4.5 Yield/failure locus

We can combine all rock failure types in a single $(\sigma_n,\tau)$ plot (Fig. 4.17). The rock would fail in tension if the Mohr circle (or state of stress) goes further to the left of $T_S$. It would fail in shear if it touches the red line $\tau = S_0 + \mu_i \sigma_n$. Last, it would develop significant compressive plastic strains if it crosses the yield cap (blue line - as you may guess, there is also an equation for it!).

Figure 4.17: Summary of basic rock failure modes.