Underpinning pile for development of underground space of existing building and construction method and disassembly and recycling method thereof

Abstract

The application discloses a underpinning pile for existing building underground space development and a construction method and a dismounting and recycling method thereof, and the underpinning pile comprises a cast-in-situ bored pile, a prefabricated hollow pile assembly and a non-bonded steel strand tensioning assembly, wherein the tensioning assembly comprises a bottom end anchor plate horizontally welded on a reinforcement cage of the cast-in-situ bored pile, a top end anchor plate arranged at a pile top of the prefabricated hollow pile assembly and a steel strand and an anchor device penetrating through the prefabricated hollow pile assembly, wherein the prefabricated hollow pile assembly is composed of a first prefabricated reinforced concrete hollow pile section, a second prefabricated reinforced concrete hollow pile section, a prefabricated steel pipe concrete hollow pile section and a pile section hollow jack which are connected in series on the steel strand, and the adjacent pile sections are embeddedly assembled and connected through anchor bolt locking. After cutting, the first and second prefabricated reinforced concrete hollow pile sections, the pile section hollow jack and the steel strand can be dismounted and recycled for reuse, so that the problem of waste caused by building waste is avoided.

Description

Technical Field

[0001] This invention relates to the field of building construction technology, and in particular to a replacement pile for the development of underground space in existing buildings, as well as its construction method and dismantling and recycling method. Background Technology

[0002] In the development of underground space in existing buildings, a large number of replacement piles are required as temporary vertical support systems. The replacement piles need to be constructed in the low-clearance environment of the existing building. After the permanent structure of the basement is completed, the vertical load of the developed underground space needs to be transferred to the permanent support structure of the basement by cutting off the replacement piles. The cut-off replacement piles become construction waste and are disposed of, resulting in waste of materials and increased disposal costs. To improve the construction efficiency of replacement piles, a process combining cement mixing piles and precast piles has emerged in this field. However, this method has drawbacks. The cement mixing pile is located in the lower section, while the precast pile is in the upper section. The precast pile is inserted into the cement mixing pile to form a single unit. However, the construction equipment for cement mixing piles occupies a large space, making it unsuitable for construction in low-clearance environments and unsuitable for the development and construction of underground spaces in existing buildings. Furthermore, since the precast pile is a single unit, it still needs to be removed after the permanent basement structure is completed. The removed replacement piles are still construction waste and require disposal. Therefore, after the permanent basement structure is completed, how to avoid material waste caused by the removed replacement piles and reduce subsequent disposal costs becomes a key challenge in this field. Summary of the Invention

[0003] The purpose of this invention is to provide a replacement pile for the development of underground space in existing buildings, as well as its construction method and dismantling and recycling method, in order to solve the problem that after the replacement piles are used as a temporary vertical support system for the construction of basement structures under existing buildings, the removed replacement piles become construction waste that needs to be disposed of and cannot be recycled and reused, resulting in waste.

[0004] To address the aforementioned technical problems, this invention provides a replacement pile for the development of underground space in existing buildings, comprising:

[0005] Drilled piles are located inside the pile hole, with their upper ends protruding above the basement floor slab elevation.

[0006] A precast hollow pile assembly, located within a pile hole and exposed above ground, comprises a precast steel-concrete hollow pile segment extending vertically through the beams and slabs of each floor at the beam-column joints of the basement structure to be constructed. In the non-ground-floor basement to be constructed, a second precast reinforced concrete hollow pile segment is embedded and assembled at the upper end of the precast steel-concrete hollow pile segment. At least one section of a first precast reinforced concrete hollow pile segment is embedded and assembled at the upper end of the second precast reinforced concrete hollow pile segment. In the basement, one or more first precast reinforced concrete hollow pile segments are installed on bored cast-in-place piles. Adjacent first precast reinforced concrete hollow pile segments are embedded and assembled. At the beams and slabs of each floor, hollow pile jacks are installed between the lower ends of the first precast reinforced concrete hollow pile segments and the precast steel pipe concrete hollow pile segments. The hollow pile jacks include hollow jacks and annular end plates vertically connected to both ends. The precast hollow pile assembly also includes multiple anchor bolts radially inserted into the adjacent pile segments embedded and assembled.

[0007] An unbonded steel strand tensioning assembly includes a bottom anchor plate horizontally welded inside the reinforcing cage of a bored pile located below the basement floor elevation, a top anchor plate horizontally set at the top of a precast hollow pile assembly at ground level, both the bottom and top anchor plates being annular plates, multiple steel strands penetrating the bottom anchor plate, the reinforcing cage, the precast hollow pile assembly, and the top anchor plate, anchorages tensioning and connecting the two ends of the steel strands to the top and bottom anchor plates, anchorages tensioning and connecting the steel strands at the lowest first precast reinforced concrete hollow pile segment, and anchorages tensioning and connecting the steel strands at the annular end plates at both ends of the pile segment hollow jack.

[0008] Furthermore, the replacement pile for developing underground space of existing buildings provided by the present invention comprises: a first precast reinforced concrete hollow pile segment including a hollow concrete body and reinforcing bars therein, with an annular protrusion at the top as a male interface and an annular groove at the bottom as a female interface; a second precast reinforced concrete hollow pile segment including a hollow concrete body and reinforcing bars therein, with annular protrusions at both the top and bottom as male interfaces; and a precast steel pipe concrete hollow pile segment including a steel pipe and a hollow concrete body cast inside, with an annular groove at the top as a female interface and a flat end at the bottom; the first precast reinforced concrete hollow pile segments are connected by embedded assembly through male and female interfaces, the female interface at the top of the precast steel pipe concrete hollow pile segment is embeddedly assembled with the male interface at the bottom of the second precast reinforced concrete hollow pile segment, and the male interface at the top of the second precast reinforced concrete hollow pile segment is embeddedly assembled with the female interface at the bottom of the first precast reinforced concrete hollow pile segment.

[0009] Furthermore, in the replacement pile for underground space development of existing buildings provided by the present invention, the hollow concrete bodies of the first precast reinforced concrete hollow pile segment, the hollow concrete bodies of the second precast reinforced concrete hollow pile segment, and the hollow concrete bodies of the precast steel pipe concrete hollow pile segment, as well as the annular end plate of the pile segment hollow jack, are all provided with multiple steel strand holes for threading steel strands through which steel strands are aligned and arranged in a circular array.

[0010] Furthermore, the replacement pile for developing underground space of existing buildings provided by the present invention has multiple anchor bolt holes on both the male and female interfaces for the installation of the anchor bolts.

[0011] Furthermore, in the replacement pile for underground space development of existing buildings provided by the present invention, the hollow concrete body, bottom anchor plate, top anchor plate and annular end plate all have the same inner diameter, and the precast steel pipe concrete hollow pile segment, the first precast reinforced concrete hollow pile segment and the second precast reinforced concrete hollow pile segment have the same outer diameter.

[0012] Furthermore, the replacement pile for underground space development of existing buildings provided by the present invention has the same inner diameter for the hollow concrete body, bottom anchor plate, top anchor plate and annular end plate, the same outer diameter for the first precast reinforced concrete hollow pile segment and the same outer diameter for the second precast reinforced concrete hollow pile segment, and the outer diameter of the precast steel pipe concrete hollow pile segment is smaller than the outer diameter of the first and second precast reinforced concrete hollow pile segments. A gap-filling layer is provided around the precast steel pipe concrete hollow pile segment, and the gap-filling layer has the same outer diameter as the first precast reinforced concrete hollow pile segment.

[0013] Furthermore, the replacement pile for the development of underground space in existing buildings provided by the present invention has annular shear reinforcement bars or studs on the periphery of the steel pipe of the precast steel pipe concrete hollow pile segment.

[0014] To address the aforementioned technical problems, the present invention also provides a construction method for the aforementioned replacement piles used in the development of underground space in existing buildings, comprising:

[0015] Step S1: Fabricate the steel cage for the bored pile, horizontally weld the bottom anchor plate inside the steel cage, insert multiple steel strands in a circular array inside the steel cage and pass through the bottom anchor plate, connect the steel strands with anchors and abut against the bottom anchor plate, and suspend the steel strands and the connected steel cage as a whole into the pile hole and expose it to the ground.

[0016] Step S2: Insert multiple sections of the first precast reinforced concrete hollow pile into the steel strand in sequence, close to the beam slab. Place the lowest section of the first precast reinforced concrete hollow pile against the reinforcing cage. Tension and connect it to the steel strand through anchors, and place it against the bottom of the lowest section of the first precast reinforced concrete hollow pile. Embed and connect adjacent sections of the first precast reinforced concrete hollow pile, and lock them together with anchor bolts. After each installation, continue to suspend and lower the steel strand and the components inserted into it along the pile hole until they are exposed to the ground.

[0017] Step S3: At a location near the beam elevation, insert the hollow jack of the installation pile section through the steel strand and connect it to the uppermost first precast reinforced concrete hollow pile section. Tension the steel strand through the anchor to abut the upper surface of the lower annular end plate. Continue to suspend and lower the steel strand and the components inserted into it along the pile hole until they are exposed on the ground.

[0018] Step S4: At the beam elevation, insert the precast steel pipe concrete hollow pile segment through the steel strand and connect it to the upper annular end plate of the hollow pile jack. Adjust and lock the height of the hollow pile jack. Tension the steel strand through the anchor to abut against the lower surface of the upper annular end plate. Continue to suspend and lower the steel strand and the components inserted into it along the pile hole until they are exposed on the ground.

[0019] Step S5: Insert the second precast reinforced concrete hollow pile segment into the steel strand and connect it to the precast steel pipe concrete hollow pile segment for embedded assembly and connection, and lock the connection with anchor bolts. Continue to suspend and lower the steel strand and the components inserted into it along the pile hole and expose it to the ground.

[0020] Step S6: Insert multiple sections of the first precast reinforced concrete hollow pile into the steel strand in sequence until the next layer of beams and slabs. Connect the lower first precast reinforced concrete hollow pile section to the second precast reinforced concrete hollow pile section for embedded assembly and lock the connection with anchor bolts. Connect adjacent sections of the first precast reinforced concrete hollow pile section for embedded assembly and lock the connection with anchor bolts. After each installation, continue to suspend and lower the steel strand and the components inserted into it along the pile hole until they are exposed to the ground.

[0021] Step S7: Repeat steps S3 to S6 until the reinforcing cage sinks to the bottom of the pile hole and the precast steel pipe concrete hollow pile segment is exposed at the ground level of the top beam slab. This completes the installation of the precast hollow pile assembly. At the top of the precast steel pipe concrete hollow pile segment at the ground level, a top anchor plate is horizontally installed. The steel strands are tensioned and connected to the top anchor plate through the anchor.

[0022] Step S8: Use the central channel formed by the central holes of the top anchor plate, the precast hollow pile assembly and the bottom anchor plate as the pouring channel. Insert the guide pipe into the pouring channel to the bottom of the pile hole and pour concrete. Pour the concrete to the top of the steel cage to form a bored pile by pouring and lifting the pipe at the same time. Then pull out the guide pipe.

[0023] Step S9: Backfill the central channel with crushed sand and gravel to complete the construction of the replacement piles.

[0024] To address the aforementioned technical problems, the present invention also provides a method for dismantling and recycling the aforementioned underpinning piles used in the development of underground space in existing buildings, comprising:

[0025] After constructing the basement structure of the existing building by using replacement piles as a temporary vertical support system, two top-tight supports are symmetrically installed between the upper and lower beams on both sides of the replacement piles. The top anchor plate is removed, the prestress of the steel strand is released, and the vertical load of the existing building after the underground space is developed is transferred from the replacement piles to the top-tight supports.

[0026] The precast steel pipe concrete hollow pile segments and steel strands extending from the beams and slabs of each floor in the basement structure were cut off. The drilled cast-in-place piles and steel strands exposed at the bottom beams and slabs were also cut off. The anchor bolts in the adjacent two pile segments were pulled out, and all anchors on the steel strands were removed. The first precast reinforced concrete hollow pile segment, the second precast reinforced concrete hollow pile segment, and the pile segment hollow jacks were pulled out from the steel strands for dismantling and recycling.

[0027] By removing the top supports, the vertical load of the existing building after the underground space development is transferred from the top supports to the structural columns of the basement structure.

[0028] Furthermore, the method for dismantling and recycling replacement piles for underground space development of existing buildings provided by the present invention further includes:

[0029] Before dismantling adjacent pile segments, the hollow jacks of the pile segments are unloaded.

[0030] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0031] The present invention provides a replacement pile for the development of underground space in existing buildings, along with its construction and dismantling / recycling methods. This system utilizes a temporary vertical support system composed of bored piles, precast hollow pile components, and unbonded steel strand tensioning components. After the construction of the basement structure in an existing building, when the precast hollow pile components between the beams and slabs of each basement level are removed, only a small proportion of the precast steel-concrete hollow pile segments extending beyond the beams and slabs are removed as construction waste. The majority of the remaining first, second, and hollow reinforced concrete pile segments, along with the hollow pile jacks, can be extracted from the steel strands, dismantled, recycled, and reused. This avoids waste caused by the piles being treated as construction waste. Furthermore, the removed steel strands can also be recycled, thereby increasing the recycling rate of the removed replacement piles, reducing construction waste disposal, and offering advantages such as energy conservation, environmental protection, and low carbon emissions.

[0032] This invention provides a method for constructing and dismantling replacement piles for underground space development of existing buildings. By combining the cast-in-place process of bored piles, the prefabrication process of precast hollow pile components, and the tensioning process of unbonded steel strand tensioning components, it improves the construction efficiency and quality of replacement piles for underground space development of existing buildings in low-clearance environments, shortens the construction cycle, and reduces construction difficulty. Bored piles replace cement mixing piles, enabling construction in low-clearance environments. The precast hollow pile components are installed one by one into the steel strands, achieving construction in low-clearance environments. The flexible bending characteristics of the steel strands also enable construction in low-clearance environments, thereby improving the construction efficiency and shortening the construction cycle of the replacement piles. The use of precast hollow pile components reduces the amount of cast-in-place structure, thus improving the construction efficiency of the replacement piles. The bored pile and the precast hollow pile assembly are tensioned together by unbonded steel strand tensioning components to form a connection without separation, which improves the integrity of the replacement pile. The anchor tensioning connection at the lower end of the precast hollow pile assembly can improve the tightness of the precast hollow pile assembly and the reinforcing cage and avoid separation. The anchor also ensures the tightness of the hollow jack of the pile segment with the adjacent first precast reinforced concrete hollow pile segment, thus avoiding separation and improving the construction quality of the replacement pile.

[0033] The present invention provides a replacement pile for the development of underground space in existing buildings, as well as its construction method and dismantling and recycling method. The precast hollow pile assembly uses precast steel pipe concrete hollow pile segments at the beam and slab locations. During the construction of the beam and slab of the basement structure, the beam and slab reinforcement can be welded to the steel pipe of the precast steel pipe concrete hollow pile segment, which reduces the construction difficulty, improves the construction convenience, and avoids the problem of needing to chisel open the concrete protective layer to connect the beam reinforcement to the precast hollow pile assembly when using precast reinforced concrete hollow pile segments.

[0034] The present invention provides a replacement pile for the development of underground space in existing buildings, as well as its construction method and dismantling and recycling method. The prefabricated hollow pile assembly is a hollow structure, which allows the mud in the pile hole to be discharged during the process of lowering each pile segment and the hollow jack of the pile segment into the pile hole, thereby reducing mud resistance and enabling each component of the prefabricated hollow pile assembly to be driven into place, avoiding the problems of disjointing and breaking, and improving the pile driving quality of the prefabricated hollow pile assembly.

[0035] The present invention provides a replacement pile for the development of underground space in existing buildings, as well as its construction method and dismantling and recycling method. Adjacent pile segments in the prefabricated hollow pile assembly are locked together by anchor bolts, which can improve the tightness and reliability of the connection between adjacent pile segments and improve the connection quality between pile segments.

[0036] The present invention provides a replacement pile for the development of underground space in existing buildings, as well as its construction method and dismantling and recycling method. The bored pile is exposed at the elevation of the basement floor slab, which can ensure that the bored pile below the basement floor slab serves as the pile foundation for the temporary support system of the vertical load of the existing building, ensuring the force transmission effect and the safety of the existing building after the addition of the basement structure. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of the elevation structure of the replacement piles used for the development of underground space in existing buildings;

[0038] Figure 2 This is a schematic diagram of the main structure of the first precast reinforced concrete hollow pile segment;

[0039] Figure 3 This is a top view of the first precast reinforced concrete hollow pile segment;

[0040] Figure 4 This is a schematic diagram of the structure from below for the first precast reinforced concrete hollow pile segment;

[0041] Figure 5 This is a schematic diagram of the main structure of the second precast reinforced concrete hollow pile segment;

[0042] Figure 6 This is a schematic diagram of the main structure of a precast steel-concrete hollow pile segment;

[0043] Figure 7 This is a schematic diagram of the elevation structure of a hollow pile jack;

[0044] Figure 8 This is a schematic diagram of the planar structure of the hollow pile jack;

[0045] Figure 9 This is a schematic diagram of the elevation structure of the steel reinforcement cage at the basement floor slab;

[0046] Figure 10 This is a schematic diagram of the planar structure where the bottom anchor plate is welded to the steel cage.

[0047] Figure 11 This is a schematic diagram of the elevation structure of the construction pile hole;

[0048] Figure 12 It is a schematic diagram of the elevation structure of the suspended steel cage being lowered into the pile hole;

[0049] Figure 13 This is a schematic diagram of the elevation structure in which a section of the first precast reinforced concrete hollow pile is inserted through a steel strand and installed onto the steel cage and suspended and lowered along the pile hole.

[0050] Figure 14 This is a schematic diagram of the elevation structure in which hollow jacks for installing pile segments are inserted through steel strands and connected to the first precast reinforced concrete hollow pile segment, and then suspended and lowered along the pile hole.

[0051] Figure 15 This is a schematic diagram of the elevation structure in which precast steel pipe concrete hollow pile segments are inserted into steel strands, connected to the hollow jacks of the pile segments, and suspended and lowered along the pile hole.

[0052] Figure 16 This is a schematic diagram of the elevation structure of the prefabricated hollow pile components being inserted and installed on steel strands and sunk to the bottom of the pile hole.

[0053] Figure 17 This is a schematic diagram of the elevation structure of a bored pile formed by pouring concrete into the pile hole.

[0054] Figure 18 This is a schematic diagram of the elevation structure where prefabricated hollow pile components are exposed by excavating the earth layer by layer under the existing building and then constructing beams and slabs.

[0055] Figure 19 This is a schematic diagram of the elevation structure where top supports are installed between the upper and lower beams and slabs of a basement structure.

[0056] Figure 20 This is a schematic diagram of the elevation structure of the precast steel pipe concrete hollow pile segment that extends below the beam and slab, used to unload the hollow jacks of the pile segment by loosening or removing the anchorages.

[0057] Figure 21 This is a schematic diagram of the elevation structure for removing the hollow jacks from the steel strands of the pile segment.

[0058] Figure 22 This is a schematic diagram of the elevation structure where the first precast reinforced concrete hollow pile segment is removed from the steel strand.

[0059] Figure 23This is a schematic diagram of the elevation structure where the second precast reinforced concrete hollow pile segment is extracted and removed from the steel strand.

[0060] Figure 24 This is a schematic diagram of the facade structure after the top support has been removed;

[0061] As shown in the figure:

[0062] 100. Replacement piles;

[0063] 110. Drilled pile; 111. Reinforcing cage; 112. Concrete;

[0064] 120. Precast hollow pile assembly; 121. First precast reinforced concrete hollow pile segment; 122. Second precast reinforced concrete hollow pile segment; 123. Precast steel pipe concrete hollow pile segment; 123-1. Steel pipe; 124. Hollow jack for pile segment; 124-1. Hollow jack; 124-2. Annular end plate; 125. Anchor bolt; 126. Anchor bolt hole; 127. Male connector; 128. Female connector; 129. Steel strand hole;

[0065] 130. Tensioning assembly; 131. Bottom anchor plate; 132. Top anchor plate; 133. Steel strand; 134. Anchorage;

[0066] 140. Pile hole;

[0067] 200. Beams and slabs;

[0068] 300, top support; 310, structural steel; 320, jack. Detailed Implementation

[0069] The present invention will now be described in detail with reference to the accompanying drawings. The advantages and features of the present invention will become clearer from the following description. It should be noted that the drawings are all in a very simplified form and use non-precise proportions, and are only used to facilitate and clarify the illustration of the embodiments of the present invention.

[0070] Please refer to Figures 1 to 10 This invention provides a replacement pile 100 for underground space development of existing buildings, comprising a bored pile 110, a precast hollow pile assembly 120, and an unbonded steel strand tensioning assembly 130, wherein:

[0071] Drilled pile 110 is located within pile hole 140, with its upper end protruding above the basement floor slab elevation. The basement floor slab is the ground floor beam slab 200. The length L1 of the reinforcing cage 111 can be the pile length below the basement floor slab + 35d or more, where d is the diameter of the longitudinal reinforcement of the reinforcing cage 111, i.e., L1 ≥ 35d.

[0072] A precast hollow pile assembly 120 is located within a pile hole 140 and protrudes above the ground, where the ground is the upper surface of the top-floor beam slab 200. The precast hollow pile assembly 120 includes precast steel-concrete hollow pile segments 123 extending vertically through each beam-column joint of the basement structure to be constructed within each floor's beam slab 200. In the non-bottom-floor basement to be constructed, a second precast reinforced concrete hollow pile segment 122 is embedded and assembled at the upper end of the precast steel-concrete hollow pile segment 123. At least one first precast reinforced concrete hollow pile segment 121 is embedded and assembled at the upper end of the second precast reinforced concrete hollow pile segment 122. In the basement of the building, one or more first precast reinforced concrete hollow pile segments 121 are installed on bored cast-in-place piles 110. Adjacent first precast reinforced concrete hollow pile segments 121 are embedded and assembled. At each floor beam 200, a pile segment hollow jack 124 is installed between the lower ends of the first precast reinforced concrete hollow pile segment 121 and the precast steel pipe concrete hollow pile segment 123. The pile segment hollow jack 124 includes a hollow jack 124-1 and annular end plates 124-2 vertically connected to its two ends. The precast hollow pile assembly 120 also includes multiple anchor bolts 125 radially inserted into the adjacent pile segments embedded and assembled. The anchor bolts 125 are used to lock the adjacent pile segments together.

[0073] The unbonded steel strand tensioning assembly 130 includes a bottom anchor plate 131 horizontally welded inside the reinforcing cage 111 of the bored pile 110 located below the basement floor elevation, and a top anchor plate 132 horizontally set at the top of the precast hollow pile assembly 120 at ground level. Both the bottom anchor plate 131 and the top anchor plate 132 are circular ring plates. Multiple steel strands 133 pass through the bottom anchor plate 131, the reinforcing cage 111, the precast hollow pile assembly 120, and the top anchor plate 132. Anchors 134 tension and connect the two ends of the steel strands 133 to the top anchor plate 132 and the bottom anchor plate 131. Anchors 134 tension and connect the steel strands 133 at the lowest first precast reinforced concrete hollow pile segment 121. Anchors 134 tension and connect the steel strands 133 at the annular end plates 124-2 at both ends of the pile segment hollow jack 124. The steel strand 133 passes through the annular end plate 124-2 of the first precast reinforced concrete hollow pile segment 121, the second precast reinforced concrete hollow pile segment 122, the precast steel pipe concrete hollow pile segment 123, and the hollow jack 124 of the pile segment of the precast hollow pile assembly 120. The welding position of the bottom anchor plate 131 should be at least 3m lower than the bottom elevation of the basement floor slab, that is, the distance L2 between the bottom anchor plate 131 and the elevation of the basement floor slab is ≥3m.

[0074] Please refer to Figure 1 , Figure 9 , Figures 11 to 17This invention also provides a construction method for a replacement pile 100 used in the development of underground space in existing buildings, comprising:

[0075] Step S1, please refer to Figures 11 to 12 A reinforcing cage 111 for the bored pile 110 is fabricated. A bottom anchor plate 131 is horizontally welded inside the reinforcing cage 111. Multiple steel strands 133 are arranged in a circular array inside the reinforcing cage 111 and pass through the bottom anchor plate 131. The steel strands 133 are connected to the bottom anchor plate 131 by anchors 134. The steel strands 133 and the connected reinforcing cage 111 are then suspended and lowered into the pile hole 140 and exposed above the ground. The construction of the pile hole 140 requires drilling and cleaning to ensure the quality of the pile hole 140. When the reinforcing cage 111 is suspended and slowly lowered using the steel strands 133, the top of the steel strands 133 is temporarily fixed above the pile hole 140 to ensure that the steel strands 133 and the connected reinforcing cage 111 remain suspended and do not sink to the bottom of the pile hole 140.

[0076] Step S2, please refer to Figure 1 , Figure 9 , Figures 12 to 14 Multiple precast reinforced concrete hollow pile segments 121 are sequentially inserted into the steel strand 133 near the beam 200. The lowest precast reinforced concrete hollow pile segment 121 is abutted against the reinforcing cage 111 and tensioned to the steel strand 133 by the anchor 134, abutting against the bottom of the lowest precast reinforced concrete hollow pile segment 121. Adjacent first precast reinforced concrete hollow pile segments 121 are embedded and connected and locked by the anchor bolt 125. The steel strand 133 and the components inserted into it are suspended and lowered as a whole along the pile hole 140 and exposed to the ground after each installation. That is, one component is installed and suspended and lowered section by section to meet the requirements of the low headroom environment. Under the condition of meeting the low headroom environment, several components can also be installed and then suspended and lowered section by section. The components refer to the first precast reinforced concrete hollow pile segment 121, the second precast reinforced concrete hollow pile segment 122, the precast steel pipe concrete hollow pile segment 123, and the pile segment hollow jack 124 in the precast hollow pile assembly 120.

[0077] Step S3, please refer to Figure 1 and Figure 14At an elevation of 200 mm near the beam slab, a hollow jack 124 is inserted through a steel strand 133 and connected to the uppermost precast reinforced concrete hollow pile segment 121. The steel strand 133 is then tensioned via an anchor 134 to abut against the upper surface of the lower annular end plate 124-2, thus connecting the hollow jack 124 to the first precast reinforced concrete hollow pile segment 121. The steel strand 133 and its inserted components are then suspended and lowered along the pile hole 140 until they protrude above the ground. Before tensioning the hollow jack 124 via the anchor 134, the stroke (i.e., height adjustment) of the hollow jack 124 can be set according to the floor height and mechanically locked.

[0078] Step S4, please refer to Figure 1 and Figure 15 At the 200mm elevation of the beam slab, a precast steel-concrete hollow pile segment 123 is inserted through the steel strand 133 and connected to the upper annular end plate 124-2 of the hollow pile jack 124. The height of the hollow pile jack 124 is adjusted and locked. The steel strand 133 is tensioned through the anchor 134 and abuts against the lower surface of the upper annular end plate 124-2, so that the precast steel-concrete hollow pile segment 123 and the hollow pile jack 124 are connected. The steel strand 133 and the components inserted through it are then suspended and lowered as a whole along the pile hole 140 and exposed to the ground.

[0079] Step S5, please refer to Figure 1 and Figure 16 The second precast reinforced concrete hollow pile segment 122 is inserted into the steel strand 133 and connected to the precast steel pipe concrete hollow pile segment 123 for embedded assembly and connection, and locked by anchor bolts 125. The steel strand 133 and the components inserted into it are then suspended and lowered as a whole along the pile hole 140 and exposed to the ground.

[0080] Step S6, please refer to Figure 1 and Figure 16 Multiple sections of the first precast reinforced concrete hollow pile 121 are sequentially inserted and installed on the steel strand 133 until the next layer of beam 200 is reached. The lower section of the first precast reinforced concrete hollow pile 121 is then embedded and assembled onto the second precast reinforced concrete hollow pile 122, and the connection is locked with anchor bolts 125. Each time the steel strand 133 and the components installed on it are installed, the entire structure is suspended and lowered along the pile hole 140 until it is exposed above the ground. In step S6, the first precast reinforced concrete hollow pile 121 is not limited to multiple sections; it can be a single section. When multiple sections are used, adjacent sections of the first precast reinforced concrete hollow pile 121 are embedded and assembled together and locked with anchor bolts 125.

[0081] Step S7, please refer to Figure 1 , Figure 9 and Figure 16 Repeat steps S3 to S6 until the reinforcing cage 111 sinks into the bottom of the pile hole 140 and the precast steel pipe concrete hollow pile segment 123 is exposed at the ground level of the top beam slab 200, thus completing the installation of the precast hollow pile assembly 120. At the top of the precast steel pipe concrete hollow pile segment 123 at the ground level, a top anchor plate 132 is horizontally installed, and the steel strand 133 is tensioned and connected to the top anchor plate 132 through the anchor 134.

[0082] Step S8, please refer to Figure 1 and Figure 17 The central channel formed by the central holes of the top anchor plate 132, the precast hollow pile assembly 120, and the bottom anchor plate 131 serves as the pouring channel. A guide pipe is inserted into the pouring channel to the bottom of the pile hole 140 to pour concrete 112. The concrete is poured to the top of the reinforcing cage 111 to form a bored pile 110 by simultaneously pouring and lifting the pipe. The guide pipe is then pulled out. Each pile segment of the precast hollow pile assembly 120, the hollow jack 124 of the pile segment, its annular end plate 124-2, and the bottom anchor plate 131 all have central holes.

[0083] Step S9: Backfill the central passage with crushed sand and gravel to complete the construction of the replacement pile 100.

[0084] Please refer to Figure 18 The replacement piles 100, after construction, serve as a temporary vertical support system for the development of the underground space of the existing building. Earthwork excavation exposes the precast hollow pile components 120. The beams and slabs 200 are constructed using the reverse construction method, and the structural columns are rebuilt using the forward construction method, thus completing the construction of the basement structure. A concrete cushion layer was constructed before the construction of the bottom beams and slabs 200.

[0085] Please refer to Figure 1 , Figures 19 to 24 This invention also provides a method for dismantling and recycling a replacement pile 100 used in the development of underground space in existing buildings, comprising:

[0086] In step S10, after constructing the basement structure of the existing building using the replacement piles 100 as a temporary vertical support system, two top-tightening supports 300 are symmetrically installed between the upper and lower floor beams 200 on both sides of the replacement piles 100. The top anchor plate 132 is removed, releasing the prestress of the steel strands 133, thus transferring the vertical load of the existing building after the underground space development from the replacement piles 100 to the top-tightening supports 300. The top-tightening supports 300 include steel sections 310 and jacks 320 installed on them, which are tightened between the upper and lower floor beams 200. Before the adjacent pile segments are dismantled, the hollow pile jacks 124 can be unloaded.

[0087] Step S11, please refer to Figures 20 to 24Within the basement structure, the precast steel-concrete hollow pile segments 123 and steel strands 133 extending from the beams and slabs of each floor 200 were removed. The drilled piles 110 and steel strands 133 exposed at the bottom beams and slabs 200 were also removed. Anchor bolts 125 were pulled out from adjacent pile segments, and all anchorages 134 on the steel strands 133 were dismantled. The first precast reinforced concrete hollow pile segment 121, the second precast reinforced concrete hollow pile segment 122, and the hollow pile jacks 124 were then removed from the steel strands 133 for dismantling and recycling. Figures 20 to 24 The example illustrates the dismantling and recycling process after cutting the precast steel-concrete hollow pile segment 123 at the upper beam slab 200, dismantling each component from top to top, and then cutting the precast steel-concrete hollow pile segment 123 at the upper beam slab 200 and cutting the steel strand 133. However, this is not limited to this method. Alternatively, after cutting all components at both the upper and lower beam slabs 200, the precast hollow pile assembly 120 can be placed horizontally and the components can be dismantled and recycled from both ends of the steel strand 133, or the steel strand 133 can be pulled out to achieve a one-time dismantling of all components. In this case, the anchor bolt 125 can be pulled out after horizontal placement. During the recycling process, it is necessary to clean the surface laitance or fill the hollow jacks 124 of the first and second precast reinforced concrete hollow pile segments with crushed sand and gravel, and then organize and recycle them. Finally, the precast steel-concrete hollow pile segment 123 protruding from the beam slab 200 is repaired using processes such as central hole sealing piles. The cutting and recycling of steel strand 133 is not limited to cutting and recycling within a certain basement level. It can be cut only at the basement top slab and basement bottom slab, without cutting at the beams and slabs of other levels. This allows for the complete dismantling and recycling of steel strand 133 from the basement bottom slab to the top slab, maximizing the recycling rate of steel strand 133 and avoiding intermediate cutting.

[0088] Step S12, please refer to Figure 24 The top support 300 will be removed to transfer the vertical load of the existing building after the underground space development to the structural columns of the basement structure. The top support 300 needs to be unloaded and then removed.

[0089] The replacement pile 100 for underground space development of existing buildings and its construction and dismantling / recycling methods provided in this embodiment of the invention utilize the replacement pile 100, composed of bored piles 110, precast hollow pile components 120, and unbonded steel strand tensioning components 130, as a temporary vertical support system. After the construction of the basement structure of the existing building, when the precast hollow pile components 120 between the beams and slabs 200 of each basement level are cut off, except for a small proportion of the precast steel pipes extending beyond the beams and slabs 200 of each level, the replacement pile 100 is used as a temporary vertical support system. Apart from the concrete hollow pile segment 123 being cut off and disposed of as construction waste, the majority of the remaining precast reinforced concrete hollow pile segments 121, 122, and hollow pile jacks 124 can be removed from the steel strand 133 for dismantling, recycling, and reuse. This avoids the waste caused by them being treated as construction waste. Furthermore, the cut steel strand 133 can also be recycled and reused, thereby improving the recycling rate of the replaced piles 100 after removal, reducing construction waste disposal, and offering advantages such as energy saving, environmental protection, and low carbon emissions. The steel strand 133 and the steel strand hole 129 utilize a non-bonding technology, enabling the pulling of the steel strand 133 and the insertion and installation of various components.

[0090] The replacement pile 100 for underground space development of existing buildings and its construction and dismantling / recycling methods provided in this invention improve the construction efficiency and quality of the replacement pile 100 for underground space development of existing buildings in low-clearance environments by combining the cast-in-place process of bored pile 110, the prefabrication process of precast hollow pile components 120, and the tensioning process of unbonded steel strand tensioning components 130. This also shortens the construction cycle and reduces the construction difficulty. The bored pile 110 replaces cement mixing piles, enabling construction in low-clearance environments. The components of the precast hollow pile components 120 are sequentially inserted and installed on the steel strands 133, achieving construction in low-clearance environments. The flexible bending characteristics of the steel strands 133 also enable construction in low-clearance environments, thereby improving the construction efficiency and shortening the construction cycle of the replacement pile 100. The precast hollow pile components 120 reduce the amount of cast-in-place structure, further improving the construction efficiency of the replacement pile 100. The bored pile 110 and the precast hollow pile assembly 120 are tensioned together by the unbonded steel strand 133 tensioning assembly 130 to form a connection without separation, which improves the integrity of the replacement pile 100. The precast hollow pile assembly 120 is tensioned and connected to the lower end of the precast hollow pile assembly 120 by the anchor 134, which can improve the tightness of the precast hollow pile assembly 120 and the reinforcing cage 111 and avoid separation. The pile segment hollow jack 124 is tightly connected to the adjacent first precast reinforced concrete hollow pile segment 121 by the anchor 134, which also avoids separation, thereby improving the construction quality of the replacement pile 100.

[0091] The replacement pile 100 for underground space development of existing buildings and its construction and dismantling / recycling methods provided in this embodiment of the invention use precast hollow pile components 120 with precast steel pipe concrete hollow pile segments 123 at the beam slab 200. When constructing the beam slab 200 of the basement structure, the reinforcing bars of the beam slab 200 can be welded to the steel pipes of the precast steel pipe concrete hollow pile segments 123, which reduces the construction difficulty, improves the construction convenience, and avoids the problem that the concrete protective layer needs to be chiseled open to connect the beam reinforcing bars to the precast hollow pile components 120 when using precast reinforced concrete hollow pile segments.

[0092] The replacement pile 100 for underground space development of existing buildings and its construction and dismantling / recycling methods provided in this embodiment of the invention use a prefabricated hollow pile assembly 120 with a hollow structure. This allows the mud in the pile hole 140 to be discharged during the process of lowering each pile segment and the hollow jack 124 in the pile segment into the pile hole 140, reducing mud resistance and ensuring that each component of the prefabricated hollow pile assembly 120 can be driven into place, avoiding problems such as discontinuity and breakage, and improving the pile driving quality of the prefabricated hollow pile assembly 120.

[0093] The replacement pile 100 for the development of underground space of existing buildings and its construction method and dismantling and recycling method provided in the embodiments of the present invention, wherein adjacent pile segments in the prefabricated hollow pile assembly 120 are locked together by anchor bolts 125, which can improve the tightness and reliability of the connection between adjacent pile segments and improve the connection quality between pile segments.

[0094] The replacement pile 100 for the development of underground space in existing buildings and its construction and dismantling and recycling methods provided in this embodiment of the invention expose the bored pile 110 at the elevation of the basement floor slab. This ensures that the bored pile 110 below the basement floor slab serves as the pile foundation for the temporary support system of the vertical load of the existing building, ensuring the force transmission effect and the safety of the existing building after the addition of the basement structure.

[0095] Please refer to this carefully. Figures 1 to 6To achieve stability in the connection between the pile segments in the precast hollow pile assembly 120, this invention provides a replacement pile 100 for the development of underground space in existing buildings, along with its construction and dismantling / recycling methods. The first precast reinforced concrete hollow pile segment 121 includes a hollow concrete body and reinforcing steel bars within it. It has an annular protrusion at its top as a male interface 127 and an annular groove at its bottom as a female interface 128. The pile length is 0.8~1.5m (approximately 1 / 4~1 / 3 of the underground floor height), and the pile diameter is 5~10mm smaller than the pile hole diameter. The second precast reinforced concrete hollow pile segment 122 includes a hollow concrete body and reinforcing steel bars within it. Both its top and bottom have annular protrusions as male interfaces 127. Its pile length is 0.8~1.5m (approximately 1 / 4~1 / 3 of the underground floor height), and the pile diameter is 5~10mm smaller than the pile hole diameter. That is, the first precast reinforced concrete hollow pile segment 121 and... The second precast reinforced concrete hollow pile segment 122 is identical in length and other references except for the interface. The precast steel pipe concrete hollow pile segment 123 includes a steel pipe 123-1 and a hollow concrete body poured inside. It has an annular groove at the top as a female interface 128 and a flat end at the bottom. The pile length is 1~1.5m (approximately the height of the basement beam + 200~500mm), and the pile diameter is 20~30mm smaller than the pile hole diameter. The first precast reinforced concrete hollow pile segments 121 are connected by embedded assembly of male interface 127 and female interface 128. The female interface 128 at the top of the precast steel pipe concrete hollow pile segment is embeddedly assembled with the male interface 127 at the bottom of the second precast reinforced concrete hollow pile segment 122. The male interface 127 at the top of the second precast reinforced concrete hollow pile segment 122 is embeddedly assembled with the female interface 128 at the bottom of the first precast reinforced concrete hollow pile segment 121. Embedded assembly connections can prevent the problem of disengagement between adjacent pile segments, especially after the prestress of steel strand 133 is applied.

[0096] Please refer to Figures 1 to 6 To improve the reliability of the connection between adjacent pile segments, the present invention provides a replacement pile 100 for the development of underground space in existing buildings, along with its construction and dismantling / recycling methods. Both the male interface 127 and the female interface 128 are provided with multiple anchor bolt holes 126 for the installation of anchor bolts 125. The figure illustrates four evenly distributed anchor bolt holes 126, but is not limited to four. The anchor bolts 125 reliably connect adjacent pile segments, preventing disengagement.

[0097] Please refer to Figures 1 to 8To facilitate the threading of steel strands 133 through the precast hollow pile assembly 120, the replacement pile 100 for the development of underground space of existing buildings and its construction method and dismantling and recycling method provided in this embodiment of the invention are provided with multiple steel strand holes 129 for threading steel strands 133 through the hollow concrete body of the first precast reinforced concrete hollow pile segment 121, the hollow concrete body of the second precast reinforced concrete hollow pile segment 122, the hollow concrete body of the precast steel pipe concrete hollow pile segment, and the annular end plate 124-2 of the pile segment hollow jack 124.

[0098] To facilitate the connection between the beam and slab reinforcement of the basement structure's beam and slab 200 and the precast steel-concrete hollow pile segment 123, this embodiment of the invention provides a replacement pile 100 for the development of underground space in existing buildings, along with its construction and dismantling / recycling methods. The precast steel-concrete hollow pile segment 123 has annular shear reinforcement or studs around its steel pipe 123-1, which facilitates the anchorage connection between the precast steel-concrete hollow pile segment 123 and the beam and slab reinforcement. The annular shear reinforcement provides the necessary interfacial shear strength.

[0099] The replacement pile 100 for underground space development of existing buildings and its construction method and dismantling and recycling method provided in this embodiment of the invention are as follows: the inner diameters of the hollow concrete body, the bottom anchor plate 131, the top anchor plate 132 and the annular end plate 124-2 are all the same, and the outer diameters of the precast steel pipe concrete hollow pile segment 123, the first precast reinforced concrete hollow pile segment 121 and the second precast reinforced concrete hollow pile segment are the same.

[0100] Please refer to this carefully. Figures 1 to 6 The replacement pile 100 for underground space development of existing buildings provided in this embodiment of the invention has the same inner diameter for the hollow concrete body, bottom anchor plate 131, top anchor plate 132, and annular end plate 124-2. The outer diameters of the first precast reinforced concrete hollow pile segment 121 and the second precast reinforced concrete hollow pile segment 122 are the same. The outer diameter of the precast steel pipe concrete hollow pile segment 123 is smaller than the outer diameters of the first and second precast reinforced concrete hollow pile segments. A filling layer is provided around the precast steel pipe concrete hollow pile segment 123, and the filling layer has the same outer diameter as the first precast reinforced concrete hollow pile segment 121. The filling layer can prevent the pile hole from necking or collapsing, and can be made of wooden formwork or other materials.

[0101] This invention is not limited to the specific embodiments described above. Obviously, the embodiments described above are only a part of the embodiments of this invention, not all of them. All other embodiments obtained by those skilled in the art based on the described embodiments of this invention are within the scope of protection of this invention. Those skilled in the art can make other modifications and variations to this invention. Therefore, if these modifications and variations of this invention fall within the scope of the claims of this invention, then this invention also intends to include these modifications and variations.

Claims

1. A replacement pile for developing underground space in existing buildings, characterized in that, include: Drilled piles are located inside the pile hole, with their upper ends protruding above the basement floor slab elevation. A precast hollow pile assembly, located within a pile hole and exposed above ground, comprises a precast steel-concrete hollow pile segment extending vertically through the beams and slabs of each floor at the beam-column joints of the basement structure to be constructed. In the non-ground-floor basement to be constructed, a second precast reinforced concrete hollow pile segment is embedded and assembled at the upper end of the precast steel-concrete hollow pile segment. At least one section of a first precast reinforced concrete hollow pile segment is embedded and assembled at the upper end of the second precast reinforced concrete hollow pile segment. In the basement, one or more first precast reinforced concrete hollow pile segments are installed on bored cast-in-place piles. Adjacent first precast reinforced concrete hollow pile segments are embedded and assembled. At the beams and slabs of each floor, hollow pile jacks are installed between the lower ends of the first precast reinforced concrete hollow pile segments and the precast steel pipe concrete hollow pile segments. The hollow pile jacks include hollow jacks and annular end plates vertically connected to both ends. The precast hollow pile assembly also includes multiple anchor bolts radially inserted into the adjacent pile segments embedded and assembled. An unbonded steel strand tensioning assembly includes a bottom anchor plate horizontally welded inside the reinforcing cage of a bored pile located below the basement floor elevation, a top anchor plate horizontally set at the top of a precast hollow pile assembly at ground level, both the bottom and top anchor plates being annular plates, multiple steel strands penetrating the bottom anchor plate, the reinforcing cage, the precast hollow pile assembly, and the top anchor plate, anchorages tensioning and connecting the two ends of the steel strands to the top and bottom anchor plates, anchorages tensioning and connecting the steel strands at the lowest first precast reinforced concrete hollow pile segment, and anchorages tensioning and connecting the steel strands at the annular end plates at both ends of the pile segment hollow jack.

2. The underpinning pile for underground space development of existing buildings according to claim 1, characterized in that, The first precast reinforced concrete hollow pile segment includes a hollow concrete body and reinforcing bars inside, with an annular protrusion at the top serving as a male interface and an annular groove at the bottom serving as a female interface; the second precast reinforced concrete hollow pile segment includes a hollow concrete body and reinforcing bars inside, with annular protrusions at both the top and bottom serving as male interfaces; the precast steel pipe concrete hollow pile segment includes a steel pipe and hollow concrete body poured inside, with an annular groove at the top serving as a female interface and a flat bottom; the first precast reinforced concrete hollow pile segments are connected by embedded assembly using male and female interfaces, the female interface at the top of the precast steel pipe concrete hollow pile segment is embeddedly assembled with the male interface at the bottom of the second precast reinforced concrete hollow pile segment, and the male interface at the top of the second precast reinforced concrete hollow pile segment is embeddedly assembled with the female interface at the bottom of the first precast reinforced concrete hollow pile segment.

3. The replacement pile for underground space development of existing buildings according to claim 2, characterized in that, The hollow concrete bodies of the first precast reinforced concrete hollow pile segment, the second precast reinforced concrete hollow pile segment, and the precast steel pipe concrete hollow pile segment, as well as the annular end plates of the pile segment hollow jacks, are all provided with multiple steel strand holes arranged in a circular array for threading steel strands.

4. The underpinning pile for underground space development of existing buildings according to claim 2, characterized in that, Both the male and female interfaces are provided with multiple anchor bolt holes for the installation of the anchor bolts.

5. The underpinning pile for underground space development of existing buildings according to claim 2, characterized in that, The hollow concrete body, bottom anchor plate, top anchor plate and annular end plate have the same inner diameter, and the precast steel pipe concrete hollow pile segment, the first precast reinforced concrete hollow pile segment and the second precast reinforced concrete hollow pile segment have the same outer diameter.

6. The underpinning pile for underground space development of existing buildings according to claim 2, characterized in that, The hollow concrete body, bottom anchor plate, top anchor plate, and annular end plate all have the same inner diameter. The first precast reinforced concrete hollow pile segment and the second precast reinforced concrete hollow pile segment have the same outer diameter. The outer diameter of the precast steel pipe concrete hollow pile segment is smaller than the outer diameters of the first and second precast reinforced concrete hollow pile segments. A gap-filling layer is provided around the precast steel pipe concrete hollow pile segment, and the gap-filling layer has the same outer diameter as the first precast reinforced concrete hollow pile segment.

7. The underpinning pile for underground space development of existing buildings according to claim 1, characterized in that, The precast steel-concrete hollow pile segment is surrounded by annular shear reinforcement bars or studs.

8. A construction method for underpinning piles for underground space development of existing buildings according to claim 1, characterized in that, include: Step S1: Fabricate the steel cage for the bored pile, horizontally weld the bottom anchor plate inside the steel cage, insert multiple steel strands in a circular array inside the steel cage and pass through the bottom anchor plate, connect the steel strands with anchors and abut against the bottom anchor plate, and suspend the steel strands and the connected steel cage as a whole into the pile hole and expose it to the ground. Step S2: Insert multiple sections of the first precast reinforced concrete hollow pile into the steel strand in sequence, close to the beam slab. Place the lowest section of the first precast reinforced concrete hollow pile against the reinforcing cage. Tension and connect it to the steel strand through anchors, and place it against the bottom of the lowest section of the first precast reinforced concrete hollow pile. Embed and connect adjacent sections of the first precast reinforced concrete hollow pile, and lock them together with anchor bolts. After each installation, continue to suspend and lower the steel strand and the components inserted into it along the pile hole until they are exposed to the ground. Step S3: At a location near the beam elevation, insert the hollow jack of the installation pile section through the steel strand and connect it to the uppermost first precast reinforced concrete hollow pile section. Tension the steel strand through the anchor to abut the upper surface of the lower annular end plate. Continue to suspend and lower the steel strand and the components inserted into it along the pile hole until they are exposed on the ground. Step S4: At the beam elevation, insert the precast steel pipe concrete hollow pile segment through the steel strand and connect it to the upper annular end plate of the hollow pile jack. Adjust and lock the height of the hollow pile jack. Tension the steel strand through the anchor to abut against the lower surface of the upper annular end plate. Continue to suspend and lower the steel strand and the components inserted into it along the pile hole until they are exposed on the ground. Step S5: Insert the second precast reinforced concrete hollow pile segment into the steel strand and connect it to the precast steel pipe concrete hollow pile segment for embedded assembly and connection, and lock the connection with anchor bolts. Continue to suspend and lower the steel strand and the components inserted into it along the pile hole and expose it to the ground. Step S6: Insert multiple sections of the first precast reinforced concrete hollow pile into the steel strand in sequence until the next layer of beams and slabs. Connect the lower first precast reinforced concrete hollow pile section to the second precast reinforced concrete hollow pile section for embedded assembly and lock the connection with anchor bolts. Connect adjacent sections of the first precast reinforced concrete hollow pile section for embedded assembly and lock the connection with anchor bolts. After each installation, continue to suspend and lower the steel strand and the components inserted into it along the pile hole until they are exposed to the ground. Step S7: Repeat steps S3 to S6 until the reinforcing cage sinks to the bottom of the pile hole and the precast steel pipe concrete hollow pile segment is exposed at the ground level of the top beam slab. This completes the installation of the precast hollow pile assembly. At the top of the precast steel pipe concrete hollow pile segment at the ground level, a top anchor plate is horizontally installed. The steel strands are tensioned and connected to the top anchor plate through the anchor. Step S8: Use the central channel formed by the central holes of the top anchor plate, the precast hollow pile assembly and the bottom anchor plate as the pouring channel. Insert the guide pipe into the pouring channel to the bottom of the pile hole and pour concrete. Pour the concrete to the top of the steel cage to form a bored pile by pouring and lifting the pipe at the same time. Then pull out the guide pipe. Step S9: Backfill the central channel with crushed sand and gravel to complete the construction of the replacement piles.

9. A method for dismantling and recycling replacement piles for underground space development of existing buildings according to claim 1, characterized in that, include: After constructing the basement structure of the existing building by using replacement piles as a temporary vertical support system, two top-tight supports are symmetrically installed between the upper and lower beams on both sides of the replacement piles. The top anchor plate is removed, the prestress of the steel strand is released, and the vertical load of the existing building after the underground space is developed is transferred from the replacement piles to the top-tight supports. The precast steel pipe concrete hollow pile segments and steel strands extending from the beams and slabs of each floor in the basement structure were cut off. The drilled cast-in-place piles and steel strands exposed at the bottom beams and slabs were also cut off. The anchor bolts in the adjacent two pile segments were pulled out, and all anchors on the steel strands were removed. The first precast reinforced concrete hollow pile segment, the second precast reinforced concrete hollow pile segment, and the pile segment hollow jacks were pulled out from the steel strands for dismantling and recycling. By removing the top supports, the vertical load of the existing building after the underground space development is transferred from the top supports to the structural columns of the basement structure.

10. The method for dismantling and recycling replacement piles for underground space development of existing buildings according to claim 9, characterized in that, Also includes: Before dismantling adjacent pile segments, the hollow jacks of the pile segments are unloaded.

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