Experimental study of the ultrasonic and mechanical properties of a naturally fractured limestone

This study investigates the changes in the ultrasonic and mechanical properties of a rock, by means of ultrasonic wave velocity measurements on a brittle limestone containing natural fractures and bedding subjected to uniaxial compression tests. The results showed that natural fractures and bedding reduced the velocity of ultrasonic waves and the mechanical strength of the limestone. Combined with the analysis of X-ray CT images of the samples, we found that the orientations of the bedding and of the pre-existing penetrating fractures affected the direction of subsequent crack propagation under uniaxial compressional loading. The initial disturbance factor D and the intactness factor s were calculated through the use of equivalent medium theory and Hoek–Brown strength model. The relationship between s and D was empirically characterized by an exponential fitting. A parameter b was introduced that can be calculated from the s–D relationship. This parameter represents a strength index for the pre-existing natural fractures. Based on the value of b, the limestones studied were classified into four types: fissures and bedding, infilled fractures and bedding, main infilled fractures, and nearly intact.