Hoek and Brown criteria for principal stress failure
Input(s)
Co: Unconfined Compressive Strength of Rock (psi)
m: Constant Depending on Property of Rock and Extent to Which It Is Broken (dimensionless)
s: Constant Depending on Property of Rock and Extent to Which It Is Broken (dimensionless)
\(\sigma_{c}\): Minimum Effective Principal Stress (psi)
Output(s)
\(\sigma_{a}\): Maximum Effective Principal Stress (psi)
Formula(s)
\[
\sigma_{\mathrm{a}}=\sigma_{\mathrm{c}}+\operatorname{Co} *\left(\mathrm{~m} * \frac{\sigma_{\mathrm{c}}}{\operatorname{Co}}+\mathrm{s}\right)^{0.5}
\]
Reference(s)
Mark D. Zoback, Reservoir Geomechanics, Cambridge University Press, UK, Page: 98.