that, In step (2), the active earth pressure coefficient Ka is determined by the following formula: ， In the formula, φ is the internal friction angle of the formation.

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