Abstract: In-situ Direct shear test of rock samples is one of the important methods to directly obtain the strength index of rock mass. In fact, similar character specimens are usually taken as a group, and linear regression analysis is carried out using graphics by using the Mohr-Coulomb failure criterion. So, how to group the specimens directly affects the strength index of the rock samples, which has a significant impact on engineering safety and investment. In this article, the grouping standards of in-situ direct shear test is evaluated through the principles, failure modes and displacement inflexions. The results show that, for shear zone with complicated component and complex failure modes and small thickness, grouping by failure modes and displacement inflexions is closer to actual conditions.

Key words: Shear Zone, In-Situ Direct Shear Test, Specimen Grouping