Dissipation Processes of Excess Pore Water Pressure from Seismic Centrifuge Tests on Liquefiable Sa

A centrifuge test, carried out on saturated loose Ticino clean sand subjected to an input motion inducing high excess pore water pressure (Δu) values and liquefaction, was analysed in the present paper. The results evidenced that significant ground surface settlements occurred during shaking suggesting that pore water pressure generation and dissipation occur simultaneously across the various strata. Thus, the rate and distribution of Δu at different depths and time in the soil depend not only on the undrained seismic response of the soil but also on its consolidation properties, namely compressibility and permeability parameters. A careful knowledge of these parameters is then required in numerical seismic site response analyses to correctly predict the soil response. The test interpretation highlighted that high Δu values leading to liquefaction yield an increase of the hydraulic conductivity (k) and a decrease of the constrained modulus (M) compared to their corresponding static values. Different trends of k and M were observed in the co-seismic and post-seismic phases. Useful relationships accounting for the changes of consolidation parameters with Δu during and after shaking, were calibrated and compared with literature data.