Enhancement of a hydro-mechanical hypoplastic model for unsaturated fine-grained soils accounting for small strain stiffness

Abstract

Due to global climate change, larger extreme seasonal and daily moisture variations have been occurring more frequently in the last decades. This phenomenon can affect geotechnical structures by inducing cyclic coupled hydro-mechanical loads. However, reproducing this behaviour from a numerical point of view requires robust constitutive models that can predict the coupling between the hydraulic and mechanical behaviour of fine-grained soils, combined with predictions of history-dependent stiffness evolution at small strains. For this reason, in the present work the hypoplastic model for unsaturated finegrained soils was further modified to better predict the water retention behaviour of unsaturated soils incorporating a smoothed hysteretic Water Retention Curve (WRC). In addition, the constitutive model wascalibrated using experimental data available on the literature of a completely decomposed tuff (CDT) from Hong Kong. At the end, the capabilities of the extended model to predict cyclic behaviour of unsaturated soils were evaluated using cyclic constant water triaxial tests at different suctions The results indicate that the extended model is able to describe with more accuracy the cyclic hydro-mechanical behaviour of the decomposed tuff if additional suction-dependency of one of its small-strain parameters is considered. Without this, the model can be calibrated to data at a given suction but its cyclic predictions for different suctions are not reasonably accurate.