“…It was previously applied to model multi-body contact behavior (Wriggers, 2006;Popp et al, 2013;Zhou et al, 2018), multiple cracks (Zheng et al, 2015) and the non-associative plasticity with non-smooth yield surfaces (Zheng et al, 2020) etc. Motivated by these works, Zhou et al (2021) presented a KKT condition for instantaneous liquefaction and treated the KKT condition by constrained variational principle. In this work, we construct a new type of KKT condition that is different from the KKT condition presented in Zhou et al (2021).…”