Three-dimensional failure mechanism of a rectangular cavity in a Hoek–Brown rock medium

• For deep cavities, three-dimensional rotational failure mechanism is proposed for calculating the work rate of external force and the internal energy dissipation.
• Collapsing magnitude increases with the increase of the strength parameter A, while decreases with the increase of the strength parameter B and rock unit weight.
• The surface equation of the three-dimensional collapsing block is derived and presented for practical use in engineering.