Experimental Research On Mechanical Characteristics Of Fractured Rock Mass With Different Inclined Angle Under Dynamic And Static Loads

Two kinds of dynamic problems of fractured rock mass are usually met in engineering. One is how to decide the acting surface of dynamic load in dynamic digging. The other is how to decrease the execution of the dynamic loading. For studying these problems, cement grout specimens are made to simulate fractured rock mass with different inclined angle by the designed specimen mould and the improved rubdown machine. Then by using the electro-hydraulic servo test machine and split Hopkinson pressure bar, specimens are loaded with static load and dynamic load with different shock velocity. On the basis of the experiments, the static and dynamic characteristics of fractured rock mass can be concluded.From the result, there is evident difference between static and dynamic characteristics of fractured rock mass. The lowest compression strength of fractured rock mass occurs when inclined angle is 45°under static loading, but under dynamic loading condition it is 30°, and it is similar for the elastic modulus. The inclined angles also have great effects on the strain rate of fractured rock mass. When inclined angle is 30°, the strain rate sensitivity is very low, but it is very evident in 60°,90°or the rock mass without fracture. At the same time, with the increase of strain rate sensitivity, the contribution of increase of strain rate sensitivity to dynamic increase factor is decreased.The existing of water in fracture also has great effects on mechanical characteristics of fractured rock mass. The softening coefficient of fractured rock masses has no variation with the inclined angle under static load condition, but the increasing hydrodynamic pressure due to dynamic load is related to inclined angle of fractured rock mass.At last, based on the above experimental results, the angle between acting surface of dynamic load and fracture surface is suggested to be 30°during dynamic digging, and the fracture surface is suggested to be vertical to the acting surface of dynamic load while defending rock mass from dynamic load.