Variations in Crack Features of Granite Specimen During Laboratory Uniaxial Compression Test Using Image Processing

Abstract

The granite is a heterogeneous rock consisting of various microscopic compositions (i.e., quartz, feldspar, biotite, etc). Changes in the digital features of these compositions are important in understanding the deformation and failure mechanisms of the rock. The video images photographed during the uni-axial compression test were used to investigate the digital changes of the cracks in the rock. The original images were first transferred into the gray and binary ones using the digital image processing. The positions of cracks were extracted using the grayscale threshold segmentation and traditional visual identification. The changes in the digital features of the cracks were furthermore explored in various stages during the specimen failure. It shows that the failure process of the granite specimen may be divided into three stages, or, stable, speeded, and complete ones; at the stable stage, the first crack initiates and propagates gradually with the great changes in the crack features; at the speeded stage, two of new cracks generate and all of cracks propagate much quickly; at the complete failure stage, all of the cracks changes gradually again until the rock approached to failure. The results presented herein may be referable in investigating the failure mechanism of the rock material.