An excavatability classification system for surface excavation in sedimentary rocks

This paper describes the development of an excavatability classification system for surface excavation of weathered sedimentary rock based on practical excavations and statistical analysis. Extensive field and laboratory studies were undertaken on three sedimentary rock sites with a range of weathering and strength conditions in the Iskandar region, South Johore, Malaysia. Rock mass descriptions were made in the field and rock material tests were carried out in the laboratory. Statistical analysis was used to study the correlation between the rock parameters and the productivity of excavation. A classification rating system based on the analysis results is proposed. The proposed classification system incorporates rock parameters such as point load strength (Is₅₀), Schmidt Rebound hammer value (R), uniaxial compressive strength (UCS), density of rock (γ), indirect tensile strength (ITS), second-cycle of slake durability index (Id₂), joint number (J _n), joint spacing (J _s), joint length (J _L), joint direction (J _d), existence of iron pan (IP), moisture content (M _c) and existence of bedding. The proposed model was then verified against further excavations on another sedimentary rock site. It was found that the productivities recorded correlated well with the proposed system when tested on a fourth site.