Claysville, PA: Pressure Grouting Enlow Mine - Oak Spring Slope Pre-Grouting
The project was performed to reduce water infiltration during the installation of the future Oak Spring access shaft (slope) into the existing Enlow Coal Mine.
Grout borings were installed at various angles to maximize coverage of the slope alignment from the available drilling locations. Casing was installed through the overburden using appropriate casing-advance methods and was grouted in place. Borings were drilled with a rotary/down-hole hammer drill rig utilizing a destructive bit up to approximately 140-feet below ground surface.
Grouting of the fractured bedrock progressed in maximum 25-foot ascending stages. Geo-Con established a grouting program that included progressive grout viscosity adjustment and flow rate limitations in response to real-time assessment of grouting parameters. The goal of the program was to achieve efficient refusal/closure of fractures while maintaining a grouting reach that would be limited to the future slope alignment. Grout passed through the header system prior to delivery to the target grout stage. Stages were isolated with a grout packer apparatus that consisted of a single pneumatic packer attached to the bottom of an aluminum grout pipe. Difficult or high-take stages were addressed with a Medium Mobility Grout containing Portland cement, bentonite and fly ash. Grout flow rates, apparent lugeon, pressure, and total gallons of grout pumped were recorded and used to generate a daily grouting report.
Difficult terrain and site obstacles including an access road and high-voltage power lines precluded grouting from several key locations along the alignment. In response, Geo-Con had to calculate and install borings at varying angles from available drill-locations to maximize coverage of the slope alignment. Accelerated schedule and coordination with other Conractors on site made planning and coordination essential to successful completion.