An Experimental Approach to Evaluate the Role of Rock Failure Modes in Mechanical Characterization of Metabasalts

Abstract

A detailed understanding on rock failure modes testi es the competence of support designs for engineering work. Studying such failure modes using physical models of rock samples under laboratory conditions can be time e cient, informative and economically viable. In this study, the mechanical behavior of massive metabasalts were characterized with reference to rock failure modes through index tests such as point load and Brazilian testing conditions. Rock failure modes under point load test are categorized as i) single plane failure mode, ii) triple junction failure mode, iii) twisted failure mode and iv) single plane (inclined). It is observed that twisted and triple junction failure modes are observed for the samples with higher point load strength values (> 6 MPa). A total of ve types of rock failure modes were observed in metabasalts under Brazilian testing conditions such as i) central multiple, ii) central, iii) noncentral, iv) central multiple + layer activation and v) conjugate failure modes. Central multiple failure mode is found to be the most common failure mode in metabasalts due to its massive nature. It is also observed that all failure modes under Brazilian test are transpired in the range of 8 to 12 MPa. Among all other perceived rock failure modes, single plane (inclined) and conjugate failure modes under point load and Brazilian tests respectively are introduced in this study. It is evident that rock failure modes, which lead to control the strength of the rocks, should be considered as an important aspect for mechanical characterization of rock materials.

Summary of the Transformational Relationship between Point Load Strength Index and Uniaxial Compressive Strength of Rocks

“…The failure state of rock under point load [31,32] could be divided into four modes, i.e., the single-sided failure, triple connection failure, twist failure, and single-sided (inclined) failure [33]. The rock sample produces a vertical tensile crack under a low constraint pressure, while it generates the bending and torsional deformation failure under a high constraint pressure [34].…”