Effective stress analysis of the stability of embankments on soft soils: Discussion

Abstract

The authors are to be congratulated for their very clear and useful paper, which points out the efficiency of the effective stress analysis applied to embankment stability on soft soils, provided that the actually observed in-situ pore pressures are introduced into the analysis. We agree with the authors in their comments on the relative merits and shortcomings of the total and effective stress approaches. In cases in which significant consolidation takes place during the construction period, the effective stress analysis is the only efficient one. Regarding the improvements carried out in the last years to the total stress analysis, summarized by the authors in their introduction, a model has been presented by the writers in which the influence of the clay stress history on the undrained shear strength is taken into account (Ballester and Sagaseta 1979). The proposed yield condition is an anisotropic extension of Tresca's criterion. It is a total stress limit condition, but it is defined by the intrinsic effective strength parameters and the clay stress history. Thus, the model parameters are: -Hvorslev's parameters ( k, +,) -degree of friction mobilisation, DM (0 5 DM 5 1) -overburden effective pressure, p,' -overconsolidation pressure, p,' -lateral earth pressure coefficient, KO The variation with depth of the last three parameters produces strength gradient with depth. If KO # 1 .O, the behavior is anisotropic. The model has been implemented into a limit equilibrium analysis by the method of characteristics and applied in a general form to surface loads on soft clays (Arroyo and Sagaseta 1982). In order to check the validity of the model, it has been applied to a number of well-documented embankment failures, namely those of