The Interpretation of CPT Data from Hydraulically Placed PFA

ABSTRACT This paper reports a site investigation on an old hydraulically placed pulverised fuel ash (PFA) deposit. The results of cone penetration tests (CPTs) at the site are reported, along with the results of oedometer compression tests on undisturbed specimens recovered during the site investigation. Review of the in-situ test data indicated that no undisturbed specimens were recovered from the softest region of the PFA. This highlights the potential danger of biased sampling in very loose non-cohesive materials unless depth profiling is undertaken by in-situ measurement. Oedometer test results on resedimented PFA are also reported. These tests showed that PFA can undergo significant secondary compression with time, which must be accounted for when estimating the engineering properties of aged PFA. The correlation between volume compressibility and cone resistance, mv=1/(α.qc) is fitted to compressibility data from undisturbed samples to determine α. The resulting CPT compressibility profile is then compared with compressibility trends estimated for aged PFA using properties measured in the oedometer tests on resedimented ash. The estimated compressibility trends show good agreement with CPT profiles. It is therefore recommended that a value of α=l1 should be used for normally consolidated PFA that has aged (i.e. been in place) for 20 years.