The interpretation of CPT data from hydraulically placed PFA

Cone penetration test (CPT) results on an ∼ 20 year old, hydraulically placed pulverised fuel ash (PFA) deposit are reported, along with the results of oedometer compression tests on ‘undisturbed’ specimens recovered during the site investigation and resedimented PFA samples. The latter showed that aged PFA can undergo significant secondary compression. The correlation between volume compressibility and cone resistance, mv = 1 / (αqc), is fitted to compressibility data from undisturbed samples to determine α. The resulting CPT compressibility profile shows good agreement with compressibility trends for aged PFA estimated from the tests on resedimented ash. It is therefore recommended that a value of α = 11 should be used for normally consolidated, aged PFA. The danger of biased sampling in very loose non-cohesive materials and the need for depth profiling by in situ measurement are highlighted.