Measuring the Shear Strength of Rock Core using a Guillotine Shearbox


Prof Doug Milne ( - University of Saskatchewan), Mr Garrett Snell ( - University of Saskatchewan), Mrs Donna Beneteau ( - University of Saskatchewan), Mr Zbigniew Szczepanik ( - University of Saskatchewan)

The shear strength of intact rock can be an important property for rock mechanics design. Although the unconfined compressive strength of rock core is often measured with laboratory testing, the shear strength of that rock is difficult to measure directly. A guillotine-type “shearbox” has been developed to directly measure the shear strength of intact rock core. An additional, alteration was made to the shearbox to apply normal forces to the shear plane. Ideally, a failure criteria or envelope can be determined when multiple tests are conducted on rock cores of similar type. Since most failure in underground mines is usually of most concern when it occurs near an excavation, failure behaviour at low confinements is more representative of field conditions. Unconfined compressive strength tests, coupled with low-confinement tri-axial tests and guillotine shear-box tests were conducted on concrete and limestone samples. The results of the different tests will be compared and discussed. This testing apparatus provides a relatively simple and inexpensive alternative, or addition to tri-axial testing. Making the failure criteria of a rock easier to attain and more representative of field conditions can assist engineers to make more educated design decisions in mining and civil projects.