Residual shear strength of tropical granitic soils in Peninsular Malaysia

Introduction: Residual shear strength is an important parameter in the assessment of long-term slope stability and reactivated landslides. However, limited information is available on the residual shear strength behaviour of tropical granitic residual soils in Malaysia. This study investigated the residual shear strength characteristics of granitic residual soils collected from three locations in the northern region of Peninsular Malaysia: Kulim Hi-Tech, Bukit Suling, and Bukit Katak. Materials and methods: Laboratory characterisations encompassed physical index testing, particle density determination, mechanical sieve–hydrometer analyses, and Multiple-Reversal Direct Shear Testing (MR-DST) conducted under fully drained, saturated conditions across effective normal stresses of 50 kPa, 100 kPa, and 150 kPa. Results: The results indicated that residual shear behaviour was predominantly friction-controlled, with adopted effective residual friction angles ranging from 18.9° to 23.5°. Regression analysis revealed strong negative linear trends between effective residual friction angle and soil index properties (plasticity index (PI), liquid limit (LL), and clay fraction (CF)). However, because these relationships were derived from three site-level observations ( n = 3) without external validation, they are presented strictly as preliminary site-specific empirical correlations and must not be interpreted as design-ready predictive tools. Conclusions: This study expands the limited database for tropical granitic residual soils in Malaysia, demonstrating that index properties provide practical preliminary screening guidance while highlighting that direct, site-specific laboratory testing remains indispensable for final geotechnical design.