Hydraulic path dependence of shear strength for compacted loess

Abstract

Shear strength is an essential geotechnical parameter for assessing the landslide potential of loess slopes under rainfall infiltration and farm irrigation conditions on the loess plateau. However, the hydraulic path dependence of shear strength for compacted loess under varying rainfall infiltration conditions has not been thoroughly investigated yet. To this end, a series of direct shear tests and nuclear magnetic resonance (NMR) measurements are carried out on compacted loess. The shear strength tests were continuously implemented on loess specimens under scanning wetting paths besides initial drying paths. The experimental data quantitatively verify the significant effect of hydraulic paths applied to specimens on shear strength of compacted loess. The unique failure envelope of shear strength of loess is identified under the effective stress framework based on intergranular stress, which verifies that the effective stress framework can consider the effect of hydraulic paths on shear strength. Based on the effective stress, a shear strength formula is proposed to characterize shear strengths under varying hydraulic paths, in which the parameters from the soil-water retention curve and shear strength at saturated state are simply required. The proposed shear strength formula can properly predict the measured shear strength data of compacted loess experiencing three hydraulic paths. Furthermore, the distribution curves of transverse relaxation time for pore water in soil under varying hydraulic paths are simultaneously measured using the NMR method. The physical mechanism for the difference in shear strength of loess subjected to different hydraulic paths can be uncovered based on soil-water evolutions in pores in microscale.

Keywords

• Shear strength
• Loess
• Hydraulic hysteresis
• Effective stress
• Nuclear magnetic resonance (NMR)