Centrifuge Modeling of Variable-Rate Cone Penetration Testing in Fly Ash and Its Implications for State Interpretation

Analysis of cone penetration tests (CPTs) typically is used to assess the stability of waste storage facilities (WSFs) to prevent failures. Materials in WSFs, such as fly ash, often contain a significant proportion of silt-sized particles, making them susceptible to partial drainage during CPT soundings. This investigation quantified the influence of drainage conditions on the CPT tip resistance ( q c ) of fly ash deposits of various densities and explored a framework for characterizing the state of fly ash based on the q c magnitudes generated in drained and undrained conditions. To achieve this, CPT soundings were performed at penetration rates that encompassed the entire range of drained to undrained conditions in fly ash deposits within a geotechnical centrifuge. The tests were performed on deposits of two different fly ash materials, the strength and critical state properties of which were characterized using triaxial compression tests. The centrifuge CPT results showed how the initial state parameter ( ψ ) affects the relationship between tip resistance and penetration rate; contractive specimens exhibited a reduction in q c with increasing rate, whereas dilative deposits had an increase in q c with pushing rate. This behavior was used to develop a framework that employs the ratio of the normalized drained penetration resistance ( Q t n , drained ) to the normalized undrained penetration resistance ( Q t n , undrained ) to identify contractive soils and evaluate the vulnerability of soil layers that can lose strength due to undrained failures. These results provide insight into the characterization of fly ash deposits with CPT in different drainage conditions and present a new concept that shows promise for estimating the in situ state.