A construction method for shield tunneling under important structures with small clear distance in karst area

Abstract

The application discloses a construction method for shield tunneling under important buildings in a small-distance tunnel in a karst area, and comprises the following steps: for a wide area, the soil between the left tunnel and the right tunnel is reinforced and isolated by using bored piles; for a narrow space and a section where bored piles cannot be used, the soil between the left tunnel and the right tunnel is reinforced and isolated by using steel pipe piles and grouting; for a section underpassing underground pipelines, the soil between the left and right tunnels and the underground pipelines is reinforced and isolated by using ground reinforcement steel flower pipes and grouting; after the shield tunneling through the reinforced and isolated section, the soil outside the tunnel is reinforced by using the reserved grouting holes on the segments in the first tunnel; a movable support trolley is installed in the first tunnel; and the support force of the support trolley in the first tunnel is removed after the shield machine in the second tunnel completely passes through the small-distance range. The application can effectively control the deformation of the first tunnel, and can improve work efficiency and reduce cost investment.

Description

Technical Field

[0001] This invention relates to a construction method for tunneling important structures with a small clearance in karst areas using shield tunneling. Background Technology

[0002] As an important part of urban underground space development and public utilities, with the increasing density of rail transit networks and urban center buildings, shield tunnel construction in rail transit faces more and more tunnel construction with small clearances, including tunnels with small clearances between different lines due to network planning (clearance less than 1 tunnel diameter), as well as parallel tunnels with small clearances on the same line.

[0003] Karst areas have complex geological conditions, with well-developed karst caves and soil caves, and abundant groundwater. Shield tunnel construction is prone to causing disasters such as surface subsidence, collapse, and even sudden water inrush. When a tunnel passes under important structures (such as rainwater and sewage pipes, schools, rivers, existing bridges, houses, high-voltage power towers, etc.) with a small clearance, the subsequent shield tunneling is prone to squeezing and disturbing the preceding tunnel, drastically increasing the construction risk. Traditional construction methods usually use single ground grouting reinforcement or in-tunnel reinforcement, which has the following problems: (1) Grout in karst areas is prone to loss along karst cave channels, and the reinforcement effect is uncontrollable; (2) No internal support is provided for the preceding tunnel, resulting in large deformation of the preceding tunnel during the construction of the subsequent tunnel, making it prone to cracking and leakage; (3) Large isolation piles cannot be implemented in areas with dense underground pipelines, and the protection measures are insufficient; (4) Multiple grouting reinforcements are required, resulting in long construction periods and high costs. Summary of the Invention

[0004] The purpose of this invention is to overcome the existing defects and provide a construction method for tunneling important structures with a small clearance in karst areas using shield tunneling. This method not only effectively controls the deformation of the preceding tunnel, but also improves work efficiency and reduces personnel and equipment costs.

[0005] The technical solution to achieve the above objective is: a construction method for tunneling under important structures with a small clearance in karst areas using shield tunneling, wherein the important structures include underground pipelines, rivers, existing bridges, buildings, and high-voltage power towers; the construction method of the present invention includes the following steps: S1. Construction preparation and karst cave treatment: Before construction, conduct a detailed survey of underground pipelines, karst cave distribution and rock surface elevation, pre-grouting and filling treatment of the karst caves revealed by the survey, and determine the scope and form of isolation and reinforcement according to the design drawings; S2. Ground isolation and reinforcement construction is carried out, which is divided into the following three methods according to the geological conditions and ground space: A. For areas with wide open spaces, bored piles are used to reinforce and isolate the soil between the left and right tunnels. During construction, closely spaced bored piles are used. Plain piles are used from the ground to 3m above the top of the tunnel, and reinforced concrete piles are used from 3m above the top of the tunnel to 3m below the bottom of the tunnel or 1m below the rock surface. B. For sections with confined spaces and where bored piles cannot be installed, the soil between the left and right tunnels is reinforced and isolated using steel pipe piles with grouting. Multiple grouting holes are arranged in a quincunx pattern on the pipe wall of the steel pipe piles, with a grouting depth from 2m below ground level to 3m below the tunnel bottom. During construction, steel pipe piles are driven using a pipe-following drilling method, with the steel pipe piles drilled in sections and connected by threaded connections between sections. After the steel pipe piles are driven, grouting is performed on the pile body, with the grouting pressure gradually increasing from 0.2MPa to 1.0MPa to reach the designed diffusion radius. C. For sections with underground pipelines above the left and right tunnels, grouting reinforcement and isolation of the soil between the left and right tunnels and the underground pipelines is carried out using steel pipes. Grouting holes are arranged in a quincunx pattern on the pipe walls. During construction, the pipes are driven obliquely from the ground to 3m below the bottom of the tunnel, avoiding the underground pipelines. The grouting depth is from 3m above the top of the tunnel to 3m below the bottom of the tunnel or 1m below the rock surface. During construction, the steel pipes are driven obliquely at a preset angle. After the steel pipes are driven, grouting is carried out. The grouting sequence is from the outside to the inside. The grouting pressure is the initial soil and water pressure +0.3 to 0.5 MPa at the borehole opening. The surface and building uplift are monitored in real time for dynamic adjustment. The grouting is completed when the pressure is gradually increased to the design final pressure and stabilized for 15 minutes. The estimated injection volume and the grout return situation of adjacent holes are also considered for comprehensive judgment. S3. Pre-tunnel excavation and in-tunnel grouting: When the shield tunneling passes through the isolation and reinforcement section, the grouting pipe is inserted into the soil outside the tunnel through the grouting holes on the segments and the additional grouting holes for the isolation and reinforcement section. Grouting is carried out symmetrically on both sides of the tunnel and skip-ring grouting is performed along the direction of shield tunneling. S4. Install a support trolley inside the tunnel. For the initial tunnel section with a small clearance, after the grouting inside the tunnel reaches the design strength, install a mobile support trolley inside the initial tunnel. The distance between the front of the support trolley and the shield excavation face of the subsequent tunnel is half the length of the support trolley. Control the support rollers of the support trolley to be in close contact with the inner wall of the assembled segments of the initial tunnel to provide radial support force. For each ring that the shield machine in the subsequent tunnel excavates, the entire support trolley moves forward one ring, always maintaining effective support for the initial tunnel until the shield machine in the subsequent tunnel passes through the small clearance range. S5. Subsequent Tunnel Excavation and Monitoring Feedback: During the excavation of the subsequent tunnel, the longitudinal distance between it and the preceding tunnel shall not be less than 30m; the shield parameters shall be strictly controlled during the excavation process, including the cutting water pressure, thrust, excavation speed, cutterhead rotation speed, mud parameters, and synchronous grouting volume, and the shield parameters shall be finely adjusted in real time based on the monitoring data of the preceding tunnel and the monitoring data of surface structures; when the deformation of the monitored surface structures reaches 60% of the warning value, the pre-embedding work of the tracking grouting pipe shall be initiated on the ground adjacent to the tunnel; when the deformation of the monitored surface structures reaches 80% of the warning value, the grouting work of the tracking grouting pipe shall be initiated. S6. Support Removal and Subsequent Handling: After the tunnel boring machine in the subsequent tunnel has completely passed through the small clearance range and the monitoring data of the preceding tunnel has remained stable, the support force of the support trolley in the preceding tunnel is removed in stages and symmetrically through the hydraulic system. Then the components of the support trolley are removed. The entire process must be carried out under monitoring to achieve a smooth transition of the force system.

[0006] In the above-mentioned construction method for tunneling important structures with small clearance in karst areas using shield tunneling, when performing step S2 in mode C, the ground reinforcement steel pipes are installed symmetrically and obliquely on both sides of the underground pipeline within the protection range of the underground pipeline, so that the ground reinforcement steel pipes on both sides of the underground pipeline intersect in the soil around the tunnel below the underground pipeline, and the ground reinforcement steel pipes closest to both sides of the underground pipeline are at least 1m away from the underground pipeline in vertical distance.

[0007] The above-described construction method for tunneling important structures with a small clearance in karst areas using shield tunneling, wherein, during step S3, the grouting pipe for the tunnel segment includes an anti-blowout device, a sleeve valve steel pipe, and a grouting core pipe; wherein the anti-blowout device includes a grouting sleeve, a check valve, a temporary steel sleeve, and multiple water-swellable rubber rings; the grouting sleeve is installed in the pre-reserved grouting holes and additional grouting holes on the tunnel segment; the check valve is installed inside the grouting sleeve; the front end of the temporary steel sleeve is coaxially connected to an annular steel plate, and the annular steel plate of the temporary steel sleeve is coaxially fixed to the inner wall of the tunnel segment with the grouting hole by several expansion bolts, and the front end face of the annular steel plate is flush with the inner wall of the tunnel segment. Rubber gaskets are placed between the surfaces; multiple water-swellable rubber rings are spaced apart on the inner wall of the temporary steel casing; the grouting holes on the sleeve valve steel pipe are wrapped with rubber sleeves, and the sleeve valve steel pipe passes through the temporary steel casing and the grouting casing in sequence and is inserted into the soil outside the tunnel; a section of grouting perforated pipe is connected to the front of the grouting core pipe, and both ends of the grouting perforated pipe are connected to the grouting core pipe through rubber sleeve plugs; multiple grout discharge holes are evenly distributed on the pipe wall of the grouting perforated pipe; the grouting core pipe is inserted into the temporary steel casing, the grouting casing and the sleeve valve steel pipe, so that the grouting perforated pipe is located inside the sleeve valve steel pipe; the rear end of the grouting core pipe is connected to the grouting pump through a grouting hose; Before grouting, an impact drill is used to break the plain concrete in the grouting holes reserved on the tunnel segments. Then, the grouting sleeve and temporary steel sleeve are installed in the grouting holes. Then, a long drill rod drill is used to break through the synchronous grouting layer during the tunnel boring process. Then, the sleeve valve steel pipe is inserted into the temporary steel sleeve and grouting sleeve and hammered into the soil outside the tunnel. Then, the grouting core pipe is inserted into the sleeve valve steel pipe. Grouting begins with a single-component cement grout made of tap water and ordinary Portland cement. Initial setting time: 1-2 hours. The cement grout must be thoroughly mixed in a mixer before grouting can begin. During the grouting process, the grout must be continuously and slowly stirred for a time not less than the initial setting time. The grout should be filtered through a screen before pumping. During the grouting process, the grouting core tube should be pulled out and moved upwards by 0.2 to 0.4 meters each time. The grouting core tube can be moved by lifting equipment or manually by using two pipe wrenches to symmetrically clamp the grouting core tube and apply force evenly on both sides at the same time to pull the grouting core tube to move. After grouting is completed, first pull out the grouting core tube, clean it and reuse it, retain the sleeve valve steel pipe, remove the temporary steel sleeve, then inject high-strength cement grout or two-component grout into the grouting sleeve to seal the grouting holes on the segment, and cut off the grouting sleeve that protrudes above the inner surface of the segment.

[0008] The above-mentioned construction method for tunneling important structures with a small clearance in karst areas using shield tunneling, wherein, in step S5, the tracking grouting pipe is a steel perforated pipe, and is installed obliquely into the ground on the side of the ground structure that is close to the tunnel, so that the grout in the tracking grouting pipe can fill the bottom soil of the foundation of the ground structure that is close to the tunnel.

[0009] The construction method of the present invention for tunneling important structures with small clearance in karst areas using shield tunneling has the following characteristics: (1) Locally adapted isolation system: Drilled piles, steel pipe piles or steel pipes are flexibly selected according to site conditions to ensure the isolation and reinforcement effect and adapt to complex environments such as narrow spaces and dense pipelines.

[0010] (2) Three-dimensional protection combining internal and external elements: ground isolation piles (pipes) block the transmission of stratum deformation, grouting inside the tunnel reinforces the soil around the outside of the tunnel, and mobile support trolleys provide immediate rigidity for the tunnel. The three work together to effectively control the deformation of the tunnel.

[0011] (3) Significantly reduce process intervals: Traditional methods require waiting 12 to 24 hours for the grout to reach its strength before proceeding to the next step; the reinforcement and isolation piles in this method can be constructed in advance; grouting and excavation can be carried out in parallel; and the mobile support trolley can be installed immediately, shortening the overall construction period by about 30%.

[0012] (4) Save materials and costs: The precise design of the isolation and reinforcement range avoids blind grouting of the entire section, reducing the amount of grouting by 20% to 30%, and avoiding repeated grouting caused by grout loss. Attached Figure Description

[0013] Figure 1 This is a schematic diagram of the structure of densely packed bored piles used in the construction method of tunnel shield tunneling under important structures in karst areas according to the present invention. Figure 2 This is a schematic diagram of the structure of the bored pile reinforcement and isolation used in the construction method of this invention; Figure 3 This is a schematic diagram of the steel pipe pile reinforcement and isolation structure used in the construction method of this invention; Figure 4 This is a schematic diagram of the steel pipe reinforcement and isolation structure used in the construction method of this invention; Figure 5 This is a cross-sectional view of the construction method of the present invention after grouting inside the tunnel; Figure 5a This is a schematic diagram of the anti-gushing device used in the construction method of the present invention during grouting inside the tunnel; Figure 5b This is a schematic diagram of the sleeve valve steel pipe used in the construction method of the present invention during grouting inside the tunnel; Figure 5c This is a schematic diagram of the grouting core pipe used in the construction method of the present invention during grouting inside the tunnel; Figure 6 This is a schematic diagram showing the scope of the construction method of the present invention, in which a support trolley is used to support the preceding tunnel. Figure 7 This is a structural schematic diagram of the construction method of the present invention when protecting ground-level buildings and structures; Figure 8 yes Figure 7 AA view in the middle. Detailed Implementation

[0014] The technical solutions in the embodiments of the present invention will now be clearly and completely described in conjunction with the accompanying drawings.

[0015] Please see Figure 1 to Figure 7 The present invention relates to a construction method for tunneling important structures under a small clearance tunnel in a karst area, the important structures involved including underground pipelines 200, waterways, existing bridges, buildings, and high-voltage power towers.

[0016] The construction method of the present invention includes the following steps: S1. Construction preparation and karst cave treatment: Before construction, conduct a detailed survey of underground pipelines, karst cave distribution and rock surface elevation, pre-fill the karst caves revealed by the survey, and determine the scope and form of isolation and reinforcement according to the design drawings.

[0017] S2. Ground isolation and reinforcement construction is carried out, which is divided into the following three methods according to the geological conditions and ground space: A. For areas with ample space, bored piles were used to reinforce and isolate the soil between the left tunnel 101 and the right tunnel 102; during construction, the bored piles 10 were arranged in close rows (see...). Figure 1 C30 underwater concrete; plain piles 11 are used from the ground to 3m above the tunnel top, and reinforced concrete piles 12 are used from 3m above the tunnel top to 3m below the tunnel bottom or 1m below the rock surface (see...). Figure 2 The verticality of the pile body is controlled within 1 / 300, and the pile position deviation is ≤50mm. B. For confined spaces and sections where bored piles cannot be implemented, such as river channels or school areas, Φ168mm steel pipe piles are used to reinforce the soil between the left tunnel 101 and the right tunnel 102. Multiple Φ15mm grouting holes are arranged in a quincunx pattern on the pipe walls of the isolation steel pipe piles 20, with a grouting depth from 2m below ground level to 3m below the tunnel bottom (see...). Figure 3 During construction, steel pipe piles are driven using the casing drilling method. The steel pipe piles are drilled in sections, and each section of the steel pipe pile is connected by thread. After the steel pipe piles are driven, the pile body is grouted. The grouting pressure is gradually increased from 0.2MPa to 1.0MPa to reach the design diffusion radius. C. For sections with underground pipelines above the left and right tunnels, Φ89mm steel perforated pipes are used for grouting reinforcement and isolation of the soil between the left and right tunnels and the underground pipeline 200. The steel perforated pipes 30 have a small diameter, requiring less equipment, and can be driven obliquely into the soil. Φ15mm grouting holes are arranged in a quincunx pattern on the pipe wall of the steel perforated pipes 30. During construction, the steel perforated pipes 30 are driven symmetrically and obliquely to 3m below the bottom of the tunnel 100 within the protection zone of the underground pipeline 200, so that the steel perforated pipes 30 on both sides of the underground pipeline 200 intersect in the soil surrounding the tunnel 100 below the underground pipeline 200. The steel perforated pipes 30 closest to the underground pipeline 200 on both sides are at least 1m vertically away from the underground pipeline 200. The grouting depth is from 3m above the tunnel top to 3m below the tunnel bottom or 1m below the rock surface (see...). Figure 4During construction, steel pipes 30 are installed at a preset angle. After the steel pipes 30 are installed, grouting is carried out. The grouting sequence is from the outside to the inside, that is, from the steel pipes 30 that are far away from the underground pipeline 200 to the steel pipes 30 that are close to the underground pipeline 200. The grouting pressure is the borehole pressure plus the initial soil and water pressure + 0.3 to 0.5 MPa. The surface and building uplift are monitored in real time and dynamically adjusted. The grouting is completed when the pressure is gradually increased to the design final pressure and stabilized for 15 minutes. The estimated injection volume and the grout return situation of adjacent holes are also taken into account. S3. Preliminary tunnel excavation and grouting: When the shield tunneling passes through the isolation and reinforcement section, using the grouting holes pre-reserved on segment 10A and the additional grouting holes specifically for this isolation and reinforcement section, the grouting pipe is inserted into the soil outside the tunnel through the grouting holes on the segment to perform grouting reinforcement within a 2m radius around the outside of the tunnel (see...). Figure 5 Grouting is carried out symmetrically on both sides of the tunnel and skips ring grouting along the direction of shield excavation, that is, grouting is done once every other ring of segments to prevent pressure superposition from causing segment displacement. The segment grouting pipe includes an anti-blowout device, a Φ45mm sleeve valve steel pipe 43, and a grouting core pipe 44; wherein, the anti-blowout device includes a grouting sleeve 41, a check valve 40, a temporary steel sleeve 42, and multiple water-swellable rubber rings 420; the grouting sleeve 41 is installed in the pre-reserved grouting holes and additional grouting holes on the segment 10A, and the check valve 40 is installed inside the grouting sleeve 41 to prevent groundwater from entering the tunnel through the grouting sleeve 41; the front end of the temporary steel sleeve 42 is coaxially connected to a ring The annular steel plate 421 of the temporary steel casing 42 is coaxially fixed to the inner wall of the segment 10A by several expansion bolts 422, and a rubber gasket 423 is provided between the front end face of the annular steel plate 421 and the inner wall of the segment 10A; multiple water-swellable rubber rings 420 are spaced apart on the inner wall of the temporary steel casing 42 to prevent groundwater from entering the tunnel through the gap between the temporary steel casing 42 and the grouting core pipe 44 during the grouting process (see...). Figure 5a The grouting hole 430 on the sleeve valve steel pipe 43 is wrapped with a rubber sleeve 43A to ensure unidirectional grouting. The sleeve valve steel pipe 43 passes through the temporary steel sleeve 42 and the grouting sleeve 41 in sequence and is inserted into the soil outside the tunnel. The rubber sleeve 43A on the sleeve valve steel pipe 43 effectively prevents water from flowing into the temporary steel sleeve 42 (see...). Figure 5b The front part of the grouting core pipe 44 is connected to a section of grouting perforated pipe 45. Multiple grout discharge holes 450 are evenly distributed on the pipe wall of the grouting perforated pipe 45. Both ends of the grouting perforated pipe 45 are connected to the grouting core pipe 44 via rubber sleeve plugs 46. The grouting core pipe 44 is inserted into the temporary steel sleeve 42, the grouting sleeve 41, and the sleeve valve steel pipe 43, so that the grouting perforated pipe 45 is located inside the sleeve valve steel pipe 43. The rubber sleeve plugs 46 at both ends of the grouting perforated pipe 45 ensure that the grouting pressure acts on the rubber sleeve 43A on the sleeve valve steel pipe 43 (see...). Figure 5cUnder the action of grouting pressure, the grouting fluid is injected into the reinforced area by opening the rubber sleeve 43A through the grouting hole on the sleeve valve steel pipe 43. Sand or groundwater outside the sleeve valve steel pipe 43 cannot enter the grouting core pipe 44 through the grouting hole on the sleeve valve steel pipe 43, effectively preventing backflow. The rear end of the grouting core pipe 44 is connected to the grouting pump through the grouting hose. Before grouting, an impact drill is used to break the 10mm thick plain concrete in the grouting hole reserved on segment 10A. Then, a grouting sleeve 41 is installed in the grouting hole, and a temporary steel sleeve 42 is installed on the inner wall of segment 10A. A long drill rod is then used to drill through the synchronous grouting layer during the shield tunneling process. Then, a sleeve valve steel pipe 43 is inserted into the temporary steel sleeve 42 and the grouting sleeve 41. The sleeve valve steel pipe 43 is driven into the soil outside the tunnel using a sledgehammer. The sleeve valve steel pipe 43 is lowered in two stages, and the two sections of the sleeve valve steel pipe 43 are connected by threads. Then, the grouting flower pipe 45 on the grouting core pipe 44 is inserted into the sleeve valve steel pipe 43. Grouting begins with a single-component cement grout, consisting of tap water and ordinary Portland 42.5R cement. Initial setting time: 1-2 hours. Cement consumption per meter of reinforcement is not less than 200 kg. Grouting can only begin after the cement grout has been thoroughly mixed in a mixer, and the mixture must be continuously and slowly stirred during the grouting process for a time not less than the initial setting time of the grout. The grout should be filtered through a screen before pumping. During the grouting process, the grouting core tube 44 should be pulled out and moved upwards by 0.2 to 0.4 meters each time. The grouting core tube 44 can be moved by using a lifting device or by manually using two pipe wrenches to symmetrically clamp the grouting core tube 44 and apply force evenly from both sides at the same time. After every 2 to 3 meters of grouting length, a section of grouting core tube should be removed or added. After grouting is completed, pull out the grouting core tube 44, clean it and reuse it, retain the sleeve valve steel pipe 43, remove the temporary steel sleeve 42, and cover the end of the grouting sleeve 41 with a cap to facilitate re-grouting construction; after confirming that re-grouting is not necessary, inject high-strength cement grout or two-component grout into the grouting sleeve 41 to seal the grouting holes on the segment 10A, and cut off the grouting sleeve 41 that protrudes above the inner surface of the segment 100.

[0018] S4. Install the tunnel support trolley. For the initial tunnel section with a small clearance, after the grouting in the tunnel reaches the design strength, install the mobile support trolley 300 in the initial tunnel 103. The running rail of the support trolley 300 can share the same rail as the trolley rail of the tunnel boring machine. The distance L1 between the front of the support trolley 300 and the shield excavation face of the subsequent tunnel 104 is half the length L of the support trolley 300 (see...). Figure 6The support rollers of the support trolley 500 are pressed tightly against the inner wall of the pre-existing tunnel 103 segments, providing radial support force. The pressure of the support cylinder is 1.2 times the soil chamber pressure or grouting pressure. For each ring that the tunnel boring machine in the subsequent tunnel 104 excavates, the entire support trolley 300 moves forward one ring, always maintaining effective support for the pre-existing tunnel 103 until the tunnel boring machine in the subsequent tunnel 104 passes through the small clearance range.

[0019] S5. Subsequent Tunnel Excavation and Monitoring Feedback: During the excavation of the subsequent tunnel, the longitudinal distance between it and the preceding tunnel should not be less than 30m. During the excavation process, shield tunneling parameters must be strictly controlled, including inlet water pressure, thrust, excavation speed, cutterhead rotation speed, mud parameters, and synchronous grouting volume. Shield tunneling parameters should be fine-tuned in real time based on monitoring data from the preceding tunnel and 400mm of surface structures. Monitoring should include: crown settlement, crown uplift, tunnel convergence, building settlement, surface settlement or uplift, and underground pipeline settlement. When monitoring changes in 400mm of surface structures... When the deformation reaches 60% of the warning value, the pre-embedding work of the tracking grouting pipe 50 is initiated on the ground adjacent to the tunnel 100 on the side of the surface structure 400. The tracking grouting pipe 50 is made of steel perforated pipe and is installed at a 60° angle from the ground to the ground on the side of the surface structure 400 adjacent to the tunnel 100. When the deformation of the surface structure 400 reaches 80% of the warning value, the grouting work of the tracking grouting pipe 50 is initiated, so that the grout in the tracking grouting pipe 50 can fill the bottom soil of the foundation 401 of the structure on the side of the surface structure 400 adjacent to the tunnel 100 (see...). Figure 7 and Figure 8 ); S6. Support Removal and Subsequent Handling: After the tunnel boring machine in the subsequent tunnel has completely passed through the small clearance range and the monitoring data of the preceding tunnel has remained stable, the support force of the support trolley in the preceding tunnel is first removed in stages and symmetrically through the hydraulic system. Then, the components of the support trolley are removed in sections and batches. The entire process must be carried out under monitoring to achieve a smooth transition of the force system and ensure the long-term stability of the tunnel structure.

[0020] Taking the section between Fengxiang Road Station and Jianggao Station on the northern extension of Guangzhou Metro Line 8 as an example, this section's narrow-clearance tunnel passes under storm and sewage pipes, rivers, bridges, schools, and buildings, where karst development is strong. After adopting the construction method of this invention for tunneling important structures under narrow-clearance shield tunnels in karst areas: Project time efficiency: Traditional methods require 85 days to complete the reinforcement of small clearance sections, while this method only requires 67 days, improving efficiency by 21%.

[0021] Economic benefits: The cost of reinforcement per linear meter was reduced from 28,000 yuan using traditional methods to 21,000 yuan, a saving of 25%. The total cost savings for the entire 585m section is approximately 4.1 million yuan. The construction period was shortened, reducing the investment in personnel and equipment costs.

[0022] Safety benefits: During construction, the deformation and settlement of heavy rain, sewage pipes, and ground buildings were all less than the warning value, and the tunnel segments in the lead tunnel did not deform or crack, achieving a "zero accident" crossing.

[0023] Environmental benefits: The grouting material is pollution-free, and the steel pipe piles in the river section adopt the filter screen to prevent pollution, thus avoiding water pollution and meeting the requirements of green construction.

[0024] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A construction method for tunneling under important structures with a small clearance in a karst area using a shield tunnel, wherein the important structures include underground pipelines, waterways, existing bridges, buildings, and high-voltage power towers; characterized in that, The construction method includes the following steps: S1. Construction preparation and karst cave treatment: Before construction, conduct a detailed survey of underground pipelines, karst cave distribution and rock surface elevation, pre-grouting and filling treatment of the karst caves revealed by the survey, and determine the scope and form of isolation and reinforcement according to the design drawings; S2. Ground isolation and reinforcement construction is carried out, which is divided into the following three methods according to the geological conditions and ground space: A. For areas with wide open spaces, bored piles are used to reinforce and isolate the soil between the left and right tunnels. During construction, closely spaced bored piles are used. Plain piles are used from the ground to 3m above the top of the tunnel, and reinforced concrete piles are used from 3m above the top of the tunnel to 3m below the bottom of the tunnel or 1m below the rock surface. B. For sections with confined spaces and where bored piles cannot be installed, the soil between the left and right tunnels is reinforced and isolated using steel pipe piles with grouting. Multiple grouting holes are arranged in a quincunx pattern on the pipe wall of the steel pipe piles, with a grouting depth from 2m below ground level to 3m below the tunnel bottom. During construction, steel pipe piles are driven using a pipe-following drilling method, with the steel pipe piles drilled in sections and connected by threaded connections between sections. After the steel pipe piles are driven, grouting is performed on the pile body, with the grouting pressure gradually increasing from 0.2MPa to 1.0MPa to reach the designed diffusion radius. C. For sections with underground pipelines above the left and right tunnels, grouting reinforcement and isolation of the soil between the left and right tunnels and the underground pipelines is carried out using steel pipes. Grouting holes are arranged in a quincunx pattern on the pipe walls. During construction, the pipes are driven obliquely from the ground to 3m below the bottom of the tunnel, avoiding the underground pipelines. The grouting depth is from 3m above the top of the tunnel to 3m below the bottom of the tunnel or 1m below the rock surface. During construction, the steel pipes are driven obliquely at a preset angle. After the steel pipes are driven, grouting is carried out. The grouting sequence is from the outside to the inside. The grouting pressure is the initial soil and water pressure +0.3 to 0.5 MPa at the borehole opening. The surface and building uplift are monitored in real time for dynamic adjustment. The grouting is completed when the pressure is gradually increased to the design final pressure and stabilized for 15 minutes. The estimated injection volume and the grout return situation of adjacent holes are also considered for comprehensive judgment. S3. Pre-tunnel excavation and in-tunnel grouting: When the shield tunneling passes through the isolation and reinforcement section, the grouting pipe is inserted into the soil outside the tunnel through the grouting holes on the segments and the additional grouting holes for the isolation and reinforcement section. Grouting is carried out symmetrically on both sides of the tunnel and skip-ring grouting is performed along the direction of shield tunneling. S4. Install a support trolley inside the tunnel. For the initial tunnel section with a small clearance, after the grouting inside the tunnel reaches the design strength, install a mobile support trolley inside the initial tunnel. The distance between the front of the support trolley and the shield excavation face of the subsequent tunnel is half the length of the support trolley. Control the support rollers of the support trolley to be in close contact with the inner wall of the assembled segments of the initial tunnel to provide radial support force. For each ring that the shield machine in the subsequent tunnel excavates, the entire support trolley moves forward one ring, always maintaining effective support for the initial tunnel until the shield machine in the subsequent tunnel passes through the small clearance range. S5. Subsequent Tunnel Excavation and Monitoring Feedback: During the excavation of the subsequent tunnel, the longitudinal distance between it and the preceding tunnel shall not be less than 30m; the shield parameters shall be strictly controlled during the excavation process, including the cutting water pressure, thrust, excavation speed, cutterhead rotation speed, mud parameters, and synchronous grouting volume, and the shield parameters shall be finely adjusted in real time based on the monitoring data of the preceding tunnel and the monitoring data of surface structures; when the deformation of the monitored surface structures reaches 60% of the warning value, the pre-embedding work of the tracking grouting pipe shall be initiated on the ground adjacent to the tunnel; when the deformation of the monitored surface structures reaches 80% of the warning value, the grouting work of the tracking grouting pipe shall be initiated. S6. Support Removal and Subsequent Handling: After the tunnel boring machine in the subsequent tunnel has completely passed through the small clearance range and the monitoring data of the preceding tunnel has remained stable, the support force of the support trolley in the preceding tunnel is removed in stages and symmetrically through the hydraulic system. Then the components of the support trolley are removed. The entire process must be carried out under monitoring to achieve a smooth transition of the force system.

2. The construction method for tunneling important structures with a small clearance in a karst area using a shield tunnel, as described in claim 1, is characterized in that... When performing step S2 in method C, the ground reinforcement steel pipes are installed symmetrically and obliquely on both sides of the underground pipeline within the protection range of the underground pipeline, so that the ground reinforcement steel pipes on both sides of the underground pipeline intersect in the soil around the tunnel below the underground pipeline, and the ground reinforcement steel pipes closest to both sides of the underground pipeline are at least 1m away from the underground pipeline in vertical distance.

3. The construction method for tunneling important structures with a small clearance in a karst area using a shield tunnel, as described in claim 1, is characterized in that... When performing step S3, the segment grouting pipe includes an anti-blowout device, a sleeve valve steel pipe, and a grouting core pipe; wherein, the anti-blowout device includes a grouting sleeve, a check valve, a temporary steel sleeve, and multiple water-swellable rubber rings; the grouting sleeve is installed in the pre-reserved grouting holes and additional grouting holes on the segment; the check valve is installed inside the grouting sleeve; the front end of the temporary steel sleeve is coaxially connected to an annular steel plate, and the annular steel plate of the temporary steel sleeve is coaxially fixed to the inner wall surface of the segment with the grouting hole by several expansion bolts, and a rubber gasket is provided between the front end face of the annular steel plate and the inner wall surface of the segment; multiple water-swellable rubber rings... Rubber rings are spaced apart on the inner wall of the temporary steel casing; the grouting holes on the sleeve valve steel pipe are wrapped with rubber sleeves, and the sleeve valve steel pipe passes through the temporary steel casing and the grouting casing in sequence and is inserted into the soil outside the tunnel; a section of grouting perforated pipe is connected to the front of the grouting core pipe, and both ends of the grouting perforated pipe are connected to the grouting core pipe through rubber sleeve plugs. Multiple grout discharge holes are evenly distributed on the pipe wall of the grouting perforated pipe; the grouting core pipe is inserted into the temporary steel casing, the grouting casing and the sleeve valve steel pipe, so that the grouting perforated pipe is located inside the sleeve valve steel pipe, and the rear end of the grouting core pipe is connected to the grouting pump through a grouting hose; Before grouting, an impact drill is used to break the plain concrete in the grouting holes reserved on the tunnel segments. Then, the grouting sleeve and temporary steel sleeve are installed in the grouting holes. Then, a long drill rod drill is used to break through the synchronous grouting layer during the tunnel boring process. Then, the sleeve valve steel pipe is inserted into the temporary steel sleeve and grouting sleeve and hammered into the soil outside the tunnel. Then, the grouting core pipe is inserted into the sleeve valve steel pipe. Grouting begins with a single-component cement grout made of tap water and ordinary Portland cement. Initial setting time: 1-2 hours. The cement grout must be thoroughly mixed in a mixer before grouting can begin. During the grouting process, the grout must be continuously and slowly stirred for a time not less than the initial setting time. The grout should be filtered through a screen before pumping. During the grouting process, the grouting core tube should be pulled out and moved upwards by 0.2 to 0.4 meters each time. The grouting core tube can be moved by lifting equipment or manually by using two pipe wrenches to symmetrically clamp the grouting core tube and apply force evenly on both sides at the same time to pull the grouting core tube to move. After grouting is completed, first pull out the grouting core tube, clean it and reuse it, retain the sleeve valve steel pipe, remove the temporary steel sleeve, then inject high-strength cement grout or two-component grout into the grouting sleeve to seal the grouting holes on the segment, and cut off the grouting sleeve that protrudes above the inner surface of the segment.

4. The construction method for tunneling important structures with a small clearance in a karst area using a shield tunnel, as described in claim 1, is characterized in that... When performing step S5, the tracking grouting pipe is a steel pipe, and it is installed obliquely into the ground on the side of the ground structure that is close to the tunnel, so that the grout in the tracking grouting pipe can fill the bottom soil of the foundation of the ground structure that is close to the tunnel.

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