Study On Formation Mechanism Of Abrupt Geological Hazards Of Southern Shaanxi Region In Condition Of Strong Rainstorm

The Southern Shaanxi region, consist of Hanzhong, Ankang and Shangluo city, is locatedin the south of Shaanxi province. Abrupt geological hazards such as landslip, collapse anddebris flow are well-developed in the whole district. New geological hazards occur duringflood season every year. From the People’s Republic of China was founded, a large-scalegeological hazards, the most serious of which caused the death of1,800people at a time,occurred every four years in Shaanxi province. The geological hazards inducing by frequentstrong rainstorm have been more developed in recent years. All the eleven hard-hits areas ofthe geological hazards inducing by the once-in-a-century strong rainstorm in2010are in thethree cities of the Southern Shaanxi region. The geological hazards have a serious threat tothe safety of life and property of the local residents. Researching the formation mechanism ofabrupt geological hazards of the Southern Shaanxi region in the condition of strong rainstormcan provide reliable theoretical foundation for disaster prevention and mitigation andengineering protection in the whole region. At the same time, it has an important referencevalue on the implementation of the immigration relocation project in the Southern Shaanxiregion.Relying on the project about the causes and countermeasures of rainstorm secondarymajor geological hazards in Southern Shaanxi region, the formation mechanism of five abruptgeological hazards resulting from strong rainstorm in July2010and2011was studied, on thebasis of a lot of previous data collection, field investigation, quantitative calculation andnumerical simulation. The main research contents are as follows.First of all, the development characteristics of five representative landslide and debrisflow referred above are studied, based on an analysis of the environmental and geologicalconditions containing meteorology and hydrology, topography, lithology, geological structures,neotectonics and earthquake, hydrogeological conditions and human engineering activities inSouthern Shaanxi region and nearby the five representative landslide and debris flow, notingthat there are two high speed rock wedge landslide debris flow, one accumulated layer landslide, one rock landslide controlled by the structural plane modeled by broken line andone valley debris flow among five geological hazards referred above.Secondly, the main influencing factors of the five representative landslide and debrisflow are analysed, noting that topography, lithology, geological structures are the controllingfactors of the formation of geological hazards and precipitation, strong rainstorm is the mostimmediately predisposing factors and human engineering activities have a certain role inpromoting the occurrence of geological hazards. The correlate orders of the influencingfactors are extreme weather, topography and geomorphology, lithology and rock massstructure, geological structure and earthquake, human engineering activities.Thirdly, the stability, the principal stress, the shear stress, the deformation and failure ofthe original slope in condition of natural, rainstorm or earthquakes is researched through limitequilibrium, stereographic projection method, and numerical simulation (FLAC and UDEC)methods, giving the corresponding factor of stability. The occurrence probability of the debrisflow is carried on the quantitative analysis.At last, the formation mechanism of five representative landslide and debris flow isresearched in accordance with high speed rock wedge landslide debris flow, accumulated layerlandslide, rock landslide controlled by the structural plane modeled by broken line and valleydebris flow.