Deformation and failure mechanism of horizontal soft and hard interlayered rock under uniaxial compression based on digital image correlation method

The deformation of bottom rock masses surrounding a tunnel may lead to floor upheaval, structural damage and track irregularity during operation when the tunnel is constructed in soft and hard interlayered rock strata with gently dipping layers. Therefore, in order to study the deformation behavior of soft and hard interlayered rock, a special metal mold was designed to restrain the displacement of a certain side of the samples for the uniaxial compression test. A series of soft and hard interbedded rock-like samples with different height-length ratios were prepared. The deformation characteristics and failure properties of horizontal soft and hard interbedded rock-like samples were studied under uniaxial compression. The test results show that the peak uniaxial compressive strength of the horizontal soft and hard interbedded rock-like samples decreases with the increasing of the height-length ratios. The failure of the horizontal soft and hard interlayered rock-like samples is a process of coupling failure of the soft layer material and the hard layer material under compressive stress. The failure process of the sample is dominated by axial splitting and buckling. Based on the digital image correlation (DIC) tech-nology, the relationship between the displacement and stress of the sample was analyzed. Under the same stress value, the displacement of the outer layer is greater than that of the inner layer. The strain and the displacement of the soft rock layer are greater than those of the hard rock layer. The test results are consistent with the engineering reality and explain well the mechanism of the soft and hard interlayered surrounding rock lifting at the bottom of the tunnel.