Dynamic compression measurements on selected granitic rocks using Split Hopkinson Pressure Bar test

The dynamic strength measurement on rocks has critical applications in areas ranging from blasting and fragmentation to design of underground structures. The present work on selected granitic rocks deals with measurements of compressive strength under dynamic loading conditions using the Split Hopkinson Pressure Bar apparatus. The tests involved two experimental setups with 19 mm and 25 mm diameter bar in order to study the strain-rate effects on dynamic compressive strength. Parametric studies have also been conducted to achieve dynamic stress equilibrium using pulse shapers. The ratio of dynamic compressive strength to static uniaxial compressive strength defined as dynamic increase factor (DIF) was found to be ∼1.7 at a strain rate of ∼550/s for Stanstead granite. Similar DIFs were obtained for the Laurentian and Barre granites. It was also noted that the use of pulse shapers can result in considerable reduction in strain rate without always achieving stress equilibrium.