Deep foundation pit supporting system close to subway structure and existing building in ultra-close distance

Abstract

The invention belongs to the technical field of foundation pit supporting, and particularly relates to a deep foundation pit supporting system close to a subway structure and an existing building in an ultra-close distance. Comprising supporting units which are arranged in a layered mode from top to bottom, each layer of supporting unit is of a composite supporting structure composed of a concrete support and a prestress combined profile steel support, the concrete supports are located on the side close to a subway structure, the supporting units are connected together in series through stand columns, and the column bottoms of the stand columns are connected with underground pile foundations in an inserted mode; through an innovative'concrete-prestressed steel support 'composite structure, layered and zoned optimized arrangement and a space closed force transfer system, the millimeter-level deformation control target is successfully achieved in a limit space which is only 3.5 m away from a subway waterproof curtain and has three sides adjacent to a building, and the construction efficiency is improved. And a core technical support is provided for safe construction of the deep foundation pit of the super high-rise building in an extremely complex urban environment.

Description

Technical Field

[0001] This invention belongs to the field of foundation pit support technology, specifically relating to a deep foundation pit support system for ultra-close proximity to subway structures and existing buildings. Background Art

[0002] With the rapid development of urban rail transit networks, numerous foundation pit projects inevitably take place along subway lines. Foundation pit construction is a highly complex undertaking, altering the initial stress of the surrounding soil and consequently affecting the stress and deformation of adjacent subway structures. According to subway structure protection requirements, the cumulative settlement (or uplift) and horizontal displacement of the subway structure must be <10mm, and the cumulative horizontal diameter convergence change must be <10mm. This places extremely high demands on the support methods, excavation deployment, and deformation control of deep foundation pits. For deep foundation pit projects of super high-rise buildings (150m above ground), especially in extremely complex environments where three sides are adjacent to existing buildings (the outer wall of the proposed super high-rise building's basement is approximately 6.0m from the boundary line) and one side is adjacent to a subway entrance (the outer wall of the proposed super high-rise building's basement is only 3.5 meters from the subway's cutoff wall), conventional foundation pit support structures or ordinary foundation pit support structures near the subway (within 50m of the subway's protection zone) cannot be effectively implemented. Summary of the Invention

[0003] This invention aims to solve the problem of disturbance caused by deep foundation pit excavation to nearby subway structures and existing buildings.

[0004] The present invention provides the following technical solution: a deep foundation pit support system for ultra-close proximity to subway structures and existing buildings, comprising support units arranged in layers from top to bottom. Each layer of support unit is a composite support structure composed of concrete supports and prestressed combined steel supports. The concrete supports are located on the side adjacent to the subway structure. Each layer of support units is connected together by columns, and the bottom of the columns is inserted into the underground pile foundation.

[0005] Furthermore, the deep foundation pit support system includes three layers of support units arranged from top to bottom; In the first layer of support unit, the two corner areas on the side closest to the subway structure are reinforced with concrete, while the two corner areas on the side away from the subway structure are prestressed composite steel supports. In the second-layer support unit, one corner area on the side adjacent to the subway structure is a concrete support, while the other corner area on the side adjacent to the subway structure and the two corner areas on the side away from the subway structure are prestressed composite steel supports. The structure of the third support unit is the same as that of the second support unit.

[0006] Furthermore, the prestressed composite steel support includes steel walers and steel beams. The steel walers overlap the steel corbels on the support piles, and the two ends of the steel walers are connected to the concrete supports. The steel walers and concrete supports form a closed support ring within the outline of the foundation pit, and the steel beams are diagonally braced at the included angle of the steel walers.

[0007] Furthermore, the concrete support includes a capping beam, main beams, and secondary beams. The reinforcement in the capping beam is welded to the main reinforcement of the support piles, and the concrete of the capping beam is poured and connected to the support piles. Several main beams are diagonally braced at fixed intervals at the angle of the capping beam, and the secondary beams are connected between the main beams to form a triangular grid.

[0008] Furthermore, a carrying beam is connected between the two columns, and a steel crossbeam rests on the carrying beam.

[0009] Furthermore, reinforced concrete trestle decks are installed on the concrete supports in the first-layer support unit.

[0010] Furthermore, the steel crossbeams are diagonally braced at 45° at the included angles of the steel walers, and several steel crossbeams are arranged at fixed intervals at each included angle of the steel walers.

[0011] Furthermore, the main beam is braced at a 45° angle at the angle between the cap beam and the main beam.

[0012] Furthermore, horizontal haunches are provided at the intersections of the cap beam, main beam, and secondary beam.

[0013] Furthermore, the components of the prestressed composite steel support are connected by bolts.

[0014] Compared with the prior art, the advantages of the present invention are: This invention provides a deep foundation pit support system for ultra-close proximity to subway structures and existing buildings. Through an innovative "concrete-prestressed steel support" composite structure, layered and zoned optimized layout, and spatial closed force transmission system, it successfully achieves millimeter-level deformation control targets in an extreme space with only 3.5 meters from the subway water-stop curtain and three sides adjacent to buildings. This provides core technical support for the safe construction of deep foundation pits for super high-rise buildings in extremely complex urban environments. Attached Figure Description

[0015] Figure 1 A schematic diagram of a deep foundation pit support system for extremely close proximity to subway structures and existing buildings; Figure 2 This is a schematic diagram of the first-layer support unit; Figure 3 Schematic diagram of the second-layer support unit Figure 4 This is a schematic diagram of the third-layer support unit.

[0016] In the diagram: 1-Concrete support; 1.1-Cap beam; 1.2-Main beam; 1.3-Secondary beam; 1.4-Horizontal haunch; 2-Prestressed composite steel support; 2.1-Steel waler; 2.2-Steel crossbeam; 3-Column; 4-Spreader beam; 5-Foundation pit; 6-Reinforced concrete trestle slab; 7-Subway structure. Detailed Implementation

[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 these drawings without creative effort.

[0018] like Figure 1 As shown, a deep foundation pit support system for extremely close proximity to subway structures and existing buildings includes support units arranged in layers from top to bottom. Each layer of support unit is a composite support structure composed of concrete supports 1 and prestressed composite steel supports 2. The concrete supports 1 are located on the side adjacent to the subway structure 7. The support units of each layer are connected together by columns 3, and the bottom of the columns 3 is inserted into the underground pile foundation. Under the extremely harsh conditions of being extremely close to the subway structure 7 and adjacent to existing buildings on three sides, precise and efficient control of deep foundation pit deformation is achieved, and the safety of nearby important facilities is effectively guaranteed.

[0019] The deep foundation pit support system consists of three layers of support units arranged from top to bottom; like Figure 2 As shown: In the first layer of support unit, the two corner areas on the side adjacent to the subway structure 7 are concrete supports 1, and the two corner areas on the side away from the subway structure 7 are prestressed composite steel supports 2. like Figure 3 As shown: In the second layer support unit, one corner area on the side adjacent to the subway structure 7 is a concrete support 1, and the other corner area on the side adjacent to the subway structure 7 and the two corner areas on the side away from the subway structure 7 are prestressed composite steel supports 2. like Figure 4 As shown: The structure of the third support unit is the same as that of the second support unit.

[0020] By deploying highly rigid concrete supports 1 on the sensitive side closest to the subway, and combining them with the flexibility and high strength of prestressed composite steel supports 2, a composite structure combining rigidity and flexibility is formed. Concrete supports 1 effectively inhibit the transmission of deep soil displacement to the subway side, while prestressed steel supports actively provide restraint and absorb deformation. Together, they strictly control the subway structure's settlement / heave, horizontal displacement, and diameter convergence caused by the excavation within a cumulative protection limit of <10mm.

[0021] The three-layer support unit dynamically adjusts the ratio and layout of concrete and steel supports according to depth and location (such as double concrete supports at sensitive corners in the first layer and single concrete supports at key corners in the lower layer), achieving the optimal distribution of support stiffness and specifically resisting soil pressure at different depths and in different areas.

[0022] like Figure 2 As shown: The prestressed composite steel support 2 includes a steel waler 2.1 and a steel crossbeam 2.2. The steel waler 2.1 overlaps the steel corbels on the support piles. Both ends of the steel waler 2.1 are connected to the concrete support 1. The steel waler 2.1 and the concrete support 1 form a closed support ring within the outline of the foundation pit. The steel crossbeam 2.2 is diagonally braced at the included angle of the steel waler 2.1. The steel crossbeam 2.2 is diagonally braced at 45° at the included angle of the steel waler 2.1. Several steel crossbeams 2.2 are arranged at fixed intervals at each included angle of the steel waler 2.1.

[0023] The components of the prestressed composite steel support 2 are connected by bolts; it is prefabricated in the factory and assembled on site, which makes the construction speed fast, has little interference with the surrounding area, and greatly shortens the exposure risk period of the foundation pit.

[0024] The prestressed characteristics of the prestressed composite steel support 2 allow for the active application of loads after installation to offset some of the soil deformation, achieving "top first, then excavate", significantly reducing the time of unsupported exposure, and making it particularly suitable for rapid construction in space-constrained areas (only 3.5 meters from the subway).

[0025] A spreader beam 4 connects the two columns 3, and a steel crossbeam 2.2 rests on the spreader beam 4; the spreader beam 4 connects the columns 3 to support the steel crossbeam 2.2, so as to achieve the uniform transmission of the supporting force to the columns 3 and the underground pile foundation, and avoid excessive local stress.

[0026] The concrete support 1 includes a capping beam 1.1, main beams 1.2, and secondary beams 1.3. The reinforcement in the capping beam 1.1 is welded to the main reinforcement of the support piles. The concrete of the capping beam 1.1 is poured and connected to the support piles. The reinforcement of the capping beam is welded to the main reinforcement of the support piles, and the concrete is poured integrally to ensure that the support piles and the support system form a stable whole and share the load. Several main beams 1.2 are diagonally braced at fixed intervals at the included angle of the capping beam 1.1. The secondary beams 1.3 connect between the main beams 1.2, dividing the structure into a triangular grid. The main beams 1.2 are diagonally braced at 45° at the included angle of the capping beam 1.1.

[0027] A horizontal haunch 1.4 is provided at the intersection of the cap beam 1.1, the main beam 1.2 and the secondary beam 1.3; the horizontal haunch 1.4 design at the concrete joint significantly enhances the joint’s shear and bending resistance and prevents failure caused by stress concentration.

[0028] The concrete support 1 and the steel waler 2.1 form a rigid closed support ring within the outline of the foundation pit. Combined with the three-dimensional force transmission network composed of the diagonal bracing (45° diagonal bracing capping beam of the main beam, 45° diagonal bracing steel waler of the steel crossbeam) and the column 3, the spatial stiffness and overall stability of the support system are greatly improved, and the soil pressure is effectively dispersed and transmitted.

[0029] A reinforced concrete trestle slab 6 is installed on the concrete support 1 in the first layer of support unit; the support structure itself is used as a construction passage and work platform to efficiently utilize the support structure, avoid additional loads from disturbing the foundation pit, and optimize the use of the narrow space.

[0030] This invention provides a practical safety guarantee solution for deep foundation pits of super high-rise buildings under extreme proximity to sensitive structures, successfully solving the problem of the inability to implement conventional support methods. It combines the advantages of high rigidity of concrete and rapid construction of steel structures, optimizes material usage (using concrete only in critical areas), shortens the construction period, and reduces overall costs. Refined deformation control minimizes the impact on adjacent subway operations and the normal use of existing buildings.

[0031] Construction Cases A deep foundation pit support system for ultra-close proximity to subway structures and existing buildings, as described in this invention, has been applied to a super high-rise residential project at the southwest corner of the intersection of Changzhi Road and Wangcun South Street in Taiyuan City. The project is a super high-rise residential building with a building height of 149.8m. The surrounding environment is complex. To the west of the foundation pit, the exterior wall of the proposed super high-rise basement is approximately 6.0m from the boundary line. To the east of the foundation pit is a subway entrance / exit, with the subway foundation bottom elevation at 767.1m occupying the project boundary line; the subway water-stop curtain is approximately 3.5m from the exterior wall of the proposed super high-rise basement on the east side. To the south of the foundation pit, the exterior wall of the proposed super high-rise basement is approximately 5.0m to 6.5m from the boundary line. To the north of the foundation pit, the exterior wall of the proposed super high-rise basement is approximately 4.5m from the boundary line.

[0032] By employing the solution of this invention, construction quality is strictly controlled, the overall performance of the foundation pit remains stable, with a cumulative maximum settlement of 21.5 mm and a horizontal displacement of 10.7 mm; the cumulative maximum settlement of the subway tunnel on the east side is 4.1 mm, and the horizontal displacement is 2.4 mm. This shortens the construction period, meets the design and construction requirements, and effectively solves the problem of overlapping structural construction.

[0033] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A deep foundation pit support system for ultra-close proximity to subway structures and existing buildings, characterized in that: It includes support units arranged in layers from top to bottom. Each layer of support unit is a composite support structure composed of concrete support (1) and prestressed composite steel support (2). The concrete support (1) is located on the side adjacent to the subway structure (7). Each layer of support units is connected together by columns (3). The bottom of the columns (3) is inserted into the underground pile foundation.

2. The deep foundation pit support system for ultra-close proximity to subway structures and existing buildings as described in claim 1, characterized in that: The deep foundation pit support system includes three layers of support units arranged from top to bottom; In the first layer of support unit, the two corner areas on the side adjacent to the subway structure (7) are concrete supports (1), and the two corner areas on the side away from the subway structure (7) are prestressed composite steel supports (2). In the second layer of support unit, one corner area on the side adjacent to the subway structure (7) is a concrete support (1), and the other corner area on the side adjacent to the subway structure (7) and the two corner areas on the side away from the subway structure (7) are prestressed composite steel supports (2). The structure of the third support unit is the same as that of the second support unit.

3. The deep foundation pit support system for ultra-close proximity to subway structures and existing buildings as described in claim 2, characterized in that: The prestressed composite steel support (2) includes a steel waler (2.1) and a steel crossbeam (2.2). The steel waler (2.1) is attached to the steel corbel on the support pile. The two ends of the steel waler (2.1) are connected to the concrete support (1). The steel waler (2.1) and the concrete support (1) form a closed support ring within the outline of the foundation pit. The steel crossbeam (2.2) is diagonally supported at the angle of the steel waler (2.1).

4. The deep foundation pit support system for ultra-close proximity to subway structures and existing buildings as described in claim 2, characterized in that: The concrete support (1) includes a cap beam (1.1), a main beam (1.2) and a secondary beam (1.3). The reinforcement in the cap beam (1.1) is welded to the main reinforcement of the support pile, and the concrete of the cap beam (1.1) is poured and connected to the support pile. Several main beams (1.2) are diagonally braced at fixed intervals at the angle of the cap beam (1.1), and the secondary beams (1.3) are connected between the main beams (1.2) to form a triangular grid.

5. The deep foundation pit support system for ultra-close proximity to subway structures and existing buildings as described in claim 3, characterized in that: A spreader beam (4) is connected between the two columns (3), and a steel crossbeam (2.2) rests on the spreader beam (4).

6. The deep foundation pit support system for ultra-close proximity to subway structures and existing buildings as described in claim 2, characterized in that: A reinforced concrete trestle slab (6) is provided on the concrete support (1) in the first layer support unit.

7. The deep foundation pit support system for ultra-close proximity to subway structures and existing buildings as described in claim 3, characterized in that: The steel beams (2.2) are braced at 45° at the included angle of the steel waler (2.1), and several steel beams (2.2) are arranged at fixed intervals at each included angle of the steel waler (2.1).

8. The deep foundation pit support system for ultra-close proximity to subway structures and existing buildings as described in claim 4, characterized in that: The main beam (1.2) is diagonally braced at 45° at the angle between the cap beam (1.1).

9. A deep foundation pit support system for ultra-close proximity to subway structures and existing buildings as described in claim 4, characterized in that: A horizontal haunch (1.4) is provided at the intersection of the crown beam (1.1), the main beam (1.2) and the secondary beam (1.3).

10. A deep foundation pit support system for ultra-close proximity to subway structures and existing buildings as described in claim 3, characterized in that: The components of the prestressed composite steel support (2) are connected by bolts.

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