Foundation pit support construction method

Abstract

The application discloses a kind of foundation pit support construction methods, it is related to foundation pit construction technical field, by mortise and tenon engagement structure and sealing consolidation mutual effect, cut off groundwater along pile board joint seepage channel, greatly improve the water stop reliability of connection position, overcome the defect that adjacent pile body between water stop connection mode is poor, node is easy to leak, both guarantee the operation safety during foundation pit excavation, and also give long-term waterproof performance of basement structure.Construction and pile foundation steel casing and concrete prefabricated plate are connected with the main structure of basement, so that the support pile and prefabricated plate formed in the early stage are directly used as permanent components of the outer wall of basement to participate in structural stress.The temporary support construction and permanent outer wall construction are combined into one, which eliminates the repeated procedures of removing temporary support and pouring permanent outer wall by formwork in the traditional method, and realizes the integrated construction of foundation pit support and permanent structure.

Description

Technical Field

[0001] This invention relates to the field of foundation pit construction technology, and in particular to a foundation pit support construction method. Background Technology

[0002] Foundation pit support technology is a crucial aspect of underground engineering construction. With the continuous advancement of urbanization and the increasing demand for underground space development, foundation pit support technology has evolved from early simple slope excavation and wooden sheet pile support to various forms such as steel sheet piles, cast-in-place piles, and diaphragm walls. In recent years, with the promotion of prefabricated construction concepts and the increasing requirements for green construction, the industry has placed higher demands on foundation pit support technology, namely, ensuring support safety while also considering the recycling of materials and improving construction efficiency.

[0003] Currently, the common construction method for foundation pit support typically involves designing and constructing the support structure and the permanent basement structure separately. During construction, temporary support structures (such as sheet piles and cast-in-place piles) are first constructed around the foundation pit, and corresponding water-stop curtains are installed to ensure slope stability and groundwater sealing during the excavation process. After the foundation pit excavation is completed, the main basement structure, including permanent components such as the floor slab, shear walls, and exterior walls, is constructed inside the support structure. After the main basement structure is completed, the temporary support structure is either dismantled and recycled or directly abandoned underground.

[0004] However, in the existing technology, temporary support and permanent basement exterior walls are constructed separately, which involves many procedures and a long construction period, increasing the overall construction cost. Furthermore, the water-stop connection method between adjacent piles in the traditional support structure is not reliable enough, and leakage is prone to occur at the joints, affecting the safety of the foundation pit construction and the long-term waterproof performance of the basement. Summary of the Invention

[0005] The main objective of this invention is to propose a construction method for foundation pit support, which aims to solve the technical problems in the prior art where temporary support and permanent basement exterior walls are constructed separately, resulting in numerous procedures, long construction periods, increased overall construction costs, and insufficient reliability of the water-stop connection method between adjacent piles in traditional support structures, which easily leads to leakage at the joints, affecting the safety of foundation pit construction and the long-term waterproof performance of the basement.

[0006] To achieve the above objectives, in a first aspect, the present invention proposes a method for constructing foundation pit support, comprising the following steps: The support structure is designed in reverse based on the permanent service conditions of the basement wall, and the construction parameters of the support structure are obtained; wherein, the construction parameters include the arrangement parameters, structural dimensions, cross-sectional parameters and reinforcement parameters of the steel casing of the pile foundation; According to the construction parameters, the foundation pit pile foundation steel casing is constructed around the foundation pit so that an insertion area for installing the precast concrete slab is formed between two adjacent foundation pile foundation steel casings; wherein, two oppositely arranged water-stop fasteners are provided on the outer wall of each foundation pit pile foundation steel casing. The precast concrete slab is fastened and installed to the insertion area along a preset installation direction to obtain a continuous retaining and water-stopping support surface; wherein, the precast concrete slab has a plug-in component adapted to the insertion area; A consolidation operation is performed at the connection position between the precast concrete slab and the steel casing of the foundation pit pile foundation to obtain a tenon-and-mortise permanent joint; wherein, the consolidation operation includes limiting, sealing and consolidation; The construction connects the basement main structure with the steel casing and precast concrete slab of the pile foundation, making the steel casing and precast concrete slab a permanent component of the basement exterior wall.

[0007] In one embodiment, the step of reverse-engineering the support structure based on the permanent service conditions of the basement walls and obtaining the construction parameters of the support structure includes: Based on the lateral earth pressure, groundwater pressure, impermeability grade, deformation control, and durability requirements of the basement exterior wall during the permanent use phase, determine the load-bearing capacity, crack resistance, and impermeability control indicators of the exterior wall. Based on the control indicators, the diameter, wall thickness, spacing, and embedment depth of the steel casing for the pile foundation, as well as the thickness, width, and reinforcement of the precast concrete slab, are determined. Based on the excavation conditions of the foundation pit during the construction phase, temporary support calculations are performed on the determined steel casing and precast concrete slab of the pile foundation. Based on the combined verification results of permanent service conditions and construction conditions, the structural parameters of the pile foundation steel casing and precast concrete slab are corrected to obtain the construction parameters of the support structure.

[0008] In one embodiment, the step of constructing the foundation pit pile foundation steel casing around the foundation pit according to the construction parameters, so as to form an insertion area for installing the precast concrete slab between two adjacent pile foundation steel casings, includes: Surveying and setting out along the perimeter of the foundation pit to determine the center line, joint line, and corner control points of the steel casing for the pile foundation; The longitudinal water-stop fasteners are prefabricated on the steel casing of the pile foundation; wherein the water-stop fasteners include fastening edges, guide grooves or connecting edge ribs; The steel casings of the pile foundations are driven one by one to the design depth, and their planar position and verticality are controlled so that an insertion area for installing the precast concrete slab is formed between two adjacent steel casings of the pile foundations.

[0009] In one embodiment, before the step of fastening and installing the precast concrete slab to the insertion area along a preset installation direction to obtain a continuous retaining and water-stopping support surface, the method further includes: For any two adjacent steel casings of the pile foundation, a corresponding precast concrete slab is prefabricated; wherein, the two ends of the precast concrete slab are formed with the plug-in member, which is at least one of the tenon, groove, dovetail edge or step edge.

[0010] In one embodiment, the step of fastening and installing the precast concrete slab to the insertion area along a preset installation direction to obtain a continuous retaining and water-stopping support surface includes: Excavation of the foundation pit is carried out inside the steel casing of the pile foundation. The precast concrete slab is hoisted to the top of the insertion area and fastened to the insertion area along the preset installation direction to form the current support layer; After the installation of the precast concrete slabs of the current support layer is completed, the excavation of the next layer of foundation pit and the installation of the precast concrete slabs continue until the continuous retaining and water-stopping support surface is formed.

[0011] In one embodiment, the step of consolidating the connection between the precast concrete slab and the steel casing of the foundation pit pile to obtain a tenon-and-mortise permanent joint includes: A water-stopping material is installed in the joint between the steel casing of the pile foundation and the precast concrete slab to form the first water-stopping barrier; wherein, the water-stopping material is an elastic water-stopping material or a water-swellable water-stopping material. The precast concrete slab is positioned to limit its movement. Grouting material is injected into the connection position between the insertion area and the corresponding insertion piece to fill the corresponding installation gap and perform consolidation work to form a second water-stopping barrier. The surface of the node is waterproofed and sealed to form the continuous retaining and water-stopping node.

[0012] In one embodiment, the step of installing a water-stopping material in the joint between the steel casing of the pile foundation and the precast concrete slab to form a first water-stopping barrier includes: Water-stopping material is installed along the seepage path in the joint between the steel casing of the pile foundation and the precast concrete slab to form the first water-stopping barrier.

[0013] In one embodiment, the step of constructing the basement main structure connected to the pile foundation steel casing and precast concrete slab, making the pile foundation steel casing and precast concrete slab a permanent component of the basement exterior wall, includes: The basement floor slab and inner lining wall are constructed sequentially to connect the pile foundation steel casing and the precast concrete slab with the basement floor slab and inner lining wall as a whole, forming the permanent component.

[0014] In one embodiment, prior to the step of performing waterproof sealing treatment on the node surface to form the continuous retaining and water-stopping node, the method further includes: The sealing performance of the first and second water-stop barriers was tested sequentially. If the test results do not meet the preset requirements, waterproofing and reinforcement work will be carried out.

[0015] In one embodiment, prior to the step of driving each of the pile foundation steel casings to the design depth and controlling their planar position and verticality to form an insertion zone for installing the precast concrete slab between two adjacent pile foundation steel casings, the method further includes: The surface of the steel casing of the pile foundation is subjected to anti-corrosion treatment.

[0016] The technical solution of this invention directly converts the support system constructed by pile foundation steel casing and precast concrete slabs into a permanent basement exterior wall, achieving a combination of temporary and permanent features. In implementation, the construction parameters of the support structure are first determined in reverse based on the permanent service conditions of the basement wall. These parameters include the arrangement parameters and structural dimensions of the pile foundation steel casing, as well as the cross-sectional parameters and reinforcement parameters of the precast concrete slabs. This ensures that the subsequently constructed pile foundation steel casing and precast concrete slabs can not only withstand lateral earth pressure and provide a water-stopping barrier during the excavation stage, but also meet the structural bearing capacity and durability requirements for the permanent use stage as the basement exterior wall. Subsequently, according to these construction parameters, pile foundation steel casings are constructed around the excavation pit, leaving an insertion area between adjacent pile foundation steel casings for installing precast concrete slabs. Each pile foundation steel casing has two pre-installed, oppositely arranged water-stopping fasteners on its outer wall, while the precast concrete slabs have fasteners adapted to the insertion area. When the precast concrete slab is pushed into the insertion area and fastened along the preset installation direction, the insertion piece and the water-stop fastener interlock and lock together, instantly forming a continuous retaining and water-stopping support surface. This eliminates the need for an additional independent water-stop curtain, reducing a construction step and shortening on-site operation time. After the fastening installation is completed, the connection between the precast concrete slab and the steel casing of the foundation pit pile is consolidated. This consolidation includes limiting, sealing, and consolidation treatment. Limiting ensures the accurate relative position of the slab and pile; sealing blocks the seepage path; and consolidation forms a tenon-and-mortise permanent joint at the connection point, bearing overall stress. This joint, through the combined effect of the tenon-and-mortise interlocking structure and the sealing consolidation, cuts off the seepage channel of groundwater along the pile-slab joint, significantly improving the water-stopping reliability of the connection. It overcomes the defects of poor reliability and easy leakage at joints in traditional temporary support structures between adjacent piles, ensuring operational safety during foundation pit excavation and providing long-term waterproofing performance to the basement structure. Subsequently, the construction of the basement main structure, connected to the pile foundation steel casing and precast concrete slabs, allowed the previously formed support piles and precast slabs to directly participate in the structural stress as permanent components of the basement exterior walls. This combined temporary support construction with permanent exterior wall construction, eliminating the repetitive steps of first dismantling the temporary support and then erecting formwork and pouring the permanent exterior wall, significantly reducing the number of procedures, shortening the construction period, and lowering the overall construction cost. This achieved integrated construction of the foundation pit support and the permanent structure. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0018] Figure 1 The flowchart is for the foundation pit support construction method provided by the present invention.

[0019] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0020] 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 a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0021] It should be noted that if the embodiments of the present invention involve directional indicators (such as up, down, left, right, front, back, etc.), the directional indicators are only used to explain the relative positional relationship and movement of the components in a specific posture. If the specific posture changes, the directional indicators will also change accordingly.

[0022] Furthermore, if the embodiments of this invention involve descriptions such as "first" or "second," these descriptions are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined with "first" or "second" may explicitly or implicitly include at least one of those features. Additionally, the use of "and / or" or "and / or" throughout the text includes three parallel solutions. For example, "A and / or B" includes solution A, solution B, or a solution where both A and B are satisfied simultaneously. Furthermore, the technical solutions of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or impossible to implement, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed by this invention.

[0023] This invention proposes a method for foundation pit support construction.

[0024] Please see Figure 1 To facilitate understanding, this method for constructing foundation pit support includes the following steps: S100. Design the support structure in reverse according to the permanent service conditions of the basement wall, and obtain the construction parameters of the support structure; wherein, the construction parameters include the arrangement parameters, structural dimensions, cross-sectional parameters and reinforcement parameters of the steel casing of the pile foundation.

[0025] Specifically, during the construction preparation phase, the support structure is first designed in reverse based on the permanent service conditions of the basement walls. This reverse design, based on the permanent structural functional requirements of the basement exterior walls during normal building use, such as lateral water and soil pressure, ground overload, and waterproofing, incorporates the pile foundation steel casing and precast concrete slabs, typically used for temporary support, into the permanent exterior wall system. This allows the selection and parameter determination of the support structure to consider both its temporary and permanent structural functions, providing a dual-objective guidance and effectively avoiding the material waste and construction delays caused by the traditional approach of having independent temporary and permanent support structures and overlapping procedures.

[0026] It is important to note that the construction parameters obtained through reverse engineering fall into two categories: one is the layout parameters and structural dimensions of the steel casing for the pile foundation, including the planar spacing, pile diameter, wall thickness, embedment depth, and top elevation of the steel casing; the other is the cross-sectional parameters and reinforcement parameters of the precast concrete slab, including the thickness, width, height, concrete strength grade, main reinforcement specifications and spacing, and stirrup specifications and distribution. By accurately calculating and determining these construction parameters, it is possible to ensure, from the outset, that the steel casing and precast concrete slab possess sufficient load-bearing capacity and deformation control capabilities during both the support and permanent service stages, laying a reliable parameter foundation for subsequent construction steps.

[0027] S200. According to the construction parameters, construct the foundation pit pile foundation steel casing around the foundation pit so that an insertion area for installing the precast concrete slab is formed between two adjacent foundation pile foundation steel casings; wherein, two oppositely arranged water-stop fasteners are provided on the outer wall of each foundation pit pile foundation steel casing.

[0028] Specifically, based on the construction parameters determined in S100, steel casings for each pile foundation are constructed sequentially along the perimeter of the foundation pit. During construction, suitable equipment such as rotary drilling rigs or long spiral drilling rigs can be used to drill holes according to the preset pile positions. Subsequently, the prefabricated steel casings are lowered to the design elevation, and the steel casings for the pile foundation are fixed and formed by pouring concrete or grouting.

[0029] It is particularly important to clarify that the spacing between two adjacent steel casings for pile foundations should strictly adhere to the arrangement spacing specified in the construction parameters. This ensures that a predetermined insertion zone naturally forms between the two adjacent steel casings, which serves as the installation space for the subsequent precast concrete slabs. By precisely controlling the planar position of the steel casings, it can be ensured that the width of the insertion zone matches the cross-sectional dimensions of the precast concrete slabs, providing reliable spatial conditions for the smooth installation of the precast slabs. Two opposing water-stop fasteners are installed on the outer wall of each steel casing. These water-stop fasteners are arranged along the vertical length of the steel casing, with each fastener located on the outer wall of the steel casing facing the adjacent insertion zones on both sides, forming a fastening groove structure with the opening facing the insertion zone. The installation of water-stop fasteners provides positioning and guidance conditions for the subsequent fastening of precast concrete slabs. On the other hand, the tight interlocking between the fasteners and the plugs forms a physical water-stop barrier at the joint, fundamentally solving the technical problems of insufficient reliability of traditional inter-pile water-stopping measures and easy leakage at the joint. This significantly improves the safety of the foundation pit construction stage and the waterproofing performance of the basement during long-term use.

[0030] S300. The precast concrete slab is fastened and installed to the insertion area along the preset installation arrangement direction to obtain a continuous retaining and water-stopping support surface; wherein, the precast concrete slab has a plug-in component adapted to the insertion area.

[0031] Specifically, after the construction of each pile foundation steel casing is completed, precast concrete slabs are installed one by one into the insertion area between adjacent pile foundation steel casings according to the preset installation arrangement direction. During installation, hoisting equipment is usually used to lift the precast concrete slabs to the upper part of the corresponding insertion area, and then slowly lower them vertically, so that the insertion parts on both sides of the precast slabs are respectively engaged with the water-stop fasteners on the outer wall of the corresponding pile foundation steel casing, until the precast slabs are in place at the design elevation.

[0032] To further clarify, the precast concrete slabs are fitted with connectors adapted to the insertion area. The cross-sectional shape of these connectors matches the interlocking grooves of the water-stop connectors. The two are connected by a mortise and tenon joint, forming a tight mechanical connection. This ensures reliable positioning between the precast slabs and the steel casing of the pile foundation, while also creating an effective water-stopping structure at the joints. After the precast concrete slabs are sequentially installed around the perimeter of the foundation pit, the slabs and the steel casing together form a continuous retaining and water-stopping support surface. This support surface forms a closed or semi-closed enclosure structure in the horizontal direction, effectively resisting the lateral pressure of the soil outside the pit during excavation, while simultaneously blocking the seepage of groundwater into the pit through the gaps between the piles. This satisfies both the safety of the support and the reliability of the water-stopping mechanism, solving the problem of independent support structures and overlapping procedures in traditional support methods.

[0033] S400, Perform consolidation work on the connection position between the precast concrete slab and the steel casing of the foundation pit pile foundation to obtain a tenon-and-mortise permanent joint; wherein, the consolidation work includes limiting, sealing and consolidation.

[0034] Specifically, after the precast concrete slab and the steel casing of the pile foundation are installed together, a systematic consolidation operation is required at the connection point between the two to ultimately form a tenon-and-mortise permanent joint with reliable force transmission and waterproof performance.

[0035] It is important to clarify that the consolidation process consists of three steps: limiting, sealing, and consolidation. These three steps are interconnected and progressively advance to ensure the structural integrity of the node.

[0036] The limiting process refers to temporarily fixing the position of the precast concrete slab within the insertion area to prevent displacement or deflection during subsequent sealing and consolidation operations. Specifically, wedges, temporary bolts, or spot welding can be used to temporarily constrain the precast slab, ensuring that the slab and the connector remain in the correct interlocking position.

[0037] The sealing process refers to the seepage-proof sealing treatment of the joint between the precast concrete slab and the steel casing of the pile foundation. Specifically, water-swellable sealing strips, elastic sealants, or grouting can be used to completely seal the contact surfaces and gaps between the connectors and the water-stop fasteners, eliminating channels for groundwater infiltration and ensuring that the long-term waterproofing performance at the joint meets the requirements for the permanent use of the basement.

[0038] The consolidation process refers to the structural connection between the precast concrete slab and the steel casing of the pile foundation at the joint, forming a unified load-bearing structure. Specifically, consolidation can be achieved through methods such as welding embedded parts, anchor bolt connections, or partial post-cast concrete, depending on the construction parameters. This ensures the joint has the capacity to transmit horizontal shear force, vertical loads, and bending moments, thereby guaranteeing a coordinated load-bearing structure between the support structure and the permanent exterior wall structure of the basement.

[0039] Through the sequential implementation of three processes, the connection between the precast concrete slab and the steel casing of the pile foundation ultimately forms a mortise and tenon joint for both temporary and permanent installations. This joint draws upon the geometric interlocking principle of traditional mortise and tenon joints, spatially interlocking the inserts of the precast slab with the water-stop fasteners of the casing. Supplemented with sealing and consolidation measures, this ensures that the joint meets the standards for permanent basement wall joints in terms of both load-bearing and waterproofing performance. This fundamentally solves the technical problems of easy leakage at traditional support joints and the inability to share temporary support with permanent structures.

[0040] S500. Construct the main structure of the basement connected to the steel casing and precast concrete slab of the pile foundation, so that the steel casing and precast concrete slab of the pile foundation become permanent components of the basement exterior wall.

[0041] Specifically, after the foundation pit support and consolidation work is completed, the construction of the basement main structure can proceed. The construction of the basement main structure typically includes permanent components such as the foundation slab, inner lining walls or shear walls, and roof slab. During construction, these permanent components should be reliably connected to the pile foundation steel casing and precast concrete slab. This can be achieved through methods such as reserving connecting steel bars, embedding connectors, and post-poured joint concrete to achieve structural integration between the two.

[0042] To further clarify, since the pile foundation steel casing and precast concrete slabs have been designed in reverse according to the permanent use conditions in the S100 stage, their cross-sectional bearing capacity, impermeability and durability all meet the use requirements of the permanent structure of the basement exterior wall. Therefore, after the main structure of the basement is completed, the pile foundation steel casing and precast concrete slabs do not need to be removed, but can directly serve as permanent components of the basement exterior wall to continue to play the functions of retaining soil, stopping water and structural protection.

[0043] In this embodiment, the support system constructed by pile-based steel casings and precast concrete slabs is directly converted into a permanent exterior wall for the basement, achieving a combination of temporary and permanent features. During implementation, the construction parameters of the support structure are first determined in reverse based on the permanent service conditions of the basement walls. These parameters include the arrangement parameters and structural dimensions of the pile-based steel casings, as well as the cross-sectional and reinforcement parameters of the precast concrete slabs. This ensures that the subsequently constructed pile-based steel casings and precast concrete slabs can not only withstand lateral earth pressure and provide a water-stopping barrier during the excavation stage, but also meet the structural bearing capacity and durability requirements for the permanent use stage as the exterior wall of the basement. Subsequently, pile-based steel casings are constructed around the excavation site according to these construction parameters, leaving an insertion area between adjacent pile-based steel casings for installing precast concrete slabs. Each pile-based steel casing has two pre-installed, oppositely arranged water-stopping fasteners on its outer wall, while the precast concrete slabs have fasteners adapted to the insertion area. When the precast concrete slab is pushed into the insertion area and fastened along the preset installation direction, the insertion piece and the water-stop fastener interlock and lock together, instantly forming a continuous retaining and water-stopping support surface. This eliminates the need for an additional independent water-stop curtain, reducing a construction step and shortening on-site operation time. After the fastening installation is completed, the connection between the precast concrete slab and the steel casing of the foundation pit pile is consolidated. This consolidation includes limiting, sealing, and consolidation treatment. Limiting ensures the accurate relative position of the slab and pile; sealing blocks the seepage path; and consolidation forms a tenon-and-mortise permanent joint at the connection point, bearing overall stress. This joint, through the combined effect of the tenon-and-mortise interlocking structure and the sealing consolidation, cuts off the seepage channel of groundwater along the pile-slab joint, significantly improving the water-stopping reliability of the connection. It overcomes the defects of poor reliability and easy leakage at joints in traditional temporary support structures between adjacent piles, ensuring operational safety during foundation pit excavation and providing long-term waterproofing performance to the basement structure. Subsequently, the construction of the basement main structure, connected to the pile foundation steel casing and precast concrete slabs, allowed the previously formed support piles and precast slabs to directly participate in the structural stress as permanent components of the basement exterior walls. This combined temporary support construction with permanent exterior wall construction, eliminating the repetitive steps of first dismantling the temporary support and then erecting formwork and pouring the permanent exterior wall, significantly reducing the number of procedures, shortening the construction period, and lowering the overall construction cost. This achieved integrated construction of the foundation pit support and the permanent structure.

[0044] In one embodiment, step S100 includes: S110. Based on the lateral earth pressure, groundwater pressure, impermeability grade, deformation control and durability requirements of the basement exterior wall during the permanent use phase, determine the load-bearing, crack resistance and impermeability control indicators of the exterior wall. S120. Based on the control indicators, determine the diameter, wall thickness, spacing, and embedment depth of the steel casing for the pile foundation, as well as the thickness, width, and reinforcement of the precast concrete slab. S130. Based on the excavation conditions of the foundation pit during the construction phase, perform temporary support calculations for the determined pile foundation steel casing and precast concrete slab. S140. Based on the combined verification results of permanent service conditions and construction conditions, the structural parameters of the pile foundation steel casing and precast concrete slab are corrected to obtain the construction parameters of the support structure.

[0045] In this embodiment, by systematically reviewing the various load and functional requirements of the basement exterior wall during its permanent use phase, three control indicators—bearing capacity, crack resistance, and impermeability—are gradually established. Based on this, the preliminary structural parameters of the pile foundation steel casing and precast concrete slab are determined. The preliminary parameters are then verified through temporary support calculations during the construction phase. Finally, through comprehensive comparison and iterative correction of the dual-condition calculation results, construction parameters for the support structure that balance permanent use functionality and construction safety requirements are obtained, providing a reliable quantitative basis for the smooth progress of subsequent construction steps.

[0046] In one embodiment, step S200 includes: S210. Conduct surveying and setting out along the perimeter of the foundation pit to determine the center line, joint line, and corner control points of the steel casing for the pile foundation. S220. Prefabricate the longitudinal water-stop fastener on the steel casing of the pile foundation; wherein the water-stop fastener includes a fastening edge, a guide groove or a connecting edge rib; S230. Drive each of the steel casings of the pile foundation to the designed depth and control their planar position and verticality so that an insertion area for installing the precast concrete slab is formed between two adjacent steel casings of the pile foundation.

[0047] In this embodiment, precise pile position control benchmarks are established through surveying and setting out. Combined with the prefabrication stage in the factory, the processing of water-stop fasteners is completed. During the on-site sinking process, the planar position and verticality of the pile foundation steel casing are monitored throughout. The three links of setting out and positioning, component prefabrication and on-site sinking systematically ensure the geometric accuracy of the insertion area between adjacent pile foundation steel casings and the structural quality of the water-stop fasteners. This lays a solid construction foundation for the subsequent accurate installation of precast concrete slabs and the reliable formation of mortise and tenon joint permanent and temporary joints.

[0048] In one embodiment, prior to step S300, the method further includes: S600. For any two adjacent steel casings of the pile foundation, perform precast concrete slab prefabrication; wherein, the two ends of the precast concrete slab are formed with the plug-in members, and the plug-in members are at least one of tenon, groove, dovetail edge or step edge.

[0049] In this embodiment, customized prefabrication work is carried out for the actual net distance of each insertion area before the precast concrete slab is fastened and installed. Based on the actual engineering conditions, various splice structures such as tenons, grooves, dovetail edges, and stepped edges are reasonably selected to form a precise and suitable fastening relationship between the end geometry of the precast concrete slab and the water-stop fastening splice of the pile foundation steel casing. While ensuring installation efficiency, the reliability of water-stopping at the joint and the overall structural integrity are comprehensively improved, providing a solid component quality guarantee for the realization of the permanent and temporary combination function of the overall support system.

[0050] In one embodiment, step S300 includes: S310. Excavation of the foundation pit is carried out inside the steel casing of the pile foundation. S320. The precast concrete slab is hoisted to the top of the insertion area and fastened to the insertion area along the preset installation arrangement direction to form the current support layer; S330. After completing the installation of the precast concrete slab of the current support layer, continue the excavation of the next foundation pit and the installation of the precast concrete slab until the continuous retaining and water-stopping support surface is formed.

[0051] In this embodiment, the excavation of the foundation pit and the installation of precast concrete slabs in the vertical space are carried out in alternating layers. With an orderly construction rhythm of "excavating one layer and installing one layer", a retaining and water-stopping support surface covering the entire depth of the foundation pit and with structural continuity is gradually formed between the steel casing of the pile foundation. Under the premise of ensuring the safety and stability of the entire foundation pit excavation process, all installation operations of the precast concrete slabs are completed efficiently. This lays a dual guarantee of structural integrity and construction continuity for the subsequent consolidation operations and the formation of the tenon-and-mortise permanent joint.

[0052] In one embodiment, step S400 includes: S410. A water-stopping material is installed in the joint between the steel casing of the pile foundation and the precast concrete slab to form a first water-stopping barrier; wherein the water-stopping material is an elastic water-stopping material or a water-swellable water-stopping material. S420. Perform a limiting operation on the precast concrete slab; S430. Inject grouting material into the connection position between the insertion area and the corresponding insertion piece to fill the corresponding installation gap and perform consolidation work to form a second water-stopping barrier. S440. Waterproof sealing treatment is applied to the surface of the node to form the continuous retaining and water-stopping node.

[0053] In this embodiment, four processes are sequentially completed at the joint: filling the first water-stopping barrier with water-stopping material, limiting the concrete precast slab to ensure grouting quality, filling the structure with grouting material to solidify the second water-stopping barrier, and waterproof sealing the joint surface. By stacking multiple water-stopping barriers layer by layer, the pile foundation steel casing and the concrete precast slab form a tenon-and-mortise permanent joint at the connection joint with the pile foundation steel casing and the concrete precast slab. This achieves the organic unity of the support function during the construction phase and the function of the basement exterior wall during the permanent use phase, while fundamentally improving the structural integrity and waterproof durability of the joint, providing a solid guarantee for the final realization of the permanent joint goal of the overall support system.

[0054] In one embodiment, step S410 includes: S411. Water-stopping material is installed on the seepage path in the joint between the steel casing of the pile foundation and the precast concrete slab to form the first water-stopping barrier.

[0055] In this embodiment, by accurately identifying and locating the seepage path within the joint between the steel casing of the pile foundation and the precast concrete slab, the water-stopping material is specifically placed at the cross-sectional position of the seepage path. The continuous and dense filling method forms an effective seal for the seepage path throughout the entire height of the joint, constructing the first water-stopping barrier. This intercepts the seepage from the source channel of groundwater infiltration, significantly improving the targeting and reliability of the joint water-stopping. This lays a solid foundation for the subsequent superposition of multiple water-stopping barriers and the realization of the overall waterproof performance of the tenon-and-mortise permanent joint.

[0056] In one embodiment, step S500 includes: S510. Construct the basement floor slab and inner lining wall in sequence, so that the pile foundation steel casing and the precast concrete slab are connected with the basement floor slab and the inner lining wall as a whole to form the permanent component.

[0057] In this embodiment, by constructing the basement floor slab and inner lining wall in sequence, the pile foundation steel casing and precast concrete slab are connected to the main basement structure in both horizontal and vertical directions to form a load-bearing whole. This transforms the support structure from a temporary function to a permanent function, forming a permanent component of the basement exterior wall with a complete structure and clear force transmission. While fully leveraging the advantages of the permanent-temporary combined construction method, the functional goals of the basement exterior wall system are simultaneously achieved from the two dimensions of structural integrity and waterproof durability, providing the final structural guarantee for the complete implementation of the entire permanent-temporary combined foundation pit support construction method.

[0058] In one embodiment, prior to step S440, the method further includes: S450. The sealing performance of the first and second water-stop barriers is tested sequentially. S460. If the test results do not meet the preset requirements, waterproofing and reinforcement work shall be carried out.

[0059] In this embodiment, before the joint waterproofing and sealing treatment, the sealing performance is tested sequentially according to the order of the first water-stop barrier and the second water-stop barrier. Targeted waterproofing reinforcement measures are taken in a timely manner for parts where the test results do not meet the preset requirements. This forms a quality closed-loop control process driven by the test results. The discovery and elimination of water-stop defects are placed before the waterproofing and sealing treatment process, ensuring that each water-stop barrier of the joint enters the final sealing process in a verified and reliable sealing state. From the perspective of construction process control, this provides a systematic guarantee for the long-term water-stop reliability of the mortise and tenon permanent joint.

[0060] In one embodiment, prior to step S230, the method further includes: S240. The surface of the steel casing of the pile foundation is subjected to anti-corrosion treatment.

[0061] In this embodiment, a systematic anti-corrosion treatment is carried out on the surface of the steel casing before the pile foundation is installed. This addresses the deterioration factors such as electrochemical corrosion, chemical corrosion, and alternating wet and dry corrosion faced by the steel casing in the underground permanent service environment. A continuous and reliable anti-corrosion protective layer is pre-established on the steel base surface. From the perspective of material durability, this provides a fundamental guarantee for the steel casing to maintain its design cross-sectional dimensions and structural performance throughout its entire service life. It effectively solves the problem of insufficient durability of steel components in permanent and temporary combined support structures caused by long-term exposure to corrosive environments, and ensures the long-term safety and reliability of the entire support system after the transition from the construction stage to the permanent service stage.

[0062] The above are merely exemplary embodiments of the present invention and do not limit the scope of the patent of the present invention. All equivalent structural transformations made using the contents of the present invention specification and drawings under the technical concept of the present invention, or direct / indirect applications in other related technical fields, are included within the scope of patent protection of the present invention.

Claims

1. A method for constructing foundation pit support, characterized in that, Includes the following steps: The support structure is designed in reverse based on the permanent service conditions of the basement wall, and the construction parameters of the support structure are obtained; wherein, the construction parameters include the arrangement parameters, structural dimensions, cross-sectional parameters and reinforcement parameters of the steel casing of the pile foundation; According to the construction parameters, the foundation pit pile foundation steel casing is constructed around the foundation pit so that an insertion area for installing the precast concrete slab is formed between two adjacent foundation pile foundation steel casings; wherein, two oppositely arranged water-stop fasteners are provided on the outer wall of each foundation pit pile foundation steel casing. The precast concrete slab is fastened and installed to the insertion area along a preset installation direction to obtain a continuous retaining and water-stopping support surface; wherein, the precast concrete slab has a plug-in component adapted to the insertion area; A consolidation operation is performed at the connection position between the precast concrete slab and the steel casing of the foundation pit pile foundation to obtain a tenon-and-mortise permanent joint; wherein, the consolidation operation includes limiting, sealing and consolidation; The construction connects the basement main structure with the steel casing and precast concrete slab of the pile foundation, making the steel casing and precast concrete slab a permanent component of the basement exterior wall.

2. The foundation pit support construction method as described in claim 1, characterized in that, The step of designing the support structure in reverse based on the permanent service conditions of the basement walls and obtaining the construction parameters of the support structure includes: Based on the lateral earth pressure, groundwater pressure, impermeability grade, deformation control, and durability requirements of the basement exterior wall during the permanent use phase, determine the load-bearing capacity, crack resistance, and impermeability control indicators of the exterior wall. Based on the control indicators, the diameter, wall thickness, spacing, and embedment depth of the steel casing for the pile foundation, as well as the thickness, width, and reinforcement of the precast concrete slab, are determined. Based on the excavation conditions of the foundation pit during the construction phase, temporary support calculations are performed on the determined steel casing and precast concrete slab of the pile foundation. Based on the combined verification results of permanent service conditions and construction conditions, the structural parameters of the pile foundation steel casing and precast concrete slab are corrected to obtain the construction parameters of the support structure.

3. The foundation pit support construction method as described in claim 2, characterized in that, The step of constructing the foundation pit pile foundation steel casing around the foundation pit according to the construction parameters, so as to form an insertion area for installing the precast concrete slab between two adjacent pile foundation steel casings, includes: Surveying and setting out along the perimeter of the foundation pit to determine the center line, joint line, and corner control points of the steel casing for the pile foundation; The longitudinal water-stop fasteners are prefabricated on the steel casing of the pile foundation; wherein the water-stop fasteners include fastening edges, guide grooves or connecting edge ribs; The steel casings of the pile foundations are driven one by one to the design depth, and their planar position and verticality are controlled so that an insertion area for installing the precast concrete slab is formed between two adjacent steel casings of the pile foundations.

4. The foundation pit support construction method as described in claim 3, characterized in that, Before the step of fastening and installing the precast concrete slab to the insertion area along the preset installation direction to obtain a continuous retaining and water-stopping support surface, the method further includes: For any two adjacent steel casings of the pile foundation, a corresponding precast concrete slab is prefabricated; wherein, the two ends of the precast concrete slab are formed with the plug-in member, which is at least one of the tenon, groove, dovetail edge or step edge.

5. The foundation pit support construction method as described in claim 4, characterized in that, The step of fastening and installing the precast concrete slab to the insertion area along a preset installation direction to obtain a continuous retaining and water-stopping support surface includes: Excavation of the foundation pit is carried out inside the steel casing of the pile foundation. The precast concrete slab is hoisted to the top of the insertion area and fastened to the insertion area along the preset installation direction to form the current support layer; After the installation of the precast concrete slabs of the current support layer is completed, the excavation of the next layer of foundation pit and the installation of the precast concrete slabs continue until the continuous retaining and water-stopping support surface is formed.

6. The foundation pit support construction method as described in claim 5, characterized in that, The step of consolidating the connection between the precast concrete slab and the steel casing of the foundation pit pile to obtain a tenon-and-mortise permanent joint includes: A water-stopping material is installed in the joint between the steel casing of the pile foundation and the precast concrete slab to form the first water-stopping barrier; wherein, the water-stopping material is an elastic water-stopping material or a water-swellable water-stopping material. The precast concrete slab is positioned to limit its movement. Grouting material is injected into the connection position between the insertion area and the corresponding insertion piece to fill the corresponding installation gap and perform consolidation work to form a second water-stopping barrier. The surface of the node is waterproofed and sealed to form the continuous retaining and water-stopping node.

7. The foundation pit support construction method as described in claim 6, characterized in that, The step of installing water-stopping material in the joint between the steel casing of the pile foundation and the precast concrete slab to form the first water-stopping barrier includes: Water-stopping material is installed along the seepage path in the joint between the steel casing of the pile foundation and the precast concrete slab to form the first water-stopping barrier.

8. The foundation pit support construction method as described in claim 7, characterized in that, The steps of constructing the basement main structure connected to the pile foundation steel casing and precast concrete slab, making the pile foundation steel casing and precast concrete slab a permanent component of the basement exterior wall, include: The basement floor slab and inner lining wall are constructed sequentially to connect the pile foundation steel casing and the precast concrete slab with the basement floor slab and inner lining wall as a whole, forming the permanent component.

9. The foundation pit support construction method as described in claim 6, characterized in that, Before the step of performing waterproof sealing treatment on the node surface to form the continuous retaining and water-stopping node, the method further includes: The sealing performance of the first and second water-stop barriers was tested sequentially. If the test results do not meet the preset requirements, waterproofing and reinforcement work will be carried out.

10. The foundation pit support construction method according to any one of claims 3 to 9, characterized in that, Before the step of driving each of the steel casings of the pile foundation to the design depth and controlling their planar position and verticality so that an insertion zone for installing the precast concrete slab is formed between two adjacent steel casings of the pile foundation, the method further includes: The surface of the steel casing of the pile foundation is subjected to anti-corrosion treatment.

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