Shield tunneling construction method for rail transit tunnel

Abstract

The application discloses a shield tunneling construction method for rail transit, which comprises the following steps: step 1, shield tunneling; step 2, spoil improvement; step 3, shield mucking; step 4, segment assembling, specifically including segment point position, segment conveying and segment assembling; step 5, synchronous grouting; and step 6, secondary grouting. After the shield machine passes through, environmental protection and tunnel stability are considered, and if it is found that the synchronous grouting is insufficient, secondary supplementary grouting is carried out through the grouting hole in the middle of the segment. The construction method can predict and calculate the tunneling parameters according to the tunnel depth, geological conditions and environmental conditions, monitor and feed back the ground subsidence deformation following the shield advancement, verify the rationality of the construction parameters, and comprehensively optimize the construction parameters according to the monitoring results.

Description

Technical Field

[0001] This invention relates to the field of tunnel boring machine (TBM) construction technology, and in particular to a TBM tunneling construction method for rail transit tunnels. Background Technology

[0002] With the development of underground space, tunnel boring machine (TBM) technology has been widely applied in engineering fields such as subways, tunnels, and municipal pipelines. In some areas, tunnels mainly pass through complex strata with high water content and high permeability. TBM tunneling causes significant disturbance to the strata, and the screw conveyor is prone to phenomena such as gushing, which endangers the stability of the tunnel excavation face. In particular, more and more urban subway lines need to pass under existing subway lines, and some newly built subway lines need to use overlapping methods for the left and right tunnels to pass under existing subway lines, which puts forward higher requirements for TBM tunneling construction.

[0003] However, the existing shield tunneling construction methods are relatively simple and cannot adjust the tunneling parameters according to the actual construction conditions, thus affecting the stability of shield tunneling construction. Summary of the Invention

[0004] This invention provides a shield tunneling construction method for rail transit tunnels to solve the problem in the prior art that the tunneling parameters cannot be adjusted according to the actual construction conditions, thereby affecting the stability of shield tunneling construction.

[0005] According to one aspect of the present invention, a method for shield tunneling construction of a rail transit tunnel is provided, comprising the following steps:

[0006] Step 1: Tunnel boring machine (TBM) excavation. Before excavation, the parameters of the designed route are determined. The current position of the TBM is determined by measurement, and the parameters for the next excavation are determined based on the monitoring results before excavation.

[0007] Step 2: Soil improvement. Based on the parameters of fluidity, consistency, permeability and friction resistance of the soil generated during the tunneling process, soil improvement is carried out. Soil improvement is achieved by injecting additives into the cutterhead, soil chamber or screw conveyor through a special device configured on the tunnel boring machine. The additives are mixed with the soil by the rotation and stirring of the cutterhead, the stirring device in the soil chamber or the rotation and stirring of the screw conveyor.

[0008] Step 3: Excavation by the tunnel boring machine. Control the advance speed and the amount of soil discharged by the screw conveyor to ensure the earth pressure balance at the excavation face and in the soil chamber.

[0009] Step 4: Segment assembly, which includes segment location, segment transportation and segment assembly;

[0010] Step 5: Synchronous grouting. After the tunnel segment detaches from the shield tail, an annular gap will be formed between the soil and the tunnel segment. Grouting is used to fill the gap in the shield tail structure in a timely manner.

[0011] Step 6: Secondary grouting. Perform ultrasonic testing on the compaction of the backfill behind the wall. If voids are found, secondary grouting will be arranged. Specifically, secondary grouting will be carried out through the grouting holes in the middle of the segment to fill the parts that were not filled by the synchronous grouting and the parts that have reduced in volume. The secondary grouting will be carried out before the segment is removed from the trolley.

[0012] Optionally, the parameters in step 1 include earth pressure on the cutterhead and soil chamber, soil discharge volume and propulsion speed, screw conveyor speed, jack thrust, grouting pressure and time, grouting method and grouting volume, grout properties, shield tunnel slope, shield attitude and segment assembly deviation.

[0013] Optionally, the additive in step 2 is a foaming agent, with a foaming agent addition rate of 5%-10%. The foaming agent addition rate refers to the volume ratio of foam solution to slag. The foam solution consists of 3% foaming additive and 97% water. The foam composition consists of 90%-95% compressed air and 5%-10% foam solution.

[0014] Optionally, in step 3, before the earth pressure balance shield machine begins normal excavation, the loosening coefficient of each stratum and groundwater factors are considered, and the theoretical soil removal volume of each ring is calculated first. During the actual excavation process, the actual soil removal volume is statistically analyzed for each ring and compared with the theoretical value. When the actual soil removal volume exceeds 5% of the theoretical soil removal volume, the changes in the surrounding rock should be judged based on the monitoring data outside and inside the tunnel and by analyzing soil samples, and the stratum characteristics should be inverted. If it is inferred that over-excavation has occurred, the speed of the screw conveyor should be adjusted to increase the soil content in the soil chamber.

[0015] Optionally, in step 4, the segment locations and segments in the interval adopt a universal wedge-shaped segment assembly. Except for the difference in reinforcement due to different burial depths, the arrangement of the wedges is exactly the same for each ring. By selecting the position of the K block, the segment can be rotated to adjust the lead of the segment in various directions to conform to the design route and various fitting curves.

[0016] Optionally, in step 4, the segment transportation is carried out by a gantry crane for vertical transportation and by an electric vehicle unit for horizontal transportation. The segment loading inside the bridge is carried out by an electric monorail hoist with a crossbeam, a segment conveyor and an assembly machine.

[0017] Optionally, in step 4, before assembling the tunnel segments, the surface of the previous lining ring should be cleaned; the pressure and stroke of the shield propulsion hydraulic cylinder should be controlled, and the shield posture and excavation face should be kept stable; according to the position and assembly sequence of the tunnel segments, they should be assembled into a ring one by one; the tightening torque of the tunnel segment connecting bolts should meet the design requirements; after the tunnel segments are assembled, after the shield tail is pulled out, the tunnel segment bolts should be tightened in time.

[0018] Optionally, in step 4, after the segment is delivered by the segment crane to the segment assembly machine, the segment assembly machine is lowered and aligned with the lifting bolts on the segment; the lifting bolts are tightened; two, three, or four jacks in the segment assembly area are retracted; the segment is locked, lifted, moved forward, rotated, and assembled into the required position using the segment assembly machine; after the segment is supported by one jack, the misalignment of the segment is brought within the allowable range by adjusting the flat plate at the head of the assembly machine; the segment is then supported by other jacks and passed through. Tighten the bolts; rotate the segment assembly machine back to the position of lifting the segment, ready to install the next segment; loosen the lifting bolts and remove it from the segment, the lifting bolts should be removed and reused; repeat the lifting and installation steps until the 3 standard blocks and 2 connecting blocks are assembled; finally, install the capping block: after the segment assembly is completed, the jack elongation and the 4 shield tail gaps should be measured, and the results should be filled in the segment assembly report; when the assembled segment is separated from the shield tail, the bolts should be tightened a second time.

[0019] Optionally, the secondary grouting process in step 6 specifically includes:

[0020] S6.1: Two-component grouting. Before grouting, select a grouting point above 6 o'clock or 12 o'clock. After putting on the grouting check valve, use an electric hammer drill to penetrate the concrete protective layer of the hole and connect the tee, cement grout pipe and water glass grout pipe. When grouting two-component grout, first inject pure cement grout for 1 minute, then open the water glass valve to mix and inject. When the hole is closed, the water glass concentration should be increased.

[0021] After a grouting hole is completed, wait 5-10 minutes before opening the grouting head to check the sealing effect. If there is a lot of water, inject again. If the leakage is small, close the ball valve and open it again after 1-2 days. If leakage still occurs, inject double-liquid grout again for secondary sealing. If there is no leakage, remove the ball valve.

[0022] During the grouting process of the water-stop ring, a pressure relief hole should be made 5 rings after the corresponding segment. A one-way check valve and a grouting ball valve should be installed in the pressure relief hole. The ball valve should be opened at the same time until grout overflows and then closed. Check the grouting effect after 10 minutes. If water overflows, the grouting hole should be sealed with double liquid grouting.

[0023] About 30 minutes after the water-stop ring is made, the tunnel boring machine should be operated to advance 5-10cm or excavate the next ring to avoid the double liquid slurry wrapping around the shield tail.

[0024] Upper supplementary grouting: It was found by opening holes at the upper part of the 5th or 7th ring behind the shield tail: a large amount of water leaked out after the opening, and it was obvious that there were voids behind the segment wall. In order to fill the voids behind the segment wall and ensure that the back wall is full, grout should be injected at the 6th, 12th or above of the corresponding segment.

[0025] Before grouting, select 6, 12 or more suitable grouting points. After installing the grouting check valve, use an electric hammer to drill through the concrete protective layer of the hole, connect the tee, cement grout pipe and water glass grout pipe, and open holes in the same way at the opposite positions in the same ring. Install the grouting head and ball valve, which serve as observation holes and pressure relief holes. When injecting single-component grout into the grouting hole, the ball valve of the observation hole at the opposite position should be opened. After it is found that a thick grout flows out of the observation hole, close the ball valve of the observation hole and stop the single-component grout injection. Then, switch to double-component grout for sealing the hole.

[0026] After a grouting hole is completed, wait 5-10 minutes before opening the grouting head to check the sealing effect. If there is a lot of water, inject grout again. If the leakage is small, close the ball valve and open it again after 1-2 days. If leakage still occurs, inject double-liquid grout again for secondary sealing. If there is no leakage, remove the ball valve.

[0027] Optionally, in step 6, a separate grouting pump is used for secondary grouting. Before grouting, the outer protective layer of the segment hoisting hole is chiseled through, and a special grouting joint is installed. The secondary grouting uses a cement-water glass dual-liquid grout with a water glass concentration of 30-42Be and a water glass to cement grout ratio of 1:1. The initial setting time of the grout is designed to be 45s-2min, and the grouting pressure is generally 0.2-0.5MPa.

[0028] Step 6 also includes the following steps:

[0029] S6.2: Grouting completion standard adopts a dual-index control standard of grouting pressure and grouting volume. That is, when the grouting pressure reaches the set value and the grouting volume reaches the set value, the quality requirements can be considered met and the grouting can be ended.

[0030] S6.3: Effect inspection. Ultrasonic testing of the backfill density behind the shield tunnel is required. Voids are not allowed. If voids are found, secondary grouting should be arranged and tested until the grouting is dense.

[0031] In summary, this application includes at least one of the following beneficial technical effects:

[0032] Before tunneling, measurements are taken, and the tunneling parameters are corrected based on the actual position of the tunnel boring machine (TBM) and the test results. This allows for more accurate control of the tunneling direction and position, preventing deviations from the predetermined route and improving the precision of the project. During tunneling, the parameters of the excavated soil are modified to enhance its impermeability, preventing significant surface subsidence or collapse at the tunnel face due to drainage consolidation. The internal friction angle of the excavated soil in the tunnel chamber and the soil at the tunnel face is reduced, decreasing wear on the cutterhead and reducing cutterhead torque. After simultaneous grouting, secondary grouting is performed based on the ultrasonic testing results of the backfill compaction. Secondary grouting ensures that the backfill material is evenly distributed around the tunnel, filling any voids or uneven areas that may have been present in the initial grouting. Insufficient soil compaction after the initial grouting can lead to ground subsidence, affecting the safety of surface buildings and infrastructure. Secondary grouting strengthens the soil structure, preventing or reducing ground subsidence. These methods enhance the stability of the tunnel boring machine (TBM) construction.

[0033] In addition to the objectives, features, and advantages described above, the present invention has other objectives, features, and advantages. The invention will now be described in further detail with reference to the figures. Attached Figure Description

[0034] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0035] Figure 1 This is a schematic diagram of the shield tunneling construction method for a rail transit tunnel according to the present invention.

[0036] Figure 2 This is a diagram showing the segment assembly and positioning of the present invention;

[0037] Figure 3 This is a schematic diagram of the segment assembly during left turns according to the present invention;

[0038] Figure 4 This is a diagram of the segment structure of the present invention;

[0039] Figure 5 This is a schematic diagram of the synchronous grouting of the present invention;

[0040] Figure 6 This is a flowchart of the synchronous grouting process of the present invention. Detailed Implementation

[0041] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings. However, the present invention can be implemented in many different ways as defined and covered below.

[0042] The following is in conjunction with the appendix Figure 1-6This application will be described in further detail.

[0043] This application discloses a shield tunneling construction method for rail transit tunnels.

[0044] Reference Figure 1 The shield tunneling construction method for rail transit tunnels includes the following steps:

[0045] Step 1: Tunnel boring machine (TBM) excavation. Before excavation, the parameters of the designed route are determined. The current position of the TBM is determined by measurement, and the parameters for the next excavation are determined based on the monitoring results before excavation.

[0046] Step 2: Soil improvement. Based on the parameters of fluidity, consistency, permeability and friction resistance of the soil generated during the tunneling process, soil improvement is carried out. Soil improvement is achieved by injecting additives into the cutterhead, soil chamber or screw conveyor through a special device configured on the tunnel boring machine. The additives are mixed with the soil by the rotation and stirring of the cutterhead, the stirring device in the soil chamber or the rotation and stirring of the screw conveyor.

[0047] Step 3: Excavation by the tunnel boring machine. Control the advance speed and the amount of soil discharged by the screw conveyor to ensure the earth pressure balance at the excavation face and in the soil chamber.

[0048] Step 4: Segment assembly, which includes segment location, segment transportation and segment assembly;

[0049] Step 5: Synchronous grouting. After the tunnel segment detaches from the shield tail, an annular gap will be formed between the soil and the tunnel segment. Grouting is used to fill the gap in the shield tail structure in a timely manner.

[0050] Step 6: Secondary grouting. Perform ultrasonic testing on the compaction of the backfill behind the wall. If voids are found, secondary grouting will be arranged. Specifically, secondary grouting will be carried out through the grouting holes in the middle of the segment to fill the parts that were not filled by the synchronous grouting and the parts that have reduced in volume. The secondary grouting will be carried out before the segment is removed from the trolley.

[0051] Before tunneling, precise measurement and analysis of the tunnel boring machine's (TBM) current position and attitude, combined with previous monitoring data, allow for the optimization and adjustment of tunneling parameters. This method precisely controls the TBM's advance direction and speed, reducing deviations and ensuring the TBM advances along the predetermined path. By controlling the cutterhead's rotational speed and thrust, disturbance to the strata is reduced, thereby stabilizing the surrounding soil and preventing unnecessary settlement or collapse. Additives (such as foam or bentonite) injected into the cutterhead face, soil chamber, or screw conveyor improve the physical properties of the excavated soil, such as increasing its fluidity, achieving appropriate consistency, and reducing permeability. This effectively controls excavated soil discharge, reduces resistance in front of the cutterhead, and lowers energy consumption. The improved excavated soil is easier to handle and transport, while reducing wear on the cutterhead and extending equipment lifespan. Controlling the advance speed and the screw conveyor's discharge volume maintains earth pressure balance at the excavation face and within the soil chamber. This control is crucial because it directly relates to excavation stability and the prevention of ground settlement. Precise control prevents ground movement or collapse caused by improper excavation; precise segment assembly is crucial for ensuring tunnel structural stability. Correct segment selection and assembly sequence guarantee the structural integrity and waterproofing of the tunnel lining. This step ensures segment sealing and structural strength, reducing potential future maintenance issues. The annular gaps formed after segments detach from the shield tail can be quickly filled by synchronous grouting, improving soil and tunnel stability. Synchronous grouting not only strengthens the soil behind the segments but also reduces water infiltration, protecting the tunnel structure. Ultrasonic testing of backfill compaction allows for secondary grouting to repair any discovered voids or uneven filling areas, a crucial step for ensuring long-term stability. It fills areas that may have been missed during initial grouting, strengthening the soil structure and significantly reducing the risk of ground settlement. In summary, each step provides solutions to potential problems during shield tunneling, comprehensively improving the stability and safety of the entire construction process. This approach effectively controls risks during shield construction and enhances the stability of shield tunneling.

[0052] In one specific implementation, the parameters in step 1 include earth pressure on the cutterhead and soil chamber, soil discharge volume and propulsion speed, screw conveyor speed, jack thrust, grouting pressure and time, grouting method and grouting volume, grout properties, shield tunnel slope, shield attitude and segment assembly deviation.

[0053] In step 1, before tunneling, the parameters of the designed route are clearly defined. The current position of the tunnel boring machine is determined by measurement, and the parameters for the next tunneling are determined based on the monitoring results before tunneling. Only after all preparations are completed can tunneling begin according to the instructions.

[0054] In this embodiment, the tunnel boring machine (TBM) operator strictly adheres to the operating procedures, and any violations are strictly prohibited. Parameter selection and operation must be strictly performed according to the instructions of the supervising engineer. In case of any emergency, tunneling must be stopped immediately, and the on-duty engineer must be notified promptly. Tunneling must not commence without new instructions. During tunneling, the on-duty engineer monitors the TBM's progress throughout the entire process and issues instructions as needed. If there is any doubt about the TBM's direction, manual measurements should be increased, and the results of automatic and manual measurements should be frequently compared to confirm their accuracy. During each ring's advancement, the earth pressure balance is strictly controlled to maintain the stability of the soil at the cut face, minimizing soil disturbance. An information feedback construction method is adopted for quality control of the TBM's advancement. Settlement monitoring is conducted during the advancement process, and settlement data is promptly reported to provide a basis for adjusting the construction parameters for the next stage.

[0055] In this embodiment, it is essential to promptly ascertain the direction and position of the tunnel boring machine (TBM) and strictly control its attitude to ensure that the deviation of the tunnel during the final stage is controlled within 10mm. Advancement measurement management should be conducted after each advancement ring. Through analysis and calculation of the measurement values, operational instructions should be issued promptly, and adjustments to the TBM jack assembly should be made to correct deviations as needed.

[0056] In one specific implementation, the additive in step 2 is a foaming agent, with a foaming agent addition rate of 5%-10%. The foaming agent addition rate refers to the volume ratio of the foam solution to the excavated soil. The foam solution consists of 3% foaming agent and 97% water; the foam composition consists of 90%-95% compressed air and 5%-10% foam solution. Excavated soil improvement is a difficult and key point in tunnel boring machine (TBM) excavation. The following issues should be addressed: improving the impermeability of the excavated soil in the soil chamber to avoid significant surface subsidence or collapse accidents at the tunnel face due to drainage consolidation; reducing the internal friction angle of the excavated soil in the soil chamber and the soil at the tunnel face to reduce the wear of the excavated soil on the cutterhead and reduce the cutterhead torque; the soil layers within the tunnel section are mainly completely weathered silty mudstone and moderately weathered silty mudstone, and the use of foaming agents can achieve ideal excavated soil improvement results.

[0057] During actual construction, the injection rate of the soil conditioner can be adjusted according to the soil improvement situation, and the foaming agent is injected in a semi-automatic mode. One central flushing port is provided on the cutterhead for high-pressure water flushing. The tunnel boring machine is equipped with five foaming circuits. The improved soil is in a fluid state, does not form mud cakes, and the soil temperature is controlled within the required range.

[0058] In one specific implementation, in step 3, before the earth pressure balance shield machine begins normal excavation, considering the loosening coefficient of each stratum and groundwater factors, the theoretical soil removal volume for each ring is calculated first. During the actual excavation process, the actual soil removal volume is statistically analyzed for each ring and compared with the theoretical value. When the actual soil removal volume exceeds the theoretical soil removal volume by 5%, the changes in the surrounding rock should be judged based on the monitoring data outside and inside the tunnel and by analyzing soil samples. The stratum characteristics should be inverted. If it is inferred that over-excavation has occurred, the speed of the screw conveyor should be adjusted to increase the soil content in the soil chamber.

[0059] When the tunnel boring machine (TBM) is excavating, a dedicated person should be on-site to monitor and count the excavation, strictly controlling the advance speed and the amount of excavated soil by the screw conveyor to ensure earth pressure balance at the excavation face and in the soil chamber. The belt tension of the conveyor belt should be checked regularly and adjusted promptly if it becomes loose. If the soil condition is found to be unfavorable, it can be adjusted by adding foam or bentonite. When loading the dump truck, the camera footage and the full / empty status of the dump truck should be closely monitored to stop the screw conveyor in a timely manner. During loading, the battery-powered truck can be moved slightly back and forth to ensure the entire dump truck is filled.

[0060] In step 3, during normal tunneling by the earth pressure balance shield machine, unstable upper or forward soil layers can easily collapse into the soil chamber, causing surface subsidence. This manifests as over-excavation, meaning the amount of soil excavated per unit advance is too high, exceeding the theoretically calculated amount. To avoid over-excavation and under-excavation, the excavated amount should be controlled at approximately 59 m³ per ring. If abnormal excavated amounts occur, the cause should be investigated immediately to prevent ground subsidence.

[0061] In this embodiment, the theoretical excavation volume for each ring is calculated in advance, taking into account factors such as the loosening coefficient of each stratum and groundwater. During the actual tunneling process, a dedicated person is assigned to record the actual excavation volume for each ring and compare it with the theoretical value to control the excavation volume per unit time. When the excavation volume exceeds 5% of the final excavation volume, the changes in the surrounding rock should be judged based on monitoring data outside and inside the tunnel, and by analyzing soil samples, and the stratum characteristics should be inverted. If it is determined that over-excavation is indeed the case, the excavation speed of the screw conveyor should be adjusted to increase the soil content in the soil chamber. To protect the superstructure or pipelines, full-chamber tunneling or non-full-chamber tunneling with pneumatic pressure may be necessary. Based on the statistical over-excavation location and over-excavation volume, the over-excavation volume is promptly replenished by tail grouting, and secondary grouting is carried out at the over-excavation location if necessary. The secondary grouting pressure is generally 0.1-0.3 MPa greater than the sum of the static water and soil pressure at the grouting point calculated at the tunnel depth. If the water-stopping effect is not good after grouting, the grouting pressure can be appropriately increased.

[0062] Reference Figure 2 , 34. In a specific implementation, in step 4, the segment locations and the segment sections are assembled using universal wedge-shaped segments. Except for the difference in reinforcement due to different burial depths, the arrangement of the wedges is exactly the same for each ring. By selecting the position of the K block, the segment is rotated to adjust the lead of the segment in various directions to conform to the design route and various fitting curves.

[0063] The segment assembly specifically includes segment placement. The segments in this section use a universal wedge-shaped assembly with a wedge diameter of 45mm. Except for variations in reinforcement due to different burial depths, the wedge arrangement is identical for each ring. The segment's lead in various directions is adjusted by selecting the position of the K-block to ensure it conforms to the design route and fits various curves. The lining ring consists of one KT block, two adjacent blocks BT1 and BT2, and three standard blocks ATL1, ATL2, and ATL3. Before assembly, segment placement must be selected. This section uses staggered joint assembly, with 16 bolts connecting the circumference. The bolt holes are evenly distributed along the circumference of the segment, providing 16 selectable points. The universal ring segments achieve staggered joint assembly by rotating N times (22.5°).

[0064] For segment transportation, a 45-ton gantry crane is used for vertical transport, and an electric vehicle unit is used for horizontal transport. The loading of segments inside the bridge frame is carried out by an electric monorail hoist with a crossbeam, a segment conveyor, and an assembly machine.

[0065] Before segment assembly, the starting sequence is as follows: Before segment assembly, the starting control for segment assembly needs to be performed on the control panel in the central operating room of the tunnel boring machine. The specific steps are as follows: start the segment assembly machine oil pump, start the propulsion system oil pump, start the auxiliary system oil pump, and select the segment assembly mode.

[0066] The segment lifting and movement involves unloading each segment one by one from the segment crane on the tunnel boring machine (TBM). Some segments are placed in the segment preparation assembly area, while others are placed in the segment storage area near trolley number 1. First, the segment crane lifts the segment from the segment transport vehicle, rotates it 90 degrees, and moves it to the segment preparation assembly area or the segment storage area near trolley number 1. The specific steps are as follows: Install lifting bolts on the segment; lower the segment crane and lock the lifting bolts; lift the segment with the segment crane and move it towards the segment assembly area; lower the segment crane and place the segment in the segment preparation assembly area; loosen the lifting bolts and move on to the next segment. The actions of the segment crane can be controlled through the segment assembly machine control box or the control box in front of the TBM operator's cab.

[0067] Before assembling the tunnel segments, three types of measurements must be taken at the following locations: the elongation of the propulsion jacks 4, 8, 12, and 16; the elongation of the articulated hydraulic cylinders; and the shield tail clearance, which is the gap between the outer skin of the upper ring tube and the inner diameter of the shield tail.

[0068] The first two components are equipped with sensors, which can be read on the host computer. These measurement results need to be recorded in the segment assembly report. During assembly, the segment assembly machine installs segments sequentially from bottom to top, with left and right segments overlapping. After the bottom segment standard block ATR2 is in place, the standard blocks ATR1 and ATR3 on both sides and the adjacent blocks BT1 and BT2 are assembled in a crosswise manner. Finally, the capping block KT is installed, with 2 / 3 of its length overlapping, pushed radially upwards, and then inserted longitudinally to form a ring. The assembly machine should be installed as centrally as possible to reduce misalignment at the joints and ensure assembly quality.

[0069] Immediately after the tunnel segments are in place, install and tighten the segment bending bolts to fix the segment position and control the joint angle. Tighten the bolts again after the segments are assembled into a ring, and then tighten them again when the shield tail reaches the 10th ring. Note: Longitudinal bolts should be installed first, followed by circumferential bolts. To maintain thrust on the working face while installing segments, the jacks at the segment being installed can be retracted. After the segment is installed, the jacks immediately tighten on that segment, while the remaining jacks remain operational. This maintains thrust on the working face and prevents the shield from staggering.

[0070] The specific assembly sequence is as follows: After the segment is delivered to the segment assembler by the segment crane, lower the segment assembler and align the lifting bolts on the segment; tighten the lifting bolts; retract 2, 3, or 4 jacks in the segment assembly area; use the segment assembler to lock the segment, lift, move forward (in the direction of advancement), rotate, and assemble the segment into the required position; after the segment is on top of one jack, adjust the flat plate at the head of the assembler to ensure the segment misalignment is within the allowable range. The segment is supported by other jacks and bolted in place; the segment assembler rotates it back to the position of lifting the segment, preparing to install the next segment. Loosen the lifting bolts and remove it from the segment; the lifting bolts should be removed for reuse; repeat steps 1-6 until the 3 standard blocks and 2 connecting blocks are assembled; finally, install the capping block: after the segment assembly is completed, measure the jack elongation and the 4 shield tail gaps, and fill the results in the segment assembly report. When the assembled segments detach from the shield tail, the bolts should be tightened a second time.

[0071] Before assembling the tunnel segments in step 4, the surface of the previous lining ring should be cleaned; the pressure and stroke of the shield propulsion hydraulic cylinder should be controlled, and the shield posture and excavation face should be kept stable; according to the position and assembly sequence of the tunnel segments, they should be assembled into a ring one by one; the tightening torque of the tunnel segment connecting bolts should meet the design requirements; after the tunnel segments are assembled, after the shield tail is pulled out, the tunnel segment bolts should be tightened in time.

[0072] In this embodiment, during segment assembly, damage to the segments and waterproof sealing strips should be prevented; the ellipticity of the assembled lining rings should be randomly checked; when assembling segments in special locations such as connecting passages, the shield attitude and shield tail gap should be pre-adjusted according to the design position of the special segments, and the segment assembly should meet the design requirements; during the vertical transportation of segments, there must be a dedicated slinger to guide the process, ensure hoisting safety, and avoid damage to the segments from impacts.

[0073] In this embodiment, no workers are allowed within the range of the segment assembler's movement while it is moving with the segments; the on-duty engineer or tunnel boring machine operator should measure the rotation of the (n-1)th ring segment before segment assembly; the segment assembly should, while taking into account the allowable clearance around the bolts, try to control the rotation of the segments within ±50mm; the circumferential joints between segments are tightened by the rotation of the assembler; the longitudinal joints are tightened by the force of the assembler's movement and the jacking force of the jacks in the assembly mode.

[0074] In this embodiment, the distance between the front ends of the inner arc of the two adjacent blocks should be verified before the capping block is assembled; to ensure smooth insertion of the capping block, the sealing strip should be wiped with soap (to reduce friction); to avoid damage to the segments, the longitudinal bolts and jacks on the adjacent blocks should be loosened before the capping block is fully inserted.

[0075] In one specific implementation, in step 4, the segment transportation is carried out by a gantry crane for vertical transport and by an electric vehicle unit for horizontal transport. The segment loading inside the bridge is carried out by an electric monorail hoist with a crossbeam, a segment conveyor and an assembly machine.

[0076] Reference Figure 5 and Figure 6 In one specific implementation, step 5 involves simultaneous grouting. During shield tunneling, as the shield advances, a ring-shaped gap approximately 95mm wide forms between the tunnel segment and the soil after the segment detaches from the shield tail. If this gap is not filled in time, the soil around the segment will loosen or even collapse, leading to adverse consequences such as surface subsidence. Therefore, grouting must be used to fill the gap at the shield tail in a timely manner. Simultaneously, back lining grouting also improves the tunnel's water-stopping performance, ensuring a uniform distribution of external forces on the segment lining and guaranteeing early stability of the segment lining.

[0077] The tunnel boring machine (TBM) is equipped with a single-liquid grouting system and a secondary double-liquid grouting system. The single-liquid grouting system uses two KSP12 grouting pumps with a grouting capacity of 24 m³ / h and a grouting tank capacity of 8 m³. Four synchronous grouting pipes and four backup synchronous grouting pipes are installed inside the shield tail. Each grouting pipe has a pressure sensor, and monitoring equipment at each grouting point monitors the grouting volume and pressure for each ring. Each grouting pipe also has two adjusting valves. When the pressure reaches its maximum, one valve shuts off the grouting pump; when the pressure reaches its minimum, the other valve opens the pump to continue grouting. The shield tail seal uses three wire brushes and one steel plate bundle. Shield tail grease is injected into the gaps between the wire brushes to ensure that soil and groundwater from the surrounding foundation, grouting material from the backing, and water and mud from the excavation face do not flow into the shield through the gaps between the inner surface of the outer shell and the outer perimeter of the segments, ensuring smooth grouting behind the shield wall.

[0078] In step 5, the grout mix ratio is determined based on the geological conditions of the strata beneath the building. A suitable grout mix ratio is then injected into the shield tail gap during excavation. This mix ratio can be adjusted appropriately according to on-site excavation parameters. Based on past construction experience in Changsha city, the grout mix ratio is shown in the table below:

[0079] Proportion sand fly ash cement Bentonite One cubic meter of pulp / kg 450 300 150 100 One cubic meter of pulp / kg 500 430 210 100 One cubic meter of pulp / kg 470 400 220 100 One cubic meter of pulp / kg 564 338 280 113

[0080] Table 1 Slurry Mix Proportion

[0081] In this embodiment, the grouting technical parameters are as follows: After the tunnel segment exits the shield tail, a ring-shaped construction space exists between the tunnel segment and the stratum. In soft rock strata, if the ring-shaped construction space is not filled with synchronous grouting in a timely manner, or if the grouting volume cannot completely fill the surrounding rock of the arch, deformation may occur, leading to excessive surface settlement. Based on the cutterhead excavation diameter and the tunnel segment outer diameter of 1.5m, the grouting volume for one ring of tunnel segments can be calculated using the following formula.

[0082] Q=L / 4×π×(D2-d2)=3.14 / 4*1.5*(6.442-6.22)=3.57m3

[0083] In this embodiment, the following measures are taken to ensure grouting: Two grouting systems (synchronous grouting and secondary grouting system) are used to ensure that the grouting volume meets the requirements. According to theoretical calculations, the construction void volume between the segment and the surrounding rock is 3.57 m3. Based on past construction experience, to achieve a better filling effect, the grouting volume should be 150%-180% of the theoretical volume of the annular gap, that is, the grouting volume per ring should be between 5.4 m3 and 6.3 m3.

[0084] In this embodiment, the grouting volume should also be controlled in conjunction with the grouting pressure. The grouting pressure is generally controlled between 2.0 and 3.5 bar. If the pressure increases significantly, grouting should be temporarily stopped to prevent the grouting pressure from penetrating the formation or damaging the tunnel lining segments.

[0085] In one specific implementation, the secondary grouting process in step 6 is as follows:

[0086] S6.1: Two-component grouting. Before grouting, select a grouting point above 6 o'clock or 12 o'clock. After putting on the grouting check valve, use an electric hammer to drill through the concrete protective layer of the hole and connect the tee, cement grout pipe and water glass grout pipe. When grouting two-component grout, first inject pure cement grout for 1 minute, then open the water glass valve to mix and inject. When the hole is closed, the water glass concentration should be increased.

[0087] After a grouting hole is completed, wait 5-10 minutes before opening the grouting head to check the sealing effect. If there is a lot of water, grout should be injected again. If the leakage is small, close the ball valve and open it again after 1-2 days. If leakage still occurs, double-liquid grout needs to be injected again for secondary sealing. If there is no leakage, the ball valve should be removed.

[0088] During the grouting process of the water-stop ring, a pressure relief hole should be made 5 rings after the corresponding segment. A one-way check valve and a grouting ball valve should be installed in the pressure relief hole. The ball valve should be opened at the same time until grout overflows and then closed. Check the grouting effect after 10 minutes. If water overflows, the grouting hole should be sealed with double liquid grouting.

[0089] About 30 minutes after the water-stop ring is made, the tunnel boring machine should be operated to advance 5-10cm or excavate the next ring to avoid the double liquid slurry wrapping around the shield tail.

[0090] Upper supplementary grouting: It was found by opening holes at the upper part of the 5th or 7th ring behind the shield tail: a large amount of water leaked out after the opening, and it was obvious that there were voids behind the segment wall. In order to fill the voids behind the segment wall and ensure that the back wall is full, grout should be injected at the 6th, 12th or above of the corresponding segment.

[0091] Before grouting, select 6, 12 or more suitable grouting points. After installing the grouting check valve, use an electric hammer to drill through the concrete protective layer of the hole, connect the tee, cement grout pipe and water glass grout pipe, and open the hole in the same way at the opposite position in the same ring. Install the grouting head and ball valve, which serve as observation holes and pressure relief holes. When injecting single liquid grout into the grouting hole, the ball valve of the observation hole at the opposite position should be opened. After it is found that a thick grout flows out of the observation hole, close the ball valve of the observation hole and stop the single liquid grout injection. Then, switch to double liquid grout for sealing the hole.

[0092] After a grouting hole is completed, wait 5-10 minutes before opening the grouting head to check the sealing effect. If there is a lot of water, inject grout again. If the leakage is small, close the ball valve and open it again after 1-2 days. If leakage still occurs, inject double-liquid grout again for secondary sealing. If there is no leakage, remove the ball valve.

[0093] In one specific implementation, the secondary grouting in step 6 is equipped with a separate grouting pump. Before grouting, the outer protective layer of the segment hoisting hole is chiseled through and a special grouting joint is installed. The secondary grouting uses a cement-water glass dual-liquid grout with a water glass concentration of 30-42Be and a water glass to cement grout ratio of 1:1. The initial setting time of the grout is designed to be 45s-2min, and the grouting pressure is generally 0.2-0.5MPa.

[0094] Step 6 also includes the following steps:

[0095] S6.2: Grouting completion standard adopts a dual-index control standard of grouting pressure and grouting volume. That is, when the grouting pressure reaches the set value and the grouting volume reaches the set value, the quality requirements can be considered met and the grouting can be ended.

[0096] S6.3: Effect inspection. Ultrasonic testing of the backfill density behind the shield tunnel is required. Voids are not allowed. If voids are found, secondary grouting should be arranged as soon as possible and tested until the grouting is dense.

[0097] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A shield tunneling construction method for rail transit tunnels, characterized in that, Includes the following steps: Step 1: Tunnel boring machine (TBM) excavation. Before excavation, the parameters of the designed route are determined. The current position of the TBM is determined by measurement, and the parameters for the next excavation are determined based on the monitoring results before excavation. Step 2: Soil improvement. Based on the parameters of fluidity, consistency, permeability and friction resistance of the soil generated during the tunneling process, soil improvement is carried out. Soil improvement is achieved by injecting additives into the cutterhead, soil chamber or screw conveyor through a special device configured on the tunnel boring machine. The additives are mixed with the soil by the rotation and stirring of the cutterhead, the stirring device in the soil chamber or the rotation and stirring of the screw conveyor. Step 3: Excavation by the tunnel boring machine. Control the advance speed and the amount of soil discharged by the screw conveyor to ensure the earth pressure balance at the excavation face and in the soil chamber. Step 4: Segment assembly, which includes segment location, segment transportation and segment assembly; Step 5: Synchronous grouting. After the tunnel segment detaches from the shield tail, an annular gap will be formed between the soil and the tunnel segment. Grouting is used to fill the gap in the shield tail structure in a timely manner. Step 6: Secondary grouting. Perform ultrasonic testing on the compaction of the backfill behind the wall. If voids are found, secondary grouting will be arranged. Specifically, secondary grouting will be carried out through the grouting holes in the middle of the segment to fill the parts that were not filled by the synchronous grouting and the parts that have reduced in volume. The secondary grouting will be carried out before the segment is removed from the trolley. The secondary grouting process in step 6 is specifically as follows: S6.1: Two-component grouting. Before grouting, select a grouting point above 6 o'clock or 12 o'clock, put on the grouting check valve, drill through the concrete protective layer of the hole with an electric hammer drill, and connect the tee, cement grout pipe and water glass grout pipe. When injecting two-component grout, first inject pure cement grout for 1 minute, then open the water glass valve to mix and inject. When the hole is closed, the water glass concentration should be increased. After a grouting hole is completed, wait 5-10 minutes before opening the grouting head to check the sealing effect. If there is a lot of water, inject again. If the leakage is small, close the ball valve and open it again after 1-2 days. If leakage still occurs, inject double-liquid grout again for secondary sealing. If there is no leakage, remove the ball valve. During the grouting process of the water-stop ring, a pressure relief hole should be made 5 rings after the corresponding segment. A one-way check valve and a grouting ball valve should be installed in the pressure relief hole. The ball valve should be opened at the same time until grout overflows and then closed. Check the grouting effect after 10 minutes. If water overflows, the grouting hole should be sealed with double liquid grouting. About 30 minutes after the water-stop ring is made, the tunnel boring machine should be operated to advance 5-10cm or excavate the next ring to avoid the double liquid slurry wrapping around the shield tail. Upper supplementary grouting: It was found by opening holes at the upper part of the 5th or 7th ring behind the shield tail that a large amount of water leaked out after the holes were opened, and it was also found that there were obvious cavities behind the segment wall. In order to fill the cavities behind the segment wall and ensure that the back wall is full, grout should be injected above the 6th or 12th point of the corresponding segment. Before grouting, select a suitable grouting point above 6 o'clock or 12 o'clock. After putting on the grouting check valve, use an electric hammer to drill through the concrete protective layer of the hole, connect the tee, cement grout pipe and water glass grout pipe, and open the hole in the same way at the opposite position in the same ring. Install the grouting head and ball valve, which serve as observation holes and pressure relief holes. When injecting single liquid grout into the grouting hole, the ball valve of the observation hole at the opposite position should be opened. After it is found that a thick grout flows out of the observation hole, close the ball valve of the observation hole and stop the single liquid grout injection. Then, switch to double liquid grout for sealing the hole. After a grouting hole is completed, wait 5-10 minutes before opening the grouting head to check the sealing effect. If there is a lot of water, grout should be injected again. If the leakage is minor, close the ball valve and reopen it after 1-2 days. If leakage still occurs, inject the double-liquid slurry again for a secondary seal. If there is no leakage, remove the ball valve.

2. The shield tunneling construction method for a rail transit tunnel according to claim 1, characterized in that: The parameters in step 1 include earth pressure on the cutterhead and soil chamber, soil discharge volume and propulsion speed, screw conveyor speed, jack thrust, grouting pressure and time, grouting method and grouting volume, grout properties, shield tunnel slope, shield attitude and segment assembly deviation.

3. The shield tunneling construction method for a rail transit tunnel according to claim 1, characterized in that: In step 2, the additive is a foaming agent, with a foaming agent addition rate of 5%-10%. The foaming agent addition rate refers to the volume ratio of foam solution to slag. The foam solution consists of 3% foaming additive and 97% water. The foam composition consists of 90%-95% compressed air and 5%-10% foam solution.

4. The shield tunneling construction method for a rail transit tunnel according to claim 1, characterized in that: In step 3, before the earth pressure balance shield machine starts normal tunneling, the loosening coefficient of each stratum and groundwater factors are considered, and the theoretical soil removal volume of each ring is calculated first. During the actual tunneling process, the actual soil removal volume is statistically recorded for each ring and compared with the theoretical value. When the actual soil removal volume exceeds the theoretical soil removal volume by 5%, the changes in the surrounding rock should be judged based on the monitoring data outside and inside the tunnel and by analyzing soil samples. The stratum characteristics should be inverted. If it is inferred that over-excavation has occurred, the speed of the screw conveyor should be adjusted to increase the soil content in the soil chamber.

5. The shield tunneling construction method for a rail transit tunnel according to claim 1, characterized in that: In step 4, the segment locations and the segment sections are assembled using universal wedge-shaped segments. Except for the difference in reinforcement due to different burial depths, the arrangement of the wedges is exactly the same for each ring. By selecting the position of the K blocks, the segments are rotated to adjust the lead of the segments in various directions to ensure that they travel in accordance with the design route and various fitting curves.

6. The shield tunneling construction method for a rail transit tunnel according to claim 1, characterized in that: In step 4, the segment transportation is carried out by gantry crane for vertical transport and battery-powered vehicle unit for horizontal transport. The segment loading inside the bridge frame is carried out by electric monorail hoist with crossbeam, segment conveyor and assembly machine.

7. The shield tunneling construction method for a rail transit tunnel according to claim 1, characterized in that: Before assembling the tunnel segments in step 4, the surface of the previous lining ring should be cleaned; the pressure and stroke of the shield propulsion hydraulic cylinder should be controlled, and the shield posture and excavation face should be kept stable; according to the position and assembly sequence of the tunnel segments, they should be assembled into a ring one by one; the tightening torque of the tunnel segment connecting bolts should meet the design requirements; after the tunnel segments are assembled, after the shield tail is pulled out, the tunnel segment bolts should be tightened in time.

8. The shield tunneling construction method for a rail transit tunnel according to claim 1, characterized in that: In step 4, after the tunnel segment is delivered to the tunnel segment assembly machine by the tunnel segment crane, the tunnel segment assembly machine is lowered, and the lifting bolts on the tunnel segment are aligned; the lifting bolts are tightened; two, three, or four jacks in the tunnel segment assembly area are retracted; the tunnel segment is locked, lifted, moved forward, rotated, and assembled into the required position using the tunnel segment assembly machine; after the tunnel segment is supported by one jack, the misalignment of the tunnel segment is brought within the allowable range by adjusting the flat plate at the head of the assembly machine; the tunnel segment is supported by other jacks and threaded with bolts. Tighten the bolts; rotate the segment assembly machine back to the position of lifting the segment, ready to install the next segment; loosen the lifting bolts and remove it from the segment, the lifting bolts should be removed and reused; repeat the lifting and installation steps until the 3 standard blocks and 2 connecting blocks are assembled; finally, install the capping block: after the segment assembly is completed, the jack elongation and the 4 shield tail gaps should be measured, and the results should be filled in the segment assembly report; when the assembled segment is separated from the shield tail, the bolts should be tightened a second time.

9. The shield tunneling construction method for a rail transit tunnel according to claim 1, characterized in that: In step 6, a separate grouting pump is used for secondary grouting. Before grouting, the outer protective layer of the segment hoisting hole is chiseled through and a special grouting joint is installed. The secondary grouting uses a cement-water glass dual-liquid grout with a water glass concentration of 30-42Be and a water glass to cement grout ratio of 1:

1. The initial setting time of the grout is designed to be 45s-2min, and the grouting pressure is 0.2-0.5MPa. Step 6 also includes the following steps: S6.2: Grouting completion standard adopts a dual-index control standard of grouting pressure and grouting volume. That is, when the grouting pressure reaches the set value and the grouting volume reaches the set value, the quality requirements can be considered met and the grouting can be ended. S6.3: Effect inspection. Ultrasonic testing of the backfill density behind the shield tunnel is required. Voids are not allowed. If voids are found, secondary grouting should be arranged and tested until the grouting is dense.

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