The Mohr-Coulomb criterion has been extensively used to model the stat
ic and dynamic behaviour of retaining walls in both analytical and num
erical studies, the main advantage being its simplicity. In the field
of computational geomechanics, more sophisticated soil models have bee
n proposed which take account of the intermediate principal stress a,,
giving rise to an increase in the equivalent friction angle when anal
ysing plane strain problems. In this paper, a kinematic elasto-plastic
soil model incorporating a Lade-Duncan failure criterion is used to c
alculate modified active and passive earth pressure coefficients for r
etaining walls. The results of the finite-element analysis are compare
d to an analytical study and found to be in good agreement once an app
roximation of the Lode angle at failure is made. (C) 1997 Elsevier Sci
ence Ltd.