What is stress path

A stress path is the locus of successive stress states of a soil element during loading, plotted as a line on a stress diagram. It shows how stress changes from the initial state to failure.

It is usually plotted in $p$-$q$ space, where $p = \frac{\sigma_1+\sigma_3}{2}$ and $q = \frac{\sigma_1-\sigma_3}{2}$, with the $K_f$ line (failure line) $q = p\sin\phi + c\cos\phi$. Each point represents a Mohr circle, so stress paths avoid drawing many circles. Total and effective stress paths differ by the pore pressure.