Vulnerability Levels of Liquefaction Zones as a Spatial Planning Concept Based the Disaster Mitigation in Pariaman City—Indonesia

Abstract

Knowledge about the liquefaction vulnerability in Pariaman city which is prone to an earthquake is very much needed in disaster mitigation based spatial planning. The liquefaction is an event of loss of the strength of the sandy soil layer caused by the vibration of the earthquake, where the liquefaction occurs in the sandy soil layer which has loose material in the form of sand that is not compact or not solid. This research was conducted by analyzing the potential of liquefaction vulnerability based on the Conus penetration to produce Microzonation of the susceptibility of subsidence due to liquefaction at 4 locations in Pariaman city, i.e., Marunggi village, Taluak village, Pauh Timur village and Padang Birik-Birik village. The Conus penetration testing is carried out using the piezocone (CPTU) method and mechanical Cunos penetration, and approach using Geographic Information System (GIS). The results showed that the potential of liquefaction was found at the sandy soil layer of sand and a mixture of sand and silt, which is characterized by the value of Cunos resistance and local resistance each smaller than 15 MPa and 150 kPa at varying depths. Based on the results of the analysis using this method, the critical conditions of liquefaction found in the medium sandy soil to solid. The fine sand layer which has the potential for liquefaction is in sand units formed from coastal deposits, coastal ridges and riverbanks. This liquefaction vulnerability zones analysis is limited to a depth of 6.00 m due to the limitations of the equipment used. The results of the analysis show that the fine sand layer which has the potential for liquefaction occurs at a depth of> 1.00-6.00 m with the division of zones, i.e., 1) High liquefaction in the sandy soil layer which has a critical acceleration (a) <0.10 g with shallow groundwater surface; 2) Medium liquefaction in the sandy soil layer which has a critical acceleration (a) between 0.10–0.20 g with shallow groundwater surface; and 3) Low and very low liquefaction in the sandy soil layer which has a critical acceleration (a) between 0.20–0.30 g with an average groundwater deep enough surface.