Characterizing the excavation process associated with removal of shotcrete reinforced underground structural liners using waterjet technology

Abstract

The primary objective of this research is to characterize the operating parameters and fragmentation mechanisms associated with the hydroexcavation of reinforced shotcrete and concrete liners used in underground mines and tunnels. Through empiric testing, this research also seeks to validate the hypothesis that waterjet removal of these support systems will result in greater selectivity and less unintended damage than conventional removal methods. The intent is to develop a viable technology that will reduce the collateral damage caused to surrounding liners during excavation, improve the adhesion between shotcrete and the substrate for longer lasting ground support, and improve overall safety for workers in underground environments.Waterjet excavation has the potential to eliminate many of the technical and operating challenges associated with conventional shotcrete removal and repair. Evidence derived through empiric laboratory testing indicates that waterjets are capable of selectively removing damaged areas of support liners without structurally compromising the substrate and adjacent intact sections of the liner. This research illustrates the contrast between the excavation process associated with both conventional mechanical impact hammers and waterjet excavation methods during empiric testing. An analysis on the fracture mechanisms and operating parameters of each method was completed. Within this analysis, instrumented shotcrete panels were physically tested to quantify vibration during excavation, and examined through visual and analytic processes to determine substrate damage and delamination. After testing was completed, this data strongly indicated that waterjet cutting causes less collateral damage to the surrounding intact liner and substrate when compared to that of conventional impact hammers. This research is intended to provide a scientific basis for additional applied research in the rapid excavation and repair of shotcrete support systems.