Abstract: To study the impact of different construction procedures for cut slope protection of expansive soils and to prevent disasters triggered by rainfall infiltration, in-situ borehole shear tests (BST) were conducted under different normal stress levels and soaking conditions. Strength characteristics of expansive soils cut slope in Nanyang were obtained with various loading paths and soaking conditions. Results show that the relationship between shear stress and displacement from BST presents weak hardening as the shear strain increases. A max drop of 56.9% in shear strength, and a decrease of 18.1 kPa in cohesion are observed. Preloading inhibits softening but fails when it increases to some threshold. The cohesion has a positive linear relationship with the preloading stress, while the internal friction angle has a negative linear relationship with the preloading stress, but internal friction angle rarely varies. In engineering practices, effect of rainfall infiltration on strength parameters should be considered. Meanwhile, the linear relationship between parameters of shear strength and preloading stress should be used to back-calculate the preloading needed according to the safety factor that the project should satisfy. The study results provide technical reference for site evaluation, parameters selection and disaster assessment of the similar sites of expansive soils.

Key words: borehole shear test, expansive soil, shear strength, loading added way, soaking