INVESTIGATION OF ONE-PASS GROUTED SUPPORT SYSTEMS FOR USE IN A HIGH-STRESS MINING ENVIRONMENT

Development of underground openings in a deep mining environment requi res a support system that is able to absorb energy as a result of dyna mic loading due to rockbursting and blasting and static loading due to convergence as she development face advances. The support system must be resistant to corrosion and be effective over the life of the excav ation, upward of ten years, yet simple and cost effective to install O ver the past two years, research has been conducted at INCO's Creighto n Mine to try and identify a one-pass grouted support system that will meet these needs. The main problem faced with simply using grouted re bar at depth, is the effect of tunnel convergence on the stiff grouted bolts. Typically, if fully grouted, stiff rebar are installed to the face of an advancing development heading, the amount of convergence th at occurs can result in failure of the bolts at the face plates used t o attach the mine screen to the back. An initial support is required t o enable crews to continue the bolting cycle in the immediate term, ye t allow for this convergence over the longer term as the drift advance s. The ideal support system will allow both to occur, giving effective immediate support while providing long-term effectiveness in allowing convergence to occur while maintaining the capacity of the bolt. This paper will investigate the expected convergence in deep development h eadings at +2200 m (+7200 ft) through the use of direct measurements u sing both flex rod extensometers grouted into the back of a developmen t heading and five-point tape extensometer stations. Measured results will be compared with simple 2-D numerical analysis so evaluate the an ticipated convergence expected to be absorbed by the belling system. T he required convergence will then be compared with load deformation re sponse of several support configurations. Several configurations of gr outed support systems were pull tested to determine load-displacement characteristics of the typical bolting system and several modified bel ling systems. Grout configurations tested included standard two-compon ent polyester waser-based resin and a two-component configuration usin g a fast set resin cartridge at the toe and slow set (10 to 14 days) c ement cartridges to fill the rest of the hole. The maximum deformation achieved with the standard rebar was less than 20 mm at a peak load o f 170 kN to 180 kN. With the cement-resin rebar, the maximum displacem ent achieved was 36 mm, with a peak load of 170 kN to 180 kN. Failure occurred at the threads in both cases. A third system was tested. One that would allow the bar itself to yield through the grout, using the South African Cone Bolt grouted with two types of modified polyester r esin. Peak loads of 170 kN were achieved with between 89 mm and 141 mm of displacement. Mixing of the resin with the smooth bar was inconsis tent and requires further investigation. Ultimately the results of the se trials will lead to recommendations for a system that will enable i mmediate support to be accomplished with a long-term support system, i nstalled on an initial single pass during the development cycle. The a dvantages to be achieved will be seen in reduced reconditioning and re work and more effective long-term ground support and reinforcement.