Narrow space site deep foundation pit supporting system and construction method thereof

Abstract

The invention discloses a narrow space site deep foundation pit supporting system and a construction method thereof, and relates to the field of deep foundation pit construction, the technical scheme is that the narrow space site deep foundation pit supporting system comprises a waterproof curtain which is arranged on the outer side of a foundation pit and surrounds the foundation pit, a supporting wall body is arranged on the inner side of the waterproof curtain, and the supporting wall body is adjacent to the waterproof curtain; a top beam is arranged at the top of the supporting wall body; a first-layer inner support is arranged between the supporting wall bodies on the side adjacent to the building, and the first-layer inner support is located on the top beam; a second-layer support is arranged between the supporting wall bodies located below the first-layer inner support, and the first-layer inner support and the second-layer inner support are supported through a plurality of latticed columns; and the supporting wall body far away from the building is supported and reinforced through a plurality of anchor cables. The method has the beneficial effects that according to the space condition of a narrow site where the foundation pit is located and the characteristics of surrounding buildings and underground structures, the supporting safety and construction operability of the deep foundation pit are effectively guaranteed; and the construction efficiency is high.

Description

Technical Field

[0001] The present invention relates to the field of deep foundation pit construction, and in particular to a deep foundation pit support system for a narrow space and a construction method thereof. Background Art

[0002] With the development of urbanization, the scale of underground space development is also increasing. Currently, most foundation pit projects are located in urban areas with dense distribution of existing buildings, municipal roads and underground pipelines. However, the impact of foundation pit excavation on the surrounding environment is very sensitive. How to carry out reasonable foundation pit support construction in small spaces has brought challenges to technical personnel in this field and also put forward new requirements for foundation pit support in the construction industry.

[0003] In the existing technology, common foundation pit excavation methods generally adopt slope excavation, anchor retaining wall support, anti-slip pile-sheet retaining wall, etc. However, slope excavation generally requires a larger site space and is difficult to implement in a small space. It is also necessary to ensure that the soil quality of the construction site is good and there are no important existing structures in the surrounding area. Although the foundation pit construction with anchor retaining wall support does not require a large site space, the anchor rods can easily damage the surrounding existing structures. Therefore, it is not suitable for situations where there are important existing structures in the surrounding area. As for the foundation pit construction with anti-slip pile-sheet retaining wall support, it usually requires the use of pile foundations with larger diameters, and anchor rods are still required in areas with poor soil quality in the retaining wall. This foundation pit support method consumes more materials, is more complex in process, and is more expensive. Summary of the Invention

[0004] In response to the above technical problems, the present invention provides a deep foundation pit support system for a narrow space and a construction method thereof.

[0005] The technical solution is as follows: a water-stop curtain is arranged outside the foundation pit and surrounds the foundation pit; a supporting wall is arranged inside the water-stop curtain, the supporting wall is adjacent to the water-stop curtain, and a crown beam is arranged on the top of the supporting wall; A first layer of internal supports is provided between the supporting walls on the side facing the building, and the first layer of internal supports is located on the crown beam; A second layer of support is provided between the support walls below the first layer of internal support, and the second layer of internal support is located in the middle of the support walls; The first layer of internal supports and the second layer of internal supports are supported by a plurality of lattice columns; The supporting wall away from the building is supported and reinforced by a plurality of anchor cables, and the anchor cables are arranged obliquely downward.

[0006] Preferably, the first layer of internal support includes a plurality of horizontal support steel sections arranged at an angle to the supporting wall, one end of the horizontal support steel section is installed on a concrete corbel provided on the crown beam through a pressure end, and the other end is installed on another corresponding concrete corbel through a movable head.

[0007] Preferably, the second layer of inner support comprises a plurality of horizontal support steel sections, and the projections of the horizontal support steel sections of the second layer of inner support coincide with the projections of the horizontal support steel sections of the first layer of inner support on the horizontal plane; A steel purlin is fixedly provided on the support wall, and the steel purlin is fixed to the steel cage of the support wall through a plurality of force transmission members; A plurality of triangular pieces are provided on the steel purlin. One end of the horizontal supporting steel is installed on the corresponding triangular piece through the pressure end, and the other end is installed on another corresponding triangular piece through the movable head.

[0008] Preferably, the pressurizing end is an H-steel, and mounting holes are respectively provided on the two flanges of the H-steel, wherein one flange is fixed to the concrete corbel or steel purlin by bolts, and the other flange is connected to the horizontal supporting steel by bolts, and a number of reinforcing ribs located on both sides of the web are provided between the two flanges of the H-steel.

[0009] Preferably, a plurality of metal corbels are provided at both ends of the horizontal supporting steel, each of the metal corbels comprises a diagonal brace and a horizontal portion, the diagonal brace is fixedly connected to the supporting wall, and the horizontal portion extends to below one end of the horizontal supporting steel.

[0010] Preferably, the horizontal supporting steel is formed by splicing several sections of steel components end to end in sequence, and each section of the steel component is composed of several parallel H-section steel beams, and the multiple steel beams are fixedly connected by several cover plates, and the cover plates are arranged perpendicular to the projections of the steel beams on the horizontal plane. Preferably, the force transmission member is a "cross" shaped structure, formed by splicing two T-shaped steels arranged back to back, and the flanges of the two T-shaped steels are fixedly connected to each other.

[0011] Preferably, the lattice column is formed by splicing four vertical angle steels, and two adjacent angle steels are fixedly connected by a chute plate; A bracket is fixedly arranged on the lattice column, a joist is arranged between the two brackets, the horizontal support steel is fixed on the joist, and the horizontal support steel is perpendicular to the projection of the joist on the horizontal plane.

[0012] The construction method of deep foundation pit support in a narrow space site includes the following steps: S1. Construction of water-stop curtain and supporting structure: Construction of water-stop curtain and supporting wall is carried out along the outside of the foundation pit, while lattice column construction is carried out inside the foundation pit simultaneously; S2. Excavation of foundation pit and anchor cable support construction: Excavate different locations of the foundation pit according to the designed elevation of the first layer of anchor cables, and arrange and construct the first layer of anchor cables on the support wall away from the building; S3. Excavation of foundation pit and installation of first-layer internal supports: According to the designed support elevation of the first layer, the first-layer internal supports are installed and supported by lattice columns; S4. Subsequent layered excavation and support construction: Continue excavating layer by layer according to the designed depth to the elevation of the next support layer, repeat the arrangement of anchor cables and the construction of the second layer of internal support, and support the first layer of internal support with lattice columns; S5. Excavate the foundation pit to the designed elevation: Under the joint action of the first layer of internal support, the second layer of internal support and the anchor cable, excavate the foundation pit to the designed bottom elevation; S6. Construction of the main structure and removal of supports: After the corresponding permanent structures such as the base plate and floor slab have reached the design strength, release the prestress step by step and remove the second layer of internal supports and the first layer of internal supports in turn.

[0013] The beneficial effects brought about by the technical solution provided by the embodiment of the present invention are: 1. Strong adaptability and reasonable structural layout: The present invention reasonably determines the layout of water-stop curtains, supporting walls, crown beams, lattice columns, steel purlins and multi-layer internal supports based on the spatial conditions of the narrow site where the foundation pit is located, the characteristics of surrounding buildings and underground structures, and effectively ensures the support safety and construction operability of deep foundation pits in limited space.

[0014] 2. Layered support and support while excavating: A support system combining multi-layer horizontal supports and anchor cables is adopted. The foundation pit is excavated in layers and sections, and internal supports and anchor cables are constructed simultaneously. This can effectively disperse the soil pressure, control the horizontal displacement and settlement of the support wall, and ensure that the construction process is continuous and safe without affecting the surrounding existing buildings and pipelines.

[0015] 3. Lattice columns, brackets, and joists limit supports: In the support system, lattice columns, brackets, and joists together form a support platform, which provides precise limits and constraints on the horizontal support steel in the height and horizontal directions, preventing the support from horizontal displacement or sinking, effectively maintaining the position of the support axis, and improving the stability of the entire support system.

[0016] 4. Easy to construct and high efficiency: All major components are prefabricated in the factory and only need to be hoisted and spliced on site, making the construction simple and efficient. The support removal process is carried out according to the principle of zoning and block-by-block and gradual unloading, which is safe and orderly and saves construction time. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 11 is a top view of the first layer inner support structure according to an embodiment of the present invention.

[0018] Figure 2 1 is a top view of the second layer inner support structure according to an embodiment of the present invention.

[0019] Figure 3 This is a partial schematic diagram of the first layer inner support structure of an embodiment of the present invention.

[0020] Figure 4 Schematic diagram of the connection node between the retaining wall and the first-layer internal support structure according to an embodiment of the present invention.

[0021] Figure 5 Schematic diagram of the connection node between the retaining wall and the second-layer internal support structure according to an embodiment of the present invention.

[0022] Figure 6 Schematic diagram of the installation state of the steel purlin according to an embodiment of the present invention.

[0023] Figure 7 Schematic diagram of the lattice column in use according to an embodiment of the present invention.

[0024] Figure 8 Schematic diagram of the upper joist and bracket of the lattice column according to an embodiment of the present invention.

[0025] Figure 9 Schematic diagram of the end installation of the steel purlin according to an embodiment of the present invention.

[0026] Figure 10 Schematic diagram of a steel section assembly according to an embodiment of the present invention.

[0027] Figure 11 Schematic diagram of the anchor cable state according to an embodiment of the present invention.

[0028] Figure 12 Schematic diagram of a support plate belt replacement according to an embodiment of the present invention.

[0029] Among them, the accompanying drawings are marked as: 1. Water-stop curtain; 2. Support wall; 3. Crown beam; 4. First-layer internal support; 5. Second-layer internal support; 6. Lattice column; 7. Anchor cable; 8. Horizontal support steel; 9. Pressurized end; 10. Concrete corbel; 11. Active head; 12. Steel purlin; 13. Triangle; 14. Metal corbel; 15. Steel beam; 16. Cover plate; 17. Force transmission member; 18. Shear member; 19. Support seat; 20. Support beam; 21. Replacement support plate belt. DETAILED DESCRIPTION

[0030] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. Of course, the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0031] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other.

[0032] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention. In addition, the terms "first", "second" and the like are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, features defined as "first", "second" and the like may explicitly or implicitly include one or more of the features. In the description of the present invention, unless otherwise specified, "multiple" means two or more.

[0033] In the description of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "installed," "connected," and "connected" should be understood in a broad sense. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections or electrical connections; they can refer to direct connections or indirect connections through an intermediate medium; and they can refer to internal connections between two components. Those skilled in the art can understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0034] Example 1 See also Figures 1 to 11 The present invention provides a deep foundation pit support system for a narrow space and a construction method thereof, comprising a water-stop curtain 1 arranged outside the foundation pit and surrounding the foundation pit, the water-stop curtain 1 comprising a plurality of triaxial mixing piles, the plurality of triaxial mixing piles being arranged in a row to form a mixing pile row, and adjacent triaxial mixing piles being overlapped with each other; A support wall 2 is provided inside the water-stop curtain 1. The support wall 2 is adjacent to the water-stop curtain 1. The support wall 2 is formed by a plurality of bored piles and high-pressure rotary jet piles arranged at intervals to form a support pile row. The bored piles and high-pressure rotary jet piles are overlapped with each other. The cross-section of the bored piles and high-pressure jet grouting piles in the vertical direction is "L"-shaped, and a crown beam 3 is set on the top of the supporting wall 2; A first layer of internal supports 4 is provided between the supporting walls 2 on the side facing the building, and the first layer of internal supports 4 is located on the crown beam 3; A second layer of support is provided between the retaining walls 2 below the first layer of internal support 4, and the second layer of internal support 5 is located in the middle of the retaining walls 2; The first layer of internal supports 4 and the second layer of internal supports 5 are supported by a number of lattice columns 6; The supporting wall 2 away from the building is supported and reinforced by a plurality of anchor cables 7, and the anchor cables 7 are arranged obliquely downward.

[0035] A reinforcement unit is provided on the outside of the water-stop curtain 1 located at the unearthed slope. The reinforcement unit includes a number of bored cast-in-place piles. The tops of the bored cast-in-place piles are connected by a crown beam 3. The pile row formed by the bored cast-in-place piles cooperates with the crown beam 3 to form a rigid retaining structure, which can significantly enhance the lateral support capacity at the slope and prevent local sliding or collapse caused by slope construction or vehicle loads.

[0036] The first layer of internal support 4 includes several horizontal support steels 8 arranged at 45 degrees to the supporting wall 2. One end of the horizontal support steel 8 is installed on the concrete corbel 10 provided on the crown beam 3 through the pressure end 9, and the other end is installed on the corresponding other concrete corbel 10 through the movable head 11.

[0037] The second layer of inner support 5 includes a plurality of horizontal support steel sections 8, and the projection of the horizontal support steel sections 8 of the second layer of inner support 5 coincides with the projection of the horizontal support steel sections 8 of the first layer of inner support 4 on the horizontal plane; A steel purlin 12 is fixedly provided on the support wall 2, and the steel purlin 12 is fixed to the steel cage of the support wall 2 through a number of force transmission members 17; A plurality of triangular pieces 13 are provided on the steel purlin 12 . One end of the horizontal support steel 8 is mounted on the corresponding triangular piece 13 through the pressurizing end 9 , and the other end is mounted on another corresponding triangular piece 13 through the movable head 11 .

[0038] The triangular member 13 is formed by welding steel sections, usually by splicing angle steel, channel steel, H-steel, etc., and welding to form a stable triangular frame structure. One side of the triangular member 13 is fixed to the outside of the steel purlin 12, and the other right-angled side is fixed to the pressure end 9 or the flexible end of the horizontal support steel section 8 by high-strength bolts.

[0039] The pressure end 9 is an H-steel with mounting holes on both flanges. One flange is fixed to the concrete corbel 10 or the steel purlin 12 by bolts, and the other flange is connected to the horizontal support steel 8 by bolts. A number of reinforcing ribs are provided between the two flanges of the H-steel on both sides of the web.

[0040] Several mounting holes are pre-machined on one side flange of the H steel, and the hole positions are aligned with the pre-buried bolt holes on the concrete corbel 10 or the steel purlin 12; During installation, the flange is pressed against the connection surface of the corbel or the steel purlin 12, and is fixed one by one through holes with high-strength bolts, so that the pressure end 9 is firmly connected to the concrete corbel 10 or the steel purlin 12, ensuring that the axial thrust is smoothly transmitted to the corbel or purlin, and then to the supporting wall 2; The movable head 11 specifically adopts a hydraulic movable head 11 structure to achieve fine-tuning and compensation of the length and axial force of the horizontal support steel 8. The hydraulic movable head 11 can provide the necessary tensioning force during installation through the built-in hydraulic jack, which is convenient for accurate application of prestressing. In the subsequent construction stage, secondary adjustments are made according to the deformation of the foundation pit and the changes in soil pressure to ensure that the support system continues to maintain the designed prestressing, further improving the stability and safety of the support system.

[0041] Several metal corbels 14 are provided at both ends of the horizontal supporting steel 8. Each metal corbel 14 includes a diagonal brace and a horizontal portion. The diagonal brace is fixedly connected to the supporting wall 2, and the horizontal portion extends to below one end of the horizontal supporting steel 8.

[0042] The horizontal support steel 8 is formed by several sections of steel components spliced end to end. Each section of the steel component is composed of several parallel H-section steel beams 15. The number of steel beams 15 is 2-5. The multiple steel beams 15 are fixedly connected by several cover plates 16. The projections of the cover plates 16 and the steel beams 15 on the horizontal plane are arranged perpendicularly. The force transmission member 17 is a "cross" shaped structure, formed by splicing two T-shaped steels arranged back to back, and the flanges of the two T-shaped steels are fixedly connected to each other.

[0043] A plurality of shear members 18 are provided at both ends of the section steel purlin 12. The shear members 18 are spaced apart from the force transmission members 17 and are inclined. One end of the shear member 18 is fixed to the section steel purlin 12 between the two force transmission members 17, and the other end is fixed to the steel cage of an adjacent bored pile. The shear member 18 is a T-shaped steel; In order to facilitate the installation of the force transmission member 17 and the shear member 18, steel plates can be welded at corresponding positions on the bored pile, and the steel plates are welded and fixed to the main reinforcement of the bored pile.

[0044] The lattice column 6 is formed by splicing four vertical angle steels, and two adjacent angle steels are fixedly connected by a chute plate; A bracket 19 is fixedly provided on the lattice column 6 , a joist 20 is provided between the two brackets 19 , and the horizontal support steel 8 is fixed on the joist 20 , and the projections of the horizontal support steel 8 and the joist 20 on the horizontal plane are perpendicular.

[0045] When the present invention is used, the water-stop curtain 1 and the supporting wall 2 are constructed along the outside of the foundation pit, and the lattice column 6 is constructed in the foundation pit simultaneously; Excavate different locations of the foundation pit according to the design elevation of the first layer of anchor cables 7, and arrange and construct the first layer of anchor cables 7 on the supporting wall 2 away from the building side; After the first layer support elevation is designed, the first layer inner support 4 is installed and supported by the lattice columns 6; Continue excavating in layers according to the designed depth to the next support layer elevation, repeat the arrangement of anchor cables 7 and the construction of the second layer of internal supports 5, and support the first layer of internal supports 4 through lattice columns 6; Under the joint action of the first layer internal support 4, the second layer internal support 5 and the anchor cable 7, the foundation pit is excavated to the designed bottom elevation; After the corresponding permanent structures such as the base plate and floor slab have reached the design strength, the prestressing force is released step by step in sequence and the second layer of internal support 5 and the first layer of internal support 4 are removed in turn.

[0046] The construction method of deep foundation pit support in a narrow space site includes the following steps: S1. Construction of water-stop curtain 1 and supporting structure: Construction of water-stop curtain 1 and supporting wall 2 is carried out along the outside of the foundation pit, and construction of lattice columns 6 is carried out simultaneously inside the foundation pit; A water-stop curtain 1 is constructed along the outer edge of the foundation pit according to design requirements. Triaxial mixing piles are typically arranged in overlapping layers to form a continuous water-stop barrier, preventing groundwater from seeping into the foundation pit. A support wall 2 is constructed immediately inside the water-stop curtain 1. The support wall 2 is constructed by staggered arrangements of bored cast-in-place piles and high-pressure jet grouting piles to form a support pile row. The tops of the support pile rows are connected by a cap beam 3 to form an integral load-bearing unit. At the same time, vertical lattice columns 6 are arranged inside the foundation pit according to the design. The lattice columns 6 are welded into a whole by four vertical angle steels and tie plates. The construction is carried out simultaneously with the support piles to ensure the stability and position accuracy of the subsequent internal support. S2. Excavation of foundation pit and construction of anchor cables 7 support: excavate different locations of the foundation pit according to the design elevation of the first layer of anchor cables 7, and arrange and construct the first layer of anchor cables 7 on the supporting wall 2 away from the building side; Arrange the anchor cable 7 holes on the supporting wall 2 away from the surrounding buildings. After drilling to the designed depth, bury multiple strands of steel wire and perform grouting reinforcement to form an anchor body. After the slurry strength reaches the design requirements, the anchor cable 7 is tensioned and locked by a jack. The anchor cable 7 is arranged obliquely and penetrates downward into the soil, effectively reinforcing the supporting wall 2, resisting the horizontal thrust of the soil, and enhancing the stability of the foundation pit sidewall. S3, foundation pit excavation and installation of the first layer of internal supports 4: according to the first layer design support elevation, the first layer of internal supports 4 are installed and supported by lattice columns 6; After excavation is completed, clean the surface of the lattice column 6, check the support center line and mark the installation center point of the horizontal support steel 8 on the crown beam 3 and the lattice column 6 using measuring instruments and spray paint; Brackets 19 are welded and installed on the lattice columns 6. Brackets 19 are connected by joists 20 to form a support platform. Subsequently, concrete corbels 10 are poured at the crown beam 3 and embedded with pre-buried bolts to fix the pressurized end 9. Pre-assemble horizontal steel supports and use hoisting equipment to install the assembled horizontal support steel 8: one end is connected to the pressurized end 9 of the concrete corbel 10, and the other end is connected to the opposite support platform through a flexible head 11, and fixed to the lattice column 6 joist 20 by bolts; After the horizontal support steel 8 is installed, adjust the length of the movable head 11, apply prestress step by step to the design value, and install an axial force meter at the same time, and cooperate with the monitoring unit to monitor the support force and deformation of the enclosure structure; S4, subsequent layered excavation and support construction: Continue to excavate layer by layer according to the designed depth to the elevation of the next support layer, repeat the arrangement of anchor cables 7 and the construction of the second layer of internal supports 5, and support the first layer of internal supports 4 through lattice columns 6; Under the joint action of the first layer internal support 4 and the first layer anchor cable 7, continue to excavate in layers and zones to the next layer support elevation; At this time, the second and third layers of anchor cables 7 are arranged and constructed in the middle of the support wall 2 according to the design requirements, and the steel purlins 12 are installed simultaneously. The purlins are connected to the steel cage of the cast-in-place piles through force transmission members 17 and shear members 18. Several triangular members 13 are provided on the steel purlins 12 for installing the horizontal support steel 8. The second layer of horizontal support steel 8 is preassembled and hoisted by crane and manual labor. One end is connected to the pressurized end 9 and fixed to the triangular member 13, and the other end is connected to the opposite triangular member 13 through the flexible head 11. Similarly, the vertical support is strengthened by the brackets 19 and joists 20 on the lattice columns 6, and prestressed to the design value to form a complete multi-level support system. S5. Excavation of foundation pit to design elevation: Under the joint action of the first layer internal support 4, the second layer internal support 5 and the anchor cable 7, the foundation pit is excavated to the design bottom elevation; S6. Construction of the main structure and removal of supports: After the corresponding permanent structures such as the base plate and floor slab have reached the design strength, release the prestress step by step and remove the second-layer internal support 5 and the first-layer internal support 4 in sequence.

[0047] Before removing the second layer of internal support 5 and the first layer of internal support 4, a replacement support plate belt 21 needs to be set between the main structure and the supporting wall 2, wherein the lowest replacement support plate belt 21 is located between the bottom plate of the structure and the supporting wall 2, and each layer of replacement support plate belt 21 is located between each top plate of the main structure and the supporting wall 2. The replacement support plate belt 21 is formed by pouring concrete as a whole, and the steel bars of the buffer plate belt are fixedly connected to the steel cages of the main structure and the supporting wall 2 respectively. The replacement support plate belt 21 is constructed synchronously with the floor slab and the wall during the pouring of the structure, and is formed as one piece to ensure that there are no construction joints or cold joints between the main structure and the supporting wall, thereby avoiding water leakage and local stress concentration. Except for the supporting strip 21 at the bottom plate, which is continuous as a whole, the supporting strip 21 at the floor plate needs to be opened at the corresponding position in order to take into account the post-cast strip of the main structure, and then closed by pouring in the later stage. After the construction of the main structure and the post-casting strip is completed and reaches the design strength, the reserved opening of the replacement support strip 21 should be closed in time, and the additional concrete should be poured tightly combined with the original replacement support strip 21 to form a complete and closed annular replacement support structure to ensure the force continuity of the replacement support strip 21 and effective constraint on the supporting wall.

[0048] The steel bars of the replacement support plate belt 21 are bent 45 degrees on the side close to the main structure to increase the shear resistance of the force transmission belt steel bars. The steel bars are planted on the side close to the supporting wall 2 with an anchor length of 15d to strengthen the connection strength with the supporting wall 2. The supporting plate belt 21 has a transverse diameter of Φ16@100 and a longitudinal diameter of Φ10@150, and is arranged in double layers and in two directions.

[0049] The internal reinforcement of the re-supporting plate belt 21 is double-layered and arranged in two directions (ie, there are two layers of steel mesh on the upper and lower sides, and each layer has both transverse reinforcement and longitudinal reinforcement).

[0050] Transverse direction: Arrange steel bars with a diameter of 16 mm and the center distance between adjacent steel bars is 100 mm.

[0051] Longitudinal direction: Arrange steel bars with a diameter of 10 mm and the center distance between adjacent steel bars is 150 mm.

[0052] This configuration is used for both the upper and lower layers to ensure that the support plate has sufficient bending stiffness and shear resistance.

[0053] The lateral earth pressure borne by the retaining wall can be transferred to the formed structural body through the replacement support plate belt 21, so that the external load is borne by the permanent structure instead of the temporary support, ensuring that the foundation pit and the surrounding environment are stable during the removal of the second layer of internal support 5 and the first layer of internal support 4; Furthermore, between two adjacent layers of the support strips 21, an effective soil support belt is formed by backfilling the soil in layers and compacting the soil in layers. The compaction degree of the backfill soil should meet the design and specification requirements to ensure its rigidity and anti-sliding stability. The backfill soil layer and the support strip 21 work together to form a superimposed "soil-structure" composite support system between the main structure and the supporting wall. On the one hand, the support strip 21 acts as a rigid structure to directly transmit the lateral earth pressure to the main structure. On the other hand, the compacted backfill soil provides continuous passive earth pressure, further limiting the displacement of the supporting wall and enhancing the overall stability and safety of the foundation pit support. Backfill construction should be carried out in layers in synchronization with the progress of the main structure construction. The layer thickness and compaction method should comply with the construction specifications for foundation pit support and foundation treatment to avoid affecting the support replacement effect due to insufficient backfill quality.

[0054] The support removal should follow the principle of "unloading first, then dismantling, zoning, block-by-block, and orderly grading". The specific operations are as follows: Prestress release Before dismantling, release the prestress of the horizontal support steel 8 step by step; After the prestress is released, it should be observed for at least 30 minutes, and the deformation of the connection nodes and the surrounding area of the foundation pit should be checked in real time. If any abnormality is found, the operation should be suspended immediately and reinforcement measures should be taken before continuing the operation.

[0055] Dismantling order of horizontal support steel 8: Loosen the high-strength bolts at each connection. During the removal process, the bolts should be removed in a staggered manner to prevent uneven force. According to the order of "accessories first, then main parts", remove in sequence: cover plate 16, steel beam 15, steel purlin 12, bracket 19 and support beam 20.

[0056] Segmentation and safety monitoring: The demolition work should be carried out step by step according to the area and block, with the corner braces to be removed first and the braces to be removed last; During the demolition period, monitoring of retaining structures, roads around the foundation pit, underground pipelines and adjacent buildings should be strengthened, the monitoring frequency should be increased, and monitoring data should be analyzed in real time.

[0057] The demolition rhythm should be adjusted dynamically according to the monitoring results. If abnormal deformation or settlement is found, the demolition should be stopped immediately and can only be continued after the hidden dangers are eliminated.

[0058] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A deep foundation pit support system for a narrow space, characterized by: It comprises a water-stop curtain (1) arranged outside a foundation pit and surrounding the foundation pit, a supporting wall (2) arranged inside the water-stop curtain (1), the supporting wall (2) being adjacent to the water-stop curtain (1), and a crown beam (3) being arranged on the top of the supporting wall (2); A first layer of internal supports (4) is provided between the supporting walls (2) located on the side facing the building, and the first layer of internal supports (4) is located on the crown beam (3); A second layer of support is provided between the support walls (2) below the first layer of internal support (4), and the second layer of internal support (5) is located in the middle of the support wall (2); The first layer of internal supports (4) and the second layer of internal supports (5) are supported by a plurality of lattice columns (6); The supporting wall (2) away from the building is supported and reinforced by a plurality of anchor cables (7), and the anchor cables (7) are arranged obliquely downward.

2. The narrow space deep foundation pit support system according to claim 1 is characterized in that: The first layer inner support (4) comprises a plurality of horizontal support steel sections (8) arranged at a 45-degree angle to the supporting wall (2), one end of the horizontal support steel section (8) being mounted on a concrete corbel (10) provided on the crown beam (3) via a pressurizing end (9), and the other end being mounted on another corresponding concrete corbel (10) via a movable head (11).

3. The narrow space deep foundation pit support system according to claim 2 is characterized in that: The second layer of inner support (5) comprises a plurality of horizontal support steel sections (8), and the projections of the horizontal support steel sections (8) of the second layer of inner support (5) and the horizontal support steel sections (8) of the first layer of inner support (4) on the horizontal plane coincide with each other; A steel purlin (12) is fixedly provided on the support wall (2), and the steel purlin (12) is fixed to the steel cage of the support wall (2) via a plurality of force transmission members (17); A plurality of triangular pieces (13) are provided on the steel purlin (12); one end of the horizontal support steel (8) is mounted on the corresponding triangular piece (13) via a pressurizing end (9); and the other end is mounted on another corresponding triangular piece (13) via a movable head (11).

4. The narrow space deep foundation pit support system according to claim 2 or 3, characterized in that: The pressurizing end (9) is an H-steel, and mounting holes are respectively provided on the two flanges of the H-steel. One flange is fixed to the concrete corbel (10) or the steel purlin (12) by bolts, and the other flange is connected to the horizontal supporting steel (8) by bolts. A plurality of reinforcing ribs are provided between the two flanges of the H-steel on both sides of the web.

5. The narrow space deep foundation pit support system according to claim 2 or 3, characterized in that: A plurality of metal brackets (14) are provided at both ends of the horizontal support steel (8), each of the metal brackets (14) comprising an oblique support rod and a horizontal portion, the oblique support rod being fixedly connected to the support wall (2), and the horizontal portion extending below one end of the horizontal support steel (8).

6. The narrow space deep foundation pit support system according to claim 2 or 3, characterized in that: The horizontal support steel (8) is formed by splicing a plurality of steel sections in sequence end to end, each of which is composed of a plurality of H-section steel beams (15) arranged in parallel, and the plurality of steel beams (15) are fixedly connected by a plurality of cover plates (16), and the projections of the cover plates (16) and the steel beams (15) on the horizontal plane are arranged perpendicularly.

7. The narrow space deep foundation pit support system according to claim 3 is characterized in that: The force transmission member (17) is a "cross" shaped structure, formed by splicing two T-shaped steels arranged back to back, and the flanges of the two T-shaped steels are fixedly connected to each other.

8. The narrow space deep foundation pit support system according to claim 6 is characterized in that: The lattice column (6) is formed by splicing four vertical angle steels, and two adjacent angle steels are fixedly connected by a chute plate; A bracket (19) is fixedly provided on the lattice column (6), a joist (20) is provided between the two brackets (19), the horizontal support steel (8) is fixed on the joist (20), and the projection of the horizontal support steel (8) and the joist (20) on the horizontal plane is perpendicular.

9. The construction method for deep foundation pit support in a narrow space according to claims 1 to 8 comprises the following steps: S1. Construction of water-stop curtain (1) and supporting structure: Construction of water-stop curtain (1) and supporting wall (2) is carried out along the outer side of the foundation pit, and construction of lattice column (6) is carried out simultaneously in the foundation pit; S2. Excavation of foundation pit and construction of anchor cables (7) support: excavation is performed at different locations of the foundation pit according to the design elevation of the first layer of anchor cables (7), and the first layer of anchor cables (7) is arranged and constructed on the supporting wall (2) away from the building side; S3, foundation pit excavation and installation of the first layer of internal support (4): after the first layer of designed support elevation is determined, the first layer of internal support (4) is installed and supported by lattice columns (6); S4, subsequent layered excavation and support construction: continue to excavate in layers according to the designed depth to the next support layer elevation, repeat the arrangement of anchor cables (7) and the construction of the second layer of internal support (5), and support the first layer of internal support (4) through lattice columns (6); S5. Excavation of the foundation pit to the design elevation: Under the joint action of the first layer of internal support (4), the second layer of internal support (5) and the anchor cable (7), the foundation pit is excavated to the design bottom elevation; S6. Construction of the main structure and removal of supports: After the permanent structures such as the corresponding base plate and floor slab have reached the design strength, the prestressing force is released step by step in sequence and the second layer of internal supports (5) and the first layer of internal supports (4) are removed in turn.

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