Synchronous construction method and structure for sectional combined type foundation pit support

Abstract

The invention discloses a segmented combined type foundation pit support synchronous construction method and structure, for a side line which needs to be reinforced and supported and has a ramp, the side line is divided into a plurality of sub-pits, every several adjacent sub-pits serve as a segment, and all the segments are constructed synchronously; during construction of each section, construction is conducted from front to back, and according to the construction sequence of the TRD continuous wall, the three-axis stirring pile, the cast-in-place pile, the first partition wall, the second partition wall, the coping beam, the inner supporting beam and the inclined supporting pile, construction of the IMS wall, the ramp coping beam and the ramp inner supporting beam is conducted synchronously at the ramp. The combined design is adopted to form multiple defense lines, the integrity, the deformation resistance and the water stopping effect are improved, the use amount of reinforced concrete is reduced, the construction time is shortened, the influence on the surrounding environment is small, and disturbance to a constructed structure can be avoided.

Description

Technical Field

[0001] This invention belongs to the field of foundation pit engineering, specifically relating to a segmented combined foundation pit support synchronous construction method and structure. Background Technology

[0002] When a foundation pit project is located near high-safety-level buildings such as subways or residential buildings, the edges of these buildings need to be reinforced to reduce horizontal deformation and surface settlement, and to ensure waterproofing. This reduces the disturbance and damage to the buildings caused by the foundation pit construction. Currently, the existing method is to use multi-pit construction. However, this method has the following problems: 1) Poor synergy of composite retaining walls: Existing TRD-cast pile composite retaining walls are usually constructed in the order of "simultaneous construction" or "cast pile construction first", which causes the water-stopping effect of the TRD wall to be disturbed by the construction of the cast pile (such as mud circulation destroying the integrity of the TRD wall), or the stiffness of the cast pile cannot effectively compensate for the deficiencies of the TRD wall (the elastic modulus of the TRD wall is about 15GPa, and that of the cast pile is about 30GPa). Therefore, the deformation resistance and water-stopping effect are insufficient.

[0003] 2) When there is a slope near the foundation pit, the existing foundation pit slope is usually reinforced with a single mixing pile, which cannot adapt to the heavy load of construction vehicles (such as pile drivers of more than 100t), and is prone to landslides or subsidence (such as slope settlement > 50mm).

[0004] 3) Disorderly construction sequence of sub-pits: In the current sub-pit construction, the support structures of each sub-pit are carried out in an overlapping manner, which causes the support structure of the previous sub-pit to be disturbed by the construction of the subsequent sub-pit, thus affecting the deformation resistance.

[0005] 4) Unreasonable timing of precast inclined pile construction: Existing precast inclined piles are usually constructed before the foundation pit is excavated. The subsequent construction of the support structure will collide with or disturb the inclined piles, causing the pile body to tilt (deviation > 1%), reducing the effect of advance support. Summary of the Invention

[0006] The purpose of this invention is to provide a segmented combined foundation pit support synchronous construction method and a segmented combined foundation pit support structure. Structurally, the combined design forms multiple lines of defense, which improves the overall integrity, deformation resistance and water-stopping effect, and reduces the amount of reinforced concrete used. In terms of construction method, it reduces construction time, has little impact on the surrounding environment, and can avoid disturbing the existing structure.

[0007] The technical solution adopted in this invention is: A segmented combined foundation pit support synchronous construction method involves dividing the edge of a sloped foundation pit into several sub-pits, with each group of several adjacent sub-pits forming a segment, and all segments being constructed synchronously. During the construction of each segment: first, a TRD (tightening wall) is constructed from front to back as the outer water-stop curtain. When the constructed TRD has reached a certain length, triaxial mixing piles are constructed from front to back on the outer side of the TRD to strengthen the foundation bearing capacity. When the constructed triaxial mixing piles reach a certain length along the line, cast-in-place piles are constructed from front to back on the inner side of the TRD to enhance the vertical support capacity. Finally, when the constructed cast-in-place piles reach a certain length along the line... When the length is reached, the adjacent partition wall 1 and the partition wall 2 opposite the TRD continuous wall are constructed as the inner layer of the water-stop curtain. When the walls around the pit are completed, the capping beam and the inner support beam are constructed to transfer the horizontal load. The capping beam is set in a ring at the top of the cast-in-place piles, partition wall 1 and partition wall 2. The inner support beam is integrally cast inside the ring of capping beams. Then, the inclined support piles are constructed with the help of the pilot hole. The inclined support piles are located outside the partition wall 2 and will diagonally support the capping beam. At the same time, at the ramp, the IMS wall is constructed outside the three-axis mixing pile to stabilize the ramp. The top of the IMS wall is equipped with a ramp capping beam. The ramp capping beam is connected to the capping beam at the top of the cast-in-place pile through the ramp inner support beam.

[0008] Preferably, if the edge of the foundation pit is close to the subway tunnel, during the construction process, the vertical / horizontal displacement, segment convergence deformation, differential settlement of the subway tunnel, as well as the pile displacement, deep horizontal displacement of the soil, support axial force, groundwater level, and surface settlement of the foundation pit are automatically monitored, and manual inspections are also carried out, and the specific construction plan is adjusted according to the feedback.

[0009] Preferably, the depth of the TRD continuous wall is 1.5 times the depth of the foundation pit, and it adopts a channel-type cutting process.

[0010] Preferably, the triaxial mixing piles are inserted 7 days after the TRD continuous wall construction.

[0011] Preferably, the cast-in-place piles are constructed when the construction of the three-axis mixing piles in the first pit of each section is completed.

[0012] Preferably, both partition wall one and partition wall two are constructed as continuous water-resistant retaining walls with prestressed concrete pipe piles as the backbone and flexible piles as the filler. Partition wall one and partition wall two are constructed when the grouting piles of the first two pits in each section are completed.

[0013] Preferably, the cross-sectional dimensions of the internal support beam are set according to the span of the sub-pit, with larger spans resulting in larger cross-sectional dimensions.

[0014] Preferably, the inclined bracing pile is a cast-in-place reinforced concrete square pile, which is constructed with the aid of pilot hole to avoid disturbing the existing structure. When using pilot hole, the depth of the pilot hole is 1 / 3 of the length of the inclined bracing pile. After the pilot hole is drilled, concrete is poured and a reinforcing cage is inserted to prevent the hole wall from collapsing.

[0015] Preferably, during the construction of the IMS wall, the mixing piles are constructed first, and then the steel sections are inserted. The steel sections are constructed using a one-in-one-out construction process, and the insertion depth of the steel sections is more than 90% of the length of the mixing piles.

[0016] A segmented composite foundation pit support structure is provided. For the edge line requiring reinforced support and with a slope, the area is divided into several sub-pits. For each sub-pit, a TRD continuous wall is used as the outer layer of the water-stop curtain. Triaxial mixing piles are used on the outer base of the TRD continuous wall to enhance the bearing capacity of the base. Cast-in-place piles are used on the inner side of the TRD continuous wall to enhance the vertical support capacity. Adjacent and opposite sides of the TRD continuous wall are respectively equipped with partition wall one and partition wall two as the inner layer of the water-stop curtain. A capping beam is set at the top of the cast-in-place piles, partition wall one, and partition wall two. An internal bracing beam is integrally cast inside the capping beam. The capping beam and the internal bracing beam are used to transfer horizontal loads. Diagonal bracing piles are set on the outer side of partition wall two to diagonally support the capping beam. At the slope, an IMS wall is set outside the triaxial mixing piles to stabilize the slope. A slope capping beam is set at the top of the IMS wall. The slope capping beam is connected to the capping beam at the top of the cast-in-place pile through the slope internal bracing beam.

[0017] The beneficial effects of this invention are: Structurally, a combined design is adopted, consisting of "TRD continuous wall, triaxial mixing piles and cast-in-place piles on the outer side of the pit + partition wall one and partition wall two on the remaining side of the pit + capping beam and internal support beam at the top of the pit + inclined support piles outside the pit + IMS wall, slope capping beam and slope internal support beam at the ramp". This forms a multi-layered defense system of "water-stopping curtain - foundation reinforcement - vertical support - horizontal separation - inclined support - slope stability", which significantly improves the integrity, deformation resistance and water-stopping effect of the support system. It strictly controls the deformation of the foundation pit (horizontal displacement ≤20mm, meeting the requirements of the subway) and the leakage rate ≤1%. The combined system also reduces the amount of reinforced concrete used (saving 15% compared with the traditional method) and shortens the construction period and cost.

[0018] In terms of construction methods, firstly, each section is constructed simultaneously, with each section constructed from front to back in the following sequence: TRD continuous wall, triaxial mixing piles, cast-in-place piles, partition wall one and partition wall two, capping beam and internal support beam, and inclined bracing piles. Simultaneous construction of IMS walls, ramp capping beams, and ramp internal support beams is also carried out at the ramps, reducing construction time and shortening the total construction cycle by more than 30% compared to traditional methods, while minimizing the impact on the surrounding environment (reducing the impact on subway operations by 50%). Secondly, triaxial mixing piles are constructed when the existing TRD continuous wall has reached a certain number of days, utilizing the early strength of the TRD continuous wall as support to avoid disturbing the TRD continuous wall during construction. Cast-in-place piles are constructed when the existing triaxial mixing piles have reached a certain length along the line, avoiding mud contamination of the triaxial mixing piles during construction. Partition wall one and partition wall two are constructed when the existing cast-in-place piles have reached a certain length along the line. The process is optimized and rationally connected, with inclined bracing piles constructed last to avoid disturbing the already constructed structure. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the pit division along the edge of the foundation pit in an embodiment of the present invention.

[0020] Figure 2 This is an overall effect diagram of the foundation pit support in an embodiment of the present invention.

[0021] Figure 3 This is a schematic diagram of a pit support in an embodiment of the present invention that is not adjacent to a slope.

[0022] Figure 4 This is a schematic diagram of the pit support for a certain adjacent slope in an embodiment of the present invention.

[0023] In the diagram: A - subway tunnel; B - pit with slope nearby; 1 - triaxial mixing pile; 2 - TRD continuous wall; 3 - cast-in-place pile; 4 - internal support beam; 5 - capping beam; 6 - partition wall one; 7 - inclined support pile; 8 - partition wall two; 9 - prestressed concrete pipe pile; 10 - flexible pile; 11 - IMS wall; 12 - internal support beam of the slope; 13 - capping beam of the slope. Detailed Implementation

[0024] The present application will be further described below with reference to the accompanying drawings and embodiments.

[0025] like Figure 1 As shown, for a certain foundation pit project, the perimeter of the foundation pit within the subway protection zone is 760m long. There is an operating subway within 5m of the perimeter (its subway tunnel A has a diameter of 6m), and there are slopes in several areas. The requirements are that the horizontal deformation of the foundation pit is ≤20mm and the surface settlement is ≤30mm. It is now necessary to strengthen the support of the perimeter within the subway protection zone and treat the slopes. The following construction methods are adopted.

[0026] S1, such as Figure 1 and Figure 2 As shown, the edge line requiring reinforcement is divided into 15 sub-pits (sub-pit 1 to sub-pit 15, each sub-pit is about 50m long), and every 3 sub-pits are divided into 1 section (sub-pit 1 to sub-pit 3 is the first section, sub-pit 4 to sub-pit 6 is the second section, and so on, for a total of 5 sections). Among them, sub-pits B with slopes nearby are sub-pits 8, 9, 11, 12 and 13.

[0027] S2. Construction of each section should be carried out simultaneously. During the construction of each section, if... Figure 3 and Figure 4 As shown: 1) First, construct the TRD continuous wall 2 as the outer water-stop curtain from front to back; TRD continuous wall 2 (Trench Cutting Re-mixing Deep Wall, uniform thickness cement-soil underground continuous wall) can block external water and soil pressure, and its water-stopping effect is better than that of traditional high-pressure jet grouting piles (permeability coefficient ≤1×10⁻). 6 In this embodiment, the depth is 1.5 times the depth of the foundation pit and the thickness is 700mm. The cement content is 25% and the water-cement ratio is 0.55. The channel-type cutting process is adopted, with a φ800mm cutting wheel and a propulsion speed of 0.5m / min.

[0028] 2) When the constructed TRD continuous wall 2 reaches a certain number of days, triaxial mixing piles are constructed from front to back on the outer foundation of the TRD continuous wall 2 to strengthen the foundation bearing capacity. The three-axis mixing pile 1 (using a mixing pile machine with three drill bits to forcibly mix cement slurry and other curing agents with the in-situ soil to form a cement-soil columnar reinforced pile) can enhance the bearing capacity of the foundation (the characteristic value of the foundation bearing capacity is increased from 120kPa to 250kPa) and thus prevent the foundation from heaving. In this embodiment, it is inserted 7 days after the construction of the TRD continuous wall 2. Its single diameter is 850mm, the spacing is 600mm (overlap 250mm), the insertion depth is 18m, the cement content is 20%, and the water-cement ratio is 0.5.

[0029] 3) When the constructed triple-axis mixing pile 1 reaches a certain length along the line, cast-in-place piles 3 are constructed from front to back inside the TRD continuous wall 2 to enhance the vertical support capacity. The cast-in-place pile 3 (a pile made by forming a pile hole in the foundation soil through mechanical drilling, steel pipe soil squeezing, etc., and then placing a steel cage in the hole and pouring concrete or other materials) serves as a vertical support structure that can withstand horizontal earth pressure. In this embodiment, construction is carried out when the construction of the triaxial mixing pile 1 in the first pit of each section is completed (i.e., when the construction of the triaxial mixing pile 1 in pits 1, 4, 7, 10 and 13 is completed). The pile has a diameter of 900mm, a spacing of 1100mm, a pile length of 22m (3m embedded in slightly weathered rock), and the concrete strength is selected as C35.

[0030] 4) When the cast-in-place piles 3 have reached a certain length along the line, the partition wall 6 adjacent to the TRD continuous wall 2 and the partition wall 8 opposite the TRD continuous wall 2 shall be constructed as the inner layer of the water-stop curtain. In this embodiment, both partition wall 6 and partition wall 8 are constructed using prestressed concrete pipe piles 9 as the backbone and flexible piles 10 (cement-soil mixing piles or high-pressure jet grouting piles) as fillers to form a continuous water-resistant retaining wall. Construction is carried out when the grouting piles 3 of the first two sub-pits in each section are completed. The flexible piles 10 have a diameter of 600mm and a length of 18m.

[0031] 5) When the walls around the pit are completed, the capping beam 5 and the inner support beam 4 are constructed to transfer the horizontal load. The capping beam 5 is set at the top of the cast-in-place pile 3, the first partition wall 6 and the second partition wall 8. The inner support beam 4 is integrally cast inside the capping beam 5. The cross-sectional dimensions of the inner support beam 4 are set according to the span of the pit. In this embodiment, for a span of 6m, the cross-sectional dimensions are 800×700mm, and for a span of 8m, the cross-sectional dimensions are 900×700mm. The capping beam 5 and the inner support beam 4 are made of concrete with a strength of C35.

[0032] 6) Then, the inclined support pile 7 is constructed with the assistance of the pilot hole. The inclined support pile 7 is located outside the second partition wall 8 and will support the top beam 5. In this embodiment, the inclined bracing pile 7 is a cast-in-place reinforced concrete square pile. As an inclined support, it can supplement the lack of horizontal support and reduce the internal force of the inner bracing beam 4. Its cross-section is 450mm×450mm, length is 18m, spacing is 4.0m, and inclination angle is 35°. Its main reinforcement consists of 8 φ25mm HRB400 steel bars, stirrups φ10mm@100mm, and concrete strength is C35. It adopts pilot hole construction to avoid disturbing the constructed structure. A φ300mm spiral drill is used for pilot hole construction. The pilot hole depth is 1 / 3 of the length of the inclined bracing pile 7. After the pilot hole is drilled, concrete is poured immediately and a steel cage is inserted to prevent the hole wall from collapsing.

[0033] S3, at the same time, such as Figure 4 As shown, at the ramp, an IMS wall 11 is constructed on the outside of the three-axis mixing pile 1 to stabilize the ramp. The top of the IMS wall 11 is provided with a ramp capping beam 13, which is connected to the capping beam 5 at the top of the cast-in-place pile 3 through the ramp inner support beam 12. The IMS wall 11 (Insertion Method of Steel member) can improve the stability of the slope and prevent landslides during construction. It is constructed by first constructing the mixing piles and then inserting the steel members. In this embodiment, the mixing piles have a cross-sectional size of 800×600mm, a cement content of 20%~25% (22%), a water-cement ratio of 0.5~0.6 (0.55), and a length of 1.3m. The steel members are constructed using a one-in-one-out construction process, using Q235B grade steel, and the insertion depth is more than 90% of the length of the mixing pile (11.7m).

[0034] S4. At the same time, during the construction process, the vertical / horizontal displacement, segment convergence deformation, differential settlement of subway tunnel A, as well as the pile displacement, deep horizontal displacement of soil, support axial force, groundwater level, and surface settlement of the foundation pit are automatically monitored. Manual inspections are also carried out, and the specific construction plan is adjusted based on the feedback.

[0035] In this embodiment: TRD continuous wall 2 construction starts simultaneously in 5 sections, with 1 TRD machine in each section, advancing 15m per day, and the construction time for each section is 10 days; 7 days after the completion of TRD continuous wall 2 construction (strength ≥1.0MPa), 1 triaxial mixing pile machine is equipped in each section to insert triaxial mixing pile 1 in the corresponding pit, with an insertion length of 20m along the line per day, and the construction time for each section is 7.5 days; after a certain number of triaxial mixing piles 1 are completed in each section, 2 bored pile machines are equipped in each section to construct φ900 bored pile 3, constructing 10 piles per day, and the construction time for each section is 16 days. 5 days; after a certain number of cast-in-place piles 3 are completed in each section, each section is equipped with 1 cast-in-place pile machine and 1 concrete pump truck to construct the partition piles, capping beam 5 and internal support beam 4, and the construction time for each section is 15 days; after the completion of partition wall 1 6, partition wall 2 8, capping beam 5 and internal support beam 4, each section is equipped with 1 spiral drilling rig (φ300mm) and 1 concrete pump truck to construct the inclined support piles 7 using the pre-drilling auxiliary process, constructing 8 piles per day, and the construction time for each section is 12.5 days; simultaneously at the slope, 1 IMS mixer and 1 crane are equipped to construct the IMS wall 11, and the construction time for each section is 10 days.

[0036] After construction: the maximum horizontal displacement of the foundation pit is 18mm (meeting the subway requirement of ≤20mm), and the leakage rate is 0.5% (far lower than the 5% of the traditional method); the total construction period is 109 days (11 days ahead of the planned 120 days), which is 71 days shorter than the traditional segmented construction method (180 days); the amount of reinforced concrete used is reduced by 18% compared with the traditional method, and the construction cost is reduced by 25%; the number of times the subway operation is affected is reduced from 12 times in the traditional method to 3 times, and the impact time is shortened by 70%.

[0037] The aforementioned support method adopts a combined design in terms of structure, consisting of "2 TRD continuous walls, 1 triaxial mixing piles, and 3 cast-in-place piles on the outer side of the pit + 6 partition walls and 8 partition walls on the remaining sides of the pit + 5 capping beams and 4 inner support beams at the top of the pit + 7 inclined support piles outside the pit + 11 IMS walls, 13 capping beams, and 12 inner support beams at the ramp". This forms a multi-layered defense system of "water-stopping curtain - foundation reinforcement - vertical support - horizontal separation - inclined support - ramp stability", which significantly improves the integrity, deformation resistance, and water-stopping effect of the support system. It strictly controls the deformation of the foundation pit (horizontal displacement ≤ 20 mm, meeting the requirements of the subway) and the leakage rate ≤ 1%. Moreover, the combined system reduces the amount of reinforced concrete used (saving 15% compared to the traditional method) and shortens the construction period and cost.

[0038] The above-mentioned support method has the following construction techniques: First, each section is constructed simultaneously, with each section constructed from front to back according to the following sequence: TRD continuous wall 2, triaxial mixing pile 1, cast-in-place pile 3, partition wall 1 6 and partition wall 2 8, capping beam 5 and internal support beam 4, and inclined bracing pile 7. Simultaneously, the IMS wall 11, ramp capping beam 13, and ramp internal support beam 12 are constructed at the ramp, reducing construction time and shortening the total construction cycle by more than 30% compared to traditional methods, with minimal impact on the surrounding environment (reducing the impact on subway operations by 50%). Second, [the following is incomplete and requires further context]. When the TRD continuous wall 2 under construction reaches a certain number of days, the triaxial mixing pile 1 is constructed. The early strength of the TRD continuous wall 2 is used as support to avoid disturbing the TRD continuous wall 2 during the construction of the triaxial mixing pile 1. When the constructed triaxial mixing pile 1 reaches a certain length along the line, the cast-in-place pile 3 is constructed to avoid mud contamination of the triaxial mixing pile 1 during the construction of the cast-in-place pile 3. When the constructed cast-in-place pile 3 reaches a certain length along the line, the first partition wall 6 and the second partition wall 8 are constructed. The process connection is optimized and reasonable. The inclined bracing pile 7 is constructed last to avoid disturbing the constructed structure.

[0039] The embodiments described above are some, but not all, of the embodiments of this application. The detailed description of the embodiments of this application is not intended to limit the scope of the claimed application, but merely to illustrate selected embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

Claims

1. A method for simultaneous construction of a segmental combined foundation pit support, characterized in that: For the side line requiring reinforced support and having a slope, it is divided into several sub-pits along the line, and each several adjacent sub-pits is taken as a section, and each section is constructed synchronously; when each section is constructed: firstly, the TRD continuous wall is constructed from front to back as the outer water-stop curtain, when the constructed TRD continuous wall reaches a certain number of days, the three-axis mixing pile is constructed from front to back at the base outside the TRD continuous wall to strengthen the bearing capacity of the base, when the constructed three-axis mixing pile reaches a certain length along the line, the cast-in-place pile is constructed from front to back at the inside of the TRD continuous wall to enhance the vertical support capacity, when the constructed cast-in-place pile reaches a certain length along the line, the adjacent partition wall one of the TRD continuous wall and the partition wall two opposite to the TRD continuous wall are constructed as the inner water-stop curtain, when the walls around the sub-pit are completed, the top beam and the inner support beam are constructed to transfer the horizontal load, the top beam is arranged at the top of the cast-in-place pile, the partition wall one and the partition wall two, the inner support beam is integrally poured inside the top beam, then the inclined support pile is constructed by using the hole guide, and the inclined support pile is located outside the partition wall two and inclines to support the top beam; at the same time, at the slope, the IMS wall is constructed outside the three-axis mixing pile to stabilize the slope, and the top end of the IMS wall is provided with the slope top beam, and the slope top beam is connected with the top beam of the cast-in-place pile through the inner support beam of the slope.

2. The method for simultaneous construction of segmental combined foundation pit support according to claim 1, characterized in that: If the side line of the foundation pit is close to the subway tunnel, during the construction process, the vertical / horizontal displacement of the subway tunnel, the segment convergence deformation, the differential settlement, the pile displacement of the foundation pit, the deep horizontal displacement of the soil body, the support axial force, the underground water level and the ground settlement are automatically monitored, manual inspection is also carried out, and the specific construction scheme is adjusted according to the feedback.

3. The method according to claim 1, wherein: The depth of the TRD continuous wall is 1.5 times of the depth of the foundation pit, and the TRD continuous wall adopts the channel cutting process.

4. The method for simultaneous construction of segmental combined foundation pit support according to claim 1, characterized in that: The three-axis mixing pile is inserted after the TRD continuous wall is constructed for 7 days.

5. The method for simultaneous construction of segmental combined foundation pit support according to claim 1, characterized in that: When the construction of the three-axis mixing pile in the first sub-pit of each section is completed, the cast-in-place pile is constructed.

6. The method for simultaneous construction of segmental combined foundation pit support according to claim 1, characterized in that: The partition wall one and the partition wall two are formed into continuous water-stopping retaining walls by taking the prestressed concrete pipe pile as the backbone and the flexible pile as the filling, and the partition wall one and the partition wall two are constructed when the construction of the cast-in-place pile in the first two sub-pits in each section is completed.

7. The method of simultaneous construction of a segmental combined foundation pit support according to claim 1, wherein: The cross-sectional size of the inner support beam is set according to the span of the sub-pit, and the larger the span is, the larger the cross-sectional size is.

8. The method of simultaneous construction of a segmental combined foundation pit support according to claim 1, wherein: The inclined support pile adopts the cast-in-place reinforced concrete square pile, and the hole guide is used to assist the construction to avoid disturbing the constructed structure, when the hole guide is used to assist the construction, the depth of the hole guide is 1 / 3 of the length of the inclined support pile, the concrete is poured immediately after the hole guide, and the steel cage is inserted to avoid the collapse of the hole wall.

9. The method of simultaneous construction of a segmental combined foundation pit support according to claim 1, wherein: When the IMS wall is constructed, the mixing pile is constructed first and then the section steel is inserted, the section steel adopts the construction process of inserting and jumping one by one, and the insertion depth of the section steel is more than 90% of the length of the mixing pile.

10. A sectional composite foundation pit support structure, characterized by: For the sideline which needs to be reinforced and has a slope, it is divided into several sub-pits along the line; for each sub-pit, a TRD continuous wall is used as an outer water-stop curtain, a triaxial mixing pile is used outside the TRD continuous wall to strengthen the bearing capacity of the foundation, a cast-in-place pile is used inside the TRD continuous wall to enhance the vertical support capacity, the adjacent surface and the opposite surface of the TRD continuous wall are respectively used as an inner water-stop curtain by using a partition wall one and a partition wall two, a top pressing beam is arranged at the top end of the cast-in-place pile, the partition wall one and the partition wall two, the inside of the top pressing beam is integrally poured with an inner support beam, the top pressing beam and the inner support beam are used to transfer horizontal load, and a diagonal strutting pile is arranged outside the partition wall two and is used to diagonally support the top pressing beam; at the slope, an IMS wall is arranged outside the triaxial mixing pile to stabilize the slope, a slope top pressing beam is arranged at the top end of the IMS wall, and the slope top pressing beam is connected with the top pressing beam at the top end of the cast-in-place pile through a slope inner support beam.

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