Dynamic cracking behaviour of rocks

• Main Author: Loo, Jin Jie.
• Other Authors: School of Civil and Environmental Engineering
• Format: Final Year Project
• Language: English
• Published: 2013
• Subjects: DRNTU::Engineering::Civil engineering::Geotechnical
• Online Access: http://hdl.handle.net/10356/53895
• Institution: Nanyang Technological University

Explosive material may be introduced in underground space construction to break hard rocks into fragments. However large amount of the materials used to achieve desired efficiency of the blasting activities is costly for the project. Money can be saved if the cracks initiation and propagation due to the blasting are able to be predicted. This study aims to analyse the cracks initiation under high strain rate (dynamic loading). Hydrocal gypsum cement was used to fabricate the specimens with various flaw inclinations for this study. Split Hopkinson Pressure Bar (SHPB) was used to provide a high strain rate loading on specimens to study the dynamic crack characteristics and failure mechanism. The specimen’s fracturing process was recorded by a high speed camera for crack analysis. The results of the dynamic loading test showed that the first cracks ever appeared in the specimens with flaw inclination less than 45° were a pair of tensile cracks whereas the specimen with flaw inclination greater than 45° were a pair of shear cracks instead. For the pair of primary cracks of the specimen with 45° of flaw inclination showed three possible strain rate-dependent crack patterns which include one pair of tensile wing cracks, one pair of shear cracks and the combination of tensile and shear cracks. Despite the difference of the primary cracks, the failure mechanism of all the specimens tested under dynamic loading was due to the coalescence of tensile cracks and shear cracks.