ZERO THICKNESS INTERFACE ELEMENTS - NUMERICAL STABILITY AND APPLICATION

Many methods have been proposed to model joints in rocks or the interf ace between soil and a structure. Many analysts have reported numerica l problems when using zero thickness interface elements while others h ave presented satisfactory results without comment of such difficultie s. The numerical behaviour of zero thickness interface elements is fur ther investigated in this paper. Some simple examples illustrate the a pplication of interface elements to practical situations and highlight the numerical difficulties that may be encountered. Both ill-conditio ning of the stiffness matrix and high stress gradients were found to c ause numerical instability. Ill-conditioning can be reduced by careful selection of the size of the 2D elements adjacent to the interface. T he problem of steep stress gradients is entirely one of inadequate mes h design. Contrary to other reports, this paper shows that the Newton- Cotes integration scheme has no benefit over Gaussian integration. Ana lyses of a retaining wall using interface elements confirm the analyti cal values of active and passive earth pressure coefficients which are commonly used in analysis and design of retaining walls.