Geomodels in Engineering – an introduction

This article is based on the introduction to the newly published book Geomodels in Engineering Geology – An Introduction, which is reviewed [on the page opposite].

What, why and when?

The Earth is an active planet in a constant state of change. These changes can take place over both long and short periods of geological time (thousands or millions of years) or much more quickly on an engineering timescale (minutes, hours or days). Geological processes continually modify the Earth’s surface, destroying old rocks, creating new ones and adding to the complexity of ground conditions: the so-called ‘geological cycle’. The all-important concept that drives this geological plate tectonics.

The benefits geologists bring to construction projects must exceed the cost of their services — that is, they must accurately improve the engineer’s ground knowledge more cheaply and effectively than any other method. They must reduce the risk of geological hazards by anticipating situations perhaps unseen by the engineers and also help to determine effective ways of dealing with risks and any problems arising during design and construction. The main role of the engineer geologist is to interpret the geology and ground correctly. Creating an initial model for the geology of the site is an excellent start. Geology (the study of the Earth) and its closest geo-relative, geomorphology (the study of the Earth’s surface), are concerned with changes over time and any geomodel has to build in any changes likely to occur in the near future, especially when the construction project may have a significant impact on the environment (Fookes, 1997).

Fig. 1. Geological structures (after Fookes, 1997).

Some degree of uncertainty will always exist in both the interpretation of the existing geology and any anticipation of significant changes over the lifetime of a project. The key types of uncertainty include data uncertainty and environmental uncertainty. Some aspects may defy the precise prediction conditions — for example, earthquakes, landslips, our limited understanding of the behaviour of complex Earth systems, or future choices by governments, businesses or individuals that will affect the socio-economic or physical environment. Many assessments rely on expert judgements based on the knowledge available, together with experience from other projects and sites. The problems associated with expert judgements include the poor quantification of uncertainty, poor problem definition and any bias of the assessor.

Fig. 2. A relic periglacial terrain: southern Britain.

To paraphrase the above, many, if not most, difficulties in ground engineering arise from either an unawareness of the ground conditions or a failure to appreciate the influence of the known ground conditions on a particular engineering situation.

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