Construction method of high-position overhanging multi-form supporting system in narrow space

Abstract

The invention provides a construction method of a high-position overhanging multi-form supporting system in a narrow space. The construction method comprises the following steps that S1, investigation design is conducted; s2, construction of cast-in-place piles, high-pressure jet grouting piles and crown beams; s3, vertical column piles and steel latticed columns are constructed; s4, earthwork excavation construction is conducted, according to distribution of diagonal braces of the support arrangement diagram, the earthwork is divided into four areas to be excavated with the diagonal braces as boundaries, and during excavation, a layered excavation mode from the ground to the top beam bottom, from the top beam bottom to the first supporting beam bottom, from the first supporting beam bottom to the second supporting beam bottom and from the second supporting beam bottom to the base design elevation is adopted; and S5, constructing an underground main body structure, and selecting a corresponding supporting form to construct an underground main body according to whether the side edge of the deep foundation pit is close to a building or a pipe gallery and an underground pipeline or not. According to the deep foundation pit supporting method, a multi-form deep foundation pit supporting scheme is adopted, the safety of deep foundation pit supporting can be guaranteed, and many construction technical problems of traditional deep foundation pit supporting can be well solved.

Description

Technical Field

[0001] The present application relates to the technical field of foundation pit construction, and in particular to a construction method of a high-position cantilevered multi-form support system in a narrow space. Background Art

[0002] At present, with the development of urban construction, the number of high-rise buildings in urban areas is gradually increasing. Due to the requirements of use function and development of underground space, high-rise buildings are generally designed with underground space of larger plane size and depth. The development of underground space involves the safety of deep foundation pits of buildings, which is especially important for densely built areas located on soft soil foundations.

[0003] In addition, due to the different environments around the foundation pit, the support forms adopted by the foundation pit are also different. One of them is that the old building is supported by anchor cables, and the new building is too close to the old building, so part of the anchor cable is located in the new foundation pit. The new foundation pit adopts reinforced concrete beam internal support, and this type of support method needs to occupy a certain space in the foundation pit, which conflicts with the anchor cable support of the old foundation pit and the underground structure of the new building also has a certain conflict with it.

[0004] As the number of buildings continues to increase, such situations will become more and more common. Traditional methods have drawbacks or cannot meet construction needs. In order to control the deformation of surrounding buildings, municipal roads and underground pipelines, reduce the impact of deep foundation pit construction on the surrounding environment, and ensure the safety of deep foundation pit construction, it is necessary to study a construction method for large-scale high-position cantilevered multi-form support systems in narrow spaces. While ensuring the safety of the foundation pit, it can improve construction efficiency and reduce construction costs. At the same time, it can well solve the construction technical problems related to large-scale high-position cantilevered support systems in narrow spaces. Summary of the invention

[0005] In order to improve the problem of conflict between deep foundation pits and surrounding buildings, pipe corridors and underground pipelines, and anchor cable support of old foundation pits, and the narrow construction site of foundation pit support, the present application provides a construction method of a high-position cantilever multi-form support system in a narrow space.

[0006] The application provides a construction method for a high-position cantilever multi-form support system in a narrow space, which adopts the following technical solution: A construction method for a high-position cantilever multi-form support system in a narrow space, comprising the following steps: S1. Survey and design: survey the surrounding environment of the foundation pit project and design deep foundation pit support scheme; S2. Construction of cast-in-place piles, high-pressure rotary jet piles and crown beams. Cast-in-place piles are constructed in the foundation pit support area, and then high-pressure rotary jet piles are constructed between the cast-in-place piles. Finally, the crown beam construction is completed to connect the cast-in-place piles and the high-pressure rotary jet piles into a whole; S3. Construction of column piles and steel lattice columns: first, construct the column piles, then lower the steel lattice columns into place, and ensure that each side of the steel lattice columns is strictly perpendicular or parallel to the corresponding main support axis direction; S4. Earthwork excavation construction, according to the distribution of the support arrangement diagram, the earthwork is divided into four areas with the support as the dividing line for excavation, and the excavation is carried out in layers from the ground to the bottom of the crown beam, the bottom of the crown beam to the bottom of the first support beam, the bottom of the first support beam to the bottom of the second support beam, and the bottom of the second support beam to the design elevation of the base; S5. For the construction of the underground main structure, choose the corresponding support form to construct the underground main structure according to whether there are buildings, pipe corridors and underground pipelines close to the side of the deep foundation pit.

[0007] Furthermore, in step S5, if there are pipe corridors and underground pipelines near the side of the deep foundation pit, the support form adopts a combination of three prestressed anchor cables and two layers of structural plates; after excavating to the bolting elevation, the lines are measured and laid out, and the prestressed anchor cables are manufactured. The drilling rig is then put in place and the curtain hole is opened, and the self-contained anchor cable is used for grouting. After drilling to the designed length, the drill rod is rotary-jetted and the anchor is withdrawn, and then maintenance is carried out and tensioning and locking are started after the anchor cable slurry reaches the designed strength requirements.

[0008] Furthermore, in step S5, if there is no building on the side of the deep foundation pit, the support form adopts a combination of two concrete supports and two layers of structural slabs; when constructing the bottom plate, external wall steel bars are reserved and a formwork is set up together with the bottom plate, the bottom plate concrete and the connected external wall are poured at the same time, and the second support and purlin are removed after the concrete strength of the bottom plate and the force transfer belt reaches the design requirements. After the removal is completed, the construction of the negative second floor external wall and the negative second floor slab begins. At this time, more than 0.5m of external wall steel bars need to be reserved for the external wall, and then the negative second floor force transfer belt is backfilled and the force transfer belt is constructed to connect the negative second floor slab and the supporting piles. After the backfilling and force transfer belt are completed, the first support, purlin and steel lattice column are removed, and then the negative first floor external wall and the negative first floor are constructed. After the construction is completed, the negative first floor force transfer belt is backfilled to the top elevation of the negative first floor slab.

[0009] Furthermore, in step S5, if the side of the deep foundation pit is close to a building, the support form adopts a combination of a concrete support and a structural plate; when constructing the bottom plate, the outer wall steel bars are reserved, and the formwork is set up together with the bottom plate, and the bottom plate concrete and the connected outer wall are poured at the same time. After the bottom plate reaches the design strength, the first support and steel lattice column are removed. After the removal is completed, the outer wall construction continues until the underground floor slab is completed, and then the force transmission belt is constructed to connect with the crown beam and the underground floor slab.

[0010] Furthermore, in step S5, before the construction of the underground main structure, if there are anchor cables left over from the original building on the side of the deep foundation pit, first perform coordinate positioning according to the existing construction drawings and the foundation pit support drawings of the original building, find the positions of the high-pressure rotary jet piles and the cast-in-place piles, then put the rotary drilling machine in place, check the positions, and drill holes to the position of the first anchor cable. The excavator is in place, the bucket is replaced with hydraulic scissors, the anchor cables in the hole are cut, and the first anchor cable is taken out; the second anchor cable is removed and the above construction process is repeated to remove it. After both anchor cables are completely removed, backfill and compaction are performed to ensure safety.

[0011] Furthermore, in step S2, long spiral drilling and grouting are used to construct the cast-in-place piles. If there is local sandy soil and long spiral drilling cannot be used, positive circulation drilling is used to construct the cast-in-place piles.

[0012] Furthermore, in step S2, after the strength of the cast-in-place pile and the high-pressure jet-jet pile reaches the design strength requirement, the pile head is broken and chiseled, and then the crown beam steel bars are tied on the top of the pile, and concrete is poured to form the crown beam.

[0013] Furthermore, in step S3, when setting the steel lattice columns, the steel lattice columns are first temporarily fixed using reinforcing steel bars, and then calibrated using a total station and a vertical adjustment device to ensure that the installation verticality of the steel lattice columns meets the design requirements before welding and fixing.

[0014] Furthermore, in step S4, when excavating from the ground to the bottom of the crown beam, excavation is carried out sequentially from east to west; when excavating from the bottom of the crown beam to the bottom of the first supporting beam, the first support is used as the boundary and excavation is carried out from the middle to the north and south sides simultaneously; when excavating from the bottom of the first supporting beam to the bottom of the second supporting beam, some earth-moving machinery and earth-moving vehicles are working on the plank road, and multiple earth-moving machinery are digging and piling up the earth under the supporting beam for construction; when excavating from the bottom of the second supporting beam to the design elevation of the base, the second support is used as the boundary and excavation is carried out from the middle to the north and south sides simultaneously.

[0015] In summary, the present application includes at least one of the following beneficial technical effects: 1. Before the foundation pit support design is carried out, a detailed survey and investigation of the surrounding environment and underground structure of the project is carried out. During the drawing design stage, in combination with the actual needs of the construction site, detailed research and discussion are carried out, and the optimal design scheme is proposed for narrow space conditions. Multiple forms of deep foundation pit support schemes are adopted to solve the construction technical difficulties of the high-position cantilever support system under narrow space conditions, so that the construction method of this application can also be greatly improved and applied in terms of applicability; 2. The construction method of the present application adopts different support forms according to the different surrounding environments. By adopting multiple forms of deep foundation pit support solutions, the safety of the high-position cantilever support system under narrow space conditions can be greatly improved. For example, when there are pipe corridors and underground pipelines on the south side of the deep foundation pit, the first support form is adopted, which is composed of cast-in-place piles + high-pressure rotary jet piles + crown beams + three prestressed anchor cables + two-layer structural plates; when there are no buildings on the east and north sides of the deep foundation pit, the second support form is adopted, which is composed of cast-in-place piles + high-pressure rotary jet piles + crown beams + two concrete supports + two-layer structural plates; when there are buildings on the west side of the deep foundation pit and the remaining anchor cables of the original buildings affect the construction, the third support form is adopted, which is composed of cast-in-place piles + high-pressure rotary jet piles + crown beams + one concrete support + one layer of structural plates. By adopting the construction method of the application, not only the safety of deep foundation pit support can be ensured, but also many construction technical problems of traditional deep foundation pit support can be well solved; 3. The construction method of the present application solves the technical difficulties in the construction of large-scale high-position cantilever support systems in narrow spaces by adopting various forms of deep foundation pit support schemes. When there are buildings or anchor cables left over from buildings near the deep foundation pit, the inherent unified foundation pit support design scheme is broken on the premise of ensuring the safety of the deep foundation pit. The design is optimized based on the actual situation on site. By reducing the number of layers and designing a single concrete support, the original two-layer structural slab and two support beams are replaced. While avoiding the original building support structure or anchor cables left over from the building, it can not only reduce construction costs, but also greatly improve the construction efficiency of deep foundation pit projects. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0017] Figure 1 It is a construction flow chart of an embodiment of the present application; Figure 2 This is a schematic cross-sectional structural diagram of a deep foundation pit embodiment of the present application when there are pipe galleries and underground pipelines adjacent to the side thereof; Figure 3 is a schematic cross-sectional structural diagram of a deep foundation pit embodiment of the present application when there is no building on the side; Figure 4 It is a schematic diagram of the cross-sectional structure when there is a building adjacent to the side of the deep foundation pit of an embodiment of the present application.

[0018] Reference numerals: 11. Cast-in-place piles; 12. High-pressure jet grouting piles; 13. Crown beams; 21. Column pile; 22. Steel lattice column; 31. First support; 32. Second support; 41. Floor slab of the first negative floor; 41. Floor slab of the second negative floor; 5. Prestressed anchor cable; 6. Base plate. DETAILED DESCRIPTION

[0019] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the drawings of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0020] Reference Figure 1 The present application embodiment discloses a construction method of a high-position cantilever multi-form support system in a narrow space, which comprises the following steps: S1. Survey and design: survey the environment around the foundation pit project and design deep foundation pit support schemes. Specifically, before designing the foundation pit support, conduct detailed surveys and investigations on the environment around the project and underground structures. During the review stage of the design drawings, conduct detailed communication based on the actual needs of the construction site, propose the best design scheme for the narrow space, and adopt various forms of deep foundation pit support schemes.

[0021] S2. Construction of bored piles 11, high-pressure rotary jet piles 12 and crown beams 13. The bored piles 11 are constructed in the foundation pit support area, and then the high-pressure rotary jet piles 12 are constructed between the bored piles 11. Finally, the crown beams 13 are constructed to connect the bored piles 11 and the high-pressure rotary jet piles 12 into a whole. The quality of the piles must be well controlled during the construction process to ensure the overall support effect of the bored piles 11 and the high-pressure rotary jet piles 12.

[0022] S3. Construction of column piles 21 and steel lattice columns 22: First, construct the column piles 21, then lower the steel lattice columns 22 into place, and ensure that each side of the steel lattice columns 22 is strictly perpendicular or parallel to the corresponding main support axis direction; specifically, when setting the steel lattice columns 22, use reinforcing steel bars to temporarily fix the steel lattice columns 22, and then use a total station and vertical adjustment equipment to calibrate, and ensure that the installation verticality of the steel lattice columns 22 meets the design requirements before welding and fixing.

[0023] S4. For earthwork excavation construction, according to the distribution of the supports in the support layout diagram, the earthwork is divided into four areas with the supports as the dividing line for excavation, and the excavation is carried out in layers from the ground to the bottom of the crown beam 13, from the bottom of the crown beam 13 to the bottom of the first support 31, from the bottom of the first support 31 to the bottom of the second support 32, and from the bottom of the second support 32 to the design elevation of the base.

[0024] S5. For the construction of the underground main structure, choose the corresponding support form to construct the underground main structure according to whether there are buildings, pipe corridors and underground pipelines close to the side of the deep foundation pit.

[0025] Among them, in step S5, if there is a pipe gallery and underground pipelines near the side of the deep foundation pit, refer to Figure 2 The support form adopts a combination of three prestressed anchor cables 5 and two layers of structural plates; after excavation to the bolting elevation, the lines are measured and laid out, and the prestressed anchor cables 5 are manufactured. Then the drilling rig is put in place and the curtain hole is opened, and the self-contained anchor cable is grouted and drilled. After drilling to the designed length, the drill rod is jetted into the anchor and withdrawn, and then maintenance is carried out and tensioning and locking are started after the anchor cable slurry reaches the designed strength requirements.

[0026] In step S5, if there is no building on the side of the deep foundation pit, refer to Figure 3 The support form adopts a combination of two concrete supports and two-layer structural plates; when constructing the bottom plate 6, external wall steel bars are reserved and a formwork is set up together with the bottom plate 6. The concrete of the bottom plate 6 and the connected external wall are poured at the same time. After the concrete strength of the bottom plate 6 and the force transfer belt reaches the design requirements, the second support 32 and the purlin are removed. After the removal is completed, the construction of the negative second floor external wall and the negative second floor slab 41 begins. At this time, more than 0.5m of external wall steel bars need to be reserved for the external wall, and then the negative second floor force transfer belt is backfilled and the force transfer belt is constructed to connect the negative second floor slab 41 and the supporting piles. After the backfilling and the force transfer belt are completed, the first support 31, the purlin and the steel lattice column 22 are removed, and then the negative first floor external wall and the negative first floor are constructed. After the construction is completed, the negative first floor force transfer belt is backfilled to the top elevation of the negative first floor slab 41.

[0027] In step S5, if the side of the deep foundation pit is close to the building, refer to Figure 4 The support form adopts a combination of a concrete support and a structural plate; when constructing the bottom plate 6, the external wall steel bars are reserved, and the formwork is set up together with the bottom plate 6, and the concrete of the bottom plate 6 and the connected external wall are poured at the same time. After the bottom plate 6 reaches the design strength, the first support 31 and the steel lattice column 22 are removed. After the removal is completed, the external wall construction continues to the negative first floor slab 41, and then the force transmission belt is constructed to connect with the crown beam 13 and the negative first floor slab 41.

[0028] In addition, in step S5, before the construction of the underground main structure, if there are anchor cables left over from the original building on the side of the deep foundation pit, first perform coordinate layout and positioning according to the existing construction drawings and the foundation pit support drawings of the original building, find the positions of the high-pressure rotary jet piles 12 and the cast-in-place piles 11, then put the rotary drilling machine in place, check the positions, and drill holes to the position of the first anchor cable. The excavator is in place, and the bucket is replaced with hydraulic scissors to cut the anchor cables in the hole and take out the first anchor cable. The second anchor cable is removed and the above construction process is repeated to remove it. After all the two anchor cables are removed, the earth is backfilled and compacted to ensure safety.

[0029] Therefore, before carrying out the foundation pit support design, a detailed survey and investigation of the project's surrounding environment and underground structure is carried out. During the drawing design stage, detailed research and discussion are carried out in combination with the actual needs of the construction site. The optimal design scheme is proposed for narrow space conditions, and various forms of deep foundation pit support schemes are adopted to solve the construction technical difficulties of high-position cantilever support systems under narrow space conditions, so that the construction method of this application can be greatly improved and applied in terms of applicability.

[0030] Moreover, the construction method of the present application adopts different support forms according to the surrounding environment. By adopting multiple forms of deep foundation pit support schemes, the safety of the high-position cantilever support system under narrow space conditions can be greatly improved. For example, when there are pipe corridors and underground pipelines near the south side of the deep foundation pit, the first support form is adopted, which is composed of cast-in-place piles 11 + high-pressure rotary jet piles 12 + crown beams 13 + three prestressed anchor cables 5 + two-layer structural plates; when there are no buildings on the east and north sides of the deep foundation pit, the second support form is adopted, which is composed of cast-in-place piles 11 + high-pressure rotary jet piles 12 + crown beams 13 + two concrete supports + two-layer structural plates; when there are buildings near the west side of the deep foundation pit, and the anchor cables left by the original buildings affect the construction, the third support form is adopted, which is composed of cast-in-place piles 11 + high-pressure rotary jet piles 12 + crown beams 13 + one concrete support + one layer of structural plates. By adopting the construction method of the application, not only can the safety of deep foundation pit support be ensured, but also many construction technical problems of traditional deep foundation pit support can be well solved.

[0031] In addition, the construction method of the present application solves the technical construction difficulties of large-scale high-position cantilever support systems in narrow spaces by adopting multiple forms of deep foundation pit support schemes. When there are buildings or anchor cables left over from buildings near the deep foundation pit, the inherent unified foundation pit support design scheme is broken on the premise of ensuring the safety of the deep foundation pit. The design is optimized based on the actual situation on site. By reducing the number of layers and using a single concrete support design, the original two-layer structural slab and two support beams are replaced. While avoiding the original building support structure or anchor cables left over from the building, it can not only reduce construction costs, but also greatly improve the construction efficiency of deep foundation pit projects.

[0032] Furthermore, in step S2, the positive circulation drilling process or the long spiral drilling and pouring process is selected according to the geological conditions and the pile diameter. Specifically, the long spiral drilling and pouring process is preferably used to construct the cast-in-place pile 11. If there is local sandy soil and the long spiral drilling cannot be used, the positive circulation drilling and pouring process is used to construct the cast-in-place pile 11. At the same time, after the strength of the cast-in-place pile 11 and the high-pressure rotary jet pile 12 reaches the design strength, the pile head is broken, and after the clearing and chiseling is completed, the steel bars of the pile top crown beam 13 are tied, and concrete is poured to form the crown beam 13.

[0033] Therefore, the long spiral drilling and grouting construction has high efficiency and fast hole-forming speed, and can be used on a large area when there are no quality problems such as hole collapse in the construction area. However, when the long spiral drilling cannot be used in the local sandy soil, positive circulation drilling construction must be adopted, which has low construction efficiency and good hole-forming quality.

[0034] In addition, in step S4, when excavating from the ground to the bottom of the crown beam 13, excavation is carried out from east to west in sequence; when excavating from the bottom of the crown beam 13 to the bottom of the first support 31, the first support 31 is used as the boundary and excavation is carried out from the middle to the north and south sides at the same time; when excavating from the bottom of the first support 31 to the bottom of the second support 32, some earth-moving machinery and earth-moving transportation vehicles are working on the plank road, and multiple earth-moving machinery are excavating and piling under the support beam; when excavating from the bottom of the second support 32 to the design elevation of the base, the second support is used as the boundary and excavation is carried out from the middle to the north and south sides at the same time. In a narrow construction site, earthwork can be transported smoothly and the safety of deep foundation pit construction can be ensured.

[0035] The implementation principle of the construction method of a high-position cantilever multi-form support system in a narrow space in the embodiment of the present application is as follows: Different support forms are adopted according to the surrounding environment. By adopting multiple forms of deep foundation pit support solutions, the safety of the high-position cantilever support system under narrow space conditions can be greatly improved. For example, when there are pipe corridors and underground pipelines near the south side of the deep foundation pit, the first support form is adopted, which is composed of cast-in-place piles 11 + high-pressure rotary jet piles 12 + crown beams 13 + three prestressed anchor cables 5 + two-layer structural plates; when there are no buildings on the east and north sides of the deep foundation pit, the second support form is adopted, which is composed of cast-in-place piles 11 + high-pressure rotary jet piles 12 + crown beams 13 + two concrete supports + two-layer structural plates; when there are buildings near the west side of the deep foundation pit and the anchor cables left by the original buildings affect the construction, the third support form is adopted, which is composed of cast-in-place piles 11 + high-pressure rotary jet piles 12 + crown beams 13 + one concrete support + one layer of structural plates. By adopting the applied construction method, not only can the safety of deep foundation pit support be ensured, but also many construction technical problems of traditional deep foundation pit support can be well solved.

[0036] In addition, the construction method of the present application solves the technical construction difficulties of large-scale high-position cantilever support systems in narrow spaces by adopting multiple forms of deep foundation pit support schemes. When there are buildings or anchor cables left over from buildings near the deep foundation pit, the inherent unified foundation pit support design scheme is broken on the premise of ensuring the safety of the deep foundation pit. The design is optimized based on the actual situation on site. By reducing the number of layers and using a single concrete support design, the original two-layer structural slab and two support beams are replaced. While avoiding the original building support structure or anchor cables left over from the building, it can not only reduce construction costs, but also greatly improve the construction efficiency of deep foundation pit projects.

[0037] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A construction method for a high-position cantilevered multi-form support system in a narrow space, characterized in that: The following steps are involved: S1. Survey and design: survey the surrounding environment of the foundation pit project and design deep foundation pit support scheme; S2. Construction of cast-in-place piles, high-pressure rotary jet piles and crown beams. Cast-in-place piles are constructed in the foundation pit support area, and then high-pressure rotary jet piles are constructed between the cast-in-place piles. Finally, the crown beam construction is completed to connect the cast-in-place piles and the high-pressure rotary jet piles into a whole; S3. Construction of column piles and steel lattice columns: first, construct the column piles, then lower the steel lattice columns into place, and ensure that each side of the steel lattice columns is strictly perpendicular or parallel to the corresponding main support axis direction; S4. Earthwork excavation construction, according to the distribution of the support arrangement diagram, the earthwork is divided into four areas with the support as the dividing line for excavation, and the excavation is carried out in layers from the ground to the bottom of the crown beam, the bottom of the crown beam to the bottom of the first support beam, the bottom of the first support beam to the bottom of the second support beam, and the bottom of the second support beam to the design elevation of the base; S5. For the construction of the underground main structure, choose the corresponding support form to construct the underground main structure according to whether there are buildings, pipe corridors and underground pipelines close to the side of the deep foundation pit.

2. The construction method of the high-position cantilever multi-form support system in a narrow space according to claim 1 is characterized in that: In step S5, if there are pipe corridors and underground pipelines near the side of the deep foundation pit, the support form adopts a combination of three prestressed anchor cables and two layers of structural plates; after excavating to the bolting elevation, the lines are measured and laid out, and the prestressed anchor cables are manufactured. Then the drilling rig is put in place and the curtain hole is opened, and the self-contained anchor cable is used for grouting. After drilling to the designed length, the drill rod is rotary-jetted and the anchor is withdrawn, and then maintenance is carried out and tensioning and locking are started after the anchor cable slurry reaches the designed strength requirements.

3. The construction method of the high-position cantilever multi-form support system in a narrow space according to claim 1 is characterized in that: In step S5, if there is no building on the side of the deep foundation pit, the support form adopts a combination of two concrete supports and two layers of structural plates; when constructing the bottom plate, external wall steel bars are reserved and a formwork is set up together with the bottom plate, the bottom plate concrete and the connected external wall are poured at the same time, and the second support and purlin are removed after the concrete strength of the bottom plate and the force transfer belt reaches the design requirements. After the removal is completed, the construction of the negative second floor external wall and the negative second floor floor slab begins. At this time, more than 0.5m of external wall steel bars need to be reserved for the external wall, and then the negative second floor force transfer belt is backfilled and the force transfer belt is constructed to connect the negative second floor floor slab and the supporting piles. After the backfilling and force transfer belt are completed, the first support, purlin and steel lattice column are removed, and then the negative first floor external wall and the negative first floor are constructed. After the construction is completed, the negative first floor force transfer belt is backfilled to the top elevation of the negative first floor slab.

4. The construction method of the high-position cantilever multi-form support system in a narrow space according to claim 1 is characterized in that: In step S5, if the side of the deep foundation pit is close to the building, the support form adopts a combination of a concrete support and a structural plate; when constructing the bottom plate, the external wall steel bars are reserved, and the formwork is set up together with the bottom plate, and the bottom plate concrete and the connected external wall are poured at the same time. After the bottom plate reaches the design strength, the first support and steel lattice column are removed. After the removal is completed, the external wall construction continues to be completed until the underground floor slab is completed, and then the force transmission belt is constructed to connect with the crown beam and the underground floor slab.

5. The construction method of the high-position cantilever multi-form support system in a narrow space according to claim 1 is characterized in that: In step S5, before the construction of the underground main structure, if there are anchor cables left over from the original building on the side of the deep foundation pit, first perform coordinate positioning according to the existing construction drawings and the foundation pit support drawings of the original building, find the positions of the high-pressure rotary jet piles and the cast-in-place piles, then put the rotary drilling machine in place, check the positions, and drill holes to the position of the first anchor cable. The excavator is in place, the bucket is replaced with hydraulic scissors, the anchor cables in the hole are cut, and the first anchor cable is taken out; the second anchor cable is removed and the above construction process is repeated to remove it. After both anchor cables are completely removed, backfill and compaction are performed to ensure safety.

6. The construction method of the high-position cantilever multi-form support system in a narrow space according to claim 1 is characterized in that: In step S2, long spiral drilling and grouting are used to construct the cast-in-place piles. If there is local sandy soil and long spiral drilling cannot be used, positive circulation drilling is used to construct the cast-in-place piles.

7. The construction method of the high-position cantilever multi-form support system in a narrow space according to claim 1 is characterized in that: In step S2, after the strength of the cast-in-place pile and the high-pressure jet-jet pile reaches the design strength, the pile head is broken and chiseled, and then the crown beam steel bars are tied on the top of the pile, and concrete is poured to form the crown beam.

8. The construction method of the high-position cantilever multi-form support system in a narrow space according to claim 1 is characterized in that: In step S3, when setting the steel lattice columns, the steel lattice columns are temporarily fixed by using reinforcing steel bars, and then calibrated by using a total station and a vertical adjustment device to ensure that the installation verticality of the steel lattice columns meets the design requirements before welding and fixing.

9. The construction method of the high-position cantilever multi-form support system in a narrow space according to claim 1 is characterized in that: In step S4, when excavating from the ground to the bottom of the crown beam, excavation is carried out from east to west in sequence; when excavating from the bottom of the crown beam to the bottom of the first supporting beam, the first support is used as the boundary and excavation is carried out from the middle to the north and south sides simultaneously; when excavating from the bottom of the first supporting beam to the bottom of the second supporting beam, some earth-moving machines and earth-moving vehicles are working on the plank road, and multiple earth-moving machines are digging and piling under the supporting beam for construction; when excavating from the bottom of the second supporting beam to the design elevation of the base, the second support is used as the boundary and excavation is carried out from the middle to the north and south sides simultaneously.

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