Instrumentation and Performance of the Third Runway North MSE Wall at Seattle-Tacoma International Airport

This paper focuses on the instrumentation and performance of a tall MSE wall. Project requirements for the expansion of Seattle-Tacoma International Airport called for the construction of a third runway to the west of the two existing runways. A significant volume of compacted earth fill was required to raise the grade a maximum of about 50 meters to meet the level of the existing runways. Although embankment side slopes were allowed for much of the filling, adjacent creeks and tributary wetlands dictated the use of three tall MSE walls to limit the extent of embankment fill. The North Safety Area of the third runway required the construction of a 26 meter MSE wall. Performance monitoring included strain gage-instrumented reinforcement strips, inclinometer installations with sondex settlement rings, optical survey of wall facing for vertical and lateral movement, and piezometers. This paper briefly presents various wall design issues, concentrating on the aspects involved in the instrumentation of the wall and the subsequently observed performance during and after construction.