Analysis of Control Factors and External Force for the Landslides in Heifangtai Area

Heifangtai landslides are concentrated in the surroundings of Loess Platform, Gansu province, with high occurrence frequency. The internal control factors for landslides have been analyzed in this paper, including the topography and geomorphology, geometrical characteristics of landslides body, geological structure, landslides controlling structure surface, rock and soil group of slope body, engineering and hydrological conditions. The external force has also been researched from the aspects of irrigation and freeze-thaw. The intermittent neotectonic uplift movement has shaped the geomorphic pattern of the loess platform connected with the second terrace of the Yellow River and the large elevation difference at the edge of the platform, all of these have been established as the geomorphic basis for the formation of landslides. Multi-slope structure of loess and rock exists in the easily sliding stratum and consequentsoft interlayer. So, the combined action of irrigation and freeze-thaw has induced the landslides. The development and disaster mode is deferent due to the various geometrical characteristics of landslides body, rock and soil group of slope, the position of the landslide controlling structure surface, hydrological conditions.