Finite element limit analysis of pullout capacity of planar caissons in clay

Rigorous upper and lower bound solutions of pullout capacity for planar caissons in clay are solved by two dimensional plane strain finite element limit analysis. The planar caisson is embedded in a deep clay layer with an undrained shear strength of zero at the mudline that increases linearly with depth. To perform finite element limit analysis, clay is modeled as the triangular element with the rigid-plastic Tresca material in an undrained condition. The planar caisson is modeled as the rigid plate element. Soil-structure interfaces with full tension are used around the contacted length between caisson and clay. Mesh adaptivity is employed to obtain very tight upper and lower bounds on the true pullout load. Parametric studies are carried out for the complete range of input dimensionless variables including adhesion factor and embedment ratio. The results of analyses are summarized in the form of the dimensionless pullout factor which is a function of the dimensionless variables. Empirical closed-form expressions for the dimensionless pullout factor and reverse end bearing factor of a planar caisson are proposed.