The knowledge of the structural geology of most open pits is a critical input into the geotechnical stability analyses and ultimately in the design of the pit. For pit design purposes, or for risk management and planning of an expanding pit, the geotechnical engineer needs to know (a) what are the expected fault orientation changes within the rock, (b) how far do the structures go into the rock face (continuity), and (c) what are the range in physical properties of faults. One of the most significant challenges is the interpretative projection of structural systems into the rock mass, beyond which they can be observed, except with drill hole intersections.
Particularly challenging for the geotechnical community is the emergence of complicated segmented structural models, that try to reflect reality more closely. This paper will review the reasons for these models and give guidelines on how these models are to be interpreted and how these should be used in detailed geotechnical evaluations.
The study of structural geology in a pit is seldom a matter of simply measuring the orientation of the observed faults, which too often is the default approach, if structures are measured at all. Rather, to understand the rock mass and to maintain a reliable structural model, the ongoing structural evaluation objectives should be to understand the structural system holistically, and define structural pattern domains, ideally with consistent fault patterns, continuity and properties.
This presentation focuses most particularly on challenges created by uncertainty of fault continuity and the repeatability of additional similar, but unobservable, faults that might impact pit slope stability assessments. If segmented fault systems are observed, defined by faults with limited continuity and rock bridges between adjacent faults of the same system, how can these be practically modelled and used in slope stability analyses?
