Effect of displacement rates on the mechanical integrity of soft-porous rock analogue containing non-persistent joints of variable lengths

We investigated the effects of displacement rates on the strength and mechanisms of fracturing by conducting three series of compressive experiments with synthetic samples analogous to soft-porous rocks. The three series correspond to (i) intact samples (without joints), (ii) samples with single joint of different lengths (10, 15, 20 and 25 mm) and (iii) samples with double joint-segments (15 mm each separated by a bridge), respectively. The samples were deformed under variable displacement rates (0.048, 0.12, 3, 4.45 and 6 mm/min). We found that the material-strength enhanced with increasing displacement rates for intact and samples with single joint-segment with limited persistent ratio; however, the strength declined substantially for samples with persistent ratio above a threshold (~0.20) and beyond a critical window of displacement rates (3–4.45 mm/min) for both the samples with single- and double-joint-segment(s). The fractures were dominated by tensile wing cracks, however, the location, timing and corresponding displacement rates concerning the appearance of secondary shearing confirmed that the extent of shearing mechanism enhanced at fast-displacement rates when the persistent ratio crossed a critical value (~0.20). Overall, the strength of material considerably reduced and the potential of damage further accelerate at faster displacement rates when the persistent ratio of non-persistent joint(s) crossed a pedantic threshold.