FRICTION BOLT ANCHORED WIRE ROPE FOR ROCK SUPPORT IN BURST-PRONE GROUND

A support system for large ground convergence conditions or burst-pron e ground must contain holding elements (rockbolts, cable bolts, etc.) that are strong yet capable of sustaining large deformations, i.e., th ey must absorb as much energy as possible. Steel wire rope anchored in a borehole by a friction bolt provides these desired yield characteri stics if the frictional anchorage is placed deep enough into the rockm ass, i.e., in non-yielding rock or beyond the expected depth of rock e jected during a rockburst. Pull-out tests were conducted on wire ropes anchored by inflated Swellex bolts to assess the feasibility of this support concept. The test results demonstrate that a Swellex bolt gene rates a frictional anchorage that allows the wire rope to slide at hig h loads and to absorb significantly more energy than either a Swellex bolt alone, or a cement-grouted cable. The rope/friction bolt combinat ion can be engineered to provide the desired energy absorption and all owable deformation by varying the installed lengths of the friction bo lt and the rope. For yielding rope support, the contact length between the rope and Swellex bolt must be short enough to ensure that the rop e can slip well before its tensile capacity is reached. A safe maximum overlap length lj about one metre for the wire rope used in this test ing When used as support in the back of drifts, a swaged button on the ropes end must be used to ultimately mobilize the full rope capacity thereby protecting against gravity-driven falls of ground.