Geological Disaster Risk Assessment In The "5.12" Meizoseismal Area The Five Village Community Of Nianzi Qingchuan County Sichuan Province.

Sichuan province suffered magnitude 8 earthquake on may 12, 2008. The Qingchuan county is the meizoseismal area of the "5.12"earthquake. Earthquake triggered a large number of secondary geological disasters. Those hazard points has a highly outbreak possibility of geological disasters in the earthquake, rainfall etc. Correct evaluation of the risks of the major geological hazards is the key geological problems of rehabilitation and the protection of people's lives and property.The paper's study and evaluate objects is the geological disasters in the five village community of NianZi. Based on the study of the engineering geological conditions,the development and distribution of the study area's geological hazards,the failure and variabile modes, dynamic characteristics analysis of debris flow,then evaluated the risk of geological disasters in the study area., After the risk assessment results obtained, determine whether it is in acceptable range in accordance with the international social standards,and propose appropriate measures for the disaster.The research has a strong practical value. The conclusions are:(1) The main geological disasters in the study area are collapse and debris flows. The collapse is consists of 10 unstable rock zone,1#～9# unstable rock zone and HaoZiWo unstable rock zone. The debris flow in the study area is stimulated by rainfall,and the source of the debris flow is the collapse deposits which formed in the "5.12"earthquake. The debris flow is "IF-sticky-heavy rain-mountain valley" type.(2) Drawn on the collapse hazard analysis:the main failure modes of collapse are sliding and dumping type. The main factors of the collapse are topography, earthquake, heavy rain and weathering. The greatest threat to the five village community of NianZi is 2# unstable rock zone ,3# unstable rock zone and HaoZiWo unstable rock zone. (3) Through the formation conditions of debris flow derived:scarp highly developed and large drop in Qing Ling ditch,so it has a good terrain conditions for the debris flow'outbreaking. The source in Qing Ling ditch'source is very rich ,reached 19.64×104m3. The Qing Ling watershed has a large and concentrated precipitation,maximum daily rainfall reached 80 ~ 100mm,24-hour maximum rainfall 110mm.So, the Qing Ling ditch has a good rainfall condition for the outbreak of debris flows. Therefore,the QingLing ditch may outbreak debris flows under the conditions of rainstorm,and will threat residents and traffic safety.(4) The damage effects of the geological disasters in the Study area are: causing casualties by threat human's life and security,destruction of homes and other buildings,threatening traffic safety by destruction of roads, bridges and culverts,destruction of crops and burying land resources.(5) Through the disaster risk assessment of collapse obtained: the collapse disasters are low risk,event of a collapse hazard Nianzi village will loss 29 people and 973,000 yuan. The higher the failure probability of the collapse the greater the risk when under different conditions. Through the disaster risk assessment of debris flows obtained: the danger of the debris flow is low to moderate, event of a debris flows hazard Nianzi village will loss 1 people and 79,000 yuan, the risk of the debris flow is moderate. On this basis, with the advantages and disadvantages of full relocation and adopt disaster control measures, eventual adoption of the disaster control measures to reduce the risk of disaster.(6) The passive safety net and the " debeis flow fence+dam+ drainage canal + culvert reconstruction " control measures are taken to the collapse and the debris flow. The passive safety net is mainly to reduce the loss of people and houses;the debeis flow fence will intercept large stone and stop it damage the downstream control measures after it accelerated;the dams will reduce the debris flow source get to the threatened area;the drainage canal is mainly exhaust the debris flow source and prevent climbing;the aim of culvert reconstruction is to make the culvert reach the design flowrate.