基于3DGIS的液化侧移区划新方法

A New Method for liquefaction-induced lateral spread zonation based on 3D GIS

场地液化是典型的地震灾害,其中最严重的为液化侧移,其区划工作是避免和减轻其灾害的重要手段,而我国这方面技术基本为空白。美国国家地震减灾计划(NEHRP)液化侧移区划技术代表目前国际先进水平,但它是一种基于单点侧移计算公式和2D GIS的方法,其可靠性和精度严重依赖高密度钻孔。基于地震区划的本质需求,摒弃NEHRP的点-面区划方式,研究一种面-面区划技术,提出基于3D GIS技术的液化侧移区划新方法。通过解决液化侧移层厚度和细粒土含量等面要素提取关键技术,获取可液化土层特征分布,结合先前提出的液化侧移等级判别标准,可给出适合小区域和中等区域液化侧移区划图。应用新方法,得到了7. 8级地震下唐山南区液化侧移等级分布图,与1976年唐山地震震后航测结果相符,表明了新方法合理可行。该方法克服了NEHRP方法依赖高密度钻孔的弊端,在保证液化侧移区划精度同时大大降低了成本,达到了科学合理且经济的目标。

Site liquefaction is a typical earthquake disaster,the most serious of which is liquefaction lateral displacement,and its zoning work is an important means to avoid and mitigate the disaster.The liquefaction lateral displacement zoning technology of NEHRP(National Earthquake Hazards Reduction Plan of US)represents the international advanced level at present,but it is a method based on single point lateral displacement formula and2D GIS.Its reliability and accuracy depend heavily on high-density boreholes.Based on the essential requirement of seismic zoning and abandoning the point-surface zoning of NEHRP,a new method of liquefaction sideways zoning based on3D GIS was proposed in this paper.By solving the key techniques of extracting surface elements such as the thickness of liquefaction lateral displacement layer and the content of fine-grained soil,the characteristic distribution of liquefiable soil layer was obtained,and combined with the criteria of liquefaction lateral displacement grade proposed previously,The zoning map of liquefaction lateral displacement suitable for small area and medium area could be given.By using the new method,the scale distribution of liquefaction lateral displacement in the south area of Tangshan under the M7.8earthquake was obtained,which was in agreement with the aerial survey results after the1976Tangshan earthquake.It was shown that the new method is reasonable and feasible.This method overcomes the drawback of NEHRP method depending on high density borehole,ensures the accuracy of liquefaction lateral displacement zoning and greatly reduces the cost.