Weathering effects on discontinuity properties in sandstone in a tropical environment: case study at Kota Kinabalu, Sabah Malaysia

The formation of mechanical discontinuities (i.e., bedding, joint planes) is one of the main effects of weathering in rock masses. It is also highly important for forecasting the geotechnical properties of a rock mass in the future. The effect is well known in most rock types, but the mechanisms of forming discontinuities and the resulting variation of mechanical discontinuities throughout a rock mass especially in sedimentary rocks such as sandstone in a tropical environment, are often still poorly understood. The aim of this research is to study and understand the discontinuity formation process in a tropical environment. In sandstone in Sabah, Malaysia, discontinuity spacing decreases with higher weathering grades as expected. Three main discontinuity sets are formed and the spacings of the discontinuity sets formed in the thickly bedded sandstone reduced. The discontinuity development is related to weathering processes and governed by pre-defined, i.e., incipient or internal, planes of weakness that originate during early stages of rock formation and in response to the past and present three-dimensional stress field(s). The paper is motivated by the need to evaluate the engineering implications of mechanical discontinuity sets that are not apparent in rock at lower grades of weathering but that will be formed as a consequence of on-going weathering processes.