Nonlinear Mohr envelopes based on triaxial data

A substantial amount of experimental evidence suggests that Mohr envelopes of many soils are not linear, particularly in the range of small normal stresses. This departure from linearity is significant for slope stability calculations since for a wide range of practical stability problems, critical slip surfaces are shallow and normal stresses acting on such surfaces are small. The present work presents a procedure for estimating parameters of the Mohr form of flock and Brown empirical failure criterion, based on triaxial data. This nonlinear Mohr envelope provides significantly better representation of experimental information than the Mohr-Coulomb criterion in cases when the data set includes tests at small enough normal stress. Application of the estimation procedure to published data sets shows that effective cohesive strength of most soils is close to zero, and Mohr envelopes are continuous at the tensile strength limit.