HARD ROCK DIRECTIONAL DRILLING TECHNOLOGY ADDS VALUE FOR THE METROWEST WATER SUPPLYTUNNEL
The Devico directional drilling system at each segment utilized a flexible NQ size core barrel yielding a BQ size core encased in a clear tube, a programmable survey tool to guide the drill rod to the desired angle or curve, and DEVISOFT software to calculate borehole position and provide adjustments.
The Devico system was used along a 533m section of the eastern segment. The boring was advanced through hard crystalline granite, 18.3m of soft clay gouge within the bottom 5 degrees of the curve (using grout), felsic volcanics, healed breccias, and argillite. The high total recovery (>95%) confirmed a construction risk reduction and allowed a TBM to be considered for the work, at considerable cost savings.
The results of the 580m borehole advanced through the suspected Bloody Bluff Fault revealed 0.3m to 2.4m thick fracture zones separated by 2m to 8m of thick zones of intact rock, along a distance less than projected. The borehole was grouted prior to the arrival of the TBM, and may have contributed to a significant reduction in groundwater control and anticipated ground support.
The Devico directional drilling system added considerable value to cost saving measures and should be considered for use in future projects to reduce construction risks and as a dispute avoidance tool for similar complex geologic zones.