A Family of Nonlinear Failure Envelopes for
Non-Cemented Soils and Rock Discontinuities
Professor, Civil Engineering Faculty, University of Beograd
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A Family of Nonlinear Failure Envelopes for
Professor, Civil Engineering Faculty, University of Beograd |
Abstract
Analytical expressions for the non-linear failure envelopes in terms of effective stresses are critically reviewed and classified in three major groups as power types, logarithmic and hyperbolic types. One simple hyperbolic type, based on the micro-mechanical model of the dilatancy type, is derived in a form of the variation of the angle of the shearing resistance with the stress level in drained conditions. The non-linear failure envelope in terms of effective stresses for noncemented granular materials and rock discontinuities is described by a family of simple three parameter expressions, which contain the basic angle of friction, the contribution angle of the highest dilatancy and the median angle pressure. Examples of the peak and residual strength envelopes ranging from rock discontinuity, crushed rock, gravel, sand-gravel mixture, sand, silt and clay, are described in terms of the proposed parameters. The cohesion intercept in noncemented soils is explained in terms of inadequate testing stress range. The recommendations for the selection of the proper testing range in drained conditions are given. The proposed description simplifies interpretation of shear test results and represents an alternative to the conventional Coulomb line. It can be used in the limit equilibrium and stress-strain analyses and in the development of the constitutive models as a better approximation than the classical linear relation.
Keywords:soil, rock discontinuity, shearing strength, effective stresses, non-linear failure envelope
