Investigation of a new drilling design for loading core specimens with triple holes to determine direct tensile strength values of rock materials

Abstract

Drilled core specimens including a reaming and two loading holes were investigated with both numerical and experimental studies to assess its usability to determine direct tensile strength values of rock materials. A new loading apparatus with rods to insert into the loading holes has been designed and manufactured to supply tension. Elimination of the gluing in the standard direct tensile strength test method is a significant advantage to make both hard and soft rocks possible to be tested. The cylindrical specimens with the diameter of NX size and length to diameter ratio of 3 were used in the tests. In this test method, reaming holes with higher diameter than that of the loading holes were drilled at the middle length of the specimens as the target location for the crack initiation. However, the drilled discs were determined to fail because of the crack initiation at sidewalls of loading holes, instead of the reaming hole. Therefore, loading with inserted rods was not found applicable. The test method and its failure mechanism were discussed for the aim of contributing to relevant studies.