Engineering Geological Models
Steve is Chair of the International Association of Engineering Geology and the Environment (IAEG) Commission C25 on Engineering Geological Models. C25 published an interim report in 2014 (Parry et al., 2014) from which the Figure (left) is taken.
Essentially the framework for the application of geological knowledge to engineering problems is an engineering geological model. This reflects the philosophy of "correct" engineering geological thinking, i.e. the best way to evaluate the potential impact the ground may have on an engineering project and vice versa.
The fundamental purpose of engineering geological models is to understand:
- The type and distribution of geological units beneath a site;
- How these geological units have been modified over time by processes such as weathering, tectonics, anthropogenic modification (i.e. engineering geological units) etc.;
- The likely geotechnical properties associated with these engineering geological units, including groundwater and gas;
- The possible variations likely in terms of both distribution and properties of these engineering geological units;
- The active (and dormant) geological processes may be present at the site during both construction and lifetime of the structure; and
- How the project will interact with the ground, both during and post construction,
The most powerful capability of an engineering geological model is anticipation and as such, when correctly undertaken, they allow the identification of uncertainties and hence provide a tool for the reduction in geotechnical risk.
An effective engineering geological model should:
- Allows the rationale design of the method of investigation to in order to obtain investigation results that can confidently be used for design and construction.
- Provides a framework for ensuring engineering geological uncertainties are identified and evaluated.
- Allows engineering geologists to be satisfied that all geological factors have been properly considered with respect to the project requirements
- Allows the correct evaluation of all results of the investigation including derived geotechnical values and subsequent selection of characteristic geotechnical values
- It allows an evaluation of “baseline" conditions
- Communicates often complex engineering geological issues and their potential hazard to the project to non-geologists,
- Ensures that such risks are understood by all involved.
- Allows engineers with little or no geological knowledge to appreciate the significance of the geology
- Helps manage the geotechnical risks associated with the project
As such an engineering geological model based on observational data within a realistic and appropriate conceptual framework should allow an evaluation of the site conditions that an experienced contractor could reasonably have foreseen based on knowledge, experience and available data i.e. unforeseen ground conditions are conditions that were neither observed based on generated data nor anticipated by the conceptual framework.
Parry, S., Baynes, F & Novotny, J. (2018). Conceptual Engineering Geological Models. Proceedings of the International Association of Engineering Geology Conference. San Francisco, 2018.
Parry, S. (2016) Engineering Geological Models and Underground Construction. 13th International Conference Underground Construction Prague 2016. Invited Speaker.
Jack, C. D. & Parry, S. (2014) Communicating geological uncertainty – the use of the conceptual engineering geological model. Proceedings of the International Association of Engineering Geology Conference. Turin, 2014.
Parry, S., Baynes, F. J., Baynes, Culshaw, M. G., Eggers, M., Keaton, J. F., Lentfer, K., Novotny, J., & Paul, D. (2014). Engineering Geological Models - an introduction: IAEG Commission 25. Bulletin of the International Association of Engineering Geology and the Environment. Volume 73, Issue 3, pp 689-706.)