Most shale and carbonate formations violate the isotropic assumption of rock media in classical fracture models due to the presence of extensive natural-fracture network. However, the current application of strain gauges cannot provide information about how natural fractures interact with induced fractures in such heterogeneous rock system. In this paper, we present the application of Digital Image Correlation (DIC) technique which can measure strain development over time, thus it can determine the fracture initiation and propagation. We apply indirect tensile experiment on Buda Limestone samples with various patterns of complex natural-fracture system while the strain development in sample is measured by Digital Image Correlation (DIC) technique.
As a benchmark, DIC technique was first conducted on a homogeneous sandstone sample. The results verify that that the maximum tensile strain is developed at the central vertical line of sample as it was expected from theoretical solutions. This DIC measurement matches the post-failure fracture pattern of specimen. In contrast to failure pattern in homogenous sandstone specimen, very complex fracture pattern was observed on several Buda Limestone specimen. Fracture slippages along natural fracture, fracture deviation toward inclined and horizontal fracture was recorded. The results of this study can help us to better understand the complex failure mechanism in naturally fractured media. DIC is a powerful technique in providing the strain development over the surface of sample in real time, thus it can provide the fracture initiation and propagation in such heterogeneous rock media.