Engineers Australia

Three dimensional geological models in ground engineering: when to use, how to build and review, benefits and potential pitfalls

Graham Rose, Philip Kirk, Camilla Gibbons and Adam Lander

Abstract

Three dimensional geological models are increasingly being used to characterise the world of ground engineering. Soil, rock, geological structures such as faults, rock fall zones and slips are often best examined in 3D. In addition, geomorphology of materials above, below or surrounding project sites must be well understood by design and construction teams to optimise both safety and costs. This is especially true for large, complex or unsafe sites or for forensic investigations in both terrestrial and offshore settings. As we shift away from a 2D (long sections, cross sections and design software programs) way of working to a fully 3D system of design it is important to follow suit with site characterisation tools. There are many advantages to thinking and working in 3D as well as some serious pitfalls when using such models.

Models must always make sense geologically and geomorphologically and preferably be reviewed by a geologist/engineer team. The geologist does not necessarily have to be a specialist engineering geologist, they could be a pure geologist but one who can thoroughly and clearly explain all issues and features to the engineering team. Models described herein are geological models first and foremost with an emphasis on being geologically and geomorphologically accurate. The modelling process introduces the engineering aspects once the geology is well understood. These models must always be used with a degree of caution and updated with new information from all sources such as pile excavation records, new drilling, earthworks changes mapping of faces in tunnels and excavations. Those who construct models must always assess confidence levels in the end-product and communicate that level of confidence or areas of ambiguity to all users.

3D Geological models are more suitable for large projects or projects that have potentially complex ground or hazardous site conditions. Examples of suitable types of project include; tunnels, deep excavations, large slopes, landslide remediation, involving soft/hard ground interfaces, areas with structural complexity such as folds or faults, slips and rock fall etc. In addition, forensic investigations may be enhanced by the application of 3D models.