Collapses of loess at the front of the Emei tableland in the Yuncheng basin and their major geological controlling factors

There developed a lot of collapse areas at the front of Emei tableland in Yuncheng Basin, especially around Xinzhuang village. Their evolution process and trend are pivotal issues for evaluating the possibility, time and location of geological hazards. Based on the geological survey in the shallow surface, combining the interpretation of remote sensing data and three-component resonance imaging technique, the surface ground evolution process of the loess collapse area for the past ten years and the present interior structure were summarized. First of all, the front of Emei tableland lies in the transition zone from loess to lacustrine deposits. Therefore, the sedimentary sequence in this area has sedimentary characteristics both of loess and lacustrine deposits. The interbeds of sand and loess in the vertical sequence provide lithological foundation for the collapse of loess. Besides that, there developed a series of fissures controlled by the active fault beneath the loess. Then, it was observed that the collapse area of loess had experienced a fast evolution process from gestation to rapid growth period since 2011 according to the interpretation results of remote sensing data. Furthermore, the three-component resonance imaging results show that there are a lot of voids connecting with each other beneath the loess collapse area. Overall, the lithology combination laid the material foundation for the collapse of loess, and the fissures in the surface around Xinzhuang village accelerated the collapse of loess at the front of Emei tableland. To sum up, this area has become a geological hazard zone at high risk.