Influence of wetting-drying cycle in road cut slope in loess in Northwest China

Abstract

Wetting-drying cycle is a strong weathering process which considerably changes the engineering properties of metastable loess. It has been considered in slope stability evaluation and slope surface protection. In this study, rainfall intensity, volumetric water contents and ground temperatures in loess road cut slopes were monitored at two study sites, Dingxi and Pingliang, northwest China, to determine infiltration depth of rainfall and frost depth. The monitored data indicated that water contents from the ground surface to −20 cm deep changed significantly, less changed below the depth of −40 cm. The surficial loess of road cut slope had experienced strong wetting-drying cycles in the rainy season. Based on the monitored data, the wetting-drying and direct shear tests were carried out in laboratory to estimate the influence of wetting-drying cycle on dry density and shear strength of undisturbed loess samples. The mean dry density and shear strength of Dingxi loess samples decreased from 1.60 g/cm3 and 30.3 kPa to 1.30 g/cm3 and 17.8 kPa after 30 cycles, respectively. Concerning the Pingliang soil samples, they decreased from 1.66 g/cm3 and 31.7 kPa to 1.40 g/cm3 and 15.7 kPa, respectively. Wetting–drying cycle significantly reduced the dry density and strength of loess samples and became a key factor leading to the failure of loess road cut slope.