THE BEHAVIOR OF RESIDUAL SHEAR STRENGTH OF LATERITE SOIL DUE TO THE ADDITION OF COARSE SAND AND LOW PLASTICITY CLAY FRACTIONS

Abstract

Residual shear strength plays a very significant role in geotechnical engineering. This concept has contributed extensively to diverse studies on soil behaviors under the influence of shear failure, both in drained and saturated conditions. In terms of landslides, the assessment of the residual shear strength after an occurrence and the progressive failure risk of slope stability has been very useful. However, information on this shear property in laterite soil appears relatively minimal. This soil type is the most frequently applied embankment for road construction in every Kalimantan region. Therefore, the purpose of this research is to determine the behavior of residual shear strength in laterite soil and the effects of adding coarse sand and clay fractions, using direct shear analysis. Subsequently, the specimens were prepared by compaction tests to obtain the optimum moisture content and uniform density, using coarse sand of varying proportions, termed 5, 10, 15, 20 and 25%, while, the shear strength treatment with wetting and drying cycle conditions was conducted under 2, 4, 6, 8 and 10 days, respectively. The results showed that the addition of the coarse sand and clay (CL) portions was able to increase the residual shear strength parameters (cohesion and internal friction angle) by 4-6%, compared to the pure state. Therefore, the introduction of clay (CL) materials ranging from 20-25% appears suitable in enhancing the residual shear strength of laterite soil. However, the extensive wetting-drying cycle tends to reduce the peak and residual shear strength.