Study on the mechanical properties of thin-layered marbleized dolomite by in situ tests in the Wudongde hydropower station, China

Abstract

Transverse isotropy is one of the most distinctive features of layered rock, and many previous researchers have studied the layered rock structure using mechanical laboratory tests; however, very little work has been done based on large-scale mechanical in situ tests. In this paper, we studied typical thin-layered strata that are composed of dolomite marble embedded with phyllite in the Wudongde hydropower station of China. To determine the deformation and failure behavior of the thin-layered rock mass during excavation, a set of large-scale cubic in situ samples were prepared. First of all, polyaxial deformation tests with confining stress were carried out on each sample, then an unloading process perpendicular to the layers was undertaken to investigate strength parameters. Based on the experimental results, the anisotropy of the thin-layered rock has been discussed. Because of the weakness of the layered discontinuities, it is more deformable when loading perpendicular to the layers. It shows that the layered discontinuities would open to induce failure when lateral pressure is released that is perpendicular to the layers during the unloading strength tests. The strength parameters from in situ tests are fitted by the conventional Mohr–Coulomb criterion, and the cohesion is about 10.33 MPa, whereas the internal friction angle is about 27.9°, which is slightly less than the strength deduced from the triaxial test in the laboratory.