A Geological Approach To Discontinuity Predictions, With Australian Case Examples

Forward determination of ground conditions is important, as geotechnical projects extend to greater depths. Systematic quantitative analysis should be routinely undertaken during rock excavations, to ascertain the defect pattern, although problems of rock inhomogeneity, material uncertainty and the pre-existing stress state make the application of rock mechanics theory difficult. Current systems do not have the capacity to make predictions using realistic geological interpretations. Of prime concern to geotechnical engineers is extrapolation, from exposed zones to inaccessible regions. This is often undertaken by applying geostatistics, assuming a random distribution to establish the relationship between discontinuities. There are problems in this approach, as discontinuities commonly exhibit a geological control. By relating fabric elements the nature of structures, relative timing and the processes involved in rock modification are identified and for each type of geological terrain, a distinct set of discontinuities is apparent. Fuzzy logic is suggested as a means of treating geological complex situations in a mathematical way. Programming of such knowledge based system involves establishing crisp and fuzzy rules, based on local conditions and regional associations, encompassing numerical and linguistic relationships. Through a preliminary literature review a number of relationships are identified. These could be verified at individual locations and a framework constructed. Examples illustrating the geological controls extended on discontinuities at specific Australian sites and the application of fuzzy logic are discussed.