Construction method for new basement and demolishing existing foundation pit support pile

Abstract

This invention relates to the field of foundation pit construction in civil engineering, and particularly to a construction method for constructing a new basement by utilizing and removing existing foundation pit retaining piles. The method includes the following steps: S1, construction preparation; S2, construction of new retaining piles and lattice columns; S3, construction of horizontal bracing; S4, excavation of the foundation pit to the design elevation; S5, construction of the basement floor slab; construction of the ground floor exterior walls; S6, construction of the floor slab; construction of the basement exterior walls; S7, cutting and removing the existing foundation pit retaining piles; S8, construction of the basement floor slab, exterior walls, and floor slabs sequentially from bottom to top. This invention reuses existing foundation pit retaining piles from adjacent existing basements during the construction of a new basement. Firstly, it eliminates the need for new retaining piles on that side. Secondly, by utilizing existing retaining piles and removing them in stages, the basement floor slab, exterior walls, and floor slabs of the new basement can be expanded to the maximum extent possible to the heel of the existing basement walls, thus increasing the usable area of ​​the new basement.

Description

Technical Field

[0001] This invention relates to the field of foundation pit construction in civil engineering, and more particularly to a construction method for constructing a new basement by utilizing and demolishing existing foundation pit retaining piles. Background Technology

[0002] In recent years, with the increase in the density of urban development, the area of ​​basements has become larger and larger, the distance between basements of adjacent buildings has become smaller and smaller, and there have even been cases where newly built basements are closely connected to existing basements.

[0003] If a new basement is adjacent to an existing basement, on the one hand, the existing foundation pit retaining structure can be fully utilized during the excavation of the new foundation pit to save on construction costs; on the other hand, the existing foundation pit retaining structure can be demolished to expand the area of ​​the new basement. Therefore, how to dynamically utilize and then demolish the existing retaining structure during the construction of the new foundation pit is a technical issue worth exploring.

[0004] For example, CN115030186B, which discloses a construction method for foundation pit support in multi-story basements where the existing diaphragm walls need to be demolished, may have the following limitations: The method involves constructing new foundation pit support without fully utilizing the existing diaphragm walls, and the new foundation pit support's lintel is directly installed on the existing basement exterior wall. 1. The existing basement exterior walls are usually thin (generally 300mm). When the new foundation pit horizontal support beam is constructed by installing rebar on the exterior wall, the waterproofing and integrity of the exterior wall are damaged, which may lead to cracking, water seepage, local stress concentration, deformation, breakage and other defects in the existing exterior wall. 2. The horizontal support of the newly built foundation pit acts directly on the exterior wall of the existing basement. This load was not considered in the original basement design, which may cause the existing basement to have large horizontal lateral displacement and deformation, thus affecting its normal use. 3. The floor slab of the newly built basement is directly laid on the exterior wall of the existing basement (i.e., shared wall), meaning that part of the load is borne by the existing basement. This load was not considered in the original basement design, which may lead to defects in the existing basement.

[0005] It is evident that it is necessary to develop economical and convenient construction methods for new basements that utilize existing foundation pit retaining piles, and to promote the advancement of construction technology for new basements adjacent to existing basements. Summary of the Invention

[0006] The purpose of this invention is to overcome the above-mentioned shortcomings and provide a construction method for utilizing and demolishing existing foundation pit retaining piles in the construction of a new basement. This method allows the floor slab, exterior walls, and floor slabs of the new basement to be expanded to the maximum extent to the heel of the existing basement walls, without requiring rebar installation or structural connection to the adjacent existing basement structure. This minimizes the impact on the adjacent existing basement and achieves the goals of saving construction time and reducing construction costs.

[0007] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: a construction method for constructing a new basement by utilizing and demolishing existing foundation pit retaining piles, wherein the existing foundation pit retaining piles are set outside the existing basement, an existing capping beam is set on the top of the existing basement, an existing trench is set between the existing foundation pit retaining piles and the existing basement, and an existing support plate is set between each floor slab of the existing basement and the existing foundation pit retaining piles, including the following steps: S1. Construction preparation: Transport relevant construction equipment, tools and materials to the construction site in an orderly manner according to the construction schedule; S2. Construct new retaining piles and lattice columns. Construct new retaining piles and lattice columns in the area of ​​the new basement, but do not construct new retaining piles on the side close to the existing basement. S3. Construct horizontal bracing. Based on the progress of the foundation pit excavation, select a portion of the existing foundation pit retaining piles to construct waist beams on the outside, construct corresponding horizontal bracing, cut and remove another portion of the unselected existing foundation pit retaining piles above the excavation surface, excavate and remove the existing trench above the excavation surface until the foundation pit is excavated to the design elevation. S4. Excavate the foundation pit to the design elevation, excavate the foundation pit in layers and sections to the design elevation, cut and remove another part of the existing foundation pit retaining piles that were not selected above the excavation surface, and excavate and remove the existing trench above the excavation surface. S5. Construct the basement floor slab. Construct the basement floor slab at the bottom of the foundation pit. The floor slab closest to the existing basement extends along the location of the removed existing foundation pit retaining piles to the outside of the existing basement floor slab. For the construction of the ground floor exterior walls, the exterior walls on the side closest to the existing basement are only constructed on the basement slab extending to the outer end of the existing basement floor slab. S6. Construct the floor slab, cut and remove the horizontal bracing and lintel at the proposed floor slab location, formwork, tie the reinforcing bars, and pour concrete to form the floor slab. The floor slab near the existing basement extends along the location of the removed existing foundation pit retaining piles to the completed lower floor exterior wall. To construct the basement exterior wall, after each floor slab is constructed, formwork is erected, steel bars are tied, and concrete is poured on that floor slab to form the basement exterior wall. The basement exterior wall on the side close to the existing basement is only constructed by continuing the work on the exterior wall already completed below. S7. Cut and remove the existing foundation pit retaining piles. Cut and remove the remaining existing foundation pit retaining piles in sections down to the floor level of the basement. The existing support plate connected to the existing foundation pit retaining piles is also removed at the same time. S8. Continue construction of the basement floor slab, exterior walls and floor slabs from bottom to top until all basement structures are completed.

[0008] Furthermore, in S3, the specific steps for applying the horizontal bracing include: S3.1. Construct the first horizontal bracing. When the foundation pit is excavated to the bottom of the first horizontal bracing, formwork is erected, steel bars are tied, and concrete is poured to form the first horizontal bracing. One end of the first horizontal bracing directly acts on the existing cap beam. S3.2. When the excavation reaches the bottom of the second horizontal bracing, a portion of the existing foundation pit retaining piles are used as a waist beam. Another portion of the unselected existing foundation pit retaining piles above the excavation face are cut and removed. Simultaneously, the existing support plate connected to the unselected existing foundation pit retaining piles is cut and removed. The existing trench above the excavation face is excavated and removed. Then the second horizontal bracing is constructed. S3.3. When the foundation pit is excavated to the bottom of the third horizontal support, cut and remove another part of the existing foundation pit retaining piles that were not selected above the excavation surface, excavate and remove the existing trench above the excavation surface, and then use the existing foundation pit retaining piles as waist beams to construct the third horizontal support. S3.4. Continue construction of the remaining horizontal bracing until the foundation pit is excavated to the design elevation.

[0009] Furthermore, the second horizontal brace, the third horizontal brace, and the remaining horizontal braces are made of reinforced concrete or steel.

[0010] Furthermore, in S3.2, when cutting and removing another portion of the existing unselected foundation pit retaining piles above the excavation face, the existing support plate connected to the unselected existing foundation pit retaining piles is simultaneously cut and removed.

[0011] Furthermore, the number of existing foundation pit retaining piles reused is 45%-55% of the total number of existing foundation pit retaining piles on that side, and the reused existing foundation pit retaining piles are selected from the existing foundation pit retaining piles at even intervals.

[0012] Furthermore, in step S6, the specific steps for constructing the floor slab include: S6.1. Construct the floor slab of the next floor above the basement floor slab, cut and remove the horizontal bracing and lintel at the location of the floor slab above the basement floor, formwork, tie the reinforcing bars, and pour concrete to form the floor slab above the basement floor. The floor slab near the existing basement extends along the location of the removed existing foundation pit retaining piles to the completed lower floor exterior wall. After the construction of the exterior walls and floor slabs, formwork is erected, steel bars are tied, and concrete is poured on the floor slabs to form the exterior walls of the basement. The exterior walls of the basement on the side close to the existing basement are only constructed by continuing the work on the exterior walls that have been completed below. S6.2 Repeat step S6.1 until the floor slab and exterior walls of the newly built basement level are completed; S6.3. Construct the basement roof slab, cut and remove the first horizontal brace and the existing cap beam, set up formwork, tie the reinforcing bars, and pour concrete to form the basement roof slab. The floor slab near the existing basement extends along the location of the removed existing foundation pit retaining piles to the completed exterior wall.

[0013] Furthermore, in the S6.1-S6.3 process, a new support plate is constructed on the outer side of the junction between the floor slab and the basement roof slab and the outer wall. The new support plate on the side closer to the existing basement is connected to the existing basement, and the new support plate on the side closer to the newly built retaining piles is connected to the newly built retaining piles.

[0014] Furthermore, after S8, the construction of a trench around the newly built basement is carried out to form a new trench.

[0015] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention reuses the existing retaining piles of the adjacent existing basement during the construction of a new basement. First, it eliminates the need to install new retaining piles on that side. Second, by utilizing the existing retaining piles and cutting and removing them in stages, the basement floor slab, exterior walls and floor slab of the new basement can be expanded to the maximum extent to the heel of the existing basement walls, thereby expanding the usable area of ​​the new basement. 2. During the construction process, this invention does not involve rebar installation or structural connection of adjacent existing basement structures, thus minimizing the impact on adjacent existing basements and avoiding disputes between different property owners. Furthermore, the newly constructed basement floor slab, exterior walls, and floor slabs on the side closest to the existing basement are integrated through localized joint construction. The construction method is mature, does not significantly increase the overall construction difficulty of the project, and saves construction time and reduces construction costs. Attached Figure Description

[0016] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings: Figure 1 This is a schematic diagram of the newly constructed basement and the existing basement according to the present invention.

[0017] Figure 2 This is a schematic diagram of the first horizontal bracing applied according to the present invention.

[0018] Figure 3This is a schematic diagram illustrating the application of the second horizontal brace in this invention.

[0019] Figure 4 This is a three-dimensional schematic diagram of the excavation to the second horizontal support according to the present invention.

[0020] Figure 5 This is a schematic diagram illustrating the application of the third horizontal brace in this invention.

[0021] Figure 6 This is a three-dimensional schematic diagram of the excavation up to the third horizontal support according to the present invention.

[0022] Figure 7 This is a schematic diagram showing the excavation to the design elevation according to the present invention.

[0023] Figure 8 This is a three-dimensional schematic diagram of the excavation to the design elevation for this invention.

[0024] Figure 9 This is a schematic diagram showing the existing foundation pit retaining piles that are reused in this invention and the existing foundation pit retaining piles that were not selected.

[0025] Figure 10 This is a schematic diagram of the construction of the basement floor slab and the exterior wall of the third basement level according to the present invention.

[0026] Figure 11 This is a three-dimensional schematic diagram of the basement floor slab and the exterior wall of the third basement level for the present invention.

[0027] Figure 12 This is a three-dimensional schematic diagram of the completed exterior wall of the third basement level of this invention.

[0028] Figure 13 This is a schematic diagram of the construction of the second basement floor slab and exterior wall according to the present invention.

[0029] Figure 14 This is a three-dimensional schematic diagram of the second basement floor slab and exterior wall for the present invention.

[0030] Figure 15 This is a three-dimensional schematic diagram of the completed exterior wall of the second basement level of this invention.

[0031] Figure 16 This is a schematic diagram illustrating the construction of the basement floor slab and exterior walls according to the present invention.

[0032] Figure 17 This is a three-dimensional schematic diagram of the basement floor slab and exterior wall for the present invention.

[0033] Figure 18 This is a three-dimensional schematic diagram of the completed exterior wall of the basement level of this invention.

[0034] Figure 19 This is a schematic diagram of the basement roof slab constructed according to the present invention.

[0035] Figure 20This is a three-dimensional schematic diagram of the basement roof slab constructed according to the present invention.

[0036] Figure 21 This is a three-dimensional schematic diagram of the completed basement roof slab of the present invention. Figure 1 .

[0037] Figure 22 This is a three-dimensional schematic diagram of the completed basement roof slab of the present invention. Figure 2 .

[0038] Figure 23 This is a schematic diagram of the arrangement of the new support plate of the present invention.

[0039] Figure 24 for Figure 23 A partially enlarged schematic diagram.

[0040] Figure 25 This is a three-dimensional schematic diagram of the basement floor slab, floor slab, and exterior wall after the completion of the joint construction of the present invention.

[0041] Figure 26 This is a schematic diagram of the completed perimeter trench around the newly constructed basement according to the present invention.

[0042] In the diagram: 1. Existing basement; 2. Existing foundation pit retaining piles; 3. New basement; 4. Existing trench; 5. Existing support slab; 6. Existing capping beam; 7. New retaining piles; 8. Lattice column; 9. First horizontal brace; 10. Second horizontal brace; 11. Partially cut-off pile; 12. Third horizontal brace; 13. Waist beam; 14. Basement floor slab; 15. Exterior wall; 16. Floor slab; 17. New trench; 18. New support slab. Detailed Implementation

[0043] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Unless otherwise specified, the embodiments and features in the embodiments of this application can be combined with each other. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0044] Please see Figure 1-26 .

[0045] by Figure 1Taking the project shown as an example, in the case of the existing basement 1 being a three-story underground, the foundation pit is supported by retaining piles. The existing foundation pit retaining piles 2 are temporary structures. After the completion of the existing basement 1, they are abandoned in the soil together with the existing capping beam 6. The newly built basement 3 is set to be three stories, with the same height as the existing basement 1. The newly built basement 3 and the existing basement 1 are adjacent to each other, and the ends of the basement floor slab 14 are in contact with each other. Unless otherwise specified, the operations such as formwork, rebar tying, and concrete pouring in this invention can be carried out according to conventional methods, and the construction method will not be described in detail.

[0046] This invention discloses a construction method for constructing a new basement using existing foundation pit retaining piles 2 and removing them. The existing foundation pit retaining piles 2 are installed outside the existing basement 1. An existing capping beam 6 is installed on the top of the existing basement 1. An existing trench 4 is installed between the existing foundation pit retaining piles 2 and the existing basement 1. Existing support plates 5 are installed between each floor slab 16 of the existing basement 1 and the existing foundation pit retaining piles 2. The method includes the following steps: S1. Construction preparation: Transport relevant construction equipment, tools and materials to the construction site in an orderly manner according to the construction schedule; S2. Construct new retaining piles 7 and lattice columns 8. According to the design plan, construct new retaining piles 7 and lattice columns 8, including new crown beams, in the area of ​​the new basement 3. Do not construct new retaining piles 7 on the side close to the existing basement 1. The lattice columns 8 are the vertical support points for the subsequent horizontal bracing. S3. Install horizontal bracing: S3.1, Construct the first horizontal brace 9, as follows: Figure 2 As shown, when the foundation pit is excavated to the bottom of the first horizontal support 9, the formwork is erected, the steel bars are tied, and the concrete is poured to form the first horizontal support 9. One end of the first horizontal support 9 directly acts on the existing cap beam 6. S3.2, Construct a second horizontal brace of 10 mm, as follows: Figure 3 and 4 As shown, when the foundation pit is excavated to the bottom of the second horizontal support 10, a portion of the existing foundation pit retaining piles 2 are used as the waist beam 13. Another portion of the unselected existing foundation pit retaining piles 2 above the excavation surface are cut and removed. Simultaneously, the existing support plate 5 connected to the unselected existing foundation pit retaining piles 2 is cut and removed. The existing trench 4 above the excavation surface is excavated and removed. Then the second horizontal support 10 is constructed. S3.3, Construct the third horizontal bracing 12, as follows Figure 5 As shown, when the foundation pit is excavated to the bottom of the third horizontal support 12, another part of the existing foundation pit retaining piles 2 that were not selected above the excavation surface is cut and removed, the existing trench 4 above the excavation surface is excavated and removed, and the existing foundation pit retaining piles 2 are used as the waist beam 13 to construct the third horizontal support 12. The second horizontal brace 10, the third horizontal brace 12, and the remaining horizontal braces are made of reinforced concrete or steel. The number of existing foundation pit retaining piles 2 that are reused is 45%-55% of the total number of existing foundation pit retaining piles 2 on this side. The existing foundation pit retaining piles 2 that are reused are selected from the existing foundation pit retaining piles 2 at even intervals. S4. Excavation of the foundation pit to the design elevation, such as Figure 8 As shown, the foundation pit is excavated in layers and sections to the design elevation. Another portion of the existing foundation pit retaining piles 2 that were not selected above the excavation surface is cut and removed. The cut-off of the existing foundation pit retaining piles 11 constitutes a partial truncation. Simultaneously, the existing support plate 5 connected to the existing foundation pit retaining piles 2 that were not selected is cut and removed. Figure 7 As shown, the existing trench 4 above the excavation face was excavated and removed; S5. Construct the basement floor slab 14, as follows Figure 9-11 As shown in the figure, 2-1 is the existing foundation pit retaining pile 2 that is reused, and 2-2 is the existing foundation pit retaining pile 2 that was not selected. The basement floor slab 14 is constructed at the bottom of the foundation pit. The floor slab near the existing basement 1 extends along the position of the removed existing foundation pit retaining pile 2 to the outside of the existing basement 1 floor slab. The basement floor slab 14 forms a "gap" at the position of the reused existing foundation pit retaining pile 2. The exterior wall 15 on the ground floor is constructed only on the slab extending to the outer end of the existing basement 1. The exterior wall 15 on the side closest to the existing basement 1 is discontinuous in shape. S6, Construct floor slab 16, as follows Figure 12-14 As shown: S6.1. Construct the floor slab 16 above the basement floor slab 14, cut and remove the horizontal bracing and lintel 13 at the location of the floor slab 16 above the basement floor, formwork, tie the reinforcing bars, and pour concrete to form the floor slab 16 above the basement floor. The floor slab 16 near the existing basement 1 extends along the location of the removed existing foundation pit retaining piles 2 to the completed lower outer wall 15. After the construction of the exterior wall 15 and floor slab 16, formwork is erected, steel bars are tied, and concrete is poured on the floor slab 16 to form the basement exterior wall 15. The basement exterior wall 15 on the side close to the existing basement 1 is only continued on the exterior wall 15 that has been completed below. S6.2 Repeat steps S6.1 until the floor slab 16 and exterior wall 15 of the newly built basement 3 are completed. Figure 15-17 As shown; S6.3, Construct the basement roof slab, such as Figure 18-21 As shown, the first horizontal brace 9 and the existing cap beam 6 were cut and removed, and the formwork, steel reinforcement was tied and concrete was poured to form the basement roof slab. The floor slab 16 near the existing basement 1 extends along the removed existing foundation pit retaining piles 2 to the completed exterior wall 15.

[0047] like Figure 22-23As shown, a new support plate 18 is constructed on the outer side of the junction of the floor slab 16 and the basement roof slab with the outer wall 15. The new support plate 18 on the side closer to the existing basement 1 is connected to the existing basement 1, and the new support plate 18 on the side closer to the newly built retaining pile 7 is connected to the newly built retaining pile 7. S7. Cut and remove the existing foundation pit retaining piles 2, such as Figure 24 As shown, the remaining existing foundation pit retaining piles 2 were cut and removed in sections down to the elevation below the basement floor slab 14, and the existing support plate 5 connected to the existing foundation pit retaining piles 2 was also removed simultaneously. S8, such as Figure 25 As shown, the construction of the basement floor slab 14, exterior walls 15, and floor slabs 16 is carried out sequentially from bottom to top until the entire basement structure is completed, as follows. Figure 26 As shown, a new trench 17 was formed by constructing a trench around the perimeter of the newly built basement 3.

[0048] The construction of the new basement 3 is now complete. During the construction process, no rebar installation or structural connection was carried out on the adjacent existing basement 1, which minimized the impact on the adjacent existing basement 1 and avoided potential disputes between different property owners.

[0049] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

Claims

1. A construction method for a new basement using a demolition existing foundation pit retaining pile, characterized in that, Includes the following steps: S1. Construction preparation: Transport relevant construction equipment, tools and materials to the construction site in an orderly manner according to the construction schedule; S2. Construct new retaining piles (7) and lattice columns (8). Construct new retaining piles (7) and lattice columns (8) in the area of ​​the new basement (3). Do not construct new retaining piles (7) on the side close to the existing basement (1). S3. Construct horizontal bracing. Based on the progress of the foundation pit excavation, select a portion of the existing foundation pit retaining piles (2) to construct a waist beam (13) on the outside, construct the corresponding horizontal bracing, cut and remove another portion of the unselected existing foundation pit retaining piles (2) above the excavation surface, excavate and remove the existing trench (4) above the excavation surface, until the foundation pit is excavated to the design elevation. S4. Excavate the foundation pit to the design elevation, excavate the foundation pit in layers and sections to the design elevation, cut and remove another part of the existing foundation pit retaining piles that were not selected above the excavation surface (2), and excavate and remove the existing trench above the excavation surface (4). S5. Construct the basement floor slab (14). Construct the basement floor slab (14) at the bottom of the foundation pit. The floor slab near the existing basement (1) extends along the location of the removed existing foundation pit retaining piles (2) to the outside of the existing basement (1) floor slab. Construction of the ground floor exterior wall (15), the exterior wall (15) on the side close to the existing basement (1) is only constructed on the basement slab extending to the outer end of the existing basement (1) floor slab; S6. Construct floor slab (16), cut and remove the horizontal bracing and lintel (13) at the location of the proposed floor slab (16), formwork, steel reinforcement binding, and concrete pouring to form floor slab (16). The floor slab (16) near the existing basement (1) extends along the location of the removed existing foundation pit retaining piles (2) to the completed lower floor exterior wall (15). The basement exterior wall (15) is constructed by setting up formwork, binding steel bars, and pouring concrete on each floor slab (16) after construction. The basement exterior wall (15) on the side close to the existing basement (1) is constructed only on the exterior wall (15) below that has been completed. S7. Cut and remove the existing foundation pit retaining piles (2), cut and remove the remaining existing foundation pit retaining piles (2) in sections to below the elevation of the basement floor slab (14), and remove the existing support plate (5) connected to the existing foundation pit retaining piles (2) at the same time. S8. Continue construction of the basement floor slab (14), exterior walls (15) and floor slab (16) from bottom to top until all basement structures are completed.

2. The construction method for building a new basement using the existing foundation pit retaining piles according to claim 1, characterized in that: In S3, the specific steps for installing the horizontal bracing include: S3.

1. Construct the first horizontal brace (9). When the foundation pit is excavated to the bottom of the first horizontal brace (9), formwork is erected, steel bars are tied, and concrete is poured to form the first horizontal brace (9). One end of the first horizontal brace (9) directly acts on the existing cap beam (6). S3.

2. Construct the second horizontal bracing (10). When the foundation pit is excavated to the bottom of the second horizontal bracing (10), use a portion of the existing foundation pit retaining piles (2) as a waist beam (13), cut and remove another portion of the unselected existing foundation pit retaining piles (2) above the excavation surface, simultaneously cut and remove the existing support plate (5) connected to the unselected existing foundation pit retaining piles (2), excavate and remove the existing trench (4) above the excavation surface, and then construct the second horizontal bracing (10). S3.

3. Construct the third horizontal bracing (12). When the foundation pit is excavated to the bottom of the third horizontal bracing (12), cut and remove another part of the existing foundation pit retaining piles (2) that were not selected above the excavation surface, excavate and remove the existing trench (4) above the excavation surface, and then use the existing foundation pit retaining piles (2) as a waist beam (13) to construct the third horizontal bracing (12). S3.

4. Continue construction of the remaining horizontal bracing until the foundation pit is excavated to the design elevation.

3. The construction method for building a new basement using the existing foundation pit retaining piles according to claim 2, characterized in that: The second horizontal brace (10), the third horizontal brace (12), and the remaining horizontal braces are reinforced concrete supports or steel supports.

4. The construction method for building a new basement using the existing foundation pit retaining piles according to claim 2, characterized in that: In S3.2, when cutting and removing another part of the unselected existing foundation pit retaining piles (2) above the excavation face, the existing support plate (5) connected to the unselected existing foundation pit retaining piles (2) is simultaneously cut and removed.

5. The construction method for building a new basement using the existing foundation pit retaining piles according to claim 2, characterized in that: The number of existing foundation pit retaining piles (2) to be reused is 45%-55% of the total number of existing foundation pit retaining piles (2) on this side. The existing foundation pit retaining piles (2) to be reused are selected from the existing foundation pit retaining piles (2) at even intervals.

6. The construction method for building a new basement using the existing foundation pit retaining piles according to claim 2, characterized in that: In S6, the specific steps for constructing the floor slab (16) include: S6.

1. Construct the floor slab (16) above the basement floor slab (14), cut and remove the horizontal bracing and lintel (13) at the location of the floor slab (16), formwork, tie the reinforcing bars, and pour concrete to form the floor slab (16) above the basement. The floor slab (16) near the existing basement (1) extends along the location of the removed existing foundation pit retaining piles (2) to the completed lower outer wall (15). After the construction of the exterior wall (15) and floor slab (16), formwork is erected, steel bars are tied, and concrete is poured on the floor slab (16) to form the basement exterior wall (15). The basement exterior wall (15) close to the existing basement (1) is only continued on the exterior wall (15) below that has been completed. S6.2 Repeat step S6.1 until the floor slab (16) and exterior wall (15) of the newly built basement (3) are completed; S6.

3. Construct the basement roof slab, cut and remove the first horizontal brace (9) and the existing cap beam (6), formwork, tie the reinforcing bars and pour concrete to form the basement roof slab, and extend the floor slab (16) close to the existing basement (1) along the location of the removed existing foundation pit retaining pile (2) to the completed exterior wall (15).

7. The construction method for building a new basement using the existing foundation pit retaining piles according to claim 6, characterized in that: During the S6.1-S6.3 process, a new support plate (18) is constructed on the outside of the junction of the floor slab (16) and the basement roof slab with the outer wall (15). The new support plate (18) on the side closer to the existing basement (1) is connected to the existing basement (1), and the new support plate (18) on the side closer to the newly built retaining pile (7) is connected to the newly built retaining pile (7).

8. The construction method for building a new basement using the existing foundation pit retaining piles according to claim 1, characterized in that: After S8, the construction of the trench around the newly built basement (3) is carried out to form a new trench (17).

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