A New Approach for Liquefaction Assessment of Pumiceous Sands

Sands consisting of pumice particles are a common soil type in several parts of the Waikato Basin and Bay of Plenty in the North Island of New Zealand. These pumice sands are highly crushable, compressible, and lightweight due to the vesicular nature of the particles. Pumiceous soils are often seen to be ‘problematic’ because their behaviour is considerably different compared to that of normal sands. Accordingly, the available empirical correlations for ordinary soils may not be applicable for the liquefaction assessment of pumiceous soils. Therefore, it is imperative to follow appropriate design recommendations for the liquefaction assessment of these soils. The development of several large- scale solar farms in the Eastern Bay of Plenty region requires more reliable approaches to assess the liquefaction susceptibility of pumiceous sands as some of the solar farm locations have thick layers of pumiceous deposits present across the site. The key geotechnical risk for solar farms in the Bay of Plenty is often related to soil liquefaction and the effects this may have on the foundations for various structures and the solar arrays. This paper will present a case study where several seismic cone penetration tests (sCPT) were performed and the obtained CPT and shear wave velocity ($V_s$) profiles were used for a site-specific liquefaction assessment. The results of the liquefaction assessment were made using the methods which reflect current good industry practice in New Zealand. In addition, a second assessment was carried out using recently developed pumice-specific correlations, which provided significantly improved cyclic resistance ratios (CRR) for pumiceous sands. In this paper, the important differences in using the newly developed and more advanced methods for liquefaction assessment of pumiceous deposits are discussed and presented.