Anchors · Back Bay
Tieback Anchors for Retention, Back Bay
A retention wall on a constrained Back Bay site required lateral support without internal bracing that would obstruct construction.
The problem
A retention wall on a constrained Back Bay site required lateral support without internal bracing that would obstruct construction.
The engineered approach
Grouted soil anchors were drilled, tested, and stressed to lock-off, tying the wall back into competent ground to keep the excavation clear.
Outcomes for the GC
- Brace-free, open excavation for the GC
- Wall deflection held within design tolerance
- Zero recordable safety incidents
How we built it
A schematic section of the anchors system for this Back Bay job. Scroll to build it in construction order, or select a callout to read the detail.
Callouts
Select a numbered part below to read what it is and what it does.
- The soldier-pile and lagging wall holds back the Back Bay fill and clay while the excavation in front of it stays open. Tying it back with anchors keeps the dig brace-free for the GC.
- Each hole is drilled down and back at a shallow angle so the anchor reaches past the active wedge into competent ground. Inclining the anchors lets them resist lateral wall load with a downward-and-back pull.
- Sheathed tendon that transfers no load to the surrounding soil; it spans the potential failure wedge so tension develops only in stable ground beyond it.
- Pressure-grouted length — about 35 ft here — where the tendon develops its capacity in stiff lower Boston Blue Clay and dense glacial till. Each anchor is proof-tested before it is accepted.
- After testing, the strand or bar tendon is jacked to its design load and locked off against the waler at the wall. The locked-off force pre-stresses the wall and limits its deflection.
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