Abstract:On the basis of unloading tests of rock sample,the deformation and fracture features of unloaded rock mass are studied in conjunction with fracture systems of some large excavation project. Research shows that the deformation of unloaded rock is of intense dilatancy in unloading direction,the fracture is characterized by tensile one,and there are tensile-shear fractures and shear fractures. The deformation and fracture feature of unloaded rock mass is dominated by the rock mass structure,and deformation and failure in unloaded rock is prone to take place compared with those in rock. Especially,the fracture system,is controlled by the rock mass structure.