Directional core drilling for the Metro West Water Supply Tunnel

The Massachusetts Water Resources Authority (MWRA) is using directional core drilling technology from the mining industry and Norwegian tunneling practice to determine geologic conditions along a proposed rock tunnel alignment. The directional core drilling system is in use on the most geologically complex section of the MWRA’s 28.3 km (17.6 mile) long MetroWest Water Supply Tunnel (MWWST) in Weston, Massachusetts. A 533 m (1750 ft) long boring is being drilled from the ground surface at a 30 degree angle from the horizontal. Specially designed coring tools are being used to “kick”, or bend the boring to the horizontal and parallel to the crown of the future tunnel at a depth of 63 m (207 ft). Continuous rock core is being recovered along the entire length of a portion of the MWWST alignment where faulted ground and soft rock alteration are known to occur. The core will be used to predict anticipated tunneling conditions and complete design work for the future MWWST contract CP-3A, the Eastern Tunnel Segment. Evaluation of the core will aid in the refinement of a grouting program and the decision of whether a tunnel boring machine may be used, resulting in possible cost savings over mining the tunnel by the conventional drill and blast method.