The mode of failure was studied on rock samples and observed in mines on local and mining scales. Modes of rock sample failure were classified in a matrix reflecting various critical stress conditions. It is hypothesized that the mode of failure effects the strength of rocks and rock mass. An example is given of rock samples of the same lithology having vary different uniaxial compressive strength for different modes of failure.

Observations on the mode of failure of samples tested in laboratory in uniaxial compression can be extended on modes of failure of square pillars of room-and-pillar mining. However, modes of rock mass failure around underground excavations are not only function of rock strength, compressive stress and structure but also a function of multiaxial stress conditions, and the geometry of mining excavations.

Examples of various modes of failure, taking place on local scale, in a variety of mining situations, are provided e.g. extension failures, shearing and bulging, pillar hour-glassing, pillar punching the roof, floor heave and horizontal convergence, and fall of ground due to stress relaxation.

Modes of failure at a mine scale are observed as collapse of rock mass often resulting in discontinuous subsidence.