The engineering characterization of altered granites through the processes of kaolinisation is critical for effective extraction and design of slopes for the china clay industry in south-west England. As part of on-going research into the engineering behaviour of variably kaolinised granites a series of instrumented uniaxial compression tests were performed on representative samples taken from a varying decomposition grade range of altered granite. Analysis of acoustic emission (AE) and strain gauge deformation measurements, together with Scanning Electron Microscope (SEM) images taken at various stages of failure, were used to characterize the fracture development and damage processes occurring during uniaxial compression. The results of the testing confirm that the degree of alteration or kaolinisation and associated changes in mineralogy of the granite is directly related to reduction in both uniaxial compressive strength and porosity. The assessment of strength and alteration grade is a fundamental component of geotechnical characterization of slopes in altered granite.
A consequence of implementation of the Quarries Regulations 1999, for the United Kingdom quarrying industry, has been a need to identify potential hazards in order to initiate, if required, more detailed geotechnical assessment of critical slopes that are deemed to pose a significant hazard to either persons or property. Hazard identification within the china clay industry requires appropriate characterization of altered or kaolinised granite. Stead et al. (2000) provided a review of the approaches to engineering characterization of altered granites, taking into account the previous work undertaken in south-west England and, in particular, Hong Kong. Characterization of altered granites usually involves categorization into classes, zones or grades according to readily recognized or simply measured variations in their characteristics. This paper presents the results of an on-going investigation into factors controlling the engineering behaviour of altered granites.