Influence of micro-texture on the geo-engineering properties of low porosity volcanic rocks

The geo-engineering properties of rocks often depend on their petrographic, mineralogical and micro-structural features, and the interaction of micro-texture and physico-mechanical properties is often relevant. A series of petro-physical and mechanical tests on low porosity volcanic rocks suggest that small changes in porosity or unit weight can cause strength variations. Petro-physical and quantitative mineralogical analysis were utilized to understand these variations. In addition, quantitative petrographic studies focusing on distribution of minerals and mineral dimensions were conducted. Microstructural studies were carried out on thin sections before and after mechanical loading to analyse the distribution of micro-and macro-cracks which formed during unconfined compression tests. The results of petro-physical, petrographic, micro-structural, and mineralogical analysis suggest, that both, the peak strength and crack initiation threshold are strongly influenced by the distribution of phenocrystals (e.g. biotite, plagioclase) and the ratio between the total content of phenocrystals to the fine-grained groundmass. On the other hand it was found that variations in petro-physical properties (e.g. unit weight) and Young’s Modulus are associated with the mass fraction of minerals.