Meso-fracture mechanism of Longmaxi shale with different crack-depth ratios: Experimental and numerical investigations

•Based on the in-situ SEM experiment, the full fracture process and mesoscale crack propagation mode of shale were discussed in detail.•Based on double-K fracture criterion, the subcritical crack length, initial and unstable fracture toughness were calculated theoretically.•The fracture morphology characteristics of Longmaxi shale were deeply investigated.•The effect of the sedimentary particle and bedding plane on crack propagation has been simulated based on particle flow code.