Water-rich sand layer subway station deep foundation pit auxiliary supporting structure and supporting method

Abstract

The invention belongs to the technical field of deep foundation pit dewatering, and aims to solve the problems that in the prior art, a water-rich sand layer subway station deep foundation pit is difficult to dewater, the stratum is complex, sand and water are prone to gushing in a conventional support, connection and cooperative stress is poor, drainage and pressure relief are not thorough, and support rigidity is insufficient. The invention provides an auxiliary supporting structure and method for a deep foundation pit of a subway station in a water-rich sand layer. The auxiliary supporting structure comprises an enclosure assembly, reinforced concrete enclosure piles, closed-angle steel sheet piles which are welded in an attached mode, connecting and reinforcing assemblies, expansion bolts, connecting steel bars, pressure relief and drainage assemblies and inter-pile water drainage pipes, and an overall supporting system is formed in cooperation with a hanging net sprayed concrete layer. The method has the beneficial effects that the supporting rigidity, the impermeability and the bearing capacity are improved, sand gushing, water gushing and collapse are prevented, and construction safety is guaranteed.

Description

Technical Field

[0001] This invention relates to the field of deep foundation pit dewatering technology, and more specifically, to an auxiliary support structure and support method for deep foundation pits in subway stations with water-rich sand layers. Background Technology

[0002] When constructing deep foundation pits for subway stations in water-rich sandy areas, the high sand and water content of the strata, along with the presence of perched water layers (clay) and other soft soil components, pose a severe challenge to the foundation pit support. Currently, the mainstream support method is "retaining piles + shotcrete wall protection + internal bracing". However, dewatering in such strata is difficult, and sand and water inrush between piles is very likely to occur during the excavation of the foundation pit, which can lead to stratum instability and foundation pit collapse, seriously threatening construction safety.

[0003] In existing support technologies, conventional excavation methods disturb a large area of ​​the strata, and the connection between the support structure and the retaining piles is not tight, making it difficult to form an effective synergistic protection. Drainage and pressure relief measures are not targeted enough, and problems such as incomplete drainage, blockage or failure of drainage pipes are prone to occur, making it impossible to reduce the water pressure inside the foundation pit in a timely manner. At the same time, the connection strength and rationality of some auxiliary support structures are lacking, resulting in insufficient rigidity of the overall support system, making it difficult to resist the lateral pressure and seepage impact of water-rich sand layers. This cannot meet the requirements for safe and rapid excavation of deep foundation pits under complex geological conditions. There is an urgent need for a comprehensive technical solution that is highly adaptable, reliable in support, and efficient in pressure relief to solve the above problems. Summary of the Invention

[0004] This invention aims to provide an auxiliary support structure and support method for deep foundation pits in subway stations with water-rich sand layers. This addresses the problems in the existing technology where deep foundation pits in subway stations with water-rich sand layers are prone to problems such as sand and water inrush between piles, poor connection and coordinated stress of support structures, incomplete drainage and pressure relief, and insufficient overall support rigidity. These issues make it difficult to resist lateral pressure and seepage impact, leading to foundation pit collapse and compromised construction safety.

[0005] The embodiments of the present invention are implemented as follows: This invention provides an auxiliary support structure for a deep foundation pit of a subway station in a water-rich sandy layer, which includes a retaining component, a connecting and reinforcing component, and a pressure relief and drainage component. The aforementioned retaining structure includes reinforced concrete retaining piles spaced along the sidewall of the deep foundation pit, and a number of pointed steel sheet piles continuously installed in the unexcavated soil layer close to the reinforced concrete retaining piles. The pointed steel sheet piles are arranged in close contact with the reinforced concrete retaining piles, and adjacent pointed steel sheet piles are welded and fixed together. The upper layer of pointed steel sheet piles is welded and fixed to the lower layer of pointed steel sheet piles. The aforementioned connection and reinforcement components include expansion bolts and connecting steel bars. The expansion bolts pass through bolt holes opened on the aforementioned pointed steel sheet piles and are anchored into the aforementioned reinforced concrete retaining piles. The connecting steel bars are welded and fixed to each of the aforementioned pointed steel sheet piles. The aforementioned pressure relief and drainage components include a pile-to-pile drainage pipe, which is installed in the gap between two adjacent reinforced concrete retaining piles through a pre-reserved hole in the aforementioned pointed steel sheet pile. The bottom of the aforementioned deep foundation pit has an earthwork excavation surface, and the pit wall of the aforementioned deep foundation pit is provided with a wire mesh shotcrete layer. The aforementioned wire mesh shotcrete layer, together with the aforementioned retaining components and the aforementioned connecting and reinforcing components, form an integral support system.

[0006] This embodiment discloses an auxiliary support structure for deep foundation pits in subway stations located in water-rich sandy strata. Through the coordinated operation of the aforementioned retaining components, connecting and reinforcing components, and pressure relief and drainage components, the reinforced concrete retaining piles and the closely arranged pointed steel sheet piles form a tightly connected protective barrier. This is further reinforced by expansion bolts and welded connecting steel bars to form a stable whole. Simultaneously, the aforementioned inter-pile drainage pipes efficiently discharge seepage water. Combined with the aforementioned shotcrete layer and wire mesh, a complete support system is formed. This auxiliary support structure for deep foundation pits in subway stations located in water-rich sandy strata solves the problems of loose connections, poor stress distribution, and incomplete drainage and pressure relief in water-rich sandy strata. It significantly improves the rigidity, impermeability, and bearing capacity of the support system, effectively resisting lateral pressure and seepage impact, avoiding the risks of sand and water inrush between piles and foundation pit collapse, and ensuring the safety of deep foundation pit construction.

[0007] Optionally, the tips of some of the aforementioned pointed steel sheet piles face the side of the undisturbed soil layer, and the driving depth of the aforementioned pointed steel sheet piles is not less than half the thickness of the undisturbed soil layer.

[0008] This configuration, by pointing the tips of several of the aforementioned pointed steel sheet piles toward the unexcavated soil layer, reduces driving resistance through the pointed structure, ensuring that the pointed steel sheet piles are quickly and stably embedded into the unexcavated soil layer. At the same time, the driving depth is not less than half the thickness of the unexcavated soil layer, which can effectively intercept seepage water and sand in the unexcavated soil layer, forming a reliable advanced support barrier, further enhancing the constraint capacity of the support structure on the water-rich sand layer, reducing the risk of sand and water inrush, and ensuring the safety of foundation pit excavation construction.

[0009] Optionally, the expansion bolts are arranged at intervals along the height direction of the pointed steel sheet piles, and the spacing between adjacent expansion bolts is the same as the spacing between adjacent reinforced concrete retaining piles.

[0010] This configuration ensures that the anchoring force of the expansion bolts on the pointed steel sheet piles is evenly distributed, enhancing the connection stability between the pointed steel sheet piles and the reinforced concrete retaining piles, forming a synergistic overall support effect. It also allows for precise matching of the spacing of the reinforced concrete retaining piles to achieve targeted reinforcement, effectively resisting the lateral pressure and seepage impact of the water-rich sand layer, and further reducing the risk of sand inrush, water inrush and collapse in the foundation pit.

[0011] Optionally, the connecting reinforcement bars are arranged in the transverse direction of the aforementioned pointed steel sheet piles.

[0012] This configuration allows the dispersed pointed steel sheet piles to be connected in series into a transversely integrated load-bearing structure, effectively transferring and dispersing the lateral pressure generated by the water-rich sand layer. This prevents individual pointed steel sheet piles from deforming or becoming unstable due to excessive local stress, further enhancing the synergistic support effect between the pointed steel sheet piles and the reinforced concrete retaining piles. It also improves the rigidity and anti-seepage and anti-collapse capabilities of the overall support system, ensuring the safety of deep foundation pit excavation.

[0013] Optionally, the inlet end of the above-mentioned drainage pipe between piles is provided with a filter structure, which is a filter screen wrapped around the outside of the inlet end.

[0014] This configuration, by installing a filter screen wrapped around the outside of the water inlet end of the aforementioned pile-to-pile drainage pipe as a filtration structure, can effectively intercept sand particles in the water-rich sand layer, preventing the drainage and pressure relief failure caused by sand particles clogging the aforementioned pile-to-pile drainage pipe, ensuring continuous and smooth discharge of seepage water, steadily reducing the water pressure inside the foundation pit, and at the same time reducing the impact of sand loss on the stability of the surrounding strata of the support structure, further enhancing the support system's resistance to sand inrush and collapse prevention capabilities, and ensuring the safety of deep foundation pit construction.

[0015] Optionally, the outlet end of the aforementioned inter-pile drainage pipe extends to the drainage system of the deep foundation pit, and a sealing element is provided between the aforementioned inter-pile drainage pipe and the reserved cavity of the aforementioned pointed steel sheet pile.

[0016] This configuration, by extending the outlet of the aforementioned inter-pile drainage pipe to the deep foundation pit drainage system, enables centralized and orderly discharge of seepage, ensuring the continuity and efficiency of pressure relief and drainage. Simultaneously, the installation of sealing elements between the inter-pile drainage pipe and the reserved cavity in the aforementioned pointed steel sheet pile prevents seepage from leaking through the gaps and causing localized sand inrush or ground disturbance, further enhancing the impermeability and sealing of the support system, ensuring drainage and pressure relief effects, maintaining the stability of the surrounding strata, and reducing construction safety risks.

[0017] In one embodiment of this invention, a support method for an auxiliary support structure of a deep foundation pit in a subway station with a water-rich sand layer is also provided, comprising the following steps: S1: Deep foundation pit excavation is carried out using a small-step excavation method. After a section of the earthwork excavation is completed, a layer of shotcrete with wire mesh is immediately applied to the earthwork excavation surface. S2: After the above-mentioned shotcrete layer with wire mesh is formed, use a hand-held pneumatic hammer to drive multiple pointed steel sheet piles tightly against the reinforced concrete retaining piles into the unexcavated soil layer. S3: Effectively weld the adjacent pointed steel sheet piles together, and weld and fix the upper pointed steel sheet piles that have been constructed to the lower pointed steel sheet piles that need to be fixed. Anchor the pointed steel sheet piles into the reinforced concrete retaining pile body by passing expansion bolts through the bolt holes on the pointed steel sheet piles. S4: Install connecting steel bars, and weld and fix the above-mentioned connecting steel bars to each of the above-mentioned sharp-angle steel sheet piles to form an integral support structure; S5: In the gap between two adjacent reinforced concrete retaining piles, insert the inter-pile drainage pipe through the pre-reserved hole on the pointed steel sheet pile to drain the seepage water in the foundation pit and reduce the water pressure. S6: Repeat steps S1 to S5 until the auxiliary support construction of the entire deep foundation pit is completed.

[0018] Optionally: In step S1, the single excavation depth of the small-step excavation is 0.5m to 1.0m, and the excavation width is adapted to the width of the aforementioned pointed steel sheet pile.

[0019] This setup significantly reduces the disturbance to the water-rich sandy strata during excavation, minimizing the risks of sand inrush, water inrush, and collapse. Simultaneously, it ensures that the excavation width matches the width of the aforementioned pointed steel sheet piles, guaranteeing the rapid integration of these piles with the reinforced concrete retaining piles for subsequent installation. This enables continuous construction with "excavation and support as needed," improving both the timeliness and adaptability of support while ensuring the safety and efficiency of deep foundation pit excavation.

[0020] Optionally: In step S2, the pointed steel sheet piles are driven in close contact with the reinforced concrete retaining piles.

[0021] This configuration allows the two elements to be tightly connected, forming a seamless collaborative support barrier. This effectively blocks the seepage channels between the water-rich sand layer and the sand, while ensuring that lateral pressure is evenly transmitted and shared. It also prevents stress concentration caused by loose bonding, which could lead to local support failure. This further enhances the overall support system's anti-seepage and anti-collapse capabilities, ensuring the safety of deep foundation pit construction.

[0022] Optionally: In step S3, the anchorage depth of the expansion bolt is not less than 150mm, and the weld height of the welded joint is not less than the thickness of the angled steel sheet pile.

[0023] This configuration ensures the anchorage strength between the aforementioned pointed steel sheet piles and the aforementioned reinforced concrete retaining piles, preventing loosening and detachment during the support process. Simultaneously, it requires that the weld height of the welded joints be no less than the thickness of the pointed steel sheet piles, ensuring the stability of the connection between adjacent pointed steel sheet piles and those in the upper and lower layers. This allows the entire support structure to form a reliable overall load-bearing system, effectively resisting the lateral pressure and seepage impact of the water-rich sand layer, reducing the risk of support failure, and ensuring the safety of deep foundation pit construction.

[0024] Optionally: In step S5, the insertion depth of the aforementioned inter-pile drainage pipe is not less than half of the distance between adjacent reinforced concrete retaining piles.

[0025] This configuration ensures that the drainage pipes between the piles penetrate deep into the seepage area of ​​the water-rich sand layer, efficiently capturing and draining the seepage between the piles, thus significantly reducing the water pressure inside the foundation pit. At the same time, it effectively covers the core seepage area between the piles, avoiding incomplete drainage due to shallow insertion, further strengthening the support system's ability to resist sand inrush and collapse, and ensuring the safety of deep foundation pit construction.

[0026] In summary, the auxiliary support structure and support method for deep foundation pits in subway stations in water-rich sandy strata disclosed in this invention solves the problems of loose connection of support structures, poor synergistic stress, and incomplete drainage and pressure relief in water-rich sandy strata. It significantly improves the rigidity, impermeability, and bearing capacity of the support system, effectively resists lateral pressure and seepage impact, avoids the risks of sand and water inrush between piles and foundation pit collapse, and ensures the safety of deep foundation pit construction. Attached Figure Description

[0027] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 This is a front view of an auxiliary support structure for a deep foundation pit of a subway station in a water-rich sandy layer, according to an embodiment of the present invention. Figure 2 This is a side view of an auxiliary support structure for a deep foundation pit of a subway station in a water-rich sandy layer, according to an embodiment of the present invention. Figure 3 This is a schematic diagram of the structure of the pointed steel sheet pile in an embodiment of the present invention.

[0029] Icons: 1-Enclosure component, 2-Connection and reinforcement component, 3-Pressure relief and drainage component, 4-Deep foundation pit, 5-Reinforced concrete retaining pile, 6-Sharp angle steel sheet pile, 7-Expansion bolt, 8-Connecting reinforcement, 9-Bolt hole, 10-Drainage pipe between piles, 11-Void, 12-Earth excavation face, 13-Wire mesh shotcrete layer. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0031] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0032] Example See Figure 1 , Figure 2 and Figure 3 This embodiment proposes an auxiliary support structure for a deep foundation pit of a subway station in a water-rich sandy layer, including a retaining component 1, a connecting and reinforcing component 2, and a pressure relief and drainage component 3. The retaining component 1 includes reinforced concrete retaining piles 5 spaced along the side wall of the deep foundation pit 4, and a number of pointed steel sheet piles 6 continuously set in the unexcavated soil layer close to the reinforced concrete retaining piles 5. The pointed steel sheet piles 6 are arranged in close contact with the reinforced concrete retaining piles 5, and adjacent pointed steel sheet piles 6 are welded and fixed together. The upper pointed steel sheet piles 6 are welded and fixed together with the lower pointed steel sheet piles 6. The connecting reinforcement component 2 includes expansion bolts 7 and connecting steel bars 8. The expansion bolts 7 pass through bolt holes 9 opened on the pointed steel sheet piles 6 and are anchored into the reinforced concrete retaining piles 5. The connecting steel bars 8 are welded and fixed to each pointed steel sheet pile 6 to form an integral reinforcement structure. The pressure relief and drainage component 3 includes a pile-to-pile drainage pipe 10, which is installed in the gap between two adjacent reinforced concrete retaining piles 5 through a pre-reserved hole 11 on the pointed steel sheet pile 6. The bottom of the deep foundation pit 4 has an earthwork excavation surface 12, and the pit wall of the deep foundation pit 4 is provided with a wire mesh sprayed concrete layer 13. The wire mesh sprayed concrete layer 13, together with the retaining components 1 and the connecting reinforcement components 2, form an integral support system.

[0033] This implementation scheme discloses an auxiliary support structure for a deep foundation pit of a subway station in a water-rich sandy layer. Through the coordinated operation of the retaining component 1, the connecting reinforcement component 2, and the pressure relief and drainage component 3, the reinforced concrete retaining piles 5 and the closely arranged sharp-angled steel sheet piles 6 form a tightly connected protective barrier. Then, the piles are anchored with expansion bolts 7 and welded with connecting steel bars 8 to form a stable whole. At the same time, the drainage pipes 10 between the piles are used to efficiently drain the seepage water between the piles. Combined with the shotcrete layer 13 with wire mesh, a complete support system is formed. Thus, this auxiliary support structure for a deep foundation pit of a subway station in a water-rich sandy layer solves the problems of loose connection of support structures, poor synergistic force, and incomplete drainage and pressure relief in water-rich sandy strata. It significantly improves the rigidity, impermeability, and bearing capacity of the support system, effectively resists lateral pressure and seepage impact, avoids the risk of sand and water inrush between piles and foundation pit collapse, and ensures the construction safety of the deep foundation pit 4.

[0034] See Figure 1 , Figure 2 and Figure 3 The pointed ends of several sheet piles 6 face the unexcavated soil layer. The driving depth of the pointed sheet piles 6 is not less than half the thickness of the unexcavated soil layer. By facing the pointed ends of several sheet piles 6 towards the unexcavated soil layer, the driving resistance can be reduced by the pointed structure, ensuring that the pointed sheet piles 6 are quickly and stably embedded in the unexcavated soil layer. At the same time, the driving depth of not less than half the thickness of the unexcavated soil layer can effectively intercept seepage water and sand in the unexcavated soil layer, forming a reliable advanced support barrier, further enhancing the constraint capacity of the support structure on the water-rich sand layer, reducing the risk of sand and water inrush, and ensuring the safety of foundation pit excavation construction.

[0035] Expansion bolts 7 are arranged at intervals along the height direction of the pointed steel sheet piles 6, and the spacing between adjacent expansion bolts 7 is the same as the spacing between adjacent reinforced concrete retaining piles 5. This ensures that the anchoring force of the expansion bolts 7 on the pointed steel sheet piles 6 is evenly distributed, strengthens the connection stability between the pointed steel sheet piles 6 and the reinforced concrete retaining piles 5, and forms a synergistic overall support effect. It also allows for precise matching of the arrangement spacing of the reinforced concrete retaining piles 5 to achieve targeted reinforcement, effectively resisting the lateral pressure and seepage impact of the water-rich sand layer, and further reducing the risk of sand inrush, water inrush and collapse of the foundation pit.

[0036] See Figure 1 , Figure 2 and Figure 3 The connecting steel bars 8 are arranged in the transverse direction along several pointed steel sheet piles 6. This allows the dispersed pointed steel sheet piles 6 to be connected in series into a transverse integral load-bearing structure, effectively transmitting and dispersing the lateral pressure generated by the water-rich sand layer. This prevents individual pointed steel sheet piles 6 from deforming or becoming unstable due to excessive local stress, further strengthening the synergistic support effect between the pointed steel sheet piles 6 and the reinforced concrete retaining piles 5, improving the rigidity and anti-seepage and anti-collapse capabilities of the overall support system, and ensuring the safety of deep foundation pit 4 excavation.

[0037] The inlet end of the pile-to-pile drainage pipe 10 is equipped with a filter structure, which is a filter screen wrapped around the outside of the inlet end (not shown in the figure). By setting the filter screen wrapped around the outside of the inlet end of the pile-to-pile drainage pipe 10 as a filter structure, sand particles in the water-rich sand layer can be effectively intercepted, avoiding the failure of drainage and pressure relief of the pile-to-pile drainage pipe 10 due to sand blockage. This ensures that the seepage water is continuously and smoothly discharged, stabilizes and reduces the water pressure inside the foundation pit, and reduces the impact of sand loss on the stability of the surrounding strata of the support structure. This further enhances the support system's ability to resist sand inrush and collapse, and ensures the construction safety of the deep foundation pit 4.

[0038] See Figure 1 , Figure 2 and Figure 3 The outlet end of the inter-pile drainage pipe 10 extends to the drainage system of the deep foundation pit 4 (not shown in the figure). A sealing element (not shown in the figure) is provided between the inter-pile drainage pipe 10 and the reserved cavity 11 of the pointed steel sheet pile 6. By extending the outlet end of the inter-pile drainage pipe 10 to the drainage system of the deep foundation pit 4, the seepage water can be discharged in a centralized and orderly manner, ensuring the continuity and efficiency of pressure relief and drainage. At the same time, the sealing element installed between the inter-pile drainage pipe 10 and the reserved cavity 11 of the pointed steel sheet pile 6 can prevent seepage water from leaking through the gap and causing local sand inrush or ground disturbance, further strengthening the anti-seepage sealing of the support system, ensuring the drainage and pressure relief effect and the stability of the surrounding strata of the foundation pit, and reducing construction safety risks.

[0039] See Figure 1 , Figure 2 and Figure 3 In one embodiment of this invention, a support method for an auxiliary support structure of a deep foundation pit in a subway station with a water-rich sand layer is also provided, comprising the following steps: S1: The deep foundation pit 4 is excavated using a small-step excavation method. After the excavation of a section of the earthwork excavation surface 12 is completed, the mesh-coated shotcrete layer 13 is immediately constructed on the earthwork excavation surface 12. S2: After the shotcrete layer 13 is formed, use a hand-held pneumatic hammer to drive multiple sharp-angled steel sheet piles 6 tightly against the reinforced concrete retaining piles 5 and continuously drive them into the unexcavated soil layer. S3: Effectively weld the adjacent pointed steel sheet piles 6 together, and weld and fix the upper pointed steel sheet piles 6 that have been constructed to the lower pointed steel sheet piles 6 that are to be fixed. Anchor the pointed steel sheet piles 6 into the reinforced concrete retaining piles 5 by passing the expansion bolts 7 through the bolt holes 9 on the pointed steel sheet piles 6. S4: Install connecting steel bars 8, and weld and fix the connecting steel bars 8 to each sharp angle steel sheet pile 6 to form an integral support structure; S5: In the gap between two adjacent reinforced concrete retaining piles 5, the inter-pile drainage pipe 10 is inserted through the hole 11 reserved on the pointed steel sheet pile 6 to drain the seepage water in the foundation pit and reduce the water pressure. S6: Repeat steps S1 to S5 until the auxiliary support construction of the entire deep foundation pit 4 is completed.

[0040] See Figure 1 , Figure 2 and Figure 3 In step S1, the single excavation depth of the small-step excavation is 0.5m to 1.0m, and the excavation width is adapted to the width of the pointed steel sheet pile 6. This can significantly reduce the disturbance of the water-rich sandy strata during excavation and reduce the risks of sand inrush, water inrush and collapse. At the same time, adapting the excavation width to the width of the pointed steel sheet pile 6 can ensure that the subsequent installation of the pointed steel sheet pile 6 into the reinforced concrete retaining pile 5 can be achieved, realizing continuous construction of "excavation and support as you go". This not only improves the timeliness and adaptability of support, but also ensures the safety and efficiency of the deep foundation pit 4 excavation construction.

[0041] In step S2, the pointed steel sheet pile 6 is driven into the reinforced concrete retaining pile 5 while maintaining a tight fit. This allows the two to be closely connected to form a seamless collaborative support barrier, effectively blocking the seepage channels of water and sand in the water-rich sand layer. At the same time, it ensures that the lateral pressure is evenly transmitted and shared, avoiding stress concentration caused by poor fit that could lead to local support failure. This further enhances the overall support system's anti-seepage and anti-collapse capabilities and ensures the construction safety of the deep foundation pit 4.

[0042] See Figure 1 , Figure 2 and Figure 3 In step S3, the anchorage depth of the expansion bolt 7 is not less than 150mm, and the weld height of the welded joint is not less than the plate thickness of the pointed steel sheet pile 6. This ensures the anchorage connection strength between the pointed steel sheet pile 6 and the reinforced concrete retaining pile 5, preventing loosening and falling off during the support process. At the same time, the weld height of the welded joint is required to be not less than the plate thickness of the pointed steel sheet pile 6, ensuring the connection stability of adjacent pointed steel sheet piles 6 and the upper and lower layers of pointed steel sheet piles 6, so that the entire support structure forms a reliable overall force system, effectively resisting the lateral pressure and seepage impact of the water-rich sand layer, reducing the risk of support failure, and ensuring the construction safety of the deep foundation pit 4.

[0043] In step S5, the insertion depth of the inter-pile drainage pipe 10 is not less than half the distance between adjacent reinforced concrete retaining piles 5. This ensures that the inter-pile drainage pipe 10 penetrates deep into the seepage area of ​​the water-rich sand layer, efficiently captures and discharges the seepage between the piles, and fully reduces the water pressure inside the foundation pit. At the same time, it can effectively cover the core seepage area between the piles, avoid incomplete drainage due to shallow insertion, further strengthen the anti-sand surge and anti-collapse capabilities of the support system, and ensure the construction safety of the deep foundation pit 4.

[0044] See Figure 1 , Figure 2 and Figure 3In this embodiment, the pointed steel sheet piles 6 are continuously driven into the undisturbed soil layer, closely attached to the reinforced concrete retaining piles 5. The pointed ends facing the soil layer can reduce the driving resistance. The welding and fixing of adjacent and upper and lower steel sheet piles, combined with the anchoring effect of expansion bolts 7 passing through bolt holes 9, can form a seamless and synergistic force-bearing structure, eliminating the seepage and sand inrush channels caused by joint gaps. The connecting steel bars 8 are arranged transversely along the steel sheet piles, further connecting the dispersed steel sheet piles into a whole, greatly improving the overall rigidity and deformation resistance of the support system. At the same time, the drainage pipes 10 between the piles extend to more than half the distance between adjacent retaining piles. Combined with the filter screen at the inlet end and the sealing design at the outlet end, it can accurately capture seepage between the piles and achieve centralized discharge, thoroughly reducing the water pressure inside the foundation pit. Combined with the mesh-coated shotcrete layer 13 on the pit wall of the deep foundation pit 4, a three-in-one support mode of "protection-reinforcement-pressure relief" is formed. For the complex geology of water-rich sand layer mixed with soft soil, it can achieve all-round safety protection for the foundation pit and ensure the stability and controllability of the construction process.

[0045] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An auxiliary support structure for deep foundation pits in subway stations with water-rich sand layers, characterized in that: It includes an enclosure component (1), a connection and reinforcement component (2), and a pressure relief and drainage component (3); The retaining component (1) includes reinforced concrete retaining piles (5) spaced along the side wall of the deep foundation pit (4), and a number of pointed steel sheet piles (6) continuously set in the unexcavated soil layer close to the reinforced concrete retaining piles (5). The number of pointed steel sheet piles (6) are arranged in close contact with the reinforced concrete retaining piles (5), and adjacent pointed steel sheet piles (6) are welded and fixed together. The upper pointed steel sheet piles (6) are welded and fixed together with the lower pointed steel sheet piles (6). The connection reinforcement component (2) includes expansion bolts (7) and connecting steel bars (8). The expansion bolts (7) pass through bolt holes (9) opened on the pointed steel sheet piles (6) and are anchored into the reinforced concrete retaining piles (5). The connecting steel bars (8) are welded and fixed to each of the pointed steel sheet piles (6). The pressure relief and drainage assembly (3) includes a pile-to-pile drainage pipe (10), which is installed in the gap between two adjacent reinforced concrete retaining piles (5) through a pre-reserved hole (11) on the pointed steel sheet pile (6). The bottom of the deep foundation pit (4) has an earthwork excavation surface (12), and the pit wall of the deep foundation pit (4) is provided with a wire mesh sprayed concrete layer (13). The wire mesh sprayed concrete layer (13), together with the retaining component (1) and the connecting reinforcement component (2), form an integral support system.

2. The auxiliary support structure for deep foundation pits of subway stations in water-rich sandy layers according to claim 1, characterized in that: The tips of several of the pointed steel sheet piles (6) face the side of the unexcavated soil layer, and the driving depth of the pointed steel sheet piles (6) is not less than half the thickness of the unexcavated soil layer.

3. The auxiliary support structure for deep foundation pits of subway stations in water-rich sandy layers according to claim 1, characterized in that: The expansion bolts (7) are arranged at intervals along the height direction of the pointed steel sheet piles (6), and the distance between adjacent expansion bolts (7) is the distance between adjacent reinforced concrete retaining piles (5).

4. The auxiliary support structure for deep foundation pits of subway stations in water-rich sandy layers according to claim 1, characterized in that: The connecting steel bars (8) are arranged in the transverse direction along the plurality of the pointed steel sheet piles (6).

5. The auxiliary support structure for deep foundation pits of subway stations in water-rich sandy layers according to claim 1, characterized in that: The inlet end of the drainage pipe (10) between piles is provided with a filter structure, which is a filter screen wrapped around the outside of the inlet end.

6. The auxiliary support structure for deep foundation pits of subway stations in water-rich sandy layers according to claim 1, characterized in that: The outlet end of the inter-pile drainage pipe (10) extends to the drainage system of the deep foundation pit (4), and a sealing element is provided between the inter-pile drainage pipe (10) and the reserved cavity (11) of the pointed steel sheet pile (6).

7. A method for auxiliary support of deep foundation pits in subway stations with water-rich sand layers, characterized in that, Includes the following steps: S1: Deep foundation pit (4) earthwork excavation is carried out by small step excavation method. After a section of earthwork excavation surface (12) is excavated, a wire mesh shotcrete layer (13) is immediately constructed on the earthwork excavation surface (12). S2: After the shotcrete layer (13) is formed, use a hand-held pneumatic pick to drive multiple pointed steel sheet piles (6) tightly against the reinforced concrete retaining piles (5) into the unexcavated soil layer. S3: Effectively weld the adjacent pointed steel sheet piles (6), and weld the upper pointed steel sheet piles (6) that have been completed to the lower pointed steel sheet piles (6) to be fixed. Anchor the pointed steel sheet piles (6) into the reinforced concrete retaining pile (5) by passing expansion bolts (7) through the bolt holes (9) on the pointed steel sheet piles (6). S4: Install connecting steel bars (8), and weld and fix the connecting steel bars (8) to each of the pointed steel sheet piles (6) to form an integral support structure; S5: In the gap between two adjacent reinforced concrete retaining piles (5), the inter-pile drainage pipe (10) is inserted through the hole (11) reserved on the pointed steel sheet pile (6) to drain the seepage water in the foundation pit and reduce the water pressure. S6: Repeat steps S1 to S5 until the auxiliary support construction of the entire deep foundation pit (4) is completed.

8. The method for auxiliary support of deep foundation pits in subway stations with water-rich sand layers according to claim 7, characterized in that: In step S1, the single excavation depth of the small-step excavation is 0.5m to 1.0m, and the excavation width is adapted to the width of the pointed steel sheet pile (6).

9. The method for auxiliary support of deep foundation pits in subway stations with water-rich sand layers according to claim 7, characterized in that: In step S2, the pointed steel sheet pile (6) maintains a close fit with the reinforced concrete retaining pile (5) during the driving process.

10. The method for auxiliary support of deep foundation pits in subway stations with water-rich sand layers according to claim 7, characterized in that: In step S3, the anchoring depth of the expansion bolt (7) is not less than 150mm, and the weld height of the welded joint is not less than the plate thickness of the pointed steel sheet pile (6).

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