Steel sheet pile cofferdam construction is a project carried out in water or near water, aiming to create a dry and safe environment for construction. Irregular construction or failure to accurately identify the impact of the environment such as the soil quality, water flow, water depth pressure, etc. of the river, lake, and ocean during construction will inevitably lead to construction safety accidents.
The main process and safety management points of steel sheet pile cofferdam construction:
I. Construction process
1. Construction preparation
○ Site treatment
The filling construction platform needs to be compacted layer by layer (the recommended layer thickness is ≤30cm) to ensure that the bearing capacity meets the requirements of mechanical operation.
The slope of the drainage ditch should be ≥1%, and a sedimentation tank should be set to prevent silt blockage.
○ Material preparation
Steel sheet pile selection: Select the pile type according to the geological report (such as Larsen IV type for soft soil and U type for gravel layer).
Check the integrity of the lock: Apply butter or sealant in advance to prevent leakage.
2. Measurement and layout
Use the total station for precise positioning, set control piles every 10m, and check the design axis and elevation deviation (allowable error ≤5cm).
3. Guide frame installation
The spacing between the double-row steel guide beams is 1~2cm larger than the width of the steel sheet piles to ensure that the verticality deviation is less than 1%.
The guide beams need to be fixed by steel welding or bolting to avoid displacement during vibration piling.
4. Steel sheet pile insertion
○ Pile driving sequence: Start from the corner pile, close the gap along the long side to the middle, or use “screen-style” group construction (10~20 piles per group).
○ Technical control:
The verticality deviation of the first pile is ≤0.5%, and the subsequent pile body is corrected by “set driving”.
○ Pile driving rate: ≤1m/min in soft soil, and high-pressure water jet is required to assist sinking in hard soil layer.
○ Closure treatment: If the remaining gap cannot be inserted with standard piles, use special-shaped piles (such as wedge piles) or weld to close.
5. Foundation pit excavation and drainage
○ Layered excavation (each layer ≤2m), support as excavation, internal support spacing ≤3m (the first support is ≤1m from the top of the pit).
○ Drainage system: The spacing between water collection wells is 20~30m, and submersible pumps (flow rate ≥10m³/h) are used for continuous pumping.
6. Backfill and pile extraction
Backfill needs to be compacted symmetrically in layers (compaction degree ≥ 90%) to avoid deformation of the cofferdam due to unilateral pressure.
Pile extraction sequence: remove from the middle to both sides in intervals, and inject water or sand simultaneously to reduce soil disturbance.
II. Safety Management
1. Risk Control
○ Anti-overturning: Real-time monitoring of cofferdam deformation (suspend construction and reinforce when the inclination rate is greater than 2%).
○ Anti-leakage: After piling, hang a mesh on the inside to spray grout or lay a waterproof geotextile.
○ Anti-drowning: Set up guardrails (height ≥ 1.2m) and lifebuoys/ropes on the working platform.
2. Response to special working conditions
○ Tidal influence: Stop work 2 hours before high tide and check the sealing of the cofferdam.
○ Heavy rain warning: Cover the foundation pit in advance and start the backup drainage equipment (such as high-power pumps).
3. Environmental management
○ Mud sedimentation treatment: Set up a three-level sedimentation tank and discharge it after meeting the standards.
○ Noise control: Limit high-noise equipment during night construction (such as using static pressure pile drivers instead).
Ⅲ. Key technical parameters reference
IV. Common problems and treatment
1. Pile deviation
Cause: hard objects in the soil layer or wrong order of piling.
Treatment: Use “correction piles” to reverse the injection or local pile filling.
2. Lock leakage
Treatment: Fill clay bags on the outside and inject polyurethane foaming agent on the inside to seal.
3. Foundation pit uplift
Prevention: Speed up the construction of the bottom plate and reduce the exposure time.
V. Summary
The construction of steel sheet pile cofferdams should focus on “stable (stable structure), dense (sealing between piles), and fast (fast closure)”, and dynamically adjust the process in combination with geological conditions. For deep water areas or complex strata, the “support first and then dig” or “combined cofferdam” (steel sheet pile + concrete anti-seepage wall) scheme can be adopted. Its construction contains the combination of force and strength. The perfect balance between man and nature can ensure the smooth progress of construction and minimize the damage and waste of natural resources.
If you have any further questions or demands, please feel free to contact Ms. Wendy. wendy@jxhammer.com
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Post time: Mar-10-2025