chapter  72
6 Pages

Shear creep of discontinuities in hard rock surrounding deep excavations

ByD. F. Malan, K. Drescher, U. W. Vogler

Time-dependent deformations around deep level mines in hard rock occur at rates well in excess of those expected from creep of the solid rock mass. It appears that the time-dependent deformation is controlled by the rheology of the fracture zone. This paper presents the results of a laboratory investigation of the shear creep of discontinuities. It was found that discontinuities with gouge infilling undergo noticeable shear creep when subjected to stress below the shear strength. The steady-state creep rate depends on the shear stress/shear strength ratio, the absolute stress magnitudes and gouge thickness. In comparison, the creep rate of mining induced extensile fractures in hard rock is negligible. Finally, a rheological model to simulate the behaviour of the discontinuities with infilling is proposed.