Deformation Mechanism of the Zhoujiashan Landslide Under the Combined Effect of Rainfall and Earthquakes in Tianshui, Northwestern China

Abstract

Tianshui is located in a geomorphologic transitional zone with well-developed tectonics. Two historical earthquakes with magnitudes greater than 7.0 have occurred in Tianshui and its surrounding areas. The strata consist of primarily loess and mudstone, and geological disasters frequently occur. The Zhoujiashan landslide is a historical earthquake landslide that is currently relatively stable. To study its deformation and stability under the combined effect of rainfall and earthquake motion, the landslide was analyzed via field investigations, shaking table tests, and numerical calculations. The fastest responses were those of the pore water pressure and volume water content in the 0.3-m-depth range under rainfall conditions. The rainfall infiltration depth is limited to approximately 2 m and has a minimal impact on the overall stability of the slope. The response to earthquake accelerations increases with increasing elevation, and earthquakes have a significant amplification effect on structures with an inherent period of 0.2–0.4 s. Under 0.1-g and 0.3-g earthquake conditions, the slope deforms and the safety factor decreases but the landslide does not suffer overall failure. Under the 0.6-g earthquake condition, the slope liquefies, leading to the overall failure of the slope. The location of the liquefaction zone in the numerical calculation is in agreement with the actual situation. Under the 0.6-g earthquake condition, the overall failure mechanism of the slope is vibration liquefaction at the sliding surface.