Consolidation properties of soft organic soils in Sri Lanka

Abstract

Most of the new coming highways in Sri Lanka are run through low-lying areas mainly to minimize the damages to the existing structures and to the livelihood of the people living in the buildup areas. The shallow subsurface of these low-lying areas consists mainly of very soft highly compressible organic soils or soft alluvial deposits. Due to the high flood levels above the existing ground surface in the low-lying areas, high embankments are needed to avoid flooding of the highway. As a result, geotechnical engineers are faced with a tremendous challenge of construction of high embankments over thick very soft highly compressible soil deposits. Due to shear failure and large settlement of the soft soil deposits under the embankment loading, these soft soil deposits must be improved before the placing of the embankment fill or during placing the fill. There are different types of treatment methods used in Sri Lanka such as preloading, preloading with vertical drains, sand columns, stone columns, piled embankment, vacuum consolidation etc. The actual method of treatment depends mainly on the thickness of the soft deposit, consolidation and shear strength properties of the soft deposit, height of the embankment etc. Therefore, it is essential that the properties of the soft soil are determined during the initial stage of the design to decide the type of the soft ground treatment method as well as during the design stage. Determination of the strength and compressibility properties of commonly found soft soil deposits using undisturbed samples is a no easy task due to the inability to recover undisturbed samples and difficulties associated with preparation of test samples and testing.