Characteristics and mechanism of the landslide in Yongguang village, Minxian County, China

More than 2330 landslides/mudflows in loess were triggered by the 2013 Minxian earthquake (M_S 6.6) in its epicentral area in Minxian County, Gansu, China. A comprehensive investigation, including in-situ and laboratory tests, was conducted for the largest landslide/mudflow in Yongguang village in order to gain a better understanding of the mechanism and rainfall impact on the landslides/mudflows. A series of triaxial laboratory tests showed that the strength of loess is significantly reduced with increased water content. The static and dynamic parameters of loess, obtained from in-situ and laboratory tests, were used to analyze ground-motion site response. The field observations and site-response analyses suggested that peak ground accelerations generated by the Minxian earthquake were in the range of 0.2–0.4 g in the epicentral area. The static and dynamic parameters of loess were also used to analyze dynamic slope stability and liquefaction potential. The results showed that loess slopes would not fail or liquefy under dry conditions and ground motions with PGA of 0.2–0.4 g, whereas loess slopes would fail or liquefy under saturated conditions. Although difficult to quantify, the water content of the loess was significantly increased, even to the point of being partially saturated, by abnormally high rainfall prior to the earthquake. Thus, the abnormal rainfall before the earthquake was a contributing factor for the massive loess landslides/mudflows in the epicentral area.