Stability Factors for Slopes with Nonassociated Flow Rule Using Energy Consideration

Abstract

From the consideration of energy balance at collapse, stability factors were computed for soil slopes with both associated and nonassociated flow rules. The effect of the pore water pressure was also incorporated. The stress variation along the rupture surface—needed to obtain the rate of dissipation of internal energy for the nonassociated flow rule—was established on the basis of the assumption of interslice forces given by Fellenius and Bishop. Both coaxial and noncoaxial nonassociated flow rules were examined. For the coaxial flow rule, the stability factors reduce quite appreciably with a decrease in the dilatancy angle (ψ). Whereas with the noncoaxial flow rule, the effect of ψ on the results was seen to be less significant. For mild slopes, the distribution of the stresses along the rupture surface on the basis of Fellenius’s method was seen to provide more conservative results as compared with Bishop’s approach; whereas the reverse was found true for steep slopes.