Construction method of soft soil tunnel station exit structure

Abstract

The present application belongs to the technical field of rail transit underground engineering, and particularly relates to a construction method of a structure of a station entrance in soft soil after a tunnel is built. The construction method of the structure of the station entrance in soft soil after the tunnel is built provided by the present application implements ground reinforcement simultaneously in advance through tunneling by a shield machine, ground reinforcement of the station entrance itself and reinforcement of the tunnel itself, so as to meet the bearing capacity requirement of the ground of the station entrance and the tunnel, and to protect the tunnel, thereby solving the problem of non-matching construction periods of the station entrance and the tunnel and the problem of protection of the shield tunnel by excavation of a foundation pit in close proximity to the shield tunnel.

Description

Technical Field

[0001] This invention belongs to the field of underground engineering technology for rail transit, and particularly relates to a construction method for tunneling followed by station entrance / exit structures in soft soil. Background Technology

[0002] As urban rail transit networks continue to expand and develop, underground space is constantly being developed and utilized, and the available underground space is being compressed. Rail transit projects exhibit various intertwined spatial relationships, and subsequent construction projects will inevitably have a certain impact on existing projects.

[0003] The conventional construction sequence for subway rail transit projects is to first complete the main station structure, then have the tunnel boring machine (TBM) arrive at the station receiving end for reception, and finally construct the station's ancillary entrance and exit structures. The station entrances and exits are usually not intersected with the tunnel plan, and their construction does not interfere with each other. However, due to limitations such as station location and surrounding environmental conditions, the station entrances and exits may intersect with the tunnel in space. A typical example is when a station entrance or exit is located directly above the tunnel. Due to the construction schedule of the station entrances and exits, the TBM cannot wait until all entrances and exits are completed before tunneling under them, thus preventing the TBM from being received from the station according to the original construction schedule. Based on the spatial relationship between the standard two-story station, entrances / exits, and tunnel, it can be determined that the vertical distance between the station entrance / exit floor slab and the tunnel is very small. In this case, to ensure the project schedule, the tunnel must be completed first, and then the station entrances / exits above it must be constructed. The excavation of the foundation pit for the station entrances / exits, which was built later, caused stress release due to the unloading of earthwork. The tunnel segments of the completed tunnel were deformed due to insufficient overburden, which aggravated problems such as tunnel uplift, segment misalignment, and elliptic deformation. In severe cases, it could lead to major dangers such as tunnel cracking and water leakage. Excavation work is carried out at extremely close range above shield tunnels, which requires strict control over the deformation of the shield tunnel structure. Before the excavation of the upper entrance and exit pits, anti-buoyancy anchors are mostly installed on the inside and outside of the tunnel to solve the problem of tunnel buoyancy. Then, strong reinforcement measures such as ground mixing piles and MJS jet grouting piles are adopted on both sides and the upper part of the tunnel to form a portal structure to isolate and protect the tunnel. Alternatively, bored piles are constructed on both sides of the tunnel, and a capping beam is set on the top of the bored piles to connect them into a whole. Rigid components such as steel pipes or anti-buoyancy pressure plates are set above the tunnel and connected to the capping beam.

[0004] Both of the above conventional methods utilize ground reinforcement measures to form a protective body for the tunnel structure, and their isolation effect is relatively significant and effective, reducing the disturbance to the tunnel to a certain extent during the excavation process. However, these two methods have the following problems: 1. The construction of mixing piles and bored piles has a significant impact on the shield tunnel, especially when constructing in close proximity to soft strata. Because soft soil is easily disturbed, the horizontal compression effect of the reinforcement construction on the shield tunnel is more obvious, increasing the lateral deformation and ellipticity of the shield tunnel. 2. In deep soft soil, the length of the anti-buoyancy anchors inside the tunnel is limited and cannot reach the bearing layer, resulting in poor anti-buoyancy effect. Similarly, the side friction resistance provided by the bored piles constructed on both sides of the tunnel is small, which is not conducive to the anti-buoyancy of the shield tunnel. 3. The excavation of the foundation pit above the shield tunnel and the construction of the retaining structure will also affect the shield tunnel. In addition, the depth of the retaining structure perpendicular to the shield tunnel direction must ensure a safe distance. If the soft soil is relatively deep, the bottom elevation of the retaining structure in this direction can only reach the top of the tunnel. Insufficient embedment depth will lead to risks such as instability of the foundation pit excavation. Summary of the Invention

[0005] In order to overcome the above-mentioned technical problems, the purpose of this invention is to provide a construction method for tunneling followed by station entrance / exit structures in soft soil.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows:

[0007] A construction method for tunneling followed by station entrance / exit structures in soft soil includes the following steps:

[0008] S1. Before the tunnel boring machine arrives, the station entrance and exit base reinforcement is carried out simultaneously with the tunnel boring machine reinforcement. The reinforcement method is to use a three-axis mixing pile machine for reinforcement construction.

[0009] S2. After the construction of the three-axis mixing piles is completed, the construction of the underground continuous wall at the station entrance within the shield tunnel area shall be completed before the shield machine arrives, forming a closed continuous wall. The shield machine can only start tunneling after the underground continuous wall reaches the preset strength.

[0010] After the construction of the diaphragm wall at the station entrance within the shield tunnel area is completed, the shield machine passes through the diaphragm wall and the three-axis mixing pile along the shield direction, tightens the segment bolts, and after excavating one ring, immediately cleans up the debris at the shield tail and repeats this process until the construction of the shield tunnel breakthrough node is completed. Then, the construction of the remaining diaphragm wall at the station entrance is carried out. 20mm steel rings and longitudinal channel steel are installed inside the shield tunnel, and a ring-shaped temporary support is installed every other ring.

[0011] S4. After the shield tunnel is completed, the excavation of the station entrance and exit foundation pit and the construction of the main structure will be carried out above the shield tunnel. Before the excavation of the station entrance and exit foundation pit, dewatering wells will be set in the foundation pit, and the large-diameter wellpoint dewatering method will be used. Water level observation wells will be set outside the station entrance and exit foundation pit, and the depth of the water level observation wells will not be less than the excavation depth of the foundation pit. During the excavation of the station entrance and exit foundation pit, the shield tunnel will be automatically monitored, and the ballast weight of the sandbags in the shield tunnel will be adjusted according to the real-time data and the excavation depth of the station entrance and exit foundation pit to meet the temporary anti-buoyancy requirements of the shield tunnel. Before the excavation of the station entrance and exit foundation pit, the capping beam will be constructed first. After the capping beam is completed, the station entrance and exit foundation pit will be excavated. After the station entrance and exit foundation pit is excavated to the bottom elevation of the concrete support, the concrete support will be poured. After the concrete support is completed and reaches the preset strength, the lower layer of earthwork will be excavated, and the main structure bottom slab will be constructed quickly. Then the side walls and the main structure top slab will be constructed.

[0012] S5. After the main structure of the station entrance and exit is completed and the monitoring data in the shield tunnel is stable, remove the dewatering wells and complete the backfilling construction on the top slab; after the strength of the main structure of the station entrance and exit reaches the preset requirements and the monitoring data in the shield tunnel is stable, remove the sandbags, ring temporary supports and longitudinal channel steel ties in the shield tunnel; finally, construct the shield tunnel track bed structure.

[0013] The construction method for tunneling before station entrances / exits in soft soil provided by this invention combines pre-tunneling reinforcement of the subway station entrance / exit foundation with tunnel reinforcement. Both are implemented simultaneously to meet the bearing capacity requirements of the entrance / exit and tunnel foundations, while also providing isolation and protection for the tunnel. The diaphragm wall retaining structure of the station entrance / exit ensures the stability of the excavation pit in deep soft soil. Furthermore, as a closed system, the diaphragm wall effectively isolates external water sources, reducing the impact of significant dewatering on the surrounding environment when dewatering of the station entrance / exit pit is substantial. Large-diameter wellpoint dewatering is employed, gradually lowering the groundwater level through information-based construction to ensure construction safety. However, excessive dewatering within the station entrance / exit pit could cause changes in groundwater levels outside the pit, leading to ground subsidence. Therefore, water level monitoring wells are installed outside the station entrance / exit pit to guide subsequent construction and implement appropriate measures. In this invention, the excavation of the station entrance and exit pit adopts the principles of "zoning, layering, segmentation, symmetry, balance, and time limit" and "support before excavation", which effectively reduces the deformation of the underground continuous wall. At the same time, the station entrance and exit structure can provide permanent anti-buoyancy conditions for the shield tunnel.

[0014] As a preferred embodiment of the present invention, a row of longitudinal three-axis mixing pile solid long piles is arranged on both sides of the waist of the shield tunnel and at the center of the tunnel. A row of longitudinal three-axis mixing pile solid long piles is arranged 2.4m outside the edge line of the shield tunnel structure on both sides to reduce the disturbance of external operations to the shield tunnel. Along the longitudinal direction of the shield tunnel and outside the station entrance and exit area, four rows of transverse three-axis mixing pile solid short piles spaced 1.5m apart are arranged and interlocked with the longitudinal three-axis mixing pile solid long piles. Within the station entrance and exit area, four rows of transverse three-axis mixing pile solid short piles are closely arranged along the longitudinal direction of the shield tunnel and interlocked with the longitudinal three-axis mixing pile solid long piles. This structure can keep the shield tunnel in a dry and closed mixing pile solidified body. The top of the shield tunnel to the ground is a three-axis mixing pile empty pile.

[0015] As a further preferred embodiment of the present invention, the reinforcement depth of the long solid piles of the triaxial mixing piles arranged longitudinally along the shield tunnel is from 3m above the shield tunnel to below the bottom of the shield tunnel, penetrating the weak soil layer to the bearing layer; the reinforcement depth of the short solid piles of the triaxial mixing piles is from 3m above the shield tunnel to 3m below the bottom of the shield tunnel; and the reinforcement depth of the empty piles of the triaxial mixing piles is from 3m above the shield tunnel to the ground.

[0016] As a further preferred embodiment of the present invention, the cement content of the empty pile of the triaxial mixing pile is 8%, and the cement content of the solid pile of the triaxial mixing pile is 22%.

[0017] As a preferred embodiment of the present invention, the diameter of the triaxial mixing pile is φ850@600, and the unconfined compressive strength of the long and short solid piles of the triaxial mixing pile is not less than 0.8MPa.

[0018] This invention adopts a method of simultaneously reinforcing the station entrance and exit foundation with the shield tunnel itself, which effectively solves the problems of the shield tunnel's own bearing capacity and the stress on the passive zone of the station entrance and exit foundation. At the same time, it helps to reduce the disturbance to the shield tunnel during the excavation of the entrance and exit soil, enhances the constraint on the shield tunnel's surroundings, and puts the shield tunnel in a sealed and water-proof environment, reducing the impact of groundwater flow on the shield tunnel.

[0019] As a preferred embodiment of the present invention, the diaphragm walls are connected by I-beams to ensure the water-stopping effect of the diaphragm walls; the diaphragm walls that conflict with the plane of the shield tunnel are arranged at an angle perpendicular to the tunneling direction of the shield machine. This process is conducive to the shield machine's cutterhead cutting the diaphragm walls in the forward direction, preventing uneven stress on the cutterhead. The interface position of the diaphragm walls within the shield tunnel range must avoid the shield machine's crossing range. The width of the diaphragm wall is 7.2m, and glass fiber reinforcement is reserved for the diaphragm walls within the shield tunnel crossing range.

[0020] As a further preferred embodiment of the present invention, the glass fiber reinforcement is installed 0.5m outward from the perimeter of the shield tunnel.

[0021] As a preferred embodiment of the present invention, the segment bolts are tightened in three stages: first during assembly, second after assembly (the next stage of tunneling cannot proceed without re-tightening), and third after the segment detaches from the shield tail.

[0022] As a preferred embodiment of the present invention, 22a double-I-beam longitudinal beams are provided on both sides of the shield tunnel, and the 22a double-I-beam longitudinal beams are welded and fixed to steel rings; the ring-shaped temporary support extends two rings in both directions from the shield tunnel area overlapping with the station entrance and exit pit; the ring-shaped temporary support uses 25C channel steel as the skeleton, with the transverse 25C channel steel tightly connected to the 22a double-I-beam longitudinal beams, and the longitudinal 25C channel steel tightly connected to the tunnel segments through wedges, ensuring the overall stability of the support system. This structure strengthens the integrity of the formed shield tunnel segments and avoids segment misalignment and cracking caused by uneven settlement during construction in the upper ultra-close distance pit.

[0023] As a preferred embodiment of the present invention, the longitudinal channel steel tie-up range covers 10 rings of tunnel segments before and after the shield tunnel passes through the station entrance / exit pit, with each ring reinforced after assembly. The longitudinal channel steel tie-up uses eight No. 10 channel steels for tying, and the No. 10 channel steels are welded and fixed to the steel lugs welded in the segment bolts, and welded to the steel rings to form a continuous steel component. This structure can increase the number of statically indeterminate constraints in the longitudinal and circumferential directions of the shield tunnel, ensuring the integrity of the shield tunnel during pit excavation.

[0024] As a further preferred embodiment of the present invention, the stacking of bagged sandbags inside the shield tunnel should avoid the monitoring point at the bottom of the shield tunnel and the temporary circumferential support position. The minimum ballast weight of the bagged sandbags is 15t / m and the maximum is 22.5t / m.

[0025] As a preferred embodiment of the present invention, the dewatering well is set to 250m. 2 / each, with a plane spacing of 10-20m, and a water depth of no less than 1m below the tunnel bottom, in order to reduce the impact of groundwater on the shield tunnel and meet the shield tunnel's own anti-buoyancy requirements.

[0026] Compared with existing technologies, the construction method of tunneling followed by station entrance / exit structure in soft soil provided by this invention has the following technical advantages:

[0027] This invention solves the problem of mismatch between the construction schedule of subway station entrances and exits and tunnels, as well as the protection of shield tunnels caused by extremely close-range excavation of foundation pits above them. In situations where the tunnel boring machine (TBM) has already started operation, but external projects cannot complete the main structure construction according to the original schedule due to other factors, and the TBM cannot be shut down unconditionally or provided with receiving conditions, the TBM is completed first, followed by construction of the station entrances and exits. Pre-reinforcement and process auxiliary measures ensure the safety of the foundation pit excavation process and reduce the impact on the shield tunnel.

[0028] Instruction manual illustrations

[0029] Figure 1 Cross-sectional view of the shield tunnel spanning the station entrance / exit;

[0030] Figure 2 Plan layout of shield tunnel reinforcement;

[0031] Figure 3 Cross-sectional layout diagram of shield tunnel reinforcement;

[0032] Figure 4 Diagram of circumferential support layout inside a shield tunnel;

[0033] Figure 5 Plan view of longitudinal channel steel tie-down structure inside a shield tunnel;

[0034] Figure 6 Cross-sectional layout of longitudinal channel steel tie-down structure inside a shield tunnel;

[0035] In the diagram: 1. Triaxial mixing pile; 1-1 Triaxial mixing pile solid long pile; 1-2 Triaxial mixing pile solid short pile; 1-3 Triaxial mixing pile solid short pile; 1-4 Triaxial mixing pile empty pile; 2. Diaphragm wall; 3. Fiberglass reinforcement; 4. Shield tunnel; 5. Dewatering well; 5-1 Water level observation well; 6. Crown beam; 7. Concrete support; 8-1 Main structure top slab; 8-2 Main structure bottom slab; 9. 20mm steel ring; 10. 22a double I-beam longitudinal beam; 11. Wedge block; 12. 25C channel steel; 13. Sandbag; 14. Segment bolt; 15. Rigid lug plate; 16. Welding; 17. 10# channel steel. Detailed Implementation

[0036] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings and examples. The following examples are used to illustrate the present invention, but are not intended to limit the scope of the invention. In the description of the present invention, it should be understood that the terms "upper," "lower," "left," "right," "top," "bottom," etc., indicating orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention. It should be understood that the terms "first," "second," etc., are used in the present invention to describe various information, but this information should not be limited to these terms; these terms are only used to distinguish information of the same type from each other. For example, without departing from the scope of the present invention, "first" information can also be referred to as "second" information, and similarly, "second" information can also be referred to as "first" information.

[0037] A preferred embodiment of the present invention provides a construction method for a tunnel-first, station entrance / exit structure in soft soil, comprising the following steps:

[0038] S1. Before the tunnel boring machine arrives, triple-axis mixing piles with a diameter of φ850@600 are used to simultaneously reinforce the station entrance and the tunnel; such as Figure 2 As shown, a row of longitudinal three-axis mixing piles 1-1 is arranged on both sides of the waist of shield tunnel 4 and at the center of the tunnel. In addition, a row of longitudinal three-axis mixing piles 1-1 is arranged 2.4m outside the structural edge of shield tunnel 4 for isolation to reduce the disturbance of external operations to shield tunnel. Along the longitudinal direction of shield tunnel 4 and outside the station entrance area, four rows of transverse three-axis mixing piles 1-3 are arranged at 1.5m intervals and interlock with the longitudinal three-axis mixing piles 1-1 (grid reinforcement). Within the station entrance area, four rows of transverse three-axis mixing piles 1-3 are densely arranged along the longitudinal direction of shield tunnel 4. -2 and the longitudinal triaxial mixing pile solid pile long pile 1-1 (full-area reinforcement) interlock with each other, and the triaxial mixing piles 1 interlock and overlap with each other. The top of the shield tunnel 4 to the ground is the triaxial mixing pile hollow pile 1-4. This structure allows the shield tunnel to be in a dry and closed mixing pile reinforced body. According to the bearing capacity requirements of the shield tunnel 4, the cement content of the triaxial mixing pile 1 is 8% and 22% respectively, corresponding to the triaxial mixing pile hollow pile 1-4 and the triaxial mixing pile solid piles 1-1, 1-2, and 1-3 respectively. It is required that the unconfined compressive strength of the triaxial mixing pile solid long pile and the triaxial mixing pile solid short pile is not less than 0.8MPa. Figure 3 As shown, the reinforcement depth of the long solid pile 1-1 of the three-axis mixing pile arranged longitudinally along the shield tunnel 4 is from 3m above the top of the shield tunnel 4 to below the bottom of the shield tunnel 4, penetrating the weak soil layer to the bearing layer; the reinforcement depth of the short solid piles 1-2 and 1-3 of the three-axis mixing pile is from 3m above the top of the shield tunnel 4 to 3m below the bottom of the shield tunnel 4; and the reinforcement depth of the empty pile 1-4 of the three-axis mixing pile is from 3m above the top of the shield tunnel 4 to the ground surface.

[0039] S2. To ensure the stability of the station entrance / exit foundation pit excavation in deep soft soil, the station entrance / exit retaining structure adopts a diaphragm wall 2; after the completion of the triaxial mixing pile 1, the diaphragm wall 2 of the station entrance / exit within the shield tunnel 4 area is quickly completed using time and space before the arrival of the tunnel boring machine, forming a closed diaphragm wall, such as... Figure 2 As shown, to ensure the water-stopping effect, I-beams are used to connect the diaphragm walls 2. The diaphragm walls 2 that conflict with the plane of the shield tunnel 4 are arranged at an angle perpendicular to the tunneling direction of the shield machine. This is beneficial for the shield machine's cutterhead to cut the diaphragm wall in the forward direction, preventing uneven stress on the cutterhead. The interface of this section of diaphragm wall 2 must avoid the shield machine's crossing range. The width of the diaphragm wall 2 is 7.2m. Fiberglass reinforcement bars 3 are pre-installed in the diaphragm wall 2 within the crossing range of the shield tunnel 4, with the installation range extending 0.5m outward from the perimeter of the shield tunnel 4. The shield machine can only proceed with the excavation after the diaphragm wall reaches the strength standard.

[0040] After the construction of the underground continuous wall 2 at the station entrance within the scope of S3 and shield tunnel 4 is completed, the shield machine will first pass through the underground continuous wall 2 and then through the three-axis mixing pile 1. During the passage, the machine will advance according to the principle of "slow speed advance and uniform speed rotation". The parameters such as the pressure, attitude, speed, grouting volume and construction accuracy of the shield machine's soil chamber will be controlled. The segment bolts 14 will be tightened. After excavating one ring, the foam, slurry, water and other debris at the shield tail will be cleaned up immediately. This process will be repeated until the shield tunnel breakthrough node is completed. Then, the remaining part of the underground continuous wall at the station entrance will be constructed. The segment bolts will be tightened in three stages: first, during assembly; second, after assembly (the next ring cannot be excavated if the bolts are not tightened again); and third, after the segment separates from the shield tail.

[0041] To enhance the integrity of the fourth segment of the shield tunnel and prevent uneven settlement during construction of the upper, closely spaced station entrance pit, which could lead to segment misalignment and cracking, a ring-shaped temporary support was arranged along the longitudinal direction of the fourth shield tunnel. For example... Figure 4 As shown, a 20mm steel ring 9 is installed inside the shield tunnel, and 22a double I-beam longitudinal beams 10 are installed on both sides. The 22a double I-beam longitudinal beams 10 are welded and fixed to the steel ring 9. The annular temporary support uses 25C channel steel 12 as the skeleton. The transverse 25C channel steel 12 is tightly connected to the 22a double I-beam longitudinal beams 10, and the longitudinal 25C channel steel 12 is tightly connected to the tunnel segment through wedges 11 to ensure the overall stability of the support system. The scope of the annular temporary support is the shield tunnel 4 that overlaps with the station entrance and exit pit and extends to both ends by 2 rings. One annular temporary support is installed every other ring.

[0042] Meanwhile, the shield tunnel No. 4, which passes under the station entrance and exit, uses longitudinal channel steel to connect the 10 rings of tunnel segments before and after it. Figure 5 As shown, each assembled ring is reinforced with another ring; the longitudinal channel steel tie points are located at the eighth point along section 4 of the shield tunnel, that is, eight No. 10 channel steels 17 are used for tie. The No. 10 channel steels are welded and fixed to the steel ear plates 15 welded in the segment bolts 14, and welded to the steel rings 9 to form a continuous steel component to enhance the longitudinal and circumferential static indeterminate constraints of the shield tunnel, ensuring the integrity of the shield tunnel during the excavation of the foundation pit.

[0043] After the completion of shield tunnel 4 (S4), the excavation of the station entrance / exit pit and the construction of the main structure will proceed above shield tunnel 4. The pit excavation will follow the principles of "zoning, layering, segmentation, symmetry, balance, and time-limited" and "support before excavation." Figure 1 As shown, before excavation of the station entrance / exit foundation pit, dewatering well 5 is installed inside the pit to carry out dewatering operations to meet the excavation work surface requirements of the station entrance / exit. According to calculation and analysis, dewatering well 5 is set to 250m. 2 / each, with a plane spacing of 10-20m, and a dewatering depth of no less than 1m below the tunnel bottom, to reduce the impact of groundwater on the shield tunnel and meet the shield tunnel's own anti-buoyancy requirements; large-diameter wellpoint dewatering method is adopted for construction, and the groundwater level is gradually and slowly lowered through information-based construction to ensure construction safety; since dewatering in the station entrance and exit foundation pit will cause changes in the groundwater outside the pit, resulting in ground subsidence outside the pit, water level observation well 5-1 is set outside the station entrance and exit foundation pit, and the depth of water level observation well 5-1 is no less than the excavation depth of the foundation pit;

[0044] During the excavation of the station entrance and exit foundation pit, automated monitoring was implemented for shield tunnel 4. Sandbags (13) were used inside shield tunnel 4 for counterweight and buoyancy resistance. The ballast weight of the sandbags (13) inside shield tunnel 4 was gradually adjusted based on real-time data and the excavation depth of the station entrance and exit foundation pit. Figure 4 As shown, this is to ensure that the temporary anti-buoyancy requirements of the shield tunnel are met; the stacking of sandbags 13 inside the shield tunnel 4 must avoid the monitoring point at the bottom of the shield tunnel and the temporary circumferential support position. The minimum ballast weight of the sandbags 13 is 15t / m and the maximum is 22.5t / m.

[0045] like Figure 1 As shown, before the excavation of the foundation pit of the retaining structure, the main structure capping beam 6 is constructed first. After the capping beam 6 is completed, the concrete support 7 is poured in time after the excavation reaches the bottom elevation of the concrete support 7 to reduce the deformation of the underground continuous wall 2. After the concrete support 7 is completed and reaches the required strength, the lower layer of earthwork is excavated, the main structure bottom slab 8-2 is constructed quickly, and then the side walls and the main structure top slab 8-1 are constructed and covered with soil to the ground.

[0046] S5. After the main structure of the station entrance and exit is completed and the monitoring data inside the shield tunnel 4 is stable, remove the dewatering well 5 and complete the backfilling construction on the top slab to provide permanent anti-buoyancy conditions for the shield tunnel 4. After the main structure of the station entrance and exit reaches the required strength and the monitoring data inside the shield tunnel 4 is stable, remove the bagged sandbags 13, the ring temporary support and the longitudinal channel steel tie in the shield tunnel 4. Finally, construct the shield tunnel track bed structure.

[0047] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and substitutions can be made without departing from the technical principles of the present invention, and these improvements and substitutions should also be considered within the scope of protection of the present invention.

Claims

1. A construction method for tunneling followed by station entrance / exit structures in soft soil, characterized in that, Includes the following steps: S1. Before the tunnel boring machine arrives, the station entrance and exit base reinforcement is carried out simultaneously with the tunnel boring machine reinforcement. The reinforcement method is to use a three-axis mixing pile machine for reinforcement construction. S2. After the construction of the three-axis mixing piles is completed, the construction of the underground continuous wall at the station entrance within the shield tunnel area shall be completed before the shield machine arrives, forming a closed continuous wall. The shield machine can only start tunneling after the underground continuous wall reaches the preset strength. After the construction of the diaphragm wall at the station entrance within the shield tunnel area is completed, the shield machine passes through the diaphragm wall and the three-axis mixing pile along the shield direction, tightens the segment bolts, and after excavating one ring, immediately cleans up the debris at the shield tail and repeats this process until the construction of the shield tunnel breakthrough node is completed. Then, the construction of the remaining diaphragm wall at the station entrance is carried out. Steel rings and longitudinal channel steel are installed inside the shield tunnel, and a ring-shaped temporary support is installed every other ring. S4. After the shield tunnel is completed, the excavation of the station entrance and exit foundation pit and the construction of the main structure will be carried out above the shield tunnel. Before the excavation of the station entrance and exit foundation pit, dewatering wells will be set in the foundation pit, and the large-diameter wellpoint dewatering method will be used. Water level observation wells will be set outside the station entrance and exit foundation pit, and the depth of the water level observation wells will not be less than the excavation depth of the foundation pit. During the excavation of the station entrance and exit foundation pit, the shield tunnel will be automatically monitored, and the ballast weight of the sandbags in the shield tunnel will be adjusted according to the real-time data and the excavation depth of the station entrance and exit foundation pit to meet the temporary anti-buoyancy requirements of the shield tunnel. Before the excavation of the station entrance and exit foundation pit, the capping beam will be constructed first. After the capping beam is completed, the station entrance and exit foundation pit will be excavated. After the station entrance and exit foundation pit is excavated to the bottom elevation of the concrete support, the concrete support will be poured. After the concrete support is completed and reaches the preset strength, the lower layer of earthwork will be excavated, and the main structure bottom slab will be constructed quickly. Then the side walls and the main structure top slab will be constructed, and the soil will be covered to the ground. S5. After the main structure of the station entrance and exit is completed and the monitoring data in the shield tunnel is stable, remove the dewatering wells and complete the backfilling construction on the top slab; after the strength of the main structure of the station entrance and exit reaches the preset requirements and the monitoring data in the shield tunnel is stable, remove the sandbags, ring temporary supports and longitudinal channel steel ties in the shield tunnel; finally, construct the shield tunnel track bed structure.

2. The construction method for tunneling followed by station entrance / exit structures in soft soil according to claim 1, characterized in that, A row of longitudinal three-axis mixing piles is arranged on both sides of the shield tunnel waist and in the center of the tunnel. A row of longitudinal three-axis mixing piles is arranged 2.4m outside the edge of the shield tunnel structure. Along the longitudinal direction of the shield tunnel and outside the station entrance area, four rows of transverse three-axis mixing piles with a spacing of 1.5m are arranged and interlocked with the longitudinal three-axis mixing piles. Within the station entrance area, four rows of transverse three-axis mixing piles with short piles are arranged closely along the longitudinal direction of the shield tunnel and interlocked with the longitudinal three-axis mixing piles. The top of the shield tunnel to the ground is an empty pile of three-axis mixing piles.

3. The construction method for tunneling followed by station entrance / exit structures in soft soil according to claim 2, characterized in that, The reinforcement depth of the long solid piles of the triaxial mixing piles arranged longitudinally along the shield tunnel is from 3m above the shield tunnel top to below the shield tunnel bottom, penetrating the weak soil layer to the bearing layer; the reinforcement depth of the short solid piles of the triaxial mixing piles is from 3m above the shield tunnel top to 3m below the shield tunnel bottom; the reinforcement depth of the hollow piles of the triaxial mixing piles is from 3m above the shield tunnel top to the ground surface; the cement content of the hollow piles of the triaxial mixing piles is 8%, and the cement content of the solid piles of the triaxial mixing piles is 22%; the pile diameter of the triaxial mixing piles is φ850@600, and the unconfined compressive strength of the long solid piles and the short solid piles of the triaxial mixing piles is not less than 0.8MPa.

4. The construction method for tunneling followed by station entrance / exit structures in soft soil according to claim 1, characterized in that, I-beams are used to connect the diaphragm walls; the diaphragm walls that conflict with the plane of the shield tunnel are arranged at an angle perpendicular to the tunneling direction of the shield machine; the interface of the diaphragm wall within the shield tunnel area must avoid the area crossed by the shield machine; the width of the diaphragm wall is 7.2m; and fiberglass reinforcement is reserved for the diaphragm wall within the area crossed by the shield tunnel.

5. The construction method for tunneling followed by station entrance / exit structures in soft soil according to claim 4, characterized in that, The fiberglass reinforcement bars are installed 0.5m outward from the perimeter of the shield tunnel.

6. The construction method for tunnel-first, station entrance / exit structure in soft soil according to claim 1, characterized in that, The segment bolts are tightened in three stages: first during assembly, second after assembly, and third after the segment detaches from the shield tail.

7. The construction method for tunneling followed by station entrance / exit structures in soft soil according to claim 1, characterized in that, The shield tunnel is equipped with 22a double I-beam longitudinal beams on both sides, which are welded and fixed to steel rings; the ring-shaped temporary support is set within the shield tunnel area that overlaps with the station entrance and exit pit and extends two rings to both ends; the ring-shaped temporary support uses 25C channel steel as the skeleton, the transverse 25C channel steel is tightly connected to the 22a double I-beam longitudinal beams, and the longitudinal 25C channel steel is tightly connected to the tunnel segments through wedges.

8. The construction method for tunnel-first, station entrance / exit structure in soft soil according to claim 1, characterized in that, The longitudinal channel steel tie setting range is 10 rings of segments before and after the shield tunnel passes through the station entrance and exit pit. Each ring is reinforced after assembly. The longitudinal channel steel tie is made of 8 No. 10 channel steels. The No. 10 channel steels are welded and fixed to the steel ear plates welded in the segment bolts, and at the same time welded to the steel rings to form a continuous steel component.

9. The construction method for tunnel-first, station entrance / exit structure in soft soil according to claim 1, characterized in that, The stacking of sandbags inside the shield tunnel must avoid the monitoring points at the bottom of the shield tunnel and the temporary circumferential support locations. The minimum ballast weight of the sandbags is 15t / m, and the maximum is 22.5t / m.

10. The construction method for tunnel-first, station entrance / exit structure in soft soil according to claim 1, characterized in that, Each dewatering well is set at 250m², with a horizontal spacing of 10-20m, and the dewatering depth is no less than 1m below the bottom of the tunnel.

Images