Modelling large plastic deformations of cohesive soils using sequential limit analysis

This paper introduces sequential limit analysis (SLA) as a method for modelling large plastic deformations of purely cohesive materials such as undrained clay. The method involves solving a series of consecutive small‐deformation plastic collapse problems using finite element limit analysis, thus ensuring high levels of accuracy, efficiency, and robustness. The techniques needed to develop an SLA implementation for two‐dimensional (plane strain) problems are described in detail, including model geometry updating routines, treatment of rigid bodies, interfaces and boundaries, and periodic remeshing and interpolation of field variables. A simple total stress‐based constitutive model is used to account for strain softening and strain rate effects. Extensive verifications and validations are performed using analytical solutions and physical model test results, comparing both collapse loads and failure mechanisms, to demonstrate the effectiveness of the SLA approach. Additional solution quality checks on the bracketing discrepancy between lower‐bound and upper‐bound limit analysis solutions, and on the incompressibility of the rigid‐plastic material, are also presented.     

Large displacement FEM modelling of the cone penetration test (CPT) in normally consolidated sand

A new finite element model based on a large strain formulation has been developed to study cone penetration in normally consolidated sand. An auto‐adaptive remeshing technique was utilized for handling the very large distortion of sand surrounding the cone tip. A frictional contact interface utilizing Mohr–Coulomb's theory was chosen to represent interactions between the surface of the cone and sand. To model the sand behaviour, the non‐associated Drucker–Prager constitutive model was selected. ABAQUS, a commercial finite element software package, was used to implement the model. The explicit solution algorithm was chosen due to its effectiveness for complicated contact problems. Analysis results proved that the model successfully captured the cone penetration behavior in sand. In addition, a chart to predict internal friction angles based on cone tip resistance for different vertical effective stresses was provided. This paper also shows a typical distribution of sleeve resistance, tip resistance—penetration relationship, and typical contours of vertical, horizontal, and shear stresses in normally consolidated sand. Finally, a non‐uniform resistance was found along the length of the friction sleeve. Copyright © 2003 John Wiley & Sons, Ltd.