Soft soil foundation axial force servo profile steel-concrete combined supporting structure and construction method

Abstract

The invention relates to a soft soil foundation axial force servo profile steel-concrete combined supporting structure and a construction method, and solves the problems that in foundation pit engineering construction, long time is often needed before the concrete strength reaches the design requirement, and deformation of an enclosure structure is easily caused. One span, closest to an underground diaphragm wall, of a basement of the structure is a side span, a passive reinforcing area is arranged between the side span and the underground diaphragm wall, a beam body is arranged closest to the outer side of the side span to form a structure side beam, and a beam body perpendicular to the structure side beam is a side span structure main beam; according to the multi-layer basement, a basement top plate structural beam plate, the multi-layer basement and a basement bottom plate are sequentially arranged on the inner side of a structural boundary beam from top to bottom, for each layer of basement, the structural beam plate is arranged on the inner side of the structural boundary beam, and a passive reinforcing area on the outer side of the structural boundary beam is an axial force servo profile steel support. Aiming at the problems that the concrete support is long in construction period and low in forming strength, and the concrete support is serious in creep and shrinkage deformation and the like, the servo profile steel-concrete combined support system capable of solving the problem of deformation control of the foundation pit support of the soft soil foundation is formed by combining the advantages of the profile steel support in the aspects of rapid construction and construction prestress.

Description

Technical Field

[0001] The invention belongs to the field of building support structures, and relates to a steel-concrete composite support structure, and in particular to an axial force servo steel-concrete composite support structure for soft soil foundation and a construction method. Background Art

[0002] With the development of urban construction, a large number of foundation pit projects have appeared in Hangzhou, Ningbo and Wenzhou, Zhejiang Province. The geological conditions in the region are mainly deep soft clay deposited in the lake-marine phase. This type of soft clay has the characteristics of high water content, low shear strength, high compressibility, high sensitivity and easy to be disturbed. Its deformation control is the pain point of the current industry. In addition, the foundation pit project in the soft soil foundation has changed from traditional strength control to deformation control, especially in complex surrounding environments, where the requirements for deformation control are extremely strict, such as the foundation pit project of TOD project next to the urban rail transit, the deep foundation pit project next to the shallow foundation house, the foundation pit project in the urban organic renewal in the old urban area, etc. The control of deformation is often required to be within 10mm, which brings huge challenges to the enclosure design.

[0003] At present, foundation pit projects in soft soil foundations often use underground continuous walls / large-diameter bored piles combined with multiple reinforced concrete horizontal internal supports for support or even combined with reverse construction, supplemented by large-area pit reinforcement. Concrete supports and reverse construction floors are widely used in soft soil foundation pits in complex environments due to their high strength, high rigidity, flexible layout, and good reliability. However, the construction process of concrete supports and reverse construction floors is complex and long, requiring processes such as formwork, steel bar binding, concrete pouring, and support removal. It often takes a long time before the concrete strength reaches the design requirements. During this period, a foundation pit exposure period is formed, that is, the foundation pit has been excavated in place but the support strength has not yet been formed. The deformation of the retaining structure continues to develop during this time. Especially in soft soil foundations, due to the high compressibility, high sensitivity and easy disturbance of the soil layer, the deformation of the retaining structure during this period is often large. In addition, the shrinkage deformation of concrete during the curing process and the creep deformation of concrete after the support is formed will increase the deformation of the retaining structure. Summary of the invention

[0004] The purpose of the present invention is to solve the problem that it often takes a long time for the concrete strength to reach the design requirements in foundation pit engineering construction, which easily causes deformation of the retaining structure. A soft soil foundation axial force servo steel-concrete composite support structure and a construction method are proposed, which can be used to control the deformation of the retaining structure caused by foundation pit creep during support construction.

[0005] The technical solution adopted by the present invention to solve its technical problems is: a soft soil foundation axial force servo steel-concrete composite support structure, an underground continuous wall is built on the side of the construction site close to the protection building, the construction site is a multi-story basement, the basement is a frame structure, including matrix-arranged lattice columns, beams are arranged between adjacent lattice columns corresponding to each basement structure, the span of the basement closest to the underground continuous wall is the side span, the side span and the underground continuous wall are the passive reinforcement area, the side span is arranged on the outermost side of the beam body to form a structural side beam, and the beam body perpendicular to the structural side beam is the main structure of the side span Beam; the multi-story basement is provided with a basement top plate structural beam plate, a multi-story basement and a basement bottom plate in sequence from top to bottom on the inner side of the structural side beam. For each basement, the inner side of the structural side beam is the underground N-layer structural beam plate, N is an integer greater than 1, and the passive reinforcement area on the outer side of the structural side beam is an axial force servo steel support, the inner end of the axial force servo steel support is against the structural side beam, and the outer end is against the underground continuous wall. A servo jack for applying prestress is provided in the middle of the axial force servo steel support, and the axial force servo steel support is provided in multiple groups and is provided one-to-one with the side span structure main beam.

[0006] This structure uses axial force servo steel support to form a prestressed servo support between the structural side beams and underground continuous walls of the concrete basement structure, and the servo prestress can be adjusted according to the deformation monitoring during the actual construction process, ensuring the formation of stable and reliable enclosure support during the basement construction process, and better protecting the protective structures around the construction site. This support structure is suitable for reverse construction, and can effectively support the outside of each basement floor when constructing from top to bottom.

[0007] Steel support has the advantages of small deadweight, easy installation, fast construction speed, convenient prestressing, and green environmental protection. It is gradually promoted and applied in foundation pit projects. However, steel support also has the following disadvantages compared with concrete support: 1) The rigidity is weaker than concrete, and its deformation control effect is not as good as concrete support; 2) When the foundation pit area is large and the plane shape is irregular, the applicability is poor; 3) The node structure is complex and has high requirements for design and construction. This structure is to effectively control the deformation of the foundation pit retaining structure in the soft soil foundation. In view of the long construction period of concrete support, slow strength formation, and serious creep and shrinkage deformation of concrete support, combined with the advantages of steel support in rapid construction and construction prestressing, the two are combined to learn from each other's strengths and give full play to their respective advantages to form a servo steel-concrete composite support system that can solve the deformation control problem of foundation pit retaining in soft soil foundation.

[0008] Preferably, steel waist beams are provided corresponding to the outer ends of the underground continuous wall and the axial force servo steel support, and steel supports, servo jacks and steel supports are arranged in sequence between the structural side beams and the steel waist beams, and reinforcements are provided at both ends of the steel support.

[0009] Preferably, for each set of axial force servo steel support, a plurality of servo jacks are horizontally arranged, and force protection boxes are arranged on both sides of the servo jacks between the steel support reinforcements at both ends.

[0010] Preferably, a prestressed anti-loosening compensation device is arranged between the ejection end of the servo jack and the reinforcement, and the prestressed anti-loosening compensation device includes a base plate fixed to the steel support reinforcement by bolts, and a groove is opened on the base plate toward the side of the servo jack, and a rubber pad and a pressure plate are arranged in sequence from the bottom of the groove to the top, and the pressure plate is against the servo jack.

[0011] Preferably, the reinforcement is an H-shaped steel with a transverse web.

[0012] Preferably, shear steel corners are provided at the junctions of the structural side beams, the shear steel corners are made of steel and are fixed with embedded parts.

[0013] Preferably, for N underground layers of structural beams and slabs where N is greater than 3, two axial force servo steel supports are provided on the outer sides of the structural side beams, one above the other.

[0014] A soft soil foundation axial force servo steel-concrete composite support construction method, using the soft soil foundation axial force servo steel-concrete composite support structure, comprises the following steps: S1, conduct a situation survey around the construction site, clarify the protection requirements of the surrounding protective structures, then clear the obstacles and level the interior of the construction site, and after completion, construct underground continuous walls, lattice columns, column piles and passive reinforcement areas in the pit; S2, after the underground continuous wall construction is completed, the site is excavated to the bottom of the basement top slab, and the top beam and basement top slab structural beam are constructed; S3, after the construction of the basement top slab structure beams and slabs is completed and the strength reaches the design requirements, the passive reinforcement area near the side of the protected structure is left with soil, and the slope surface is sprayed with anchors. The rest of the area is excavated to the bottom of the underground first floor slab, and the underground first floor structure beams and slabs outside the passive reinforcement area are constructed. The structural side beams are constructed near the passive reinforcement area. When constructing the structural side beams and side span main beams, the anchor bolts and the embedded end plates and embedded steel bars of the shear steel axils are embedded; S4, after the construction of the underground structural beams and structural side beams outside the passive reinforcement area is completed and the strength reaches the design requirements, a triangular plate is welded at the axil angle of the side span main beam and the structural side beam in combination with the embedded end plate to form a shear steel axil angle. After completion, the passive reinforcement area within the scope of a single construction unit is excavated in combination with the zoning and block construction method, with 1 to 3 spans as the construction unit, and the remaining passive reinforcement areas continue to retain soil. After excavation to the bottom of the first axial force servo steel support beam within the scope of a single construction, the steel waist beam, reinforcement, steel support, servo jack and cover plate are installed in sequence. After installation, the initial prestress is applied according to the design requirements; after the construction of the axial force servo steel support of a single construction unit is completed and prestress is applied, the remaining construction units are constructed in sequence; S5, after the first axial force servo steel composite support is fully constructed and prestressed, the second underground structural beam and slab are constructed in sequence according to steps S3 and S4, and the axial force servo steel support of the second underground layer is installed, until the N underground structural beams and axial force servo steel support are completed. During the construction process, the axial force application value of the servo jack is adjusted in combination with the deformation monitoring results of the underground continuous wall and the surrounding protective structures; S6, after the construction of the structural beams and axial force servo steel supports of the Nth underground floor is completed and prestressed, the pits are excavated to the bottom of the pit in sections and the basement floor is constructed. During the construction of the basement floor, the passive reinforcement area is excavated and constructed simultaneously, and the bracket replacement structure is constructed on the basement floor close to the underground continuous wall. The bracket replacement structure includes the replacement bracket and embedded steel bars and embedded end plates. After the basement floor reaches the design strength, the steel waist beam reinforcement is constructed and the servo jack is installed, and prestress is applied according to the design requirements; S7, after the basement floor corbel replacement structure is prestressed, the N-layer underground axial force servo steel support is removed, the N-layer underground structural beam slab in the passive reinforcement area is constructed, and the corbel replacement structure is constructed according to step S6; S8, according to step S7, dismantle the axial force servo steel supports of each layer from bottom to top, construct the structural beams and slabs of each layer underground at the soil retention position, and construct the bracket replacement support structure; S9: After the underground structure construction is completed and formed into a whole, and the monitoring data of the foundation pit and protective structures are stable, the corbels are removed and the support structure is replaced to complete the construction.

[0015] As a preferred embodiment, in S1, retained soil is provided between the underground continuous wall and the structural side beams, and cement mixing piles are used for reinforcement to form a passive reinforcement zone. The passive reinforcement zone close to the protected building side is strengthened compared with the rest of the area, thereby improving the physical and mechanical properties of the soil in the passive reinforcement zone and effectively preventing the displacement of the underground continuous wall during the construction of the basement structure.

[0016] The beneficial effects of the present invention are as follows: 1. The present invention forms a passive reinforcement zone by setting retained soil between the underground continuous wall and the concrete support / top-down floor slab and using cement mixing piles for reinforcement. The passive reinforcement zone close to the protected building side is strengthened compared with the rest of the area, thereby improving the physical and mechanical properties of the soil in the passive reinforcement zone and effectively preventing the displacement of the underground continuous wall during the construction of the basement structure.

[0017] 2. The passive reinforcement area of ​​the present invention adopts block excavation measures, and adopts axial force servo steel composite support combined with steel waist beam. The steel composite support and steel waist beam adopt standard components, which are prefabricated in the factory and connected by bolts. They are easy to install, fast in construction speed, and reliable in quality. The support is formed in a relatively short time after excavation and retention of soil, which is beneficial to reducing deformation during soil retention excavation.

[0018] 3. The medium-sized steel support of the present invention is additionally provided with a servo system, which can adjust the applied prestress in real time in combination with the deformation of the enclosure structure and the protected building, so as to achieve the purpose of controllable deformation.

[0019] 4. In the present invention, side beams are added at the junction of the concrete support / reverse-constructed floor slab and the steel support in combination with the basement structure design. The side beams can withstand large shear forces and bending moments. At the same time, shear steel axil angles are added between the structural side beams and the side span structure main beams to avoid problems such as cracks and shear damage in the underground structure beams and slabs due to stress concentration when the prestress of the axial force servo steel composite support is too large.

[0020] 5. The present invention adds a corbel replacement structure when replacing the support of the structural bottom plate and floor slab, and applies prestress in combination with the design calculation and deformation monitoring results to avoid the loss of prestress caused by the removal of the upper support during the support removal process, which leads to increased deformation of the enclosure structure and protected buildings.

[0021] 6. The present invention can be combined with the design calculation of axial force to adjust the number of steel sections, the number of jacks and the number of layers of each steel support in each span of steel combination support. Double-layer steel support can be used when the axial force displacement is large, thereby effectively controlling the deformation of the enclosure structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The present invention will be further described below in conjunction with the accompanying drawings.

[0023] Figure 1 It is a plan view of an axial force servo steel-concrete composite support of the present invention.

[0024] Figure 2 It is a cross-sectional view of an axial force servo steel-concrete composite support of the present invention.

[0025] Figure 3 The present invention Figure 1 A partial enlarged plan view of the steel prestressed support.

[0026] Figure 4 The present invention Figure 2 A partial enlarged cross-sectional view of the steel prestressed support.

[0027] Figure 5 It is a schematic diagram of the structure splitting of the prestressed anti-loosening compensation device of the present invention.

[0028] Figure 6 It is a schematic diagram of the structural combination of the prestressed anti-loosening compensation device of the present invention.

[0029] Figure 7 It is a schematic diagram of the corbel replacement structure of the present invention.

[0030] Figure 8-Figure 20 The following are the construction step diagrams of the axial force servo steel-concrete composite support replacement construction of the present invention.

[0031] In the figure: 1. Protective structures, 2. Underground continuous wall, 3. Steel waist beam, 4. Passive reinforcement area, 5. Structural side beam, 6. Side span main beam, 7. Axial force servo steel support, 8. Lattice column, 9. Basement top plate structural beam, 10. Underground first floor structural beam, 11. Underground second floor structural beam, 12. Underground third floor structural beam, 13. Basement floor, 14. Shear steel axil, 15. Steel support, 16. Servo jack, 17. Security box, 18. Reinforcement, 19. Prestressed anti-loosening compensation device, 20. Replacement bracket, 21. Side span, 22. Bracing bracket replacement structure, 1901, base, 1902, rubber pad, 1903, pressure plate, 1904, bolt. DETAILED DESCRIPTION

[0032] The present invention will be further described below through specific embodiments in conjunction with the accompanying drawings.

[0033] Embodiment 1: A soft soil foundation axial force servo steel-concrete composite support structure, such as Figure 1-6As shown. An underground continuous wall 2 is constructed on one side of the construction site near the protective structure 1. There are four basements in the construction site. The basement is a frame structure, including lattice columns 8 arranged in a matrix. Beams are arranged between adjacent lattice columns corresponding to each basement structure. The span of the basement closest to the underground continuous wall is a side span 21. The side span and the underground continuous wall are between a passive reinforcement area 4. A beam is arranged on the outermost side of the side span to form a structural side beam 5. The beam perpendicular to the structural side beam is a side span structural main beam 6. The multi-story basement is provided with a basement top plate structural beam 9, a first underground structural beam 10, a second underground structural beam 11, a third underground structural beam 12 and a basement bottom plate 13 from top to bottom on the inner side of the structural side beam. For each basement, the inner side of the structural side beam 5 is an underground N-layer structural beam, N is an integer of 1-3, and the passive reinforcement area 4 on the outer side of the structural side beam is an axial force servo steel support 7. The inner end of the axial force servo steel support 7 is against the structural side beam 5, and the outer end is against the underground continuous wall 2. A servo jack 16 for applying prestress is arranged in the middle of the axial force servo steel support. The axial force servo steel support 7 is arranged in multiple groups and corresponds to the side span structure main beam 6. The intersection of the structural side beam 5 and the structural side beam is provided with a shear steel axil angle 14, which is made of steel and fixed with embedded parts. For the underground three-story structural beam slab, two axial force servo steel supports 7 are arranged on the outer side of the structural side beam 5.

[0034] like Figure 1 , 2 As shown, the outer ends of the underground continuous wall 2 and the axial force servo steel support 7 are provided with steel waist beams 3 correspondingly. Figure 3 , 4 As shown, a steel support 15, a servo jack 16, and a steel support 15 are sequentially arranged between the structural side beam and the steel waist beam, and reinforcements 18 are respectively arranged at both ends of the steel support. The reinforcement is an H-shaped steel with a web plate placed horizontally. For each set of axial force servo steel supports, multiple servo jacks are arranged horizontally, and a force box 17 is arranged on both sides of the servo jack 16 between the steel support reinforcements at both ends.

[0035] like Figure 4-6 As shown, a prestressed anti-loosening compensation device 19 is arranged between the ejection end of the servo jack 16 and the reinforcement 18, and the prestressed anti-loosening compensation device includes a base plate 1901 fixed to the steel support reinforcement by bolts 1904, and a groove is opened on the base plate toward the servo jack side, and a rubber pad 1902 and a pressure plate 1903 are arranged in the groove from the bottom of the groove to the top, and the pressure plate is against the servo jack.

[0036] Example 2: A construction method for a soft soil foundation axial force servo steel-concrete composite support, using the support structure in Example 1, such as Figure 8-20 As shown. It includes the following steps: S1. Conduct a situation survey around the construction site, clarify the protection requirements of the surrounding protective structures 1, then clear the obstacles and level the interior of the construction site, and after completion, construct the underground continuous wall 2, lattice columns 8, column piles and passive reinforcement area 4 in the pit; set up soil retention between the underground continuous wall and the structural side beams, and use cement mixing piles to reinforce the passive reinforcement area. The passive reinforcement area close to the protective structure is stronger than the rest of the area, improving the physical and mechanical properties of the soil in the passive reinforcement area, and effectively reducing the displacement of the underground continuous wall during the construction of the basement structure; S2, after the underground continuous wall construction is completed, the site is excavated to the bottom of the basement top plate 9, and the top beam and the basement top plate structural beam are constructed; Figure 8 As shown; S3, after the construction of the basement top slab structure beams and slabs is completed and the strength reaches the design requirements, the passive reinforcement area 4 near the side of the protected building is left with soil, and the slope surface is sprayed with anchors, and the rest of the area is excavated to the bottom of the first underground floor slab, and the first underground floor structure beams and slabs 10 outside the passive reinforcement area are constructed, and the structural side beams are constructed near the passive reinforcement area. When constructing the structural side beams and side span main beams, the anchor bolts and the embedded end plates and embedded steel bars of the shear steel axils are embedded; if Fig. 9 As shown; S4, after the construction of the underground structural beams and structural side beams outside the passive reinforcement area is completed and the strength reaches the design requirements, a triangular plate is welded at the axil corners of the side span main beam and the structural side beam in combination with the embedded end plate to form a shear steel axil corner. After completion, combined with the zoning and block construction method, 1 to 3 spans are used as construction units to excavate the passive reinforcement area within the scope of a single construction unit, and the remaining passive reinforcement areas continue to retain soil. After excavation to the bottom of the first axial force servo steel support beam within the scope of a single construction, the steel waist beam, reinforcement, steel support, servo jack and cover plate are installed in sequence. After installation, the initial prestress is applied according to the design requirements; after the construction of the axial force servo steel support 7 of a single construction unit is completed and prestress is applied, the remaining construction units are constructed in sequence; Fig.10 As shown; S5, after the first axial force servo steel composite support is fully constructed and prestressed, the underground second-floor structural beam slab 11 is constructed in a loop according to steps S3 and S4, and the underground second-floor axial force servo steel support is installed, until the underground third-floor structural beam slab 12 and the axial force servo steel support 7 are completed. During the construction process, the axial force application value of the servo jack is adjusted in combination with the deformation monitoring results of the underground continuous wall and the surrounding protective structures; Figure 11-14 As shown; S6, after the construction of the structural beams and axial force servo steel supports of the Nth underground layer is completed and prestressed, the pits are excavated to the bottom of the pit in sections and the basement floor is constructed. During the construction of the basement floor, the passive reinforcement area is excavated and constructed simultaneously, and the bracket replacement support structure 22 is constructed on the basement floor near the underground continuous wall. The bracket replacement support structure is as follows: Figure 7As shown in the figure, the structure of the bracket replacement includes replacing the bracket and pre-embedded steel bars and end plates; after the basement floor reaches the design strength, the steel waist beam reinforcement is constructed and the servo jack is installed to apply prestress according to the design requirements; Fig.15 , 16 As shown; S7, after the basement floor bracket replacement structure is prestressed, the underground three-layer axial force servo steel support is removed, the underground three-layer structural beam and slab in the passive reinforcement area is constructed, and the bracket replacement structure is constructed according to step S6; Fig.17 As shown; S8, according to step S7, remove the axial force servo steel supports of each layer from bottom to top, construct the structural beams and slabs of each layer underground at the soil retention position, and construct the bracket replacement support structure; Fig.18 , 19 As shown; S9: After the underground structure is completed and formed into a whole, and the monitoring data of the foundation pit and protective structures are stable, the brackets are removed and the support structure is replaced to complete the construction. Fig. 20 shown.

Claims

1. A soft soil foundation axial force servo steel-concrete composite support structure, the construction site is built with an underground continuous wall on the side of the protective structure, the construction site is a multi-story basement, the basement is a frame structure, including lattice columns arranged in a matrix, and beams are arranged between adjacent lattice columns corresponding to each basement structure, characterized in that: The span of the basement closest to the underground continuous wall is the side span, and the passive reinforcement area is between the side span and the underground continuous wall. A beam body is arranged on the outermost side of the side span to form a structural side beam, and the beam body perpendicular to the structural side beam is the side span structural main beam; the multi-story basement is provided with a basement top plate structural beam plate, a multi-story basement and a basement bottom plate from top to bottom on the inner side of the structural side beam. For each floor of the basement, the inner side of the structural side beam is the underground N-layer structural beam plate, N is an integer greater than 1, and the passive reinforcement area on the outer side of the structural side beam is an axial force servo steel support, the inner end of the axial force servo steel support is against the structural side beam, and the outer end is against the underground continuous wall. A servo jack for applying prestress is arranged in the middle of the axial force servo steel support, and multiple groups of the axial force servo steel supports are arranged in a one-to-one correspondence with the side span structural main beams.

2. The soft soil foundation axial force servo steel-concrete composite support structure according to claim 1 is characterized by: The outer ends of the underground continuous wall and the axial force servo steel support are correspondingly provided with steel waist beams, and steel supports, servo jacks, and steel supports are arranged in sequence between the structural side beams and the steel waist beams, and reinforcements are respectively arranged at both ends of the steel support.

3. The soft soil foundation axial force servo steel-concrete composite support structure according to claim 2 is characterized in that: For each set of axial force servo steel support, a plurality of servo jacks are horizontally arranged, and force protection boxes are arranged between the steel support reinforcements at both ends on both sides of the servo jacks.

4. The soft soil foundation axial force servo steel-concrete composite support structure according to claim 2 is characterized in that: A prestressed anti-loosening compensation device is arranged between the ejection end of the servo jack and the reinforcement. The prestressed anti-loosening compensation device includes a base plate fixed to the steel support reinforcement by bolts. A groove is opened on the base plate toward the side of the servo jack. A rubber pad and a pressure plate are arranged in sequence from the bottom of the groove to the top. The pressure plate is against the servo jack.

5. The soft soil foundation axial force servo steel-concrete composite support structure according to claim 2, characterized in that: The reinforcement is an H-shaped steel with a transverse web.

6. The soft soil foundation axial force servo steel-concrete composite support structure according to claim 2, characterized in that: A shear steel corner is provided at the intersection of the structural side beam and the side span structural main beam 6. The shear steel corner is made of steel and is fixed by embedded parts.

7. The soft soil foundation axial force servo steel-concrete composite support structure according to claim 1, characterized in that: For the underground N-layer structural beam-slab with N greater than 3, two axial force servo steel supports are set up on the outer side of the structural edge beam.

8. A construction method for a soft soil foundation axial force servo steel-concrete composite support, using the soft soil foundation axial force servo steel-concrete composite support structure as claimed in claims 1 to 7, characterized in that: The following steps are included: S1, conduct a situation survey around the construction site, clarify the protection requirements of the surrounding protective structures, then clear the obstacles and level the interior of the construction site, and after completion, construct underground continuous walls, lattice columns, column piles and passive reinforcement areas in the pit; S2, after the underground continuous wall construction is completed, the site is excavated to the bottom of the basement top slab, and the top beam and basement top slab structural beam are constructed; S3, after the construction of the basement top slab structure beams and slabs is completed and the strength reaches the design requirements, the passive reinforcement area near the side of the protected structure is left with soil, and the slope surface is sprayed with anchors. The rest of the area is excavated to the bottom of the underground first floor slab, and the underground first floor structure beams and slabs outside the passive reinforcement area are constructed. The structural side beams are constructed near the passive reinforcement area. When constructing the structural side beams and side span main beams, the anchor bolts and the embedded end plates and embedded steel bars of the shear steel axils are embedded; S4, after the construction of the underground structural beams and structural side beams outside the passive reinforcement area is completed and the strength reaches the design requirements, a triangular plate is welded at the axil angle of the side span main beam and the structural side beam in combination with the embedded end plate to form a shear steel axil angle. After completion, the passive reinforcement area within the scope of a single construction unit is excavated in combination with the zoning and block construction method, with 1 to 3 spans as the construction unit, and the remaining passive reinforcement areas continue to retain soil. After excavation to the bottom of the first axial force servo steel support beam within the scope of a single construction, the steel waist beam, reinforcement, steel support, servo jack and cover plate are installed in sequence. After installation, the initial prestress is applied according to the design requirements; after the construction of the axial force servo steel support of a single construction unit is completed and prestress is applied, the remaining construction units are constructed in sequence; S5, after the first axial force servo steel composite support is fully constructed and prestressed, the second underground structural beam and slab are constructed in sequence according to steps S3 and S4, and the axial force servo steel support of the second underground layer is installed, until the N underground structural beams and axial force servo steel support are completed. During the construction process, the axial force application value of the servo jack is adjusted in combination with the deformation monitoring results of the underground continuous wall and the surrounding protective structures; S6, after the construction of the structural beams and axial force servo steel supports of the Nth underground floor is completed and prestressed, the pits are excavated to the bottom of the pit in sections and the basement floor is constructed. During the construction of the basement floor, the passive reinforcement area is excavated and constructed simultaneously, and the bracket replacement structure is constructed on the basement floor close to the underground continuous wall. The bracket replacement structure includes the replacement bracket and embedded steel bars and embedded end plates. After the basement floor reaches the design strength, the steel waist beam reinforcement is constructed and the servo jack is installed, and prestress is applied according to the design requirements; S7, after the basement floor corbel replacement structure is prestressed, the N-layer underground axial force servo steel support is removed, the N-layer underground structural beam slab in the passive reinforcement area is constructed, and the corbel replacement structure is constructed according to step S6; S8, according to step S7, dismantle the axial force servo steel supports of each layer from bottom to top, construct the structural beams and slabs of each layer underground at the soil retention position, and construct the bracket replacement support structure; S9: After the underground structure construction is completed and formed into a whole, and the monitoring data of the foundation pit and protective structures are stable, the corbels are removed and the support structure is replaced to complete the construction.

9. The soft soil foundation axial force servo steel-concrete composite support structure according to claim 8, characterized in that: In S1, retained soil is set between the underground continuous wall and the structural side beam, and cement mixing piles are used for reinforcement to form a passive reinforcement zone. The passive reinforcement zone close to the protected building side is strengthened compared with the rest of the area, improving the physical and mechanical properties of the soil in the passive reinforcement zone and effectively reducing the displacement of the underground continuous wall during the construction of the basement structure.

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