Modelling the suction-dependent plastic shakedown limit of unsaturated fine/coarse soil mixture with consideration of soil-water retention curve: Fid-Bau Portal

Modelling the suction-dependent plastic shakedown limit of unsaturated fine/coarse soil mixture with consideration of soil-water retention curve

Su, Yu / Cui, Yu-Jun

Abstract

Abstract An interlayer soil was identified in the French conventional rail tracks, corresponding to a mixture of subgrade fine soil and ballast grains. Experimental results show that the permanent strain of such fine/coarse soil mixture can be at stable or unstable state, depending on the stress level with respect to the plastic shakedown limit σ dth (the maximum stress level for the stable permanent strain). As the water content of soil mixture changed, the matric suction $ψ$ changed subsequently, leading to a change of σ dth. In this study, a model incorporating the soil–water retention curve was proposed to describe the variation of σ dth with $ψ$ for the soil mixture at varying coarse grain content f v. This proposed model implied the plastic shakedown limit under saturated state σ dth-sat, the plastic shakedown limit under a reference state σ dth-ref, the matric suction corresponding to the reference state $ψ$ ref, and the parameters related to the soil water retention curve. The model was validated using three series of studies in literature. Based on an existing approach implying a representative permanent strain rate 1/a s, the σ dth under varying $ψ$ and f v values was determined for these three series. For each series, the obtained σ dth was divided into two groups: the first group was used to determine the model parameter B in the relationship between σ dth and $ψ$ , while the second group was adopted to validate the proposed model with the previous determined parameter B. A reasonably good agreement was obtained between the measurements and the calculations for these three series of studies. A comparison between the proposed model and a representative existing model was made, showing the performance of the proposed model in describing the variations of σ dth with $ψ$ for soil mixture at varying f v.