Assessment parameters of rock masses for excavation in relation to moisture content

Abstract

The influence of moisture content on weathered rock arise frequent issues to the excavation works. A systematic approach of field and laboratory assessments were structured with geological data collection and excavation trial at two sites which Bentong site consist of sandstone and shale while Ulu Kinta site is characterized by granite to propose suitable assessment parameters of rock mass for excavation in relation to moisture content. Field study includes geological mapping and discontinuity survey in order to characterize the weathering state. Thirty-six trial tests were carried out during sunny days and after rainy days. Fourteen trials on sandstone and shale respectively and eight for granite. From field study, joint spacing are 0.1–2 m with maximum of four joint sets. Block size shows decreasing trend ranges from 1–0.1 m3 is slightly weathered to completely weathered rock mass. The result showed that block size more than 0.6 m3 could not be excavated. When involves block size ranges from 0.15–0.5 m3, the productivity less than 15 m3/h for all type of rock for slightly weathered rock mass. In highly weathered, block size ranges from 0.1–0.8 m3, productivity increase between 10–45 m3/h. Block size ranges 0.1–0.8 m3 does not influenced much on the productivity of completely weathered resulting 25–50 m3/h. It was found that increment of moisture content help to increase the productivity when the block size measured less than 0.3 m3 for all types of rocks. The productivity increased by 20–50% when excavated after heavy rain on moderately and highly weathered sandstone and shale. This study prove that moisture content could affects the excavation performance significantly on highly weathered rock mass. The effects are minimal on slightly, moderately and completely weathered rock mass. The block size does not become important factor in controlling the excavation performance in the completely and slightly weathered rock.