Combined support method for super-deep foundation pit in soft soil area

Abstract

The soft soil area super deep foundation pit combined support method comprises the following steps: a closed water stop system construction; once digging and first opening type working platform construction; pile column integrated structure construction; guide precast pile construction; precast plate production; first precast plate insertion construction; twice digging to set a first plane support system; thrice digging to carry out second precast plate insertion construction and set a second plane support system at the height of the top of the second precast plate; four times digging to set a third plane support system; five times digging to carry out third precast plate insertion and second opening type working platform construction, and then set a fourth plane support system at the height of the top of the third precast plate; six times digging to the position of the middle of the third precast plate and then carry out bottom raft construction, and complete the excavation operation of the soft soil area super deep foundation pit combined support. The support process is simplified, the number of complicated dismantling components is reduced, the construction process is optimized, and the work efficiency is improved.

Description

Technical Field

[0001] This application relates to the field of civil engineering technology, specifically to a combined support method for ultra-deep foundation pits in soft soil areas. Background Technology

[0002] Currently, the commonly used support and excavation methods in foundation pit construction mainly include: simple support method, foundation trench support method, inclined column support, anchor support and wall support method. However, when these technologies are applied to ultra-deep foundation pits in soft soil areas, some drawbacks often arise. For example, the simple support method not only has a shallow excavation depth but also requires slope treatment, making it unsuitable for deep foundation pits in urban areas. The trench support method also has a limited excavation depth, typically suitable for foundation pits of 5-10 meters. The inclined column support method uses a method of first excavating with slope and then backfilling with inclined support, which has poor water-stopping effect and is not suitable for deep foundation pits with thick soft soil. Anchor support mainly uses soil nails, anchor rods, and anchor cables, but for foundation pits in urban areas, the installation of anchors can affect surrounding buildings, making it unsuitable for large-scale application. Wall support methods include cement-soil walls, slab walls, and diaphragm walls. Cement-soil walls and slab walls require complex internal support systems, making it inconvenient for construction machinery to enter and exit, thus affecting the project progress. While diaphragm walls do not require complex internal support structures, they are the most expensive, least economical, have the longest construction period, and the grouting and wall protection pollutes the environment.

[0003] Therefore, it is of great importance to develop an economically feasible, low-carbon, environmentally friendly, technically reliable, and highly applicable combined support method for ultra-deep foundation pits in soft soil areas. Summary of the Invention

[0004] The purpose of this application is to address the aforementioned problems in the prior art by providing a combined support method for ultra-deep foundation pits in soft soil areas.

[0005] To achieve the aforementioned objectives, this application employs the following technical solution: A combined support method for ultra-deep foundation pits in soft soil areas includes:

[0006] S00, Construction of closed-type waterstop system: Construction of inclined roof-type waterstop curtain and lateral stepped waterstop curtain respectively;

[0007] Among them, the depth of the lateral stepped water-stop curtain always changes symmetrically in a stepped manner along the depth of the inclined roof-type water-stop curtain, and the two always intersect, eventually forming a closed water-stop system.

[0008] S10. Excavation and construction of the first open-type working platform: The first excavation is carried out on the soil inside the pit within the closed water-stopping system.

[0009] The excavation depth is to the middle of the closed water-stop system. The excavation shape is an inverted trapezoid. Then, at this depth, a flexible cushion layer is made of sand or rammed earth. The flexible cushion layer is connected to the inverted roof-shaped water-stop curtain on both sides.

[0010] Reinforcing bars and side formwork are laid on the flexible cushion layer to carry out the in-situ casting of the open-type working platform, with the middle part set as the soil intake.

[0011] S20. Construction of integrated pile-column structure: Construction of multiple sets of integrated pile-column structures on an open-type working platform;

[0012] The piles buried in the soil are pile foundations, which extend beyond the bottom of the foundation pit and are constructed directly to the designed depth; the piles exposed above the soil are structural columns, which are used for the combined support of the foundation pit in the later stages.

[0013] As the soil is excavated, the lengths of the pile foundation and structural columns change, forming an integrated pile-column structure and an open-type working platform that are connected by their respective steel cages to form a single unit.

[0014] S30. Construction of precast guide piles: Precast guide piles are manufactured in the factory.

[0015] Static drilling or pilot hole drilling is first carried out at the predetermined pile positions during construction, and then the precast guide piles are precisely hoisted and implanted in units.

[0016] S40. Precast panel production: The first precast panel, the second precast panel, and the third precast panel are precast in the factory.

[0017] The width of the precast slab is determined by the spacing of the guide precast piles, and the thickness of the third precast slab is greater than the thickness of the second precast slab, which is greater than the thickness of the first precast slab.

[0018] Both ends of the precast slab have built-in sliding buckles that can move up and down along the external sliding groove of the guide precast pile to match the buckle.

[0019] Among them, the sliding buckle is a concave C-shaped steel pipe. The outer side of the C-shaped steel pipe is provided with small back ribs, which are set as side templates at both ends during the production of precast slabs, and finally form a whole.

[0020] The first, second, and third precast slabs are of the same length, denoted as L, and are inserted between adjacent precast slabs from the outside to the inside and from top to bottom along the three rows of sliding grooves on the outside of the guide precast piles.

[0021] An overlap length of 1 / 3L is required between the first precast slab and the second precast slab, and between the second precast slab and the third precast slab.

[0022] S50. First Precast Slab Insertion Construction: After the construction of the guide precast piles and the production of the precast slabs are completed, along the perimeter of the foundation pit, following the outermost row of sliding grooves of the guide precast piles, the first precast slabs are inserted and overlapped and sealed in units from top to bottom until the total length of the first precast slabs inserted into the soil reaches L.

[0023] S60. After the second excavation reaches 1 / 3 of the depth of the first precast slab, the first planar support system is installed: After the first precast slab is inserted, the second excavation begins.

[0024] For secondary excavation and subsequent excavation, the closed-type water-stopping system is removed at the same depth as the soil in the pit.

[0025] The secondary excavation begins around the perimeter of the foundation pit and continues until it reaches 1 / 3 of the depth of the first precast slab. At this depth, the first planar support system is then installed.

[0026] S70. After excavating three times to 2 / 3 the depth of the first precast slab, the second precast slab is installed, and a second plane support system is set at the top of the second precast slab. After the first plane support system is completed, three excavations are started, and the corresponding closed water-stop system is removed at the same time, until 2 / 3 the depth of the first precast slab is reached.

[0027] At this depth, the second precast slab is inserted. Referring to the precast slab insertion in step S50, along the perimeter of the foundation pit, following the sliding groove in the middle row of the guide precast piles, the second precast slab is inserted and overlapped and sealed in units from top to bottom.

[0028] When the total length of the second precast slab embedded in the ground reaches L, the overlap length between the first and second precast slabs is 1 / 3L.

[0029] After the second precast slab is installed, referring to the method of the first planar support system in step S60, the second planar support system is installed at the top height of the second precast slab.

[0030] S80. After four excavations to 1 / 3 the depth of the second precast slab, the third plane support system is installed: After the second plane support system is completed, four excavations are started, and the corresponding closed water-stop system is removed simultaneously, until 1 / 3 the depth of the second precast slab is reached.

[0031] Referring to the method of the first planar support system in step S60, a third planar support system is set at 1 / 3 of the depth of the second precast slab;

[0032] S90. After five excavations to 2 / 3 the depth of the second precast slab, the third precast slab is inserted and the second open-type working platform is constructed simultaneously. The fourth plane support system is set at the top of the third precast slab. After the third plane support system is completed, the fifth excavation begins, and the closed water-stop system is completely removed until 2 / 3 the depth of the second precast slab is reached.

[0033] At this depth, the third precast slab is inserted. Referring to the precast slab insertion in step S50, along the perimeter of the foundation pit, following the innermost row of grooves on the guide precast pile, the third precast slab is inserted and overlapped and sealed in a unit-by-unit manner from top to bottom.

[0034] When the total length of the third precast slab embedded in the ground reaches L, the overlap length between the second and third precast slabs is 1 / 3L. Then, referring to the construction of the open-type working platform in step S10, the operation of the second open-type working platform is completed at the height of the top of the third precast slab.

[0035] Referring to the method of the first planar support system in step S60, a fourth planar support system is set at the height of the top of the third precast slab;

[0036] After six excavations to the middle of the third precast slab, the bottom raft slab is constructed, completing the excavation of the ultra-deep foundation pit combined support in the soft soil area. After the fourth plane support system is completed, the sixth excavation begins, reaching the middle of the third precast slab.

[0037] The construction of the bottom sealing layer is carried out. After the bottom sealing layer hardens, the reinforcement cage of the bottom raft slab is tied, the formwork is erected, and the cast-in-place concrete is poured. After the bottom raft slab hardens, the excavation operation of the ultra-deep foundation pit combined support in the soft soil area is completed.

[0038] Furthermore, in step S00, the construction of the inclined roof-type water-stop curtain involves deep cement mixing or high-pressure jet grouting from both sides of the foundation pit at a set angle, ultimately converging at the middle of the foundation pit to form the curtain roof line, with the length of one side of the inclined roof-type water-stop curtain being consistent with the depth of the foundation pit; the construction of the lateral stepped water-stop curtain involves deep cement mixing or high-pressure jet grouting from the other two sides of the foundation pit along the direction of the inclined roof-type water-stop curtain, gradually lengthening from both sides towards the middle, converging at the curtain roof line to form the lateral stepped water-stop curtain.

[0039] Furthermore, in step S00, using the SMW method for pile construction, I-beams are inserted into the lateral stepped waterstop curtain.

[0040] Furthermore, in step S30, the precast guide piles are divided into precast guide corner piles and precast guide side piles.

[0041] Furthermore, in step S30, the precast guide corner piles are rectangular piles, and during precasting, three rows of sliding grooves are embedded on the two adjacent sides of the precast guide corner piles.

[0042] Furthermore, in step S30, during the prefabrication of the guide prefabricated side piles, three rows of external sliding grooves are symmetrically embedded on the opposite two sides of the guide prefabricated side piles.

[0043] Furthermore, in step S30, the chute is an outwardly protruding O-shaped track, which is welded into the steel cage during the production of the two types of precast guide piles to form a single unit.

[0044] Furthermore, in step S60, the planar support system includes bifurcated corner supports and horizontal supports.

[0045] Furthermore, in step S60, a clamp-type corbel is installed on the structural column, expansion bolt holes are drilled on the inner side of the guide precast side pile, and then the corresponding corbel is installed. Expansion bolt holes are drilled on the two adjacent inner sides of the guide precast corner pile, and then the corresponding corner corbel is installed to form bifurcated corner support and horizontal support.

[0046] Furthermore, the bifurcation corner supports and horizontal supports are all made of structural steel.

[0047] Compared with the prior art, this application has the following beneficial effects:

[0048] 1) Compared with open-type mixing piles or jet grouting piles for water-stopping curtains, the closed-type water-stopping system in this invention can not only effectively shorten the length of the water-stopping curtain, but also form a closed water-stopping loop; in addition, soil can be directly excavated on the upper part of the inclined roof-type water-stopping curtain without the need for further support, avoiding the cumbersome double steps of excavation and support in conventional water-stopping curtains. Therefore, this invention has significant technical and economic advantages.

[0049] 2) Compared with the underground continuous wall structure, the present invention adopts a combination of prefabricated precast piles and precast slabs with prefabricated assembly and step-by-step installation in units, which not only improves construction efficiency, but also reduces project cost to a large extent. It eliminates the need for grouting for wall protection and enhances environmental protection. In addition, the precast slabs are installed and used according to thickness. The deeper the excavation of the foundation pit, the thicker the precast slab. This arrangement is not only scientific, but also further reduces material consumption. Therefore, the present invention has significant technical, economic and environmental benefits.

[0050] 3) This invention utilizes a closed-type water-stopping system to pre-form an open-type working platform, and then constructs the underground main structure (i.e., "pile-column integrated structure") on this platform. The open-type working platform can also form the basement floor slab later, which can improve the construction progress of the basement. In addition, the open-type working platform is fixed together with the pile-column integrated structure, and the open-type working platform acts as a connecting beam, which can effectively improve the horizontal resistance of the pile-column integrated structure, thereby improving its support capacity.

[0051] 4) Compared with the commonly used support and excavation methods in foundation pits, the present invention adopts a combined support and excavation system formed by the integrated pile and column structure and the plane support system, which simplifies the support process. Moreover, only the plane support system needs to be removed later, which reduces the number of cumbersome dismantling components, optimizes the construction process, and improves work efficiency. Attached Figure Description

[0052] Figure 1 This is an elevation view of a closed-loop water-stop system;

[0053] Figure 2 This is a top view of a closed-loop water-stopping system;

[0054] Figure 3 This is a three-dimensional schematic diagram of a closed-loop water-stop system;

[0055] Figure 4 This is the first construction elevation drawing of an open-type work platform;

[0056] Figure 5 This is the first construction plan of an open-type work platform;

[0057] Figure 6 This is an elevation view of the integrated pile-column structure construction.

[0058] Figure 7 This is a construction plan of the integrated pile-column structure;

[0059] Figure 8 This is a construction elevation view of the precast guide piles;

[0060] Figure 9 This is a construction plan of the precast guide piles;

[0061] Figure 10 This is the elevation view of the first precast slab installation.

[0062] Figure 11 This is a schematic diagram of the installation of the first precast slab at the corner;

[0063] Figure 12 This is the first elevation drawing of the planar support system;

[0064] Figure 13This is the plan view of the first planar support system;

[0065] Figure 14 This is the elevation view of the construction of the second planar support system;

[0066] Figure 15 This is a plan view after the second precast slab is installed;

[0067] Figure 16 This is a schematic diagram of the installation of the second precast slab at the corner;

[0068] Figure 17 This is the elevation view of the third planar support system;

[0069] Figure 18 This is an elevation view of the second open-type working platform and the fourth planar support system;

[0070] Figure 19 This is a plan view after the third precast slab is installed;

[0071] Figure 20 This is a schematic diagram of the installation of the third precast slab at the corner;

[0072] Figure 21 This is an elevation view of an ultra-deep foundation pit with combined support in a soft soil area after the excavation work is completed.

[0073] Figure 22 This is a flowchart of the excavation and construction process for combined support of ultra-deep foundation pits in soft soil areas.

[0074] In the diagram, 1. Excavation pit; 2. Inclined roof-type water-stop curtain; 3. Curtain roof line; 4. Lateral stepped water-stop curtain; 5. Soil inside the pit; 6. Ground surface; 7. Open-type working platform; 8. Flexible cushion layer; 9. Soil intake; 10. Pile-column integrated structure; 101. Pile foundation; 102. Structural column; 11. Guide precast pile; 111. Guide precast corner pile; 112. Guide precast side pile; 12. First precast slab; 13. Second precast slab; 14. Third precast slab; 15. Sliding buckle; 16. Sliding groove; 17. Bottom raft slab; 18. Forked corner support; 19. Horizontal support; 20. Sealing cushion layer. Detailed Implementation

[0075] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this application are within the scope of protection of this application.

[0076] Those skilled in the art should understand that, in the disclosure of this application, the terms "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, the above terms should not be construed as limitations on this application.

[0077] Referring to the accompanying drawings in the instruction manual, from Figures 1 to 22 Further explanation of the technical solution of the present invention: The excavation and construction process of ultra-deep foundation pit combined support in soft soil areas is shown in the figure. Figure 22 As shown, the specific implementation steps include the following:

[0078] S00, Construction of a closed-loop waterstop system:

[0079] like Figures 1 to 3 As shown, the closed-type water-stopping system adopts the overlapping construction process of deep cement mixing or high-pressure jet grouting, including the construction of the inclined roof-type water-stopping curtain 2 and the lateral stepped water-stopping curtain 4. The operation of the inclined roof-type water-stopping curtain 2 involves deep cement mixing or high-pressure jet grouting from both sides of the foundation pit 1 at a certain angle, ultimately converging in the middle of the foundation pit 1 to form the curtain roof line 3, and the length of one side of the inclined roof-type water-stopping curtain 2 is consistent with the depth of the foundation pit 1; synchronously The construction of the lateral stepped water-stop curtain 4 involves deep cement mixing or high-pressure jet grouting, gradually extending from both sides of the foundation pit 1 along the direction of the sloping roof-shaped water-stop curtain 2 towards the middle, converging at the curtain roof line 3 to form the lateral stepped water-stop curtain 4. The depth of the lateral stepped water-stop curtain 4 always changes symmetrically in a stepped manner along the depth of the sloping roof-shaped water-stop curtain 2, and the two always intersect, ultimately forming a closed water-stopping system. Furthermore, if necessary, to enhance the lateral restraint of the lateral stepped water-stop curtain 4, the technology of SMW method piles can be adopted, and I-beams can be inserted into the lateral stepped water-stop curtain 4 to resist soil pressure and stabilize the pit wall.

[0080] S10. Excavate the soil in one go and construct the first open-type working platform 7:

[0081] like Figure 4 and Figure 5As shown, the first excavation is carried out on the soil 5 in the pit within the closed water-stop system. The closed water-stop system cannot be removed during the first excavation. The excavation depth is up to the middle of the closed water-stop system, and the excavation shape is an inverted trapezoid. Then, a flexible cushion layer 8 is constructed at this depth using sand or rammed earth. The flexible cushion layer 8 is connected to the inverted roof-shaped water-stop curtain on both sides. Finally, referring to the practice of reinforced concrete structures, steel bars and side forms are laid on the flexible cushion layer 8, and the in-situ casting of the open-type working platform 7 is carried out. The middle is set as an opening, which is the soil extraction port 9, to facilitate the subsequent excavation of the soil 5 in the pit.

[0082] S20, Construction of Integrated Pile-Column Structure 10:

[0083] like Figure 6 and Figure 7 As shown, drawing inspiration from a single-pile-one-column geotechnical structure, multiple sets of integrated pile-column structures 10 are constructed on an open-type working platform 7. The piles 101 are buried in the soil, extending beyond the bottom of the foundation pit 1 and directly to the designed depth. The structural columns 102 protrude from the soil and are used for later combined support of the foundation pit 1. As the soil is excavated, the lengths of the piles 101 and structural columns 102 change inversely. The resulting integrated pile-column structure 10 and the open-type working platform 7 are connected as a single unit through their respective steel reinforcement cages.

[0084] Construction of S30 and precast guide pile 11:

[0085] like Figure 8 and Figure 9 As shown, the precast guide pile 11 is a prefabricated reinforced concrete component unit prefabricated in the factory. It is divided into two types: precast guide corner piles 111 and precast guide side piles 112. The splicing method between the precast units is the same as that of conventional precast piles. The precast guide pile 11 is a rectangular pile. During prefabrication, for the precast guide corner pile 111, three rows of sliding grooves 16 are embedded on its adjacent two sides. For the precast guide side pile 112, three rows of external sliding grooves 16 are symmetrically embedded on its opposite two sides. The sliding grooves 16 are protruding O-shaped tracks made of steel and are welded to the reinforcing cage of the precast guide pile 11 during production to form a whole. The construction of the precast guide pile 11 is carried out by referring to the process of static drilling or pilot hole pile installation. That is, static drilling or pilot hole installation is carried out first at the predetermined pile position, and then the precast guide pile 11 is precisely hoisted and installed in units.

[0086] S40, Precast Panel Production:

[0087] The precast slabs are divided into a first precast slab 12, a second precast slab 13, and a third precast slab 14. These are prefabricated reinforced concrete component units prefabricated in a factory. The overlapping and sealing method between the precast units is consistent with that of conventional precast slabs. The width of the precast slabs is determined by the spacing of the guide precast piles 11, and the thickness of the precast slabs increases with the excavation depth of the foundation pit 1 to resist the increasing earth pressure. That is, the thickness of the third precast slab 14 is greater than the thickness of the second precast slab 13, which is greater than the thickness of the first precast slab 12. Based on the overlapping technology of CO-type steel pipe pile cofferdams, each end of the precast slab has a built-in sliding buckle 15. This sliding buckle 15 can slide along the external groove of the guide precast pile 11. 16 The matching buckle moves up and down. The sliding buckle 15 is a concave C-shaped steel pipe. The outer side of the C-shaped steel pipe is provided with a small back rib to facilitate a secure connection with the precast slab and enhance friction. It is also used as a side template at both ends of the precast slab during production, ultimately forming a whole. The first precast slab 12, the second precast slab 13, and the third precast slab 14 have the same length, denoted as L. They are inserted into the adjacent guide precast piles 11 from the outside to the inside and from top to bottom along the three rows of sliding grooves 16 on the outside of the guide precast piles 11. An overlap length of 1 / 3L is required between the first precast slab 12 and the second precast slab 13, and between the second precast slab 13 and the third precast slab 14.

[0088] S50, Installation of the first precast slab 12:

[0089] like Figure 10 and Figure 11 As shown, after the construction of the guide precast piles 11 and the production of the precast slabs are completed, along the perimeter of the foundation pit 1, following the outermost row of sliding grooves 16 of the guide precast piles 11, the first precast slabs 12 are inserted and overlapped and sealed in units from top to bottom until the total length of the first precast slabs 12 in the soil reaches L.

[0090] S60. After secondary excavation to 1 / 3 the depth of the first precast slab 12, the first planar support system is installed:

[0091] like Figure 12 and Figure 13As shown, after the first precast slab 12 is inserted, secondary excavation begins. Secondary excavation and subsequent excavation require the removal of the corresponding closed-type water-stop system, meaning the closed-type water-stop system is removed simultaneously with the soil 5 in the pit at the same depth. Secondary excavation begins around the perimeter of the foundation pit 1 and continues until 1 / 3 of the depth of the first precast slab 12 is reached. At this depth, the first planar support system is then installed. The planar support system includes bifurcated corner supports 18 and horizontal supports 19. The bifurcated corner supports 18 and horizontal supports 19 between the guide precast piles 11 and the structural columns 102 are obtained by referencing the method of connecting the horizontal inner supports with corbels in conventional foundation pit 1 excavation. Specifically, clamp-type corbels are installed on the structural columns 102, expansion bolt holes are drilled on the inner side of the guide precast side piles 112, and then corresponding corbels are installed. Similarly, expansion bolt holes are drilled on the two adjacent inner sides of the guide precast corner piles 111, and then corresponding corner corbels are installed. Both the bifurcated corner supports 18 and the horizontal supports 19 are made of structural steel.

[0092] S70. After excavating three times to 2 / 3 the depth of the first precast slab 12, the second precast slab 13 is installed, and a second planar support system is set at the top of the second precast slab 13.

[0093] like Figure 14 As shown, after the first plane support system is completed, three excavations are carried out, simultaneously removing the corresponding closed-type water-stop system, until 2 / 3 of the depth of the first precast slab 12 is reached. Then, at this depth, the second precast slab 13 is installed. Referring to the precast slab installation in step S50, along the perimeter of the foundation pit 1, following the sliding grooves 16 in the middle row of the guide precast piles 11, the second precast slab 13 is gradually inserted and overlapped and sealed in units from top to bottom. The total length of the second precast slab 13 embedded in the soil should also reach L. At this time, the overlap length between the first precast slab 12 and the second precast slab 13 is 1 / 3L. After the second precast slab 13 is installed, referring to the plane support system in step S60, the second plane support system is completed at the top height of the second precast slab 13.

[0094] After excavating four times to 1 / 3 the depth of the second precast slab 13, a third planar support system is installed:

[0095] like Figures 15 to 17 As shown, after the second plane support system is completed, four excavations are carried out, and the corresponding closed water-stop system is removed simultaneously, up to 1 / 3 of the depth of the second precast slab 13. Then, referring to the plane support system in step S60, a third plane support system is installed at 1 / 3 of the depth of the second precast slab 13.

[0096] After five excavations to 2 / 3 the depth of the second precast slab 13, the third precast slab 14 is inserted simultaneously, and the construction of the second open-type working platform 7 is carried out. Then, a fourth planar support system is set at the top height of the third precast slab 14.

[0097] like Figures 18 to 20 As shown, after the third plane support system is completed, the fifth excavation begins, and the entire closed water-stop system is removed, up to 2 / 3 of the depth of the second precast slab 13. Then, at this depth, the third precast slab 14 is inserted. Referring to the precast slab insertion in step S50, along the perimeter of the foundation pit 1, following the innermost row of sliding grooves 16 of the guide precast piles 11, the third precast slab 14 is inserted and overlapped in units from top to bottom, sealing the joint. The total length of the third precast slab 14 embedded in the soil should also reach L. At this point, the overlap length between the second and third precast slabs 13 is 1 / 3L. Then, referring to the construction of the open-type working platform 7 in step S10, the second open-type working platform is completed at the top height of the third precast slab 14. Finally, referring to the plane support system in step S60, a fourth plane support system is installed at the top height of the third precast slab 14.

[0098] After excavating six times to the middle of the third precast slab 14, the bottom raft slab 17 was constructed, completing the excavation work for the combined support of the ultra-deep foundation pit 1 in the soft soil area.

[0099] like Figure 21 As shown, after the fourth plane support system is completed, the sixth excavation begins, reaching the middle of the third precast slab 14. Then, the bottom sealing layer 20 is constructed. The bottom sealing layer 20 can be constructed by referring to the method of plain concrete layer. After the bottom sealing layer 20 is hardened, the steel cage of the bottom raft slab 17 is tied, the formwork is erected, and the cast-in-place concrete is poured. After the bottom raft slab 17 is hardened, the excavation operation of the combined support of the ultra-deep foundation pit 1 in the soft soil area is completed.

[0100] The parts not described in detail in this application are prior art, and therefore are not described in detail in this application.

[0101] It is understood that the term "a" should be understood as "at least one" or "one or more", that is, in one embodiment, the number of an element can be one, while in another embodiment, the number of the element can be multiple, and the term "a" should not be understood as a limitation on the number.

[0102] Although this paper frequently uses terms such as 1. foundation pit, 2. inclined roof-type water-stop curtain, 3. curtain roof line, 4. lateral stepped water-stop curtain, 5. soil in the pit, 6. ground surface, 7. open-type working platform, 8. flexible cushion layer, 9. soil intake, 10. integrated pile-column structure, 10. pile foundation, 101. structural column, 102. guide precast pile, 11. guide precast corner pile, 111. guide precast side pile, 112. first precast slab, 12. second precast slab, 13. third precast slab, 14. sliding buckle, 15. sliding groove, 16. bottom raft slab, 17. bifurcation corner support, 18. horizontal support, 19. bottom sealing cushion layer, etc., the possibility of using other terms is not excluded. The use of these terms is merely for the convenience of describing and explaining the essence of this application; interpreting them as any additional limitation would be contrary to the spirit of this application.

[0103] This application is not limited to the above-described preferred embodiments. Anyone can derive other products in various forms under the guidance of this application. However, regardless of any changes made to their shape or structure, any product with the same or similar technical solution as this application falls within the protection scope of this application.

Claims

1. A combined support method for ultra-deep foundation pits in soft soil areas, characterized in that, The construction steps include the following: S00, Construction of closed-type waterstop system: Construction of inclined roof-type waterstop curtain and lateral stepped waterstop curtain respectively; Among them, the depth of the lateral stepped water-stop curtain always changes symmetrically in a stepped manner along the depth of the inclined roof-type water-stop curtain, and the two always intersect, eventually forming a closed water-stop system. S10. Excavate the soil and construct the first open-type working platform: Excavate the soil in the pit within the closed water-stopping system for the first time. The excavation depth is to the middle of the closed water-stop system. The excavation shape is an inverted trapezoid. Then, at this depth, a flexible cushion layer is made of sand or rammed earth. The flexible cushion layer is connected to the inverted roof-shaped water-stop curtain on both sides. Reinforcing bars and side formwork are laid on the flexible cushion layer for the in-situ casting of the open-type working platform, with the middle part set as the soil intake. S20. Construction of integrated pile-column structure: Construction of multiple sets of integrated pile-column structures on an open-type working platform; The piles buried in the soil are pile foundations, which extend beyond the bottom of the foundation pit and are constructed directly to the designed depth; the piles exposed above the soil are structural columns, which are used for the combined support of the foundation pit in the later stages. As the soil is excavated, the lengths of the pile foundation and structural columns change, forming an integrated pile-column structure and an open-type working platform that are connected by their respective steel cages to form a single unit. S30. Construction of precast guide piles: Precast guide piles are manufactured in the factory. Static drilling or pilot hole drilling is first carried out at the predetermined pile positions during construction, and then the precast guide piles are precisely hoisted and implanted in units. S40. Precast panel production: The first precast panel, the second precast panel, and the third precast panel are precast in the factory. The width of the precast slab is determined by the spacing of the guide precast piles, and the thickness of the third precast slab is greater than the thickness of the second precast slab, which is greater than the thickness of the first precast slab. Both ends of the precast slab have built-in sliding buckles that can move up and down along the external sliding groove of the guide precast pile to match the buckle. Among them, the sliding buckle is a concave C-shaped steel pipe. The outer side of the C-shaped steel pipe is provided with small back ribs, which are set as side templates at both ends during the production of precast slabs, and finally form a whole. The first, second, and third precast slabs are of the same length, denoted as L, and are inserted between adjacent precast slabs from the outside to the inside and from top to bottom along the three rows of sliding grooves on the outside of the guide precast piles. An overlap length of 1 / 3L is required between the first precast slab and the second precast slab, and between the second precast slab and the third precast slab. S50. First Precast Slab Insertion Construction: After the construction of the guide precast piles and the production of the precast slabs are completed, along the perimeter of the foundation pit, following the outermost row of sliding grooves of the guide precast piles, the first precast slabs are inserted and overlapped and sealed in units from top to bottom until the total length of the first precast slabs inserted into the soil reaches L. S60. After the second excavation reaches 1 / 3 of the depth of the first precast slab, the first planar support system is installed: After the first precast slab is inserted, the second excavation begins. For secondary excavation and subsequent excavation, the closed-type water-stopping system is removed at the same depth as the soil in the pit. The secondary excavation begins around the perimeter of the foundation pit and continues until it reaches 1 / 3 of the depth of the first precast slab. At this depth, the first planar support system is then installed. S70. After excavating three times to 2 / 3 the depth of the first precast slab, the second precast slab is installed, and a second plane support system is set at the top of the second precast slab. After the first plane support system is completed, three excavations are started, and the corresponding closed water-stop system is removed at the same time, until 2 / 3 the depth of the first precast slab is reached. At this depth, the second precast slab is inserted. Referring to the precast slab insertion in step S50, along the perimeter of the foundation pit, following the sliding groove in the middle row of the guide precast piles, the second precast slab is inserted and overlapped and sealed in units from top to bottom. When the total length of the second precast slab embedded in the ground reaches L, the overlap length between the first and second precast slabs is 1 / 3L. After the second precast slab is installed, referring to the method of the first planar support system in step S60, the second planar support system is installed at the top height of the second precast slab. S80. After four excavations to 1 / 3 the depth of the second precast slab, the third plane support system is installed: After the second plane support system is completed, four excavations are started, and the corresponding closed water-stop system is removed simultaneously, until 1 / 3 the depth of the second precast slab is reached. Referring to the method of the first planar support system in step S60, a third planar support system is set at 1 / 3 of the depth of the second precast slab; S90. After five excavations to 2 / 3 the depth of the second precast slab, the third precast slab is inserted and the second open-type working platform is constructed simultaneously. The fourth plane support system is set at the top of the third precast slab. After the third plane support system is completed, the fifth excavation begins, and the closed water-stop system is completely removed until 2 / 3 the depth of the second precast slab is reached. At this depth, the third precast slab is inserted. Referring to the precast slab insertion in step S50, along the perimeter of the foundation pit, following the innermost row of grooves on the guide precast pile, the third precast slab is inserted and overlapped and sealed in a unit-by-unit manner from top to bottom. When the total length of the third precast slab embedded in the ground reaches L, the overlap length between the second and third precast slabs is 1 / 3L. Then, referring to the construction of the open-type working platform in step S10, the operation of the second open-type working platform is completed at the height of the top of the third precast slab. Referring to the method of the first planar support system in step S60, a fourth planar support system is set at the height of the top of the third precast slab; After six excavations to the middle of the third precast slab, the bottom raft slab is constructed, completing the excavation of the ultra-deep foundation pit combined support in the soft soil area. After the fourth plane support system is completed, the sixth excavation begins, reaching the middle of the third precast slab. The construction of the bottom sealing layer is carried out. After the bottom sealing layer hardens, the reinforcement cage of the bottom raft slab is tied, the formwork is erected, and the cast-in-place concrete is poured. After the bottom raft slab hardens, the excavation operation of the ultra-deep foundation pit combined support in the soft soil area is completed.

2. The combined support method for ultra-deep foundation pits in soft soil areas as described in claim 1, characterized in that, In step S00, the construction of the inclined roof-shaped water-stop curtain involves deep cement mixing or high-pressure jet grouting from both sides of the foundation pit at a set angle, ultimately converging at the middle of the foundation pit to form the curtain roof line, with the length of one side of the inclined roof-shaped water-stop curtain being consistent with the depth of the foundation pit; the construction of the lateral stepped water-stop curtain involves deep cement mixing or high-pressure jet grouting from the other two sides of the foundation pit along the direction of the inclined roof-shaped water-stop curtain, gradually lengthening from both sides towards the middle, converging at the curtain roof line to form the lateral stepped water-stop curtain.

3. The combined support method for ultra-deep foundation pits in soft soil areas as described in claim 2, characterized in that, In step S00, using the SMW method for pile construction, I-beams are inserted into the lateral stepped waterstop curtain.

4. The combined support method for ultra-deep foundation pits in soft soil areas as described in claim 1, characterized in that, In step S30, the precast guide piles are divided into precast guide corner piles and precast guide side piles.

5. The combined support method for ultra-deep foundation pits in soft soil areas as described in claim 4, characterized in that, In step S30, the precast guide corner pile is a rectangular pile. During prefabrication, three rows of sliding grooves are embedded on the two adjacent sides of the precast guide corner pile.

6. The combined support method for ultra-deep foundation pits in soft soil areas as described in claim 5, characterized in that, In step S30, during the prefabrication of the guide prefabricated side piles, three rows of external sliding grooves are symmetrically embedded on the opposite two sides of the guide prefabricated side piles.

7. The combined support method for ultra-deep foundation pits in soft soil areas as described in claim 6, characterized in that, In step S30, the chute is an outwardly protruding O-shaped track, which is welded into the steel cage during the production of the two types of precast guide piles to form a whole.

8. The combined support method for ultra-deep foundation pits in soft soil areas as described in any one of claims 4-7, characterized in that, In step S60, the planar support system includes bifurcated corner supports and horizontal supports.

9. The combined support method for ultra-deep foundation pits in soft soil areas as described in claim 8, characterized in that, In step S60, a clamp-type corbel is installed on the structural column, expansion bolt holes are drilled on the inner side of the precast guide pile, and then the corresponding corbel is installed. Expansion bolt holes are drilled on the two adjacent inner sides of the precast guide corner pile, and then the corresponding corner corbel is installed to form bifurcated corner support and horizontal support.

10. The combined support method for ultra-deep foundation pits in soft soil areas as described in claim 8, characterized in that, Both the bifurcation corner support and the horizontal support are made of structural steel.

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