Evaluation of correlations between SPT N and undrained shear strength for fine grained soils of Sri Lankan geological conditions

Abstract

Undrained shear strength is one of the essential parameters in most of the applications of geotechnical engineering. Unconsolidated undrained (UU) triaxial test is the most commonly practiced method of determining the undrained shear strength which takes a considerable time and effort to produce its results, since the sampling stage. Such correlations seldom exist pertinent to Sri Lankan soils. Hence, it is important to have reliable correlations between easily executable, commonly used test results and undrained shear strength of Sri Lankan soils to easily and promptly predict the soil structure interaction phenomenon, especially in local geotechnical engineering applications. Thus, in this study, an attempt has been made to correlate the standard penetration test (SPT) with experimentally determined unconsolidated undrained triaxial test parameters, and the undrained shear strength estimated from the field vane shear test data. This analysis consists of three main stages, namely analysis of the available correlations, analysis of the available data set based on the soil and sampling properties to develop a correlation and the analysis on a set of reliable data with a defined deviation factor. A correlation between SPT N60 and undrained shear strength has been proposed for Sri Lankan silty soils. Further, possible analysis methods for developing correlations for other different soil types have also been addressed. In addition, existing drawbacks and difficulties associated with developing such correlations related to Sri Lankan context are also described.