Putting Geological Focus Back into Rock Engineering Design

Abstract

The trend today to ever increasing modelling sophistication demands that much more attention be paid by practitioners to achieving better appreciation and characterization of geology and rockmass variability, so that rock–structure interaction effects can be analysed more realistically in better calibrated models. This paper is thus directed towards focussing attention on risk-based geological characterization as basis for helping modellers and designers improve calibration of their models. A sequential approach of appropriate input parameter refinement is outlined as a path forward methodology for consistently achieving maximum reliability in modelling. Processes that are needed for identifying key controlling geological structural features and rockmass domain characteristics that may be critical influences on true rockmass behaviour are explored so that rationalization steps can be followed in model building to ensure that actual behaviour drivers are not only properly represented, but are reliably characterized through rigorous calibration. Suggestions for the use of the observational and quantitative GSI charts at various scales appropriate to specific geological domains are presented as a means for achieving such calibration. Illustration is then given of how quantification can be achieved of rock quality variability throughout the complete range of rock competence, from intact pseudo-homogeneous high strength rockmasses subject to brittle spalling, through blocky, folded or foliated rockmasses, where kinematic controls are typically of paramount importance, through to completely degraded, fault process core zones and saprolites, where material matrix strength almost entirely dominates behaviour. Guidelines are given for suggested ranges of classification applicability for use with the Hoek–Brown failure criterion.