For the Three Gorges granite specimens

the conventional triaxial compression and the confining pressure reduction test under constant axial strain and stress are carried out. The lateral deformational characteristics of brittle rock under different stress paths or different loading control modes are studied; and it is found that the critical lateral strains are always in the range of ?0.004 5 and ?0.003 5. Based on the analysis of the complete stress-strain curves and the damage mechanism of the Three Gorges granite

it is put forward that the brittle rock mainly occurs lateral damage and exhibits the similar damage evolutionary rule under different stress paths and loading control modes; and the critical failure generally occurs at a damage variable level of 0.7 to 0.8. Finally

a damage model considering the unloading effect and a failure criterion in strain space are established

in which the lateral damage variable is seen as a critical variable.