Classification on shape of granitoid boulder based on size and surface roughness from various weathering zones for site investigation purposes

Abstract

Boulder is often posed challenges to earthwork activities such as cut slope and foundation excavation especially in tropical weathered rock like Malaysia. In addition, the guidelines for hard material or rock excavation related to boulder provided by Department of Works Malaysia (JKR) are limited and there is a need to be revised. Therefore, this study aims to establish a classification chart of boulder's shape in different weathering zones for site investigation purposes. The parameters of size, volume and characteristics of surface roughness from moderately to completely weathered zone were measured and analysed statistically. Results of this study show that the increase of weathering zone from zone 3 to 5 significantly reducing the size and volume of boulder with reduction of 27% and 38.3%, respectively. Boulder in Zone 3 to Zone 5 can be classified into six typical sphericities: very flat, flat, sub- flat, sub-spherical, spherical and well-spherical. The results also revealed that the physical parameters of boulder can be classified into six classes based on Roundness Ratio (Rr) and Surface Roughness Index (SRI). Based on these results, a boulder shape classification chart was developed and useful as a guideline for engineering application especially in soil investigation purposes.