Rate-dependent mechanical behavior of jointed rock with an impersistent joint under different infill conditions

Transition in the rate-dependent mechanical response of rock was investigated due to the presence of impersistent joint with different infill conditions. Four types of samples, i.e. intact, jointed with no grouting, jointed and grouted with cement, and jointed and grouted with epoxy, were fabricated using model material. A series of dynamic split Hopkinson pressure bar (SHPB) tests was conducted on prepared samples with strain rates varying between 53–130 s−1 along with static uniaxial compression tests (10−4 s−1). Progression of fracture/failure along samples was monitored using high-speed imaging and digital image correlation (DIC). Strength was observed to be significantly lower for jointed samples as compared to intact samples. However, the increasing trend of strength with strain rates remained similar for all types of samples. Epoxy was observed to be a better grout due to greater improvement in the strength of epoxy grouted jointed samples than cement grouted samples under both static and dynamic conditions. Significant changes were observed in fracture behavior (initiation, pattern and mechanism) with strain rate for intact and jointed unfilled/grouted samples. Fracturing was dominated by shear and tensile cracks at high strain rates compared to tensile cracks at low strain rates in all samples. Unlike static loading conditions, the location of cracks initiation shifts away from joint tips with increasing strain rate and depending upon existing infill conditions (unfilled/grouted).