Case Study: Helical Tiebacks

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A Summary Of The Helical Tiebacks Challenge


Helical Tieback Support From TerraFirma Foundation SystemsA gabion basket retaining wall, 250 ft in length, was earmarked for construction alongside a wooded hillside in Portland, Oregon. This wall would facilitate slope excavations and foundation support for the intention of building and maintaining a rambling trail beneath. The pre-construction hillside environment prevented project site access via truck mounted, or standard, track drill rigs. Hand auger boring measurements carried out to depths of roughly nine ft at the wall base, and inside the proposed retained soil, discovered extremely stiff to medium stiff clayey silt. Consequently, the wall’s taller sections would need anchors, or helical tiebacks, to offer lateral stability.


Work Completed:

The design of the OR gabion wall utilized seventy-three helical tiebacks. These were employed to support working design loads of five, ten, fifteen and twenty kips. These tiebacks were fitted at a six degree from horizontal downward trajectory, and were spaced at either ten or five ft. All tiebacks were developed to a torque correlated optimum capacity of at least double the working load of the design. Then, the tiebacks were linked to the C Channel walers and broad flange beam inside the gabion baskets. Afterward, crushed rocks were positioned round the walers and tiebacks. The fitting and testing of the tiebacks was finished in a week.


To view the complete details of this case study, you may download the report here (pdf): Case Study: Helical Tiebacks

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