Dendrobium Mine Longwall Pre-driven Recovery Roads Including Developing Cuttable Grout Pillars

Longwall face recovery is a complex geotechnical challenge with high potential for losses due to the occurrence of ground control problems. In recent times, the use of pre-driven recovery roads has improved the overall efficiency and safety of moving longwall equipment from panel to panel. In 2015 Dendrobium Mine and Golder Associates developed a grout pillar design that could be constructed within the pre-driven recovery road prior to the holing and recovery of the longwall equipment. The challenging ground conditions often experienced in longwall pre-driven recovery roads provided the main impetus for the decision to construct large yieldable grout pillars in a roadway that will be subjected to a cantilevering roof and a yielding fender on holing. Due to the resulting increase in support density, recovery road conditions have improved as shown by roadway monitoring data. Longwall operators have considerably less exposure to potential hazards during bolting operations with reduced bolt up time resulting in increased longwall productivity. All elements of support including 47 grout pillars had to be safe to cut and remove via the mine conveyor system. Due to lack of surface access, all materials to construct the grout pillars were transported up to 14 km from the mine portals. Grout pillar formwork design initially incorporating fabric bladders and steel formwork has since been replaced with a lattice of fibreglass (FG) dowels and hessian coated FG mesh, sprayed with a Gypsum based plaster. Air-driven placer pumps were replaced by electric placers with greater reliability and grout quality control procedures ensured that the target pillar strength was reached before holing of the longwall. Pre-driven recovery road support design incorporating cuttable grout pillars has been combined with the development of a grout delivery system and containing formwork to deliver key productivity and safety improvements during longwall recovery.