Nonlinear failure envelope of a nonplastic compacted silty-sand

Accurate evaluation of shear strength of compacted fill materials represents a key issue in performing reliable stability analyses of embankment slopes. In engineering practice, the shear strength of compacted soils is expressed in terms of a linear failure envelope usually derived from consolidated-undrained (CU) triaxial tests with pore water pressure measurements. Experimental evidence indicates, however, that the failure envelope of many soils is not linear, particularly within the range of low effective normal stresses. The present study addresses the nonlinear character of failure envelope of a nonplastic compacted silty-sand. Linear and nonlinear strength functions were fitted to experimental results from CU triaxial tests to derive the strength parameters of linear and nonlinear failure envelopes. For the investigated soil and typical range of mean effective normal stresses of interest in embankment slope design, the nonlinear failure envelope appears to give a more accurate representation of the experimental information compared to the linear strength model.