Publication Details

Indraratna, B, Khabbaz, M, Puswewala, A & Bandara, W, Effects of tsunami on coastal ground conditions and appropriate measures for rail track rehabilitation, Proceedings of the International Symposium on Tsunami Reconstruction with Geosynthetics - Protection, Mitigation and Rehabilitation of coastal and Waterway Erosion Control, 2005, 51-71, Thailand: Asian Center for Soil Improvement and Geosynthetics.


On boxing day, 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 extensive damage to infrastructure and fatalities of unprecedented proportions. Widespread destruction included several kilometres of rail tracks, dislocating the track elements from the remoulded surface soil. Near the beach town of Hikkaduwa, the ferocity of the waves was evident with the total destruction of tracks within 150 m from the shore, and overturning a crowded intercity train (over 1000 fatalities). In this paper, the relevant aspects imperative for the robust reconstruction of dwelling and rail tracks on such devastated ground are elucidated, based on the field observations and soil tests conducted several weeks later at the site of the train disaster. Visual examination and CPT tests indicated 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 re-deposited. Revised ballast grading and enhanced track conditions are considered, including the essential need for the formation soil stabilization. The use of geocomposites (i.e. bonded geogrid-geotextile layers) and associated benefits are described, with the aim of achieving reduced track settlement, increased resilient modulus and decreased ballast degradation. The benefits of increasing the confining pressure on track are also highlighted in relation to particle breakage.

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