Shield launching and receiving hole sealing and reinforcing construction method

Abstract

The invention discloses a shield launching and receiving hole sealing and reinforcing construction method, and relates to the technical field of shield construction.The method comprises the steps that firstly, according to the stratum condition, a deep mixing pile or a high-pressure jet grouting pile is used for reinforcing an end soil body and detecting; glass fiber reinforced plastic ribs are used for replacing common steel bars to construct the underground diaphragm wall, and the underground diaphragm wall is connected through double U-shaped buckles; then, an extension steel lantern ring is installed and matched with a matched rubber cord fabric air bag to achieve sealing; a groove is chiseled before shield tunneling, and tunneling parameters are accurately controlled; and finally, whole-ring secondary grouting is conducted on the hole segment, and the steel lantern ring is dismantled after the hole segment is detected to be qualified. According to the method, through combined reinforcement, novel sealing and precise construction control, the problems of water gushing, sand gushing, sealing failure and the like in a complex stratum are effectively solved, the risk of manual wall chiseling is avoided, the engineering cost is reduced, and the construction period is shortened.

Description

Technical Field

[0001] This invention relates to the field of tunnel boring machine (TBM) construction technology, specifically a method for sealing and reinforcing the tunnel entrances for both launching and receiving tunnels. Background Technology

[0002] In shield tunneling, the launching and receiving phases are high-risk stages, especially in complex strata such as fine sand and water-rich gravel, where accidents like water and sand inrush and soil collapse are prone to occur. Traditional end-face reinforcement methods are difficult to adapt to high water pressure and highly permeable strata, resulting in unstable reinforcement effects. Conventional portal sealing relies on rubber curtain plates, which have insufficient local sealing performance and are prone to failure due to cutterhead disturbance and pressure changes. When using ordinary steel reinforcement for diaphragm walls, manual chiseling is required, which is not only time-consuming and risky but may also disturb the surrounding soil. At the same time, the distinction between shallow and deep burial in deep tunnels is unclear, and the design of retaining structures is often overly conservative, resulting in wasted costs. Furthermore, the lack of precise control standards for parameters such as shield thrust and soil chamber pressure further exacerbates construction risks. These problems seriously affect the safety, efficiency, and economy of shield tunneling, becoming key bottlenecks restricting the progress of shield tunneling projects in complex strata. Summary of the Invention

[0003] To fill a market gap, this invention provides a method for sealing and reinforcing the tunnel entrances for shield launching and receiving.

[0004] To achieve the above objectives, the present invention provides the following technical solution: a method for sealing and reinforcing the tunnel entrances of shield tunneling machines, comprising the following steps: S1. Based on the geological conditions at the tunnel entrance, deep mixing piles or high-pressure jet grouting piles are used to reinforce the soil at the starting and receiving ends of the shield tunnel. The reinforcement range covers the area at the tunnel entrance at risk of collapse. After the reinforcement is completed, the reinforcement effect is tested by horizontal core sampling and borehole testing. S2. Fiberglass reinforced plastic (GFRP) bars are used to replace ordinary steel bars in the underground continuous wall at the opening. The GFRP bars are mechanically connected to the steel bars on the outside of the opening through double U-shaped clips. The U-shaped clips are arranged in an alternating and opposite manner. The stirrups of the underground continuous wall form a closed space skeleton. S3. Install an extended steel collar between the sidewall of the tunnel entrance and the sealing device. The steel collar is made of steel plate. Its theoretical length is calculated based on the safety distance of the rubber curtain plate, the length of the cutterhead and the thickness of the sidewall. The actual length is 50mm longer than the theoretical length. The steel collar is fixed to the sidewall with long bolts through the pad. After installation, ensure that the safety distance between the rubber curtain and the cutterhead of the shield is not less than 200mm. S4. Depending on whether a steel collar is installed at the opening, a suitable rubber curtain airbag sealing structure is adopted. The rubber curtain airbag includes an integrally formed solid plate and an airbag, which is fixed to the side wall or steel collar bolt by a steel pressure plate. The initial pressure of the airbag is determined by converting the formation water pressure according to the similarity ratio. S5. Before the shield tunneling begins, a groove is chiseled in the GFRP reinforced diaphragm wall corresponding to the center cutter position of the shield. During tunneling, the thrust, cutterhead speed, and advance speed are controlled, and the active earth pressure of the soil in the collapse zone of the tunnel face is also taken into account. S6. After the shield tunneling machine starts and receives the tunnel, the surrounding segments of the tunnel entrance are grouted in a ring-like manner. A two-component grout of cement and water glass is used. After the grouting is completed, the sealing effect is checked through the observation hole of the steel ring. After confirming that there is no water or sand, the steel ring is removed.

[0005] Furthermore, in S1, when high-pressure jet grouting piles are used for reinforcement, the uniaxial compressive strength of the reinforced body is not less than 1.5MPa, the pile diameter is 800mm, and after the reinforcement is completed, the core is extracted by drilling on the ground and core is extracted by drilling at the tunnel entrance. The number of inspection points is not less than 2% of the number of grouting holes. If there are less than 20 holes, at least 2 points are inspected.

[0006] Furthermore, in S2, the spacing between the double U-shaped clips is no greater than 400mm, and the number of U-shaped clips connecting a single GFRP bar to the reinforcing bar is no less than 2.

[0007] Furthermore, in S2, the diameter of the stirrups in the diaphragm wall is not less than 14mm, the stirrup spacing is not greater than 100mm, and the stirrups are arranged in a closed manner to form a spatial skeleton with the main reinforcement.

[0008] Furthermore, in S3, the steel collar is made of a steel plate with a thickness of 20mm and a radial width of 200mm-500mm. The bolt holes on the end face of the steel collar are evenly arranged along the circumference, and the bolt hole spacing is 50mm-100mm.

[0009] Furthermore, in S4, the solid plate of the rubber curtain airbag has a radial width of 300mm-500mm and a thickness of 10mm-20mm, and the airbag diameter is 150mm-300mm and a thickness of 5mm-10mm.

[0010] Furthermore, in S6, the volume ratio of cement grout to water glass in the cement-water glass dual-liquid grout used for secondary grouting is 1:1.

[0011] Furthermore, the secondary grouting process in S6 is as follows: five grouting points are evenly distributed on each of the last 10 ring segments, and cement and water glass grout are used for grouting in sequence. After the grouting pressure reaches 0.3-0.5MPa, the pressure is stabilized for 3-5 minutes. All grouting points are inspected by opening holes, and the water output is observed through the observation holes of the steel sleeve ring. After there is no water or sand, the steel sleeve ring is removed. During the grouting process, the surface settlement is monitored simultaneously. When the settlement rate exceeds 0.5mm / d, grouting is suspended and the parameters are adjusted.

[0012] Furthermore, when deep mixing piles are used for reinforcement in S1, the construction process is as follows: site leveling, mixer erection, setting up guide positioning steel plates, mixer positioning, mixing and pile formation, and residual soil treatment. During the mixing and pile formation process, the cement content is ensured to be no less than 15%.

[0013] Furthermore, when chiseling the groove in S5, the outline of the groove is first drawn on the GFRP reinforcement underground continuous wall according to the size of the center cutter. After cutting the outline with a diamond wire saw, the concrete and GFRP reinforcement in the groove are manually removed. The depth of the groove is 10-20mm greater than the protruding length of the center cutter. The groove wall is leveled with polymer cement slurry.

[0014] Compared with existing technologies, the beneficial effects of this invention are: by combining deep mixing piles and high-pressure jet grouting piles for reinforcement, and with the help of glass fiber reinforced underground continuous walls, soil stability and direct shield cutting are achieved, avoiding the risks of manual wall chiseling; the rubber curtain airbag and the extended steel sleeve form an integral seal, which greatly reduces the probability of water and sand inrush, and the sealing reliability in deep buried water-rich strata is significantly better than that of traditional methods.

[0015] Based on the collapse arch theory and the filling theory, the depth and shallow burial boundaries of the tunnel are clearly defined. The retaining structure is designed according to the active earth pressure in the collapse zone to avoid excessive reinforcement and reduce project costs. Components such as steel sleeves and GFRP bars can be reused to reduce material waste, simplify the construction process, and shorten the construction period. Attached Figure Description

[0016] Figure 1 This is a flowchart of the construction process of the present invention; Figure 2 This is a schematic diagram of the sealing structure of the shield tunneling starting portal without steel sleeve according to the present invention; Figure 3 This is a schematic diagram of the shield tunneling starting portal sealing structure with a steel collar according to the present invention; Figure 4 This is a schematic diagram of the steel collar installation structure for the opening of the present invention. Detailed Implementation

[0017] Please see Figure 1-4 This invention provides a technical solution: a method for sealing and reinforcing the tunnel entrances of shield tunneling machines, comprising the following steps: S1. Based on the geological conditions at the tunnel entrance, deep mixing piles or high-pressure jet grouting piles are used to reinforce the soil at the starting and receiving ends of the shield tunnel. The reinforcement range covers the area at the tunnel entrance at risk of collapse. After the reinforcement is completed, the reinforcement effect is tested by horizontal core sampling and borehole testing. When using deep mixing piles for reinforcement, the verticality of the piles and the uniformity of mixing must be monitored in real time during construction to avoid pile breakage or leakage. In areas with thick sand layers and high permeability, construction parameters should be adjusted promptly, increasing the number of mixing cycles or employing a re-mixing process to ensure thorough mixing of the cement grout with the soil. When using high-pressure jet grouting piles for reinforcement, the drilling depth and jet grouting pressure must be strictly controlled, and the grout injection speed should be dynamically adjusted according to changes in the geological strata to ensure the formation of a continuous and complete water-stopping curtain. After reinforcement, in addition to routine testing, additional testing points should be added to key areas to ensure the reinforcement effect meets the requirements for impermeability and bearing capacity.

[0018] S2. Fiberglass reinforced plastic (GFRP) bars are used to replace ordinary steel bars in the underground continuous wall at the opening. The GFRP bars are mechanically connected to the steel bars on the outside of the opening through double U-shaped clips. The U-shaped clips are arranged in an alternating and opposite manner. The stirrups of the underground continuous wall form a closed space skeleton. Before connecting GFRP bars to steel bars, clean the surface of the GFRP bars of oil and any damaged areas to ensure a clean and smooth connection surface. When installing U-shaped clips, use a torque wrench to strictly control the bolt tightening torque to ensure the connection strength meets the standards. During the pouring of the diaphragm wall, adopt a layered pouring and vibration compaction method to avoid quality defects such as honeycombing and pitting. After pouring, timely curing should be carried out for a period of no less than 14 days to ensure the concrete strength steadily increases and meets the subsequent shield cutting and load-bearing requirements.

[0019] S3. Install an extended steel collar between the sidewall of the tunnel entrance and the sealing device. The steel collar is made of steel plate. Its theoretical length is calculated based on the safety distance of the rubber curtain plate, the length of the cutterhead and the thickness of the sidewall. The actual length is 50mm longer than the theoretical length. The steel collar is fixed to the sidewall with long bolts through the pad. After installation, ensure that the safety distance between the rubber curtain and the cutterhead of the shield is not less than 200mm. After the steel collar is processed, it needs to be derusted and treated with anti-corrosion agents to extend its service life. During installation, first adjust the horizontal and vertical alignment of the steel collar to ensure precise alignment with the sidewall of the opening and the sealing device. The pad must be installed flat and firmly, fitting tightly against the steel collar and sidewall to avoid uneven stress that could lead to deformation. Bolt tightening should be done symmetrically, gradually tightening the bolts to ensure even stress at all connection points. After installation, check the stability of the steel collar; if necessary, conduct compression and deformation resistance tests.

[0020] S4. Depending on whether a steel collar is installed at the opening, a suitable rubber curtain airbag sealing structure is adopted. The rubber curtain airbag includes an integrally formed solid plate and an airbag, which is fixed to the side wall or steel collar bolt by a steel pressure plate. The initial pressure of the airbag is determined by converting the formation water pressure according to the similarity ratio. Before installing the rubber curtain airbag, check its integrity for any damage or leaks. Adjust the sealing device position according to the actual opening dimensions, ensuring a tight fit between the solid plate and the steel collar or sidewall. Tighten the bolts symmetrically to prevent uneven stress on the airbag. Clean any impurities from the airbag before inflation. Monitor pressure changes in real time during inflation, inflating slowly according to the design pressure to avoid sudden pressure increases that could damage the airbag. After installation, conduct a sealing test by injecting water or pressurizing to verify the sealing effect. Only proceed to the next step after confirming there are no leaks.

[0021] S5. Before the shield tunneling begins, a groove is chiseled in the GFRP reinforced diaphragm wall corresponding to the center cutter position of the shield. During tunneling, the thrust, cutterhead speed, and advance speed are controlled, and the active earth pressure of the soil in the collapse zone of the tunnel face is also taken into account. Before the tunnel boring machine (TBM) begins excavation, specialized technical briefings are conducted for operators, clarifying the control requirements for tunneling parameters and emergency response procedures. During tunneling, the TBM's attitude is monitored in real time, and the horizontal and vertical stability of the TBM is maintained by adjusting the jack stroke and thrust distribution. Close attention is paid to the soil condition at the tunnel face; if abnormalities such as water inrush or sand inrush are detected, tunneling is immediately stopped, and the emergency grouting plan is activated. Construction resumes only after the soil has stabilized. Simultaneously, tunneling data, including thrust, cutterhead rotation speed, and advance speed, is meticulously recorded to provide a basis for subsequent construction optimization.

[0022] S6. After the shield tunneling machine is launched and received into position, the surrounding segments of the tunnel entrance are grouted in a ring-like manner using cement and water glass grout. After the grouting is completed, the sealing effect is checked through the observation hole of the steel ring. After confirming that there is no water or sand, the steel ring is removed. Before secondary grouting, clean debris from the grouting holes of the tunnel segments to ensure unobstructed grouting channels. During grouting, follow the principle of "outer periphery first, then core; low pressure first, then high pressure," gradually increasing the grouting pressure to ensure the grout evenly fills the gaps between the tunnel segments and the voids in the strata. After grouting is completed, regularly monitor the water output and quality of the observation holes. If seepage occurs, replenish the grout promptly. Before removing the steel sleeve ring, thoroughly inspect the soil settlement and structural stability around the tunnel entrance. After confirming there are no safety hazards, remove the steel sleeve ring and related auxiliary facilities in sequence, avoiding damage to the structure caused by violent removal.

[0023] In S1, when high-pressure jet grouting piles are used for reinforcement, the uniaxial compressive strength of the reinforced body shall not be less than 1.5MPa, the pile diameter shall be 800mm, and after the reinforcement is completed, the core samples shall be extracted by drilling on the ground and drilling at the tunnel entrance. The number of inspection points shall not be less than 2% of the number of grouting holes. If there are fewer than 20 holes, at least 2 points shall be inspected.

[0024] The following detailed procedures must be followed for reinforcement construction and quality inspection: Before construction, the site must be leveled and compacted, and underground obstacles must be removed to ensure that the drilling rig's working surface is firm and flat. Based on the reinforcement range and the designed pile positions, a total station is used to accurately lay out and position the piles. The deviation of the pile positions must not exceed 50mm, and the piles should be marked with lime or wooden stakes.

[0025] After the drilling rig is in place, adjust the verticality of the rig body, controlling the deviation to within 1%, to ensure that the borehole is vertically pointed towards the reinforcement area. During the drilling process, mud slurry is used to protect the borehole wall and prevent it from collapsing. The drilling depth must exceed the design reinforcement depth by 500mm to ensure full coverage of the reinforcement area.

[0026] During high-pressure jet grouting, the grouting pressure is controlled at 20-25 MPa, the grout flow rate is 80-120 L / min, the rotation speed is 10-15 r / min, and the lifting speed is 5-10 cm / min. The grout is prepared using 42.5 grade ordinary Portland cement with a water-cement ratio of 1:1-1.5:1. If necessary, 3%-5% admixtures are added to enhance the strength and stability of the solidified body.

[0027] After reinforcement, curing is required for 7-14 days. Quality inspection will be carried out after the strength meets the standard. When drilling and core sampling on the ground, the core diameter of the drilling rig should not be less than 100mm, and the core sampling depth should penetrate the entire reinforced body. Three sets of core samples should be continuously taken from each test point and sent to the laboratory for uniaxial compressive strength testing to ensure that the strength is not less than 1.5MPa.

[0028] For core sampling inspection at the tunnel entrance, inspection holes should be evenly distributed around the entrance ring, with a spacing of 2-3 meters. The hole depth should be consistent with the depth of the solidified material. After core sampling, the integrity of the core sample should be observed, and a permeability coefficient test should be performed. The permeability coefficient should not exceed 1.0 × 10⁻⁶. - 8 cm / s. The number of inspection points shall be strictly set at 2% of the number of grouting holes. If the total number of grouting holes is less than 20, at least 2 inspection points shall be set. If the inspection fails, additional grouting holes shall be added around the area of ​​failure for supplementary reinforcement.

[0029] When deep mixing piles are used for reinforcement in S1, the construction process is as follows: site leveling, mixer erection, setting up guide positioning steel plates, mixer placement, mixing and pile formation, and residual soil treatment. During the mixing and pile formation process, ensure that the cement content is not less than 15%.

[0030] Site leveling: Remove weeds, gravel, construction waste, and other debris from the construction area. Lay a gravel cushion layer on soft ground with a compaction coefficient of not less than 0.95 to ensure stability and no settlement after the mixer is erected. After leveling, the elevation error of the site should be controlled within ±50mm to facilitate subsequent equipment positioning and construction operations.

[0031] Mixer erection: A twin-shaft deep mixing pile machine is selected. The frame is firmly installed, with the verticality deviation of the columns not exceeding 0.5%. The power system and grouting system are debugged and functioning normally to ensure stable operation during construction. After the frame is in place, it must be aligned with the center line of the designed pile position, with a deviation not exceeding 30mm.

[0032] Setting up guide positioning steel plates: The guide positioning steel plates are made of steel plates with a thickness of 10-12mm. According to the pile layout diagram, pile holes are reserved on the steel plates. The hole diameter is 20mm larger than the diameter of the mixing pile. The steel plates are fixed on the frame to ensure that the mixing pile does not deviate from the design pile position during the pile formation process, thereby improving the verticality and positional accuracy of the pile.

[0033] Mixer Positioning: Align the mixer drill bit with the pile hole on the guide positioning steel plate, recheck the verticality of the machine body and the pile position deviation, and fix the frame after confirming that everything is correct, ready to drill. Before the drill bit sinks, the cement slurry needs to be pre-mixed on the ground to ensure that the slurry concentration is uniform. The cement content should be strictly controlled above 15%, which can be adjusted appropriately according to the soil moisture content. When the moisture content is high, the content can be increased to 18%-20%.

[0034] Grouting for pile formation: A "four-mixing, two-spraying" construction process is adopted, meaning grout is sprayed and mixed twice during drill bit descent and twice during drill bit lifting. The descent speed is controlled at 0.5-1.0 m / min, the lifting speed at 0.3-0.5 m / min, and the mixing speed at 30-40 r / min to ensure thorough mixing of the grout with the soil. During pile formation, the grouting pressure (controlled at 0.5-1.0 MPa) and grout flow rate are monitored in real time to prevent grout interruption or leakage. The verticality deviation of the pile body should not exceed 1%, and the pile diameter deviation should not exceed ±50 mm.

[0035] Residual Soil Disposal: Residual soil generated during the pile mixing process must be promptly removed to the designated storage area using an excavator to avoid polluting the construction site and surrounding environment. The height of the residual soil pile should not exceed 1.5m, and transportation vehicles should be contacted in a timely manner to remove it from the site, ensuring a clean and orderly construction site and not affecting subsequent construction procedures.

[0036] In S2, the spacing between double U-shaped clips shall not exceed 400mm, and the number of U-shaped clips connecting a single GFRP bar to the reinforcing bar shall not be less than 2. The diameter of the stirrups in the diaphragm wall shall not be less than 14mm, the stirrup spacing shall not exceed 100mm, and the stirrups shall be enclosed and form a spatial skeleton with the main reinforcement.

[0037] The specific construction requirements are as follows: Before connection, the GFRP bars and reinforcing bars must be cleaned of oil, rust, damage, and other defects to ensure the connection surfaces are clean and dry. The surface of the GFRP bars needs to be sandblasted to increase the friction with the U-shaped clips. If there is rust on the surface of the reinforcing bars, it needs to be removed with a wire brush to ensure reliable connection.

[0038] The U-shaped clips are made of Q235 steel, and the inside of the clips must be textured with anti-slip grooves to enhance the grip with the reinforcing steel. When connecting a single GFRP bar to a rebar, at least two clips should be used, and the distance between the two clips should be controlled between 300 and 400 mm. The clips should be tightened using a torque wrench, with a bolt torque of not less than 50 N·m, ensuring a tight fit between the clips and the reinforcing steel without any loosening.

[0039] The double U-shaped clips are arranged in an alternating reverse pattern, meaning the openings of the two clips face opposite directions and are staggered along the length of the reinforcing bar, forming a two-way constraint and improving the anti-slip capability of the connection node. After the connection is completed, each connection node must be inspected to ensure that the clips are not deformed and the bolts are not loose. If necessary, an anti-slip test should be conducted, with the test load not less than 80% of the design value of the tensile strength of the GFRP reinforcement.

[0040] The specific structural and construction requirements for the spatial framework are as follows: The stirrups are made of HRB400 grade steel bars, with a preferred diameter of 14mm or 16mm, determined based on the thickness of the diaphragm wall and the stress conditions, ensuring that the stirrups have sufficient shear strength and stiffness. The stirrups are fabricated into closed rings, and the joints are made by single-sided lap welding, with a weld length of not less than 10d, and the weld is full and free of defects such as slag inclusions and porosity.

[0041] The spacing of the stirrups must be strictly controlled within 100mm, and they should be evenly distributed within the cross-section of the diaphragm wall. An additional stirrup should be added 50mm from the top and bottom of the wall. In the denser zone, the stirrup spacing can be reduced to 50mm. The stirrups are connected to the main reinforcement bars by binding or welding. The binding point spacing should not exceed 200mm, and the welding points should be spot welded to ensure a firm connection between the stirrups and the main reinforcement bars, forming a complete spatial skeleton.

[0042] After the spatial framework is formed, the dimensional deviations and verticality of the framework need to be checked. The length deviation of the framework should not exceed ±10mm, the width and height deviations should not exceed ±5mm, and the verticality deviation should not exceed 0.5%. After the framework is installed in the underground continuous wall section, it needs to be fixed with positioning steel bars to prevent the framework from shifting during concrete pouring and to ensure that the reinforcement of the underground continuous wall meets the design requirements.

[0043] In S3, the steel collar is made of a steel plate with a thickness of 20mm and a radial width of 200mm-500mm. The bolt holes on the end face of the steel collar are evenly arranged around the circumference, and the bolt hole spacing is 50mm-100mm.

[0044] Ensure the steel collar has sufficient strength and rigidity to withstand the tunnel boring machine's thrust and soil pressure. The radial width is determined based on factors such as the thickness of the tunnel entrance sidewalls and the size of the sealing device, and is generally 200-500mm, ensuring a safe distance of not less than 200mm between the rubber curtain and the cutterhead of the tunnel boring machine.

[0045] The bolt holes on the end face of the steel collar are evenly arranged around the circumference, with the hole diameter being 2mm larger than the diameter of the connecting bolts. The spacing between the bolt holes is controlled between 50 and 100mm to ensure uniform stress on the bolts. The number of bolt holes is determined based on the circumference of the steel collar, with no less than 10 bolt holes per meter of circumference to ensure a firm connection between the steel collar and the side wall and pad.

[0046] After the steel collar is processed, it needs to be rust-removed and corrosion-prevented. Sandblasting is used to remove surface rust and oxide scale, achieving a rust removal grade of Sa2.5. Then, two coats of anti-rust paint and one coat of topcoat are applied to improve the corrosion resistance of the steel collar and extend its service life.

[0047] During installation, first, a shim plate is pre-installed on the side wall of the opening. The shim plate is made of 10mm thick Q235 steel plate, and bolt holes corresponding to the steel collar are pre-drilled on the shim plate. The shim plate is firmly fixed, and the surface is flat, with a flatness deviation of no more than 2mm / m. Align the steel collar with the bolt holes on the shim plate and the side wall, and fix it with long bolts. When tightening the bolts, use a symmetrical tightening method to ensure that each bolt is subjected to uniform force.

[0048] After installation, check the installation accuracy of the steel collar. The deviation between the center line of the steel collar and the center line of the tunnel should not exceed ±10mm, and the verticality deviation should not exceed 0.5%. Ensure that the tunnel boring machine can smoothly enter the steel collar. At the same time, check the sealing performance between the steel collar and the side wall and the pad. If necessary, apply sealant to the contact surface to prevent water and sand leakage.

[0049] In S4, the radial width of the solid plate of the rubber curtain airbag is 300mm-500mm and the thickness is 10mm-20mm, and the diameter of the airbag is 150mm-300mm and the thickness is 5mm-10mm.

[0050] The rubber-lined airbag is made of a composite material of natural and synthetic rubber, possessing excellent elasticity, wear resistance, and aging resistance. The solid plate and airbag are integrally molded through a high-temperature vulcanization process, ensuring a firm connection and preventing delamination. The radial width of the solid plate is determined based on the opening size and sealing requirements, ranging from 300 to 500 mm, with a thickness of 10 to 20 mm, ensuring sufficient rigidity to withstand bolt tightening force and soil pressure. The airbag diameter is 150 to 300 mm, with a thickness of 5 to 10 mm, ensuring a tight fit against the shield shell after inflation, achieving a sealing effect.

[0051] Bolt holes are pre-drilled in the solid plate, evenly distributed around the circumference. The hole diameter is 2mm larger than the diameter of the connecting bolt, and the hole spacing is 50-100mm. The bolt holes correspond to the bolt hole positions on the steel collar or side wall to ensure that the bolts can pass through smoothly for fixing. The area around the bolt holes is thickened, with a thickness 5mm greater than the rest of the solid plate, to prevent the solid plate from deforming and being damaged when the bolts are tightened.

[0052] The surface of the airbag needs to be textured with anti-slip material to increase friction with the shield shell and prevent the airbag from sliding relative to the shell during tunneling, which would affect the sealing effect. The airbag has pre-drilled inflation and pressure testing holes. The inflation holes are connected using quick-connect couplings, and the pressure testing holes are fitted with pressure gauges for easy monitoring of the airbag pressure during construction.

[0053] During installation, first align the solid plate of the rubber curtain airbag with the steel pressure plate and steel collar, and fix it with long bolts. When tightening the bolts, apply force symmetrically and evenly to ensure that the solid plate and steel collar fit tightly without gaps. After installation, inflate the airbag to the design initial pressure. The initial pressure is determined by converting the ground water pressure according to a similarity ratio. After inflation, check the airbag's sealing performance to ensure that there is no air leakage and that the airbag fits tightly and reliably against the shield shell.

[0054] When chiseling the groove in S5, first draw the outline of the groove on the GFRP reinforced underground continuous wall according to the size of the center cutter. After cutting the outline with a diamond wire saw, manually remove the concrete and GFRP reinforcement in the groove. The depth of the groove is 10-20mm greater than the protruding length of the center cutter. The groove wall is leveled with polymer cement slurry.

[0055] Before marking the lines, the dimensions of the shield tunnel's center cutterhead and the length of the protruding cutterhead must be accurately measured. Based on the measurement results, the groove outline is drawn on the GFRP reinforced diaphragm wall with ink lines. The outline is 10mm larger than the actual size of the center cutterhead to ensure that the center cutterhead can be smoothly placed into the groove. After marking the lines, the position and size of the outline need to be checked again, and the deviation should not exceed ±5mm.

[0056] When using a diamond wire saw, select an 11mm diameter diamond wire saw and control the cutting speed at 2-3m / h. During the cutting process, continuously spray water onto the cutting area to cool it down, preventing overheating damage to the GFRP reinforcement and concrete, and reducing cutting dust pollution. The cutting sequence is to cut the vertical contour line first, then the horizontal contour line, ensuring that the contour lines are cut neatly without any jagged edges or gaps.

[0057] When manually removing concrete and GFRP reinforcement from the trench, use a small pneumatic pick and chisel to gently remove them, avoiding excessive force that could cause cracking and detachment of the concrete around the trench walls. During the removal process, promptly clean up any debris and dust inside the trench to keep it clean. The trench depth should be strictly controlled so that the protruding length of the center cutter is 10-20mm, ensuring that the center cutter is flush with the surface of the diaphragm wall after insertion, and the flatness deviation of the trench bottom does not exceed 3mm.

[0058] The trench wall leveling treatment uses polymer cement grout, which is prepared by mixing 42.5 grade ordinary Portland cement, acrylic emulsion, quartz sand, and water in a certain proportion. After thorough mixing, it is applied to the trench wall with a trowel to a thickness of 5-10 mm, ensuring that the trench wall is smooth and free of defects such as honeycomb or pitting. After leveling, curing is carried out for no less than 7 days to ensure that the polymer cement grout reaches the required strength and to prevent trench wall detachment from affecting construction during subsequent tunnel boring.

[0059] In S6, the secondary grouting uses a cement and water glass dual-liquid grout with a volume ratio of cement grout to water glass of 1:1.

[0060] The cement is fully dissolved, resulting in a uniform, lump-free grout. The water glass solution must be filtered to remove impurities before use to ensure the grout's purity. The cement grout and water glass are mixed at a 1:1 volume ratio and then delivered using a dual-liquid grouting pump. The mixing time is controlled within 30 seconds to prevent the grout from solidifying inside the pipe. The initial setting time of the dual-liquid grout is controlled within 30-60 seconds, and the final setting time within 1-2 minutes, ensuring rapid solidification after grouting for effective sealing and water prevention; ensuring a long-lasting and reliable sealing effect.

[0061] The secondary grouting process in S6 is as follows: Five grouting points are evenly distributed on each of the last 10 rings of segments. Cement and water glass grout are used for grouting in sequence. After the grouting pressure reaches 0.3-0.5MPa, the pressure is stabilized for 3-5 minutes. All grouting points are inspected by opening holes. The water output is observed through the observation holes of the steel sleeve ring. After there is no water or sand, the steel sleeve ring is removed. Surface settlement is monitored simultaneously during the grouting process. When the settlement rate exceeds 0.5mm / d, grouting is suspended and the parameters are adjusted.

[0062] The specific operational requirements are as follows: One grouting point is arranged at the top of the arch, the left and right arch waists, and the bottom of the arch in the last 10 rings of segments, for a total of 5 points. The points are evenly distributed. The grouting holes are drilled on the segments with an electric drill. The hole diameter is 25mm. The drilling depth penetrates the segments and the outer sealing gasket of the segments to ensure that the grout can be injected into the gap between the segments and the soil.

[0063] The principle of "grooving from bottom to top and symmetrical grouting" is adopted. First, the arch bottom points are grouted, then the arch waist points are grouted, and finally the arch top points are grouted. The grouting points of each ring segment are grouted in sequence. After completing one ring, the next ring is grouted. This avoids mutual interference of grouting pressure and ensures that the grout is filled evenly.

[0064] The flow rate is adjusted in real time according to changes in grouting pressure. When the pressure increases, the flow rate is reduced, and when the pressure is too low, the flow rate is increased to avoid grout loss or incomplete filling.

[0065] After grouting at all grouting points is completed, a drilling machine is used to drill holes around each grouting point for inspection. The drilling depth is 200mm. Observe whether there is any grout overflow or water seepage in the drill holes. If water seepage or incomplete grout filling is found, grouting reinforcement is required. At the same time, the ball valve of the observation hole on the steel collar is opened to observe the water flow. If the water flow is less than 5L / h and no water or sand flows out, it indicates that the sealing effect is good. If the water flow is large or sand flows out, grouting should be continued through the grouting holes of the segments until no water or sand flows out of the observation hole.

[0066] During the grouting process, a total station and a level are used to monitor the surface settlement around the tunnel entrance in real time. The monitoring frequency is once every 30 minutes, and the monitoring points are arranged within a range of 5-10m around the tunnel entrance, with a spacing of 5m. If the monitoring shows that the surface settlement rate exceeds 0.5mm / d, grouting is immediately suspended, the cause is analyzed, and the grouting parameters are adjusted. Grouting is resumed only after the settlement rate stabilizes within the allowable range.

[0067] The steel sleeve ring can only be removed after confirming that the grouting and sealing effect meets the standards. The removal sequence is as follows: first, remove the bolts connecting the steel sleeve ring to the side wall and the pad plate; then, use a crane to lift the steel sleeve ring away from the opening. During the removal process, avoid collisions with the pipe segments and the opening sealing device. After the steel sleeve ring is removed, clean up the grout and debris around the opening in a timely manner to create conditions for subsequent construction.

Claims

1. A method for sealing and reinforcing the tunnel entrances of shield tunneling machines, characterized in that, Includes the following steps: S1. Based on the geological conditions at the tunnel entrance, deep mixing piles or high-pressure jet grouting piles are used to reinforce the soil at the starting and receiving ends of the shield tunnel. The reinforcement range covers the area at the tunnel entrance at risk of collapse. After the reinforcement is completed, the reinforcement effect is tested by horizontal core sampling and borehole testing. S2. Fiberglass reinforced plastic (GFRP) bars are used to replace ordinary steel bars in the underground continuous wall at the opening. The GFRP bars are mechanically connected to the steel bars on the outside of the opening through double U-shaped clips. The U-shaped clips are arranged in an alternating and opposite manner. The stirrups of the underground continuous wall form a closed space skeleton. S3. Install an extended steel collar between the sidewall of the tunnel entrance and the sealing device. The steel collar is made of steel plate. Its theoretical length is calculated based on the safety distance of the rubber curtain plate, the length of the cutterhead and the thickness of the sidewall. The actual length is 50mm longer than the theoretical length. The steel collar is fixed to the sidewall with long bolts through the pad. After installation, ensure that the safety distance between the rubber curtain and the cutterhead of the shield is not less than 200mm. S4. Depending on whether a steel collar is installed at the opening, a suitable rubber curtain airbag sealing structure is adopted. The rubber curtain airbag includes an integrally formed solid plate and an airbag, which is fixed to the side wall or steel collar bolt by a steel pressure plate. The initial pressure of the airbag is determined by converting the formation water pressure according to the similarity ratio. S5. Before the shield tunneling begins, a groove is chiseled in the GFRP reinforced diaphragm wall corresponding to the center cutter position of the shield. During tunneling, the thrust, cutterhead speed, and advance speed are controlled, and the active earth pressure of the soil in the collapse zone of the tunnel face is also taken into account. S6. After the shield tunneling machine starts and receives the tunnel, the surrounding segments of the tunnel entrance are grouted in a ring-like manner. A two-component grout of cement and water glass is used. After the grouting is completed, the sealing effect is checked through the observation hole of the steel ring. After confirming that there is no water or sand, the steel ring is removed.

2. The method for sealing and reinforcing the tunnel entrances for shield tunneling as described in claim 1, characterized in that, In S1, when high-pressure jet grouting piles are used for reinforcement, the uniaxial compressive strength of the reinforced body shall not be less than 1.5 MPa, the pile diameter shall be 800 mm, and after the reinforcement is completed, the core samples shall be taken from the ground borehole and the core samples shall be taken from the borehole at the entrance of the tunnel. The number of inspection points shall not be less than 2% of the number of grouting holes. If there are less than 20 holes, at least 2 points shall be inspected.

3. The method for sealing and reinforcing the tunnel entrances for shield tunneling as described in claim 1, characterized in that, In S2, the spacing between the double U-shaped clips is no more than 400mm, and the number of U-shaped clips connecting a single GFRP bar to the reinforcing bar is no less than 2.

4. The method for sealing and reinforcing the tunnel entrances for shield tunneling as described in claim 1, characterized in that, In S2, the diameter of the stirrups in the diaphragm wall is not less than 14mm, the stirrup spacing is not greater than 100mm, and the stirrups are arranged in a closed manner to form a spatial skeleton with the main reinforcement.

5. The method for sealing and reinforcing the tunnel entrances for shield tunneling as described in claim 1, characterized in that, In S3, the steel collar is made of a steel plate with a thickness of 20mm and a radial width of 200mm-500mm. The bolt holes on the end face of the steel collar are evenly arranged along the circumference, and the bolt hole spacing is 50mm-100mm.

6. The method for sealing and reinforcing the tunnel entrances for shield tunneling as described in claim 1, characterized in that, In S4, the solid plate of the rubber curtain airbag has a radial width of 300mm-500mm and a thickness of 10mm-20mm, and the airbag diameter is 150mm-300mm and a thickness of 5mm-10mm.

7. The method for sealing and reinforcing the tunnel entrances for shield tunneling as described in claim 1, characterized in that, In S6, the volume ratio of cement grout to water glass in the cement-water glass dual-liquid grout used for secondary grouting is 1:

1.

8. The method for sealing and reinforcing the tunnel entrances for shield tunneling as described in claim 1, characterized in that, The secondary grouting process in S6 is as follows: five grouting points are evenly distributed on each of the last 10 ring segments, and cement and water glass grout are used for grouting in sequence. After the grouting pressure reaches 0.3-0.5MPa, the pressure is stabilized for 3-5 minutes. All grouting points are inspected by opening holes, and the water output is observed through the observation holes of the steel sleeve ring. After there is no water or sand, the steel sleeve ring is removed. During the grouting process, the surface settlement is monitored simultaneously. When the settlement rate exceeds 0.5mm / d, grouting is suspended and the parameters are adjusted.

9. The method for sealing and reinforcing the tunnel entrances for shield tunneling as described in claim 1, characterized in that, When deep mixing piles are used for reinforcement in S1, the construction process is as follows: site leveling, mixer erection, setting up guide positioning steel plates, mixer placement, mixing and pile formation, and residual soil treatment. During the mixing and pile formation process, the cement content must be no less than 15%.

10. The method for sealing and reinforcing the tunnel entrances for shield tunneling as described in claim 1, characterized in that, When chiseling the groove in S5, first draw the outline of the groove on the GFRP reinforcement underground continuous wall according to the size of the center cutter. After cutting the outline with a diamond wire saw, manually remove the concrete and GFRP reinforcement in the groove. The depth of the groove is 10-20mm greater than the protruding length of the center cutter. The groove wall is leveled with polymer cement slurry.

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