Analysis of the causes of large-scale loess landslides in Baoji, China

Landslide hazards are common in western China. Understanding the mechanism of landslides in loess-covered regions is particularly important for landslide risk assessment. A detailed landslide survey including large-scale slide drilling and geophysical exploration was carried out at the edge of the Loess Plateau on the north side of the Wei River in China. We reconstructed the geomorphological evolution model of the Wei River and analyzed slope structures and lithology. Engineering geologic conditions and active fault properties in the landslide regions were investigated. The results showed that paleogeomorphology of the north slope of the river gradually lowered from south to north. Ancient landforms showed a gradual transition to the south Sanmen Lake Basin from the piedmont alluvial plain during the Pliocene to early Pleistocene. The lake basin in the southern part of the study area gradually retreated, and the Wei River formed in the early Pleistocene. The main river flow shifted northward because of neotectonic movement and periodic climate changes until the Holocene, and then gradually moved southward to produce the current landforms. The active Wei River fault at the edge of the Loess Plateau acted as a route of water infiltration, weakening the structural planes. Erosion and rise of the groundwater table caused old (occurrence during the Late Pleistocene) and ancient (occurrence before the Late Pleistocene) landslides to form on the edge of the plateau along active fractures and interfaces of Pliocene sand, gravel and clay. These were multiple deep-seated rotational slides and/or multiple perched translational landslides. Slope stability analysis indicated that the complex landslides that occurred in the loess areas in recent years were closely related to the distribution of water and Pliocene clay.