Hoek-Brown Rock Mass Strength Calculator
Geotechnical engineering & underground mining: Compute Generalized Hoek-Brown (2002) non-linear failure envelope, rock mass compressive and tensile strengths, deformation modulus ($E_{rm}$), and equivalent Mohr-Coulomb parameters.
Rock Mass & Intact Rock Properties
Rock Mass Criterion Parameters
Hoek-Brown $m_b$
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Frictional parameter
Hoek-Brown $s$ & $a$
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$s$ (intact fraction) / $a$
Rock Mass Compressive $\sigma_{c,mass}$
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MPa (uniaxial strength)
Peak Strength $\sigma_1'$ (@ $\sigma_3'$)
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MPa (axial failure stress)
Deformation Modulus $E_{rm}$
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GPa (in-situ stiffness)
Equiv. Mohr-Coulomb ($c', \phi'$)
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Cohesion / Friction angle
Hoek-Brown Non-Linear Failure Envelope
The non-linear Hoek-Brown envelope accounts for inter-block interlocking and progressive tensile fracturing at low confining pressures.
Generalized Hoek-Brown Formulation (2002)
The Generalized Hoek-Brown failure criterion for jointed rock masses is formulated as:
$$\sigma_1' = \sigma_3' + \sigma_{ci} \left( m_b \frac{\sigma_3'}{\sigma_{ci}} + s \right)^a$$
$$m_b = m_i \exp\left( \frac{GSI - 100}{28 - 14D} \right), \quad s = \exp\left( \frac{GSI - 100}{9 - 3D} \right)$$
$$a = \frac{1}{2} + \frac{1}{6} \left( e^{-GSI/15} - e^{-20/3} \right)$$
The deformation modulus of the jointed rock mass $E_{rm}$ is determined using the Hoek & Diederichs (2006) sigmoid formulation, modeling the steep degradation from intact modulus $E_i$ as $GSI$ decreases.
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