Application of Combined Geological and Engineering Methods in Identifying and Evaluating Landslide Behaviour (Case Study: Havanan Landslide, South of Birjand, South Khorasan)

Landslide is a natural phenomenon that causes severe erosion of the earth's surface and may cause financial and human risks. The Havanan landslide has occurred in the mountains south of Birjand. The lithological, topographic and structural conditions of the area are such that, in the rainy season the conditions for reactivation of the landslide are provided. Due to the creeping movement of materials downwards, the old portion of the Havanan village is gradually being destroyed, and its fields are being damaged due to being located at the edge of the valley. In this paper, using geological, geoelectric, seismic and area mapping studies, the surface and subsurface conditions of the earth have been studied. According to local evidence, the Havanan landslide is a large transitional landslide. Although the main motion is a plane slip, the presence of several flat areas in the region indicates the occurrence of local rotational slides. The geoelectric study showed that the sliding mass thickness is between 10 to 30 meters, and the base rock is a sound ultramafic. According to the two stages of on-site mapping, the sliding mass moves an average of 23 mm per year. Also, the appearance of new cracks in the walls of houses, and the sounds heard occasionally, indicate the slow creep movement of the sliding mass.