Steel coil pipes

The manufacturing and installation of steel casing is a crucial step in the construction of bored pile foundations, directly affecting the quality of the piles.

The casing is made in a round column form with steel plate, commonly using 8mm and 10mm thickness, rolled into steel casings with diameters of 1.3m and 1.1m. Each section of the steel casing is typically about 1.25m high, varying based on actual usage. The circular shape is formed through rolling, ensuring the casing's roundness for quality assurance of the桩. Welding must meet requirements, with tight seams and no water penetration; single-sided welding is permissible but must be securely welded. The length of the steel casing is determined by the water depth on-site and the elevation of the pile top.

Steel casing is used during the process of manual excavation for pile foundation, as the soil is unstable, it presents significant difficulty in constructing reinforced concrete retaining walls. Therefore, steel casing is employed to protect the bore piles, preventing cave-ins and ensuring construction progress and safety. A steel casing is a circular barrel made of iron sheet, with both ends open and tailored to the size of the pile bore.

Nature:

Generally larger than pile diameter by 20-40cm, the burial depth is determined by the soil characteristics, the deviation in the plane position must not exceed 5cm, and the inclination must be less than 1%.

Cautionary Notes:

The internal diameter of the protective sleeve should be 200 to 400mm larger than the pile diameter.

The centerline of the pipe sleeve should align with the centerline of the pile, with a permissible flatness error of 50MM unless otherwise specified in the design. The vertical line should not be inclined by more than 1%. The actual positioning can be measured in the dry area, while in the water area, it can rely on the guide frame for positioning.

3 For land reclamation and island construction, the protective tubes can be installed by digging a pit and burying method. The clay soil filled at the bottom and around the protective tubes must be compacted in layers.

4. Waterway piercings should be set with strict attention to the flat position, vertical inclination, and the connection quality between the two sections must meet the above requirements. During sinking, methods such as weighting, vibration, hammering, and assisted by soil removal inside the tube can be used.

The protective casing should be 0.3M above ground level or 1.0 to 2.0M above water level. When there is pressure water in the borehole, it should be higher than the stable pressure water level by more than 2.0M. If the pressure water level is unstable or much higher than the groundwater level after stabilization, a trial pile should be constructed first to assess the feasibility of using bored pile foundations in such areas. In areas affected by tidal waters, it should be 1.5 to 2.0M above the highest construction water level, and measures to stabilize the water head within the protective casing should be adopted.

6. The embedment depth of the casing should be determined according to design requirements or the hydrogeological conditions of the pile location. It should not be less than 1.0m in clay, and preferably not less than 1.5m in sandy soil. Generally, the embedment depth should be between 2 to 4 meters, and in special cases, it should be increased to ensure the smooth progress of drilling and concrete pouring. For riverbeds affected by erosion, the casing should be submerged below the local erosion line by at least 1.0 to 1.5 meters. For bored piles affected by water level fluctuations or underwater construction, the height and depth of the casing should be increased, and it should be driven into an impermeable layer if necessary.

The sleeve joint must have no protrusions inside, and it should be resistant to tension, pressure, and not leak.

Function:

1. Positioning 2. Protecting the orifice and preventing ground stones from falling into the hole 3. Maintaining mud level (pressure) to prevent cave-ins 4. One of the references for controlling pile top elevation 5. Preventing the backflow of sediment during drilling

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