Characteristics of opposite-slip loess landslides and its collision induced mechanism in the Baoji area, Shaanxi.

Opposite-slip landslides are a unique form of landslide geohazard in loess areas. They are mainly distributed in slopes on both sides of the second- or third-order tributary (gully). The landslides on both banks of a gully slip toward each other. The gully is narrow, deep and steep usually, and extends far. Opposite-slip loess landslides do not happen simultaneously. The early occurring slide mass strongly collides with the slope mass on the opposite bank after its sliding, leading to the occurrence of collisional joint fractures, weakening its mechanical properties and forming potential sliding surfaces in the slope mass．When the early-occurring slide mass suffers from rainfall immersion and flowing water scouring in the gully, the potential slide surfaces expand and are connected, which induces instability and down-slip of the collided slope. Therefore, it is necessary to further study the collision damage effect of opposite-slip loess landslides so as to provide a scientific basis for the forecast of landslide occurrence in groups in loess areas.