Engineering geophysics and the 2017 New Zealand Ground Investigation Specification guidelines

Abstract

Geophysical methods have been key components of ground investigations globally, alongside direct testing (e.g., boreholes, trial pits), for decades. While direct testing provides “point” information relative to the total volume of soil, rock, and fluids involved in the engineering question, geophysical methods can cost-effectively survey large subsurface volumes, can supply spatially continuous data (as opposed to “point” data), and are non-invasive (useful for contaminated sites). Nevertheless, geophysical methods are indirect surveys and can contain inherent ambiguity as well as resolution and site-specific limitations. Thus, clear guidelines that delineate strengths and limitations of the plethora of geophysical techniques available to the ground engineer are important, if a ground investigation is to be successful. Here, attention is drawn to the New Zealand Ground Investigation Specification that was released in 2017. Specifically, chapter 11 of the Master Specification Volume 1 contains inherent flaws regarding several geophysical techniques and applications. New Zealand has a highly variable geology, climate variability, and seismicity, along with active volcanism and broad areas underlain by glacial deposits deposited by formerly extensive glaciers. Hence, a national ground investigation guide that encompasses state-of-the-art knowledge in the application of surface geophysics to developing geological models would be welcome.