• Santanu Misra

      Articles written in Journal of Earth System Science

    • Is the outcrop topology of dolerite dikes of the Precambrian Singhbhum Craton fractal?

      Nibir Mandal Atin Kumar Mitra Santanu Misra Chandan Chakraborty

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      In the Precambrian Singhbhum Craton of eastern India, newer dolerite dikes occur profusely with varying outcrop lengths. We have analysed the nature of their length-size and orientation distributions in relation to the theory of fractals. Two orientational sets of dikes (NW-SE and NE-SW) are present. Both the sets show strongly non-power-law size distributions, as reflected in non-linear variations in logarithmic space. We analyzed thousands of data, revealing that polynomial functions with a degree of 3 to 4 are the best representatives of the non-linear variations. Orientation analysis shows that the degree of dispersions from the mean trend tends to decrease with increasing dike length. The length-size distributions were studied by simulating fractures in physical models. Experimental fractures also show a non-power-law distribution, which grossly conforms to those of the dolerite dikes. This type of complex size distributions results from the combined effects of nucleation, propagation and coalescence of fractures.

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


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      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 (${\sim}$0.20) and beyond a critical window of displacement rates (3–4.45 mm/min) for both the samples with single- and double-joint-segment(s). The fractures were dominated by tensile wing cracks, however, the location, timing and corresponding displacement rates concerning the appearance of secondary shearing confirmed that the extent of shearing mechanism enhanced at fast-displacement rates when the persistent ratio crossed a critical value (${\sim}$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.

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