Tieback Wall Construction—Results and Controls

The tiebacks were used in conjunction with soldier piles and lagging to support the vertical-walled excavation for the Operations Control Center Building of the Washington Metropolitan Area's rapid transit system (Metro). Utilizing wire-strand tendons, the tiebacks were anchored in terrace deposits of clay and sand. Practical testing procedures which were developed on the job to ensure system's safety, while permitting timely execution of the work, are examined in detail. An evaluation is made of three methods used to install tiebacks during the course of construction. Horizontal and vertical movements of soldier piles in each of the four walls are analyzed and depicted graphically, such that movement, type of material, and construction activity can be correlated. Emphasis is place on the importance of establishing a system to monitor the performance of tied-back walls during and after excavation.