A continuum damage model is generalized to simulate both the progressive failure and the formation of localization bands in brittle rock structures under both tensile and compressive loading. The model is implemented into a finite element code to simulate the constitutive behaviour of a number of brittle rock structures which might actually be found in the laboratory or in the field. The effect of closed cracks is included in the calculations. Since, in the present work, finitely extended bodies are considered, the damage in a given direction can no longer be supposed uniformly distributed throughout the body considered