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CROSS Safety Report

Inadequate underpinning

Report ID: 72 Published: 1 April 2007 Region: CROSS-UK

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Overview

Works were stopped on site after it was discovered the contractor had completely ignored the specified 5-bay sequence and timing of the underpinning works shown on the design drawings.

Key Learning Outcomes

For the construction team:

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

  • Quality control and competent supervision on site can help to ensure that the structure is built in accordance with the design

Full Report

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This reporter (who was the designer) attended site to meet a party wall surveyor and the structural engineer, acting for the adjoining owner, for a building on one edge of the site. The groundworks contractor had proceeded with underpinning to the adjoining property in advance of the contract being signed but, more alarmingly, had completely ignored the specified 5-bay sequence and timing of the works shown on the reporter’s drawings.

Of the 5 bays in the sequence for the section of wall the contractor had started working on, 2 were concreted but not dry packed and a third had been excavated but not concreted, i.e. 60% of the wall was in an unsupported condition. The reason given by the site operative was that the cement for the dry pack had not been delivered to site so they had got on with the next task.

Obviously, instructions were given there and then to make safe the situation and the party wall surveyor stopped further excavation taking place. By proceeding in advance of any approvals, no-one who might have had cause to inspect the site was aware that work had started. The contractor had appeared to be competent and experienced.

Obviously, instructions were given there and then to make safe the situation and the party wall surveyor stopped further excavation taking place

The manager of the company had met with the reporter and the client's project manager on site before any work took place and they clearly understood correct underpinning procedures. The building inspector has been calling into site regularly to inspect underpinning works being carried out in other areas and all these other works had been handled in an appropriate manner.

The issue seems to be that just one or two unsupervised persons on a site with little or no understanding of structures can unwittingly create a dangerous situation very quickly when they have safety critical works such as underpinning to do. Perhaps activities that have the potential to de-stabilise existing structures should come under similar legislation to demolition which requires the works to be supervised by a demonstrably competent foreman at all times.

Expert Panel Comments

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Underpinning as a construction activity is already covered by broadly the same strict requirements as demolition. The failure in this instance appears to be a lack of training given to the operatives and a lack of adequate supervision, both of which are covered in regulations. There should be an agreed safe system of work statement from the contractor and this should be explained to the operatives on site.

In this case the procedure was not followed or was ignored. Designers or engineers involved with underpinning, and indeed all structural works, should satisfy themselves that the contractor, and the sub-contractor if there is one, fully understand the importance of the works. Key lessons here are to ensure the adequacy of communications, the importance of having safe systems, and the need for monitoring. Other reports of a similar nature will be welcomed.

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