Effect of unloading damage on deformation characteristics of jointed rock mass
WANG Ruihong1，2，JIANG Yuzhou1，LI Jianlin2，LIU Jie2
(1. Key Laboratory of Geotechnical Mechanics and Engineering of the Ministry of Water Resources，Yangtze River Scientific Research Institute，Wuhan，Hubei 430010，China；2. Key Laboratory of Geological Hazards on Three Gorges Reservoir Area，Ministry of Education，China Three Gorges University，Yichang，Hubei 443002，China)
Abstract：The mechanical properties of jointed rock mass are significantly different under loading and unloading conditions. However，the current research on the damage characteristics of jointed rock mass under unloading conditions is relatively less，especially the influence of different unloading degree on mechanical properties of jointed rock mass is not considered. In order to understand the influence of unloading degree，joint dip angle and confining pressure on the deformation characteristics of rock mass，the repeated loading tests are performed in laboratory. The results show that with the increment of unloading value，the peak strength decreases. It has little effect on the rock mass ultimate strength when unloading degree is low. With the increase of unloading value，the reduction of the rock ultimate strength increases. The characteristics of brittle stress drop is obvious under the low confining pressure condition，whereas with the increase of confining pressure，the rock mass deformation from failure to residual strength increases and the influence of unloading degree on rock mass mechanical properties decreases gradually. The joint dip angle and unloading degree have great effect on the Poisson's ratio. The Poisson's ratio of jointed rock specimen is bigger than that of intact rock specimen，and it reaches a maximum value when the joint dip angle is 45°. The Poisson's ratio increases with the unloading degree，and the unloading degree is higher，the increase rate of Poisson's ratio is faster. The confining pressure，joint dip angle and the unloading damage degree are associated with the elastic modulus of jointed rock mass. With the increase of confining pressure，the value of elastic modulus increases but the increase rate decreases. The reduction degree of elastic modulus increases with the increase of unloading degree. Moreover，the impact of unloading degree on elastic modulus is different for rock specimens with different joint dip angles，in which the rock specimens with 45° and 60° joint dip angles are most deeply influenced.
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2016, Vol. 35 
