Continuing our coverage of the 2014 AIA COTE Top Ten green projects, this article is part of a series of 10 pieces that examine a specific, defining design challenge or innovation of each of this year's winners.
A squishy bog is not an easy place to build a permanent structure, let alone a secure U.S. border station. “Conceptually, you could say we built an island floating upon this wetland bog,” says Matt Kreilich, AIA, design principal and partner of Snow Kreilich Architects, referring to the 19-acre site of the new U.S. Land Port of Entry on the Canadian border near Warroad, Minn.
Sited near the 1,500-square-mile Lake of the Woods and a slew of nature preserves, the project respects the sensitive wetlands ecosystem while accommodating a sprawling program and tight security requirements. The interconnecting driveways and structures are proportioned to handle the large turning radii of trucks and trailers that must be maneuvered, inspected, and sometimes detained at the border. All this pavement rests upon a mat of engineered fill. The fill layer, roughly 4 to 5 feet deep, overlays a permeable geotextiles fabric that keeps that fill from dissolving into the carbon-rich swamp.
Even more elaborate geotechnical engineering features underpin the three linked structures of the T-shaped facility, containing offices, visitor’s center, vehicle inspections, a firing range, and holding cells. The buildings, clad with a rainscreen of sustainably harvested cedar, stand atop a continuous-grade beam of steel-reinforced concrete. This structural platform, in turn, spans a grid of pile caps, which transfer the load to several hundred steel pipe piles driven 40 to 50 feet deep into the muck. Each concrete-filled pile, 9? inches in diameter, was hammered down until it met a load capacity of 60 tons, says Daniel Murphy, principal at Meyer Borgman Johnson, the project’s structural engineer. The piles do not rest upon bedrock, but instead use the force of friction along their shaft to obtain the specified resistance. Utility lines are then fixed to the underside of the rigid structural slab and grade beams, “so that they all move together,” says Kreilich.
Back on the surface, large stone pavers, quarried in-state, are laid around the buildings to form a hydrology-sensitive vehicle barrier. The spaces between the stones are perfect for planting native sedum and filtering storm runoff. These stone and sedum beds, surrounded by rows of larch and birch trees that help break the wind, are only part of a site-encompassing landscape design by Coen + Partners. Native prairie grasses and water filtration ponds slow and treat stormwater runoff. This wet meadow ecosystem was restored to land that formerly belonged to private owners.
As it turns out, restoring the wetlands was also good for security. The difficult terrain made it unnecessary to erect the standard 10-foot-high chain-link fence topped with barbed wire that encloses most U.S. land ports of entry. Instead, officers enjoy panoramic views of the flat landscape from the glazed office area, which is designed for their quality of life as well as their surveillance duties. Snow Kreilich also considered officers’ comfort in orienting the building so as to shield the outdoor inspection areas from the winter wind, and in running a continuous rain and sun canopy across all three buildings.