Interpreting geotechnical measurements and observations: Does one size fit all?

This paper illustrates via simple real life examples, the constraints and limitations of three common geotechnical assessment techniques. The purpose of these case studies is to highlight the need for geotechnical engineers to not only choose the right tool for their analysis, but also to fully understand and appreciate the limitations of these techniques in the context of the project requirements. In the first example, a borehole and test pit excavated within close proximity to one another is shown to lead to different interpretations of stratigraphy, and potential implications for the project in question are discussed. In the second example, PDA tests undertaken on the same driven pile at the same time are shown to result in inferred pile capacities which vary by over 20%, as a consequence of the way the data is processed and assumptions made, highlighting the need to avoid ‘black box thinking’ when interpreting geotechnical observations and measurements. Finally, an example is presented of an assessment of “native soil modulus” in the context of flexible pipeline design. Conventional methods of assessing the stiffness of the ground, which may be conservative for the design of a foundation, are shown to be potentially unconservative for the purposes of design of the pipeline. In this case, it is necessary to understand the wider project context and performance criteria of the pipeline, in order to provide appropriate geotechnical design advice.