Abstract:

As a new landslide type, its genetic mechanism of landslide is triggered by lateral shear disturbance. The large scale landslide occurred at Longjiapo,Cengong in Guizhou Province on June 29,2012. The landslide, with its volume ranging from 300×10⁴ to 400×10⁴ m³, became a 20 m weir dam in height blocking up the Mapo River in the lower part and a dammed-lake with about  7×10⁴ m³ in volume. Based on site investigation, the authors provide detailed characteristics of the landslide and  analyze the mechanism of the landslide. It is combined with in-situ grain size composition experimentation, aerial photography and other means. The results indicate that, there were weathered thick accumulation body in the landslide area, and that inclination direction of rock stratum and terrain condition of slope were the favorable fundamental conditions to the landslide. The south part of slide areas, which was a natural guiding gutter of groundwater, had been filled in large amounts of silty clay. In that case, it exerted a large additive gravity force on the ground, and it also induced local groundwater enrichment in the slope body. After the rainfall, part of water seeped into the soil mass and reduced the shearing strength of soils. Then, the slope body in the south area slid firstly, and the motion took great lateral shear perturbation to the main slide area. The main slide area was driven to slide. It deserves intensive study as it is pretty special that the lateral shear disturbance triggered a large landslide. Hence, in addition to its characteristics of rock and soil in the landslide, the geo-conditions of both sides must be investigated in disaster early warning and mitigation.

Key words: Longjiapo landslide, accumulation body, lateral shear disturbance, weir dam, failure mechanism, characteristics of surface rupture