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CROSS Safety Report

Changes in temporary works scheme

Report ID: 603 Published: 1 April 2017 Region: CROSS-UK

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Overview

Changes in the construction programme on site led to the construction of the superstructure of a building, without the liner wall below it being completed.

Key Learning Outcomes

For contractors:

  • Quality control and competent supervision on site can help to ensure that the structure is built in accordance with the design. It will also ensure there is adequate consideration of the interfaces between temporary works and permanent works.

  • Consider appointing a competent temporary works coordinator (TWC) on site who should be able to identify and address the risk of programme changes

  • Any changes made to the construction programme that can impact on the design intent should be reviewed and approved by the design engineer

For structural design engineers:

  • This report highlights the potential value of visits by the design team at key construction stages to identify any potential problems

  • If you are unable to attend site, consider asking the contractor for site photos of the installation of critical structural elements

  • Ask clients and contractors to make you aware of any changes to the brief during construction so that you can consider the impact of the changes on your design

Full Report

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A multi-storey above ground structure was designed so that the superstructure rested on a basement liner wall, which in turn was dowelled into the secant piled retaining wall. The temporary works designer placed raking props and whaling beams against the secant wall in the temporary case. This prevented completion of the liner wall. A sequence was specified in which all props were removed, and the liner wall completed before construction of the superstructure started.

Due to changes in construction programme, time pressure and lack of clarity about who was responsible for the overall temporary works strategy, the sequence of construction was changed.  The construction of the superstructure proceeded without the liner wall being completed.

Due to changes in construction programme, time pressure and lack of clarity about who was responsible for the overall temporary works strategy, the sequence of construction was changed

By the time this was spotted, a significant portion of the superstructure was being supported by a partially complete liner wall, with a greatly reduced number of dowels into the secant wall. Work was immediately stopped on this structure until it was deemed safe and delays were incurred as the superstructure could not be continued until the liner wall was completed.

Expert Panel Comments

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There have been innumerable failures consequent on change or unauthorised change with unforeseen consequences. Nothing should be changed on site without approval from the design authority and this is a classic case of lack of adequate consideration of the interfaces between temporary works and permanent works.

Was a temporary works coordinator and a temporary works supervisor appointed to help ensure this situation could not occur? The permanent works designers should have provided for at least one safe method of construction, and this should not have been changed without reference back to them.

Changes made to designs on site can have severe adverse consequences and again there are similarities with the Edinburgh schools (Inquiry into the construction of Edinburgh Schools - February 2017). Procedures must be followed, and responsibilities allocated at the start of every project for controlling change.

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