New design equation for undrained pullout capacity of suction caissons considering combined effects of caisson aspect ratio, adhesion factor at interface, and linearly increasing strength

Undrained pullout capacity of suction caisson in clays with homogeneous and linearly increasing strengths with depth was investigated by two-dimensional axisymmetric finite element analysis. Effects of the caisson aspect ratios, the complete range of adhesion factors at soil-caisson interface, and the full range of dimensionless strength gradients on the dimensionless pullout factor of suction caissons were comprehensively examined. Based on a nonlinear regression to the derived finite element solutions, a new design equation of the undrained pullout capacity of suction caissons was proposed, considering the practical ranges of caisson aspect ratios, the complete range of adhesion factors at soil-caisson interface, and a general profile of both homogeneous and linearly increasing strengths with depth. The proposed equation was validated through a comparison of existing solutions and published experimental data.