Estimation of Modulus of Deformation Using Rock Mass Rating—A Review and Validation Using 3D Numerical Modelling

The Himalayan region has enormous potential for hydropower development. However, variations in geological and geotechnical conditions pose challenging tasks for the designers. If these variations are not tackled in a timely manner during underground excavations, especially for caverns, instabilities may occur, resulting in time and cost over-runs. For sustainable hydropower development, minimizing these over-runs is necessary. The modulus of deformation (Ed) of a rock mass is an essential input parameter required in the design of underground excavations. This study involves collecting the results of extensive in situ tested values for various hydroelectric projects in the Himalayan regions, along with the rock mass rating (RMR) values at 35 test sites. Ed is estimated empirically based on statistical analysis. Comparisons were made with the empirical equations already available in the literature, using RMR and the proposed equation for estimating Ed. Although different researchers have proposed many equations for estimating the value of Ed using RMR, a gap exists in validating such equations. In this regard, the proposed equation for Ed was verified by carrying out 3D numerical-modelling studies using FLAC3D, an explicit finite-difference software for an underground powerhouse cavern and comparing the displacement values with the field instrumentation data.