Geology for Engineers: the Geological Model, Prediction and Performance

Abstract

Abstract This First Glossop Lecture explores the borderland between geology and engineering, partly historically and through the attitude and education of the practitioners but mainly by consideration of site investigation practice and the use of the geological model in the characterization of a site for engineering purposes. It starts with a historical overview, including the work of Glossop, to introduce the subject matter. The text is illustrated by tables and line drawings, many of which are block models. All models are annotated so that they largely speak for themselves. Text boxes are included for readers with less geological or geotechnical knowledge. Considered simply, the geology at any one site is a product of its history. The engineering geological environment of the site includes the geological history and the current geomorphological processes and climatic conditions. The development of the geological model for any site therefore requires specific consideration of the regional and local geological and geomorphological history and current ground surface conditions. This concept is examined from the scale of plate tectonics to the smallest geological features and micro climate. Simple models of various terrains, rock associations and surface environments and their effect on the geology and geomorphology are presented as geology for engineers, and these are used together with case histories from Britain and overseas to illustrate the development of a model for any particular site. Conclusions are drawn, based on experience of the use of models in practice. Appendices give details of various engineering geological environments. At each stage of site investigation, the status and capability of the model to anticipate are reviewed. Examples are given of varying approaches to each stage dependent upon the local geology and the project, and estimates are given of the potential improvement in geological knowledge at each stage depending on local circumstances. Geological mapping is an underused but important component in getting the model right. The geologist's role is to get the geology right. The model is also simply examined from risk and uncertainty viewpoints, geometry of local site geology, small scale features, sampling and also from a cost effectiveness perspective. The power of the model is more in its ability to anticipate conditions than to predict them precisely. Anticipation is turned into reality by the ground investigation. A Geological Enviromnental Matrix (GEM) to help anticipate the geology at any one site is presented and examples given of the matrix tested in operation. The paper concludes with consideration of unforeseen and unforeseeable geological conditions in a contractual situation; and discussion on the education, training, research and experience of geologists and engineers in improving teaching, communication and understanding in the borderland of geology and engineering. On any site, an experienced and appropriate geotechnical team is needed to get both the geological and the companion geotechnical models right, to outline objectives and questions to be answered and to determine activities to achieve these. The current status of development in engineering geology on a parochial and world scene is briefly judged. At present engineering geology is largely seen as a service profession, but the potential for developments in understanding the earth and earth's processes for the benefit of mankind through engineering is exciting. Engineering geology should not lose its distinct role but communication and interaction with engineering need fostering.