Open excavation construction method for double-layer steel sheet pile cofferdam underwater tunnel with drainage pressure reduction cavity

Abstract

The invention relates to the technical field of underwater tunnel and deep foundation pit engineering construction, in particular to a double-layer steel sheet pile cofferdam underwater tunnel open excavation construction method with a drainage pressure reduction cavity, and the construction method comprises the specific steps that outer side steel sheet piles are driven in an underwater construction area along the outer contour of a tunnel foundation pit, and an outer layer cofferdam used for retaining soil is formed; inner side steel sheet piles are arranged on the inner side of the outer-layer cofferdam to form an inner-layer cofferdam for water stopping, and a drainage pressure reduction cavity is formed between the inner-layer cofferdam and the outer-layer cofferdam; a drainage device is arranged in the drainage pressure-reducing cavity, and active precipitation is conducted on the drainage pressure-reducing cavity through the drainage device; foundation pit excavation is conducted in the inner-layer cofferdam, and open excavation construction of the tunnel main body structure is completed in the dry operation environment; by means of the arrangement that the double-layer steel sheet pile cofferdam and the drainage pressure reduction cavity are combined, water pressure can be transferred and released from the water stop cofferdam, the water pressure borne by the inner-layer water stop cofferdam can be reduced, and the water stop safety of the cofferdam is improved.

Description

Technical Field

[0001] This invention relates to the field of underwater tunnel and deep foundation pit construction technology, specifically to a method for open-cut construction of underwater tunnels with double-layer steel sheet pile cofferdams and drainage and pressure relief chambers. Background Technology

[0002] When constructing tunnels using the open-cut method in underwater environments such as rivers and seas, it is necessary to first build a cofferdam to form a dry working pit. In existing technologies, single-row steel sheet pile cofferdams or underground continuous wall cofferdams are commonly used.

[0003] To ensure the water-stopping effect, single-row steel sheet pile cofferdams require the use of high-performance water-stopping steel sheet piles throughout, and the requirements for driving accuracy and interlocking quality are extremely high. Once there are defects in a local area, leakage is likely to occur, resulting in high construction risks and high costs. Although underground continuous wall cofferdams have better water-stopping performance, they are expensive, have a long construction period, and are significantly limited by the conditions of underwater construction.

[0004] Therefore, existing open-cut construction methods for underwater tunnels cannot simultaneously achieve both water-stopping safety and economy, and a new construction method is urgently needed to solve this problem. In view of this, we propose an open-cut construction method for underwater tunnels with a double-layer steel sheet pile cofferdam featuring a drainage and pressure-reducing chamber. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings mentioned in the background section and provide a method for open-cut construction of underwater tunnels with double-layer steel sheet pile cofferdams and drainage and pressure-reducing chambers.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: A method for open-cut construction of an underwater tunnel with a double-layer steel sheet pile cofferdam and a drainage and pressure-reducing chamber, the specific steps of which are as follows: Step 1: Drive outer steel sheet piles along the outer contour of the tunnel foundation pit in the underwater construction area to form an outer cofferdam for retaining soil; Step 2: Install inner steel sheet piles on the inner side of the outer cofferdam to form an inner cofferdam for water stoppage. A drainage and pressure relief cavity is formed between the inner and outer cofferdams. Step 3: Install a drainage device in the drainage and pressure relief chamber to actively lower the water level in the drainage and pressure relief chamber to below the bottom elevation of the foundation pit, thereby reducing the water pressure acting on the outside of the inner cofferdam. Step 4: Excavate the foundation pit within the inner cofferdam and complete the open-cut construction of the tunnel main structure in a dry working environment.

[0007] Preferably, at least one layer of internal support is horizontally installed inside the drainage and pressure relief chamber for connecting the inner cofferdam and the outer cofferdam. The internal support is used to transfer the soil pressure from the outer cofferdam to the inner cofferdam or the foundation pit support system.

[0008] Preferably, the bottom of the drainage and pressure-reducing chamber is covered with a gravel filter layer, and multiple pressure-reducing drainage wells with filter pipes are arranged in the gravel filter layer; The pressure-reducing drainage well is connected to a drainage pump, which serves as a drainage device.

[0009] Preferably, the outer sheet piles are Larssen sheet piles, and the inner sheet piles are high-performance sheet piles with water-stop interlocking joints on the connecting surfaces.

[0010] Preferably, the distance between the inner cofferdam and the outer cofferdam is set to 2-4m.

[0011] Preferably, the inner support is made of steel cross bracing and is located near the upper part of the drainage and pressure relief chamber.

[0012] Preferably, in step four, the foundation pit excavation process adopts a layered, segmented, and symmetrical excavation method, and the internal support is set up step by step as the foundation pit excavation depth increases.

[0013] Preferably, after the open-cut construction of the main tunnel structure is completed, the foundation pit and the drainage and pressure relief cavity are backfilled in sequence, the dewatering is gradually stopped, the inner support is removed, and the inner steel sheet piles and the outer steel sheet piles are removed in sequence.

[0014] Compared with the prior art, the beneficial effects of the present invention are: 1. The underwater tunnel open-cut construction method of double-layer steel sheet pile cofferdam with drainage and pressure relief chamber can transfer and release water pressure from the water-stop cofferdam by combining the double-layer steel sheet pile cofferdam with the drainage and pressure relief chamber, thereby reducing the water pressure borne by the inner water-stop cofferdam and improving the water-stop safety of the cofferdam. 2. Active drainage can transform uncontrollable water pressure problems into controllable precipitation problems, improving construction reliability; it can create a stable dry working environment for the inner cofferdam, which is conducive to improving construction quality and efficiency; and the steel sheet piles and internal supports can be repeatedly recycled, meeting the requirements of green construction. Attached Figure Description

[0015] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings: Figure 1 This is a schematic cross-sectional view of the overall structure of the present invention.

[0016] The meanings of the labels in the diagram are as follows: 1. Outer sheet piles; 2. Inner sheet piles; 3. Internal bracing; 4. Pressure-reducing drainage well. Detailed Implementation

[0017] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Unless otherwise specified, the embodiments and features in the embodiments of this application can be combined with each other. 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.

[0018] Please see Figure 1 The present invention will describe the above technical solution in detail through the following embodiments: This embodiment presents a method for open-cut construction of underwater tunnels with double-layer steel sheet pile cofferdams featuring drainage and pressure-reducing chambers. The purpose is to provide a method for safe water-stopping underwater tunnel construction by reducing the water pressure borne by the cofferdam water-stopping unit, thereby reducing the cost of cofferdam projects while ensuring construction safety.

[0019] Specifically, the construction method involves the following steps: First, outer sheet piles 1 are driven along the outer contour of the tunnel pit in the underwater construction area to form an outer cofferdam for retaining soil; inner sheet piles 2 are installed inside the outer cofferdam to form an inner cofferdam for water stoppage, and a drainage and pressure relief cavity with a spacing of 3m is formed between the inner and outer cofferdams; in order to improve the water stoppage performance, high-performance sheet piles with water-stopping locks on the connecting surface are used for the inner sheet piles 2 near the drainage and pressure relief cavity, while conventional Larssen sheet piles are used for the outer sheet piles 1.

[0020] To improve structural stability, this embodiment has two layers of inner supports 3 horizontally installed in the drainage and pressure relief chamber to connect the inner and outer cofferdams, and to transfer the soil pressure from the outer cofferdam to the inner cofferdam or the support system inside the foundation pit.

[0021] After excavating to the design elevation within the drainage and pressure-reducing chamber, a gravel filter layer is laid at its bottom, and a pressure-reducing drainage well 4 is installed, which is connected to a drainage pump. Considering the need to drain the water from the drainage and pressure-reducing chamber to facilitate subsequent excavation, a gravel filter layer is laid at the bottom of the drainage and pressure-reducing chamber, and a pressure-reducing drainage well 4 with a filter pipe is installed within the gravel filter layer. The water in the chamber is discharged in a timely manner by connecting the drainage pump to the outlet of the pressure-reducing drainage well 4. That is, the drainage pump actively lowers the water level in the drainage and pressure-reducing chamber to below the bottom elevation of the foundation pit, thereby reducing the water pressure acting on the outside of the inner cofferdam. Finally, the foundation pit is excavated within the inner cofferdam, and the open-cut construction of the tunnel main structure is completed in a dry working environment. During the foundation pit excavation process, a layered, segmented, and symmetrical excavation method is adopted, and internal supports 3 are installed at each level as the foundation pit excavation depth increases.

[0022] Finally, after the open-cut construction of the main tunnel structure is completed, the foundation pit and drainage pressure relief cavity are backfilled in sequence, the dewatering is gradually stopped, the inner support 3 is removed, and the inner steel sheet pile 2 and the outer steel sheet pile 1 are removed in sequence.

[0023] It should be noted that if the embodiments of the present invention involve directional indicators (such as up, down, left, right, front, back, etc.), the directional indicators are only used to explain the relative positional relationship and movement of the components in a specific posture. If the specific posture changes, the directional indicators will also change accordingly.

[0024] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

Claims

1. A method for open-cut construction of an underwater tunnel with a double-layer steel sheet pile cofferdam and a drainage and pressure-reducing chamber, characterized in that: The specific steps of the construction method are as follows: Step 1: Drive outer steel sheet piles (1) along the outer contour of the tunnel foundation pit in the underwater construction area to form an outer cofferdam for retaining soil; Step 2: Install inner steel sheet piles (2) on the inner side of the outer cofferdam to form an inner cofferdam for water stoppage, and form a drainage and pressure relief cavity between the inner cofferdam and the outer cofferdam; Step 3: Install a drainage device in the drainage and pressure relief chamber to actively lower the water level in the drainage and pressure relief chamber to below the bottom elevation of the foundation pit, thereby reducing the water pressure acting on the outside of the inner cofferdam. Step 4: Excavate the foundation pit within the inner cofferdam and complete the open-cut construction of the tunnel main structure in a dry working environment.

2. The method for open-cut construction of an underwater tunnel with a double-layer steel sheet pile cofferdam and a drainage and pressure-reducing chamber as described in claim 1, characterized in that: The drainage and pressure relief chamber is horizontally equipped with at least one layer of inner support (3) for connecting the inner cofferdam and the outer cofferdam. The inner support (3) is used to transfer the soil pressure from the outer cofferdam to the inner cofferdam or the foundation pit support system.

3. The method for open-cut construction of an underwater tunnel with a double-layer steel sheet pile cofferdam and a drainage and pressure-reducing chamber as described in claim 2, characterized in that: The bottom of the drainage pressure relief chamber is covered with a gravel filter layer, and multiple pressure relief drainage wells (4) with filter pipes are installed in the gravel filter layer. The pressure relief drainage well (4) is connected to the drainage pump, which serves as a drainage device.

4. The method for open-cut construction of an underwater tunnel with a double-layer steel sheet pile cofferdam and a drainage and pressure-reducing chamber as described in claim 3, characterized in that: The outer sheet pile (1) is a Larsen sheet pile, and the inner sheet pile (2) is a high-performance sheet pile with a water-stop lock on the connecting surface.

5. The method for open-cut construction of an underwater tunnel with a double-layer steel sheet pile cofferdam and a drainage and pressure-reducing chamber as described in claim 4, characterized in that: The distance between the inner and outer cofferdams is set to 2-4m.

6. The method for open-cut construction of an underwater tunnel with a double-layer steel sheet pile cofferdam and a drainage and pressure-reducing chamber as described in claim 2, characterized in that: The inner support (3) is made of steel profiles and is located near the upper part of the drainage pressure relief chamber.

7. The method for open-cut construction of an underwater tunnel with a double-layer steel sheet pile cofferdam and a drainage and pressure-reducing chamber as described in claim 2, characterized in that: In step four, the foundation pit excavation process adopts a layered, segmented, and symmetrical excavation method, and the internal support (3) is set up step by step as the foundation pit excavation depth increases.

8. The method for open-cut construction of an underwater tunnel with a double-layer steel sheet pile cofferdam and a drainage and pressure-reducing chamber as described in claim 2, characterized in that: After the open-cut construction of the main tunnel structure is completed, the foundation pit and the drainage and pressure relief chamber are backfilled in sequence, the dewatering is gradually stopped, the inner support (3) is removed, and the inner steel sheet pile (2) and the outer steel sheet pile (1) are removed in sequence.

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