Understanding the effect of CPT resolution on calculated lateral pile resistance to assist adoption of synthetic CPTs in geotechnical design

The emerging technology of synthetic cone penetrometer tests (CPT) offers the potential for profiles of geotechnical resistance to be derived from 2D or 3D geophysical seismic survey data at any location across a site. This avoids the need for interpolation between geotechnical CPTs, alleviating the uncertainty introduced into the design process if a geotechnical CPT is not at the final location of a foundation or anchor. However, synthetic CPTs have a lower vertical resolution than geotechnical CPTs, which may range from a few tens of centimetres to more than a metre, depending on the acquisition equipment, sediment properties, depth and interpretation approach. The reduced resolution of synthetic CPTs can affect geotechnical design outcomes, potentially resulting in under- or over-design. In this study, the effect of CPT resolution on lateral pile resistance is explored to inform on the minimum resolution of synthetic CPTs that would be acceptable for geotechnical design and, in turn, the requirements for geophysical survey equipment and interpretation. Geotechnical CPT profiles from a case study site are systematically reduced in resolution from the field resolution of 0.01 m to a minimum resolution (i.e. maximum data interval) of 2.5 m. Use of artificially reduced-resolution geotechnical CPT data as a proxy for synthetic CPT data enables the comparative assessment of predicted pile volume and capacity in the same deposit at multiple resolutions. Results show an increased variation in predicted pile volume as CPT resolution decreases, and hence data interval increases. In this case study, for all trialled CPTs, a CPT data interval of 0.5 m enables a predicted minimum required pile volume within 3% of, but consistently below, that predicted with the full-resolution geotechnical CPT with a data interval of 0.01 m. This translates to a reduction in pile capacity of the same order of magnitude. Results also show that even the lowest resolution CPT (data interval of 2.5 m) provides a more accurate pile prediction than linear interpolation of full-resolution CPTs (0.01 m) from adjacent boreholes. The method presented here could be applied to preliminary CPTs, or extant knowledge of ground conditions near to or from a prospective site, to inform on the requirements for the geophysical survey or, retrospectively, to assess the confidence of relying on synthetic CPTs derived from acquired geophysical survey data for geotechnical design.