A simple regression based approach to estimate deformation modulus of rock masses

• The relationships between the deformation modulus (Em) and the RMR89 were evaluated.
• An empirical equation was developed to estimate indirectly the Em.
• The experimental Em values were used to control the performance of the empirical equation.
• The empirical equation obtained in the present study has a meaningful performance.

Rock mass characterization has a crucial importance in rock engineering applications including foundation design, slope design, support design and others. For these purposes, it is necessary to determine some input parameters for design, such as deformation modulus (Em), uniaxial compressive strength (σci) and Poisson ratio (υ). The Em is an important input parameter and the practical and economical way to determine this parameter is to apply a rock mass classification system and estimate using the rock mass properties. Data from four different sites were used in the study. The values of Em were calculated using the existing empirical equations based on the Rock Mass Rating (RMR89) system. Furthermore, pressuremeter tests were carried out to determine the Em in one of the sites. The relationship between the RMR89 and the Em was obtained via simple regression analysis using the Em calculated from empirical equations based on RMR89 system. Afterwards, performance of the equation obtained from regression analyses was examined and compared the predicted Em values with experimental values with respect to the R2 values using the data of fourth site. Overall R2 value was found to be as 0.75.