Investigation for the initiation of a loess landslide based on the unsaturated permeability and strength theory

Background: The Yanlian landslide, occurring on 21-22 October 2010, destroyed many facilities of a big oil refinery in Shaan’xi Province, China. It led to a suspending of the refinery work for a week and caused near 700 million RMB economic losses. Results: Site exploration shows that the sliding mass is unsaturated-saturated loess. The groundwater is rich in the landslide and shortage in the surrounding slopes. Further investigation finds that the water drop released from the vapor heating furnaces on the top of the slope is the only source of the groundwater. Laboratory tests were performed to get the unsaturated strength parameters and hydraulic conductivity of the loess layers which were applied to a pre-failure slope model to simulate the water infiltration process and the stress field based on which the factor of safety is figured out to analyze the slope stability. Analysis shows that during the first ten years, the factor of safety has no prominent decrease. In the following 5 years, the slope stability decreases significantly till failure. Conclusions: A little water infiltration has minor effects on slope stability for some time. As a result it is easy to be ignored. However, when the period of water infiltration is long enough to raise the groundwater level, it will have detrimental influence on the stability. In conclusion, any minor water produced by engineering or other activities for a long period may have harmful effect on slope stability. Therefore it is essential to take account of this kind of water and adopt measures to curb the surface water infiltration and to drain the groundwater. © 2015, Li et al.