The structure degradation of a silty loess induced by long-term water seepage

Loess is a typical silt-sized Aeolian soil that is widely deposited and possesses a fragile soil structure susceptible to collapse upon wetting. The instability of shallow loess slopes is well documented, but deeper failures triggered by rainfall and irrigation can also occur. In the case of long-term seepage, clay particles and salts have been observed to leach out of the loess slopes. This paper presents a systematic laboratory study of the effects of water conditions on the mechanical behaviour of silty loess, with isotropic compression and bender element tests carried out on natural and reconstituted loess recovered at 10 m depth from a site in China. The results show that saturation causes reduction in both the compression yield stress and small strain stiffness of the soil, and that after being exposed to seepage, they decrease further. The possible mechanism of structure degradation is investigated by means of microscopic and chemical analyses, and it is found that seepage will cause the pore ions concentration to reduce with a loss of clay mineral bonding strength, resulting in the detachment of silt particles from aggregates. This work highlights the importance of monitoring the water outflow in the field at the loess slope edge, since it may causes large deformation in the long-term. •The effects of three different water conditions on the mechanical behaviour of a silty loess are studied.•Isotropic compression together with bender element tests is carried out on loess specimens.•The possible mechanism of structure degradation induced by seepage is investigated.