Some microstructural aspects of strength variation in rocks

The experimental study of rock strength revealed a remarkable mechanical variation in closely related rocks. This variation is explained through a quantitative analysis of microstructures. The oriented dry rock specimens were loaded at a constant stress rate and the uniaxial compressive strength with deformation. was recorded together. Microstructures were analysed in thin sections using petrographic image analysis. making it possible to determine size, shape and the shape-preferred orientation of individual grains, grain size distribution and modal composition. The typical grain size has been found to be the main microstructural factor controlling strength variation in groups of rocks which are closely related mineralogically. The increase of strength anisotropy is connected with an increasing degree of shape-preferred orientation of rock-forming minerals. (C) 2001 Elsevier Science Ltd. All rights reserved.