Influence of strain rate and cyclic compression on physico-mechanical behaviour of rock

Effect of cyclic loading and strain rate are considered to be most important parameters which govern th e rock mass in various loading environments. They are directly related to the long-term stability of any structure. The present investigation mainly deals with the response of cyclic loading and varying strain rate on physico-mechanical properties of Chunar sandstone which is considered to be nearly isotropic, fine grained and homogeneous in nature. It is found th at compressive strength decreases as the number of cycles increases, but in this case after 400 cycles, decrease percentage in strength is not significant. The failure strength increased with increase in strain rate between 1O- 5 /s to IO- I /s. Young's modulus also shows the same trend Mechanical response of rock mass plays an important role in the design of rock structures, slopes, dam foundations, underground spaces, drilling, blasting etc. Though in recent studies of fracture mechanics, more attention is being given to evaluate the behaviour of rocks in fatigue under varying strain rates and at post-failure behaviour stage, but much more detailed studies are required to fully understand the behaviour of rocks. Rock structures are subjected to pulsating load due to different activities during rock excavation and their prediction is an intricate problem. Main operations in mining like drilling and blasting can be optimized with adequate knowledge of mechanical properties and fracture characteristics of rock material. The failure strength of the rock increases with increase in the strain rate, in deciding operations, more energy is consumed for removing a given volume of rock. On the other hand, the rock becomes more brittle at higher strain rate, thu s involving less energy to displace the given volume of rock. Thus, an attempt has been made in the present investigation to understand the mechanical behaviour of Chunar sandstone under cyclic loading and varying strain rates. Burdine l studied the stress-strain behaviour of Berren sandstone under uniaxial, triaxial cyclic loading and reported that the fatigue strength of rock is strongly dependent on the grain size and interlocking material between the grain and grain