Unforeseeable Ground Conditions in Construction Claims

David Kinlan recently brought to my attention the article titled Unforeseeable Ground Conditions in Construction Claims published by HK>A and available here. David and I had an exchange and felt that it was important that we provided some additional information. The HK>A authors have drafted an interesting article that covers both legal and site investigation practices and identifies and explains the importance of gaining a detailed understanding of the ground conditions at a site for proposed development. It explores and provides some examples of contract claims and their findings. This is all very useful information, and we applaud them for highlighting just how important a proper assessment of likely ground conditions is and the possible pitfalls that one may encounter.?

However, as a geotechnical professional who has acted as an expert witness and has dealt with many contractual claims and insurance claims, I thought it important to also highlight some additional points which the HK>A did not address.?

The article has a strong emphasis on the interpretation of ground conditions. However, the authors limit their review solely to the use of intrusive geotechnical investigations namely penetration tests, trial pits, and boreholes with no consideration of other equally valuable sources of information to assist with interpretation such as geophysical techniques.?

The authors provide an example of 2 possible interpretations of the ground conditions from the information obtained from 3 boreholes (shown in Figures 6 and 7 in the article and below).

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Figure 6 and, in general, drawing soil types between boreholes is no longer accepted as a valid method for determining soils especially when the spacing of boreholes are quite distant.?

Whilst the two 2D model interpretations shown in Figure 6 and 7 could be both valid based solely on the borehole logs, a competent engineering geologist would use other information in the interpretation of ground conditions between sampling locations.?

For example, a geophysical survey would have provided valuable information to allow the interpretation and interpolation of the ground conditions between boreholes. This would likely reveal the ground conditions in Figure 7. In addition, an engineering geologist familiar with the types of conditions may have provided a desk study with further useful interpretation and interpolation between the points if for instance the top of rock layer is likely to be highly variable. The addition of the interpretation of geological processes that form the transported soils and the weathering processes of underlying rock would likely have assisted in this example, even without the addition of a geophysical survey.

Modern best practice by engineering geologists is to use a Geological Model or Ground Model that presents the distribution in 3D space of the engineering geological units, hydrogeological conditions and geological processes and how those might change in time, their controls and boundary conditions and groundwater, geomorphological processes and geohazards that have been observed or interpreted to occur on and around the site. The Model should characterise units of the ground with similar engineering properties and describe boundaries where changes in conditions may occur.

The Geological Model does not rely solely on intrusive geotechnical investigations. Uncertainty in the Geological Model is often characterised. Depending upon project and reporting requirements, the Model that is presented may have a specific project-related focus and may be better described as, for example, a hydrogeological model or a rock mass model.

The HK>A article concludes with -

“an employer or a contractor must interpret available soil data which is largely a matter of engineering sense and experience combined with educated guesswork. The interpretation of soil data is the root cause of most of the unforeseeable soil conditions claims.”

This statement hits the nail on the head. However, it must be an interpretation of ALL soil sampling data available AND the interpretation of soil conditions between sampling locations together with an appreciation of the limitations of the interpretation so the ‘educated guesswork’ is of the highest possible quality.