Riverbank stability study at the University of Alberta, Edmonton: Discussion

Abstract

tions of this approach when studying natural slopes. If we assume a slope has a factor of safety of unity and are trying to determine the shear strength, we should know the piezometric level along the assumed failure plane. Conversely, if we know the shear strength we must know the piezometric level if we are to determine the factor of safety. Figure 9 in Professor Thomson's paper presents the data in a form that permits one to readily appreciate the relationship between the pore pressure coefficient and required residual angle of shearing resistance. Figure 9 could just as easily be plotted as pore pressure versus factor of safety for the residual shear strength value of twelve degrees. This would have illustrated even more clearly that, if there is little or no cohesion, the accurate determination of the piezometric level is just as important a parameter as the angle of shearing resistance. I doubt if we have been giving as much emphasis to determining piezometric levels in various strata during field investigations as we have to laboratory determination of the shear strength, whereas the stability of a slope depends on both, and one might be just as difficult to estimate as the other. Professor Thomson's case history is a valuable contribution to the literature, illustrating the importance of the influence of local geology and groundwater levels on the stability of slopes.