MECHANISM OF LARGE-SCALE SLIDE AT EDGE OF LOESS PLATEAU ON NORTH OF WEIHE RIVER IN BAOJI URBAN AREA,SHAANXI PROVINCE

Landslide mechanism is the key of understanding, reasonable assessment, effective prevention and control of landslides. It is quite difficult to achieve. Meanwhile, loess landslide mechanism has been one of the research hotspots in Chinese engineering geological circles over last decades. This study carries out detailed landslide survey and inventory combined with typical large scale slide drilling and geophysical exploration at the edge of loess plateau on north of Weihe river in Baoji urban area. There have been quite many achievements on latest quaternary geology, tectonic geology and loess studies in the recent years. The Weihe river valley evolution process is rebuilt. The slope structure and lithological association with engineering geological characteristics of stratigraphic which prone to failure are carried out. Active fault and tectonic joints or fissures are investigated as well. This study reveals the follows. The paleogeomorphology of north side of Weihe river is higher than the south part. The north land changed to the south Sanmen lake basin during Pliocene to early Pleistocene. Then the south lake basin gradually retreated and the Weihe river formed in early Pleistocene. The Weihe river mainstream periodicity north offset due to neotectonic movement and periodic climate change until Holocene epoch, and then gradually south offset. Hence, the present geomorphologic pattern is formed. The active Weihe north fault at the edge of loess plateau by sub-graben, horst bulge and half-graben provides not only water infiltration channels but also weak structure planes for slide failure surfaces tracking. The cause and model of paleo-slide and old-slide at the edge of loess plateau are induced by integrated erosion and rising of groundwater table. The main or sub-scarp and failure surface tracking along active fractures and Pliocene sand gravel and clay interface or internal clay are featured by garben-horst style multiple deep-seated rotational slide or multiple perched translational slide and its combination. They are controlled by Pliocene clay and tectonic fractures. They are special complex slides in loess landslides.