Evaluation of liquefaction potential of Western and Eastern Coastal Areas in Sri Lanka

Abstract

There has been an increasing concern on earthquake related disasters in Sri Lanka after 2004 tsunami. It is partly due to the fact that that most of the important structures in Sri Lanka are founded on loose sandy soils along the coastal areas. During a strong earthquake, there is a huge possibility that these loose sand deposits may liquefy causing significant damage to the structures founded on them. In addition, some of the coastal areas suffer frequent floods, which may magnify the damage due to liquefaction. Standard Penetration Test (SPT) and Cone Penetration Test (CPT) are widely used for the site specific evaluation of liquefaction potential of sandy soils. In this paper, results of the analysis of liquefaction potential based on SPT resistance values are presented. Here, 46 bore holes from Colombo and east- coast were analyzed, and the liquefaction potential was evaluated by means of a factor of safety against different earthquake magnitudes and different ground water levels. From the analysis results, liquefiable areas and the depths of liquefiable areas were identified. It was observed from the analysis of 24 boreholes in Colombo area that, 3-13 m depths from ground surface are liquefiable during a 6.5 magnitude earthquake, while on average 4-10 m depths are liquefiable in Batticaloa, Mutur, and Ampara areas in the east coast under normal ground water conditions.