The static modulus of deformation is among the parameters that best represent the mechanical behaviour of a rock and of a rock mass, in particular, when it comes to underground excavations. This is why most numerical finite element and boundary element analyses for studies of the stress and displacement distribution around underground excavations are based on this parameter. The deformation modulus is therefore a cornerstone of many geomechanical analyses.
All in situ measurements of the static modulus of deformation used today are time-consuming and imply notable costs and operational difficulties. Because of this, the deformation modulus is often estimated indirectly from classification systems. In other cases the modulus is assumed based on the experience of the engineering geologist or from literature data.
The aim of this paper is to outline some aspects of field deformation measurements, and, from results of these, to review indirect estimates based on descriptive systems for characterization or classification of rock masses. Results from several in situ deformation tests have been analysed and compared with the rock mass conditions at each site. The test results have also been compared with deformation values estimated from rock mass classification systems and from the rock mass index (RMi), a system for characterization of rock masses. The Central Soil and Materials Research Station (CSMRS), New Delhi has performed most of the tests in India, Bhutan and Nepal.