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CROSS Safety Report

Undermined bridge wing wall collapses

Report ID: 577 Published: 1 April 2016 Region: CROSS-UK

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Overview

A masonry wing wall of a bridge collapsed and fell as a single section coming to rest against an adjacent pile after being undermined on site.

Key Learning Outcomes

For construction professionals:

  • Consider appointing a competent temporary works coordinator (TWC) on site who can ensure all temporary works are carefully considered and planned

  • Prior to the commencement of major work or high risk activities consider carrying out a joint risk review by designers, contractors, and others as appropriate at a suitably high level across all disciplines and organisations

For civil and structural design engineers:

  • Any temporary works issues and requirements should be highlighted in risk registers and on construction drawings

Full Report

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The masonry wing wall of a bridge fell as a single section and came to rest against an adjacent pile (Figure 1). Staff had been in the immediate area prior to the collapse but left following some observed movement in the previous 30 minutes. The wall collapsed because adjacent excavations had undermined the supporting ground.

Image
Figure 1: displaced wall resting on pile

Although the roles and responsibilities placed on individuals on site was clear, there was a lack of direction on who held ultimate responsibility for identifying the need for temporary works. This action relied on the recognition of the requirement by the site team, the temporary works coordinator (TWC) and/or the designers.

Although the roles and responsibilities placed on individuals on site was clear, there was a lack of direction on who held ultimate responsibility for identifying the need for temporary works

A requirement for temporary works was identified by the designers but this became diluted and was not picked up on site. A management issue was that some responsibilities, which might have been better if handled separately, were allocated to one individual. Ultimately it was decided that the event was caused by a lapse due to lack of foresight.

It was recommended that:

  • Designers review their risk registers and highlight temporary works issues 

  • No one individual should be expected to prepare, review, and authorise either works control documents or design certificates. Reviews are to be independent.

  • Formal documented handover meetings are undertaken between the design organisation and the project team

  • Prior to the commencement of major work or high risk activities a joint risk review is carried out by designers, contractors, and others as appropriate at a suitably high level across all disciplines and organisations

Expert Panel Comments

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When working on congested sites adjacent to existing infrastructure, the risk of the works affecting the stability of old structures, with low confidence on as-built condition, is high. Designers should be alert to this and draw attention to the risks, with a default position in favour of temporary works to remove or reduce uncertainty. Contractors should be aware and devise appropriate methods that recognise the uncertainties and associated risks. Communication between contractor and designer is essential, preferably at many levels to raise confidence that risks are sufficiently understood.

Designers should be alert to this and draw attention to the risks, with a default position in favour of temporary works to remove or reduce uncertainty

Who is responsible for temporary works?

The sole responsibility for temporary works lies with the contractor. A capable contractor will have appointed a temporary works co-ordinator (TWC) who will assess the need for temporary works. BS5975:2008+A1:2011 Code of Practice for Temporary Works sets out the procedures. Reference should also be made to Regulations 19 and 22 of CDM Regulations 2015 (CDM 2015), which imposes obligations on contractors in relation to stability of structures and excavation.

On site it is the TWC who has ultimate authority and control, having regard to advice from the permanent works designers and the temporary works designers. The Contractor can only assess what is reasonably evident. It is for the permanent and temporary works designers to ensure that significant residual risks are communicated to the contractor via the pre-construction information pack.

Overseeing complex works on site

The suggestion that, prior to commencement of high-risk activities, there should be a joint review is a sensible move and to be welcomed. This should be chaired by an individual with appropriate technical, contractual, and statutory knowledge of the situation and type of works involved. To supplement the paperwork, it is prudent for those with experience to observe the works during execution just to be sure nothing has been overlooked. It is often much easier to see danger in real life than it is by looking at drawings.

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