Rock mass parameters for a shale rock, m_b, s, and a of the Hoek and Brown failure criterion as given in the equation are 2.4, 0.01 and 0.52 respectively. The uni-axial compressive strength (σ_Ci) of intact sh!le is 50 MPa.
$${\sigma _1} = {\sigma _3} + {\sigma _{ci}}{\left( {{m_b}\frac{{{\sigma _3}}}{{{\sigma _{ci}}}} + S} \right)^a}$$
The global rock mass strength of shale in MPa is

A. 1.2

B. 10.29

C. 20.83

D. 50,00

Answer: Option B