Modeling of the accumulation process of the excess pore water pressure for pyroclastic soils

Purpose: The generation of undrained excess pore water pressure in saturated granular soils subjected to cyclic loadings, has been studied for many years but it is still an important area of research as demonstrated by the devasting liquefaction-induced damage such as earthquakes (e.g., Italy 2012; New Zealand 2010–2011 and 2016). Methods: Concerning the undrained response of pyroclastic soils, the mechanism of pore pressure build-up is analysed under undrained conditions to define the susceptibility to liquefaction, whose definition is essentially to define Early Warning Systems for rainfall-induced landslides and for liquefaction phenomena under cyclic and dynamic loading (Olivares et al., 2019, Minutolo et al., 2020). Results: The results obtained from the experimental program carried out through undrained cyclic triaxial tests (de Cristofaro et al., 2021) performed on different pyroclastic soils, Cervinara (Italy) and Rangiriri (New Zealand), allowed to describe the mechanism of excess pore water pressures within the Steady State Theory using the state parameter ψ of Been & Jefferies (1985). The parameter ψ seems to be useful also in comparing the results obtained on pyroclastic soils with those on ordinary sands. The state parameter ψ has a clear physical significance that could be used to define a more reliable model of undrained pore pressure buildup for soils of different natures. Conclusions: The research work concludes with the presentation of a new model proposal to define the mechanism of excess pore water pressures as a function of the history and stress state of the material investigated, using parameters (Ѱ e λ) of the Steady State Theory. In this regard, the parameters of the simplified pore water pressure forecasting model proposed by Chiaradonna et al. in 2016 are explained under the light of the critical state soil mechanics. Functional relationships between the model parameters and those of the critical state has been established using the experimental results obtained on different types of soils. The proposed analytical expressions represent an effective way for the model calibration, overcoming the needs of best-fitting procedures on experimental results of cyclic tests. The modified proposed model seems to be an universal one usable for different materials.