Deformation of rock mass with crack is considered in the context of failure control. The classical analytical solutions obtained for imponderable rock mass with crack give infinite values of stresses at tips, which disagrees with the reality. The phenomenological theory is proposed for calculating total displacements in the vicinity of a crack based on the qualitative differences in the weight actions: tension takes place above the crack while compression arises under it. The dimensionless parameter characterizing ratio of the upper edge displacements of the crack to its lower edge displacements is substantiated for description of the rock mass behavior.