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CROSS Safety Report

Collapse of outfall structure to watercourse

Report ID: 653 Published: 1 July 2017 Region: CROSS-UK

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Overview

An outfall conveying surface water drainage to a watercourse collapsed as it had not been constructed properly.

Key Learning Outcomes

For construction professionals:

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

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An outfall conveying surface water drainage to a watercourse collapsed as it had not been constructed properly (Figure 1). The approved design required a 'toe' to the spillway to be taken at least 0.6m below the stream bed. No such toe was constructed and as a result the spillway slab became undercut by scour from the flow of water in the stream which caused the structure to collapse.

The reporter states that this is an example of a much wider problem, namely the lack of proper site supervision, on current civil engineering projects. Changes in contractual arrangements for civil engineering have seen an unwise reliance upon legal guarantees, rather than the services of a competent Clerk of Works or Resident Engineer, says the reporter.

Image
Figure 1: collapse of outfall structure to watercourse

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