Evaluation of liquefaction hazard along Line 2 of Rasht Metro by the use of AHP fuzzy method

Rasht City is capital of Gilan Provence and is considered as one of the metropolitans along the south coast of the Caspian Sea. In terms of geological setting, the city is situated to the north of the Alborz Mountains and in the Gorgan-Rasht sedimentary zone. The area is characterized by many active faults, with the Khazar fault being regarded as the most effect one, which can produce a gravity acceleration of 0.3g for a major earthquake. According to geotechnical data from exploration boreholes, the ground surface along Line 2 of Metro in the city comprises mainly a sequence of silts and clays with interlayers of gravel and sand. Due to high level of groundwater table, abundance of fine-grained soils, high seismicity potential, and production of ground vibration during movement of the train, liquefaction can be expected to occur along the Metro line. The aim of this paper is therefore to evaluate the liquefaction hazard potential along the Line 2 of Metro of the Rasht City by preparing a hazard zonation map. Liquefaction hazard zonation mapping was carried out using data gathered from 14 exploration boreholes drilled to a depth down to 40 meters integrated into Analytical Hierarchy Process (AHP) in the GIS modelling system. In this regards, five layers of information including soil type, SPT number, overburden pressure, plastic index and maximum gravity acceleration were considered. The results indicate that the range of liquefaction hazard varies between low to very high, and the maximum rate of liquefaction is expected in BC2 and I2 stations (Sazeman-e-Ab and Husain Abad areas, respectively). Soil type and groundwater table are recognized to be the most effecttive agents in inducing potential liquefaction.