Modelling the permanent strain of fine/coarse soil mixture with consideration of the effects of coarse grain content and suction by incorporating soil-water retention curve

Experimental observations showed that the permanent strain epsilon(p)(1) of fine/coarse soil mixture was significantly affected by the number of loading cycles N, deviator stress sigma(d), coarse grain content f(v) and matric suction psi. In this study, a fatigue model incorporating soil-water retention curve (SWRC) was developed, allowing the combined effects of N, sigma(d), f(v) and psi on epsilon(p)(1) to be accounted for. Several studies were selected from literature to verify the proposed model. The model parameters were determined by fitting the variations of epsilon(p)(1) with N, sigma(d), f(v) and psi under saturated condition, and then adopted to predict the results under unsaturated condition. Results showed that the proposed model was capable of describing epsilon(p)(1) in the case of plastic shakedown. Comparisons with three representative existing models show that the proposed model incorporating psi provides better predictions of epsilon(p)(1) than the existing models incorporating the water content, for both the case of constant dry density of fine soil fraction rho(d-f) and the case of constant dry density of mixture rho(d). This was explained as follows: for the latter case, keeping the rho(d) constant, an increasing f(v) induced a decreasing rho(d-f) and hence a decrease of psi. For both cases, the effect of rho(d-f) on epsilon(p)(1) was rather reflected by psi than by water content.