Reducing Risk with Comprehensive, Accurate Data

Client

Massachusetts Water Resources Authority, Boston, MA

Project objective

The proposed MetroWest Water Supply Tunnel project involved a US$728 million aqueduct, to be constructed in a 2000 foot wide area known to contain extremely hard rock mixed with soft clay-like sedimentary rock, conditions typically difficult for the operation of tunnel boring machines.

The client wished to obtain better definition of the geology in the targeted zone than was possible using vertical cored borings. Due to the complex local bedrock geology, the client chose Kinectrics’ Directional Drilling system in order to avoid missing problem areas. Several previous attempts at core sampling employing vertical methods had proven insufficient in producing the essential data.

Scope of work

Boring on this four-month phase of the project started at ground surface and proceeded in an easterly direction. The overall length of the boring was approximately 1,750 feet. Drilling through the overburden soil was performed at an angle of approximately 30 degrees to the horizontal, using conventional drilling methods. The boring then advanced in the bedrock to a depth o 200 feet, about 20 feet above the crown of the tunnel.

Kinectrics performed frequent Precision Directional Drilling of the boring from the top of the rock until the crown of the tunnel was reached. The process, during the curved portion of the work, involved conventional drilling for a length of about 9 feet, followed by withdrawal of the drill string, insertion of the Directional Drilling tool and Directional Drilling for about 9 feet. Withdrawal of the drill string, followed by re-insertion of the conventional drill head was repeated, alternating with Directional Drilling, until the desired point about 20 feet above the crown of the tunnel was reached.

At that point the drill was horizontal and aligned along the line of the tunnel, with about 1,050 feet of drilling remaining to reach the location of shaft 5A. Directional Drilling was also required over the last 1,050 feet to keep the horizontal boring remains confined to an allowable drilling envelope that was no closer than 10 feet, and no further than 30 feet, from the perimeter of the proposed tunnel.

The recovery of high-quality rock core samples was the primary objective of this work and continuous core samples were obtained during both conventional and Directional Drilling.

Results

Directional Drilling by Kinectrics successfully produced reliable continuous core samples at the required alignments. Samples were of sufficient quality and quantity to support accurate reliable geological analysis of the proposed tunnel project location.

Client benefits

The Massachusetts Water Resource Authority concluded that, "Kinectrics’ Precision Directional Drilling proved to be a valuable tool in exploring an area of complex geological conditions." "A better representation of the rock at the tunnel elevation was obtained, offering designers and contractors a better chance of estimating the true cost of the tunnel."

For more information, contact

info@kinectrics.com