A Dual DIC System for Analysis of Dynamic Mechanical Properties of Large Sandstone under Uniaxial Compression Load

In this paper, an experiment is carried out to acquire the dynamic mechanical properties of a simulated sandstone tunnel by a dual DIC system. The sandstone tunnel is simulated by large sandstone with a prefabricated hole in the center. The speckle size required by DIC system was evaluated, and the results showed that for large specimens a marker pen could be used to spot speckles and make sure that the diameters of speckle points in an image should be ranged from three to five pixels. The dual DIC system is composed of a low-speed camera and a high-speed camera. The low-speed camera is used to record the speckle patterns of the sandstone in one side during the whole process of compression load, and the high-speed camera is placed in the other side to record speckle patterns for 11.5 seconds before and after failure. It is realized that monitoring whole process of deformation and instantaneous failure in two directions is required. Measurement results are effectively analyzed. The results are shown as follows: At the initial stage of loading the sandstone is in an elastic stage without macroscopic cracks. With the increase in compression load the sandstone has several small stress releases and several obvious macroscopic cracks. In the final stage of loading, the distribution of normal stress and shear stress are almost the same, and cracks are subjected to the coupling effect of normal stress and shear stress. The two ends of the prefabricated hole perpendicular to the applied load direction are prone to cracks parallel to the applied load direction.