Stillaguamish River Crossing - Arlington, WA

The crossings of the Stillaguamish River, Ebey Island and the South Ebey Slough had drilled lengths of 3,396, 5,700 and 1,400 feet respectively. A 20-inch diameter pipeline was installed at the two Ebey crossings, while at the Stillaguamish a 16-inch pipeline was installed.

The Stillaguamish River Crossing, although substantially shorter than the Ebey Island Crossing, was the most technically demanding

crossing. The majority of the drilling was undertaken with a Mears 660 Rig which was set up on the lower side of the river for the pilot hole that was drilled at a depth of 130 feet. On completion of the pilot hole, the 660 Rig was moved to the other end of the crossing and a Mears 160 Rig was then used to assist from the pipe side for reaming procedures.

While drilling through the predominantly silt and clay formations, Mears encountered two gravel/cobble layers. To address these obstacles and prevent drill pipe failures, a temporary 12-inch steel surface casing was installed for a length of 300 ft.

After hole opening operations had begun, a perched water table was encountered that caused water flow through the drilled hole. Mears was able to contain this water using a combination of down-hole cementing and a vertical grouting program. The grouting program was undertaken by Northwest Cascade, Inc. and consisted of drilling 126 vertical pressure grout wells in a predetermined pattern. Drilling and pullback operations were able to continue after the grouting of the formation was completed. Thus, Mears and the Olympic Pipe Line team were able to successfully circumvent complications and complete the project.