Classifying failure modes of Hong Kong rocks under uniaxial compression loading using high speed imaging technique

Abstract

Uniaxial compression test is one of the most popular laboratory tests carried out in Hong Kong to determine the mechanical properties of rocks. Apart from the strength and defonnation modulus values, the failure modes are also normally recorded. In this study, twenty local cylindrical granite and tuff specimens are tested under uniaxial compression. With the aid of a high-speed camera, it becomes possible for us to observe the cracking process in detail, which provide important clues on the relationship between failure mode and uniaxial compressive strength of the test specimens. The ranges of the UCS for the tested 11 granite specimens and 9 tuff specimens are 27.02-225 .22 MPa (mean = 136.32 MPa) and 85 .06 - 247.63 MPa (mean = 154.54 MPa) respectively. Regarding the cracking process, the development of zig-zag cracks is common in granite, while the development of a dominant inclined shear crack is common in tuff. The failure mode of granite is mainly axial splitting, while the failure modes of tuff include shearing along a single plane, along a wedge, and dendritic shearing. Multiple fracturing mode occurs in both granite and tuff.