@misc{KnittelTafiliGrandasTaveraetal., author = {Knittel, Lukas and Tafili, Merita and Grandas Tavera, Carlos Eduardo and Triantafyllidis, Theodoros}, title = {New perspectives on preshearing history in granular soils}, series = {Scientific reports}, volume = {13}, journal = {Scientific reports}, issn = {2045-2322}, doi = {10.1038/s41598-023-31419-9}, abstract = {The design of deep dump slopes for opencast mines usually requires information about the soil resistance to liquefaction during earthquakes. This resistance depends not only on the initial stress, the initial density, and the amplitude of the cyclic loading, but also on the preshearing, that is, the deviatoric stress path applied to the soil before the cyclic loading. To explore the influence of preshearing on the subsequent soil behaviour, a set of triaxial tests with a combination of undrained preshearing and drained stress cycles using two sample preparation methods is presented. It is shown that the preshearing as well as the preparation method have a major influence on the strain accumulation upon cyclic loading. Simulations of the experiments with four advanced constitutive models reveal that neither the long-lasting effect of preshearing nor the preparation method can adequately be captured by all of the models. This deficiency of the constitutive models can lead to unsafe designs due to the overestimation of the cyclic resistance to liquefaction and to the underestimation of long term settlements.}, language = {en} } @incollection{GrandasTaveraTriantafyllidisKnittel, author = {Grandas Tavera, Carlos Eduardo and Triantafyllidis, Theodoros and Knittel, Lukas}, title = {A Constitutive Model with a Historiotropic Yield Surface for Sands}, series = {Recent developments of soil mechanics and geotechnics in theory and practice}, booktitle = {Recent developments of soil mechanics and geotechnics in theory and practice}, editor = {Triantafyllidis, Theodoros}, publisher = {Springer}, address = {Cham}, isbn = {978-3-030-28515-9}, pages = {13 -- 43}, abstract = {A simple, yet versatile yield surface in the stress space is combined with a hypoplastic equation to simulate the influence of recent deformation history on the mechanical behaviour of sand. This yield surface is used to describe the intensity of anelastic flow. In the model, the state is fully described by the current stress, the void ratio and a novel back stress-like tensor. This new state variable determines the shape and size of the yield surface and accounts for recent deformation/stress history. The direction of the anelastic flow upon shearing is obtained from a generalization of the Taylor's dilatancy rule. As a distinctive feature of the model, this dilatancy is able to reproduce the strong contractancy upon reversals observed in experiments without the need of additional state variables. The model corrects some known shortcomings of previous hypoplastic models like overshooting and the excessive accumulation of stress/strain upon strain/stress cycles of small amplitude (ratcheting). Laboratory tests are simulated to show the capabilities of the model to reproduce the soil behaviour under monotonic and cyclic loading conditions after different deformation histories.}, language = {en} }