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Abstract The mechanical properties of rock-like brittle materials are closely related to the confining pressure. In order to study the dynamic mechanical properties of rock under confining pressure and get its axial stress-strain curve under distinct confining pressures and strain rates，the underground engineering rock are subjected to impact compression experiments with the split Hopkinson pressure bar(SHPB) of diameter 100 mm with active confining pressure device. At the same time，the dynamic stress equilibrium of SHPB experiment is analyzed. Experimental results show that：(1) The dynamic compressive strength and toughening effects of rock are more prominent under confining pressure and appears development trends to ductile characteristic，which reveals a strong confining pressure effect. (2) Under the same range of confining pressure，rock?s peak strength and peak strain change with the strain rate and reveal significant strain rate dependence. The dynamic strength increase factor keeps an approximately linear relationship with the logarithm of strain rate and dynamic strength appears approximately linearly increase with the stain-rate upwards. (3) The rock demonstrates the obvious fragility characteristic under axial dynamic load. It damages under the action of many stresses combined and mainly by the tensile stress. With the confining pressure increasing，the rock sample reverses from brittle to ductile. Failure modes are characterized by compression shear damage going with tensile strain damage and unloading damage.
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Received: 20 May 2011
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2011, Vol. 30 
