A paint booth in which new 737 airplanes would be painted was planned inside an existing hangar building at the Boeing Renton Plant. The paint booth required a new below-ground basement foundation consisting of a large concrete mat (120 X 40 feet in plan) and perimeter walls supported on deep piles. Shoring for the foundations would be inside the existing build and would extend beneath the piles caps for the existing building.

Conventional sheets were not feasible at this site because of limiting overhead inside the building the fact that the shoring needed to extend below the existing pile caps without damaging these foundation elements. In addition, there were severe dewatering restrictions at this site with groundwater within 3 feet of ground surface.

Frozen soil was selected since it can be installed below existing pile caps without damaging them and freeze pipes can be installed in relatively low overhead conditions. A frozen soil wall was installed around the site perimeter and extended to a depth of 40 feet in an attempt to cutoff or limit the amount of groundwater inflow from below the 15-foot deep excavation. Angled freeze pipes were installed a select locations to limit the amount lateral wall movement to a small amount.

The frozen soil wall effectively retained soil and groundwater for the foundation excavation. Because of soil variability groundwater cutoff into the excavation from below was not complete; however, the frozen soil did limit the rate of inflow to an acceptable amount and kept the contractor below permit levels. Existing building slab and foundations were unaffected from the excavation because the frozen soil wall had limited ground movements to a negligible amount.