Centrifuge Modeling of Cone Penetration Testing and Dewatering of Coal Combustion Product Deposits

Damage to embankments containing slurry-deposited coal combustion product (CCP) can lead to static liquefaction or slope failure, resulting in the release of the contained material. Characterization of the mechanical and hydraulic properties of CCP deposits provides the fundamental basis for the design, operation, and closure of CCP facilities. In this study, centrifuge experiments were performed to evaluate the changes in the cone penetration test (CPT) tip resistance (q_c) due to differences in drainage conditions and the location of the water table within an initially dense fly ash deposit. To accomplish this, centrifuge equipment that enables dewatering and rewetting of CCP deposits in flight was built and commissioned. Test results show the dependency of the CPT q_c on the penetration rate, consisting of an increase in q_c as the penetration conditions transition from drained to undrained due to the dense state of the deposit that led to the generation of negative excess pore pressures during penetration. The changes in pore water pressure/suction, gravimetric water content, CPT q_c, and shear wave velocity during dewatering and rewetting were monitored to deduce changes in fly ash strength and stiffness. The finding can help develop or refine correlations between the CPT tip resistance and the in situ state of CCP deposits as well as relate properties measured in the laboratory to the in situ hydraulic response of CCPs.