Tsunami affected coastal soil disturbance and implications on reconstruction with special reference to low-cost dwellings and rail tracks

摘要

On 26 December 2004, the largest earthquake for more than 4 decades (magnitude 9.0) occurred between the Australian and Eurasian plates in the Indian Ocean (along the overly stressed Sunda trench) to the west of Aceh Province (Northern Sumatra). The quake triggered a series of waves that increased in height rapidly close to the shore (tsunami) spreading thousands of kilometers across the Bay of Bengal. In the Eastern and Southern coastal belt of Sri Lanka, the floodwaters reached almost 1 km inland, causing unprecedented damage to infrastructure and over 4000 fatalities. Widespread destruction included several kilometres of rail tracks, dislocating the track elements from the remolded surface soil. Near the beach town of Hikkaduwa, the ferocity of the waves was evident with the total destruction of tracks within 100 m from the shore, and overturning a crowded intercity train. Based on visual examination and CPT tests conducted several weeks later at the site of the train disaster, it was observed that the sandy topsoil was turbulently blended with transported marine sediments including organic fines. Under excessive hydraulic gradients, the geotechnical properties of surface soils up to a meter or more have been significantly altered. At some locations near the surface, the void ratios have almost doubled once the waves receded and the soil redeposited. In this paper, the relevant aspects of dwellings reconstruction and rail tracks on devastated coastal soils are elucidated. Guidelines for reconstructing robust costeffective foundations are discussed, based on the first author’s own experience. Revised ballast grading and enhanced track conditions are considered, including the benefits of increasing track confining pressure and the essential need for soft formation stabilization.