The conceptual ground model

Abstract

The range of possible subsurface conditions that can be predicted, knowing the geological processes that formed the ground beneath a site, is self-evident to the geological or geotechnical advisor. This information underpins the conceptual ground model. Many construction cost over runs are caused by unforeseen ground conditions. Avoiding this requires a better desk study and ground investigation (including geophysical survey), as well as the development of a ground model that includes the known and suspected features on, below and adjacent to an engineering site. Such a model will assist in identifying the likely implications of the ground for a proposed engineering project. It is helpful to portray the conceptual ground model as a threedimensional block model that allows the scale of the features, in relation to the size of the project, to be appreciated. In addition, the geology should be characterised in engineering terms by the geological/geotechnical advisor, which means that geotechnical properties and their likely lateral and vertical variation, must be assessed within the context of the model.The difficulty in understanding the ground conditions at a construction site has its origin, in part, in the way that geological knowledge advances. Geological mapping has been carried out in Britain since the late 18th century when the canal network was constructed. The process of updating British geological maps is still continuing (see CIRIA Special Publication 149, A guide to British stratigraphical nomenclature, Powell 1998). The geologist has to interpret the information as it is made available from boreholes, trenches and