Synthetic cone penetrometer test (CPT) data for geotechnical design: evaluating the impact of resolution

Abstract

The emerging technology of synthetic cone penetrometer tests (CPT) offers the potential for profiles of geotechnical resistance to be derived from two or three-dimensional geophysical seismic survey data at any location across a wind farm site, alleviating dependence on in situ geotechnical CPT testing and interpolation between test locations. However, the lower vertical resolution of synthetic CPT data compared with in situ geotechnical CPT data introduces uncertainty in design outcomes. In this thesis, the effect of CPT resolution on lateral pile performance is explored to inform on the minimum resolution of synthetic CPT profiles for design. 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 comparative assessment of predicted pile volume and capacity in the same deposit at multiple resolutions. Results show increased variation in predicted pile volume as CPT resolution decreases, and hence data interval increases. Predicted minimum required pile volume remains within 3 % of, but consistently below, that predicted with the full resolution geotechnical CPT, translating to a reduction in pile capacity of the same order of magnitude. The effect on design outcomes is expanded further to include comparison between co-located in situ geotechnical and geophysical data from another wind farm site investigation. This has demonstrated that, with synthetic CPTs, it is possible to obtain minimum monopile dimensions within 2 % of those calculated with the in situ geotechnical CPT, corresponding to within 5 % of the required capacity. The application of time series complexity measures to CPT profiles has revealed that resolution is not the driving factor behind complexity but more to do with the soil type and the multi-faceted geotechnical design concept. The results from this research highlight the potential for the use of synthetic CPTs in pile design to facilitate the expansion of offshore wind by reducing the time required for geotechnical site investigations and uncertainty in design outcome from interpolating between in situ geotechnical CPTs.

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Identifiers

ORCID for Susan Gourvenec: orcid.org/0000-0002-2628-7914

ORCID for Jamie Crispin: orcid.org/0000-0003-3074-8493

ORCID for Jared A Charles: orcid.org/0000-0002-2256-3846

ORCID for Tim Henstock: orcid.org/0000-0002-2132-2514

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