Temporary vs Permanent Ground Anchors: Design Life, Testing and Applications
A ground anchor transfers load from a retaining structure, such as a capping beam or a shotcrete facing, into stable ground beyond the failure plane. The anchor is drilled and grouted in place, then stressed to a design load and locked off, creating a tension element that holds the structure against lateral earth pressure. Understanding the load path, from the structure through the anchor’s free length and into the bonded zone, is the starting point for deciding which type of anchor a project actually needs.
Anchors are usually classed as temporary or permanent, and that classification affects almost every part of the design, from corrosion protection through to testing requirements and how the anchor is documented at project close out.
Temporary Ground Anchors
Temporary ground anchors are designed to remain in service for a limited period, typically the length of an excavation, basement construction phase or slope stabilisation works, and are often designed for a service life of two years or less. Because the exposure period is shorter, corrosion protection requirements are generally less onerous than for permanent anchors, though anchors are still grouted and, in aggressive ground, may still need additional protection.
Temporary anchors are common on basement excavations, road and rail cuttings during construction, and short term slope stabilisation ahead of permanent works. Once their job is done, they may be decommissioned, released from load, or left in place if agreements with adjoining owners allow it.
Permanent Ground Anchors
Permanent ground anchors are designed to remain in service for the life of the structure, which can mean fifty years or more, depending on the project. This longer design life drives a much higher standard of corrosion protection, typically double corrosion protection systems with encapsulated tendons, along with more rigorous testing and long-term monitoring in some cases.
Permanent anchors are used where the retaining structure itself is permanent, such as retaining walls supporting roads, rail corridors, or buildings, and where replacing or supplementing the anchor later would be difficult or disruptive.
Key Differences
Design Life
Temporary anchors are typically designed for service periods measured in months, while permanent anchors are designed for decades. This single distinction drives most of the other differences between the two anchor types, since a longer design life demands greater certainty around long-term performance.
Corrosion Protection
Temporary anchors generally use single protection, such as a cement grout cover over the tendon, while permanent anchors use double corrosion protection systems that combine grout cover with a sheathed or encapsulated tendon. The extra protection adds cost, but it is essential for anchors expected to perform reliably for many years underground.
Testing and Monitoring
Both anchor types are tested, but the rigour differs. Temporary anchors typically undergo proof testing on a sample of anchors to confirm the design assumptions, while permanent anchors more often require extended creep testing and, in some cases, ongoing load monitoring after installation to confirm long-term performance under sustained load.
Access and Removal Constraints
Temporary anchors are sometimes decommissioned or cut back once their job is complete, particularly where they cross a neighbouring property boundary and an easement was not negotiated. Permanent anchors are installed with the expectation that they will remain load-bearing indefinitely, so access for future testing or monitoring is often considered at the design stage.
Project Use Cases
Temporary anchors typically support basement shoring, road and rail cuttings during construction, and short-term slope stabilisation before permanent works are complete. Permanent anchors typically support retaining walls for infrastructure and buildings, long-term slope stabilisation where the ground will always need holding back, and structures where future access for anchor replacement is not practical. Terracon Civil’s ground anchoring services cover both categories, often alongside soil nailing and shotcrete facing on the same site.
Procurement Questions
When scoping an anchor package, it helps to confirm the anchor loads and design life required, ground conditions and any known aggressive soil or groundwater chemistry, access constraints for drilling rigs, and whether neighbouring property agreements are needed for anchors crossing a boundary. Clarifying these questions early, ideally before tender, reduces the risk of late design changes once drilling begins.
Programme dates matter too. Permanent anchor testing regimes, particularly extended creep tests, can take longer than teams expect, so building realistic time into the program avoids last-minute compression of the testing schedule.
Documentation and Handover
Every anchor installation should be backed by clear documentation, including installation records, test certificates, stressing and lock-off loads, and as-built drawings showing anchor position and inclination. For permanent anchors, this documentation forms part of the long term asset record and may be referenced decades later if the structure is assessed or modified. Reviewing available slope stabilisation methods alongside anchor documentation gives asset owners a fuller picture of how the ground support system was designed to perform over time.
Frequently Asked Questions
Not usually without redesign. Temporary anchors are built to a lower corrosion protection standard, so converting one to permanent duty would generally require additional protection measures or replacement rather than simply extending its service life.
Through stressing and testing after installation, which typically includes proof loading to a percentage above the design load, with the anchor’s performance recorded against acceptance criteria set by the engineer.
In most cases, once locked off and tested, permanent anchors require little ongoing maintenance, though some projects specify periodic load checks, particularly on critical infrastructure.
Depending on the project and any easement agreements, temporary anchors may be released from load, cut back below ground level, or left in place if there is no conflict with future works on the neighbouring site.
Planning an Anchor Package for Your Site?
Whether your project needs a short-term solution or anchors designed to last the life of the structure, getting the classification right early shapes cost, program and long-term performance. Contact Terracon Civil and send through your anchor loads, design life, access limits and program dates for a scope review.
