Determination of Maximum Penetration Depth of Suction Caissons in Sand

The suction caisson is a large top-closed cylindrical steel structure in diameter, short in length and much thinner in skirt wall thickness. The total resistance of the suction caisson during installation consists of the tip resistance and the skirt wall friction. However, since the thickness of the skirt wall is very small, the skirt wall friction may produce additional vertical stress and shear stress in soil at the skirt tip level, and this additional vertical stress and shear stress will contribute to the increase in the skirt tip resistance. At the same time, seepage induced by suction also causes the tip resistance to reduce significantly. A modified slip-line field is proposed in this study estimating the tip resistance in terms of the slip-line theory. The expression obtaining the minimum suction to install the suction caisson is also proposed in terms of the force equilibrium. In addition, the critical suction is determined based on the mechanism of sand piping. Thus, the maximum penetration depth of the suction caisson can be reached when the critical suction equals the minimum suction. Results from calculations of the minimum suction and the maximum penetration depth have been proved to be in a good agreement with the measured data.