The Southwest Pipeline Project (SWPP) is a regional rural water distribution system which provides potable water service for both domestic and livestock use to the residents of southwest North Dakota. Located adjacent to Renner Bay in Lake Sakakawea in North Dakota, the project site is approximately 300 feet from the banks of the bay.
The microtunnel launch shaft was originally designed as a concrete caisson shaft. JWF offered an alternative method of shaft support using a ground freezing system to provide ground water control. The shaft was 26.5 feet in diameter and 150 feet deep. Pipelines were drilled vertically into the ground around the circumference of the shaft and coolant was pumped into the pipes. When the walls were completely frozen, concrete caisson segments were lowered into place and the shaft was excavated. The precast concrete segments were specially manufactured in Europe and could either be sunk as a conventional caisson or underpinned. The segments served as the support of excavation during construction and will remain as the permanent liner for the wet well.
The tunnel will be one of the longest microtunnel drives in the United States at 2,700 feet. The 73.5-inch microtunnel with a 60-inch concrete intake pipe, will require recovery of the microtunnel boring machine in Lake Sakakawea at a depth of approximately 100 feet.