Study On Risk Evaluation Of Seismic Geological Hazards In Baoji City

Geological hazards caused by earthquake have brought extensive concern because of their great disaster force. China is a multi-earthquake nation, so earthquake-induced geological disasters are very serious, especially in mountainous areas, which is even more harmful than that the earthquake directly caused. Baoji situates at the junction of Sino-Korean paraplatform, Qilian fold system and the Qinling fold system. It has complex geological structure and geographical environment, which leads to an area with many and prone geological disasters, especially under the action of the next possible earthquake. For this reason, this paper built up a seismic geological hazard assessment model under the action of seismic forces of Baoji city, studied and evaluated the geological hazards of Baoji city under the next possible earthquake in details. Then an area map of the distribution and extent of geological disasters in the earthquake was prepared, in order to provide some basis for decision making of Baoji city's geological disasters prevention planning.In this study, based on a full engineering investigation, inspection, testing and statistics of the geological disasters in the earthquake in Baoji city, the types of geological hazards were identified, which included landslides, soil liquefaction, seismic subsidence and so on. Firstly, landslide hazard is the major geological disaster in the study area, so the author selected the typical loess landslides to analyse their formated conditions and the happening mechanism comprehensively, and calculated their stabilities by the limit equilibrium method. According to the characteristics of the landslides in regions, factors for the evaluation were determined, including slope angle, slope height, sliding soil cohesion, internal friction angle and ground motion acceleration. Then by AHP method, the weight of the evaluation factors had been determined, and the landslide stability rating had been determined by the fuzzy comprehensive evaluation method,too. Secondly, sand liquefaction is also an important seismic hazard, so this paper established a sand liquefaction evaluation model with gray theory, by which the potential of liquefaction in the floodplain and first terrace was calculated. Liquefaction standard was made by code for seismic design of buildings, and the results were basdsically consistent by comparation. The third is seismic subsidence disaster. Based on the dynamic triaxial test, the layer-sum method was used to calculate seismic subsidence volume then seismic subsidence levels were divided according to the criteria, and the risk level of the region was determined finally.After full reference of results and methods of previous research, the author drew the ArcGIS technology into geological hazard assessment, used the ArcGIS software to partition the single disaster types of dangerous evaluation results for different probability of exceedance (10% and 2% probability of exceedance in 50 years), then mapped the geological hazard zonation (high risk zone, medium-risk zone, low-risk zone, risk-free zone), and superposed the single disasters types of disasters, got an Integrated regional disaster forecast map of probability in different probability of exceedance. These basic data, maps and research results will provide a reliable basis for the prediction, prevention and integrated mitigation measures of the earthquake disasters in Baoji city's buildings and lifeline projects.