Job Description: A highway contractor required temporary excavation support to construct a new bridge abutment for the Chestnut Street Bridge in Grove City, Pennsylvania. The design engineer for the contractor decided a soldier pile wall with timber lagging would be required to support the excavation until the new abutment could be constructed. The soldier piles, however, could not be embedded deep enough to develop sufficient resistance to the overturning loads due to shallow bedrock. Therefore, tiebacks were specified near the top of the wall.
Analysis and Design: The design engineer for the contractor provided us with the required resistance loads and we assisted him in determining the required length and helix configuration of the helical screw tieback. Tiebacks were also to be post-tensioned to reduce deflection of the temporary excavation support wall.
Installation: Eight tiebacks were installed to an average length of 35 feet and at a 20 degree down angle from horizontal. The tiebacks were terminated with a Dywidag bar adapter and Dywidag threadbar for post-tensioning. The tiebacks were post-tensioned after installation of the whaler beam.