RISK ASSESSMENT FOR LUOJIAQINGGANGLING ROCKFALL

China is a country with many mountains. The risk assessment of rockfall has gained more attention due to the increase of rockfall hazard in mountainous areas. Rockfall risk analysis is inherently complex and difficult. Such difficulties are due to many factors. They include high uncertainties of rockfall occurrence and transport, lack of historical data, strongly site-specific nature of rockfall, difficulty in quantifying and modelling spatial rockfall distribution, quantifying the heterogeneity of vulnerability of different elements at risk and variability in temporal vulnerability, These factors lead many limitations in quantitative risk assessment. Rock falls in Luojiaqinggangling, Sichuan Province are a scarce example to study risk assessment quantitatively due to the complete field data and rich historical data. Based on the engineering geological investigation, topographical survey and statistic analysis, this paper confirms the provenance, accumulation area, maximum transport distance, annual probability of occurrence and four potentially unstable blocks A-D. Rockfall risk for exposed people in Luojiaqinggangling is estimated by the product of three conditional probabilities (annual probability of occurrence, reach probability and temporal-spatial probability) and vulnerability. Based on the rich statistical data of historical rockfall, the annual probability of occurrence is derived from a magnitude-cumulative frequency (MCF) distribution of rockfall events. Considering the size statistical characteristics of the historical rockfall and the position uncertainties of unstable blocks in provenance, this paper conducts the inversion analysis of slope restitution and friction coefficients. It uses the two-dimensional simulation software Rockfall. On these basis, the arrival probabilities of unstable blocks A-D were obtained after numerous random simulation and statistical analysis. Pedestrians and residents that are confirmed as the affected body based on field investigation, temporal-spatial probability depends on the mobility of the exposed elements. It is calculated using empirical equation according to the movement feature of affected body. The vulnerability was determined combining the kinetic energy of rockfall and the location of affected body. According to the product of occurrence probability, arrival probability, temporal distribution probability and vulnerability, the quantitative risk assessment of this rockfall is achieved. The results show that the risk values of block A and D are in a unacceptable risk range, and the risk values of blocks B and C are in a warning range. Those unstable blocks could threaten the life safety of the residents, therefore, it is essential to take appropriate measures for the disaster prevention and mitigation.