A suggested geologic model complexity rating system

Abstract

A geologic model captures selected geologic qualities in a region and at a site. An engineering geologic model is relevant to a project and includes specific project aspects. Geology expressed quantitatively, describing variability and uncertainty, is needed in projects employing reliability-based design. Geologists use line style to convey confidence in interpretation of location and nature of lithologic contacts and faults. Mapped lines have error related to scale, terrain, and methods, and uncertainty related to interpretation and allotted field time. A geologic model complexity rating system suggested herein has nine components, four of which are related to regional-scale geologic complexity and frive of which pertain to site-scale complexity, terrain characteristics, information quality, geologist competency, and time allotted to prepare the model. Rating criteria and scores are organized into four levels. Simple, uniform, predictable conditions are assigned scores of 3, whereas complex, unpredictable conditions have scores of 81; intermediate conditions have scores of 9 or 27. Possible cumulative scores range from 27 to 729. Cumulative scores can be converted into a form suitable for reliability based design by defining the highest possible score as the mean value for the geologic model and the actual score as the model standard deviation. Conditions with a maximum score would have coefficient of variations COV = 1.0. The lowest possible COV would be 0.037 (=27/729). Geologic model COVs could be added to geotechnical COVs. This paper seeks to encourage geologists to translate their interpretive understanding into geotechnical parameters needed by engineers for use in Ground Models.