A method for foundation pit excavation and support construction of a low-pile pile cap in a flow-plastic silt beach area

Abstract

The present application relates to a kind of flow plastic silt beach area low pile cap foundation pit excavation and supporting construction method, along with the direction parallel to trestle, the cap foundation pit construction area is divided into A area and B area, wherein, away from the side of trestle, A area is close to the side of trestle, B area;After pile construction is completed, first remove the drilling platform of A area, insert and drive steel sheet pile around A area, form cap foundation pit A area steel sheet pile cofferdam, using long arm excavator completes cap foundation pit A area excavation, then remove the drilling platform of B area, complete cap foundation pit B area excavation, finally remove the steel sheet pile between cap foundation pit A area and B area, A area and B area steel sheet pile cofferdam are merged to form a whole cofferdam, and cap pouring construction is carried out in cofferdam.The present application uses zoning support, block excavation to cap foundation pit, can use small excavating equipment to carry out construction, avoid the problem of high cost, great risk caused by using large crawler crane construction and island construction.

Description

Technical Field

[0001] This invention belongs to the field of bridge engineering technology and relates to the construction of bridge abutments, specifically to a method for excavation and support construction of low pile abutment foundation pits in fluid-plastic silt tidal flat areas. Background Technology

[0002] When constructing low-pile pier caps in a fluid-plastic silt mudflat area, it is typically necessary to erect a pile drilling platform in the pier construction area, along with a temporary bridge for river passage. After the pile foundation construction is completed, the drilling platform is dismantled, the pier cap pit is excavated, and the pier cap concrete is poured. Because the pier construction area is fluid-plastic silt, support is required around the pit during excavation. Currently, there are two main methods for pier cap pit excavation and support:

[0003] Method 1: Dismantle the entire drilling platform, drive steel sheet piles or interlocking steel pipe piles around the foundation construction area to form a cofferdam, and then excavate the foundation pit. Because the construction environment is fluid silt, the excavation equipment can only operate from a trestle bridge. However, due to the large area of ​​the foundation pit, exceeding the working range of ordinary long-arm excavators, a large crawler crane with a grab bucket is required for excavation. This method results in high equipment costs, low construction efficiency, and significant challenges and risks associated with large-area cofferdam support in silt.

[0004] Method 2: Dismantle the entire drilling platform, fill the pier construction area with crushed stone or gravel to form an island, creating a land environment, then drive steel sheet pile cofferdams, and use excavators to excavate the pier foundation pit. However, this method requires a large amount of filling material, making construction costs uncontrollable. Moreover, the island construction and filling will cause horizontal compression to surrounding temporary structures (such as river crossing trestle bridges, adjacent pier drilling platforms, and support trestle bridges), leading to structural instability and posing a significant risk. Summary of the Invention

[0005] The purpose of this invention is to address the above-mentioned problems by providing a method for excavating and supporting low-pile foundation pits in fluid-plastic silt tidal flat areas that requires no large-scale machinery, is easy to operate, has controllable construction costs, and has low safety risks.

[0006] The technical solution of the present invention is as follows:

[0007] A method for excavation and support construction of low-pile foundation pits in fluid-plastic silt tidal flat areas, wherein the pile foundation of the foundation is constructed using a drilling platform, and a passageway is erected along one side of the drilling platform, characterized in that:

[0008] (1) Divide the foundation pit construction area into area A and area B along the direction parallel to the trestle bridge. Area A is the side away from the trestle bridge, and area B is the side closer to the trestle bridge.

[0009] (2) After the pile foundation construction is completed, the drilling platform in area A is first removed, and steel sheet piles are driven around area A to form a steel sheet pile cofferdam in area A of the foundation pit. Multiple corbels are welded on the inner side of the steel sheet piles of the cofferdam, 30-50cm above the original ground line. Steel walers are erected on the corbels, and temporary support rods are welded between the steel walers and the steel casing of the pile foundation construction. Water-stop cloth is laid on the outer side of the steel sheet pile cofferdam, and sandbags are used to fix the water-stop cloth to prevent it from moving due to the rise and fall of the river water.

[0010] (3) Use a long-arm excavator to excavate the silt in area A of the foundation pit to below the bottom elevation of the foundation. When the long-arm excavator is working, stand on the drilling platform in area B.

[0011] (4) Drain the water in area A of the foundation pit and pour a concrete cushion layer;

[0012] (5) The long-arm excavator retreats to the trestle; dismantle the drilling platform in area B, and drive the steel sheet pile cofferdam in area B of the foundation pit according to the method in step (2), and set up walers, temporary support rods and waterproof cloth;

[0013] (6) The long-arm excavator excavates the silt in area B of the foundation pit to below the bottom elevation of the foundation, pumps out the water in area B of the foundation pit and pours the concrete cushion layer.

[0014] (7) Remove the sheet piles in sections A and B of the foundation pit and merge the sheet pile cofferdams in sections A and B to form a single cofferdam.

[0015] (8) Install horizontal and diagonal bracing within the overall cofferdam, and then remove the temporary support rods between the sheet piles and the steel casing;

[0016] (9) Cut off the steel casing of the pile head and break the pile head, and carry out the construction of the pile cap in the cofferdam.

[0017] This invention employs a zonal support and segmented excavation construction method for the foundation pit. On the one hand, the cofferdam area of ​​each zone is relatively small, and temporary supports are set between the cofferdam and the steel casing for pile foundation construction, resulting in high safety of the support structure. On the other hand, due to the small width of the cofferdam, small mechanical equipment such as ordinary long-arm excavators can be used for excavation, avoiding the high cost and risk associated with using large crawler cranes and island construction. In addition, this invention first removes part of the pile foundation drilling platform, and the remaining part of the drilling platform can be used as a standing platform for long-arm excavators in the early excavation area of ​​the foundation pit, thereby enabling ordinary long-arm excavators to reach any position in the foundation pit and meet construction requirements. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the elevation structure of the pile cap foundation drilling platform;

[0019] Figure 2 This is a schematic diagram of the plan structure of the drilling platform for the pile cap foundation;

[0020] Figure 3 This is a schematic diagram of the elevation structure of the steel sheet pile cofferdam in area A after the drilling platform in area A was dismantled.

[0021] Figure 4 This is a schematic diagram of the plan structure of the steel sheet pile cofferdam to be built in area A after the drilling platform in area A is dismantled;

[0022] Figure 5 This is a schematic diagram showing the state of the excavator excavating area A of the foundation;

[0023] Figure 6 This is a schematic diagram showing the state of the foundation A area after the bottom sealing concrete has been poured.

[0024] Figure 7 This is a schematic diagram of the elevation structure of the area B after the drilling platform B area was demolished and the cofferdam of area B area was built and the foundation of area B area was excavated.

[0025] Figure 8 This is a schematic diagram of the plan structure of the construction of the cofferdam in area B after the drilling platform in area B was dismantled and the foundation in area B was excavated.

[0026] Figure 9 This is a schematic diagram showing the state of the foundation B area after the bottom sealing concrete has been poured.

[0027] Figure 10 This is a schematic diagram of the elevation structure of the cofferdam formed by removing the temporary sheet piles in sections A and B of the pier cap;

[0028] Figure 11 This is a schematic diagram of the overall cofferdam structure of the foundation;

[0029] Figure 12 This is a schematic diagram showing the construction process of the foundation concrete pouring. Detailed Implementation

[0030] The specific construction method of this invention is as follows:

[0031] like Figure 1 , Figure 2 As shown, the construction area for the low-pile abutment of the bridge is located in a fluid-plastic silt tidal flat area 100. Since the construction equipment cannot be positioned on the ground, the pile foundation of the abutment is constructed using a drilling platform 101, and a passage trestle 102 is erected along one side of the drilling platform. Steel casing 1 is used for positioning and guidance during pile foundation drilling.

[0032] The foundation pit construction area is divided into Zone A and Zone B along a direction parallel to the trestle bridge. Zone A is the side furthest from the trestle bridge, and Zone B is the side closest to the trestle bridge.

[0033] like Figure 3 , Figure 4As shown, after the pile foundation construction is completed, the drilling platform in area A is first removed, and steel sheet piles 2 are driven around area A to form a steel sheet pile cofferdam for the foundation pit in area A. Multiple corbels 3 are welded to the inner side of the steel sheet piles of the cofferdam at a height of 30-50cm above the original ground line. Steel walers 4 are erected on the corbels, and temporary support rods 5 are welded between the steel walers 4 and the steel casing 1 of the pile foundation construction to ensure the stability of the steel sheet pile structure. Waterstop cloth 6 is laid around the steel sheet pile cofferdam to prevent external water from entering the cofferdam, and sandbags 7 are used to fix the waterstop cloth to prevent it from moving due to the rise and fall of the river water.

[0034] like Figure 5 , Figure 6 As shown, a long-arm excavator 103 was used to excavate the silt in area A of the foundation pit to below the bottom elevation of the foundation. The long-arm excavator 103 was positioned on the drilling platform in area B during construction.

[0035] Drain the water in area A of the foundation pit and pour a concrete cushion layer.

[0036] like Figure 7 , Figure 8 , Figure 9 As shown, the long-arm excavator 103 retreats to the trestle bridge 102; the drilling platform in area B is dismantled, and steel sheet piles 2 are driven around area B according to the construction method of steel sheet pile cofferdam in area A to form cofferdam in area B of the foundation pit, and corbels 3, walers 4, temporary support rods 5 and waterproof cloth 6 are set on the inner side of the steel sheet piles of the cofferdam.

[0037] Using a long-arm excavator 103, the silt in area B of the foundation pit was excavated to below the bottom elevation of the foundation. The water in area B of the foundation pit was pumped out and a concrete cushion layer 8 was poured.

[0038] like Figure 10 , Figure 11 As shown, the sheet piles in sections A and B of the foundation pit are removed, and the sheet pile cofferdams in sections A and B are merged to form an integral cofferdam.

[0039] Horizontal bracing 9 and diagonal bracing 10 are installed inside the overall cofferdam, and then the temporary support rod between the steel sheet pile 2 and the steel casing 1 is removed.

[0040] like Figure 12 As shown, following the conventional construction method for pile caps, the steel casing of the pile head is cut off and the pile head is broken, and the 104 pile cap is poured inside the cofferdam.

Claims

1. A method for excavation and support construction of a low-pile foundation pit in a fluid-plastic silt tidal flat area, wherein the pile foundation of the foundation is constructed using a drilling platform, and a passageway is erected along one side of the drilling platform, characterized in that: (1) Divide the foundation pit construction area into area A and area B along the direction parallel to the trestle bridge. Area A is the side away from the trestle bridge, and area B is the side closer to the trestle bridge. (2) After the pile foundation construction is completed, the drilling platform in area A is first removed, and steel sheet piles are driven around area A to form a steel sheet pile cofferdam in area A of the foundation pit. Multiple corbels are welded on the inner side of the steel sheet piles of the cofferdam, 30-50cm above the original ground line. Steel walers are erected on the corbels, and temporary support rods are welded between the steel walers and the steel casing of the pile foundation construction. Water-stop cloth is laid on the outer side of the steel sheet pile cofferdam, and sandbags are used to fix the water-stop cloth to prevent it from moving due to the rise and fall of the river water. (3) Use a long-arm excavator to excavate the silt in area A of the foundation pit to below the bottom elevation of the foundation. When the long-arm excavator is working, stand on the drilling platform in area B. (4) Drain the water in area A of the foundation pit and pour a concrete cushion layer; (5) The long-arm excavator retreats to the trestle; dismantle the drilling platform in area B, and drive the steel sheet pile cofferdam in area B of the foundation pit according to the method in step (2), and set up walers, temporary support rods and waterproof cloth; (6) The long-arm excavator excavates the silt in area B of the foundation pit to below the bottom elevation of the foundation, pumps out the water in area B of the foundation pit and pours the concrete cushion layer. (7) Remove the sheet piles in sections A and B of the foundation pit and merge the sheet pile cofferdams in sections A and B to form a single cofferdam. (8) Install horizontal and diagonal bracing within the overall cofferdam, and then remove the temporary support rods between the sheet piles and the steel casing; (9) Cut off the steel casing of the pile head and break the pile head, and carry out the construction of the pile cap in the cofferdam.

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