Failure criteria (Mohr-Coulomb)

Input(s)

$\sigma_{a}$: Principle Stress (psi)

$\sigma_{b}$: Second Strongest Stress (psi)

B: Angle Between Fault and Direction of Principle Stress (degrees)

Output(s)

$\tau$: Shear Stress (psi)

$\sigma$: Normal Stress (psi)

Formula(s)

$$ \begin{gathered} \tau=0.5 *\left(\sigma_{\mathrm{a}}-\sigma_{\mathrm{b}}\right) * \sin (2 * \beta) \\ \sigma=0.5 *\left(\sigma_{\mathrm{a}}+\sigma_{\mathrm{b}}\right)+0.5 *\left(\sigma_{\mathrm{a}}-\sigma_{\mathrm{b}}\right) * \cos (2 * \beta) \end{gathered} $$

Reference(s)

Mark D. Zoback, Reservoir Geomechanics, Cambridge University Press, UK, Page: 89.