Developing an initial normal-loading, subsequent passive changes in local normal load/stiffness-allowable direct shear tester of discontinuities and investigating the shear behaviors of discontinuities

A widespread case of discontinuity shearing is among the local shallow rock blocks sliding along non-planer, rough, non-anchored discontinuities, which is characterized by initial normal load in addition to free subsequent change in local normal load/stiffness, provoked by shear dilatancy (INL). The existing direct shear apparatuses of rock discontinuities fitted for those cases are rare, and it is lack of understanding the shear behaviors of discontinuities under such INL boundary conditions. Here, we develop an INL direct shear tester of discontinuities for shear strength. This tester takes advantage of the direct shear test apparatus modified after the YZ-5 model without a servo-controlled system to permit the accomplishment of those boundary conditions. Shear behaviors of unfilled discontinuities and infilled ones under INL boundary conditions are investigated. Moreover, the possible influence of clay content on those shear behavior of infilled discontinuities is clarified. The developed tester made it possible to test the shear performance of the local shallow rock blocks sliding along non-planer, rough, non-anchored discontinuities. This work contributed to a limited body of researches on the shear behaviors of discontinuities under those INL boundary conditions. Limitations of this work are also revealed.