Foundation pit support structure under weathered rock geological layer limited space and construction method of foundation pit support structure

Abstract

The invention discloses a foundation pit support structure under a weathered rock geological layer limited space and a construction method of the foundation pit support structure. The construction method comprises the steps that Larsen steel sheet piles are provided; a foundation pit support hole is formed through hole guiding construction; backfill material filling construction is conducted, specifically, the backfill material below the excavation bottom line of the foundation pit is cement mortar doped with fibers, and the backfill material above the excavation bottom line of the foundation pit is undisturbed soil taken out through hole guiding construction; the Larsen steel sheet piles are inserted, the two sides of the Larsen steel sheet piles are embedded and fixed through the backfill materials below the excavation bottom line of the foundation pit, and the two sides of the Larsen steel sheet piles are extruded and fixed through the backfill materials above the excavation bottom line of the foundation pit; the horizontal waterproof curtain is formed by pressurizing and grouting through the grouting pipes on the Larsen steel sheet piles, and the foundation pit support structure of the plate wall waterproof composite structure is formed through the foundation pit support holes, the backfill materials, the Larsen steel sheet piles and the waterproof curtain. The foundation pit support structure can be constructed under the condition that the operation space is limited, and the method has the advantages of being good in water stopping effect and high in safety.

Description

Technical Field

[0001] The invention relates to the technical field of foundation pit retaining engineering, and in particular to a foundation pit retaining structure in a confined space of a weathered rock geological layer and a construction method thereof. Background Art

[0002] In traditional underground engineering construction, deep foundation pit construction requires the construction of supporting structures such as retaining structures and supports first, and then slope excavation. In the construction of deep foundation pits adjacent to existing structures, it is necessary to consider both the safety of the foundation pit construction process in this section and the impact of foundation pit excavation on the safety of existing structures. When the distance between the foundation pit in this section and the adjacent existing structure is close, the deep foundation pit construction in this section does not have enough operating space for support and slope excavation construction. Due to the small net spacing between engineering piles such as bored cast-in-place piles, there is no operating space for engineering piles with larger diameters to construct retaining piles as foundation pit retaining structures. Therefore, how to construct foundation pit retaining structures under the condition of limited operating space due to the small distance from the adjacent existing structure has become an urgent problem in this field. Summary of the invention

[0003] The purpose of the present invention is to provide a foundation pit retaining structure and a construction method thereof in a confined space of a weathered rock geological layer, so as to solve the problem that the foundation pit retaining structure cannot be constructed under the condition of limited operating space due to a small distance from adjacent existing structures.

[0004] In order to solve the above technical problems, the present invention provides a construction method of a foundation pit retaining structure in a confined space of a weathered rock geological layer, comprising:

[0005] Provide Larsen steel sheet piles with grouting pipes installed, so that the grouting pipes are distributed on both sides of the Larsen steel sheet piles;

[0006] The foundation pit retaining holes are formed by conducting guide hole construction downward through the weathered rock geological layer along the foundation pit edge;

[0007] The backfill material is filled in the foundation pit retaining hole. The backfill material below the bottom line of the foundation pit excavation is cement mortar mixed with fiber, and the backfill material above the bottom line of the foundation pit excavation is the original soil taken out during the hole construction.

[0008] Insert Larsen steel sheet piles with grouting pipes installed on both sides into the backfill material to the bottom of the foundation pit retaining hole, so that the backfill material is distributed on both sides of the Larsen steel sheet piles, and the Larsen steel sheet piles are embedded on both sides through the backfill material below the bottom line of the foundation pit excavation, and the Larsen steel sheet piles are squeezed and fixed on both sides through the backfill material above the bottom line of the foundation pit excavation;

[0009] Pressurized grouting is carried out from the water-facing surface to the water-receiving surface of the Larsen steel sheet pile through the grouting pipe to form a horizontal water-stop curtain in the soil layer below the bottom of the foundation pit retaining hole. The foundation pit retaining structure of a plate-wall water-stop composite structure is formed by the foundation pit retaining hole, backfill materials, Larsen steel sheet piles and the water-stop curtain.

[0010] Furthermore, the present invention provides a method for constructing a foundation pit retaining structure in a confined space of a weathered rock geological layer, which uses a rotary drilling rig or a drill to drill holes through the weathered rock geological layer on the foundation pit edge line to take soil and perform hole construction to form a foundation pit retaining hole.

[0011] Furthermore, the construction method of the foundation pit retaining structure in the confined space of the weathered rock geological layer provided by the present invention comprises: before inserting the Larsen steel sheet pile, a plurality of horizontal steel bars are vertically welded at intervals on the concave surface of the Larsen steel sheet pile, and the horizontal steel bars of the adjacent concave surfaces on the inner and outer sides of the Larsen steel sheet pile are staggered.

[0012] Furthermore, the construction method of the foundation pit retaining structure in the confined space of the weathered rock geological layer provided by the present invention adopts cement and yellow sand in a 1:1 ratio, and adds 1% of fiber to form a cement mortar doped with fiber.

[0013] Furthermore, the construction method of the foundation pit retaining structure in the confined space of the weathered rock geological layer provided by the present invention adopts cement-based permeable crystallized cement slurry to perform pressure grouting from the water-facing surface to the water-retaining surface of the Larsen steel sheet pile through a grouting pipe.

[0014] Furthermore, the present invention provides a construction method for a foundation pit retaining structure in a confined space of a weathered rock geological layer, in which foundation pit retaining holes, backfill materials, Larsen steel sheet piles, and a horizontal water-stop curtain are constructed in sections along the foundation pit edge.

[0015] In order to solve the above technical problems, the present invention also provides a foundation pit retaining structure in a confined space of a weathered rock geological layer, comprising a foundation pit retaining hole constructed along the foundation pit edge downward through the weathered rock geological layer, Larsen steel sheet piles inserted in the foundation pit retaining hole, backfill materials filled in the foundation pit retaining hole and distributed on both sides of the Larsen steel sheet piles, the backfill materials located below the bottom line of the foundation pit excavation are embedded ends formed by embedding Larsen steel sheet piles on both sides with cement mortar doped with fibers, the backfill materials located above the bottom line of the foundation pit excavation are free ends formed by extruding and fixing Larsen steel sheet piles on both sides with original soil, a grouting pipe is inserted into the foundation pit retaining hole to perform pressurized grouting from the water-facing surface to the water-receiving surface of the Larsen steel sheet pile to form a horizontal water-stop curtain in the soil layer below the bottom of the foundation pit retaining hole, the foundation pit retaining hole, backfill materials, Larsen steel sheet piles and horizontal water-stop curtain form a board wall water-stop composite structure.

[0016] Furthermore, in the foundation pit retaining structure in a confined space of a weathered rock geological layer provided by the present invention, a plurality of horizontal steel bars are vertically welded at intervals on each concave surface of the Larsen steel sheet pile.

[0017] Furthermore, in the foundation pit retaining structure in a confined space of a weathered rock geological layer provided by the present invention, the horizontal steel bars of adjacent concave surfaces on both sides of the Larsen steel sheet piles are staggered.

[0018] Furthermore, in the foundation pit retaining structure in a confined space of a weathered rock geological layer provided by the present invention, grouting pipes are provided along the height of at least part of the concave surfaces on both inner and outer sides of the Larsen steel sheet piles.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] The invention provides a foundation pit retaining structure in a limited space of a weathered rock geological layer and a construction method thereof. A foundation pit retaining hole is formed by hole construction, backfill material is filled in the foundation pit retaining hole and Larsen steel sheet piles are inserted therein, and the backfill material located below the bottom line of foundation pit excavation is cement mortar doped with fiber to embed the Larsen steel sheet piles on both sides, so as to improve the deformation resistance of the Larsen steel sheet piles; the backfill material located above the bottom line of foundation pit excavation is original soil to squeeze and fix the Larsen steel sheet piles on both sides, so as to prevent the Larsen steel sheet piles from being offset or deformed due to the disturbance of the original soil by the hole in the adjacent section or due to collision and the like; a board-wall composite structure is formed by the backfill material in the foundation pit retaining hole and the Larsen steel sheet piles, so that the Larsen steel sheet piles are sunk and stably fixed in the foundation pit retaining hole, thereby enhancing the stability of the foundation pit retaining structure and ensuring the safety of the foundation pit under stress; and the problem that the foundation pit retaining structure cannot be constructed under the condition that the operating space is limited due to a small distance from the adjacent existing structure is solved. The fibers in the cement mortar can solidify with groundwater to stabilize the Larsen steel sheet piles. At the same time, the fibers can enhance toughness, improve the strength of the early solidified body, and effectively transfer and disperse stress, thereby reducing the generation and expansion of cracks.

[0021] The foundation pit retaining structure and construction method thereof provided by the present invention in a confined space of a weathered rock geological layer can prevent groundwater from penetrating above the bottom line of the foundation pit excavation by constructing a horizontal water-stopping curtain at the bottom of the foundation pit retaining hole, and the backfill material located below the bottom line of the foundation pit excavation is a cement mortar doped with fiber to embed Larsen steel sheet piles on both sides to form a vertical water-stopping curtain located on both sides of the Larsen steel sheet piles, thereby solving the problem of groundwater leakage in the retaining system due to construction reasons, and providing high-quality conditions for the construction of the later basement structure. The foundation pit retaining structure of the board-wall water-stopping composite structure is formed by the foundation pit retaining hole, backfill material, Larsen steel sheet pile and water-stopping curtain, which improves the stress performance of the foundation pit retaining structure and improves the three-sided water-stopping effect of the foundation pit retaining structure.

[0022] The foundation pit retaining structure and construction method thereof in a confined space of a weathered rock geological layer provided by the present invention can solve the problem of deep foundation pit retaining projects that are unable to carry out traditional support and slope excavation in a confined operating space, and can complete the construction of a high-strength, low-deformation foundation pit retaining structure system in a relatively short period of time, thereby avoiding the risk of collapse caused by the foundation pit being exposed due to the lack of a retaining structure for a long time. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a flow chart of the construction method of the foundation pit retaining structure in the confined space of the weathered rock geological layer;

[0024] Figure 2 It is a schematic diagram of the plan structure of Larsen steel sheet piles provided with grouting pipes and horizontal steel bars;

[0025] Figure 3 It is a schematic diagram of the plane structure of the foundation pit retaining hole;

[0026] Figure 4 It is a schematic diagram of the plane structure of filling the backfill material in the foundation pit retaining space;

[0027] Figure 5 It is a schematic diagram of the plan structure of the foundation pit retaining structure in the confined space of the weathered rock geological layer;

[0028] Figure 6 yes Figure 5 Schematic diagram of the cross-sectional structure at AA in the middle;

[0029] Figure 7 yes Figure 5 Schematic diagram of the cross-sectional structure at BB in the middle;

[0030] As shown in the figure:

[0031] 100. Foundation pit retaining structure; 110. Foundation pit retaining hole; 111. Foundation pit excavation bottom line; 120. Backfill material; 121. Free end; 122. Embedded end; 130. Larsen steel sheet pile; 131. Grouting pipe; 132. Horizontal steel bar; 140. Horizontal water-stop curtain. DETAILED DESCRIPTION

[0032] The present invention is described in detail below in conjunction with the accompanying drawings: The advantages and features of the present invention will become more apparent from the following description. It should be noted that the accompanying drawings are in very simplified form and in non-precise proportions, and are only used to conveniently and clearly assist in explaining the purpose of the embodiments of the present invention.

[0033] Please refer to Figures 5 to 7The embodiment of the present invention provides a foundation pit retaining structure 100 in a confined space of a weathered rock geological layer, comprising a foundation pit retaining hole 110 constructed along the foundation pit edge and downwardly through the weathered rock geological layer, a Larsen steel sheet pile 130 inserted into the foundation pit retaining hole 110, and backfill materials 120 distributed on both sides of the Larsen steel sheet pile 130 filled in the foundation pit retaining hole 110. The backfill materials 120 located below the bottom line of the foundation pit excavation are cement mortar doped with fibers to form an embedded end 120 formed by embedding the Larsen steel sheet pile 130 on both sides. 2. The backfill material 120 located above the bottom line of the foundation pit excavation is a free end 121 formed by double-sided extrusion and fixing of the Larsen steel sheet pile 130 with the original soil. The grouting pipe 131 is inserted into the foundation pit retaining hole 110 to perform pressure grouting from the water-facing surface to the water-receiving surface of the Larsen steel sheet pile 130 to form a horizontal water-stop curtain 140 in the soil layer below the bottom of the foundation pit retaining hole 110. The foundation pit retaining hole 110, the backfill material 120, the Larsen steel sheet pile 130 and the horizontal water-stop curtain 140 form a board-wall water-stop composite structure.

[0034] Please refer to Figure 5 In the foundation pit retaining structure 100 in a confined space of a weathered rock geological layer provided by an embodiment of the present invention, a plurality of horizontal steel bars 132 are welded vertically at intervals on each concave surface of the Larsen steel sheet pile 130. In order to improve the fixing effect with the backfill material, each horizontal steel bar 132 on each concave surface can be in two parallel rows, wherein the horizontal steel bars 132 can be welded with discarded steel bar heads at the construction site, which meets the "material saving" requirements of green construction, reduces a large amount of scrap steel processing, and promotes the recycling of resources. Alternatively, the horizontal steel bars 132 can be replaced with bolts to improve the fixing effect between the Larsen steel sheet pile 130 and the backfill material 120. In order to improve the effect of balanced fixing, the horizontal steel bars 132 of adjacent concave surfaces on the inner and outer sides of the Larsen steel sheet pile 130 can be staggered.

[0035] Please refer to Figure 5 In order to construct a horizontal water-stop curtain 140 in the soil layer not below the bottom of the foundation pit retaining hole 110, the foundation pit retaining structure 100 in the confined space of the weathered rock geological layer provided by an embodiment of the present invention has a grouting pipe 131 arranged on at least part of the concave surface on both sides of the inner and outer sides of the Larsen steel sheet pile 130 along its height.

[0036] Please refer to Figures 1 to 7 The embodiment of the present invention provides a construction method of a foundation pit retaining structure 100 in a confined space of a weathered rock geological layer, which may include the following steps:

[0037] Step 201: Provide a Larsen steel sheet pile 130 with a grouting pipe 131 installed, so that the grouting pipe 131 is distributed on both sides of the Larsen steel sheet pile 130. The grouting pipe 131 can be installed in at least a portion of the concave surface of the Larsen steel sheet pile 130.

[0038] Step 202: boring down through hard geological layers such as weathered rock geological layers along the foundation pit edge to form foundation pit retaining holes 110. To improve construction progress, a rotary drilling machine or a drill rig can be used on the foundation pit edge to drill through the weathered rock geological layers to take soil for boring to form foundation pit retaining holes 110.

[0039] Step 203, backfill material 120 is filled in the foundation pit retaining hole 110, wherein the backfill material 120 below the foundation pit excavation bottom line is cement mortar mixed with fiber, and the backfill material 120 above the foundation pit excavation bottom line is the original soil taken out during the hole construction. The backfill material 120 can ensure the safety of the foundation pit construction process of this bid section and the stability of the existing structure of the adjacent bid section.

[0040] Step 204, inserting a Larsen steel sheet pile 130 with grouting pipes 131 installed on both sides into the backfill material 120 to the bottom of the foundation pit retaining hole 110, so that the backfill material 120 is distributed on both sides of the Larsen steel sheet pile 130, and the Larsen steel sheet pile 130 is embedded on both sides by the backfill material 120 below the bottom line of the foundation pit excavation, where an embedded end 122 is formed, and the stability, reliability and firmness of the Larsen steel sheet pile 130 are improved by the embedded end 122. Cement and yellow sand can be mixed in a ratio of 1:1, and 1% of fiber can be added to form a cement mortar doped with fiber, wherein the embedded end 122 is located at or passes through the medium-weathered mixed rock layer or the strongly weathered mixed rock layer; the Larsen steel sheet pile 130 is extruded and fixed on both sides by the backfill material 120 above the bottom line of the foundation pit excavation, where a free end 121 is formed. Before inserting the Larsen steel sheet pile 130, multiple horizontal steel bars 132 can be welded vertically and spaced apart on the concave surface of the Larsen steel sheet pile 130, and the horizontal steel bars 132 of adjacent concave surfaces on both sides of the Larsen steel sheet pile 130 are staggered and distributed, for example, staggered and evenly distributed by 50%. The horizontal steel bars 132 are used to enhance the contact surface with the backfill material 120, reduce lateral displacement, and improve the fixing effect of the Larsen steel sheet pile 130.

[0041] Step 205: Perform pressure grouting from the water-facing surface to the water-retaining surface of the Larsen steel sheet pile 130 through the grouting pipe 131, form a horizontal water-stop curtain 140 in the soil layer below the bottom of the foundation pit retaining hole 110, and form a foundation pit retaining structure 100 of a board-wall water-stopping composite structure through the foundation pit retaining hole 110, backfill material 120, Larsen steel sheet pile 130 and the water-stop curtain. Cement-based permeable crystallized cement slurry can be used to perform pressure grouting from the water-facing surface to the water-retaining surface of the Larsen steel sheet pile 130 through the grouting pipe 131, fill the pores and crack channels by pressure, and form a horizontal water-stop curtain 140.

[0042] In order to ensure construction safety and foundation pit stability, an embodiment of the present invention provides a construction method for a foundation pit retaining structure 100 in a confined space of a weathered rock geological layer. The foundation pit retaining holes 110, backfill materials 120, Larsen steel sheet piles 130, and horizontal water-stop curtains 140 are constructed in sections along the foundation pit edge, for example: 5m each section.

[0043] The embodiment of the present invention provides a foundation pit retaining structure 100 and a construction method thereof in a confined space of a weathered rock geological layer. A foundation pit retaining hole 110 is formed by hole construction. A backfill material 120 is filled in the foundation pit retaining hole 110 and a Larsen steel sheet pile 130 is inserted therein. The backfill material 120 located below the bottom line of the foundation pit excavation is cement mortar doped with fiber to embed the Larsen steel sheet pile 130 on both sides to improve the anti-deformation capacity of the Larsen steel sheet pile 130. The backfill material 120 located above the bottom line of the foundation pit excavation is original soil to embed the Larsen steel sheet pile 130 on both sides. The pile 130 is fixed by extrusion on both sides to prevent the Larsen steel sheet pile 130 from being offset or deformed due to the disturbance of the original soil by the adjacent section of the lead hole or due to collision. The Larsen steel sheet pile 130 is sunk and stably fixed in the foundation pit retaining hole 110 through the backfill material 120 in the foundation pit retaining hole 110 and the Larsen steel sheet pile 130, thereby strengthening the stability of the retaining system and ensuring the safety of the foundation pit. The problem of being unable to construct the foundation pit retaining structure 100 under the condition of limited operating space due to the small distance from the adjacent existing structure is solved. The fibers in the cement mortar can solidify together with the groundwater to stabilize the Larsen steel sheet pile 130. At the same time, the fibers can enhance the toughness, improve the strength of the early solidified body, and effectively transmit and disperse stress, thereby reducing the generation and expansion of cracks.

[0044] The foundation pit retaining structure 100 and the construction method thereof provided in the weathered rock geological layer confined space provided by the embodiment of the present invention can prevent groundwater from penetrating above the bottom line of the foundation pit excavation by constructing a horizontal water-stopping curtain 140 at the bottom of the foundation pit retaining hole 110, and the backfill material 120 located below the bottom line of the foundation pit excavation is cement mortar doped with fiber to embed Larsen steel sheet piles 130 on both sides to form vertical water-stopping curtains located on both sides of the Larsen steel sheet piles 130, thereby solving the problem of groundwater leakage in the retaining system due to construction reasons, and providing high-quality conditions for the construction of the later basement structure. The foundation pit retaining structure 100 of the board-wall water-stopping composite structure formed by the foundation pit retaining hole 110, the backfill material 120, the Larsen steel sheet pile 130 and the water-stopping curtain improves the stress performance of the foundation pit retaining structure 100 and improves the three-sided water-stopping effect of the foundation pit retaining structure 100.

[0045] The foundation pit retaining structure 100 and the construction method thereof in the confined space of the weathered rock geological layer provided in the embodiment of the present invention can solve the deep foundation pit retaining project in which traditional support and slope excavation are not possible in the confined operating space, and can complete the construction of a high-strength, low-deformation foundation pit retaining structure 100 system in a relatively short time, thereby avoiding the risk of collapse caused by the foundation pit being exposed for a long time without a retaining structure.

[0046] The foundation pit retaining structure 100 and its construction method in the confined space of the weathered rock geological layer provided by the embodiment of the present invention can solve the difficulty of the foundation pit retaining structure 100 in the complex geological environment to go deep into the geological layer for construction, can ensure the smooth construction of underground projects, and ensure the construction progress and construction quality. The foundation pit retaining structure 100 illustrated in the figure is constructed in the geological layers from top to bottom: miscellaneous fill, hard clay, fully weathered mixed rock, strongly weathered mixed rock (soil-like), strongly weathered mixed rock (massive), medium weathered mixed rock, slightly weathered mixed rock. However, it is not limited to the construction of weathered rock geological layers, and can be applied to the construction of other hard geological layers.

[0047] The present invention is not limited to the above-mentioned specific implementation modes. Obviously, the above-mentioned embodiments are only some embodiments of the embodiments of the present invention, but not all embodiments. Based on the described embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field belong to the scope of protection of the present invention. Those skilled in the art can make other levels of modifications and changes to the present invention. In this way, if these modifications and changes of the present invention fall within the scope of the claims of the present invention, the present invention is also intended to include these changes and changes.

Claims

1. A construction method for a foundation pit retaining structure in a confined space of a weathered rock geological layer, characterized in that: include: Provide Larsen steel sheet piles with grouting pipes installed, so that the grouting pipes are distributed on both sides of the Larsen steel sheet piles; The foundation pit retaining holes are formed by conducting guide hole construction downward through the weathered rock geological layer along the foundation pit edge; The backfill material is filled in the foundation pit retaining hole. The backfill material below the bottom line of the foundation pit excavation is cement mortar mixed with fiber, and the backfill material above the bottom line of the foundation pit excavation is the original soil taken out during the hole construction. Insert Larsen steel sheet piles with grouting pipes installed on both sides into the backfill material to the bottom of the foundation pit retaining hole, so that the backfill material is distributed on both sides of the Larsen steel sheet piles, and the Larsen steel sheet piles are embedded on both sides through the backfill material below the bottom line of the foundation pit excavation, and the Larsen steel sheet piles are squeezed and fixed on both sides through the backfill material above the bottom line of the foundation pit excavation; Pressurized grouting is carried out from the water-facing surface to the water-receiving surface of the Larsen steel sheet pile through the grouting pipe to form a horizontal water-stop curtain in the soil layer below the bottom of the foundation pit retaining hole. The foundation pit retaining structure of a plate-wall water-stop composite structure is formed by the foundation pit retaining hole, backfill materials, Larsen steel sheet piles and the water-stop curtain.

2. The construction method of the foundation pit retaining structure in the confined space of the weathered rock geological layer according to claim 1 is characterized in that: On the edge of the foundation pit, a rotary drilling rig or a drilling rig is used to drill holes through the weathered rock geological layer to obtain soil for guide hole construction to form foundation pit retaining holes.

3. The construction method of the foundation pit retaining structure in the confined space of the weathered rock geological layer according to claim 1 is characterized in that: Before inserting the Larsen steel sheet pile, multiple horizontal steel bars are welded at intervals on the concave surface of the Larsen steel sheet pile vertically, and the horizontal steel bars of adjacent concave surfaces on both sides of the Larsen steel sheet pile are staggered.

4. The construction method of the foundation pit retaining structure in the confined space of the weathered rock geological layer according to claim 1 is characterized in that: Cement and yellow sand are mixed in a ratio of 1:1 and 1% of fiber is added to form a cement mortar mixed with fiber.

5. The construction method of the foundation pit retaining structure in the confined space of the weathered rock geological layer according to claim 1 is characterized in that: Cement-based permeable crystalline cement slurry is used to perform pressure grouting from the water-facing surface to the water-receiving surface of the Larsen steel sheet pile through a grouting pipe.

6. The construction method of the foundation pit retaining structure in the confined space of the weathered rock geological layer according to claim 1 is characterized in that: The guide holes, backfill materials, Larsen steel sheet piles and grouting are constructed in sections along the edge of the foundation pit.

7. A foundation pit retaining structure in a confined space of a weathered rock geological layer, characterized in that: The method comprises a foundation pit retaining hole constructed along the foundation pit edge line downward through the weathered rock geological layer, Larsen steel sheet piles inserted into the foundation pit retaining hole, backfill materials filled in the foundation pit retaining hole and distributed on both sides of the Larsen steel sheet piles, the backfill materials located below the foundation pit excavation bottom line are embedded ends formed by embedding Larsen steel sheet piles on both sides with cement mortar doped with fiber, the backfill materials located above the foundation pit excavation bottom line are free ends formed by extruding and fixing Larsen steel sheet piles on both sides with original soil, a grouting pipe is inserted into the foundation pit retaining hole to perform pressurized grouting from the water-facing surface to the water-retaining surface of the Larsen steel sheet pile to form a horizontal water-stop curtain in the soil layer below the bottom of the foundation pit retaining hole, the foundation pit retaining hole, backfill materials, Larsen steel sheet piles and horizontal water-stop curtain form a board-wall water-stop composite structure.

8. The foundation pit retaining structure in a confined space of a weathered rock geological layer according to claim 7 is characterized in that: A plurality of horizontal steel bars are welded vertically and spaced apart on each concave surface of the Larsen steel sheet pile.

9. The foundation pit retaining structure in a confined space of a weathered rock geological layer according to claim 8, characterized in that: The horizontal steel bars of adjacent concave surfaces on both sides of the Larsen steel sheet pile are staggered.

10. The foundation pit retaining structure in a confined space of a weathered rock geological layer according to claim 7, characterized in that: Grouting pipes are arranged along the height of at least part of the concave surfaces on both inner and outer sides of the Larsen steel sheet pile.

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