Empirical Approach for Evaluation of Compressive Strength of Shale

A sound knowledge regarding the strength and stiffness properties of rock material could significantly improve engineering geological assessments. Shales are known as the most problematic rock material worldwide. Uniaxial compressive strength UCS is an essential input parameter for development of almost any engineering design. However, appropriate core specimen for measurement of UCS in the lab is often a real dilemma. Accordingly, extensive attempts have been made for strength estimation based on other parameters. In this research, an empirical equation is suggested for estimating UCS of shale based on Young’s modulus and porosity. This equation was achieved based on statistical analysis of lab experiments obtained over a wide range of geographical locations. A further attempt was made to describe mathematical meaning of the statistical results based on theory poroelasticity. Accordingly, at low porosity values both Young’s modulus and porosity significantly contribute in prediction of the UCS. This was attributed to poroelastic behavior of shale under these conditions. At high porosity values, however, E was the dominant parameter. One of the advantages of this research is that suggested equation is independent of the geographical location, while it is based on two input parameters Young’s modulus, and porosity.