Abstract In order to study the loosening effect induced by rock mass excavation under high in-situ stress,a laboratory experimental simulation system was designed. By the rapid failure of a rock bar,the system is capable of simulating rapid unloading for jointed rock mass,thus is able to simulate the loosening effect of jointed rock mass under excavation load transient unloading(ELTU),by which,the relationship of in-situ stress level and structural plane opening displacement can be studied. Regression analysis results show that,the opening displacement value is in positive relationship with the square value of in-situ stress. The proportion of displacement on each joint in the total displacement induced by excavation load transient unloading is dependent on the amount and location of joints.
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