Sponsored by CDC NIOSH, research was performed at the Colorado School of Mines Edgar Experimental Mine to evaluate high-pressure waterjets for the scaling of loose rocks in mine openings. The research is motivated by the desire to develop a remote scaling technique as a method of reducing accidents associated with rock scaling. An additional benefit of the method is to improve the adhesion characteristics of shotcrete applied as a support membrane. Ten experiments were performed by scaling a freshly blasted rock surface. Half of the experiments consisted of perimeter holes fully loaded with ANFO, and smoothwall blasting was employed with the remaining experiments. Five different nozzle designs were evaluated: a single orifice straight nozzle, a duel orifice self-rotating nozzle, a single orifice straight nozzle with two different mechanical oscillating systems, and a single orifice acoustically pulsed nozzle. Two scaling experiments were performed with each nozzle type, one with each type of blasting system. Hand scaling was performed after each experiment as a control. Two experiments were conducted in reverse order with hand scaling performed first. This paper summarizes the results of the experimental program, and provides a comparison of the performance of each nozzle type. A comparison of results with conventional and smoothwall blasting is also presented.
1. INTRODUCTION
Controlled blasting practices to reduce collateral rock damage and minimize the fracture envelope created around underground excavations,
Remote scaling technologies to efficiently remove loose and unstable rock created during blasting,
Advanced roof support technologies and installation practices, including rock bolts, shotcrete, and thin-membrane liners,
Monitoring methodologies to detect ground loading and remotely identify the presence of loose and unstable rock.
A large number of accidents in underground mining are caused by rock falls. Of these accidents, a significant percentage of injuries occur while attempting to scale loose and fragmented rock from the periphery of underground workings. It is likely that many of these accidents can be prevented through the implementation of integrated concepts that relate ground control issues with technical innovations in drill and blast drifting and tunneling. Such systems would utilize:This paper summarizes the results of a National Institute of Occupational Safety and Health (NIOSH) funded project to evaluate one component of this overall strategy by testing the effectiveness of using highpressure waterjet technology as part of a mechanized scaling system to safely remove loose and unstable rock from underground mine openings. Additional details of the work performed can be found in [1]. The project builds upon previous research in waterjet scaling and was performed at the Colorado School of Mines (CSM) Edgar Experimental Mine. The relative effectiveness of five nozzles designs, including a single orifice straight nozzle, a duel orifice self-rotating nozzle, a single orifice straight nozzle with two different mechanical oscillating systems, and a single orifice, acoustically pulsed nozzle, was examined. It is believed that the utilization of a properly designed waterjet scaling system will provide significant improvements in employee safety over that of conventional manual or mechanized scaling methods by removing miners from high-risk areas and reducing their potential exposure to rock falls.
