Combined foundation pit retaining wall and implementation method

Abstract

This invention discloses a composite foundation pit retaining wall and its implementation method, relating to the field of civil engineering technology. The method includes: constructing a cement-soil wall along the edge of the foundation pit; inserting composite steel sections into the cement-soil wall and constructing a short wall outside the composite steel sections to form an external short wall; rigidly connecting a top ring beam to the top of the composite steel sections and the top of the external short wall, and connecting a support column to one end of the top ring beam; setting support columns and concrete beams connected to the support columns at predetermined intervals to form the composite foundation pit retaining wall; re-constructing the main structural slab and structural load-bearing components based on the composite foundation pit retaining wall, and performing grouting and extraction of the composite steel sections; recovering and repairing the composite steel sections to complete the implementation of the foundation pit retaining wall. This invention can improve the load-bearing capacity of foundation pit retaining walls, expand their application range, and save resources.

Description

TECHNICAL FIELD

[0001] The present application relates to the civil engineering technical field, in particular to a combined foundation pit retaining wall and implementation method. BACKGROUND

[0002] The foundation pit retaining wall generally belongs to a temporary structure, and its use function is not considered after the foundation pit excavation and the underground main structure construction are completed. To reduce the waste amount of the foundation pit engineering, the recyclable retaining wall is an important development direction of the future foundation pit engineering. In the soft soil foundation pit engineering, the H-shaped steel is inserted in the cement soil wall, which is the most common recyclable retaining wall, and the process is also called the steel cement soil wall. The working principle is that the H-shaped steel is used as the main stress core material of the foundation pit retaining wall, the cement soil wall is used as the water stop curtain, and the H-shaped steel is recycled after the completion of the foundation pit. However, the traditional steel cement soil wall has the following defects: (1) the stress core material of the traditional process is generally the independently inserted H-shaped steel, each H-shaped steel can only be rigidly connected at the top through the top ring beam, and the H-shaped steels cannot be rigidly connected below the top ring beam, so the overall stress resistance of the H-shaped steel is poor; (2) the traditional process only relies on the H-shaped steel as the stress core material, and the bearing capacity is much lower than that of the reinforced concrete retaining wall such as the underground continuous wall and the cast-in-place pile, so the traditional process cannot be applied to the deep soft soil foundation pit; (3) the recyclable depth of the H-shaped steel of the traditional process is shallow, especially when the total length of the H-shaped steel exceeds 30 m, the frictional resistance between the H-shaped steel and the cement soil is too large, and it is extremely difficult to start and recycle. The above technical bottlenecks greatly limit the application range of the steel cement soil wall. SUMMARY

[0003] The purpose of the present application is to provide a combined foundation pit retaining wall and implementation method, which can improve the bearing capacity of the foundation pit retaining wall, expand the application range, and save resources.

[0004] To achieve the above purpose, the present application provides the following scheme:

[0005] The present application also provides a combined foundation pit retaining wall implementation method, which comprises:

[0006] Constructing a cement soil wall along the foundation pit boundary line;

[0007] Inserting a combined steel into the cement soil wall and constructing a short wall outside the combined steel to form an external short wall; the combined steel is composed of multiple steels connected by welding or bolts, and a grouting sleeve is placed in the cavity formed by the connection of the steels, and a bottom sealing plate is connected to the bottom of each steel; a grouting hole is formed in the bottom sealing plate;

[0008] Rigidly connecting a top ring beam at the top of the combined steel and the top of the external short wall, and connecting a support column to one end of the top ring beam;

[0009] Support columns and concrete beams connected to the support columns are set according to the set spacing. The concrete beams are connected to the external short wall through reserved steel bars, and the concrete beams pass through the combined steel section to connect the combined steel section and the external short wall to form a combined foundation pit retaining wall.

[0010] Based on the combined foundation pit retaining wall, the main structural slab and structural force transmission components are sequentially back-constructed, and the combined steel is pulled out and grouted. The combined steel is then recovered and repaired, thus completing the implementation of the foundation pit retaining wall.

[0011] Optionally, a retarder is added during the construction of the cement-soil wall.

[0012] Optionally, the embedded length of the combined steel section is not less than 0.8H, and the embedded depth of the external short wall is not more than 0.3H; where H is the excavation depth of the foundation pit.

[0013] Optionally, the formation process of the composite foundation pit retaining wall specifically includes:

[0014] During the excavation process, the exposed cement-soil walls are removed according to the set intervals, and support columns are constructed; all support columns except those connected to the top ring beam are connected to the external short wall through the concrete crossbeam.

[0015] Optionally, based on the composite foundation pit retaining wall, the main structural slab and structural force transmission components are sequentially rebuilt, and the composite steel sections are pulled out and grouted. The composite steel sections are then recovered and repaired to complete the implementation of the foundation pit retaining wall, specifically including:

[0016] Based on the aforementioned composite foundation pit retaining wall, the foundation pit is excavated, and each support and concrete beam is removed sequentially from bottom to top. The main underground structural slabs and structural force transmission components of each layer are then back-constructed to form the underground main structure. After the underground main structure is completed, jacks and cranes are used to lift the composite steel sections. At the same time, grouting is performed using the grouting sleeves during the lifting process. The lifted composite steel sections are then recovered and inspected, thus completing the implementation of the foundation pit retaining wall.

[0017] A composite foundation pit retaining wall includes: an external short wall, a top ring beam, a cement-soil wall, composite steel sections, supporting columns, concrete beams, and reserved reinforcing bars;

[0018] The top of the external short wall is fixed with the top ring beam; one end of the top ring beam is connected to the support column; the combined steel section is set inside the cement-soil wall; the support column is detachably connected to the concrete beam; the concrete beam is detachably connected to the external short wall through the reserved reinforcing bars, and the concrete beam passes through the combined steel section; wherein, the combined steel section is composed of multiple steel sections connected by welding or bolts, and a grouting sleeve is placed in the cavity formed by the connection of each steel section, and a bottom sealing plate is connected to the bottom of each steel section; grouting holes are opened on the bottom sealing plate.

[0019] Optionally, the bottom of each of the steel sections is connected to the bottom sealing plate by welding or bolting; the bottom sealing plate is used to close the area enclosed by the web and flanges of the steel section.

[0020] Optionally, the composite steel profile consists of three steel profiles connected in parallel to form a first cavity and a second cavity; the grouting sleeve is located in the first cavity and / or the second cavity.

[0021] Optionally, the external short wall includes cast-in-place piles, interlocking piles, or diaphragm walls.

[0022] Optionally, the cement-soil wall includes cement-soil mixing piles, channel-cut cement-soil walls, milled deep-mixed cement-soil walls, or jet grouting piles.

[0023] According to specific embodiments provided by the present invention, the present invention discloses the following technical effects:

[0024] This invention discloses a composite foundation pit retaining wall and its implementation method. The method includes backfilling and grouting of the foundation pit using the composite foundation pit retaining wall during the excavation process. The composite foundation pit retaining wall includes an external short wall, a top ring beam, a cement-soil wall, composite steel sections, support columns, concrete beams, and reserved reinforcing bars. In the specific excavation process, the composite foundation pit retaining wall is first constructed in the foundation pit. Then, based on the composite foundation pit retaining wall, the foundation pit is excavated and the main structural slab and structural force transmission components are backfilled. After the foundation pit is excavated, the foundation pit is grouted using the composite steel sections and the grouting sleeves therein. After the composite steel sections are completely pulled out, they are recovered and inspected, completing the implementation and application of the foundation pit retaining wall. This method can improve the load-bearing capacity of the foundation pit retaining wall, expand its application range, and save resources. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 Cross-sectional view of the combined foundation pit retaining wall for the main structural slab of the basement in this invention;

[0027] Figure 2 This is a plan view of AA in this embodiment;

[0028] Figure 3 This is a plan view of BB in this embodiment;

[0029] Figure 4 This is the CC plan view in this embodiment;

[0030] Figure 5 This is the elevation view of the combined steel profile in this embodiment;

[0031] Figure 6 This is the EE plan view in this embodiment;

[0032] Figure 7 This is the FF plan view in this embodiment;

[0033] Figure 8 This is a schematic diagram of the construction of the cement-soil wall in this embodiment;

[0034] Figure 9 This is a schematic diagram of the lowered composite steel section in this embodiment;

[0035] Figure 10 This is a schematic diagram of the construction of the external short wall in this embodiment;

[0036] Figure 11 This is a schematic diagram of the construction top ring beam and the first support in this embodiment;

[0037] Figure 12 This is a schematic diagram showing the excavation of the foundation pit to the bottom in this embodiment;

[0038] Figure 13 This is a complete basement structure diagram completed based on the combined foundation pit retaining wall in this embodiment;

[0039] Figure 14 This is a schematic diagram of the extraction and grouting of the combined steel section in this embodiment;

[0040] Figure 15 This is a schematic diagram of the foundation pit retaining wall after the combined steel section recycling is completed in this embodiment;

[0041] Figure 16 This is a flowchart illustrating the implementation method of the combined foundation pit retaining wall of the present invention.

[0042] Attached symbols:

[0043] 1. External short wall; 2. Composite steel section; 3. Cement-soil wall; 4. Concrete beam; 5. Support column; 6. Reserved steel reinforcement; 7. Grout; 8. Main structural slab; 9. Structural force transmission component; 20. Steel section; 21. Grouting sleeve; 22. Bottom sealing plate; 40. Top ring beam. Detailed Implementation

[0044] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0045] The purpose of this invention is to provide a combined foundation pit retaining wall and its implementation method, which can improve the load-bearing capacity of the foundation pit retaining wall, expand its application scope, and save resources.

[0046] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0047] like Figures 1-16 As shown, this invention provides a composite foundation pit retaining wall, comprising: an external short wall 1, a top ring beam 40, a cement-soil wall 3, a composite steel section 2, a support column 5, a concrete beam 4, and pre-reserved reinforcing bars 6; its relationship with the completed basement structure within the foundation pit is as follows:

[0048] The structure comprises an external short wall 1, a main structural slab 8, a top ring beam 40, and multiple structural force transmission components 9; the top ring beam 40 is fixed to the top of the external short wall 1; the main structural slab 8 is fixedly connected to the external short wall 1 through each of the structural force transmission components 9; one end of one of the structural force transmission components 9 is connected to the top of the main structural slab 8, and the other end is fixedly connected to the top ring beam 40; the main structural slab 8 and each of the structural force transmission components 9 are constructed by backfilling and grouting using a combined foundation pit retaining wall.

[0049] The combined steel section 2 is installed inside the cement-soil wall 3; each of the supporting columns 5 is detachably connected to the concrete beam 4; the concrete beam 4 is detachably connected to the external short wall 1 through the reserved reinforcing bars 6, and the concrete beam 4 passes through the combined steel section 2; wherein, the combined steel section 2 is composed of multiple steel sections 20 connected by welding or bolts, and a grouting sleeve 21 is placed in the cavity formed by the connection of each steel section 20, and a bottom sealing plate 22 is connected to the bottom of each steel section 20; the bottom sealing plate 22 is provided with grouting holes.

[0050] In this embodiment, the bottom of each of the steel sections 20 is connected to the bottom sealing plate 22 by welding or bolts; the bottom sealing plate 22 is used to enclose the area enclosed by the web and flange of the steel section 20. The composite steel section 2 consists of three sections, connected in parallel to form a first cavity and a second cavity; the grouting sleeve 21 is located within the first cavity and / or the second cavity. The external short wall 1 includes cast-in-place piles, interlocking piles, or diaphragm walls; the cement-soil wall 3 includes cement-soil mixing piles, channel-cut cement-soil walls 3, milled deep-mixed cement-soil walls 3, or jet grouting piles type cement-soil walls 3.

[0051] Based on the above technical solution, the following embodiments are provided:

[0052] The composite foundation pit retaining wall is mainly constructed by backfilling and grouting using cement-soil wall 3, composite steel section 2, external short wall 1, top ring beam 40, concrete crossbeam 4, and structural force transmission component 9.

[0053] The cement-soil wall 3 can be a cement-soil mixing pile, a channel-cut cement-soil wall, a milled deep-mix cement-soil wall, or a jet grouting pile type cement-soil wall. The cement-soil wall 3 is arranged along the excavation edge of the foundation pit. A retarder is added to the cement-soil wall 3 during mixing.

[0054] The composite steel section 2 is arranged inside the cement-soil wall 3. The composite steel section 2 includes steel section 20, grouting sleeve 21, and bottom sealing plate 22. In this embodiment, the steel section 20 is an H-beam, with multiple H-beams arranged side-by-side to form a composite steel section 2. The flanges of each H-beam are connected by welding or bolts to form a whole, and the bottom of the H-beam is V-shaped. The bottom sealing plate 22 is a V-shaped steel plate, located at the bottom of the composite steel section 2, enclosing the area enclosed by the web and flanges of the H-beam. The grouting sleeve 21 is arranged vertically along the web of the H-beam, and its bottom passes through the bottom sealing plate 22. A lubricating and friction-reducing agent is applied to the outer surface of the composite steel section 2. The embedded length of the composite steel section 2 is not less than 0.8H (H is the excavation depth of the foundation pit, i.e., the sum of the height of the external short wall and the height of the top ring beam).

[0055] The external short wall 1 can be a cast-in-place pile, an interlocking pile, or a diaphragm wall. The external short wall 1 is located outside the cement-soil wall 3 and is arranged closely to the cement-soil wall 3. The embedment depth of the external short wall 1 is no more than 0.3H (H is the excavation depth of the foundation pit). Furthermore, the top ring beam 40 is set on top of the external short wall 1 and the composite steel section 2.

[0056] The concrete beam 4 is installed inside the foundation pit. The concrete beam 4 is connected to the external short wall 1 through the reserved steel bars 6. The concrete beam 4 passes through the composite steel section 2, connecting the composite steel section 2 and the external short wall 1 to form a whole.

[0057] The structural force transmission component 9 is a reinforced concrete structure, with one end connected to the main structural slab 8 of the basement and the other end connected to the external short wall 1. The structural force transmission component 9 and the composite steel section 2 are arranged alternately in the plane. The grouting during the pull-out is cement grout or two-component grout. When the composite steel section 2 is pulled out, grouting is simultaneously performed on the lower part of the sealing plate 22 through the grouting sleeve 21.

[0058] The overall implementation process is as follows:

[0059] (1) Construct cement-soil wall 3 along the edge of the foundation pit, and add retarder to cement-soil wall 3.

[0060] (2) Insert the composite steel section 2 into the cement-soil wall 3, and then construct the external short wall 1. The embedded length of the composite steel section 2 shall not be less than 0.8H, and the embedded depth of the external short wall 1 shall not be more than 0.3H.

[0061] (3) Excavate the foundation pit, construct the top ring beam 40 and the first support, and rigidly connect the top ring beam 40 with the external short wall 1 and the combined steel section 2.

[0062] (4) Continue to excavate downwards, remove the exposed cement-soil wall 3, construct the next support and concrete beam 4, the concrete beam 4 is connected to the external short wall 1 through the reserved steel bar 6, the concrete beam 4 passes through the composite steel section 2, and the concrete beam 4 connects the composite steel section 2 and the external short wall 1 to form a whole.

[0063] (5) Continue excavating downwards, repeating step (4) until the bottom of the pit is reached.

[0064] (6) Construct the lowest underground main structure slab 8 and structural force transmission components 9.

[0065] (7) Remove each support and concrete beam 4 from bottom to top, and rebuild the underground main structure slab 8 and structural force transmission components 9 on each floor.

[0066] (8) After the underground main structure is completed, jacks and cranes are used to lift the combined steel section 2. At the same time, grouting is carried out by grouting sleeve 21. The lifting and grouting pressure acts upward on the bottom plate 22, which not only helps to lift the combined steel section 2, but also fills the gap left after the combined steel section 2 is lifted with grout 7.

[0067] (9) The recovered combined steel section 2 is repaired and then applied to the next foundation pit project.

[0068] like Figures 1-16 As shown, the present invention also provides a method for implementing a combined foundation pit retaining wall, comprising:

[0069] Step 100: Construct a cement-soil wall 3 along the edge of the foundation pit. A retarder is added during the construction of the cement-soil wall 3.

[0070] Step 200: Insert the combined steel section 2 into the cement-soil wall 3, and construct a short wall on the outside of the combined steel section 2 to form an external short wall 1; the combined steel section 2 is composed of multiple steel sections connected by welding or bolts, and a grouting sleeve 21 is placed in the cavity formed by the connection of each steel section, and a bottom sealing plate 22 is connected to the bottom of each steel section; grouting holes are opened on the bottom sealing plate 22.

[0071] Step 300: A top ring beam 40 is rigidly connected to the top of the combined steel section 2 and the top of the external short wall 1, and a support column 5 is connected to one end of the top ring beam 40.

[0072] Step 400: Set up support columns 5 and concrete beams 4 connected to the support columns 5 according to the set spacing; the concrete beams 4 are connected to the external short wall 1 through the reserved steel bars 6, and the concrete beams 4 pass through the combined steel section 2, connecting the combined steel section 2 and the external short wall 1 to form a combined foundation pit retaining wall.

[0073] Specifically, the following steps are included:

[0074] During the excavation process, the exposed cement-soil wall 3 is removed according to the set spacing, and support columns 5 are constructed; all support columns 5 except those connected to the top ring beam 40 are connected to the external short wall 1 through the concrete crossbeam 4.

[0075] Step 500: Based on the combined foundation pit retaining wall, the main structural plate 8 and structural force transmission component 9 are rebuilt in sequence, and the combined steel section 2 is pulled out and grouted. The combined steel section 2 is then recovered and repaired to complete the implementation of the foundation pit retaining wall.

[0076] Specifically, the following steps are included:

[0077] Based on the combined foundation pit retaining wall, the foundation pit is excavated and each support and concrete beam 4 is removed sequentially from bottom to top. The main underground structural slabs 8 and structural force transmission components 9 are then back-constructed to form the underground main structure. After the underground main structure is completed, jacks and cranes are used to lift the combined steel section 2. At the same time, the grouting sleeve 21 is used for lifting and grouting. The lifted combined steel section 2 is then recovered and inspected to complete the implementation of the foundation pit retaining wall.

[0078] In this embodiment, the embedded length of the combined steel section 2 is not less than 0.8H, and the embedded depth of the external short wall 1 is not more than 0.3H; where H is the excavation depth of the foundation pit.

[0079] Based on the above technical solution, taking a project with a four-story underground structure and an excavation depth of 20m as an example:

[0080] (1) Construct an 800mm thick channel-type cutting cement-soil mixing wall along the edge of the foundation pit, and add a retarder to the cement-soil wall 3.

[0081] (2) Three H700x300x13x24 steel sections are used to form a composite steel section 2. The composite steel section 2 is inserted into the cement-soil wall 3, with a clear plane spacing of 500mm. Then, a 600mm thick underground continuous wall external short wall 1 is constructed. The embedment depth of the composite steel section 2 is 25m, and the embedment depth of the external short wall 1 is 5m.

[0082] (3) Excavate the foundation pit, construct the top ring beam 40 and the first support, and rigidly connect the top ring beam 40 with the external short wall 1 and the combined steel section 2.

[0083] (4) Continue excavating downwards to the bottom of the second support, remove the exposed cement-soil wall 3, construct the second support and concrete beam 4, the concrete beam 4 is connected to the external short wall 1 through the reserved steel bar 6, the concrete beam 4 passes through the composite steel section 2, and the concrete beam 4 connects the composite steel section 2 and the external short wall 1 to form a whole.

[0084] (5) Continue to excavate downwards, repeating step (4), and set up a total of four supports until the bottom of the pit is reached.

[0085] (6) Construct the lowest underground main structure slab 8 and structural force transmission components 9.

[0086] (7) Remove each support and concrete beam 4 from bottom to top, and rebuild the underground main structure slab 8 and structural force transmission components 9 on each floor.

[0087] (8) After the underground main structure is completed, the combined steel section 2 is lifted by jacks and cranes, and grouting is carried out by grouting sleeve 21. Grouting is filled with grout 7, and the grouting pressure of a single hole is not less than 2MPa.

[0088] (9) The recovered combined steel section 2 is repaired and then applied to the next foundation pit project.

[0089] As can be seen from the above embodiments, the following differences exist compared to existing processes:

[0090] (1) Recyclable steel profiles are modular, not single pieces but multiple pieces spliced ​​together to bear the load as a whole.

[0091] (2) The bottom of the steel section is sealed. After the composite steel section is inserted into the cement soil, the cement soil will not enter the interior of the steel section, reducing the lifting resistance. At the same time, the exposed cement soil is broken up while the foundation pit is being excavated, which can reduce the resistance of the cement soil above the bottom of the pit when the steel section is lifted.

[0092] (3) Grouting during the pulling process can reduce the difficulty of pulling out the steel section by using the grouting pressure, and can also quickly fill the voids in the cement-soil after pulling out. Existing technologies all perform grouting after the steel section is completely pulled out, but this embodiment performs grouting while pulling out. Sealing the bottom plate + pulling out grouting + breaking the cement-soil above the bottom of the pit allows this embodiment to recover longer steel sections.

[0093] (4) Key differences between this embodiment and previous similar combinations. Previous similar technologies, such as double-row pile support structures, only allow for rigid connection between the front and rear rows of retaining piles via a top ring beam at the top of the piles. Below the top ring beam, rigid connection is not possible. In the deeper lower sections, the front and rear rows of piles bear loads independently, resulting in poor overall integrity and low bearing capacity. In contrast, this embodiment uses a steel-cement-soil wall in front and a reinforced concrete short wall on the outside. During excavation, the exposed cement-soil in the front row can be removed, and the steel section can be directly connected using a concrete beam to encase the steel section. This results in stronger overall integrity between the front steel section and the rear short wall.

[0094] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0095] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the core ideas of the present invention. Furthermore, those skilled in the art will recognize that, based on the ideas of the present invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A method for implementing a combined foundation pit retaining wall, characterized in that, include: Construct a cement-soil wall along the edge of the foundation pit (3); The composite steel section (2) is inserted into the cement-soil wall (3), and a short wall is constructed on the outside of the composite steel section (2) to form an external short wall (1); the composite steel section (2) is composed of multiple steel sections (20) connected by welding or bolts, and a grouting sleeve (21) is placed in the cavity formed by the connection of each steel section (20), and a bottom sealing plate (22) is connected to the bottom of each steel section (20); grouting holes are opened on the bottom sealing plate (22); A top ring beam (40) is rigidly connected to the top of the combined steel section (2) and the top of the external short wall (1), and a support column (5) is connected to one end of the top ring beam (40). Support columns (5) and concrete beams (4) connected to the support columns (5) are set according to the set spacing; the concrete beams (4) are connected to the external short wall (1) through the reserved steel bars (6), and the concrete beams (4) pass through the combined steel section (2) to connect the combined steel section (2) and the external short wall (1) to form a combined foundation pit retaining wall; during the excavation process, the exposed cement soil wall (3) is removed according to the set spacing, and support columns (5) are constructed; all support columns (5) except the support columns (5) connected to the top ring beam (40) are connected to the external short wall (1) through the concrete beams (4); Based on the combined foundation pit retaining wall, the main structural slab (8) and structural force transmission components (9) are sequentially back-constructed, and the combined steel section (2) is pulled out and grouted, and the combined steel section (2) is recovered and repaired to complete the implementation of the foundation pit retaining wall.

2. The method for implementing the combined foundation pit retaining wall according to claim 1, characterized in that, The cement-soil wall (3) is constructed with a retarder.

3. The method for implementing the combined foundation pit retaining wall according to claim 1, characterized in that, The embedded length of the combined steel section (2) is not less than 0.8H, and the embedded depth of the external short wall (1) is not more than 0.3H; where H is the excavation depth of the foundation pit.

4. The method for implementing the combined foundation pit retaining wall according to claim 1, characterized in that, Based on the combined foundation pit retaining wall, the main structural slab (8) and structural force transmission components (9) are sequentially back-constructed, and the combined steel section (2) is pulled out and grouted. The combined steel section (2) is then recovered and repaired to complete the implementation of the foundation pit retaining wall, specifically including: Based on the combined foundation pit retaining wall, the foundation pit is excavated and each support and concrete beam (4) is removed from bottom to top. The main structure slab (8) and structural force transmission components (9) of each underground layer are then back-constructed to form the underground main structure. After the underground main structure is completed, the combined steel section (2) is lifted using jacks and cranes. At the same time, the grouting sleeve (21) is used for lifting and grouting. The combined steel section (2) after lifting is then recovered and inspected to complete the implementation of the foundation pit retaining wall.

5. A composite foundation pit retaining wall, characterized in that, include: External short wall (1), top ring beam (40), cement-soil wall (3), composite steel section (2), support column (5), concrete beam (4) and reserved steel bar (6); The top of the external short wall (1) is fixed with the top ring beam (40); one end of the top ring beam (40) is connected to the support column (5); the combined steel section (2) is set inside the cement-soil wall (3); the support column (5) is detachably connected to the concrete beam (4); during the excavation process, the exposed cement-soil wall (3) is removed according to the set interval, and the support column (5) is constructed; all support columns (5) except the support column (5) connected to the top ring beam (40) are connected through the concrete beam (4). The concrete beam (4) is detachably connected to the external short wall (1) via the reserved reinforcing bar (6), and the concrete beam (4) passes through the combined steel section (2); wherein the combined steel section (2) is composed of multiple steel sections (20) connected by welding or bolts, and a grouting sleeve (21) is placed in the cavity formed by the connection of each steel section (20), and a bottom sealing plate (22) is connected to the bottom of each steel section (20); grouting holes are provided on the bottom sealing plate (22).

6. The combined foundation pit retaining wall according to claim 5, characterized in that, The bottom of each of the steel sections (20) is connected to the bottom plate (22) by welding or bolting; the bottom plate (22) is used to close the area enclosed by the web and flange of the steel section (20).

7. The combined foundation pit retaining wall according to claim 5, characterized in that, The combined steel section (2) consists of three steel sections (20), which are connected in parallel to form a first cavity and a second cavity; the grouting sleeve (21) is located in the first cavity and / or the second cavity.

8. The combined foundation pit retaining wall according to claim 5, characterized in that, The external short wall (1) includes cast-in-place piles, interlocking piles, or diaphragm walls.

9. The combined foundation pit retaining wall according to claim 5, characterized in that, The cement-soil wall (3) includes cement-soil mixing piles, channel-type cutting cement-soil walls, milled deep mixing cement-soil walls, or jet grouting piles.

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