Mechanical-acoustic-optical combined characterization for uniaxial compression failure of soft-hard interbedded rock-like material

The interbedded structures and soft-hard rock interfaces within soft-hard interbedded rock mass (SHIRM) lead to complex mechanical behaviors and failure modes, which pose significant safety challenges for tunnel construction. In view of this, this study first prepared soft-hard interbedded rock-like (SHIRL) samples with varying bedding dip angles ( θ ) using extensive mix ratio tests. Subsequently, a novel mechanical-acoustic-optical (MAO) combined experimental system, which integrates the RMT-150B rock mechanics experimental system, acoustic emission (AE) monitoring, and optical strain measurement, was developed to capture the uniaxial compression failure process of SHIRL samples. The tests were conducted under displacement-controlled loading at an axial loading rate of 0.005 mm/s. Finally, the mechanical properties, failure modes, and MAO responses of SHIRL samples were systematically analyzed through experimental testing and finite-discrete element method (FDEM). The results indicated that the stress-strain curves of SHIRL samples under uniaxial compression were categorized into three distinct types: plastic-softening, brittle, and fully brittle. As the θ increased, the crack-closure stress, plastic deformation stress, uniaxial compressive strength, and peak strain of the samples first decreased and then increased. The brittleness index of the sample increases with the increase of the bedding angle. AE characteristic parameters and strain fields, during failure, exhibited pronounced bedding effects and stage-specific evolution features. The MAO information obtained during the uniaxial compression failure of SHIRL samples showed strong correlations. The study provided a detailed and multidimensional characterization of the progressive failure process and failure modes of SHIRL samples through integrated MAO information. The failures of SHIRL samples under uniaxial compression were categorized into CT, SP, and TP modes.