Abstract: The stress state of rock mass is very complex in practical engineering; it’s not just a simple loading or unloading; such as the dams of hydraulic engineering, considering from its mechanical condition, the dam foundation excavation main shows the unloading at the direction of excavation (other directions may be unloading or loading); after construction of the dam , it main shows loading from the mechanical condition, so it has an important engineering significance to study the mechanical properties of rock mass’ reloading after a unloading damage. The results show that: the confining pressure for intermittent jointed rock deformation modulus has little effect; the elastic modulus of rock has no apparent relationship with the confining pressure; jointed rock mass deformation modulus and elastic modulus are significantly lower than intact rock under the same confining pressure: jointed rock peak strain increases linearly with the confining pressure; and there is a good correlation between the two. Compared to the intact rock samples, joint rock the peak strain of jointed rock grows faster with confining pressure increasing. The lower the confining pressure is, the greater of the impact of unloading on rock strength is. With confining pressure increasing, different of damage caused by different unloading amount of rock samples will decrease.

Key words: jointed rock, unloading before peak, mechanical test