The water pressure at the excavation face may adversely affect the stability of the sheet pile cofferdam and may cause the cofferdam to collapse. In particulate soils, too much pore water pressure can lead to piping, and underground uplift may occur in viscous or highly compacted soils.
When the seepage force is too large, when the effective stress of the soil in the pipeline will be close to 0, the loss of soil shear capacity can be considered fast, the soil can not bear any vertical load, the cofferdam passive resistance is significantly reduced. In extreme cases, this will result in the complete loss of the stability of the cofferdam, the complete collapse of the steel sheet piles
, so that cofferdam construction workers in life poses a serious threat to safety. Penetrating the network can help the designer to predict the probability of a pipeline in a section. Calculation of export hydraulic gradient and critical hydraulic gradient of the comparative calculation, you can get the safety factor against pipeline. The safety factor for pure sand is usually between 15 and 20. Since the cofferdams and rectangular cofferdams are much more complex at the corners of the three-dimensional feature than the straight part, special care is taken in the design.
Increasing the depth of the steel sheet piles can increase the seepage path, reduce the hydraulic gradient, and improve the anti-pipeline safety. The whole coefficient gives an approximation of the safe cut-off depth of cofferdams discharged in uniform non-cohesive soils, impermeable layers and excavated surface puddles.
Clayey soils or high-density granular soils can be used to calculate the buoyancy of buoyancy based on buoyancy if the water pressure in the shed is calculated from the uplifting effect of the drift net. The matrix will raise the mean water pressure and then convert it to the inner Weir in the role of the cofferdam outside the wells can be set to reduce the water level, reduce the cofferdam at the seepage toe or downhole pumped water to reduce the water table. When the cap cold-formed steel sheet piles cofferdam stabilizes the water. In addition, it is possible to ensure the safety of the piling water within the cofferdam and to make contingency plans for any emergency or construction and pumping.