Influence of petrographic characteristics on physico-mechanical properties of ultrabasic rocks from central Greece

Abstract

Ultrabasic rocks show a variety of engineering properties that may affect quarrying operations, tunnelling, mining, slope stability and the use of rock as a construction material. The physico-mechanical properties are influenced by the mineralogical and textural characteristics as well as the weathering of the rock. For this reason, the relationships between petrographic and physico-mechanical properties of fresh (peridotites) and serpentinized (serpentinites) ultrabasic rocks from central Greece, were investigated using correlation analysis. Thin sections, from the 47 samples, were prepared and examined under the polarizing microscope with the aim of describing the main mineralogical composition, the grain size, the serpentinization percentage and the structure of the rocks. The mineralogical and textural characteristics of some of them were also studied by X-ray diffraction analyses and the scanning electron microscope. The 47 samples were tested to determine dry and saturated unit weight, effective porosity, uniaxial compressive strength and static modulus of elasticity. The relationships between these properties and the petrographic characteristics are described by simple regression analyses. The research demonstrates that the physico-mechanical characteristics are strongly influenced by the petrographic characteristics except for mineral grain size. Negative linear correlations exist between serpentinization percentage and dry unit weight, while the effective porosity has a strong positive relationship with degree of serpentinization. Positive relationships are also obtained between the mechanical properties and dry unit weight and micropetrographic index Ips, while the increase of effective porosity causes a decrease in the index Ips (logarithmically in peridotites, and exponentially in serpentinites). The mechanical properties are exponentially related (negatively) to the serpentinization percentage in serpentinites and logarithmically (negatively) in peridotites. The serpentine plays a very important role in strength and elasticity modulus reduction, while the primary minerals have a smaller effect on the mechanical properties.