King Street Station Restoration
Seattle Department of Transportation
The American Council of Engineering Companies of Washington (ACEC) awarded Hart Crowser a National Finalist Gold Engineering Excellence Award for Structural Systems for this project. It also won an honor award (the highest level) in the Seattle Section ASCE Local Outstanding Civil Engineering Achievement Awards.
The historic King Street Station has been a major transportation hub and beacon for the city since 1906, boarding four million rail passengers annually. But the building had a problem. Without significant upgrades, it wouldn’t survive the next major earthquake. The purpose of the restoration was to strengthen the building’s resistance to seismic forces and to renovate the interior space for changes in building use.
The primary geotechnical aspects of the restoration included site-specific ground response analysis, liquefaction hazard analysis, evaluation of the existing timber pile foundations, and the design and installation of new helical piles. The result of the renovation is a seismically upgraded building that will continue to provide Seattle with a major transportation hub and support the future growth of the City’s public transportation network.
In addition to achieving the primary goal of a seismic upgrade, Hart Crowser found ways to optimize the design and construction for unexpected cost savings and increased environmental stewardship.
Geothermal Well Field and Heat Pumps. Hart Crowser recommended the use of the site for geothermal heating and cooling. This was one of the first projects within the downtown Seattle core to install a geothermal well field and heat pumps to reduce the building’s energy consumption. The geothermal system also allowed for a reduction in the size of the building’s heating and cooling system.
High Capacity Helical Piles. Helical piles are typically used to support low loads in tight construction settings. Hart Crowser took this technology to another level in engineering practice with 12-inch-diameter shafts (more than 4 times larger than typical), and one or two 24-inch diameter helices (2 to 3 times larger), resulting in capacities up as high as 350 kips, or about 5 times higher than ever before achieved.
Geophysical Exploration Methods. Hart Crowser used state of the art geophysical exploration methods to evaluate the depth of the existing piles. Using downhole sonar and ground penetrating radar, we concluded that the existing pile tips were within a strong soil bearing layer and thus able to be relied upon for ongoing support, even though they were installed circa 1906. This eliminated the need for $500,000 of ground improvement below the pile tips that was recommended by others in an earlier phase of the work.
Sustainability and Green Building. From the project start, one of the City’s main goals for this project was to promote sustainable design and achieve a LEED Silver building certification. The team’s efforts were so successful, the building achieved LEED Platinum building certification. By restoring an existing building instead of creating a new building, this project not only preserved a historic landmark but also reduced greenhouse gas emissions. Seismic retrofit allows for preservation of the building and saves energy by taking advantage of the nonrecoverable energy embodied in an existing building and extending its use, saving over 1 million gallons of gasoline and eliminating over 8,800 metric tons of CO2. In addition, the geothermal heating and cooling, operable windows for ventilation, and other green building measures reduced the annual energy consumption by 68 percent, resulting eliminating 206 metric tons of CO2 annually. Hart Crowser directly contributed to 6 of the LEED credits related to Sustainable Sites, Energy & Atmosphere, and Materials & Resources. Construction, operation, and demolition of buildings account for 48 percent of the United States’ greenhouse gas emissions. The conservation and improvement of our existing built resources, including re-use of historic buildings, is crucial to combating climate change.