Effect evaluation of grass on shallow stability of unsaturated volcanic soil slope in seasonal cold region

This study investigates effects of grass on hydro-thermal-mechanical properties and shallow stability of unsaturated soil slope. A field measurement consisted of two cut slopes, namely bare slope and grassed slope, was carried out. Field measurement results show that grass has effects on reducing the volumetric water content and increasing matric suction. There is a greater gap in matric suction between grassed soil slope and bare soil slope when the snow appears. Besides, the soil temperature in grassed slope is lower than bare slope in warm seasons. However, contrasted result of the soil temperature is recorded in winter. The triaxial tests were conducted for studying mechanical properties of grassed saturated soil with different grass ages. Experimental results reveal that there is an increase in peak shear strength and effective cohesion of grassed soil as the grass age increases, whereas a slightly higher effective angle of internal friction is observed. Furthermore, the volumetric strain decreased with the rise in grass root volume ratio. The approach of coupled nonisothermal-seepage numerical analysis for unsaturated soil slope considering impacts of grass is suggested. It is followed by slope stability analysis considering enhanced shear strength of soil due to grass roots. The good agreement regarding soil temperature and volumetric water content between simulation and field measurement indicates that the proposed approach is feasible to consider the influences of grass on the hydro-thermal behaviors of unsaturated soil slope. Furthermore, the higher values of factor of safety (FOS) of grassed slope present that the grass is effective in resisting the shallow landslide-prone area.