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Resumen:
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Travertine is an anisotropic rock considered as one of the most popular stone materials in the building industry. Due to its bedding and lamination planes, the determination of rock strength properties regarding anisotropic orientation is a critical issue. In this research, different techniques were applied to estimate the compressive and flexural strengths of four types of travertines, selected from Hamedan and Markazi Provinces located in the west and central parts of Iran. For this purpose, after sample preparation and assessment of mineral composition, fabric (texture and structure) and pore characteristics (pore shape and pore sizes), the selected samples were characterized using physical and mechanical tests. These properties were evaluated with respect to two major anisotropic orientations (perpendicular and parallel to the bedding/lamination axis). Statistical analyses, including simple and multiple linear regressions, were utilized to correlate physical and mechanical parameters with compressive and flexural strength, and to establish some new equations. Based on the test results, it can be concluded that the percentage/type of matrix and porosity have a more important effect on the physical and mechanical properties than the rock structure. Data analysis in simple regression shows that bulk specific gravity (saturated surface dry) and Brazilian tensile strength are the most and least influential factors on compressive strength at perpendicular and parallel directions, respectively. In addition, effective porosity and Brazilian tensile strength are the most and least influential factors on flexural strength at both directions, respectively. Based on best subset multiple regression method, one or two equations were extracted for calculating compressive and flexural strength in the perpendicular and parallel directions. Also, pore shape factor and pore radius were used as independent parameters in multiple regression to establish some new equations for predicting compressive and flexural strength considering cutting directions. These parameters have more influence on flexural strength than compressive strength, because the parameters show significant correlation with flexural strength. Consequently, the results of statistical analyses show that the proposed equations are not necessarily composed of parameters with the higher/stronger determination coefficient in simple regression. Therefore, prediction studies not only offer some rational approaches, they also give a better insight into the main factors determining rock strength.
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