Abstract

Colombo-Katunayake Expressway is a major road project in Colombo, Sri Lanka. The project involves construction of a 25.8 km freeway linking the airport and Colombo. The majority of the route traverses flood plain and marshy ground consisting of very soft peats, organic soils and clays up to 15 m thick. Constuction of road embankments over these soils involves risks of embankment instability and excessive settlement. Soft ground treatments adopted to overcome the problems include methods of preloading and surcharging, prefabricated vertical drains, sand compaction piles and stone columns. Instrumentation and monitoring of the road embankments have also been implemented during constructioin using settlement plates, settlement stakes, piezometers, observation wells and inclinometers. Extensive geotechnical investigations, including boreholes, cone penetration tests, vane shear tests and laboratory soil tests, have been carried out to investigate the subsurface profile and soil properties. This information has been collated, compiled, interpreted and summarised. The field monitoring information has been used in back-analysis to calibrate the geotechnical model that represents actual soil characteristics. This paper focuses on the properties and characteristics of the soft peats, organic soils and clays interpreted from the geotechnical investigations and field performance.

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