Rock Mass Characterization for Dam Foundations

Abstract

Classification systems define rock mass zones that represent the potential behavior of the rock mass when subjected to load changes. Rock mass characterization, as opposed to rock mass classification, is described by an example of the right‐abutment ridge, Thomson Dam, Australia. Geological investigations demarcate the discontinuities into sets covering specific zones or domains. Samples from these rock zones are retrieved and indexed and the zones are then bounded and classified. From selected sites, discontinuity samples are retrieved and laboratory‐tested for strength and stiffness. Rock material moduli and joint stiffnesses are combined using two simple models representing the constraints of equilibrium and compatibility, and produce the predicted rock mass' anisotropic moduli. Measured in situ rock mass moduli are compared with predicted moduli. Of the various discontinuity types, the bedding plane thrust faults have the lowest strengths and greatest deformational potential. Fault gouge and its association with clay content control the friction angle and deformability potential.