Building components · Substructure & Ground
Ground Anchor
Explains the anchor as a tension load path into ground that is not itself moving, and why where the load ends up matters more than the element carrying it.
Educational reference entry. What this element has to do, and whether any particular arrangement of it is adequate, depends on the whole assembly, the loading, the exposure, local requirements, the manufacturer's instructions and qualified professional design.
Overview
What a ground anchor is
A ground anchor is a tensioned element — commonly a bar or a strand — installed through the ground behind a retaining structure and bonded into ground well beyond it. Load applied at the face of the structure is carried along the anchor and delivered into that distant bonded length.
The point of it is where the load ends up. Retained ground tends to move along a surface behind the wall, and an anchor is arranged so that its bonded length lies beyond that surface, in ground that is not part of the mass trying to move. An anchor bonded within the moving mass transfers load to something that is itself going somewhere.
Boundaries
How it differs from nearby elements
The distinctions that keep this entry from being a restatement of its neighbours.
- It is not a pile. A pile is loaded principally in compression and carries load downward; an anchor is loaded in tension and carries load backward into ground behind the structure.
- It is not a retaining stem. The stem is the structural face resisting the retained ground; an anchor is one of the ways a stem may be held, and many stems have none.
- It is not a wall tie. A wall tie is a published material connecting the leaves of a wall across a cavity; an anchor is a tension element extending into the ground well beyond the structure it restrains.
Terminology
Common names and aliases
These names describe the same element. The library keeps one entry per component so that a trade term or a regional name never becomes a second, thinner page.
- tieback
- ground anchorage
- anchor tendon
Dependencies
What it depends on
What has to be right elsewhere for this element to do its job.
- What its bonded length is formed in, since the anchor can only deliver load into ground that is not itself moving.
- The tension it is installed at and whether that tension is retained, because an anchor that has relaxed is no longer doing what it was installed to do.
- Its protection against corrosion, since it is a tension element in permanently wet ground.
- Whether it can be tested or monitored after installation, given that everything about it is buried.
Considerations
Topics that genuinely apply here
Subjects worth discussing about this element. These are discussion topics, never measured values, ratings or performance claims.
The anchor's value is entirely a matter of where its load is delivered, which is why the position of the bonded length relative to the assumed failure surface is the design question.
A tensioned steel element in the ground is exposed to corrosion along its whole length, and its protection is part of the anchor rather than an addition to it.
Testing records, lock-off loads and anchor positions are the only evidence that a buried tension element is doing anything at all.
Anchor heads are commonly the only accessible part, and where they are covered over the anchor becomes unmonitorable.
Materials
Commonly formed from
Material families this element is commonly realised in. This states common practice only — it is not a statement that any of these materials suits this component in a particular building, which depends on the whole assembly and on qualified review.
Materials
Commonly incorporates
Materials this element commonly contains as a distinct constituent part, rather than being made of.
Assemblies
Building systems this element is met in
The role this component fills inside each assembly. A role describes what the element does there — it is not a statement that this component suits that system in any particular building.
Clarifications
Commonly misunderstood
- That an anchor holds a wall by gripping the ground immediately behind it. That ground is commonly the ground that wants to move, and the anchor reaches past it.
- That anchors are permanent by default. Some are installed as temporary works for a construction stage and are not intended to carry load for the life of the structure, and which kind is present is a matter of record rather than of appearance.
Conversations
Questions for qualified professionals
Questions worth asking someone with the project in front of them. This page cannot answer them.
- Where does the bonded length of each anchor sit relative to the assumed failure surface?
- Were the anchors tested, and what records exist of the loads they were locked off at?
- Are these anchors temporary works or permanent, and what does the structure rely on afterwards?
- What corrosion protection was specified, and can any part of the anchor be inspected?
Go deeper
Related Build Design Hub guides
Planning guidance behind the decisions this element involves.
Preparation
Related planning checklists
Owner-side preparation before the conversation where this element comes up.
What this entry does not do
- This entry describes a position. It states no load, length, spacing, inclination or testing regime, and none can be inferred from it.
- Ground anchor design, installation and testing are specialist geotechnical work; nothing here indicates whether anchors are appropriate for any retaining structure.
Substructure & Ground Elements
The prepared surfaces, layers and buried members between undisturbed ground and the first structure above it.
Browse all substructure & ground entries →