The Halibut Point Marine Multi-Use Dock in Sitka, Alaska: Con-Tech Systems Ltd.

This project consisted of five breasting dolphins and two mooring dolphins. The ground conditions made it impossible for the 36-inch diameter piling to be driven to the depth required for adequate loading. Therefore, the piling had to be anchored to bedrock on the ocean floor.

CTS Materials used:

Breasting Dolphins 1, 2, 3, 4 = 103/78 Hollow TITAN IBO bar

Breasting Dolphin 5 = 103/51 Hollow TITAN bar IBO

Mooring Dolphins 1, 2 = 2.5” gr. 150 Solid bar IBO

The typical method used for rock anchoring deep water piling is to drive the piling directly into bedrock. The piling is then cleaned out of all debris material to expose the bedrock and insert a smaller steel casing inside the larger pile which extends from the top of the piling down to bedrock. A down-the-hole hammer is then used to drill a hole into the bedrock. A solid all thread bar is placed down the casing and into the hole drilled into the bedrock. The anchor is then grouted using grout tubes.

On this project, dense glacial till was encountered, thus making it difficult to drive the large steel piling to bedrock. This meant that the piling could not be cleaned out and the use of the rock anchor detail originally designed for the project could not be used. McGraw Custom Construction, being the contractor and the owner of this project, explored the possibility of using IBO® rods. The IBO® rods would be a good fit for this project which called for drilling through dense glacial till and then 20 feet into bedrock. The one-step process with the use of the IBO® rods (not having to go into the usual multi-step process) saved time for the project and reduced labour by at least 50 per cent.

The feed system and hydraulic drifter used for drilling the TITAN IBO bars were supplied by TEI-Rock drills of Montrose, CO. The drifter was a EURODRILL HD5012.

The deepest hole drilled with the 103/78 bar was in approximately 120 feet of water. At this depth, there was enough hammering energy to drill 30 feet into the ocean floor. The 103/51 bar was utilized on anchors as deep as 140 feet and was able to drill 40 feet into the ocean floor.

When the drilling started, the question was whether to utilize water to evacuate the cuttings or a combination of water and air. At the end, water was used when drilling through the overburden and then air was introduced in minimal amounts to help clear the holes once drilling started in bedrock.

The project is ongoing and was estimated to finish by April 2011. For more information on this design/construction approach, you can contact McGraw Custom Construction and/or Con-Tech Systems Ltd. online at www.contechsystems.com, by email, ctswest@contechsystems.com, or by phone at 604 946-5571.