Rock mass characterization is required for many applications in rock engineering practice for example: excavation design, underground powerhouses and seepage treatment in dam sites. Deformation modulus is one of main input parameters for design and numerical modeling analysis. Although there are many ways to determine the deformation modulus of a rock mass by using various in-situ and laboratory testing techniques, the application of rock mass classification systems is one of the more practical ways. Two methods of rock mass classification systems: RMR (Bieniawiski 1989) and "n" (Jasarevic & Kovacevic 1996), together with seismic wave velocity measurements (Pv), were used to determine the deformation modulus of a carbonate rock mass at the Namroud dam site in Iran. A new parameter, "CR" (classification ratio), which is the ratio of RMR/n is introduced. An empirical equation was derived to estimate the deformation modulus of the rock mass at the dam site. A classification chart was also introduced for a quick evaluation of rock mass quality and deformability.
Deformation modulus of a rock mass is a vital element for analyzing the rock mass behavior in rock engineering applications. There are many parameters that affect the deformability modulus of a rock mass notably the geological conditions of a site and the development of local tectonic stresses. Therefore it is generally impossible to develop a universal law that can be used to predict the deformability. Traditionally, in-situ tests such as plate-loading and jacking are common to determine the deformation modulus but the cost of performing such tests are very high. Many authors have developed empirical relationships to predict the value of deformation modulus for a rock mass. Some of the proposed empirical equations are listed in Table 1.