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CROSS Safety Report

Long term risks for ground anchors

Report ID: 87 Published: 1 October 2007 Region: CROSS-UK

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Overview

A reporter is concerned about the inspection and maintenance of ground anchors that are used for strategic flood defences.

Key Learning Outcomes

For asset owners/managers:

  • Putting a process in place for the inspection, assessment and monitoring of assets that can be affected by corrosion can help to protect your assets

  • Maintenance requirements should be set out in a ‘maintenance philosophy statement’ such as that suggested in CIRIA C611 ‘safe access for maintenance and repair’ and placed in the Health & Safety file

  • Be aware that management plans may need to take cognisance of the consequential effects that climate change and rising sea levels may have on infrastructure

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Two reporters have been involved in several projects or potential projects where riverside sites have been considered for redevelopment. In each case, the river wall forms part of the strategic flood defences for the area and typically comprises of driven steel sheet piling held back by tensioned ground anchors up to 30m (or more) in length and raked at angles between 25° and 50° to the horizontal. Generally, these works date from the mid - 1970's or early 80's.

Maintaining anchors

The Environment Agency is usually responsible for ensuring that the anchors are maintained by their owners, but it can often be difficult to establish ownership and who should be carrying out or commissioning maintenance. The reporters have not yet come across a site where routine inspection has been undertaken, despite almost 30 years having passed since installation. Even when ownership is clear, records are not readily available which indicate the types of anchor used, their positions, original prestress loads or procedures for maintenance, checks and inspections.

This means that there are no benchmarks against which the condition and ongoing performance of the anchors can be checked. Sometimes records can be traced, but this is invariably very time consuming, involves numerous enquiries and often relies on good luck.

The Environment Agency is usually responsible for ensuring that the anchors are maintained by their owners, but it can often be difficult to establish ownership and who should be carrying out or commissioning maintenance.

Anchor inspections

Where they have commissioned inspections, the reporters have found that most anchors have lasted well, are in fair condition and any loss of original prestress was not of major concern. However, isolated cases of significant rusting of anchor heads have been noted together with instances where anchors are no longer stressed at all. This suggests that, had monitoring not been implemented as part of the process of redeveloping a site, failures could have occurred and gone unnoticed.

Development of sites with ground anchors is difficult, complex and costly. Where development takes place, checks would normally have to be carried out to verify the integrity of the ground anchors. If development is uneconomic, and this may well prove to be the case for some sites, inspection and maintenance may never be undertaken, either due to lack of funding, inability to establish responsibility or ignorance of the need to do so on the part of the owner.

Health and Safety File

Experience of the reporters so far has been on tidal riverside sites where the environment is aggressive and the consequences of failure of the flood defence potentially very significant. Their concerns, however, also apply to other environments and locations including highways, railways and structures. CDM Regulations have required, since 1994, compilation of a Health and Safety File for all major developments with key details of construction and maintenance schedules. This is issued to the client on completion of a project. However, experience suggests that these are quickly mislaid or lost by the owner or not passed on to future purchasers.

The reporters doubt whether the owners or managers which may be affected recognise the importance of the anchors beneath them. Possible approaches to managing this risk might include:

  • Establishing a central register of ground anchors into which records of all new anchors together with details which would facilitate their future maintenance must be deposited

  • Compiling a register of all existing sites with ground anchors together with as much relevant information or sources of information as possible

  • Providing a secure repository for existing records, which may otherwise be destroyed

Perhaps, say the reporters, one of the main engineering Institutions could act as a catalyst and enabler for this? The survival of such valuable records relating to major and strategically significant infrastructure is surely too important to leave to chance?

Expert Panel Comments

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This is example of components that may corrode without anyone being aware of the risks and where the failure of a single component could lead to overstressing of nearby structural elements. There have been a number of failures of ground anchors worldwide and these may increase with time and the effects of aging.

For new schemes clients should be made aware of the long-term liabilities and obligations at an early stage in the project. Maintenance requirements should be set out in a ‘maintenance philosophy statement’ such as that suggested in CIRIA C611 ‘safe access for maintenance and repair’ and placed in the Health & Safety file. 

There have been other cases where no records were kept, and the condition of anchors is unknown. CROSS intends to bring this report to the attention of the conference on Ground Anchors and Anchored Structures in Service to be held at the Institution of Civil Engineers (ICE) in November 2007 and being organised by the British Geotechnical Society and ICE. It will also be brought to the attention of the Environment Agency.

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