Strength Properties of Fibre Glass Dowels Used for Strata Reinforcement in Coal Mines

Glass-Reinforced Polymer (GRP) bolts, commonly known as Fibre Glass (FG) dowels are increasingly applied for strata reinforcement in mines. The most popular dowels used in coal mines are the 22 mm diameter fully threaded type. A series of tests were undertaken to evaluate various strength properties of FG dowels. These include tensile failure tests by the double-embedment method, single and double guillotine shear tests, double shear tests in concrete medium and punch shear tests. Punch shear tests were used to evaluate the dowel shear strength parallel and perpendicular to the fibre glass strands or elements direction of extrusion. The study found that the tensile strength of the 22 mm diameter fibre glass dowels was in the order of 30 t. In the shear testing, the peak shear load was influence by the encapsulation grout type and the level of fibre glass axial pre-tension. Also, there was a nearly fivefold difference in the shear strength value of fibre glass dowels tested parallel as against perpendicular to the dowel axis.