Tieback Anchors
Pre-stressed ground anchors providing active lateral support for retaining structures.
Tieback anchors (also called ground anchors or tiebacks) are pre-stressed steel tendons installed through a retaining wall into stable ground behind the excavation. Unlike passive soil nails, tiebacks are actively tensioned during installation to provide immediate lateral support to the wall system. Each anchor consists of a free (unbonded) length that transfers the prestress force from the wall face to the bonded (grouted) zone in stable ground beyond the potential failure surface. Tiebacks are used with soldier pile walls, sheet pile walls, secant pile walls, and diaphragm walls to provide lateral support during and after excavation. They are essential for deep excavations in urban environments where wall deflection must be minimized to protect adjacent structures.
Technical Specifications
Common Applications
Installation Process
- 1Drill anchor hole through wall face at design angle (typically 15–30° below horizontal)
- 2Advance drill through free-length zone into bond zone in stable ground
- 3Insert steel tendon (strand bundle or bar) with spacers and sheathing on free length
- 4Grout bond zone from bottom up with neat cement grout under pressure
- 5Allow grout to cure (typically 3–7 days to reach test strength)
- 6Install bearing plate, wedge plate, and stressing hardware at wall face
- 7Stress anchor to proof test load (133% of design load per PTI specifications)
- 8Lock off anchor at design load; record lift-off and elongation data
Frequently Asked Questions
What is the difference between temporary and permanent tiebacks?
Temporary tiebacks (service life <2 years) typically use bare strand with single corrosion protection. Permanent tiebacks require double corrosion protection (encapsulation + grout) per PTI standards and more rigorous testing.
How are tiebacks tested?
Every tieback is proof-tested to 133% of design load. Performance tests (on 5% of production anchors) include incremental loading with creep measurements. Extended creep tests verify long-term load-holding capacity.
Can tiebacks extend beyond the property line?
This is a common legal issue. Tiebacks extending under adjacent property require easements or permission. Alternatives include internal bracing, raker systems, or soil nailing (which stays within the soil mass).
What is lock-off load?
Lock-off load is the force remaining in the anchor after stressing and locking the wedges. It is typically 60–80% of the design load, accounting for seating losses and long-term relaxation.
How long do permanent tiebacks last?
With double corrosion protection per PTI DC35.1, permanent tiebacks have a design life of 75–100 years. Regular monitoring (lift-off tests) can verify ongoing performance.
What is the maximum capacity of a tieback?
Individual tiebacks can be designed for 500+ tons using multi-strand tendons (up to 37 strands). Capacity is limited by bond zone length, grout-to-ground bond strength, and tendon steel area.
Can tiebacks be de-stressed and removed?
Temporary tiebacks can be de-stressed by releasing the wedges. The strand is typically cut at the wall face and abandoned in place (the free length and bond zone remain in the ground).
What soil conditions are best for tiebacks?
Tiebacks work best when a competent bond zone (dense sand, stiff clay, or rock) exists beyond the potential failure surface. They are less effective in soft clays or loose sands where bond zone capacity is limited.