Analysis on the Development Characteristics and Hydrodynamic Conditions for the Massive Debris Flow in Tianshui

Through a field investigation, the disastrous situation, causal factors, disaster characteristics, scope and distribution of massive mountain torrent geo-hazard on July 25 in Tianshui were systematically identified, and the development characteristics and causes were analyzed. The results show that the main types of geo-hazard caused and exacerbated by the heavy rainfall are mud stone landslides and loess landslides, followed by small debris flow, soil collapse and soil slope instability. The geological hazards had the characteristics as follows: universality, obviously group-occurring, local outbreak, deeply concealed, potentially hazardous and of significant disaster chain mode. The rainfall during the geological hazard had such characteristics as highly intensive and wide in range, which leads to the saturation of rock and soil of the mountain, and reduces the shear strength of rock and soil significantly. The massive mountain torrent geological hazard is exacerbated with the superposition effect of the earthquake and rain.