Strength Correlation Factor for Residual Soils

Abstract

Complete weathering of parent rock has resulted in the formation of residual soils that cover most of the land area of Sri Lanka. The physiography of the island demands that new engineering structures be located on sloping ground, thus posing many problems. The residual soils are heterogeneous due to variable weathering of the jointed rock mass. The heterogeneity of residual soils is due to the influence of relict joints, presence of boulders, and variability of the soil matrix. The repercussion of this heterogeneity is that properties of small samples of residual soils are unrepresentative of the mass, thus rendering conventional methods of field testing, laboratory testing, and analysis procedures for slope stability unsuitable. Heretofore, there have been no testing and analytical models available to represent residual soils. This paper describes an alternative method to predict shear strength parameters of residual soils by a correlation factor obtained from a multistage triaxial test and conventional slope stability analysis. Three landslides were investigated and analyzed to obtain the field shear strength parameters using the back analysis technique. On comparison with laboratory strength parameters, obtained from multistage triaxial tests, a correlation factor was ascertained. This correlation factor can be used to modify laboratory shear‐strength parameters to obtain field shear‐strength values of residual soils for design purposes.