The effects of micro-textural properties on the strength and deformation characteristics of rocks with andesite and rhyodasite compositions exposed in gökçeada Gökçeada’da yüzeylenen andezit ve riyodasit bileşimli kayalarin içyapi özelliklerinin dayanim ve deformasyon özelliklerine etkileri


Ündül Ö. , AYSAL N.

Jeoloji Muhendisligi Dergisi, vol.40, no.2, pp.123-148, 2016 (Refereed Journals of Other Institutions) identifier

Abstract

© 2016, TMMOB - Jeoloji Muhendisleri Odasi. All rights reserved.The onset of dilation and uniaxial compressive strength of rocks are known to be affected by mineralogical, petrographical and microstructural features. In this study, volcanic rock samples with different micro-textural characteristics from different locations in Gökçeada (Turkey) were evaluated considering the effect of mineralogical, petrographical and microstructural features on their physical and mechanical properties. Furthermore, detailed analyses were also used to understand the cracking processes under axial loads. The analyses of the cracking processes were evaluated by using thin sections obtained from the mechanically tested specimens. The results from the quantitative mineralogical and petrographical studies and observations from thin sections revealed that the mineral mass fractions have an effect on the specific gravity and loss-on-ignition (LOI) values. On the other hand, uniaxial compressive strength (UCS) and elastic properties are mostly affected by petrographic variables (e.g., mineral content). The UCS values tend to decrease with a relative increase in the groundmass with respect to the phenocryst content and vice versa. Biotite is the only mineral that influences the UCS individually. Geometric features (e.g., Feret’s diameter and perimeter) of opaque minerals and biotite are found to be important constituents influencing the Young’s modulus of the rocks. Under axial loads, crack propagation is strongly dependent on the proportional distribution of the phenocryst and groundmass. It is observed that increasing groundmass content leads to predominantly axial cracks. The cracks tend to bend or propagate as a boundary crack when they reach the boundary of an unaltered phenocryst. Thus, axial and shear cracks co-exist with increasing amounts of phenocrysts, which hinder the crack propagation. Occasionally, cracks can penetrate the altered or opaque phenocrysts, depending on the degrees of orientation (with respect to applied load) of the same minerals. Furthermore, the synthesis of the measurements obtained from UCS tests and thin section observations reveals that an increase in the amount of phenocrysts, which promote the formation of more shear cracks in addition to axial cracks, causes an increase in the radial strain and Poisson’s ratio. The other factors investigated have minor effects on the physical and mechanical properties of the studied rocks.