Skip to main content

CROSS Safety Report

Emergency motorway lane closure during concrete repairs

Report ID: 926 Published: 1 July 2020 Region: CROSS-UK

This report is over 2 years old

Please be aware that it might contain information that is no longer up to date. We keep all reports available for historic reference and as learning aids.

Overview

This report highlights how confusion during concrete repair works led to an unplanned emergency lane closure of a bridge carrying a motorway.

Key Learning Outcomes

For asset owners, operators and construction professionals:

  • Regular inspections and interventions can help maintain a structure before it deteriorates beyond repair

  • The execution of the works should be supervised by a competent person who can advise on the changing extent of the repairs, and how these would affect structural safety

  • An emergency procedure document can be used to brief the site supervision team to ensure they are informed of possible risks

For civil and structural design engineers:

  • Consider how the design intent can be effectively communicated to contractors on site, particularly on high risk or complex projects
  • On projects where there is a high level of uncertainty over the design approach, consider attending site to oversee the works

Full Report

Find out more about the Full Report

Our secure and confidential safety reporting system gives professionals the opportunity to share their experiences to help others. If you would like to know more, please visit the reporting to CROSS-UK page.

The incident involved an unplanned emergency lane closure of a bridge carrying a motorway. The closure was required to mitigate the risk of overload of the bridge after excessive concrete removal to the soffit during repair works.

The bridge consisted of 3 spans with half joints for a central suspended span. Leaking road surface water through the half joint and longitudinal central reserve joint had contributed to extensive concrete repairs being required.

The repairs were to mitigate the risk of spalling concrete from falling and further reducing the structural capacity (Figures 1 and 2).

Image
Figure 1: initial damage to soffit of concrete bridge deck
Image
Figure 2: loose concrete removed from damaged area

A structural assessment was carried out prior to the concrete repairs which put detailed constraints on the amount of concrete to be removed from the soffit, as well as limits on the extent of repairs overnight. These constraints were highlighted on the drawings. They were also the first key risk identified in the pre-construction information (from CDM 2015) passed to the contractor and subsequently the subcontractor.

Communication issues on site

A sequence of misunderstandings led to a larger area of removal, which exceeded the specified constraints. The extensive areas of spalling on the central span near the half joint led the site team to believe, incorrectly, that the constraints were only applicable to this area, not the side spans.

The hydro-demolition team cut out a much larger area of concrete than had been planned (Figure 3). An assessment was then carried out by the designers which found that the structure did not now have enough capacity for the required live loading.

Image
Figure 3: hydro-demolition to concrete soffit of bridge

Poor deck reinforcement detailing, combined with the extensive concrete removal, meant that permanent, significant deformation and damage could have occurred. This led to an instruction to immediately close the lane above the repair area and to repair the soffit the following nights (Figure 4).

Image
Figure 4: repaired section to concrete soffit of bridge

Lessons learned from the incident

The incident highlighted specific lessons learnt for the scheme, but also wider lessons learnt for concrete removal schemes:

  • The start of shift briefings to the hydro-demolition sub-contractor were not highlighting key constraints

  • A clearer visual method of highlighting the constraints on the drawings may improve clarity on site to cover, where operatives may not be reading the full details of the agreed procedures

  • Hydro-demolition teams should always be made aware of constraints and the maximum areas they can remove

  • The areas should be approved and accepted by a competent supervisor from the designer’s team prior to its removal, especially when working in a protected area enclosed by non-transparent sheeting

  • An emergency procedure document needs to be prepared before the start of works and briefed to the site supervision team to avoid leaving a site team uninformed of possible risks and/or placing them in a situation where they are forced to make an un-informed decision under intense pressure

  • The sample hammer survey used to form the original scope of works indicated repair areas significantly smaller than the final repair areas found on site with the full, detailed hammer survey

  • This led to constant programme and cost pressure on teams and less use of the previous repair extent drawing which highlighted the constraints. Full hammer surveys of the whole structure immediately prior to scheme procurement would allow proactive planning of works instead of reactive planning.

  • Concrete repairs recommended in several previous principal inspections and management strategies were not given funding until extensive deterioration that risked affecting bridge capacity had occurred. This possibly highlights limited funding to manage a large stock of deteriorating structures, forcing reactive instead of cost-effective proactive maintenance.

An emergency procedure document needs to be prepared before the start of works and briefed to the site supervision team to avoid leaving a site team uninformed of possible risks and/or placing them in a situation where they are forced to make an un-informed decision under intense pressure

Expert Panel Comments

Find out more about the Expert Panels

Expert Panels comment on the reports we receive. They use their experience to help you understand what can be learned from the reports. If you would like to know more, please visit the CROSS-UK Expert Panels page.

Apart from the technical issues in this report, recurring themes can be identified:

  • Communication of design intent which is vital but not always easily achieved
  • As in report 894, designer absence from site is detrimental, particularly on a project like this where there must be uncertainty
  • An objective when planning must be to detect error before it progresses too far

More widely, this report shows yet again that the concept of structural safety must include recognition that structures deteriorate. Some structural forms are more prone to this than others and bridge deck half joints are one such arrangement.

More widely, this report shows yet again that the concept of structural safety must include recognition that structures deteriorate

As well as reducing the load carrying capacity, the exposure and debonding of a significant amount of reinforcement may well change the failure mechanism of that span to one where there is less warning of failure.

Maintaining a bridge while in service

It is of interest to note that concrete repairs previously recommended had not been carried out. It is probable that if the repair had been done earlier, then the extent would have been less.

Whilst financial models often advocate delaying expenditure, this may not be the most economical solution if the subsequent repair is more extensive/complex.

All asset owners aspire to maintain their asset to maximise the life. However, available budgets do not always permit this. Therefore, it is important to determine the condition of the asset and then identify what work can be done to address any issues within the budget.

Large asset owners, responsible for hundreds of structures, use management processes to prioritise work. This relies on regular inspections and interventions must always take place before any structure deteriorates beyond repair.

Supervision and planning during repair work

The execution of the works such as those described need to be supervised by a competent person. They should be able to advise on the changing extent of the repairs, and how these would affect structural safety.

Often, more substantial demolition and repairs are required than were originally planned. The reporter is right about the necessity for a readily available emergency procedure document (contingency plan) – and everyone being aware of its contents.

Share your knowledge

Your report will make a difference. It will help to create positive change and improve safety.

Our secure and confidential safety reporting system gives professionals the opportunity to share their experiences to help others.