GIS-based assessment of liquefaction potential for selected earthquake scenarios

Abstract

The liquefaction phenomena is a complex condition in saturated cohesionless soils caused by dynamic loads i.e. earthquakes that can cause significant damage to structures and infrastructures. The focus of the research of this paper is to define the potential of liquefaction using in-situ methods, particulary SPT investigations for a characteristic location - Ohrid city, Republic of Macedonia. Being on the Coast of Ohrid Lake, the soils of this location are with near surface water tables, and are also characterized by layers of relatively loose saturated sand, with low to high content of fines. A liquefaction potential assessment by means of an Fs (factor of safety) and PL (probability of liquefaction), was carried out for a number of locations with available results from geotechnical investigations, using the deterministic and probabilistic relations proposed by Boulanger & Idriss. The dynamic inputs for deriving the CSR (cyclic stress ratio) were parameters of PGA and Mw for two selected seismic scenarios, in accordance with the seismic hazard for the selected location. The results served as a basis for deriving a methodology for local zoning of this type of hazard, using the GIS software. The final product are 4 maps of factor of safety against liquefaction and probability map of liquefaction for the two analyzed scenario, which refer to the critical layer with potential of liquefaction. The results led to several conclusions related to the soil conditions and characteristics, the advantages of the in-situ methods, the need for additional terrain investigations as well as comparison between deterministic and probabilistic approaches. Also, they highlight the necessity for this type of investigations as a preventative measure for urban planning.