A method for constructing a dark-excavated rectangular tunnel under an existing subway station at zero distance

Abstract

The present application relates to the technical field of tunnel construction, and discloses a method for constructing a dark-excavated rectangular tunnel that passes under an existing subway station at zero distance. The above method includes: determining the location of a new tunnel under an existing subway station; taking precipitation measures and reinforcing the ground around the location of the new tunnel before construction; constructing a transition section of the new tunnel; the new tunnel passes under the existing subway station, and the station retaining piles are cut; the engineering piles located in the middle of the new tunnel are removed, and the main reinforcement of the engineering piles is connected to the secondary lining structure; the engineering piles located on both sides of the new tunnel are retained, and the engineering piles are planted with reinforcement and connected to the secondary lining structure; and the inner lining wall is constructed on the secondary lining structure. The patent of the present invention solves the problems of large limitations in underpass construction, complex structural force transmission, obvious station structure settlement, anti-floating problems and poor waterproof performance, and achieves the effect of simple and clear force transmission of each structure, stable structure, effective control of station settlement, solution of anti-floating problems and waterproof performance.

Description

Technical Field

[0001] The present invention relates to the technical field of tunnel construction, and in particular to a method for constructing a dark-excavated rectangular tunnel that passes under an existing subway station at zero distance. Background Art

[0002] In the existing technology, due to the complexity of subway lines, the subway structures implemented in the early stage do not reserve conditions for long-term planned lines, especially for adjacent subway stations. This makes the implementation of subsequent projects very difficult and the construction cost too high, bringing a series of problems to subway construction. Conventional civil engineering implementation plans for subway stations with good ground conditions are station retaining piles + internal supports. The main structure bearing system is to set bearing piles or pull-out piles under the bottom plate / under the structural columns. If the construction of the subway station does not take the planned line setting into consideration, it will affect the implementation of the subsequent subway line. Since the subsequent tunnel project is adjacent to the existing subway station, the line cannot avoid the existing subway station in plane and can only be implemented by passing under it. In view of the current situation, the construction method of using the dark excavation method can solve the existing problems. However, the selection of the cross-sectional shape of the dark excavation method and the treatment of the existing pile group have a significant impact on the structural system of the existing subway station. In addition, the force transmission between the existing structure, the new structure and the foundation becomes a key issue for the smooth implementation of the project.

[0003] Secondly, in the prior art, a circular cross-section, a horseshoe-shaped cross-section and other structural forms are used to adopt the underground excavation method to pass under the existing subway station. However, when the pipe shed and the advanced small duct are constructed at zero distance under the existing subway station, the soil layer between the arch and the existing subway station floor is relatively thin, and the construction space for the arch reinforcement is limited, and it is easy to damage the waterproof layer under the existing subway station floor. If direct excavation is carried out, the vibration during construction may easily cause the upper interlayer soil to loosen and fall, endangering the construction workers. In addition, this cross-sectional form is not conducive to the vertical force transmission of the upper station structure-engineering piles-underground excavation structure. The completed force system may easily cause the existing structure to sink and the tunnel structure to deform too much due to the long-term vibration of the upper train load, affecting the structural safety.

[0004] Finally, existing methods add pullout piles and anchors to the existing subway station floor to compensate for the frictional resistance loss caused by pile foundation cutting. This method can easily damage the existing subway station's structural load-bearing and waterproofing systems, resulting in significant water leakage during construction. If implemented in an existing operating station, it would affect some station functions and cause significant inconvenience to passengers. Another approach involves removing existing engineering piles and connecting the remaining main reinforcement to the steel grid of the initial support for the tunnel. While this approach addresses the station's anti-floating effect during construction to some extent, the initial support is a temporary structure with a relatively thin thickness. Once the structure is subjected to significant stress, the engineering piles, along with the initial support grid, can easily separate from the secondary lining and cause cracking. This damages the waterproofing layer between the initial support and the secondary lining, rendering the waterproofing ineffective and failing to provide permanent anti-floating effect. Furthermore, if a subway station has a large number of engineering piles, it is possible that some of the piles will fall on either side of the tunnel. For circular or horseshoe-shaped tunnel structures, the engineering pile reinforcement is difficult to effectively connect to the initial support, resulting in a flawed load-bearing system.

[0005] In summary, there are significant limitations in constructing a circular / horseshoe-shaped tunnel with zero-distance underpass through a subway station with an engineering pile group. Therefore, for the situation where zero-distance underpass under an existing subway station is required, without affecting the operation of the existing subway station, how to solve the problems of complex structural force transmission and poor support structure stability between the existing subway station and the newly built tunnel in the existing technology? This may cause the existing subway station structure to sink during construction, and its anti-floating ability and waterproof performance are low, which in turn leads to high construction safety risks and low reliability. Summary of the Invention

[0006] In response to the above problems, the present invention aims to provide a method for constructing a dark-excavated rectangular tunnel that passes under an existing subway station at zero distance, thereby resolving the technical problems raised in the above background technology. To achieve the above objectives, the present invention provides the following technical solution: a method for constructing a dark-excavated rectangular tunnel that passes under an existing subway station at zero distance, comprising the following steps:

[0007] S1, determine the location of the new tunnel under the existing subway station;

[0008] S2: Before construction, dewatering measures and ground reinforcement shall be carried out around the new tunnel site;

[0009] S3, construction of the new tunnel transition section;

[0010] S4: A new tunnel will be built under the existing subway station and the station retaining piles will be cut;

[0011] S5, the engineering piles located in the middle of the new tunnel were removed, where the main reinforcement of the engineering piles was connected to the secondary lining structure;

[0012] S6, retain the engineering piles on both sides of the new tunnel, plant reinforcement and connect them to the secondary lining structure;

[0013] S7, construct inner lining wall on the secondary lining structure.

[0014] Preferably, the step S1 includes:

[0015] Before constructing a new tunnel, drill holes around it to check the water level. If the water level is too high and affects the underground excavation, a combination of external dewatering and full-section grouting will be used to carry out the construction.

[0016] If the conditions for installing equipment are available outside the cave, a pipe well will be drilled and a high-power deep-water pump will be installed to reduce water levels in order to increase the reduction curve and enhance the pressure reduction effect. The water stopping inside the cave will be achieved by a grouting measure that combines deep hole grouting with sleeve valve pipe grouting.

[0017] Preferably, the grouting is carried out from bottom to top, in two longitudinal steps, with an overlap length of 3m to 4m;

[0018] The scope of grouting is defined as "the soil inside the excavation line is completely grouted, and the soil outside the excavation line is grouted no more than 3m";

[0019] The unconfined compressive strength of the soil outside the excavation line reaches 0.8 MPa, and the unconfined compressive strength of the soil inside the hole reaches 0.5 MPa.

[0020] Preferably, step S3 includes:

[0021] Draft the dimensions of the new tunnel based on the track surface of the new tunnel and the floor elevation of the existing subway station;

[0022] Based on the surrounding rock grade and the dimensions of the new tunnel, the CRD method was used for construction;

[0023] The small sections of each step are constructed by reserving core soil using the step method, and mechanized static blasting technology is used for collaborative operations.

[0024] Preferably, the step S4 includes:

[0025] When the new tunnel is constructed to the station retaining piles, the station retaining piles that intrude into the tunnel body shall be chiseled out;

[0026] A gap of at least 50mm is reserved between the removed station retaining piles and the initial support, and a grid steel frame is erected in the initial support. At the same time, the grid steel frame is densely arranged in the area of ​​the removed station retaining piles.

[0027] Preferably, the spacing between the longitudinal connecting reinforcements within 1.0m on both sides of the station guard pile is increased to a circumferential spacing of 0.2m, and the increased length of the longitudinal connecting reinforcements is strengthened by expanding the diameter of the station guard pile by 1.0m.

[0028] Preferably, step S5 includes: if the engineering piles are located in the middle of the newly built tunnel, and the initial support and secondary lining structure are constructed outside the engineering piles, the engineering piles are retained; after the secondary lining structure outside the engineering piles is erected, a post-casting strip is reserved at the engineering piles, and when the strength of the secondary lining structure outside the engineering piles reaches more than 80%, the engineering pile area is constructed.

[0029] Preferably, the construction engineering pile area is specifically:

[0030] When the pilot tunnel is excavated to the top, the engineering piles in the upper part of the pilot tunnel are chiseled out to the bottom of the cushion layer of the existing subway station floor, and the main reinforcement of the engineering piles is reserved to the bottom of the initial support. During the initial support, the grid steel frame in the initial support is tightly attached to the cushion layer of the existing subway station floor, forming a rigid contact. At the same time, grouting pipes are embedded in the pilot tunnel floor, and cement slurry is injected into the grid steel frame foundation to harden the grid steel frame foundation. The bottom of the grid steel frame is padded with square wood wedges, and the initial support is tightened to fit and fix it to the existing subway station floor.

[0031] When the pilot tunnel is excavated to the bottom, the engineering piles in the lower part of the pilot tunnel are chiseled out, and the main reinforcement of the engineering piles is reserved to the top surface of the initial support. Grouting pipes are reserved along the grid steel frame behind the initial support to fill the initial support with grouting. Dynamic compensation grouting is performed during the grouting process, and the grouting pressure is not greater than 0.5Mpa.

[0032] Waterproofing measures are constructed on the removed upper and lower engineering piles and engineering pile main reinforcements, and then the secondary lining structure is constructed in the post-pouring zone reserved for the engineering pile positions, and the upper and lower engineering pile main reinforcements are anchored into the secondary lining structure, and then concrete is poured together for solidification.

[0033] Preferably, step S6 includes:

[0034] If the engineering piles are located on both sides of the new tunnel and infringe upon the secondary lining structure but not upon the tunnel limit, there is no need to remove the engineering piles and the area within the engineering piles does not require initial support during construction;

[0035] Three rows of grid steel frames with a spacing of 500mm are set up on both sides of the engineering piles, and waterproofing measures are implemented after the initial support is completed;

[0036] Steel bars are implanted on opposite sides of the pile body with circumferential and vertical spacing of 200mm, and water-expanding waterstop strips are used around the steel bars to enhance waterproofing.

[0037] During the construction of the secondary lining structure, the steel bars embedded in the engineering piles shall be cast integrally with the secondary lining structure. At the same time, the length of the steel bars embedded in the engineering piles shall not exceed the thickness of the secondary lining structure.

[0038] Preferably, the step S7 includes: after the initial support and the secondary lining structure are completed, a molded 200mm thick inner lining waterproof concrete wall is set in the secondary lining structure, and a φ8@200 mesh is hung in the inner lining waterproof concrete wall.

[0039] Compared with the prior art, the present invention has the following beneficial effects:

[0040] The present invention constructs a new tunnel excavated in a rectangular shape. By combining existing engineering piles, the rectangular tunnel formed after construction has a more reasonable overall structure and guaranteed structural strength. At the same time, it can be highly combined with the existing engineering piles, can transmit force through a shorter force transmission route, and the force is clearly and clearly formed, and a stronger vertical support is formed, which further effectively controls the settlement of the existing subway station above. At the same time, due to the strong rigidity of the structural system, the impact of the existing subway train above on the new tunnel under long-term vibration is also reduced, and the problem of loosening and falling of soil caused by vibration during the construction of the reserved soil for the vault in previous designs is avoided, thereby ensuring the safety of construction workers. The rectangular section construction is more precise and easy to control the shield limit, which solves the limitations of the existing construction process with a circular section / horseshoe section.

[0041] The grouting construction of the present invention performs dewatering operations before construction according to the implementation conditions to form an effective water-stop curtain, so as to eliminate the adverse effects of groundwater and pressurized water layers on underground excavation operations, reduce the water content in the excavation range, and reduce the safety risks of water and sand gushing during construction; full-section grouting can improve the geological conditions of the original stratum, play a role in stabilizing the soil, reduce the risk of soil collapse during excavation, and at the same time reduce the effect of settlement of the existing line above.

[0042] Before constructing under an existing subway station, the present invention first conducts a construction test on the transition section of its periphery, determines the structural support parameters according to the construction conditions of the test section, prepares for the underpass, and increases the reliability of the implementation.

[0043] The present invention constructs a new tunnel under the existing subway station structure to form a rectangular tunnel. By spraying concrete between the rectangular tunnel and the existing subway station, the initial support of the rectangular tunnel periphery is highly integrated with the main structure of the station, realizing the zero-distance process of underpass construction and increasing the stability between the rectangular tunnel and the existing subway station during operation.

[0044] The existing subway station floor of the present invention is tightly connected to the secondary lining structure through the main reinforcement of the engineering piles located in the middle of the newly built tunnel. The engineering piles located on both sides of the newly built tunnel are reinforced, and at the same time, the embedded reinforcement is connected to part of the secondary lining structure. Two reinforcement methods are used. Different construction is carried out at different positions of the engineering piles, which solves the damage to the stress and waterproofing system of the existing subway station structure caused by conventional technology of adding anti-pullout piles, anti-pullout anchor rods and other measures to the existing subway station floor. In addition, the main reinforcement of the engineering piles and the secondary lining structure are cast together to form an overall stress system, which can provide permanent anti-floating effect for the existing subway station structure.

[0045] The support of the rectangular tunnel structure by the engineering piles of the present invention, the close arrangement of the mortar anchor rods and the grid steel frame can effectively control the structural settlement of the rectangular tunnel. At the same time, the station retaining piles are arranged above the rectangular tunnel. For stations that use retaining piles as a bearing system, the settlement of the station body is further reduced. At the same time, waterproof structures are arranged on the engineering piles, rectangular tunnel support, and secondary lining structure, and the inner lining wall is covered with mesh, thereby improving the overall waterproof performance of the rectangular tunnel. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 This is a schematic diagram of the plan structure of the new tunnel passing under the existing subway station in the present invention.

[0047] Figure 2 This is a schematic diagram of the AA section structure of the newly built tunnel passing under the existing subway station in the present invention.

[0048] Figure 3 This is a schematic diagram of the connection structure between the newly built tunnel and the engineering piles of the present invention.

[0049] Figure 4 This is a schematic diagram of the BB section structure of the newly built tunnel passing under the existing subway station in the present invention.

[0050] Figure 5 It is a schematic diagram of the truncation structure of the retaining structure pile of the present invention.

[0051] Figure 6 Schematic diagram a of the engineering pile anchored into the secondary lining structure of the present invention.

[0052] Figure 7 This is a schematic diagram b of the large-scale sample of the engineering pile anchored into the secondary lining structure of the present invention.

[0053] Figure 8 This is a schematic diagram of the grouting reinforcement of the transition section of a newly built tunnel according to the present invention.

[0054] Figure 9 This is a schematic diagram of the grouting reinforcement of the newly built tunnel under the existing subway station section according to the present invention.

[0055] In the figure: 1. Station retaining piles; 1-1. Removed part of the station retaining piles; 2. Existing subway station; 2-1. Existing subway station floor; 2-2. Station columns; 3. Engineering piles; 3-1. Main reinforcement of engineering piles; 4. New tunnel; 4-1. Initial support; 4-2. Secondary lining structure; 4-3. Inner lining wall; 5. Mortar anchor rods; 5-1. Locking foot anchor rods; 5-2. Middle partition wall; 6. Rebar; 7. Grille steel frame; 8. Concrete; 9. Main reinforcement of secondary lining structure; 10. Inside of excavation line; 11. Outside of excavation line. DETAILED DESCRIPTION

[0056] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0057] In the description of the present invention, it should be noted that the terms "center", "up", "down", "left", "right", "vertical", "horizontal", "inside", "outside" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the devices or components referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention. In addition, the terms "first", "second", and "third" are only used for descriptive purposes and should not be understood as indicating or implying relative importance. In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", and "set" should be understood in a broad sense, for example, they can be fixedly connected, detachably connected, or connected in one piece; they can be mechanically connected or electrically connected; they can be directly connected, or indirectly connected through an intermediate medium, or they can be internal connections between two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances. The following describes an embodiment of the present invention based on its overall structure.

[0058] See also Figures 1-9 The present invention provides a technical solution: the main purpose of the present invention is to adopt a construction method that has simple and clear structural force transmission, can effectively control the structural settlement of the existing subway station, solve the structural anti-floating problem and have waterproof performance, in the case of zero-distance underpass of the existing subway station without affecting the operation of the existing subway station.

[0059] (1) Determine the location of the new tunnel under the existing subway station

[0060] According to the position distribution of the existing subway station 2 and the engineering piles 3 and other structures thereunder, the position and depth range of the new tunnel 4 below the existing subway station 2 are calculated and confirmed.

[0061] (2) Before construction, dewatering and ground reinforcement should be carried out around the new tunnel location, such as Figure 1 、 Figure 2 、 Figure 9 As shown:

[0062] Before construction of the new tunnel, boreholes were drilled to check water levels. If excessive water levels impeded underground excavation, a combination of external dewatering and full-section grouting was implemented to provide favorable conditions for underground excavation. If conditions permitted, pipe wells were drilled outside the pilot tunnel and high-power deep-water pumps were installed for dewatering, increasing the dewatering curve and enhancing the pressure relief effect.

[0063] To minimize the impact of subsidence caused by dewatering operations, dewatering of the subsurface within the existing subway station's burial depth of 2 was not performed, with the primary focus being on dewatering the confined water. A combination of deep-hole grouting and sleeve-valve pipe grouting was employed to seal the pilot tunnel. This reinforced the ground while forming an effective water-blocking curtain, eliminating the adverse effects of subsurface and confined water on the tunneling operation.

[0064] Grouting is carried out from bottom to top in two longitudinal steps, with an overlap length of 3m to 4m. The grouting range is as follows: grouting is completed 10 meters inward from the excavation line, and grouting is not more than 3 meters in the soil layer 11 meters outward from the excavation line, forming a cylindrical reinforcement area as a closed water-blocking curtain. After the reinforcement is completed, core sampling is performed to determine the strength. The unconfined compressive strength of the external soil must reach 0.8MPa, and the unconfined compressive strength of the soil inside the tunnel must reach 5MPa to ensure that the underground excavation is safe.

[0065] According to the implementation conditions, dewatering operations are carried out before construction to reduce the moisture content in the excavation area and minimize the safety risks of water and sand gushing during construction. Full-section grouting can improve the geological conditions of the original stratum, stabilize the soil, reduce the risk of soil collapse during excavation, and reduce the settlement of the existing lines above.

[0066] (3) Construction of new tunnel transition section, such as Figure 1 、 Figure 2 、 Figure 8 As shown:

[0067] The existing subway station 2 is constructed with multiple station columns 2-2 supporting the existing subway station floor 2-1 and roof. Based on the track surface of the new tunnel 4 and the elevation of the existing subway station floor 2-1, the dimensions of the new tunnel 4 were determined to meet tunnel clearance requirements. Appropriate excavation methods, such as the CRD method, were then employed based on the surrounding rock grade and the dimensions of the new tunnel 4. Construction can be divided into six steps, with small sections in each step using a step-by-step method to reserve core soil and mechanized static blasting. Due to strict settlement control requirements during the underpass section, a 15-meter test section was established during the transition section. Structural support parameters were determined based on the performance of the test section to prepare for the underpass.

[0068] The construction sequence of the transition section of the newly built tunnel 4 is pilot tunnel excavation, initial spraying of concrete, installation of anchor rods, hanging of steel mesh, erection of grilles, middle partition wall steel frame, locking foot anchor pipes and pre-buried initial support 4-1 back grouting pipes, spraying of concrete to the designed thickness, and the excavation strictly adheres to the 18-character policy of "pipe ahead, strict grouting, short excavation, strong support, early closure, and frequent measurement" to complete the initial support 4-1. After the completion of the initial support 4-1, waterproofing and secondary lining structure 4-2 construction are carried out. After the construction is completed, the middle partition wall 5-2 is demolished, and the mesh lining wall 4-3 (waterproof concrete) is constructed. Finally, the shield machine empty push guide platform is poured, and the shield machine completes the empty push operation.

[0069] (4) The new tunnel passes under the existing subway station section and cuts the station retaining piles, such as Figure 2 、 Figure 4 、 Figure 5 As shown:

[0070] When the new tunnel 4 is constructed to the existing subway station 2, the removed portion 2 of the station retaining piles 1 that intrude into the tunnel should be chiseled out. Static cutting machinery should be used for cutting, and the top elevation of the cutting should be the top elevation of the initial support 4-1.

[0071] After the station retaining pile 1 is broken, a gap of 50 mm should be reserved between the bottom of the station retaining pile 1 and the primary support 4-1. Concrete 8, for example, C25 concrete, should be sprayed in the gap, and a grid steel frame 7 should be erected in the primary support 4-1. The grid steel frames 7 should be densely arranged at the position where the station retaining pile 1 is broken.

[0072] Within the 1.0m radius on either side of the demolished pile, the longitudinal connecting reinforcement spacing within the lattice steel frame 7 was increased to a circumferential spacing of 0.2m. The longitudinal connecting reinforcement was increased in length by 1.0m outward from the pile diameter. After the station retaining piles 1 were treated and initial support 4-1 was completed, subsequent structural construction, including the waterproofing layer, secondary lining 4-2, and inner lining wall 4-3, was carried out. The construction procedures were similar to those for the transition section of the new tunnel 4.

[0073] The newly built tunnel 4 adopts a rectangular cross-section structure and is set up close to the existing subway station floor 2-1: this avoids the problem of loosening and falling soil caused by vibration during the construction of the reserved soil for the arch in previous designs, ensuring the safety of construction workers. The rectangular cross-section construction is more precise and easy to control the shield limit.

[0074] The rectangular cross-section can be regarded as a portal frame structure. The top is closely attached to the existing subway station floor 2-1, allowing for a shorter force transmission route. The force is clearly and distinctly applied, and strong vertical support is formed, further effectively controlling the settlement of the existing subway station 2 above. At the same time, due to the strong rigidity of the structural system, the impact of the long-term vibration of the existing subway trains above on the newly built tunnel is also reduced.

[0075] (5) Remove the engineering piles located in the middle of the new tunnel. The main reinforcement of the engineering piles is connected to the secondary lining structure of the new tunnel, such as Figure 3 、 Figure 5 , Figure 6 and Figure 7 As shown:

[0076] If the engineering pile 3 is located in the middle of the newly built tunnel 4, a small mechanical static force is used to remove the engineering pile 3.

[0077] Before the engineering pile 3 is removed, since the engineering pile 3 plays the role of bearing the upper load, it is considered that if the pile 3 is removed directly after excavation, the pressure of the bottom plate will be directly transferred to the initial support 4-1 of the newly built tunnel 4. If the structural strength and rigidity of the initial support 4-1 are too low, it may cause excessive deformation of the station structure in advance.

[0078] Therefore, during the implementation stage of the initial support 4-1 and the secondary lining structure 4-2, the engineering piles 3 at this location will not be removed temporarily. The initial support 4-1 and the secondary lining structure 4-2 will be implemented in the area outside the scope of the engineering piles 3 in priority. At the same time, after the construction of the secondary lining structure 4-2 outside the engineering piles 3 is completed, it is necessary to reserve a post-casting strip within the scope of the engineering piles 3. After the strength of the secondary lining structure 4-2 around the engineering piles 3 reaches more than 80% after construction, and the overall rigidity of the newly built tunnel 4 is sufficient, the engineering piles 3 at this location will be removed and the engineering pile 3 area will be constructed to control the deformation of the upper station structure.

[0079] The process for constructing the engineering pile 3 area is as follows:

[0080] When the pilot tunnel is excavated to the top, the tops of the engineering piles 3 must be chiseled down to the base of the existing subway station floor slab 2-1's cushion layer, preserving the main reinforcement 3-1 of the engineering piles. Then, densely packed primary support 4-1 can be constructed. The grid steel frame 7 of primary support 4-1 should be in close contact with the base of the existing subway station floor slab 2-1, ensuring rigid contact. During construction, care should be taken to protect the waterproof layer and cushion layer of the existing subway station floor slab 2-1.

[0081] Three φ42, 1.5m long grouting pipes are embedded in the bottom plate of each pilot tunnel, and cement slurry is injected into the pipes to harden the steel frame foundation. The bottom of the grid steel frame 7 is padded with square timber wedges, and by tightening the initial support 4-1 structure and fitting it together with the existing subway station bottom plate 2-1, an effective vertical force transmission route is formed.

[0082] When the pilot tunnel is excavated to the bottom, the pile heads of the remaining engineering piles 3 are chiseled out to the lower surface of the initial support 4-1. At the same time, the main reinforcement 3-1 of the engineering piles is reserved. Grouting pipes are reserved along the grid steel frame 7 behind the initial support 4-1. After the completion of the initial support 4-1, cement slurry is grouted around the back to fill the gaps and improve the overall self-stability. The pressure during grouting is not greater than 0.5Mpa, and dynamic compensation grouting is carried out according to the monitoring situation.

[0083] Then construct the waterproof layer. Special treatment is required for waterproofing at the location where engineering pile 3 is chiseled out. Waterproof material is applied to the head area of ​​engineering pile 3. In addition, water-expanding waterstop strips are used around the main reinforcement 3-1 of engineering pile to strengthen waterproofing. Then construct the secondary lining structure 4-2. Anchor the main reinforcement 3-1 of engineering pile 3 reserved at the top and bottom of engineering pile 3 into the secondary lining structure 4-2 and weld it to the internal secondary lining structure main reinforcement 9. The anchoring length of the main reinforcement 3-1 of engineering pile must meet the requirements of the specification, and concrete 8 is poured together.

[0084] This solves the problem of damage to the structural stress and waterproofing system of the existing subway station 2 caused by conventional technologies such as adding pull-out piles and pull-out anchor rods to the existing subway station base plate 2-1. In addition, the main reinforcement 3-1 of the engineering piles and the secondary lining structure 4-2 are cast together to form an overall stress system, which can provide permanent anti-floating effect for the existing subway station 2 structure.

[0085] (6) The engineering piles on both sides of the new tunnel are retained and reinforced and connected to the secondary lining structure of the new tunnel. Figure 2 、 Figure 3 、 Figure 4 、 Figure 5 As shown:

[0086] If the engineering piles 3 are located on both sides of the newly built tunnel 4 and invade the secondary lining structure 4-2 but not the tunnel limit, there is no need to remove the engineering piles 3. The engineering piles 3 can be used to participate in the system's joint load-bearing. The initial support 4-1 of the newly built tunnel 4 does not need to be set up at the engineering piles 3. The engineering piles 3 can be used as part of the initial support 4-1 to play a retaining role. During the construction of the initial support 4-1, three rows of closely spaced grid steel frames 7 are set on both sides of the engineering piles 3. The grid steel frames 7 are spaced 500mm apart. Mortar anchor rods 5 (locking anchor rods 5-1 can be added for enhanced fixation) are fixed to the grid steel frames 7 to stabilize the initial support 4-1. The grid steel frames 7 are designed in an annular shape, with two pieces on the top and bottom of the inner wall of the newly built tunnel 4, and one piece on each side, for a total of six pieces. The grid steel frames 7 are welded to form an annular structure.

[0087] After the initial support 4-1 is completed, the waterproof layer is constructed. Special treatment is required for waterproofing within the scope of engineering pile 3. The pile body needs to be coated with waterproof material. Then, steel bars 6 are implanted in the engineering pile 3 at intervals of 200mm in the circumferential and vertical directions. Water-expanding waterstop strips are used around the steel bars 6 to strengthen waterproofing. Then, the secondary lining structure 4-2 is constructed. The steel bars 6 implanted in the engineering pile 3 are integrally cast with the secondary lining structure 4-2. The length of the embedded steel bars in the engineering pile 3 shall not exceed the thickness of the secondary lining structure 4-2.

[0088] In the case where some engineering piles 3 fall on both sides of the newly built tunnel 4, the engineering piles 3 can be used as part of the primary support to support the external soil without removing the engineering piles 3; the circumferential and vertical reinforcement of the piles are cast together with the secondary lining structure 4-2 to form an overall force system, which can effectively transmit the load vertically and provide permanent anti-floating effect for the existing subway station 2 structure.

[0089] (7) Construction of inner lining wall on the secondary lining structure, such as Figure 3 、 Figure 8 , Figure 9 As shown:

[0090] After the completion of the initial support structure 4-1 and the secondary lining structure 4-2, due to the impact of the engineering piles 3 and the intermediate partition wall 5-2, the secondary lining structure 4-2 had numerous construction joints and a significant potential for leakage. To reduce the risk of leakage later in the new tunnel 4, a 200mm thick cast-in-place waterproof concrete lining wall was installed within the secondary lining structure 4-2, with a φ8@200 mesh installed inside the wall. The inner lining wall 4-3 was cast integrally using a trolley, improving the tunnel's waterproofing and serving as a structural safety reserve.

[0091] The invention solves the water leakage problem caused by the failure of the waterproof layer between the initial support 4-1 and the secondary lining structure 4-2 during the construction process of anchoring the main reinforcement 3-1 of the engineering pile under the existing subway station 2 into the secondary lining structure 4-2 and casting it together with the secondary lining structure 4-2 by planting reinforcement, thereby playing a role in strengthening the waterproof system.

[0092] In order to ensure the structural stability between the existing subway station 2 structure and the completed rectangular tunnel, automated monitoring can be selected:

[0093] (8) Automated monitoring, such as Figure 2 As shown:

[0094] To ensure the safety and normal operation of the existing subway station 2 and the safe construction of the new tunnel 4, monitoring projects include monitoring of the tracks, structures, expansion joints, roadbed, and the new tunnel 4 itself, and analysis and assessment are carried out. The 10m area above the newly built underground tunnel 4 is the key monitoring area, monitored using a remote automated monitoring system; the 10-30m area above the new tunnel 4 is primarily monitored using conventional monitoring methods.

[0095] The present invention constructs the newly excavated tunnel 4 in a rectangular shape, forming a rectangular tunnel. The present invention constructs the newly excavated tunnel 4 in a rectangular shape. By combining the existing engineering piles 3, the rectangular tunnel formed after construction has a more reasonable overall structure and ensures structural strength. Furthermore, the present invention can be highly integrated with the existing engineering piles 3, enabling force transmission via a shorter force transmission route, resulting in clear and distinct force distribution and strong vertical support. This further effectively controls the settlement of the existing subway station 2 above. Furthermore, due to the strong rigidity of the structural system, the impact of the existing subway trains above on the newly built tunnel 4 under long-term vibration is reduced, avoiding the problem of loosening and falling soil caused by vibration during construction of the reserved soil for the vault in previous designs, thereby ensuring the safety of construction workers. The rectangular cross-section construction is more precise and easier to control the shield limit, thus resolving the limitations of existing circular / horseshoe-shaped cross-section construction processes.

[0096] The grouting construction of the present invention performs dewatering operations before construction according to the implementation conditions to form an effective water-stop curtain, so as to eliminate the adverse effects of groundwater and pressurized water layers on underground excavation operations, reduce the water content in the excavation range, and reduce the safety risks of water and sand gushing during construction; full-section grouting can improve the geological conditions of the original stratum, play a role in stabilizing the soil, reduce the risk of soil collapse during excavation, and at the same time reduce the effect of settlement of the existing line above.

[0097] Before constructing under the existing subway station 2, the present invention first conducts a construction test on the transition section of its periphery, determines the structural support parameters according to the construction conditions of the test section, prepares for the underpass, and increases the reliability of the implementation.

[0098] The present invention constructs a new tunnel 4 under the structure of the existing subway station 2 to form a rectangular tunnel. By spraying concrete 8 between the rectangular tunnel and the existing subway station 2, the initial support 4-1 outside the rectangular tunnel is highly integrated with the structure of the existing subway station 2, realizing the zero-distance process of underpass construction and increasing the stability between the rectangular tunnel and the existing subway station 2 during operation.

[0099] The existing subway station floor 2-1 of the present invention is tightly connected to the secondary lining structure 4-2 through the main reinforcement of the engineering piles 3 located in the middle of the newly built tunnel 4. The engineering piles 3 located on both sides of the newly built tunnel 4 are reinforced with anchors, and at the same time, the anchors are connected to part of the secondary lining structure 4-2 in two reinforcement methods. Differentiated construction is carried out at different positions of the engineering piles 3, which solves the damage caused to the stress and waterproofing system of the existing subway station 2 structure by conventional technology of adding pull-out piles, pull-out anchor rods and other measures to the existing subway station floor 2-1. In addition, the main reinforcement of the engineering piles 3 and the secondary lining structure 4-2 are cast together to form an overall stress system, which can provide permanent anti-floating effect for the structure of the existing subway station 2.

[0100] The support of the rectangular tunnel structure by the engineering piles 3 of the present invention, the close arrangement of the mortar anchor rods 5 and the grid steel frame 7 can effectively control the structural settlement of the rectangular tunnel. At the same time, the station retaining piles 1 are arranged above the rectangular tunnel. For stations that use retaining piles as a bearing system, the settlement of the existing subway station 2 is further reduced; at the same time, a waterproof structure is arranged on the engineering piles 3, the rectangular tunnel support, and the secondary lining structure 4-2, and the inner lining wall 4-3 is covered with a mesh, thereby improving the overall waterproof performance of the rectangular tunnel.

[0101] It is obvious to those skilled in the art that the present invention is not limited to the details of the above-mentioned exemplary embodiments, and that the present invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the present invention. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-restrictive. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, it is intended that all changes that fall within the meaning and scope of the equivalent elements of the claims are included in the present invention, and any figure marks in the claims should not be regarded as limiting the claims involved.

Claims

1. A method for constructing a dark-excavated rectangular tunnel that passes under an existing subway station at zero distance, characterized in that: The following steps are involved: S1, determine the location of the new tunnel under the existing subway station; S2: Before construction, dewatering measures and ground reinforcement shall be carried out around the new tunnel site; S3, construction of the new tunnel transition section; S4: A new tunnel will be built under the existing subway station and the station retaining piles will be cut; S5, the engineering piles located in the middle of the new tunnel were removed, where the main reinforcement of the engineering piles was connected to the secondary lining structure; S6, retain the engineering piles on both sides of the new tunnel, plant reinforcement and connect them to the secondary lining structure; S7, construct inner lining wall on the secondary lining structure.

2. The method for constructing a dark-excavated rectangular tunnel under an existing subway station at zero distance according to claim 1 is characterized in that: The step S2 comprises: Before constructing a new tunnel, drill holes around it to check the water level. If the water level is too high and affects the underground excavation, a combination of external dewatering and full-section grouting will be used to carry out the construction. If the conditions for installing equipment are available outside the cave, a pipe well will be drilled and a high-power deep-water pump will be installed to reduce water levels in order to increase the reduction curve and enhance the pressure reduction effect. The water stopping inside the cave will be achieved by a grouting measure that combines deep hole grouting with sleeve valve pipe grouting.

3. The method for constructing a rectangular tunnel with zero distance under an existing subway station according to claim 2 is characterized in that: The grouting is carried out from bottom to top, in two steps, with an overlap length of 3m to 4m; The scope of grouting is "the soil inside the excavation line is completely grouted, and the soil outside the excavation line is grouted no more than 3m"; The unconfined compressive strength of the soil outside the excavation line reaches 0.8 MPa, and the unconfined compressive strength of the soil inside the hole reaches 0.5 MPa.

4. The method for constructing a rectangular tunnel with zero distance under an existing subway station according to claim 1 is characterized in that: The step S3 comprises: Draft the dimensions of the new tunnel based on the track surface of the new tunnel and the floor elevation of the existing subway station; Based on the surrounding rock grade and the dimensions of the new tunnel, the CRD method was used for construction; The small sections of each step are constructed by reserving core soil using the step method, and mechanized static blasting technology is used for collaborative operations.

5. A method for constructing a dark-excavated rectangular tunnel under an existing subway station at zero distance according to any one of claims 1 to 3, characterized in that: The step S4 comprises: When the new tunnel is constructed to the station retaining piles, the station retaining piles that intrude into the tunnel body shall be chiseled out; A gap of at least 50mm is reserved between the removed station retaining piles and the initial support, and a grid steel frame is erected in the initial support. At the same time, the grid steel frame is densely arranged in the area of ​​the removed station retaining piles.

6. The method for constructing a dark-excavated rectangular tunnel that passes under an existing subway station at zero distance according to claim 5 is characterized in that: The spacing between the longitudinal connecting reinforcements within 1.0m on both sides of the station retaining piles is increased to a circumferential spacing of 0.2m, and the increased length of the longitudinal connecting reinforcements is strengthened by expanding 1.0m outward from the diameter of the station retaining piles.

7. A method for constructing a dark-excavated rectangular tunnel under an existing subway station at zero distance according to any one of claims 1 to 3, characterized in that: The step S5 comprises: If the engineering piles are located in the middle of a newly built tunnel, and the initial support and secondary lining structures are being constructed outside the engineering piles, the engineering piles will be retained; after the secondary lining structures outside the engineering piles are erected, a post-casting strip will be reserved at the engineering piles, and the engineering pile area will be constructed after the strength of the secondary lining structures outside the engineering piles reaches more than 80%.

8. The method for constructing a rectangular tunnel with zero distance under an existing subway station according to claim 7 is characterized in that: The construction engineering pile area is specifically: When the pilot tunnel is excavated to the top, the engineering piles in the upper part of the pilot tunnel are chiseled out to the bottom of the cushion layer of the existing subway station floor, and the main reinforcement of the engineering piles is reserved to the bottom of the initial support. During the initial support, the grid steel frame in the initial support is tightly attached to the cushion layer of the existing subway station floor, forming a rigid contact. At the same time, grouting pipes are embedded in the pilot tunnel floor, and cement slurry is injected into the grid steel frame foundation to harden the grid steel frame foundation. The bottom of the grid steel frame is padded with square wood wedges, and the initial support is tightened to fit and fix it to the existing subway station floor. When the pilot tunnel is excavated to the bottom, the engineering piles in the lower part of the pilot tunnel are chiseled out, and the main reinforcement of the engineering piles is reserved to the top surface of the initial support. Grouting pipes are reserved along the grid steel frame behind the initial support to fill the initial support with grouting. Dynamic compensation grouting is performed during the grouting process, and the grouting pressure is not greater than 0.5Mpa. Waterproofing measures are constructed on the removed upper and lower engineering piles and engineering pile main reinforcements, and then the secondary lining structure is constructed in the post-pouring zone reserved for the engineering pile positions, and the upper and lower engineering pile main reinforcements are anchored into the secondary lining structure, and then concrete is poured together for solidification.

9. The method for constructing a dark-excavated rectangular tunnel under an existing subway station at zero distance according to claim 1, characterized in that: The step S6 comprises: If the engineering piles are located on both sides of the new tunnel and infringe upon the secondary lining structure but not upon the tunnel limit, there is no need to remove the engineering piles and the area within the engineering piles does not require initial support during construction; Three rows of grid steel frames with a spacing of 500mm are set up on both sides of the engineering piles, and waterproofing measures are implemented after the initial support is completed; Steel bars are implanted on opposite sides of the pile body with circumferential and vertical spacing of 200mm, and water-expanding waterstop strips are used around the steel bars to enhance waterproofing. During the construction of the secondary lining structure, the steel bars embedded in the engineering piles shall be cast integrally with the secondary lining structure. At the same time, the length of the steel bars embedded in the engineering piles shall not exceed the thickness of the secondary lining structure.

10. The method for constructing a dark-excavated rectangular tunnel that passes under an existing subway station at zero distance according to claim 1, characterized in that: The step S7 includes: after the initial support and the secondary lining structure are completed, a 200mm thick inner lining waterproof concrete wall is set in the secondary lining structure, and a φ8@200 mesh is hung in the inner lining waterproof concrete wall.

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