Prestressed support system for foundation pit and construction method thereof

Abstract

The present application provides a prestressed support system for a foundation pit and a construction method thereof, including steel supports, lattice columns, supporting beams, portal frames, connecting beams, hanging plates, and supporting arches. The steel supports apply horizontal prestress to the foundation pit retaining structure along the axial direction; the lattice columns are hollow structures, which are used to be placed in the foundation pit to vertically support the support system; the supporting beams are erected on the lattice columns to support the steel supports; the portal frames are erected on the supporting beams and are arranged around the steel supports to limit the movement of the steel supports; the connecting beams connect the adjacent steel supports respectively to enhance the rigidity of the support system; the hanging plates are used to connect the ends of the steel supports to the foundation pit retaining structure; and the supporting arches are arranged at the positions where the lattice columns bear the supporting beams. The prestressed support system and its construction method can safely and effectively support and protect the retaining structure of large-span foundation pits, ensure construction safety, and improve the construction efficiency, economic benefits, and environmental benefits of engineering construction through modular recyclable and reusable components and standardized installation methods.

Description

Technical Field

[0001] The present invention relates to the technical field of building construction, and in particular to a foundation pit prestressed support system and a construction method thereof. Background Art

[0002] Foundation pit engineering is widely used in urban construction, subway projects, and underground integrated pipeline corridors. In actual construction, due to the complex environment surrounding the construction site, there are often underground structures in the adjacent areas around the foundation pit. To protect the existing underground buildings from being affected, the conventional support method of supporting piles and prestressed anchor cables cannot be used due to site limitations. Therefore, a corresponding support structure is needed to further support the foundation pit.

[0003] For example, during the construction of some large buildings, the specific support structure design requires comprehensive consideration of site conditions, construction schedule, and ground conditions. First, due to the large span of the foundation pit, the support structure has a significant impact on the stability of the foundation pit and the displacement and deformation of the supporting piles during construction. The stability of the foundation pit retaining structure is crucial to the construction and the safety of the surrounding environment. Therefore, to ensure safe and effective support and protection for large-span foundation pits, the continuity of the support structure and the mechanical stability of the entire structure must be considered. Second, the construction and removal of the support structure will affect the entire project schedule. For example, reinforced concrete support structures often require on-site pouring and waiting for the concrete to harden before continuing construction. Moreover, the removal of reinforced concrete structures is time-consuming and labor-intensive. Therefore, the support structure should be designed to facilitate on-site installation and subsequent removal as much as possible to reduce the amount of construction work. Third, the design and construction of the support structure should be based on the perspective of recyclability, maximizing the reusability of building materials to achieve economic and environmental benefits.

[0004] Therefore, for the support of large-span foundation pits during construction, it is necessary to develop a safe and effective support system and construction method to solve the problems of continuity and stability of the large-span foundation pit support structure during construction, as well as the construction efficiency of the support structure and the recycling of building materials, so as to improve the construction quality and construction safety of the building structure. Summary of the Invention

[0005] In order to solve the problems of continuity and stability of large-span foundation pit support structures, as well as the construction efficiency of support structures and recycling of building materials during construction, the present application provides a foundation pit prestressed support system and a construction method thereof, which can safely and effectively support and protect the retaining structure of large-span foundation pits, ensure construction safety, and improve the construction efficiency, economic benefits and environmental benefits of engineering construction through modular recyclable and reusable components and standardized installation methods.

[0006] The technical solution adopted by the embodiment of the present application to solve its technical problems is: a prestressed support system for a foundation pit, which is used to provide horizontal support force for the foundation pit retaining structure of the building under construction, and is characterized in that it includes steel supports, lattice columns, supporting beams, portal frames, connecting beams, hanging plates, and support arches.

[0007] The steel support applies horizontal prestressing force to the foundation pit retaining structure along the axial direction.

[0008] The lattice column is a hollow structure and is used to be placed in a foundation pit to vertically support the support system.

[0009] The supporting beams are mounted on the lattice columns to support the steel supports.

[0010] The portal is mounted on the joist and surrounds the steel support to restrict movement of the steel support.

[0011] The connecting beams connect adjacent steel supports respectively to enhance the rigidity of the support system.

[0012] The hanging plate is used to connect the steel support end and the foundation pit retaining structure.

[0013] The support arch is arranged at the position where the lattice column carries the supporting beam.

[0014] In a specific embodiment, the steel support is a segmented structure, including a middle section and a fixed end and a movable end located at both ends and respectively connected to the hanging plate; the movable end of the steel support is provided with a retractable adjustment part to adjust the steel support to the required length and apply prestress.

[0015] In a specific embodiment, the hanging plate includes a vertically arranged bonding plate for achieving contact force, the upper end of the bonding plate in contact with the steel support is provided with an external extension plate extending toward the outside of the enclosure structure and used to achieve fixed connection, and the lower end is provided with an internal extension plate extending toward the inside of the enclosure structure.

[0016] In a specific embodiment, the construction method of the foundation pit prestressed support system is characterized by comprising the steps of:

[0017] S1. Design the support system and process each component;

[0018] S2. Install lattice columns in the foundation pit;

[0019] S3. Excavate downward to build the first-floor support system, construct a crown beam on top of the foundation pit retaining structure, and install hanging plates on the crown beam;

[0020] S4. Install arch supports, joists, steel supports, portal frames, and connecting beams on the lattice columns, and apply prestress to the steel supports;

[0021] S5. Continue excavating downwards, construct purlins on the inner side of the foundation pit retaining structure, install hanging plates on the purlins, and construct the next layer of support system according to step S4;

[0022] S6, repeat step S5 to complete the last layer support system;

[0023] S7. Continue to excavate downwards and construct anchor rods and waist beams at corresponding positions of the foundation pit retaining structure, and construct the bottom plate of the building at the bottom of the foundation pit;

[0024] S8. Construct the floor slab of this layer, backfill the fertilizer tank of the foundation pit of this layer, pour the concrete force transmission belt and remove the support system of this layer after the strength requirements are met;

[0025] S9. Repeat step S8 until the first-floor support system is dismantled, and then remove the lattice columns.

[0026] In a specific implementation scheme, in step S4, prestress is applied to the steel support in stages to achieve the design value of the prestress and eliminate the deformation of the components of the support system; after the prestress is applied, the steel support is re-prestressed according to the monitored changes in the prestress of the steel support and the degree of deformation of the foundation pit retaining structure to improve safety.

[0027] In a specific implementation scheme, in step S8, a double-wall structure is also provided in the fertilizer trough of the foundation pit, and the double-wall structure includes buttresses, end plates, and cover plates arranged outside the side walls of the building. One end of the buttress is connected to the side wall of the building, and the other end of the buttress is connected to the end plate arranged along the direction of the side wall of the building. The cover plate is connected to the top of the buttress and the end plate; the interior of the double-wall structure is backfilled before the construction of the cover plate.

[0028] In a specific embodiment, the steel support is obliquely connected to the crown beam and the surrounding purlin. The crown beam and the surrounding purlin are provided with protrusions at the connection parts with the steel support to adapt to the installation of the hanging plate and bear the prestress applied by the steel support.

[0029] In a specific embodiment, the purlin is provided with a load-bearing member connected to the enclosure structure to improve safety; the steel support is provided with a hanger connected to the foundation pit enclosure structure at the end connected to the purlin to prevent the steel support from falling off.

[0030] In a specific embodiment, the bottom of the lattice column is passed through a column pile provided in a foundation pit, and the lattice column is connected to a steel cage provided in the column pile.

[0031] In a specific embodiment, the waterproofing construction at the connection between the lattice column and the bottom plate of the building body comprises the following steps:

[0032] T1. First, pour the cushion layer, lay the waterproof membrane on the cushion layer, turn the waterproof membrane up along the lattice column, and set the waterproof protective layer on the waterproof membrane;

[0033] T2. Tie the bottom plate reinforcement and weld it to the lattice columns. Install a waterstop steel plate with the water-facing side facing downward at the upper edge of the waterproof membrane of the lattice columns.

[0034] T3. Reserve an empty slot above the connection between the bottom plate and the lattice column, and pre-set a waterstop steel plate with the water-facing side facing downward on the side wall of the empty slot;

[0035] T4. Pour the bottom slab concrete and apply waterproof coating at the intersection of the bottom of the reserved slot between the lattice column and the bottom slab;

[0036] T5. Pour concrete into the empty groove reserved in the base plate.

[0037] The advantages of the embodiments of the present application are:

[0038] 1. The prestressed support system is designed with segmented steel supports, which is convenient for processing and on-site assembly. The telescopic adjustment of the movable end of the steel support not only facilitates the arrangement of load-bearing equipment for prestressing, but also improves the adjustment flexibility during assembly and connection of the steel support and the convenience during disassembly.

[0039] 2. The components of this prestressed support system can be fabricated early in the project and quickly installed on-site, eliminating the impact of reinforced concrete support structures on construction schedules. Furthermore, post-use dismantling is minimal, further accelerating construction speed. The components of the prestressed support system can be recycled and reused after disassembly, conserving construction materials and improving both economic and environmental benefits.

[0040] 3. The construction method of the prestressed support system standardizes and systematizes the operation process of modular components, which can not only achieve safe support for large-span foundation pits in the horizontal direction, but also can be applied to the support construction of deep foundation pit retaining structures.

[0041] 4. The waterproofing measures in the construction method of the prestressed support system can effectively avoid the impact of the support system components on the waterproof performance of the building during construction, avoid waterproofing rework in the later stage, and thus further improve the engineering construction quality of the support system and its construction method.

[0042] 5. The double-wall structure and concrete force transmission belt set up in the foundation pit fertilizer trough by this prestressed support system construction method avoid the adverse effects of excessive soil pressure around the foundation pit on the building structure, thereby improving the strength of the building structure and the safety of engineering construction. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1This is a schematic diagram of a foundation pit prestressed support system according to the present invention;

[0044] Figure 2 This is a schematic diagram of the steel support erection of a prestressed support system for a foundation pit according to the present invention;

[0045] Figure 3 This is a schematic diagram of the installation of a portal frame of a foundation pit prestressed support system according to the present invention;

[0046] Figure 4 This is a schematic diagram of the fixed end and movable end of a steel support of a foundation pit prestressed support system of the present invention;

[0047] Figure 5 This is a schematic diagram of the middle section of a steel support system for a foundation pit prestressed support system according to the present invention;

[0048] Figure 6 This is a schematic diagram of a connecting beam of a foundation pit prestressed support system according to the present invention;

[0049] Figure 7 This is a schematic diagram of column piles and lattice columns of a foundation pit prestressed support system according to the present invention;

[0050] Figure 8 This is a partial cross-sectional diagram of a foundation pit prestressed support system column pile and lattice column of the present invention;

[0051] Figure 9 This is a schematic diagram of waterproofing at the connection between the lattice columns and the bottom plate of a foundation pit prestressed support system of the present invention;

[0052] Figure 10 A schematic diagram of the hanger bars of the purlin bearing members of the foundation pit prestressed support system of the present invention;

[0053] Figure 11 A schematic diagram of the embedded reinforcement of the purlin bearing member of the prestressed support system of a foundation pit according to the present invention;

[0054] Figure 12 Schematic diagram of a support arch of a prestressed support system for a foundation pit according to the present invention;

[0055] Figure 13 Schematic diagram of working conditions P1-P6 of a construction method of a foundation pit prestressed support system according to the present invention;

[0056] Figure 14 Schematic diagram of working conditions P7-P12 of a construction method of a foundation pit prestressed support system according to the present invention;

[0057] Figure 15 Schematic diagram of working conditions P13-P17 of a construction method of a prestressed support system for a foundation pit according to the present invention.

[0058] Description of main reference numerals:

[0059] 1-convex body; 2-lattice column; 3-steel support; 301-movable end; 302-fixed end; 303-middle section; 4-connecting beam; 5-support beam; 6-enclosing structure; 7-waterstop steel plate; 8-attached plate; 9-waterproof coating; 10-base plate; 11-column pile; 12-waterproof protective layer; 13-waterproof membrane; 14-cushion; 15-empty groove; 16-support arch; 17-gantry; 18-crown beam; 19-purlin; 20-construction depth of foundation pit; 21-anchor rod; 22-concrete force transmission belt; 23-floor slab; 24-hanger bar; 25-embedded bar; 26-hanging plate. DETAILED DESCRIPTION

[0060] The present application provides a prestressed foundation pit support system and a construction method thereof to solve the problems of continuity and stability of the large-span foundation pit support structure, as well as the construction efficiency of the support structure and the recycling of building materials during the construction process. The overall concept is as follows:

[0061] See also Figure 1 The present invention provides a prestressed foundation pit support system for providing horizontal support for the foundation pit retaining structure 6 of a building under construction, comprising steel supports 3, lattice columns 2, joists 5, portal frames 17, connecting beams 4, hanging plates 26, and support arches 16. The steel supports 3 apply horizontal prestress to the foundation pit retaining structure 6 along the axial direction; the lattice columns 2 are hollow structures used to be placed in the foundation pit to provide vertical support for the support system; the joists 5 are mounted on the lattice columns 2 to support the steel supports 3; the portal frames 17 are mounted on the joists 5 and surround the steel supports 3 to restrict their movement; the connecting beams 4 connect adjacent steel supports 3 to enhance the rigidity of the support system; the hanging plates 26 are used to connect the ends of the steel supports 3 to the foundation pit retaining structure 6; and the support arches 16 are arranged at the positions where the lattice columns 2 support the joists 5. The prestressed support system is designed with modular recyclable and reusable components. It can be processed in the early stages of the project and quickly installed on site, making it easy to disassemble later. It can safely and effectively support and protect the retaining structure 6 of a large-span foundation pit, thereby improving the construction efficiency, economic benefits and environmental benefits of the project.

[0062] The steel support 3 in this example is a segmented structure, including a middle section 303 and fixed ends 302 and movable ends 301 at both ends, which are connected to the hanging plate 26 respectively. The movable end 301 of the steel support 3 is provided with a retractable adjustment member to adjust the steel support 3 to the required length and apply prestress. Figure 2-Figure 5In this example, the steel support 3 utilizes a tubular structure, with the fixed end 302, movable end 301, and middle section 303 axially connected via a flange structure. The fixed end 302 of the steel support 3 can be connected to the hanging plate 26 via the flange, facilitating modular manufacturing and on-site installation. Installation can be achieved through custom manufacturing or on-site splicing. Furthermore, the middle section 303 of the steel support 3 can be axially configured as a single section or a segmented structure, allowing for more flexible assembly lengths through the design and manufacture of standard sections. When the middle section 303 utilizes a segmented structure, the segments can be bolted together via flanges located at both ends. The steel support 3 can be pre-assembled on the ground according to the measured width of the foundation pit. The movable end 301 of each steel support 3 has a flexible adjustment margin to accommodate variations in the pit's cross-sectional width and support length requirements. The segmented structure of the steel support 3 and its adjustable movable end 301 not only facilitate the placement of load-bearing equipment for prestressing, but also enhance the flexibility of assembly and connection, as well as the ease of disassembly.

[0063] The axis deviation, flexural deformation, and end face perpendicularity error of the assembled steel support 3 must be within the allowable range. Prestress can be applied by installing a pre-axial force device at the movable end 301. For example, a hydraulic jack can be placed at the top pressure position of the movable end 301. After the prestress reaches a predetermined value, a pad can be installed at the movable end 301 and firmly fixed. Then, the hydraulic jack can be removed to complete the installation of the steel support 3.

[0064] In this example, the lattice column 2 is welded by 4 angle steels and gusset plates 8. Figure 2 During construction, the position of the gusset plate 8 is fine-tuned according to the specific situation. During hoisting, the deformation under the hoisting load is strictly controlled, and the installation positioning is accurate. For example, in this example, the center line deviation of the lattice column 2 is ±5mm, the elevation deviation range of the top and bottom of the lattice column 2 is 0~20mm, and the verticality deviation of the lattice column 2 is not greater than 1 / 200 of its length.

[0065] See also Figure 2 、 Figure 3 Under each steel support 3, lattice columns 2 are welded with bracing arches 16 on the corresponding sides of the gusset plates 8 to support the joists 5. Bracing arches 16 can be fabricated from steel plates. In this example, the joists 5 are made from two H-shaped steel sections, securely welded to the bracing arches 16. Connecting plates are welded to the upper and lower flanges of the H-shaped steel sections, and ribs are welded to the webs to enhance the structural strength of the joists 5.

[0066] See also Figure 3 The gantry 17 is a frame structure welded on the joist 5 and can be made of angle steel. Its function is to fix the steel support 3 to prevent it from moving. Figure 6 , connecting beams 4 are set for adjacent steel supports 3 and connected respectively to prevent the steel supports 3 from deformation.

[0067] In this example, the connection and prestressing of the steel support 3 and the foundation pit retaining structure 6 are achieved through the hanging plate 26. Figure 4 The hanging plate 26 includes a vertically arranged bonding plate for achieving contact force. The upper end of the bonding plate in contact with the steel support 3 is provided with an extension plate extending toward the outside of the retaining structure 6 and used for achieving fixed connection, and the lower end is provided with an inner extension plate extending toward the inside of the retaining structure 6. During use, the bonding plate is tightly attached to the vertical surface of the foundation pit retaining structure 6, and transmits the prestress received by the contact with the steel support 3 to the retaining structure 6 of the foundation pit. The outer extension plate overlaps the upper horizontal surface of the foundation pit retaining structure 6, and can be further fastened by providing a through-hole structure and expansion bolts on the outer extension plate. The inner extension plate can prevent the steel support 3 from becoming unstable and falling. In some embodiments, the fixed end 302 and the movable end 301 of the steel support 3 can be connected to the hanging plate 26 by bolts.

[0068] This embodiment also provides a construction method for a foundation pit prestressed support system, comprising the following steps:

[0069] S1. Design the support system and process each component;

[0070] S2, construct and install lattice column 2 in the foundation pit;

[0071] S3, excavate downward to build the first-floor support system, construct the crown beam 18 on the top of the foundation pit retaining structure 6, and install the hanging plate 26 on the crown beam 18;

[0072] S4. Install the support arch 16, the joist 5, the steel support 3, the portal frame 17, and the connecting beam 4 on the lattice column 2, and apply prestress to the steel support 3;

[0073] S5, continue to excavate downwards, construct the purlin 19 inside the foundation pit retaining structure 6, install the hanging plate 26 on the purlin 19, and construct the next layer of support system according to step S4;

[0074] S6, repeat step S5 to complete the last layer support system;

[0075] S7, continue to excavate downwards and construct anchor rods 21 and waist beams at corresponding positions of the foundation pit retaining structure 6, and construct the bottom plate 10 of the building body at the bottom of the foundation pit;

[0076] S8, construct the floor slab 23 of this layer, backfill the fertilizer tank of this layer, pour the concrete force transmission belt 22 and remove the support system of this layer after reaching the strength requirement;

[0077] S9. Repeat step S8 until the first-floor support system is dismantled, and then remove the lattice column 2.

[0078] In this example, see Figure 7、 Figure 8 The bottom of the lattice column 2 is inserted into the column pile 11 set in the foundation pit, and the lattice column 2 is connected to the steel cage set in the column pile 11. The steel support 3 is obliquely intersected with the crown beam 18 and the surrounding purlin 19. The crown beam 18 and the surrounding purlin 19 are provided with a protrusion 1 at the connection part with the steel support 3 to adapt to the installation of the hanging plate 26 and bear the prestress applied by the steel support 3. For details, please refer to Figure 12 The convex body 1 is formed by the crown beam 18 or the surrounding purlin 19 protruding outward on one side of the foundation pit to form at least one vertical surface for contacting and bearing force with the bonding plate of the hanging plate 26, and an upper horizontal surface overlapped with the extended flat plate of the hanging plate 26. The steel plate can be embedded in the interior of the convex body 1 and become one with the crown beam 18 or the surrounding purlin 19 through concrete pouring. The outward protruding vertical surface constructed by the convex body 1 can also realize the connection mode of the crown beam 18 or the surrounding purlin 19 and the steel support 3 at the corresponding oblique angle.

[0079] During construction, according to the design plan, the column piles 11 are constructed before the foundation pit is excavated. Before construction, a check is carried out to avoid the column piles 11 being set at positions that overlap with structural columns, walls, etc., to ensure that the verticality error of the column pile 11 drilling holes, as well as the pile foundation settlement, horizontal displacement, and differential settlement meet the design requirements. When using the bored pile construction method, measures should be taken to ensure that the column pile 11 steel cage does not deform and is placed in the center of the column pile 11 body. The lattice column 2 is welded to the column pile 11 steel cage, and the verticality is controlled during installation. The bottom of the lattice column 2 is inserted into the concrete of the column pile 11 to a certain depth and the insertion depth is strictly controlled to ensure that the lattice column 2 has a reliable anchoring depth. Within the overlapping depth of the lattice column 2 and the column pile 11 steel cage, the stirrups of the steel cage can be denser to enhance the stability of the structural connection. To control the axial direction of the lattice column 2, a temporary sling can be set up on the ground to suspend and protect the lattice column 2. The temporary sling can be removed after the concrete of the column pile 11 reaches 70% of the design strength. The pile holes above the building floor 10 are filled with sand. When excavating the foundation pit, the excavation speed and excavation sequence must be controlled within 2 meters around the lattice column 2 to avoid lateral additional earth pressure on the lattice column 2.

[0080] After the lattice columns 2 are constructed and installed, excavation is carried out downward within the foundation pit to construct the first-floor support system. When excavation reaches a certain distance below the designed installation location of the first-floor steel supports 3, positioning measurements and layout are performed. The position of the crown beam 18, to which the steel supports 3 of this layer are connected, is determined according to the design requirements. Crown beam 18 can be constructed using a monolithic concrete pouring method atop the foundation pit retaining structure 6. The center position of the steel supports 3 is determined on crown beam 18, and the cross-line method can be used to accurately locate the center position, facilitating the installation of the steel supports 3. A hanging plate 26 is installed on the protruding body 1 of crown beam 18 and secured to the protruding body 1 with expansion bolts.

[0081] Bracing arches 16 are welded to the gusset plates 8 on both sides of the lattice columns 2 at the same elevation as the steel supports 3. The pre-fabricated joists 5 are then mounted on the bracing arches 16 and welded securely. The steel supports 3 are then erected on the joists 5. Using on-site lifting equipment, the steel supports 3 are assembled using a splicing method to accommodate the varying lengths required for the foundation pit's cross-sectional width. During installation, the coaxiality and end face verticality of the steel supports 3 must be checked to ensure compliance with operational requirements. The steel structure must be free of weld marks, cracks, and other quality defects. The movable ends 301 and fixed ends 302 of each layer of steel supports 3 should be uniformly located on the same side, and high-strength bolts should be used to connect the flanges.

[0082] In this example, each layer of the support system consists of seven steel supports 3 of varying lengths. After the steel supports 3 are laid and installed, portal frames 17 are installed at the corresponding planned locations to secure the steel supports 3 and prevent them from moving. During installation, the portal frames 17 are securely welded to the joists 5. Connecting beams 4 made of sectioned steel are then installed between adjacent steel supports 3. The ends of the connecting beams 4 are clamp-type structures, which clamp and hold the adjacent steel supports 3 to prevent them from moving and deforming, thereby enhancing the rigidity of the support system.

[0083] When prestressing the first-floor steel supports 3, to prevent excessive deflection during prestressing, the self-weight deflection of the steel supports 3 is corrected to horizontal before prestressing. Prestressing can be applied in stages to achieve the design prestress value and eliminate deformation of the support system components. After prestressing is completed, the steel supports 3 are re-prestressed based on the monitored changes in prestress in the steel supports 3 and the degree of deformation of the foundation pit retaining structure 6 to improve safety. Specifically, two hydraulic jacks can be symmetrically arranged at the movable ends 301 of the steel supports 3 to simultaneously apply prestress. Initial prestress can be applied to the steel supports 3, and pads can be placed and securely fixed at the movable ends 301 to ensure secure installation. The design prestress can be applied in five stages: 20%, 40%, 60%, 80%, and 100% of the design prestress value. The first stage applies a low prestress, held for 2 minutes, and each subsequent stage is held for 5 minutes to eliminate component deformation, ensure prestress effectiveness, and minimize stress loss. In this example, an axial force gauge for measuring prestress is installed at the movable end 301 of the steel support 3. If the jack's travel is insufficient, a steel wedge can be inserted to reload the jack to the designed prestress. Once the prestress is fully applied, the pad at the movable end 301 is securely fixed, and the jack is then unloaded.

[0084] Increase the monitoring frequency within 12 hours after the first prestressing. If prestress loss or obvious convergence of deformation rate of retaining structure 6 is found, prestress must be re-added to the design value. When the temperature difference between day and night is too large, resulting in loss of prestress of steel support 3, prestress should be re-added to the design value during the low temperature period of the same day. Strengthen the detection of prestress of steel support 3 during earth excavation. When prestress loss is found during the detection and the horizontal displacement rate of the pile of retaining structure 6 exceeds the warning value, increase the prestress of steel support 3 to control deformation. When the change of prestress of steel support 3 is greater than 3%, re-prestressing is implemented, and the re-prestressing must meet the design safety requirements.

[0085] The prestressed support system of this embodiment is a three-layer structure. After the construction of the first layer support system, the excavation of the foundation pit continues in a layered and segmented manner to prevent mechanical collision. The excavation is carried out manually with small machinery to reduce the exposure time without support. When the excavation reaches a certain distance from the bottom of the designed installation position of the second layer of steel support 3, the purlin 19 is constructed on the inner side of the foundation pit retaining structure 6. In some embodiments, the purlin 19 can be provided with a steel structure load-bearing member connected to the foundation pit retaining structure 6 to enhance the load-bearing safety; for example, the load-bearing members of this embodiment include hanger bars 24 and embedded bars 25, please refer to Figure 10 、 Figure 11 The lower end of the hanger bar 24 is embedded in the structure of the purlin 19, and the upper end is vertically welded to the main reinforcement of the pile body of the retaining structure 6. One end of the planting bar 25 is embedded in the structure of the purlin 19, and the other end is horizontally connected to the pile body of the retaining structure 6 adjacent to the purlin 19. Furthermore, the end of the steel support 3 connected to the purlin 19 can be equipped with a hanger connected to the foundation pit retaining structure 6 to prevent the steel support 3 from falling off.

[0086] During the construction of the purlin 19, rebar 25 can be planted on the pile body of the retaining structure 6, and hanger bars 24 can be welded to the main reinforcement of the pile body of the retaining structure 6 above the purlin 19. The pile body of the retaining structure 6 at the purlin 19 should be roughened to enhance the stability of the structural connection. Hanging plates 26 are installed on the protruding body 1 structure of the purlin 19, and the construction and prestressing of the second-layer support system are completed according to the component installation method of the first-layer support system. It should be pointed out that after the construction of the second-layer support system is completed, the prestressing of its upper-layer support system is reviewed and adjusted to meet the design requirements, and adjustments are made according to the deformation and force monitoring of the on-site retaining structure 6.

[0087] Similarly, the above construction steps are followed to continue excavating downward, constructing the purlin 19, installing related components, and applying prestressing force to construct the third layer, which is the final layer of the support system in this example. It should be noted that as construction progresses downward, the specifications of the related components of the prestressed support system can be gradually improved to enhance the structural strength. For example, in this example, the steel support 3 of the first layer support system uses a 609mm diameter and 16mm wall thickness pipe, the second layer uses a 800mm diameter and 16mm wall thickness pipe, and the final layer, which is the third layer, uses a 800mm diameter and 20mm wall thickness pipe. This meets the foundation pit support force requirements that vary with depth and improves the project safety factor.

[0088] In this embodiment, after the installation of the last layer of support system is completed, the earthwork is continued downward to the elevation of the first anchor rod 21 to carry out the construction of the first anchor rod 21 and the waist beam; then the earthwork is continued to the elevation of the second anchor rod 21 to carry out the construction of the second anchor rod 21 and the waist beam, thereby further enhancing the stability of the foundation pit structure. After the construction of the second anchor rod 21 is completed, the earthwork is excavated to the bottom of the foundation pit for the installation and construction of the tower crane, and the bottom plate 10 of the building body is constructed at the bottom of the foundation pit, and then the floor slab 23 of the last layer is constructed. It should be pointed out that when constructing the bottom plate 10 of the building body, further waterproofing work can be carried out on the intersection of the bottom plate 10 and the lattice column 2, please refer to Figure 9 In this example, the waterproofing construction of the connection between the lattice column 2 and the bottom plate 10 of the building body includes the following steps:

[0089] T1. First, pour the cushion layer 14, lay the waterproof membrane 13 on the cushion layer 14, turn the waterproof membrane 13 up along the lattice column 2, and set the waterproof protective layer 12 on the waterproof membrane 13;

[0090] T2, tie the bottom plate 10 steel bars and weld them to the lattice column 2, and set the water-stop steel plate 7 with the water-facing side facing downward at the upper edge of the waterproof membrane 13 of the lattice column 2;

[0091] T3. Reserve an empty slot 15 above the connection between the bottom plate 10 and the lattice column 2, and pre-set a water-stop steel plate 7 with the water-facing side facing downward on the side wall of the empty slot 15;

[0092] T4, pouring concrete for the base plate 10, and applying waterproof coating 9 at the intersection of the bottom of the empty groove 15 reserved for the lattice column 2 and the base plate 10;

[0093] T5. Pour concrete into the empty groove 15 reserved in the base plate 10.

[0094] In this example, the waterproof membrane 13 is a 4mm thick SBS waterproof membrane. The waterproof membrane 13 is laid 300mm up at the position of the lattice column 2. The waterproof protective layer 12 is a 5mm mortar. The waterproof coating 9 is a 4mm thick penetrating crystallization waterproof coating. C40 micro-expansive concrete is used to cast the empty groove 15.

[0095] When backfilling the foundation pit fertilizer trough at each level, it is considered that the surrounding backfill soil pressure will act on the building. At this time, the concrete strength of the building's outer wall and floor slab 23 has not yet stabilized. At the same time, the floor slab 23 has a large span and a small bearing capacity. Excessive soil pressure will have an irreversible effect on the structure. In order to ensure the structural stress safety of the building, a double wall structure is also provided in the foundation pit fertilizer trough of each level. The double wall structure includes buttresses, end plates, and cover plates arranged outside the side walls of the building. One end of the buttress intersects with the side wall of the building, and the other end of the buttress intersects with the end plate arranged along the side wall of the building. The cover plate is connected to the top of the buttresses and end plates. Before the cover plate is constructed, the interior of the double wall structure is backfilled. In this example, the backfill material is fluidized solidified soil. Furthermore, support pile buttresses are provided on the support piles of the foundation pit retaining structure 6 to enhance the support stability of the retaining structure 6. After the last layer of fertilizer trough is backfilled, the concrete force transfer belt 22 is poured. In this example, a C20 concrete force transfer belt 22 with a thickness of not less than 1m is poured at the height corresponding to each floor slab 23. After the concrete force transfer belt 22 reaches the strength requirement, the steel support 3 of that layer, as well as the supporting beam 5, gantry 17, connecting beam 4 and other components, are removed. When removing the steel support 3, a crane is used to tie the steel support 3 with steel wire ropes. A jack is placed at the movable end 301 to apply a top force. The pad is removed, and the jacking force is released. After removing the jack, the high-strength connecting bolts of the flange of the steel support 3 are removed. The steel support 3 is then hoisted out in sections for recycling. During the removal of the steel support 3, various monitoring of the foundation pit retaining structure 6 is strengthened, and the removal plan is adjusted according to the monitoring results. A graded unloading method is adopted to avoid stress mutations that have adverse effects on the retaining structure 6 and the main structure of the building. Following the same steps, the construction of the second and first floor slabs 23, the setting of the double wall structure, the backfilling of the foundation pit fertilizer trough, the pouring of the concrete transfer belt 22, the dismantling of the steel support 3 and the supporting beam 5, the portal frame 17, the connecting beam 4 and other related components are completed in sequence. Then, the structural columns are cut and removed, the structural columns remaining in the floor slab 23 are cleaned, and a higher grade micro-expansive concrete is used for pouring.

[0096] For specific construction methods, please refer to Figure 13-15Conditions P1-P17. In condition P1, the retaining structure 6, column piles 11, and lattice columns 2 of the foundation pit are constructed; in condition P2, the earthwork is excavated to the required foundation pit construction depth 20, which is the construction elevation of the first-layer support system, and the crown beam 18 is constructed and the first-layer support system is erected; in condition P3, the earthwork is continued to be excavated to the required foundation pit construction depth 20, which is the construction elevation of the second-layer support system in this example, and the purlin 19 of this layer is constructed and the support system of this layer is erected; in condition P4, the earthwork is continued to be excavated to the required foundation pit construction depth 20, which is the construction elevation of the last-layer support system in this example. At the elevation, build the purlin 19 of this layer and set up the support system of this layer; in working condition P5, continue to excavate the earth to the required foundation pit construction depth 20, that is, the construction elevation of the first anchor rod 21 in this example, and construct the anchor rod 21 and the waist beam at this position; in working condition P6, continue to excavate the earth to the required foundation pit construction depth 20, that is, the construction elevation of the second anchor rod 21 in this example, and construct the anchor rod 21 and the waist beam at this position; in working condition P7, continue to excavate the earth to the required foundation pit construction depth 20, that is, the bottom elevation of the foundation pit; in working condition P8, construct The bottom plate 10 of the building body and the floor slab 23 of the last layer are constructed; in working condition P9, the foundation pit fertilizer tank is backfilled to the predetermined position below the floor slab 23 of the last layer, and then the concrete force transfer belt 22 is poured; in working condition P10, after the concrete force transfer belt 22 reaches the design strength, the relevant components of the last layer support system are removed; in working condition P11, the second layer building structure and floor slab 23 of this example are constructed; in working condition P12, the foundation pit fertilizer tank is further backfilled to the predetermined position below the floor slab 23 of the second layer, and then the concrete force transfer belt 22 is poured; in working condition P13, after the concrete force transfer belt 22 reaches the design strength, the relevant components of the last layer support system are removed; in working condition P14, the second layer building structure and floor slab 23 of this example are constructed; in working condition P15, the foundation pit fertilizer tank is further backfilled to the predetermined position below the floor slab 23 of the second layer, and then the concrete force transfer belt 22 is poured; in working condition P16, the concrete force transfer belt 22 is poured After the concrete force transfer belt 22 reaches the design strength, the related components of the second-layer support system are removed; in working condition P14, the first-floor building structure and floor slab 23 of this example are constructed; in working condition P15, the foundation pit fertilizer trough is continued to be backfilled to the predetermined position below the floor slab 23 of the first floor, and then the concrete force transfer belt 22 is poured; in working condition P16, after the concrete force transfer belt 22 reaches the design strength, the related components of the first-floor support system and the lattice column 2 are removed; in working condition P17, the building structure and floor slab 23 are continued to be constructed upwards to complete the backfilling of the foundation pit fertilizer trough.

[0097] In summary, the present invention provides a prestressed support system for foundation pits and a construction method thereof, which can safely and effectively support and protect the retaining structures of large-span foundation pits, ensure construction safety, and improve the construction efficiency, economic benefits and environmental benefits of the project through modular recyclable and reusable components and standardized installation methods.

[0098] Finally, it should be noted that the above embodiments are merely examples for the purpose of illustrating the present invention and are not intended to limit the embodiments. Those skilled in the art will readily appreciate that other variations or modifications based on the above descriptions are possible. It is not necessary and impossible to provide an exhaustive list of all embodiments. However, obvious variations or modifications arising therefrom remain within the scope of protection of the present invention.

Claims

1. A prestressed support system for a foundation pit, used to provide horizontal support for the foundation pit retaining structure of a building under construction, characterized in that: include: Steel support, which applies horizontal prestressing to the foundation pit retaining structure along the axial direction; Lattice columns are hollow structures used to be placed in foundation pits to provide vertical support for the support system. Joists, which are erected on lattice columns to support the steel supports; A gantry frame, which is installed on the joists and surrounds the steel supports to limit the movement of the steel supports; Connecting beams connect adjacent steel supports to enhance the rigidity of the support system; Hanging plates, which are used to connect the ends of the steel supports with the foundation pit retaining structure; as well as Support arches, which are set at the position where the lattice columns carry the joists; The steel support is a segmented structure, including a middle section and fixed and movable ends located at both ends and connected to the hanging plates respectively; the movable ends of the steel support are provided with retractable adjustment parts to adjust the steel support to the required length and apply prestress; The hanging plate includes a vertically arranged bonding plate for achieving contact force, the upper end of the bonding plate in contact with the steel support is provided with an extension plate extending toward the outside of the enclosure structure and for achieving fixed connection, and the lower end is provided with an inner extension plate extending toward the inside of the enclosure structure; Among them, a double-wall structure is also provided in the foundation pit fertilizer trough, and the double-wall structure includes buttresses, end plates, and cover plates arranged on the outside of the side walls of the building. One end of the buttress is connected to the side wall of the building, and the other end of the buttress is connected to the end plate arranged along the direction of the side wall of the building. The cover plate is connected to the top of the buttress and the end plate; the interior of the double-wall structure is backfilled before the construction of the cover plate.

2. The construction method of a foundation pit prestressed support system according to claim 1, characterized in that: Including steps: S1. Design the support system and process each component; S2. Install lattice columns in the foundation pit; S3. Excavate downward to build the first-floor support system, construct a crown beam on top of the foundation pit retaining structure, and install hanging plates on the crown beam; S4. Install arch supports, joists, steel supports, portal frames, and connecting beams on the lattice columns, and apply prestress to the steel supports; S5. Continue excavating downwards, construct purlins on the inner side of the foundation pit retaining structure, install hanging plates on the purlins, and construct the next layer of support system according to step S4; S6, repeat step S5 to complete the last layer support system; S7. Continue to excavate downwards and construct anchor rods and waist beams at corresponding positions of the foundation pit retaining structure, and construct the bottom plate of the building at the bottom of the foundation pit; S8. Construct the floor slab of this layer, backfill the fertilizer tank of the foundation pit of this layer, pour the concrete force transmission belt and remove the support system of this layer after the strength requirements are met; S9. Repeat step S8 until the first-floor support system is dismantled, and then remove the lattice columns.

3. The construction method of a foundation pit prestressed support system according to claim 2, characterized in that: In step S4, prestressing is applied to the steel support in stages to achieve the design value of the prestressing and eliminate deformation of the components of the support system; After the prestressing is completed, the steel support is re-prestressed according to the monitored changes in the prestress of the steel support and the degree of deformation of the foundation pit retaining structure to improve safety.

4. The construction method of a foundation pit prestressed support system according to claim 3, characterized in that: The steel support is obliquely connected to the crown beam and the surrounding purlin. The crown beam and the surrounding purlin are provided with protrusions at the connection parts with the steel support to adapt to the installation of the hanging plate and bear the prestress applied by the steel support.

5. A construction method for a foundation pit prestressed support system according to any one of claims 3 to 4, characterized in that: The purlin is provided with a load-bearing member connected to the enclosure structure to improve safety; the steel support is provided with a hanger connected to the foundation pit enclosure structure at the end connected to the purlin to prevent the steel support from falling off.

6. The construction method of a foundation pit prestressed support system according to claim 5, characterized in that: The bottom of the lattice column is passed through a column pile arranged in a foundation pit, and the lattice column is connected to a steel cage arranged in the column pile.

7. The construction method of a foundation pit prestressed support system according to claim 6, characterized in that: The waterproof construction of the connection between the lattice column and the bottom plate of the building body includes the following steps: T1. First, pour the cushion layer, lay the waterproof membrane on the cushion layer, turn the waterproof membrane up along the lattice column, and set the waterproof protective layer on the waterproof membrane; T2. Tie the bottom plate reinforcement and weld it to the lattice columns. Install a waterstop steel plate with the water-facing side facing downward at the upper edge of the waterproof membrane of the lattice columns. T3. Reserve an empty slot above the connection between the bottom plate and the lattice column, and pre-set a waterstop steel plate with the water-facing side facing downward on the side wall of the empty slot; T4. Pour the bottom slab concrete and apply waterproof coating at the intersection of the bottom of the reserved slot between the lattice column and the bottom slab; T5. Pour concrete into the empty groove reserved in the base plate.

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