9.4.5 Rock Dowels
Grouted rock dowels consist of steel reinforcing bars (rebar) that are cemented into boreholes. These bars may or may not be subjected to post-tensioning. Untensioned dowels, therefore, do not provide any additional normal force across the failure plane. However, they provide additional shearing resistance across the potential failure surface plane.
Rock dowels are commonly used to provide support for steeply dipping, slabby rock formations. They are also used to provide anchor keys and tiebacks for shearing resistance at the toe and flanks of retaining walls. Dowels can also be used to anchor draped wire mesh, pin wire mesh to the face of a highwall, hold strapping in place, or anchor restraining nets or cables.
Rock dowels can be anchored in place with pumped grout or by utilizing cartridges of resin similar to the thread bar application. When resin cartridges are used, the rebar is rotated and driven through the cartridges with the drill, thus breaking the package and mixing the resin.
Figure 21: Standard rock bolt and cable bolts
Figure 22: Types of rock bolt and dowels