DANGCHUAN 2# LANDSLIDE OF APRIL 29, 2015 IN HEIFANGTAI AREA OF GANSU PROVINCE: CHARACTERISTICES AND FAILURE MECHANISM

A small scale of loess landslide occurred at Heifangtai in Dangchuan village of Yongjing county. Its occurrence is at 7:50 of April 29, 2015. The site is at the edge of the loess plateau. The instability of loess has a volume of 5104m3. It runs from the forth terrace to the second terrace of the Yellow river. After 3 hours later, however, a large scale of mudstone occurred at this place. Its volume is of 3.5105m3. The mudstone deposit is 780meters long, 100meters wide and the largest thickness of deposit is 17meters. The landslide is one of the few catastrophic landslides. This paper examines the sliding displacement monitoring and the crack distribution. Such examinations are combined with site geological investigation, low-altitude photogrammetry, site engineering geological survey and site moisture content test. This paper analyses the basic characteristics of the landslide and the formation and reasons of landslide by preliminary understanding. The results show that:(1)There are two sliding cases at Dangchuan 2# landslide from the time. There is only one sliding case time in first time sliding and three sliding cases in second times landslide from sliding mode and deposit characteristic. Dangchuan 2# landslide has four times sliding cases in all. (2)The area of the first sliding is 8396m2. Deformation distribution area is only at the edge of plateau and is smaller compared with the sliding area. The long-term creep deformation at the bottom of loess is the inducing factors of the first time landslide. (3)The area of the second sliding is 27422m2. There is rarely any crack at this part and the crack has no obvious deformation before the second times sliding. The liquefaction of the loess at the bottom of landslide plays a very important role in the second times sliding. The landslide has the characteristics such as sudden occurrence, movement long distance and destructive stronger. (4)The Dangchuan section begins to start mass type static liquefaction loess landslide and the boundary of landslide is the sinkholes, which is of great significance that is the research about other section of early recognition of loess landslide and monitoring and early warning of loess landslide.