Ultimate bearing capacity at the tip of a pile in rock based on the modified Hoek-Brown criterion

A method for calculating the ultimate bearing capacity at the tip of a pile that is embedded in rock, according to the theory of plasticity, was presented in a previous paper [1] using the original Hoek-Brown failure criterion [2], Hoek et al. [3] modified their original model, in order to apply it to highly fractured media (RMR [< or =] 25), incorporating a new exponent "a" ranging between 0.5 and 0.65. A value of the exponent of a=0.5 corresponds to the original criterion.