Empirical correlation for estimation of unsaturated soil shear strength

Most land surface in Malaysia is covered by residual soil with relatively deep groundwater elevation, thus the soil presence in the saturated condition. Stability of slope in such soil is governed by the shear strength of unsaturated soil, for which matric suction plays an important role. The focus of this project is to study the relationship between the matric suction and the shear strength. Five empirical models are adopted to predict the shear strength of unsaturated soil by utilizing the saturated shear strength parameters and soil water characteristic curve of two soils retrieved from two sites in UTM campus i.e. fine-grained soil (Kolej 12) and coarse-grained (Balai Cerapan). Previous studies suggested that the effect of suction is most significant within the transition zone of SWCC curve. In this case, the transition zone is 10-80 kPa for Kolej 12 and 2-60 kPa for Balai Cerapan soil. The saturated shear strength parameters for Kolej 12 and Balai Cerapan soil are (c´=20 kPa, φ´=27°) and (c´=22 kPa, φ´=33°) respectively. Analysis by empirical correlation also shows that for fine-grained soil at first site, the shear strength increase linearly with suction. In this case, φ^b is 11.7°. on the other site, linear increment of shear strength is depicted by coarse-grained soil with constant φ^b of 17.9°.