ORIGINAL PAPER The Use of Rock Mass Classification Systems to Estimate the Modulus and Strength of Jointed Rock J. L. Justo E. Justo J. M. Azan ˜o ´n P. Durand A. Morales Received: 16 June 2007 / Accepted: 9 June 2008 / Published online: 24 March 2009 Ó Springer-Verlag 2009 Abstract Three-dimensional, elastic and elasto-plastic finite element (FE) programs have permitted calculation of the displacements and the factor of safety (FOS) for the excavation for a tower, 132.70 m high (above foundation) on the island of Tenerife. The tower is supported by a 2 m thick reinforced concrete slab on jointed, vesicular and weathered basalt and scoria. The installation of rod extensometers at different depths below the slab has per- mitted comparison between measured and calculated displacements and the estimation of in situ deformation modulus. The moduli deduced from the simple empirical equations proposed by Hoek et al. (In: NARMS-TAC, 2002) and Gokceoglu et al. (Int J Rock Mech Min Sci 40:701–710, 2003) as a function of GSI, and Nicholson and Bieniawski (Int J Min Geol Eng 8:181–202, 1990) as a function of RMR, provide an acceptable fit with the mea- sured settlements in this type of rock. Good correlation is also obtained with the empirical equation presented by Verman et al. (Rock Mech Rock Eng 30(3):121–127, 1997) that incorporates the influence of confining stress in the deformation modulus. The FOS obtained from different correlations with geomechanical classifications is within a relatively narrow range. These results increase our confi- dence in the use of classification schemes to estimate the deformation and stability in jointed rock. Keywords Modulus of deformation  Jointed rock  Basalt  Finite elements  Rock mass classification  Elasto-plastic methods  Stability of slopes 1 Introduction The rock mass deformation modulus is one fundamental piece of input for elastic finite elements (FEs) calculation. In a 68 story, 246 m high tower (MLC Centre Tower) in Syd- ney with five parking stories on a massive rock (quartz sandstone with clayey cement), McMahon and McMahon (1980) found good fit with the extensometer settlements using a deformation modulus equal to the median of the moduli from the cores. However, the strength and defor- mability of a mass of jointed rock are heavily dependent upon the joint pattern. In this case, it is not logical to use the modulus obtained from uniaxial compression tests on the cores to obtain the deformation of the rock mass. To take into account the joint pattern, several authors have correlated the strength and deformation modulus of the rock mass with several geomechanical indices (Bieniawski 1974, 1979; Serafim and Pereira 1983; Boyd 1993; Hoek 1994; Mitri et al. 1994; Hoek et al. 1995, 2002; Hoek and Brown 1997; Hoek and Diederichs 2006; Verman et al. 1997; Sonmez and Ulusay 1999; Palmstro ¨m and Singh 2001; Barton 2002; Gokceoglu et al. 2003; Kayabasi et al. 2003; Cai et al. 2004; Zhang and Einstein 2004; Sonmez et al. 2004, 2006). A 132.70 m high tower (above foundation), on jointed rock, has been completed recently on Tenerife (Fig. 1). The 40 story high building, with 35 stories above ground level and 5 basement floors, is the tallest apartment building in Spain; an attached building, with 2 stories above ground level and 4 underground levels, is located on one of its sides. J. L. Justo (&)  E. Justo  P. Durand  A. Morales Department of Continuum Mechanics, University of Seville, E.T.S. Arquitectura, Avenida Reina Mercedes 2, 41012 Seville, Spain e-mail: jlj@us.es J. M. Azan ˜o ´n Department of Geodynamics, University of Granada, Granada, Spain 123 Rock Mech Rock Eng (2010) 43:287–304 DOI 10.1007/s00603-009-0040-6