Evaluation of empirical approaches in estimating the deformation modulus of rock masses

The rock mass deformation modulus is an important parameter for analysis of the mechanical behaviour rock structures. Due to high cost, time consuming activity and difficulties in interpretation of in-situ measurements, a number of empirical methods have been developed to estimate the deformation modulus on the basis of classification systems. However, due to a large number of empirical equations, the practical rock engineers have encountered the question which empirical relationship provides the most reliable estimation of the deformation modulus. This paper combines a review of empirical equations and statistical analyses based on the case studies from Iranian geography. Results of ninety-nine plate jacking tests from three dams and hydropower projects were used to evaluate the predictive performance of these empirical methods. Statistical analyses show that the Hoek and Diederichs (Int J Rock Mech Min Sci 43:203-215, 2006) and Ajalloeian and Mohammadi (Bull Eng Geol Environ 73:541-550, 2014) relationships provide the most precise and accurate estimation of the deformation modulus based on the in-situ measurements.