Vertical shaft enclosure structure for shield to obliquely penetrate through subway bottom and construction method of vertical shaft enclosure structure

Abstract

The invention discloses a vertical shaft enclosure structure for a shield to obliquely penetrate through a subway bottom and a construction method of the vertical shaft enclosure structure for the shield to obliquely penetrate through the subway bottom, the vertical shaft, the enclosure structure and a retaining wall are constructed on one side of an existing enclosure structure of an operating subway, and the depth of the vertical shaft is flush with the bottom of the existing enclosure structure. The vertical shaft is used for carrying out cut-off construction on the existing enclosure structure of the shield obliquely penetrating through the subway bottom; the vertical shaft structure is arranged on the outer side of the existing building envelope of the station, foundation pit supporting systems such as a vertical shaft supporting structure, a waterproof curtain and a support are additionally arranged, the existing building envelope is utilized, the occupied space is small, the traffic relief difficulty is small, and the influence on ground traffic is small; according to the vertical shaft structure, the existing enclosure structure can be broken firstly and then shield tunneling can pass through, vibration and deformation of an existing station caused by shield pile grinding are reduced, and station structure safety and operation safety are guaranteed.

Description

TECHNICAL FIELD

[0001] The present application relates to a kind of metro shield construction enclosure structure, specifically, a kind of vertical shaft enclosure structure for shield oblique crossing subway bottom and its construction method. BACKGROUND

[0002] With the increasing number of transfer stations, when the station of newly added line intersects with the existing operating station, the shield needs to pass under the existing operating station in the starting section or receiving section. When the shield tunnel is close to the existing operating station, the shield tunnel excavation process conflicts with the enclosure structure of the existing operating station. In such cases, direct pile grinding or subsurface excavation method is often used, but there are the following technical difficulties: 1. When the shield plane is inclined or the tunnel has a certain slope, if direct pile grinding method is used, the shield cutter head and the existing enclosure structure cannot completely overlap, and even the cutter head contacts the structure at a certain point first. The existing enclosure structure is unevenly stressed, the pile grinding effect is poor, and the shield thrust may shift sideways, affecting the safety of the station.

[0003] 2. The scheme of using subsurface excavation method to break the existing enclosure structure needs to be combined with open-cut shaft, stratum reinforcement, horizontal tunnel excavation, etc. The existing enclosure structure is broken in the horizontal tunnel, which is complicated and has high engineering cost and high construction risk.

[0004] 3. Protecting the operation safety of the station is the key of such projects. Direct pile grinding or subsurface excavation method is easy to cause a certain degree of lateral displacement and vertical settlement of the station. It is a key and difficult point to propose corresponding measures to control the deformation of the main structure of the station and the existing enclosure structure after the existing enclosure structure is broken.

[0005] In the cutting of the enclosure structure in shield construction, the shield cutter head and the existing enclosure structure are at a certain angle, the cutter head cannot fully adhere to the pile, and is easy to produce deflection and affect the shield posture. Or the station has been in operation for a long time, the structure has diseases, and the protection requirements are strict. Or the geological conditions are complex, and long-term slow pile grinding is easy to cause stratum loss and other complex working conditions that affect the safety and normal operation of the operating station. SUMMARY

[0006] To solve the above technical problems, the present application provides a method for breaking the existing enclosure structure of an operating subway station crossed by a shield, mainly to develop a vertical shaft structure and its design method for breaking the existing enclosure structure before the shield crosses the operating station, reducing the disturbance to the safety and operation safety of the operating station structure.

[0007] The present application adopts the following technical solutions: A vertical shaft enclosure structure for shield slanting through the bottom of a subway, comprising a vertical shaft constructed on one side of an existing enclosure structure of an operating subway, an enclosure structure and a retaining wall, the depth of the vertical shaft being flush with the bottom of the existing enclosure structure, the vertical shaft being used for the cut-off construction of the existing enclosure structure obstructing the shield slanting through the bottom of the subway, the retaining wall being provided at the upper part of the other side of the vertical shaft excavation for the support of the side soil layer, wherein the vertical shaft comprises a vertical shaft crown beam, a vertical shaft waist beam and a vertical shaft foundation pit excavated from top to bottom to the existing enclosure structure of the operating subway, the enclosure structure being composed of a closed rectangular enclosure body of a plurality of vertical shaft support piles, a plurality of vertical shaft waterproof curtains, a plurality of vertical shaft support structures and lap rotary jet piles of the existing enclosure structure, and the existing enclosure structure itself, the depth of the plurality of vertical shaft support piles being below the shield bottom elevation, the vertical shaft support pile segments cut off by the shield passing being all made of glass fiber reinforcement to ensure the stability of the soil body; the vertical shaft waterproof curtain between the two vertical shaft support piles forms a waterproof enclosure side wall, the upper part of the vertical shaft waterproof curtain being flush with the vertical shaft support pile, and the lower part of the vertical shaft waterproof curtain entering the impermeable layer by 1.5 m, the vertical shaft crown beam being a ring provided at the top of the vertical shaft support pile and the vertical shaft waterproof curtain, a plurality of the vertical shaft waist beams being connected to form a rectangular ring, a ring being provided every 4 m from top to bottom and connected to the vertical shaft support pile, the vertical shaft waterproof curtain and the existing enclosure structure at the lower part of the vertical shaft crown beam, a support beam being provided in the middle of the vertical shaft waist beam, the support beam being connected between the middle vertical shaft crown beam or vertical shaft waist beam and the existing enclosure structure as a transverse force support; the bottom of the vertical shaft is filled with plain concrete.

[0008] Preferably, in order to ensure the stability of the soil layer at the vertical shaft excavation site, a reverse arch stress preparation layer is provided, when the shield cuts the vertical shaft position, due to the arc excavation characteristics of the shield. The waterproof layer is waterproof mortar, and the support layer is graded gravel or strip stone compacted.

[0009] The bottom of the vertical shaft is provided with a reverse arch stress preparation layer, the reverse arch stress preparation layer is provided with a waterproof layer, an expansive cement dry powder layer, a support layer and a plain concrete layer from bottom to top, the waterproof layer is provided on the excavation surface of the vertical shaft bottom, the expansive cement dry powder layer is provided thereon, which is used to make the expansive cement dry powder layer quickly expand and harden after the waterproof layer is broken by the shield reaching the excavation, and a reverse arch stress layer is formed on the upper side of the shield surface excavation.

[0010] Preferably, the station existing enclosure is broken and suspended, in order to reduce the overall settlement caused by the self-weight of the existing enclosure, the pile is broken by jumping or segmented breaking; for the existing enclosure of bored pile, the vertical is segmented by 1.5m, and the segment is broken by jumping, the broken area is backfilled with C15 plain concrete, the adjacent pile body is broken after the plain concrete reaches the design strength, after the completion of the segment breaking, the previous segment is broken by the same process until the breaking is completed; for the existing enclosure of underground continuous wall, the segment is broken by 1.5m vertically, and the segment is broken by 1m horizontally, the segment is broken by jumping, after the completion of the segment breaking, the previous segment is broken by the same process until the breaking is completed, the segmented and zoned breaking can effectively control the vertical displacement of the existing enclosure of the station during the breaking process.

[0011] Preferably, the lap jetting pile of the several vertical shaft support structures and the existing enclosure is arranged in a triangular shape by three double-pipe jetting piles, and is arranged at the junction of the vertical shaft support pile and the existing enclosure.

[0012] Preferably, the embedded segment of the existing enclosure is reduced after the breaking, in order to reduce the risk of lateral displacement of the pile bottom, a support is arranged at 0.5m above the breaking segment, which can effectively control the lateral displacement of the existing enclosure of the station.

[0013] Preferably, the breaking construction of the existing enclosure adopts water drill or rope saw cutting, and the segment is taken out.

[0014] Preferably, after the breaking construction of the existing enclosure is completed, the plain concrete is backfilled to 1m above the tunnel top, and the remaining range of the vertical shaft above the plain concrete surface elevation is backfilled with clay which has poor permeability, good soil strength and low cost.

[0015] Based on the construction requirements, a construction method for the vertical shaft enclosure of the shield inclined through the subway bottom is provided, and the steps are as follows: Step 1) Determine the depth of the foundation pit, determine the depth of the foundation pit according to the vertical elevation of the shield, the conflict position of the shield and the existing support pile, the bottom elevation of the foundation pit is generally the bottom elevation of the enclosure or the bottom elevation of the shield tunnel, which can ensure that the space for breaking the conflict support structure after the vertical shaft is excavated.

[0016] Step 2) Design the foundation pit support according to the surrounding environmental load, the stratum condition, the vertical shaft excavation depth, etc., determine the vertical shaft support scheme, the bottom elevation of the foundation pit support structure, the vertical shaft support arrangement, and the size of each component.

[0017] Step 3) Use three-dimensional finite element analysis method to analyze the numerical simulation of the vertical shaft construction on the existing operating station, to ensure that the operating station meets the requirements of relevant specifications and departments during the construction process.

[0018] Step 4) construction of the vertical shaft supporting structure and water stop curtain. Three rotary jet piles are constructed at the joint of the new and old structures for jointing.

[0019] Step 5) layered excavation to the support bottom, construction of the support structure, and excavation to the envelope structure breaking elevation.

[0020] Step 6) after the existing envelope structure of the station is broken, it is in a suspended state. In order to reduce the overall subsidence due to the self-weight of the existing envelope structure, the pile is broken in sections or segmented. For the existing envelope structure of the cast-in-place pile, it is segmented vertically at 1.5m per section, and the section is broken by jumping piles. The C15 plain concrete is backfilled in the broken area, and the adjacent pile body is broken after the plain concrete reaches the design strength requirement. After the completion of the breaking of one section, the previous section is broken by using the same process until the breaking is completed. For the existing envelope structure of the underground continuous wall, it is segmented vertically at 1.5m per section, and the section is segmented horizontally at 1.2m per section, and the section is broken by jumping areas. After the completion of the breaking of one section, the previous section is broken by using the same process until the breaking is completed. The segmented and zoned breaking can effectively control the vertical displacement of the existing envelope structure of the station during the breaking process.

[0021] Step 7) after the required breaking section is completely chiseled, the reverse arch stress preparation layer is constructed at the bottom of the vertical shaft to 1m of the top of the tunnel, and the upper part is backfilled with clay.

[0022] Step 8) shield tunneling through, automatic monitoring of the station structure during the tunneling process to ensure normal operation of the station.

[0023] The beneficial effects of the present application compared with the prior art are as follows: 1) The vertical shaft structure of the present application is arranged outside the existing envelope structure of the station, and a new vertical shaft supporting structure, water stop curtain, support and other foundation pit supporting systems are arranged, and the existing envelope structure is utilized, so that the occupied space is small, the traffic is easy to solve, and the influence on the ground traffic is small.

[0024] 2) The vertical shaft structure of the present application can realize the breaking of the existing envelope structure before the shield tunneling through, reduce the vibration and deformation of the existing station caused by the shield pile grinding, and ensure the safety of the station structure and the operation safety.

[0025] 3) The design method of the vertical shaft structure of the present application adopts three-dimensional finite element simulation to analyze the influence of the construction stage on the subway structure, effectively predicts the deformation of the subway, feeds back the analysis results, further deepens the design, and provides a basis for subsequent construction and monitoring control. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 It is a perspective view of the vertical shaft structure; Figure 2 It is a plane schematic view of the vertical shaft structure; Figure 3Fig. 2 is a schematic view of a vertical shaft structure profile; Figure 4 Fig. 3 is a schematic view of breaking a vertical shaft support pile segment; Figure 5 Fig. 4 is a sectional view of a counter-arch stress-preparation layer; DETAILED DESCRIPTION The present application will be further understood by the following description of the embodiments, but the specific embodiments given by the applicant should not be regarded as limiting the technical solutions of the present application, and any change to the definition of components or technical features, or formal but not substantial change to the overall structure should be regarded as within the protection scope defined by the technical solutions of the present application.

[0027] In the present application, unless otherwise explicitly specified or limited, the terms "mounting", "connecting", "fixing" and the like should be understood in a broad sense. For example, it can be fixed connection, or detachable connection, or integral connection; it can be mechanical connection, or electrical connection; it can be direct connection, or indirect connection through an intermediate medium, or internal communication of two elements, or only surface contact, or surface contact connection through an intermediate medium. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0028] A shaft retaining structure for shield tunneling under a subway line includes a shaft 1, a retaining structure 2, and a retaining wall 3 constructed on one side of an existing retaining structure 4 of the operating subway. The depth of the shaft 1 is flush with the bottom of the existing retaining structure 4. The shaft 1 is used to cut off the existing retaining structure 4 that obstructs the shield tunneling under the subway line. The retaining wall 3 is located on the upper part of the other side of the shaft 1 excavation and is used for lateral soil support. The shaft 1 includes a shaft cap beam 6, a shaft waist beam 7, and a shaft pit 8 excavated from top to bottom to the existing retaining structure 4 of the operating subway. The retaining structure 2 consists of a number of shaft support piles 9, a number of shaft water-stop curtains 10, a number of overlapping jet grouting piles 11 of the shaft support structure 9 and the existing retaining structure 4, and the existing retaining structure 4 itself, forming a closed rectangular retaining body. The depth of the shaft support piles 9 is at the bottom of the shield tunnel. Below the height, the shaft support piles 9 that are cut off by the shield tunneling are all reinforced with glass fiber reinforced bars 13 to ensure soil stability; a shaft water-stop curtain 10 is set between two shaft support piles 9 to form an impermeable retaining sidewall. The upper part of the shaft water-stop curtain 10 is flush with the shaft support piles 9, and the lower part of the shaft water-stop curtain 10 extends 1.5m into the impermeable layer. The shaft cap beam 6 is set in a ring at the top of the shaft support piles 9 and the shaft water-stop curtain 10. Several shaft waist beams 7 are connected to form a rectangular ring, set every 4m from top to bottom, and connected to the shaft support piles 9, the shaft water-stop curtain 10 and the existing retaining structure 4 at the bottom of the shaft cap beam 6. A support beam 15 is set in the middle of the shaft waist beam 7. The support beam 15 is connected between the middle shaft cap beam 6 or shaft waist beam 7 and the existing retaining structure 4 as a lateral force support. Preferably, in order to ensure the stability of the soil layer at the shaft excavation site, an anti-arch load-bearing preparatory layer is set up. When the shield cuts the shaft location, due to the arc excavation characteristics of the shield, an anti-arch load-bearing layer is formed on top of it.

[0029] The bottom of the shaft is provided with a reverse arch load-bearing preparation layer. The reverse arch load-bearing preparation layer is provided with a waterproof layer 101, an expansive cement dry powder layer 102, a support layer 103 and a plain concrete layer 104 from bottom to top. On the excavation surface of the bottom of the shaft, the waterproof layer is provided with an expansive cement dry powder layer. This is used to allow the expansive cement dry powder layer to expand and harden quickly after the shield tunneling machine breaks through the waterproof layer. At the same time, a reverse arch load-bearing layer is formed on the upper side of the shield tunneling face.

[0030] The waterproof layer is waterproof mortar, and the support layer is made of graded crushed stone or stone strips that have been compacted. Specifically, when the tunnel boring machine (TBM) cuts the anti-arch load-bearing preparatory layer, the partially hardened or unhardened expansive cement powder layer will be randomly distributed from the soil layer onto the cutting surface under the action of the TBM's blades. This will form a cement wall of a certain strength on the sidewall of the cut soil section. In addition, the cutting and squeezing of the sidewall by the TBM blades and the leakage of some groundwater will cause the soil layer above the sidewall to harden rapidly, eventually forming an anti-arch load-bearing layer on the inner wall of the cut TBM, providing favorable conditions for the subsequent segment construction of Tunnel 5.

[0031] Preferably, the existing retaining structure 4 of the station will be suspended after demolition. To reduce the overall settlement caused by the self-weight of the existing retaining structure 4, a skip-pile demolition or segmented demolition will be adopted. If the existing retaining structure 4 is a cast-in-place pile, it will be demolished in 1.5m sections vertically, and each section will be demolished by skip-pile demolition. The demolished area will be backfilled with C15 plain concrete. After the plain concrete reaches the design strength requirements, the adjacent piles will be demolished. After one section is demolished, the same procedure will be used to demolish the previous section until the demolition is completed. If the existing retaining structure 4 is a diaphragm wall, it will be demolished in sections by area. Vertically, it will be demolished in 1.5m sections, and horizontally, it will be demolished in 1m sections, with skip-section demolition. After one section is demolished, the same procedure will be used to demolish the previous section until the demolition is completed. Segmented and zoned demolition can effectively control the vertical displacement of the existing retaining structure 4 of the station during the demolition process.

[0032] Preferably, the overlapping jet grouting piles 11 of several shaft support structures 9 and existing retaining structures 4 are arranged in a triangular pattern by three double-pipe jet grouting piles 25, and are respectively set at the connection between the shaft support piles 9 and the existing retaining structures 4.

[0033] Preferably, after the existing retaining structure 4 is demolished, the embedded section is reduced. In order to reduce the risk of kicking due to lateral displacement of the pile bottom, a support is set 0.5m above the demolished section to effectively control the lateral displacement of the existing retaining structure 4 of the station.

[0034] Preferably, the existing enclosure structure 4 is demolished by using a water drill or wire saw to cut it and remove it in sections.

[0035] Preferably, after the existing retaining structure 4 is demolished, the anti-arch load-bearing preparatory layer is backfilled to 1m above the top of the tunnel, and the remaining area of ​​the shaft above the plain concrete surface elevation is backfilled with clay that has poor permeability, good soil strength, and low cost.

[0036] Based on construction requirements, a construction method for the retaining structure of a vertical shaft used for shield tunneling under a subway line is provided, comprising the following steps: Step 1) Determine the depth of the foundation pit. The depth of the foundation pit is determined based on the vertical elevation of the shield and the conflict position between the shield and the existing support piles. The bottom elevation of the foundation pit is generally the bottom elevation of the retaining structure or the bottom elevation of the shield tunnel, to ensure that the space for the demolition of the conflict support structure can be met after the shaft is excavated.

[0037] Step 2) Design the foundation pit support based on the surrounding environmental load, stratum conditions, and shaft excavation depth, and determine the shaft support scheme, the bottom elevation of the foundation pit support structure, the shaft support layout, and the dimensions of each component.

[0038] Step 3) Use the three-dimensional finite element analysis method to conduct numerical simulation analysis of the shaft construction on the existing operating station to ensure that the operating station meets the relevant specifications and requirements of the competent authorities during the construction process.

[0039] Step 4) Construct the shaft support structure and water-stop curtain. Three jet grouting piles are installed at the junction of the old and new structures for overlapping.

[0040] Step 5) Excavate in layers to the bottom of the support, construct the support structure, and continue excavating until the retaining structure is demolished.

[0041] Step 6) After the existing retaining structure of the station is demolished, it will be in a suspended state. To reduce the overall settlement caused by the self-weight of the existing retaining structure, a skip-pile demolition or segmented demolition will be adopted. For the existing retaining structure being cast-in-place piles, vertical demolition will be carried out in 1.5m sections, with each section being demolished using a skip-pile method. The demolished areas will be backfilled with C15 plain concrete. After the plain concrete reaches the design strength requirements, adjacent piles will be demolished. After one section is demolished, the same procedure will be used to demolish the previous section until the demolition is completed. For the existing retaining structure being a diaphragm wall, segmented demolition will be adopted, with vertical demolition in 1.5m sections and horizontal demolition in 1.2m sections, using a skip-zone demolition method. After one section is demolished, the same procedure will be used to demolish the previous section until the demolition is completed. Segmented and zoned demolition can effectively control the vertical displacement of the existing retaining structure of the station during the demolition process.

[0042] Step 7) After all the sections to be broken are chiseled away, a preparatory layer for the anti-arch load is constructed at the bottom of the shaft up to 1m from the top of the tunnel, and the upper part is backfilled with clay.

[0043] Step 8) The tunnel boring machine passes through. During the tunneling process, the station structure is automatically monitored to ensure normal station operation.

[0044] The above description is merely a preferred embodiment of the present invention and does not constitute any limitation on the structure of the present invention. Any simple modifications, equivalent changes, or alterations made to the above embodiments based on the technical essence of the present invention shall still fall within the scope of the technical solution of the present invention.

Claims

1. A shaft retaining structure for shield tunneling under a subway line, comprising a shaft, a retaining structure, and a retaining wall constructed on one side of an existing retaining structure of the operating subway, wherein the depth of the shaft is flush with the bottom of the existing retaining structure, and the shaft is used for the construction of cutting off the existing retaining structure for the shield tunneling under the subway line, characterized in that: The shaft includes a shaft cap beam, a shaft waist beam, and a shaft foundation pit excavated from top to bottom to the existing retaining structure of the operating subway. The retaining structure consists of several shaft support piles, several shaft water-stop curtains, several overlapping jet grouting piles connecting the shaft support structure and the existing retaining structure, and the existing retaining structure itself, forming a closed rectangular retaining body. The depth of several of the shaft support piles is below the bottom elevation of the shield tunnel. The shaft support pile segments cut off by the shield tunnel are all made of fiberglass. Reinforcing bars are added to ensure soil stability. A water-stop curtain is installed between the two shaft support piles to form an impermeable retaining wall. The upper part of the water-stop curtain is flush with the shaft support piles, and the lower part of the water-stop curtain enters the impermeable layer. The shaft cap beam is a ring set on top of the shaft support piles and the shaft water-stop curtain. A support beam is set in the middle of the shaft waist beam. The support beam connects the middle shaft cap beam or shaft waist beam and the existing retaining structure as a lateral force support.

2. The shaft retaining structure for shield tunneling under a subway line according to claim 1, characterized in that: The bottom of the shaft is provided with a reverse arch load-bearing preparation layer. The reverse arch load-bearing preparation layer is provided with a waterproof layer, an expansive cement dry powder layer, a support layer and a plain concrete layer from bottom to top. The waterproof layer is provided on the excavation surface at the bottom of the shaft. The expansive cement dry powder layer is used to allow the expansive cement dry powder layer to expand and harden quickly after the shield tunneling machine breaks through the waterproof layer. At the same time, a reverse arch load-bearing layer is formed on the upper side of the shield tunneling face.

3. The shaft retaining structure for shield tunneling under a subway line according to claim 1, characterized in that: The overlapping jet grouting piles of several vertical shaft support structures and existing retaining structures are arranged in a triangular pattern using three double-pipe jet grouting piles, which are respectively set at the junction of the vertical shaft support piles and the existing retaining structure; several vertical shaft waist beams are connected in a rectangular ring, with one ring set every 4m from top to bottom, and are located at the bottom of the vertical shaft cap beam and connected to the vertical shaft support piles, the vertical shaft water-stop curtain, and the existing retaining structure.

4. The shaft retaining structure for shield tunneling under a subway line according to claim 1, characterized in that: After the existing retaining structure is demolished, the embedded section is reduced. In order to reduce the risk of kicking due to lateral displacement of the pile bottom, a support is set 0.5m above the demolished section to effectively control the lateral displacement of the existing retaining structure of the station.

5. A shaft retaining structure for shield tunneling under a subway line according to claim 1, characterized in that: The demolition of the existing enclosure structure was carried out by cutting with a water drill or wire saw and removing it in sections.

6. A shaft retaining structure for shield tunneling under a subway line according to claim 10, characterized in that: After the existing retaining structure is demolished, plain concrete is backfilled to 1m above the top of the tunnel. The remaining area of ​​the shaft above the plain concrete surface is backfilled with clay, which has poor permeability, good soil strength, and low cost.

7. A construction method for a vertical shaft retaining structure for a shield tunnel obliquely passing under a subway as described in claim 1, characterized in that: The steps are as follows: Step 1) Determine the depth of the foundation pit. The depth of the foundation pit is determined based on the vertical elevation of the shield and the conflict position between the shield and the existing support piles. The bottom elevation of the foundation pit is generally the bottom elevation of the retaining structure or the bottom elevation of the shield tunnel, to ensure that the space for the demolition of the conflicting support structure can be met after the vertical shaft is excavated. Step 2) Design the foundation pit support based on the surrounding environmental load, stratum conditions, and shaft excavation depth, and determine the shaft support scheme, the bottom elevation of the foundation pit support structure, the shaft support layout, and the dimensions of each component. Step 3) Use the three-dimensional finite element analysis method to conduct numerical simulation analysis of the shaft construction on the existing operating station to ensure that the operating station meets the relevant specifications and requirements of the competent authorities during the construction process; Step 4) Construct the shaft support structure and water-stop curtain. Three jet grouting piles are installed at the junction of the old and new structures for overlapping; Step 5) Excavate in layers to the bottom of the support, construct the support structure, and continue excavating until the retaining structure is demolished. Step 6) After the existing retaining structure of the station is demolished, it will be in a suspended state. To reduce the overall settlement caused by the self-weight of the existing retaining structure, skip-pile demolition or segmented demolition will be adopted. For the existing retaining structure being cast-in-place piles, vertical demolition will be carried out in 1.5m sections, and each section will be demolished using skip-pile demolition. The demolished areas will be backfilled with C15 plain concrete. After the plain concrete reaches the design strength requirements, the adjacent piles will be demolished. After one section is demolished, the same procedure will be used to demolish the previous section until the demolition is completed. For the existing retaining structure being a diaphragm wall, segmented demolition will be adopted, with vertical demolition in 1.5m sections and horizontal demolition in 1.2m sections, using skip-section demolition. After one section is demolished, the same procedure will be used to demolish the previous section until the demolition is completed. Segmented and zoned demolition can effectively control the vertical displacement of the existing retaining structure of the station during the demolition process. Step 7) After all the sections to be demolished are removed, a preparatory layer for the anti-arch load is constructed at the bottom of the shaft up to 1m from the top of the tunnel, and the upper part is backfilled with clay. Step 8) The tunnel boring machine passes through. During the tunneling process, the station structure is automatically monitored to ensure normal station operation.

Images