Neohypoplasticity—Estimation of Small Strain Stiffness

Behaviour of soils under small cycles is examined in the triaxial apparatus and the results are used for the calibration of several constitutive relations. The small strain relation is not exactly linear and stiffness \( E_{ijkl}\) in \(\dot{\sigma _{ij}}= E_{ijkl}\dot{\varepsilon _{kl}}\) is not constant. The popular hypoplastic (HP) model describes the small strain behaviour using the intergranular strain (Niemunis, Herle, Mech Cohesive-Frictional Mater 2(4):279–299 1997). However, this idea with an additional strain has several shortcomings. A better approach is the paraelastic (PE) model (Niemunis et al, Acta Geotech 6(2):67–80 2011; Prada Sarmiento, Paraelastic description of small-strain soil behaivour 2012). In this study the paraelasticity has been used already while evaluating of the raw data from triaxial test results. Similarly a simplified high cycle accumulation (HCA) formula (Niemunis et al, Comput Geotech 32(4):245–263 2005) and a simple assumption of stress dependence of \( E_{ijkl}\) have been used to purify the measured test data. A general curve-fitting strategy for testing of different constitutive models is developed. Some shortcomings of PE and HCA could be observed.