Improved rotational hardening rule for cohesive soils and definition of inherent anisotropy

Abstract

Summary Improved, microfabric‐inspired rotational hardening rules for the plastic potential and bounding surfaces associated with the generalized bounding surface model for cohesive soils are presented. These hardening rules include 2 new functions, fη and fI0, that improve the simulation of anisotropically consolidated cohesive soils. Three model parameters are associated with the improved hardening rules. A detailed procedure for obtaining suitable values for these parameters is presented. The first 2 parameters affect the simulation of constant stress ratio loading where, because of the presence of fη, the third parameter is inactive. The second new function, fI0, accelerates the rotation of the plastic potential and bounding surfaces during shearing, which is particularly important for overconsolidated soils tested in extension. This paper also describes the proper manner in which to define the inherent anisotropy. This seemingly straightforward test has rarely been discussed in sufficient detail.

Adaptive anisotropic constitutive modeling of natural clays

“…As is demonstrated in Figure 4, the previously proposed equilibrium states of anisotropy can be reproduced by choosing relevant values of RH parameters, as are shown in Table 1. Also, by assuming , the variation of equilibrium anisotropy state transforms to a straight line as in Nieto Leal et al 53 . Moreover, Figure 5 shows the comparison of actual and simulated values of the equilibrium state of anisotropy for Otaniemi clay 36 .…”

“…Involving both components of plastic strain increment in the evolution of anisotropy is another option that can be found in the works of Pestana and Whittle 19 , Wheeler et al 36 ,. Nieto Leal et al 53 . by assuming separate contribution of plastic strain components in the evolution of anisotropy.…”

BS-CLAY1: Anisotropic bounding surface constitutive model for natural clays

“…Given the above, a popular approach in considering the effects of soil anisotropy within a modeling framework has been the development of elastoplastic soil constitutive models that involve inclined yield curves (Sivasithamparam and Rezania, 2017). This methodology for representing the inherent anisotropy has its roots in the works of Sekiguchi (1977) and Hashiguchi (1977) and was subsequently followed by other researchers such as Banerjee and Yousif (1986), Anandarajah and Dafalias (1986), Dafalias (1986a), Whittle and Kavvadas (1994), Ling et al (2002), Wheeler et al (2003), Dafalias et al (2006), Jiang et al (2012), Karstunen et al (2013), , Yang et al (2015a, b), Sivasithamparam and Castro (2016), Karstunen et al (2015), Coombs (2017), Nieto Leal et al (2018), Rezania et al (2017a, b), Rezania et al (2018), Chen and Yang (2020). In these works, the rotated YS is either fixed (Sekiguchi & Ohta, 1977;Zhou et al, 2005) or it can change its inclination by adopting a rotational hardening (RH) rule to simulate the development or erasure of anisotropy during plastic straining (Chen and Yang, 2020;Dafalias et al, 2020;Dafalias and Taiebat, 2014;Dafalias and Taiebat, 2013;Dafalias et al, 2006;Wheeler et al, 2003;Yang et al, 2015a, b) S-CLAY1 model (Wheeler et al, 2003) is an extension of the MCC model with an inclined YS and a simple RH rule to simulate the anisotropic response of soft clays at large plastic strains.…”