Prefabricated pile-beam-wall-anchor prestressed retaining structure for foundation pit and construction method

Abstract

The application discloses a prefabricated foundation pit pile-beam-wall-anchor rod prestressed enclosure structure technical system and a construction method, which comprises the following steps: a. measuring and laying out a stake to determine a pile position, and setting a prefabricated pile; b. excavating earthwork to a prefabricated beam bottom elevation; c. hoisting the prefabricated beam; d. prestressed tendon perforation, tensioning and anchoring; e. prefabricated beam inside grouting, beam body anchor rod setting; f. continuing to excavate earthwork to a next prefabricated beam bottom elevation; g. continuing to hoist the prefabricated beam, prestressed tendon perforation, tensioning and anchoring; h. hoisting a prefabricated shear wall plate, and installing double-row flat-hole T-shaped steel plate support strips; i. prefabricated shear wall plate back grouting and anchor rod setting; j. installing an eight-shaped steel support; k. repeating steps b to j until the whole prefabricated foundation pit enclosure structure construction is completed; and l. acceptance and monitoring. The technical scheme of the application follows the principle of 'layered, segmented and part-positioned earthwork excavation and integrated prefabricated assembly', and has the advantages of reasonable structure design, strong bearing capacity, high assembly rate and fast construction speed.

Description

Technical Field

[0001] This invention belongs to the field of prefabricated building technology, specifically relating to prefabricated foundation pit pile-beam-wall-anchor prestressed retaining structure and construction method. Background Technology

[0002] Prefabricated construction technology represents a significant transformation from traditional wet construction methods, offering substantial social benefits such as improved working conditions and enhanced civilized construction practices. In recent years, the Ministry of Housing and Urban-Rural Development has continuously issued a series of laws, regulations, and related provisions, gradually promoting the application of prefabricated construction technology in new buildings across China. This new technology has become a major issue for the transformation and upgrading of the construction industry. While its application in building structures has yielded remarkable results, it is also crucial for the development of innovative technologies in underground structure construction.

[0003] The prefabricated pile-anchor integral foundation pit retaining structure technologies disclosed by Gao Luheng of Jiangsu Vocational College of Engineering, including "A Construction Method for Prefabricated Pile-Anchor Integral Foundation Pit Retaining Structure (CN107178085B)," "A Construction Method for Prefabricated Pile-Anchor Integral Foundation Pit Retaining Structure (CN107178086B)," "A Construction Method for H-shaped Steel Anchor Composite Pile-Prefabricated Panel Wall Foundation Pit Retaining Structure (CN108222017B)," and "An Improved Construction Method for H-shaped Steel Anchor Composite Pile-Prefabricated Panel Wall Foundation Pit Retaining Structure (CN108487255B)," effectively apply prefabricated assembly structures to foundation pit retaining structures, which is of great significance for promoting the reform of construction methods on a larger scale in the industry.

[0004] However, in practical engineering projects, it has been found that existing technologies require numerous support devices during the hoisting of prefabricated components. These support devices are difficult to install, and the installation of anchor bolts has a significant impact on the prefabricated structure after hoisting. Furthermore, the support devices need to be disassembled after assembly, leading to low safety and increased costs. This application, however, strengthens the overall structure of the foundation pit retaining wall, allowing for the combined design of the retaining structure and underground structure. It requires fewer support devices, resulting in higher prefabrication and assembly rates, optimized processes, and convenient construction, effectively solving this pain point. Furthermore, it encourages collaborative research and development between universities and enterprises to develop more new technologies, processes, and methods tailored to on-site construction, contributing significantly to the application of new prefabricated construction technologies in my country. Summary of the Invention

[0005] The purpose of this invention is to provide a prefabricated foundation pit pile-beam-wall-anchor prestressed retaining structure and construction method to solve the problems mentioned in the background art.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] The prefabricated foundation pit pile-beam-wall-anchor prestressed retaining structure includes precast piles, precast beams, precast shear wall panels, anchors, transverse prestressing tendons, inclined prestressing tendons, double-row flat-hole T-shaped steel plate support strips, V-shaped steel supports, and semi-triangular pyramidal anchoring grooves for prestressing tendons. The precast piles and precast beams are connected by transverse and inclined prestressing tendons. The precast shear wall panels are placed in sections within the area formed by the precast piles and precast beams. The precast piles are connected to the precast beams... Prestressed tendon through-holes are provided on the pile body at the joint, and prestressed ducts are provided inside the precast beam. The prestressed tendon semi-triangular cone anchor grooves are staggered on the upper and lower parts of the precast beam. The upper and lower ends of the precast shear wall panel are connected to the precast beam, and the adjacent precast shear wall panels are provided with temporary fixed double-row flat hole T-shaped steel plate support strips. The precast shear wall panel and the precast beam body are provided with anchor holes, and each layer of the structural surface is provided with the figure-eight steel support.

[0008] The construction method for prefabricated foundation pit pile-beam-wall-anchor prestressed retaining structure includes the following steps:

[0009] a. Measure and set out the stake positions, and drive precast piles. -- b. Excavate the earthwork to the bottom elevation of the precast beam. -- c. Hoist the precast beam. -- d. Drill holes, tension, and anchor the prestressing tendons. -- e. Grout the inside of the precast beam and install anchor rods in the beam body. -- f. Continue excavating the earthwork to the bottom elevation of the next precast beam. -- g. Continue hoisting the precast beam, drilling holes, tensioning, and anchoring the prestressing tendons. -- h. Hoist the precast shear wall panels and install double-row flat-hole T-shaped steel plate support strips. -- i. Grout the back of the precast shear wall panels and install anchor rods. -- j. Install V-shaped steel supports. -- k. Repeat steps b to j until the entire prefabricated foundation pit retaining structure construction is completed. -- l. Acceptance and monitoring; specific steps are as follows:

[0010] a. Measurement and layout to determine pile positions, and driving precast piles. First, measure and lay out the pile positions according to the drawings and construction plan. Static driving pile method should be used for on-site construction. Before driving the precast piles, use rubber plugs to seal all the reserved holes in the pile body to prevent sand and gravel from blocking the pile body ducts during the pile driving process and affecting subsequent processes. When the soil layer is hard, the verticality of the pile body should be observed in time during the driving. The pile driving error should be controlled within 1%. The pile splice position should be located more than 600mm above and below the pile beam connection node.

[0011] b. Excavate the earthwork to the bottom elevation of the precast beam. After all the precast piles have been driven in, earthwork excavation will begin. The earthwork excavation will be carried out using the central island method, in layers, sections, and parts. During the earthwork excavation, the earthwork at the location of the precast beam will be excavated first, and the earthwork at the location of the precast beam will be excavated to the bottom elevation of the precast beam. Depending on the soil conditions, some earthwork will be reserved. Over-excavation should be avoided. The original earthwork will be used to support and assist the subsequent hoisting and positioning of the precast beam, ensuring effective connection between the precast beam and the precast pile. When there are complex geological conditions such as soft soil and high water content in the area where the precast pile and precast beam are connected, it may lead to excessive settlement after the precast beam is positioned. Under the premise of timely dewatering, the earthwork at the precast beam location will be excavated to a position above the bottom elevation of the pile, and hard materials will be used for padding and reinforcement.

[0012] c. Before the full-scale hoisting of the precast beams, remove the rubber plugs from the pre-drilled holes in the precast piles. The precast beams can be partially hoisted 6 hours in advance to determine the pre-settlement after the precast beams are hoisted into place. Based on the pre-settlement obtained from the test, the earthwork excavation elevation of the precast beam hoisting area is fully adjusted. After the precast beam hoisting elevation is verified to be correct, in order to control uneven settlement after the precast beams are placed on the earthwork, steel pads are laid on the earthwork at the precast beam placement location before the formal full-scale hoisting of the precast beams. The thickness of the steel pads should not be less than 15mm. When there are complex geological environments such as soft soil and high water content in the area where the precast piles and precast beams are connected, and steel pads need to be laid, the thickness of the steel pads should be reserved in the early earthwork excavation elevation.

[0013] d. Drilling, tensioning, and anchoring of prestressing tendons: After the precast beams are hoisted and the connection positions of the precast beams and precast piles are verified to be correct, excavate the soil within the prestressing anchorage area at the bottom of the beams. After leaving a working surface, proceed with the drilling, tensioning, and anchoring of prestressing tendons. First, drill the transverse prestressing tendons at the bottom of the beams of two adjacent precast beams. There should be no fewer than two transverse prestressing tendons. During the drilling process, the tendons should be inserted through the pre-reserved semi-triangular cone-shaped anchorage groove at the bottom of one end of the precast beam. Alternatively, a guide wire method can be used to assist in drilling the prestressing tendons. After the transverse prestressing tendons are drilled and in place, proceed with the drilling of the oblique prestressing tendons. The number of oblique prestressing tendons is designed according to the load conditions, and there should be no fewer than three oblique prestressing tendons in the same direction. After all prestressing tendons are drilled, proceed with the tensioning and anchoring of the prestressing tendons. The transverse prestressing tendons are tensioned symmetrically, while the oblique prestressing tendons are anchored at one end and tensioned at the other. That is, the oblique prestressing tendons are first fixed at the semi-triangular cone anchorage groove at the bottom of the precast beam, and then tensioned and anchored at the semi-triangular cone anchorage groove at the top of the precast beam. After all the prestressing tendons are tensioned and anchored, the prestressing ducts are grouted. When the load on the foundation pit retaining structure is complex, in order to ensure the strength of the pile-beam connection node, under the premise of applying prestress, the precast beam is a composite beam. A continuous reinforcing bar is set in the upper part of the composite beam, and the continuous reinforcing bar passes through the precast pile and is reliably connected to the upper reinforcing bar of the adjacent composite beam. At this time, the tensioning and anchoring position of the oblique prestressing tendons is at the semi-triangular cone anchorage groove at the bottom of the precast beam, and the upper prestressing tendons are cast in place in the composite layer of the precast beam using anchors.

[0014] e. Grouting inside the precast beam and installing anchor rods in the beam body. After the pile-beam connection is completed, when there is a gap between the precast beam and the soil on the side of the foundation pit, grouting is first performed inside the precast beam. The grouting material is micro-expansion fine stone concrete with a quick-setting agent added to it. After the grouting strength reaches the design strength, anchor rods are installed at the anchor rod holes in the precast beam body. This forms a structure that strengthens the retaining structure by installing anchor rods in the precast beam body on the basis of the prestressed connection of the precast pile beam.

[0015] f. Continue excavating the earthwork to the bottom elevation of the next precast beam. After the anchor rods of the precast beam body are installed, continue excavating the earthwork downwards to the bottom elevation of the next precast beam. At this time, when continuing to excavate the earthwork downwards, after the earthwork at the bottom of the precast beam that has been hoisted and positioned is excavated, clean up the steel pads that have fallen off at the bottom of the precast beam and reuse them in a timely manner. The earthwork excavation in the middle of the foundation pit should be carried out in layers and sections until the bottom elevation of the next precast beam is reached. The earthwork excavation is consistent with the technical requirements in step b.

[0016] g. Continue hoisting the precast beams, drilling, tensioning and anchoring the prestressing tendons. After the earthwork is excavated to the bottom elevation of the precast beams, appropriate treatment is carried out. After the process is accepted, continue hoisting the precast beams, drilling, tensioning and anchoring the prestressing tendons. The hoisting of the precast beams is consistent with the technical requirements of step c, and the drilling, tensioning and anchoring of the prestressing tendons is consistent with the technical requirements of step d.

[0017] h. Hoisting and installing precast shear wall panels, and installing double-row flat-hole T-shaped steel plate support bars. After the above-mentioned pile-beam frame hoisting construction is completed, the hoisting work of precast shear wall panels will be carried out. In order to improve the efficiency of modular hoisting of precast shear wall panels, the precast shear wall panels in each pile-beam frame module can be hoisted and positioned in sections. Before the precast shear wall panels are hoisted and positioned, positioning pins are set on the top surface of the precast beam at the positioning location of the precast shear wall panels. During on-site hoisting of the precast shear wall panels, the precast shear wall panels directly abut against the beam. Precast shear wall panels are positioned in sections on the positioning pins on the top of the precast beams. Then, double-row flat-hole T-shaped steel plate support strips are used to fix the sections to the upper and lower precast beams. At the same time, the vertical joints between the precast piles and the precast shear wall panels, as well as the vertical joints between two precast shear wall panels, are fixedly connected using double-row flat-hole T-shaped steel plate support strips. The double-row flat-hole T-shaped steel plate support strips serve as temporary reinforcement between precast components and also "seal" the joints for subsequent grouting work, simplifying the process.

[0018] i. Grouting and anchor bolt installation after precast shear wall panels are installed. After the precast shear wall panels are hoisted and all the above-mentioned completed procedures are inspected and an acceptance record is formed, grouting work is carried out after the precast shear wall panels are installed. After the grouting strength reaches the design strength, anchor bolts are installed in the anchor bolt holes on the precast shear wall panels.

[0019] j. Install V-shaped steel supports. To enhance the stability of the completed structure, install V-shaped steel supports on the overall structure of precast piles, precast beams, and precast shear wall panels. Each V-shaped steel support must span the precast piles, precast beams, and precast shear wall panels and be reliably fixed to the structural surface. The angle between the V-shaped steel support and the horizontal plane is 45°~60°.

[0020] k. Repeat steps b to j until the construction of the entire prefabricated foundation pit retaining structure is completed. Once the above procedures are completed, it marks the completion of the first layer of foundation pit retaining structure assembly and construction. Using the same technical measures, repeat steps b to j until the construction of the entire prefabricated foundation pit retaining structure is completed.

[0021] 1. Acceptance and monitoring: After the entire prefabricated foundation pit retaining structure is completed, the foundation pit retaining structure shall be accepted and an acceptance record shall be formed. During the subsequent internal structure construction, the pile top displacement, local structural deformation, anchor bolt effectiveness, water leakage and other conditions in the foundation pit retaining structure shall be monitored in real time. If any problems are found, reinforcement treatment shall be carried out in a timely manner.

[0022] The technical effects and advantages of this invention are as follows:

[0023] The overall technical solution of this invention follows the principle of "layered excavation of earthwork, segmented hoisting of prefabricated components, pile-wall-anchor composite structure design, cross-prestressed reinforced connection nodes, double-row flat-hole T-shaped steel plate support bars for auxiliary hoisting and fixing, and figure-eight steel support for cross-connection". The structure is reasonably designed, the assembly construction efficiency is high, and the load-bearing capacity is strong. Moreover, following the scheme of "layered, segmented, and part-specific earthwork excavation, and integrated prefabrication and assembly", the green construction level is high, the safety and reliability are high, and the construction period can be effectively shortened. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the overall structure of the present invention;

[0025] Figure 2 This is a schematic diagram of the prestressed pile-beam connection node in this invention;

[0026] Figure 3 This is a schematic diagram of the structure of the double-row flat-hole T-shaped steel plate support strip in this invention;

[0027] Figure 4 This is a schematic diagram of the figure-eight steel support structure in this invention;

[0028] Figure 5 This is a flowchart of the present invention.

[0029] In the diagram: 1. Precast pile; 2. Precast beam; 3. Precast shear wall panel; 4. Anchor rod; 5. Horizontal prestressing tendon; 6. Diagonal prestressing tendon; 7. Double-row flat hole T-shaped steel plate support strip; 8. V-shaped steel support; 9. Semi-triangular cone-shaped anchor groove for prestressing tendon. Detailed Implementation

[0030] The following will refer to the appendices in the embodiments of the present invention. Figures 1-5 The technical solutions in the embodiments of the present invention are clearly and completely described herein. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. The specific embodiments described herein are merely illustrative of the present invention and are not intended to limit the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention. Example

[0031] like Figures 1-5As shown, this invention provides a prefabricated foundation pit pile-beam-wall-anchor 4 prestressed retaining structure, including precast piles 1, precast beams 2, precast shear wall panels 3, anchors 4, transverse prestressing tendons 5, oblique prestressing tendons 6, double-row flat-hole T-shaped steel plate support strips 7, V-shaped steel supports 8, and prestressing tendon semi-triangular pyramidal anchoring grooves 9; the precast piles 1 and precast beams 2 are connected by transverse prestressing tendons 5 and oblique prestressing tendons 6, and the precast shear wall panels 3 are placed in sections within the section formed by the precast piles 1 and precast beams 2. The precast pile 1 has prestressed tendon through holes at the connection node with the precast beam 2. The precast beam 2 has prestressed ducts inside, and the upper and lower parts of the precast beam 2 have staggered prestressed tendon semi-triangular cone anchor grooves 9. The upper and lower ends of the precast shear wall panel 3 are connected to the precast beam 2 and adjacent precast shear wall panels 3 are provided with temporary fixed double-row flat hole T-shaped steel plate support strips 7. The precast shear wall panel 3 and the precast beam 2 are provided with anchor rod holes 4. Each layer of the structural surface is provided with V-shaped steel support 8.

[0032] All prefabricated components are pre-produced in the PC factory and hoisted on site using mechanized methods. Each prefabricated component is numbered according to the construction plan before leaving the factory, and is then placed in the correct position during on-site installation.

[0033] Precast pile 1 and precast beam 2 can be constructed using steel or reinforced concrete structures. At the joint between precast pile 1 and precast beam 2, transverse prestressing tendons 5 and diagonal prestressing tendons 6 are provided. Therefore, to ensure the reinforcement threading work during on-site construction, the diameter of the reinforcement threading ducts inside precast pile 1 and precast beam 2 should be 3mm-5mm larger than the outer diameter of the prestressing tendons. When the excavation depth exceeds 8m, or under complex geological conditions such as high soil pressure or high soil moisture content, at the connection joint between precast pile 1 and precast beam 2, precast beam 2 is designed as a composite beam. The ends of the composite beam must be equipped with auxiliary connecting steel plates and additional reinforcing bars passing through the pile body. There should be no fewer than 6 additional reinforcing bars, each with a diameter of no less than 16mm. After passing through the pile body, the additional reinforcing bars are anchored on each side into the upper part of the composite beam and reliably connected to the upper main reinforcement of the composite beam.

[0034] In each section, the precast shear wall panel 3 is vertically connected to the precast pile 1 and horizontally connected to the precast beam 2. Both are reliably connected by double-row flat-hole T-shaped steel plate support bars 7. The double-row flat-hole T-shaped steel plate support bars 7 are fixed to the pile-wall and wall-beam by high-strength bolts, and the precast shear wall panel 3 is promptly fixed in place by anchor rods 4.

[0035] A single V-shaped steel support 8 must span across the precast shear wall panel 3, the upper and lower precast beams 2, the precast piles 1, and the precast shear wall panels 3 in adjacent sections on the entire retaining structure surface. When the excavation depth exceeds 8m, or under complex geological conditions such as high soil pressure and high soil moisture content, the V-shaped steel support 8 must be designed with double rows of supports. The width of the V-shaped steel support 8 must be no less than 160mm, the thickness no less than 20mm, the length of a single V-shaped steel support 8 must be no less than 2.5m, and the angle between the V-shaped steel support 8 and the horizontal plane must be 45°~60°.

[0036] The semi-triangular cone-shaped anchorage groove 9 of the prestressing tendon is reserved during the production of the precast beam 2PC in the factory. The semi-triangular cone-shaped anchorage groove 9 of the prestressing tendon is mainly used for the tensioning and anchoring of the inclined prestressing tendon 6. The groove depth is not less than 60mm and the inclined angle is 45°. The bottom width of the semi-triangular cone-shaped anchorage groove 9 of the prestressing tendon should be able to meet the anchorage requirements of the cross prestressing tendons at the pile-beam joint.

[0037] The construction method of prefabricated foundation pit pile-beam-wall-anchor 4-prestressed retaining structure includes the following steps:

[0038] a. Measure and set out the pile positions, drive precast pile 1 -- b. Excavate the earthwork to the bottom elevation of precast beam 2 -- c. Hoist precast beam 2 -- d. Drill, tension, and anchor the prestressing tendons -- e. Grout the inside of precast beam 2, and drive anchor rods 4 into the beam body -- f. Continue excavating the earthwork to the bottom elevation of the next precast beam 2 -- g. Continue hoisting precast beam 2, drilling, tensioning, and anchoring the prestressing tendons -- h. Hoist precast shear wall panel 3, and install double-row flat-hole T-shaped steel plate support strips 7 -- i. Grout the back of precast shear wall panel 3 and drive anchor rods 4 -- j. Install V-shaped steel supports 8 -- k. Repeat steps b to j until the entire prefabricated foundation pit retaining structure construction is completed -- l. Acceptance and monitoring, the specific steps are as follows:

[0039] a. Measurement and layout to determine pile positions, and driving precast pile 1. First, measure and lay out the pile positions according to the drawings and construction plan. Since the precast pile 1 is designed with prestressed ducts and other reserved holes, static pile driving should be used on site to protect the integrity of the pile body. Before driving precast pile 1, all reserved holes in the pile body should be sealed with rubber plugs, especially the openings of the prestressed tendon ducts, to prevent sand and gravel from blocking the pile body ducts during the pile driving process and affecting subsequent processes. When the soil layer is hard, the verticality of the pile body should be observed in time during driving, and the final pile driving error should be controlled within 1%. The pile splice position should not be designed within 600mm above or below the pile-beam connection node. Considering that precast pile 1 needs to be connected to precast beam 2 in the subsequent process, the driving of precast pile 1 should focus on controlling the pile top elevation.

[0040] b. Earthwork excavation to the bottom elevation of precast beam 2: After all precast piles 1 have been driven in, earthwork excavation can begin. The earthwork excavation adopts the "central island method" and is carried out in "layers, sections, and parts". Since the precast beam 2 needs to be hoisted and connected to the precast piles 1 and the precast beam 2 in the subsequent process, during the earthwork excavation, the earthwork at the location of the precast beam 2 should be excavated first. The earthwork within a certain range at the location of the precast beam 2 should be excavated to the "bottom elevation of precast beam 2". Considering the possibility of sinking after the precast beam 2 is hoisted into place, a larger amount of earthwork can be left depending on the soil conditions. Over-excavation should be avoided. This original earthwork will be used to support and assist the hoisting of the precast beam 2 in the subsequent process, ensuring effective connection between the precast beam 2 and the precast piles 1. When there are complex geological conditions such as loose soil and high water content in the area where the precast pile 1 connects to the precast beam 2, it will lead to excessive settlement after the precast beam 2 is in place. Therefore, under the premise of timely dewatering, the soil at the precast beam 2 is excavated to an appropriate position above the pile bottom elevation and reinforced with hard materials.

[0041] c. Hoisting Precast Beam 2: Before the full hoisting of precast beam 2, remove the rubber plug from the pre-drilled hole in precast pile 1. Precast beam 2 can be partially hoisted 6 hours in advance to determine the pre-settlement after placement. Based on the measured pre-settlement, the excavation elevation of the area where precast beam 2 is placed will be adjusted. After the hoisting elevation of precast beam 2 is verified, to control uneven settlement after placement, a steel pad with a thickness of at least 15mm will be laid on the soil at the placement location before the full hoisting of precast beam 2. Therefore, when complex geological conditions such as soft soil and high water content occur at the connection between precast pile 1 and precast beam 2, and a steel pad is required, the thickness of the steel pad should be considered in the initial excavation elevation.

[0042] d. Drilling, tensioning, and anchoring of prestressing tendons: After the precast beam 2 is hoisted and the connection positions of the precast beam 2 and precast pile 1 are verified to be correct, the soil within the prestressing anchorage area at the bottom of the beam is excavated. After leaving a suitable working surface, the drilling, tensioning, and anchoring of prestressing tendons can be carried out. First, the transverse prestressing tendons 5 at the bottom of the beam body of the two adjacent precast beams 2 are drilled. There should be no less than 2 transverse prestressing tendons 5. During the drilling process, the tendons are inserted through the pre-reserved semi-triangular cone-shaped anchorage groove at the bottom of one end of the precast beam 2. Alternatively, the guide wire method can be used to assist in drilling the prestressing tendons. After the transverse prestressing tendons 5 are drilled and in place, the drilling of the oblique prestressing tendons 6 is carried out. The number of oblique prestressing tendons 6 can be designed according to the load conditions, and there should be no less than 3 oblique prestressing tendons 6 in the same direction. After all the prestressing tendons have been drilled, the tensioning and anchoring of the prestressing tendons can be carried out. The transverse prestressing tendons 5 are tensioned symmetrically, and the oblique prestressing tendons 6 are anchored at one end and tensioned at the other end. That is, the oblique prestressing tendons 6 are first fixed at the semi-triangular cone anchoring groove at the bottom of the precast beam 2, and then tensioned and anchored at the semi-triangular cone anchoring groove at the top of the precast beam 2. After all the prestressing tendons are tensioned and anchored, the prestressing ducts are then grouted. When the load on the foundation pit retaining structure is complex, in order to ensure the strength of the pile-beam connection node, under the premise of applying prestress as mentioned above, the precast beam 2 can be designed as a composite beam. A continuous reinforcing bar is set on the upper part of the composite beam, and the continuous reinforcing bar passes through the precast pile 1 and is reliably connected to the upper reinforcing bar of the adjacent composite beam. At this time, the tensioning and anchoring position of the inclined prestressing tendon 6 is at the semi-triangular cone anchoring groove at the lower part of the precast beam 2, and the upper prestressing tendon is cast in place in the composite layer of the precast beam 2 using anchorage.

[0043] e. Grouting inside precast beam 2 and installation of anchor rods 4 in the beam body: After the pile-beam connection is completed, if there is a gap between the precast beam 2 and the soil on the side of the foundation pit, grouting can be carried out inside the precast beam 2 first. The grouting material is micro-expansion fine stone concrete with a quick-setting agent added to it. After the grouting strength reaches the design strength, anchor rods 4 are installed at the anchor rod holes of the precast beam 2. This forms a structure that strengthens the retaining structure by installing anchor rods 4 in the precast beam 2 on the basis of the prestressed connection of the precast pile 1 beam.

[0044] f. Continue excavation to the bottom elevation of the next precast beam 2: After the anchor bolts 4 of precast beam 2 are installed, continue excavating downwards to the bottom elevation of the next precast beam 2. While continuing to excavate downwards, after the bottom of the precast beam 2, which has been hoisted and positioned, is excavated, clean up any steel pads that have fallen off at the bottom of the precast beam 2 and reuse them promptly. Excavation in the middle of the foundation pit should be carried out in layers and sections until the bottom elevation of the next precast beam 2 is reached. The excavation process follows the same technical requirements as in step b.

[0045] g. Continue hoisting precast beam 2, and perform prestressing tendon drilling, tensioning, and anchoring: After the earthwork is excavated to the bottom elevation of precast beam 2, appropriate treatment is carried out, and the process is accepted as qualified before continuing the hoisting of precast beam 2, prestressing tendon drilling, tensioning, and anchoring work. The hoisting of precast beam 2 is consistent with the technical requirements of step c, and the prestressing tendon drilling, tensioning, and anchoring work is consistent with the technical requirements of step d.

[0046] h. Hoisting the precast shear wall panel 3 and installing the double-row flat-hole T-shaped steel plate support strips 7: After the above-mentioned pile-beam frame hoisting construction is completed, the hoisting work of the precast shear wall panel 3 can be carried out. In order to improve the efficiency of the modular hoisting construction of the precast shear wall panel 3, the precast shear wall panel 3 in each pile-beam frame module can be hoisted and positioned in sections. Before the precast shear wall panel 3 is hoisted and positioned, a positioning pin can be set on the top surface of the precast beam 2 at the position of the precast shear wall panel 3. When the precast shear wall panel 3 is hoisted on site, the precast shear wall panel 3 can directly abut against the positioning pin on the top of the precast beam 2. The precast shear wall panel 3 is positioned in sections, and then the double-row flat-hole T-shaped steel plate support strips 7 are used to fix and connect the sections to the upper and lower precast beams 2. At the same time, the vertical joints between the precast pile 1 and the precast shear wall panel 3, and the vertical joints between the two precast shear wall panels 3 are all fixedly connected by the double-row flat-hole T-shaped steel plate support strips 7. The double-row flat-hole T-shaped steel plate support strip 7 serves as a temporary reinforcement between prefabricated components and also acts as a "sealing" mechanism for subsequent grouting work, simplifying the process.

[0047] i. Grouting and anchor bolt installation after precast shear wall panel 3: After the precast shear wall panel 3 is hoisted and all the above-mentioned completed procedures are inspected and an acceptance record is formed, the grouting work after the precast shear wall panel 3 is carried out. After the grouting strength reaches the design strength, the anchor bolts 4 are installed in the anchor bolt holes on the precast shear wall panel 3.

[0048] j. Installing the V-shaped steel supports 8: To enhance the stability of the completed structure, V-shaped steel supports 8 are installed on the overall structure of precast piles 1, precast beams 2, and precast shear wall panels 3. Each V-shaped steel support 8 must span over the precast piles 1, precast beams 2, and precast shear wall panels 3 and be reliably fixed to the structural surface. The angle between the V-shaped steel support 8 and the horizontal plane is 45°~60°.

[0049] k. Repeat steps b to j until the entire prefabricated foundation pit retaining structure construction is completed: After the above procedures are completed, it marks the completion of the first layer of foundation pit retaining structure assembly and construction. Using the same technical measures, repeat steps b to j until the entire prefabricated foundation pit retaining structure construction is completed.

[0050] 1. Acceptance and Monitoring. After the entire prefabricated foundation pit retaining structure is completed, an acceptance inspection of the foundation pit retaining structure will be organized, and an acceptance record will be formed. During the subsequent construction of the internal structure, the pile top displacement, local structural deformation, anchor bolt effectiveness, water leakage, and other conditions in the foundation pit retaining structure need to be monitored in real time. If any problems are found, reinforcement measures should be taken in a timely manner.

[0051] The present invention has a reasonable structural design, high assembly construction efficiency, strong load-bearing capacity, and follows the scheme of "layered, segmented, and part-specific earthwork excavation and integrated prefabrication and assembly". It has a high level of green construction, is safe and reliable, and can effectively shorten the construction period.

[0052] Finally, it should be noted that the above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A prefabricated foundation pit pile-beam-wall-anchor prestressed retaining structure, comprising precast piles, precast beams, precast shear wall panels, anchor bolts, transverse prestressing tendons, inclined prestressing tendons, double-row flat-hole T-shaped steel plate support strips, figure-eight steel supports, and semi-triangular pyramidal anchoring grooves for prestressing tendons; characterized in that: The precast piles and precast beams are connected by transverse and diagonal prestressing tendons. The precast shear wall panels are placed in sections within the segments formed by the precast piles and precast beams. The precast piles have prestressing tendon perforations at the connection points with the precast beams. The precast beams have prestressing perforations inside, and the upper and lower parts of the precast beams have staggered semi-triangular pyramidal anchoring grooves for the prestressing tendons. The upper and lower ends of the precast shear wall panels are connected to the precast beams, and adjacent precast shear wall panels are provided with temporary fixed double-row flat-hole T-shaped steel plate support strips. The precast shear wall panels and precast beams are provided with anchor holes. Each layer of the structural surface is provided with a figure-eight steel support. Each figure-eight steel support must span the precast piles, precast beams, and precast shear wall panels and be reliably fixed to the structural surface.

2. The construction method of the prefabricated foundation pit pile-beam-wall-anchor prestressed retaining structure as described in claim 1, characterized in that, Includes the following steps: a. Measurement and layout to determine pile positions, and driving precast piles. First, measure and lay out the pile positions according to the drawings and construction plan. Static driving pile method should be used for on-site construction. Before driving the precast piles, use rubber plugs to seal all the reserved holes in the pile body to prevent sand and gravel from blocking the pile body ducts during the pile driving process and affecting subsequent processes. When the soil layer is hard, the verticality of the pile body should be observed in time during the driving. The pile driving error should be controlled within 1%. The pile splice position should be located more than 600mm above and below the pile beam connection node. b. Excavate the earthwork to the bottom elevation of the precast beam. After all the precast piles have been driven in, earthwork excavation will begin. The earthwork excavation will be carried out using the central island method, in layers, sections, and parts. During the earthwork excavation, the earthwork at the location of the precast beam will be excavated first, and the earthwork at the location of the precast beam will be excavated to the bottom elevation of the precast beam. Depending on the soil conditions, some earthwork will be reserved. Over-excavation should be avoided. The original earthwork will be used to support and assist the subsequent hoisting and positioning of the precast beam, ensuring effective connection between the precast beam and the precast pile. When there are complex geological conditions such as soft soil and high water content in the area where the precast pile and precast beam are connected, it may lead to excessive settlement after the precast beam is positioned. Under the premise of timely dewatering, the earthwork at the precast beam location will be excavated to a position above the bottom elevation of the pile, and hard materials will be used for padding and reinforcement. c. Before the full-scale hoisting of the precast beams, remove the rubber plugs from the pre-drilled holes in the precast piles. The precast beams can be partially hoisted 6 hours in advance to determine the pre-settlement after the precast beams are hoisted into place. Based on the pre-settlement obtained from the test, the earthwork excavation elevation of the precast beam hoisting area is fully adjusted. After the precast beam hoisting elevation is verified to be correct, in order to control uneven settlement after the precast beams are placed on the earthwork, steel pads are laid on the earthwork at the precast beam placement location before the formal full-scale hoisting of the precast beams. The thickness of the steel pads should not be less than 15mm. When there are complex geological environments such as soft soil and high water content in the area where the precast piles and precast beams are connected, and steel pads need to be laid, the thickness of the steel pads should be reserved in the early earthwork excavation elevation. d. Drilling, tensioning, and anchoring of prestressing tendons: After the precast beams are hoisted and the connection positions of the precast beams and precast piles are verified to be correct, excavate the soil within the prestressing anchorage area at the bottom of the beams. After leaving a working surface, proceed with the drilling, tensioning, and anchoring of prestressing tendons. First, drill the transverse prestressing tendons at the bottom of the beams of two adjacent precast beams. There should be no fewer than two transverse prestressing tendons. During the drilling process, the tendons should be inserted through the pre-reserved semi-triangular cone-shaped anchorage groove at the bottom of one end of the precast beam. Alternatively, a guide wire method can be used to assist in drilling the prestressing tendons. After the transverse prestressing tendons are drilled and in place, proceed with the drilling of the oblique prestressing tendons. The number of oblique prestressing tendons is designed according to the load conditions, and there should be no fewer than three oblique prestressing tendons in the same direction. After all prestressing tendons are drilled, proceed with the tensioning and anchoring of the prestressing tendons. The transverse prestressing tendons are tensioned symmetrically, while the oblique prestressing tendons are anchored at one end and tensioned at the other. That is, the oblique prestressing tendons are first fixed at the semi-triangular cone anchorage groove at the bottom of the precast beam, and then tensioned and anchored at the semi-triangular cone anchorage groove at the top of the precast beam. After all the prestressing tendons are tensioned and anchored, the prestressing ducts are grouted. When the load on the foundation pit retaining structure is complex, in order to ensure the strength of the pile-beam connection node, under the premise of applying prestress, the precast beam is a composite beam. A continuous reinforcing bar is set in the upper part of the composite beam, and the continuous reinforcing bar passes through the precast pile and is reliably connected to the upper reinforcing bar of the adjacent composite beam. At this time, the tensioning and anchoring position of the oblique prestressing tendons is at the semi-triangular cone anchorage groove at the bottom of the precast beam, and the upper prestressing tendons are cast in place in the composite layer of the precast beam using anchors. e. Grouting inside the precast beam and installing anchor rods in the beam body. After the pile-beam connection is completed, when there is a gap between the precast beam and the soil on the side of the foundation pit, grouting is first performed inside the precast beam. The grouting material is micro-expansion fine stone concrete with a quick-setting agent added to it. After the grouting strength reaches the design strength, anchor rods are installed at the anchor rod holes in the precast beam body. This forms a structure that strengthens the retaining structure by installing anchor rods in the precast beam body on the basis of the prestressed connection of the precast pile beam. f. Continue excavating the earthwork to the bottom elevation of the next precast beam. After the anchor rods of the precast beam body are installed, continue excavating the earthwork downwards to the bottom elevation of the next precast beam. At this time, when continuing to excavate the earthwork downwards, after the earthwork at the bottom of the precast beam that has been hoisted and positioned is excavated, clean up the steel pads that have fallen off at the bottom of the precast beam and reuse them in a timely manner. The earthwork excavation in the middle of the foundation pit should be carried out in layers and sections until the bottom elevation of the next precast beam is reached. The earthwork excavation is consistent with the technical requirements in step b. g. Continue hoisting the precast beams, drilling, tensioning and anchoring the prestressing tendons. After the earthwork is excavated to the bottom elevation of the precast beams and the process is accepted, continue hoisting the precast beams, drilling, tensioning and anchoring the prestressing tendons. The hoisting of the precast beams is consistent with the technical requirements of step c, and the drilling, tensioning and anchoring of the prestressing tendons is consistent with the technical requirements of step d. h. Hoisting and installing precast shear wall panels, and installing double-row flat-hole T-shaped steel plate support bars. After the above-mentioned pile-beam frame hoisting construction is completed, the hoisting work of precast shear wall panels will be carried out. In order to improve the efficiency of modular hoisting of precast shear wall panels, the precast shear wall panels in each pile-beam frame module can be hoisted and positioned in sections. Before the precast shear wall panels are hoisted and positioned, positioning pins are set on the top surface of the precast beam at the positioning location of the precast shear wall panels. During on-site hoisting of the precast shear wall panels, the precast shear wall panels directly abut against the beam. Precast shear wall panels are positioned in sections on the positioning pins on the top of the precast beams. Then, double-row flat-hole T-shaped steel plate support strips are used to fix the sections to the upper and lower precast beams. At the same time, the vertical joints between the precast piles and the precast shear wall panels, as well as the vertical joints between two precast shear wall panels, are fixedly connected using double-row flat-hole T-shaped steel plate support strips. The double-row flat-hole T-shaped steel plate support strips serve as temporary reinforcement between precast components and also "seal" the joints for subsequent grouting work, simplifying the process. i. Grouting and anchor bolt installation after precast shear wall panels are installed. After the precast shear wall panels are hoisted and all the above-mentioned completed procedures are inspected and an acceptance record is formed, grouting work is carried out after the precast shear wall panels are installed. After the grouting strength reaches the design strength, anchor bolts are installed in the anchor bolt holes on the precast shear wall panels. j. Install V-shaped steel supports. To enhance the stability of the completed structure, install V-shaped steel supports on the overall structure of precast piles, precast beams, and precast shear wall panels. Each V-shaped steel support must span the precast piles, precast beams, and precast shear wall panels and be reliably fixed to the structural surface. The angle between the V-shaped steel support and the horizontal plane is 45°~60°. k. Repeat steps b to j until the construction of the entire prefabricated foundation pit retaining structure is completed. Once the above procedures are completed, it marks the completion of the first layer of foundation pit retaining structure assembly and construction. Using the same technical measures, repeat steps b to j until the construction of the entire prefabricated foundation pit retaining structure is completed.

1. Acceptance and monitoring: After the entire prefabricated foundation pit retaining structure is completed, the foundation pit retaining structure shall be accepted and an acceptance record shall be formed. During the subsequent internal structure construction, the pile top displacement, local structural deformation, anchor bolt effectiveness, water leakage and other conditions in the foundation pit retaining structure shall be monitored in real time. If any problems are found, reinforcement treatment shall be carried out in a timely manner.

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