Field characterisation and mapping of pumiceous deposits in central North Island, NZ

Abstract

Pumice materials are frequently encountered in many engineering projects in the central part of the North Island, New Zealand. Because of their lightweight, highly crushable and compressible nature, existing empirical correlations developed for hard-grained (quartz) sands are not applicable, and therefore they are problematic from an engineering and construction viewpoint. With engineering developments currently on-going in the region, a better understanding of the characteristics and locations of these pumiceous layers has become necessary. This paper attempts to identify the field characteristics of pumice deposits based on conventional geotechnical methods for the purpose of mapping the locations of pumiceous layers across the Bay of Plenty and Waikato regions. For this purpose, existing geotechnical data within the target regions, including standard penetration tests (SPT), cone penetration tests (CPT), seismic dilatometers (sDMT), machine boreholes and associated laboratory testing, were compiled. In addition, pumice deposits were identified within the existing data as well as the extent of the stratigraphic unit(s) and typical trends within the data set and correlations across various test types were analysed. It is envisioned that the outputs presented in the paper will be beneficial to researchers, practicing geotechnical engineers, roading authorities and council planners in terms of providing better engineering understanding of these problematic soils.