@misc{GrandasTaveraNitschMachaček, author = {Grandas Tavera, Carlos Eduardo and Nitsch, Antonia and Machaček, Jan}, title = {A 1D Hypoplastic constitutive model for expansive soils}, series = {Acta Geotechnica}, volume = {17}, journal = {Acta Geotechnica}, issn = {1861-1133}, doi = {10.1007/s11440-022-01548-y}, pages = {4313 -- 4331}, abstract = {This paper presents a simple hypoplastic constitutive model that describes the essential features of the material behaviour of partially saturated clayey soils observed in oedometric compression tests. The model is formulated in terms of net stress and degree of saturation. The total strain rate is decomposed into a portion related to the changes in saturation and a portion for the evolution of net stress. However, no distinction is made between plastic and elastic strains. With this strain rate decomposition, the maximum swelling strain/stress are obtained by simulating wetting processes under constant stress/strain conditions. In addition to the void ratio, the model includes two scalar variables to track the loading history (preloading). The calibration of the model constants using common laboratory tests is discussed. Confined and unconfined swelling tests under oedometric conditions with subsequent loading and unloading phases carried out on three different materials were satisfactorily simulated by the model. Its promising results call for an extension to a 3D formulation.}, language = {en} } @misc{MachačekStaubachGrandasTaveraetal., author = {Machaček, Jan and Staubach, Patrick and Grandas Tavera, Carlos Eduardo and Wichtmann, Torsten and Zachert, Hauke}, title = {On the automatic parameter calibration of a hypoplastic soil model}, series = {Acta Geotechnica}, volume = {17}, journal = {Acta Geotechnica}, number = {11}, issn = {1861-1125}, doi = {10.1007/s11440-022-01669-4}, pages = {5253 -- 5273}, abstract = {This paper presents an approach for the automatic parameter calibration (AC) of a hypoplastic constitutive soil model. The calibration software developed in this work simplifies the parameter calibration, reduces the subjective "human" factor on the calibration result and lowers the entry hurdle for the use of the hypoplastic constitutive model. The performance of the software was demonstrated by comparing automatically calibrated parameter sets for two sands and their related simulations of the underlying experimental data with simulations using two reference parameter sets. The first reference parameter set was calibrated the classical way, "by hand", and the second was calibrated using the AC tool ExCalibre. Two different optimization methods were used, namely the Differential Evolution (DE) and the Particle Swarm Optimization (PSO). The simulations performed with the parameters obtained from the AC agree well with the experimental data and show improvements over the reference parameter sets. With respect to the optimization method, the performance of the DE proved superior to that of the PSO. Various measures of comparison were examined to quantify the discrepancy between experiment and simulation. By repeating 500 calibration runs, the dispersion of parameters was determined and correlations between different parameters of the hypoplastic model were found.}, language = {en} }