Deep foundation pit supporting structure of soil nail retaining wall under integral row pile supporting and construction method

Abstract

The invention discloses a deep foundation pit supporting structure of a soil nail retaining wall under integral row pile supporting and a construction method. The deep foundation pit supporting structure is suitable for deep foundation pit engineering of an underground pipeline crossing area. The structure comprises a top beam, row pile assemblies, soil nail assemblies and a reinforcing mesh structure, the row pile assemblies are constructed on the two sides of a projection area of the underground pipeline, an overall stress system is formed through embedded steel bars and the reinforcing mesh structure, reverse pouring is achieved in combination with a lengthened guide pipe, and pipeline migration is avoided. According to the construction method, layered excavation, instant supporting and jumping methods are adopted for hole forming, soil nail assemblies are arranged in a quincunx shape, prestress is applied, and the deformation of a pipeline area is controlled to be smaller than or equal to 30 mm. The problems that traditional supporting is interrupted, the pipeline migration cost is high, and the construction period is long are solved, the supporting integrity is enhanced, the construction period is shortened, the engineering cost is reduced, and the method is suitable for deep foundation pit engineering under the urban dense pipeline environment.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of deep foundation pit support in civil engineering, and particularly relates to a local reverse construction soil nailing retaining wall structure suitable for an underground pipeline crossing area and a construction method, and is particularly suitable for deep foundation pit support engineering in a densely populated urban pipeline environment. BACKGROUND

[0002] With the acceleration of urbanization, the distribution of underground pipelines (such as water supply and drainage, gas, and power pipelines) is increasingly dense and complex, especially the increasing burial depth of large-diameter pipelines and inspection wells, which poses a serious challenge to the support construction of urban deep foundation pits. Deep foundation pit support, as a key link in construction engineering, its core function is to control the deformation of the foundation pit, protect the surrounding environment and underground facilities. In the prior art, deep foundation pit support mainly adopts pile row support, soil nailing wall support or a combination of the two, but in the underground pipeline crossing area, the traditional support technology has significant defects, which are as follows: Deficiency of Prior Art 1. Disruption of underground pipeline area support leading to structural instability In the prior art, pile row support needs to be continuously constructed to form a closed soil retaining system, and the underground pipeline projection area cannot be excavated, resulting in the interruption of pile row at this point, forming a weak link in support.

[0003] Early deep foundation pit projects are mostly located on the edge of the city, with fewer underground pipelines, and the support design prioritizes structural continuity, forming a traditional mode of "pipeline relocation first, then continuous construction". The prior art focuses on the "continuity" design of the support structure, believing that pile row must be continuous to ensure overall stiffness, and there has never been an alternative support scheme under the condition of "local discontinuity".

[0004] 2. High cost and long duration of pipeline relocation In early urban construction, the density of underground pipelines is low, and the relocation cost is controllable, forming an inertial thinking of "conflict means relocation"; to avoid support interruption, the traditional method needs to relocate or temporarily change the line of the conflict pipeline, which not only involves a lot of coordination work (such as pipeline ownership unit approval, traffic diversion, etc.), but also generates high relocation fees, and the relocation period is as long as 2-3 months, prolonging the construction period.

[0005] 3. Insufficient local area support stiffness leading to excessive deformation Pile row support and soil nailing wall support originate from different engineering scenarios (pile row is suitable for deep foundation pits, and soil nailing wall is suitable for shallow foundation pits), so the prior art considers pile row and soil nailing wall as independent support systems, focusing on the strength design of a single structure, ignoring the necessity of coordinated stress of the two.

[0006] When the soil nailing wall alone supports the pipeline area, the soil nails and the row piles are not rigidly connected, and the two are independently stressed, which is easy to cause deformation concentration in the pipeline crossing section, and to cause soil collapse or pipeline damage.

[0007] 4. Traditional construction process cannot adapt to soft stratum and pipeline protection requirements The existing technology focuses on the "construction in sequence" process (excavation before support), and does not optimize the matching relationship between excavation depth and support timing. In soft strata, traditional row pile construction is prone to hole collapse, and construction interference between adjacent piles leads to a decrease in pile quality; soil nailing construction is usually carried out uniformly after excavation to the designed depth, and the soil is exposed for a long time, and the pipeline area is prone to instability.

[0008] II. Improvement necessity The existing technology faces problems such as support interruption, high pipeline relocation cost, insufficient local rigidity, and mismatched construction process in complex urban underground pipeline environments, resulting in reduced engineering safety and poor economy. Therefore, there is an urgent need for a deep foundation pit support technology that can avoid pipeline relocation, enhance the overall support integrity, and adapt to layered top-down construction, to solve the inherent defects of traditional methods in complex pipeline scenarios - this is the core problem that the patent based on the local top-down method of soil nailing retaining wall deep foundation pit support structure under the condition of overall row pile support wants to solve. SUMMARY

[0009] The purpose of the present application is to provide a soil nailing retaining wall deep foundation pit support structure under the condition of overall row pile support, which realizes the overall stress and continuous construction of the support system through the local support structure design of non-migration pipelines in deep foundation pit engineering with underground pipeline crossing, to solve the problems of insufficient stability and high cost caused by traditional support interruption, without the need to relocate existing pipelines.

[0010] To achieve the above purpose, the soil nailing retaining wall deep foundation pit support structure under the condition of overall row pile support of the present application comprises a corbel, a row pile assembly, a soil nailing assembly and a steel mesh structure; the corbel is continuously arranged along the edge of the foundation pit, and a vertical pouring channel is provided inside the corbel; a length-extendable guide pipe is installed in the pouring channel; The area surrounded by the underground pipeline, the row pile assembly on both sides of the underground pipeline and the corbel is referred to as the underground pipeline projection area; The row pile assembly is symmetrically distributed on both sides of the underground pipeline projection area, and the side facing the soil nailing retaining wall is provided with a planted reinforcement; the steel mesh structure is fixedly connected with the planted reinforcement and the soil nailing assembly, forming an overall stress system; The guide pipes are uniformly and intermittently arranged, the upper ends of the guide pipes are at the same height, and the guide pipes all extend out of the corbel and are used for connecting grouting pipes; the vertical lengths of the guide pipes are arranged in an arithmetic sequence, the bottom end of the shortest guide pipe is located in the upper part of the underground pipeline projection area, and the longest guide pipe is located in the bottom part of the underground pipeline projection area.

[0011] The conduits are evenly spaced along the length of the crown beam, and the distance between adjacent channels is 1.0-2.0 meters.

[0012] The pile row assembly adopts bored piles, the pile diameter is 600-800 mm, and the pile spacing is ≤1.2 meters; the dowels are spaced along the height direction of the pile body, the embedding depth is ≥10d, and the exposed length is welded with the reinforcement mesh structure.

[0013] The application further discloses a construction method of the deep foundation pit supporting structure of the soil nailing retaining wall under the whole pile row supporting, and the method comprises the following steps: S1. First, the underground pipeline projection area is positioned on the ground, the pile row assembly is constructed on both sides of the underground pipeline projection area, the dowels are embedded on the side of the pile body facing the retaining wall after the strength of the pile body reaches 75%, and the reinforcement mesh structure is laid on the soil nailing assembly formed on the soil wall surface after each layer is excavated. S2. The crown beam is constructed, the pouring channel vertically penetrating through is reserved, and the extendable conduit is installed for each pouring channel; the dowels are embedded on one side of the lower surface of the crown beam; S3. The earthwork is excavated in layers in the underground pipeline projection area, and the pile row is exposed, the depth of each layer is 1.5±0.5 meters, the soil nailing assembly is constructed on the soil wall surface formed after each layer is excavated, and the reinforcement mesh structure is laid, so that the reinforcement mesh structure is fixedly connected with the dowels and the soil nailing assembly respectively. S4. The formwork is supported, the concrete is poured to the excavation surface through the conduit, the soil nailing retaining wall is formed, and the formwork is removed after curing; steps S3-S4 are repeated until the designed depth.

[0014] In step S2, the crown beam is constructed by adopting the jump punching method, the construction interval of adjacent holes is ≥24 hours, and the strength grade of the concrete is C30.

[0015] In step S4, the concrete pouring adopts the layer-by-layer vibrating process, the pouring thickness of each layer is ≤500 mm, and the vibrating rod is inserted into the lower layer of concrete with a depth of ≥100 mm.

[0016] In step S3, when the soil nailing assembly is constructed on the soil wall surface formed after each layer is excavated, the component soil nails of the soil nailing assembly are arranged in a plum blossom type, the cement mortar or fine stone concrete with a strength grade of C20 is used for full-length grouting of the rod bodies of the soil nails, the total length of a single soil nail is 6000 mm, and the distance between the soil nails is 1000 mm. In step S3, after the formwork is removed, the component soil nails of the soil nailing assembly are immediately tensioned and locked.

[0017] The application has the following advantages: The traditional method needs to "move the pipeline to let the pile"; the present application is changed to "let the pile be empty, and supplement the wall by reverse construction", leaving a gap for the pipeline to pass through at the place where the underground pipeline passes through the pile row, and the pipeline can safely pass through without moving. Through the means of "supplementing the position by reverse construction soil nailing retaining wall", "connecting the whole", and the like, the supporting stress requirement is met, the existing pipeline does not need to be moved, the direct cost is saved, and the traffic, environmental and social costs caused by the relocation are reduced.

[0018] The pipeline passing area adopts the combined structure of "piling body embedded tendon + crown beam reserved reinforcement + cast-in-place retaining wall", so that the pile row and the soil nailing wall form a rigid whole, and the stability and safety of the supporting system are significantly improved, and the risk of collapse in the weak area is eliminated.

[0019] The full reverse construction method reduces the exposure time of the soil body and shortens the construction period; at the same time, the dust, noise and safety hazards are simultaneously reduced.

[0020] The construction occupation area is only 1 / 3-1 / 2 of the traditional slope scheme, effectively alleviating the traffic pressure of the narrow urban site, traffic artery and dense building area, and reducing the interference on the surrounding residents and urban operation to the minimum.

[0021] The present application realizes the reverse construction pouring of concrete in the pipeline area by pouring the channel in cooperation with the guide pipe 12, solves the problem of supporting interruption, and the rigid connection of the embedded tendon 21 and the reinforcement mesh structure 4 combines the pile row and the soil nailing wall into a whole, realizes the collaborative stress of "pile row-soil nailing wall", improves the supporting stiffness, and solves the problem of supporting in the pipeline area.

[0022] The grouting positions of the plurality of guide pipes 12 evenly cover the vertical area of the underground pipeline projection area, improving the uniformity and effectiveness of the concrete grouting in the underground pipeline projection area. The guide pipes 12 are arranged in equal intervals in the longitudinal direction (the longitudinal direction refers to the bottom end arranged in equal intervals in the longitudinal direction), ensuring the uniformity of concrete pouring. The water stop strip prevents mud leakage during pouring, improving the construction quality.

[0023] The dense pile row spacing and deep embedded tendon depth ensure the connection strength, the welding of the exposed section makes the pile row and the soil nailing wall form a rigid whole, and the deformation of the pipeline area is controlled to be ≤30mm.

[0024] By using the construction method of the present application, the layered excavation and immediate support reduce the exposure time of the soil body, the super-long design (length 6000mm) of the soil nailing assembly 3 and the tensioning process restrict the deformation in advance; the reverse construction pouring avoids pipeline relocation, avoids the long construction period caused by pipeline relocation, improves the construction efficiency, and shortens the period.

[0025] The skip-punch method can avoid the collapse of the adjacent hole caused by simultaneous construction; the 24-hour interval makes the poured concrete reach the initial setting / early strength, reduces the disturbance, and ensures the integrity of the crown beam. The layered vibration ensures the compactness of the concrete, avoids the air bubbles or honeycomb defects caused by the guide pipe pouring, and improves the impermeability of the retaining wall.

[0026] The prestressed soil nail applies a "active force" opposite to the potential displacement to the whole sliding wedge before the soil body has obvious relaxation, so that the anti-sliding force which needs to rely on the continuous deformation of the soil body to gradually develop is mobilized in advance, and the pipeline is prevented from being damaged due to long-term deformation accumulation, and the pipeline crossing area is especially suitable for soft stratum and needs to strictly control the deformation (≤30 mm, displacement rate ≤0.5 mm / d).

[0027] The planar arrangement of the soil nail on the wall surface is in the shape of a plum blossom (also called "herringbone shape" or "interlaced shape"), so that the stress of adjacent soil nails is more uniform, and a weak zone is avoided. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 is a structural schematic view of the soil nail retaining wall deep foundation pit supporting structure under the whole row pile support in the application.

[0029] Figure 2 is a left view of Figure 1 .

[0030] Figure 3 is a top view of Figure 1 .

[0031] Figure 4 is a three-dimensional structural schematic view of the soil nail retaining wall deep foundation pit supporting structure under the whole row pile support.

[0032] Figure 5 is a structural schematic view of the reserved steel joint under the corbel.

[0033] Figure 6 is a top structural schematic view of the soil nail retaining wall deep foundation pit supporting structure under the whole row pile support after pouring the first layer of concrete.

[0034] Figure 7 is a schematic view of the influence part of the existing underground pipeline on the supporting structure.

[0035] Figure 8 is a photo of the construction site of the application. Figure 7 and Figure 8 are used to enhance the intuitive understanding of the application.

[0036] 1, corbel 1 Installation position: continuously arranged along the edge of the foundation pit.

[0037] Structural relationship: a vertical pouring channel is provided inside, and a side of the lower surface is embedded with a planted bar 21.

[0038] Working principle: install a guide pipe 12 through the pouring channel, and connect the row pile assembly 2 to form a whole supporting system.

[0039] Technical function: Enhance the integrity of the row pile, provide vertical pouring channel, and constrain the deformation of the foundation pit edge.

[0040] 2, row pile assembly 2 Installation position: symmetrically distributed on both sides of the underground pipeline projection area.

[0041] Structural relationship: bored piles are used, the pile body is implanted into the soil nail retaining wall side with embedded steel bars 21, and the pile spacing is ≤1.2 meters.

[0042] Working principle: form a soil retaining structure by dense arrangement, and realize force transmission by welding embedded steel bars 21 and steel mesh structure 4.

[0043] Technical function: bear the main soil retaining load and prevent the collapse of the foundation pit side wall.

[0044] 3, soil nail assembly 3 Installation position: at the surface of the soil wall, arranged in a quincunx shape.

[0045] Structural relationship: fixedly connected with the steel mesh structure 4, and the full length is grouted with C20 cement mortar or fine stone concrete.

[0046] Working principle: pre-stress is applied through super-long design (6000mm) and tensioning process to constrain soil deformation.

[0047] Technical function: mobilize the anti-skid force in advance and control the deformation of the pipeline area ≤30mm.

[0048] 4, steel mesh structure 4 Installation position: laid at the surface of the soil wall.

[0049] Structural relationship: respectively welded and fixed with embedded steel bars 21 and soil nail assembly 3 to form an overall force system.

[0050] Working principle: disperse the tensile force of the soil nail and transfer the local load to the row pile assembly 2.

[0051] Technical function: enhance the integrity of the supporting structure and prevent local peeling of the soil.

[0052] 5, guide pipe 12 Installation position: through the corbel 1, and the vertical length is arranged in an arithmetic sequence.

[0053] Structural relationship: the upper end extends out of the corbel to connect the grouting pipe, and the bottom end covers the upper part to the bottom of the underground pipeline projection area.

[0054] Working principle: realize layered reverse construction through the lengthening design.

[0055] Technical function: grouting forms a soil nail retaining wall, avoids pipeline migration, and realizes the continuity of the support of the underground pipeline projection area.

[0056] 6, Anchor 21 Installation position: The row pile assembly 2 is towards the side of the soil nail retaining wall and the lower side of the corbel 1.

[0057] Structural relationship: The embedded depth is greater than or equal to 10d (d is the diameter of the steel bar), and the exposed length is welded with the steel bar mesh structure 4.

[0058] Working principle and technical effect: The row pile is rigidly connected with the soil nail wall, and the internal force between the row pile and the soil nail wall is transmitted, forming an overall stress system.

[0059] 7, Underground pipeline projection area (the steel bar mesh structure 4 is arranged in the area, and the underground pipeline projection area is not labeled) Installation position: The area surrounded by the underground pipeline 51, the row pile assembly 2 on both sides and the corbel 1.

[0060] Structural relationship: The core protection object of the support system, the guide pipe 12 and the soil nail assembly 3 play a role in this area.

[0061] Working principle and technical effect: The local reverse construction support replaces the traditional pipeline migration, defines the weak support area, and guides the replacement support scheme after the row pile is interrupted.

[0062] 8, Underground pipeline 51 Installation position: Non-active installation, inherent structure before construction.

[0063] Structural relationship: As a support protection object, limit the continuous construction of the row pile assembly 2.

[0064] It is necessary to avoid disturbance to it through a non-migration support scheme, which triggers the need for local reverse construction support, and verifies the pipeline protection effect of the support structure. DETAILED DESCRIPTION

[0065] As shown in Figures 1 to 8 The overall row pile support of the soil nail retaining wall deep foundation pit support structure of the present application, comprising a corbel 1, a row pile assembly 2, a soil nail assembly 3 and a steel bar mesh structure 4; the corbel 1 is continuously arranged along the edge of the foundation pit, and a vertical pouring channel is provided in the inside, a lengthened guide pipe 12 is adaptively installed in the pouring channel, and the guide pipe 12 is used in Figure 1 and Figure 4 The red line is used.

[0066] The area surrounded by the underground pipeline 51, the row pile assembly 2 on both sides of the underground pipeline 51 and the crown beam is referred to as an underground pipeline projection area; the horizontal section of the underground pipeline projection area is a rectangle, the long side of the rectangle is subject to the size required by the construction machinery + 0.3-0.5m construction allowance, and the short side of the rectangle is subject to the minimum construction operation space on both sides, which is most affected by the design thickness of the soil nailing retaining wall, to ensure that the soil nailing retaining wall can be smoothly constructed.

[0067] The row pile assembly 2 is symmetrically distributed on both sides of the underground pipeline projection area, and the side facing the soil nailing retaining wall (underground pipeline projection area) is provided with a planted bar 21; the steel bar mesh structure 4 is fixedly connected with the planted bar 21 and the soil nailing assembly 3, forming an overall force system; the planted bar is a conventional technology, Figure 5 The planted bar 21 on the crown beam is shown, and the planted bar 21 on the row pile assembly 2 is not shown.

[0068] The guide pipes 12 are uniformly and spacedly arranged, the upper ends of the guide pipes 12 are at the same height, the guide pipes 12 all extend out of the crown beam and are used for connecting the grouting pipes, the vertical lengths of the guide pipes 12 are arranged according to an arithmetic progression, the bottom end of the shortest guide pipe 12 is located at the upper part of the underground pipeline projection area, and the longest guide pipe 12 is located at the bottom of the underground pipeline projection area.

[0069] The guide pipe 12 is a D150mm PVC pipe, the length of which is segmented and lengthened according to the depth of the foundation pit; the planted bar 21 is made of HRB400 grade threaded steel with a diameter of 20mm.

[0070] The present application realizes the reverse pouring of the pipeline area concrete by the pouring channel and the guide pipe 12, solves the problem of support interruption; the rigid connection of the planted bar 21 and the steel bar mesh structure 4 combines the row pile and the soil nailing wall into a whole, realizes the collaborative stress of the row pile-soil nailing wall, improves the support stiffness, and solves the problem of pipeline area support.

[0071] The grouting positions of the plurality of guide pipes 12 uniformly cover the vertical area of the underground pipeline projection area, improving the uniformity and effectiveness of the concrete grouting of the underground pipeline projection area.

[0072] The guide pipes 12 are uniformly and spacedly arranged along the length direction of the crown beam 1, and the spacing between adjacent channels is 1.0-2.0 meters. In the embodiment, the spacing between the guide pipes 12 is preferably 1.5 meters; the guide pipes 12 and the inner wall of the pouring channel are filled with (embedded with) water-swelling sealing strips. The equal spacing arrangement ensures the uniformity of the concrete pouring. The sealing strips prevent mud leakage during pouring, improving the construction quality.

[0073] The pile row assembly 2 adopts a cast-in-situ bored pile, the pile diameter is 600-800 mm, and the pile spacing is ≤1.2 m; the dowel bars 21 are arranged at intervals along the height direction of the pile body, the embedding depth is ≥10d (d is the diameter of the steel bar), the exposed length is welded with the reinforcement mesh structure 4, and the spacing and the length of the welding points are determined by the operating personnel according to the conventional technology. The spacing between the dowel bars is 500 mm, and the epoxy resin adhesive can be used for anchoring; the reinforcement mesh structure 4 is a reinforcement mesh with a diameter of 8 mm, bidirectional arrangement and a spacing of 200 mm. The bidirectional arrangement means that the reinforcement mesh is composed of steel bars in two directions (usually horizontal and vertical directions), and forms a grid-shaped whole.

[0074] The spacing between the dense pile rows and the embedding depth of the deep dowel bars ensure the connection strength, the welding exposed section makes the pile row and the soil nailing wall form a rigid whole, and the deformation of the pipeline area is controlled to be ≤30 mm.

[0075] The construction method of the deep foundation pit supporting structure of the soil nailing retaining wall under the whole pile row supporting disclosed by the present application comprises the following steps: S1. First, the underground pipeline projection area is positioned on the ground, the pile row assembly 2 is constructed on both sides of the underground pipeline projection area, and after the strength of the pile body reaches 75%, the dowel bars 21 are embedded on the side of the pile body facing the retaining wall; S2. The corbel 1 is constructed, the pouring channel vertically penetrating through is reserved, and the extendable guide pipe 12 is installed for each pouring channel; the guide pipe 12 is an extendable D150 mm PVC pipe, and the underground retaining wall concrete is poured through the PVC pipe in the subsequent process. The dowel bars 21 are embedded on one side of the lower surface of the corbel 1; S3. The soil is excavated in layers in the underground pipeline projection area, and the pile row is exposed, the depth of each layer is 1.5±0.5 m, the soil nailing assembly 3 is constructed on the formed retaining wall surface after each layer is excavated, and the reinforcement mesh structure 4 is laid, so that the reinforcement mesh structure 4 is fixedly connected with the dowel bars 21 and the soil nailing assembly 3 respectively; S4. The formwork is supported, the concrete is poured to the excavation surface through the guide pipe 12, the soil nailing retaining wall is formed, and the formwork is removed after curing; the steps S3-S4 are repeated until the designed depth.

[0076] In the step S3, the soil nailing assembly 3 is a C20 grouting soil nailing, the length is 6000 mm, the spacing is 1000 mm, and the soil nailings are arranged in a quincunx shape, and the tension stress is controlled to be 70% of the design value.

[0077] By using the construction method of the present application, the layered excavation and the immediate support reduce the exposure time of the soil, the overlength design (length of 6000 mm) of the soil nailing assembly 3 and the tensioning process constrain the deformation in advance; the reverse pouring avoids the pipeline migration, avoids the long construction period caused by the pipeline migration, improves the construction efficiency, and shortens the period.

[0078] The earthwork excavation adopts a long-arm backhoe excavator, a long-arm (effective length 15 m) excavator and a large excavator are used in cooperation, and the earthwork is excavated in layers and symmetrically. The long-arm excavator stands at the periphery of the foundation pit to take out the earth, and due to the difficulty in transferring the long-arm excavator, it is not conducive to direct loading into a truck, so the taken-out earth is temporarily piled up in a relatively open position away from the foundation pit, and then a large excavator is used to load and transport out.

[0079] In the conventional section with small pile spacing and no underground pipeline crossing, a reinforcement mesh (usually φ6~φ8@150~200mm) is directly hung between the piles, and then sprayed with concrete (C20~C25) to form a continuous pile-to-pile soil retaining surface.

[0080] Function: close the soil between piles, prevent local peeling and seepage, and is an economical and rapid support method.

[0081] In step S2, when the crown beam 1 is constructed, the holes are formed by jumping and hitting, the construction interval of adjacent holes is ≥24 hours, and the concrete strength grade is C30. The construction sequence of the jumping and hitting method is to construct every other hole, the hole diameter is larger than the guide pipe 12 by 20mm, and the hole wall is protected by mud. The jumping and hitting method avoids hole collapse caused by interference between adjacent holes, 24h interval ensures the initial strength of the concrete, and improves the integrity of the crown beam 1.

[0082] In step S4, the concrete pouring adopts a layered vibrating process, the pouring thickness of each layer is ≤500mm, and the vibrating rod is inserted into the lower layer of concrete with a depth of ≥100mm. The concrete slump is controlled within 180±20mm, a φ50mm insertion type vibrating rod is used, and the vibrating time is 15-30s / point. The layered vibration ensures the compactness of the concrete, avoids air bubbles or honeycomb defects caused by guide pipe pouring, and improves the impermeability of the retaining wall.

[0083] In step S3, after each layer is excavated, the soil nail assembly 3 is constructed on the formed soil wall surface, the soil nails of the soil nail assembly 3 are arranged in a plum blossom pattern, the soil nail rod body is fully grouted with C20 strength grade cement mortar or fine stone concrete, the total length of a single soil nail is 6000mm, and the spacing between the soil nails is 1000mm (here, it refers to the soil nails arranged in a grid spacing of 1000mm×1000mm in the plane).

[0084] In step S3, after the formwork is removed, each component soil nail of the soil nail assembly (3) is immediately tensioned and locked; the locking force is preferably 15-20kN, and further preferably 18kN.

[0085] Immediate tensioning generates prestress in the soil nails, which actively constrain the deformation of the soil body; the locking force is applied by a hydraulic jack, and the error is small.

[0086] The prestressed soil nail applies a reverse 'active force' to the whole sliding wedge before the soil body has obvious relaxation, thereby mobilizing the anti-sliding force which originally needs to rely on the continuous deformation of the soil body to gradually develop, and avoiding the pipeline damage due to long-term deformation accumulation.

[0087] The planar arrangement of the soil nails on the wall surface is in a quincunx shape (also called 'pinwheel shape' or 'interlaced shape'), so that the stress of adjacent soil nails is more uniform, and a weak zone is avoided.

[0088] The application is particularly suitable for deep foundation pit engineering with a buried depth of underground pipeline 51 greater than or equal to 3 m and a pipe diameter greater than or equal to 500 mm, and application scenarios include a comprehensive pipe gallery under a city trunk road, a pipeline dense area for old community reconstruction, and the like.

[0089] The above examples are only used to illustrate but not to limit the technical solutions of the application, although the application is described in detail with reference to the above examples, it should be understood by those skilled in the art that the application can still be modified or replaced equivalently without departing from the spirit and scope of the application, and any modification or partial replacement should be covered in the scope of the claims of the application.

Claims

1. A deep foundation pit support structure with integral pile support and soil nailing retaining wall, characterized in that: It includes a capping beam (1), a pile assembly (2), a soil nail assembly (3), and a steel mesh structure (4); the capping beam (1) is continuously set along the edge of the foundation pit, and a vertically set pouring channel is opened through it, and an extendable guide pipe (12) is adapted to be installed in the pouring channel. The area enclosed by the underground pipeline (51), the pile assembly (2) on both sides of the underground pipeline (51), and the capping beam is called the underground pipeline projection area; The pile assembly (2) is symmetrically distributed on both sides of the underground pipeline projection area, and the side facing the soil nail retaining wall is provided with a rebar (21); the steel mesh structure (4) is fixedly connected to the rebar (21) and the soil nail assembly (3) to form an overall stress system; Multiple conduits (12) are evenly spaced, with the upper ends of each conduit (12) at the same height. They all extend out of the crown beam and are used to connect to the grouting pipe. The vertical lengths of each conduit (12) are arranged in an arithmetic sequence. The bottom end of the shortest conduit (12) is located at the upper part of the underground pipeline projection area, and the longest conduit (12) is located at the bottom of the underground pipeline projection area.

2. The deep foundation pit support structure of the integral pile-supported retaining wall with soil nailing as described in claim 1, characterized in that: Each catheter (12) is evenly spaced along the length of the coronal beam (1), with a spacing of 1.0-2.0 meters between adjacent channels.

3. The deep foundation pit support structure of the integral pile-supported retaining wall with soil nailing as described in claim 1, characterized in that: The pile assembly (2) adopts bored cast-in-place piles with a pile diameter of 600-800 mm and a pile spacing of ≤1.2 m; the rebar (21) is set at intervals along the height of the pile body, with an implantation depth of ≥10d and an exposed length welded to the steel mesh structure (4).

4. The construction method of the deep foundation pit support structure of the integral pile support with soil nailing retaining wall as described in claim 1, characterized in that... Includes the following steps: S1. First, locate the underground pipeline projection area on the ground, construct pile assembly (2) on both sides of the underground pipeline projection area, and after the pile strength reaches 75%, insert rebar (21) on the side of the pile facing the retaining wall. S2. Construct the cap beam (1), reserve a vertical through-pouring channel, and install an extendable conduit (12) for each pouring channel; insert a rebar (21) into one side of the lower surface of the cap beam (1). S3. Excavate the soil in layers in the underground pipeline projection area and expose the piles. The depth of each layer is 1.5±0.5 meters. After each layer is excavated, construct soil nail components (3) on the formed soil wall and lay steel mesh structure (4) so ​​that the steel mesh structure (4) is fixedly connected to the rebar (21) and soil nail components (3) respectively. S4. Set up the formwork and pour concrete into the excavation face through the guide pipe (12) to form a soil nail retaining wall. After curing, remove the formwork. Repeat steps S3-S4 until the design depth is reached.

5. The construction method according to claim 4, characterized in that: In step S2, when constructing the cap beam (1), the skip drilling method is used to form holes, the construction interval between adjacent holes is ≥24 hours, and the concrete strength grade is C30.

6. The construction method according to claim 4, characterized in that: In step S4, the concrete pouring adopts a layered vibration process, with each layer having a thickness of ≤500mm and the vibrator inserted into the lower layer of concrete to a depth of ≥100mm.

7. The construction method according to claim 4, characterized in that: In step S3, when the soil nail assembly (3) is constructed on the soil wall after each layer is excavated, the soil nails of the soil nail assembly (3) are arranged in a quincunx pattern. Each soil nail rod is grouted with C20 strength grade cement mortar or fine stone concrete along its entire length. The total length of a single soil nail is 6000 mm, and the spacing between soil nails is 1000 mm. In step S3, after demolding, the soil nails of the soil nail assembly (3) are immediately tensioned and locked.

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