Under the stability of mine workings is understood the preservation within a given period of time the required size and shape of its cross-section in accordance with the requirements of the rules of technical operation and safety. ...

Sedimentary rocks usually have a layered structure, and the strength characteristics at the contacts of layers (cohesion s_k and angle of internal friction φ_k ) can vary from zero to their values in the material of the layer (c_m and φ_m ).