The strength properties of fibre glass dowels used for ground control in coal mines
Glass-Reinforced Polymer (GRP) bolts, commonly known as Fibre Glass (FG) dowels or plastic dowels are increasingly applied for strata reinforcement in mines as well as in concrete reinforcement in civil engineering. The most popular dowels used in Australian coal mines are the 22 mm diameter fully threaded type. FG bolts are cuttable, easy to handle, lightweight and corrosion resistant. The tested dowels were all black in colour, which is a favoured colour in coal mines. A series of tests were undertaken to evaluate various strength properties of FG dowels. These tests include the tensile failure test by the double-embedment method, single guillotine shear test, double shear test both in steel frame and in concrete blocks, and finally the punch shear test. The study found that the tensile strength by pull testing of the 22 mm diameter fibre glass dowels was in the order of 27 t. The shear strength testing of dowels in both single guillotine and double shear steel frames were in agreement with each other. In general the shear strength values of dowels tested, using single shear guillotine testing, were around 20% of the axial strength in comparison with 70% in the same diameter steel rebar tests. The peak shear load values obtained from double shear tests in concrete blocks was influenced by the encapsulation grout type and the level of fibre glass axial pre-tension. The punch shear tests revealed that there was a more than threefold increase in the punch shear strength value of fibre glass dowels tested perpendicular as against parallel to the dowel axis.
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