The Jefferson House Memory Care Community is a new facility under construction on a bluff above the existing Madison House Assisted Living Facility in the Totem Lake neighborhood of Kirkland in King County, WA. The project is part of the Koelsch Senior Communities. Upon completion, Jefferson House will be a 3-story, 70,897 square foot residential care facility with 60 memory care assisted living units plus 64 surface and garage parking spaces. Construction is anticipated to complete in summer 2018. Excavation began in May 2017, with delivery of the first FlexMSE units in late June and completion of the FlexMSE wall in mid-November 2017. It is the largest segmental vegetated MSE wall in the US at this time. The building site was an undeveloped 1.77 acre short plat of a larger 6.15 acre parcel which included Madison House, a 146-unit assisted living facility. Koelsch acted as general contractor on this project, with development by their sister company RJ Development.
Solution & Results
The architect was Richard Swanson, design engineered by TerraCon Consultants for the FlexMSE wall system. Trexiana and Layfield USA worked with their customer, ACF West, the civil contractor, Tastad Construction, and civil engineer, TerraCon Consultants, during each phase of design and installation. This is a new system for King County. Fraser Age Vashon till is the native soil for the project site. The till covers upland slopes throughout the Kirkland Quadrangle and is a mixture of clay, silt, sand, cobbles, and few boulders. The FlexMSE wall extends the South, West, and North sides of the site. The South Wall maximum height is 35’ and extends 213.5’. The West Wall has both a Lower Section (max 14.17’ H & 185’ L) and Upper Section (max 35.42’ H & 149’ L). The North Section (max 12.09’ H & 37.5 L) and West Section also have a Stair Wall descending between them. The wall system maintains a ¼:1 Slope from top of wall to existing slope, per design. This slope was maintained by the installation of batters during construction. Construction challenges included overfilled bags at the beginning of construction, bags being damaged in transit, and undercalculation of total bags required. These issues were promptly resolved by the construction team. The handrail for the edge of the MSE wall also had some design changes during construction of the MSE wall.
Each filled FlexMSE bag is 12”Wx5”Hx2.5’L and weighs 70-80lbs. Each bag installs with an interlocking plate. Bags below grade were filled with a gravel borrow matching backfilled area. Bags above grade received a 70% granular and 30% organic fill to provide drainage and compost for the vegetated wall system. Every three courses of bags received uniaxial geogrid reinforcement via tieback, 30’ tieback for the South and West lower walls, 25’ tieback for the West Upper and North walls, and an 8’ tieback for the top layer before finish grade. Backfill was compacted to 95% between layers of geogrid. 14,400 filled Flex MSE bags were used to complete the wall system. Live staking at 3 plants per bag will complete the vegetated wall system, increasing the strength of the MSE wall system as vegetation grows.