A tieback is a horizontal wire or rod, or a helical anchor used to reinforce retaining walls for stability. With one end of the tieback secured to the wall, the other end is anchored to a stable structure which has been driven into the ground or anchored into earth with sufficient resistance. Tieback general theory is based on the assumption that once the tiebacks penetrate soil sufficiently beyond the Wedge of Collapse, they hold the soil in place by acting in tension.
Helical tie backs are a reliable alternative to the removal and reconstruction of retaining walls, which is expensive, and a disruptive solution. It is also an alternative to other unsightly and costly wall bracing systems.
While there are a number of potential causes of cracked and bowing retaining walls, the most common is pressure from the soil on the wall. When clay soils get wet, it expands and puts pressure on the wall. When the force exceeds the strength of the wall, the wall begins to crack and break. This reduces the structural integrity of the wall, and when the wetting cycle is repeated, this causes further weakening and movement.
So what is a helical wall tie back? The lead section of the tie back anchor can be equipped with one or more helical bearing plates ranging from 6” to 16” diameters. Plates are welded onto a steel shaft, each one acting as a separate anchor for maximum holding capacity. The lead section is followed by extension rods as it is drilled through the no load zone directly behind the wall and into the load zone. Attached to the end of the final extension rod is a thread bar.
When screwed into the soil, the helical anchor acts as a deep, end-bearing tension member to secure the retaining wall.
Helical tiebacks have a number of advantages:
- They do not need a casing to protect soils from collapsing.
- They do not rely on friction like drilled tiebacks which may be weakened by looser pockets.
- Helical tiebacks tie at the end of their embedment, which offers the best support.
