In 2000, the Queensland mines inspectorate identified overtorquing of cuttable dowels as a cause of failure. In some instances the head of the dowel broke off behind the plate. If the dowels are over-torqed, the dowel could be damaged and its ability to sustain shear stresses reduced.
In response to this problem, Roadway Reinforcement Services responded to enquiries from Mark Johnston (services superintendent, Oaky Creek Coal) to design a thrust dowel in order to overcome the overtorquing of fiberglass dowel. The TFD dowel was developed and was quickly introduced at Oaky North followed by Central Colliery. A few month later the use of dowels spread to Oaky No1, Moranbah North, Tahmoor West Wallsend and Ulan.
Ghass Skybey, business development manager, said the objective of the system was to improve the safe installation of Fiberglass Dowels by eliminating torquing. The TFD, available in 19.5mm and 22.2mm, is fitted with hexagonal domed head by means of injection moulding. Minimum length is 600 mm with tensile strengths of 195kN and 285kN and shear strengths of 55kN and up to 82.5kN respectively.
It is claimed that the hexagonal domed head provides even load distribution on the load indicator plate. Also that the TFD eliminates problems associated with nut break-out.
