Modeling and Implementation of the Isotache Concept for Long-Term Consolidation Behavior

A practical use of the isotache concept in creep settlement prediction is newly introduced in this study. The isotache concept introduces a unique relationship between the strain and the consolidation pressure corresponding to the strain rate in association with viscosity. The authors have proposed a method to simply introduce the isotache concept, which uses a compression curve normalized by preconsolidation pressure $\left[\epsilon –\log \left({\sigma }^{\prime }/{\sigma }_p^{\prime }\right)\right]$ and a strain rate dependency relationship between the preconsolidation pressure (${\sigma }_p^{\prime }$) and strain rate ($\dot{\epsilon }=d\epsilon /\mathit{dt}$). The strain rate dependency relationship is modeled as an equation based on power law. According to the authors’ method, the slope of the strain rate dependency relationship ($\log {\sigma }_p^{\prime }–\log \dot{\epsilon }$), which coincides with $C_{\alpha e}/C_c$, can be calculated as a function of strain rate, showing that $C_{\alpha e}/C_c$ is not constant but decreases with decreasing strain rate. In engineering practice, consolidation settlement is generally estimated based on the compression curve obtained from the 24-h incremental loading oedometer test, which corresponds to a strain rate of about $1\times {10}^{-7}\hspace{0.17em}{\text{s}}^{-1}$. Using the compression index $C_c$ at the consolidation pressure and initial void ratio $e_0$, creep settlement can be easily calculated as a function of $C_c/\left(1+e_0\right)$ and in situ strain rate (several orders of magnitude smaller than $1\times {10}^{-7}\hspace{0.17em}{\text{s}}^{-1}$).