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CROSS Safety Report

Failure of existing basement wall

Report ID: 385 Published: 1 July 2014 Region: CROSS-UK

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Overview

A basement retaining wall failed when a new basement was formed by excavating 1.8m.

Key Learning Outcomes

For construction professionals:

  • Quality control and competent supervision on site can help to ensure that the structure is built in accordance with the design and prevent the removal of bracing members as highlighted in this report

  • Having a competent temporary works designer/adviser in place to supply an engineered solution can ensure all temporary works are carefully considered and planned

  • Verification of temporary works erection by a competent person who can oversee and coordinate the whole process can also ensure the works are installed correctly

  • The need for collaboration over boundaries should be recognised where multiple parties are involved

  • The transfer and coordination of relevant information is important to overcome interface issues

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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A basement retaining wall failed when a new basement was formed by excavating 1.8m. Some temporary works had been designed and installed by the demolition contractor. However, the demolition contractor had no knowledge of the follow-on works. No checks had been carried out on the wall. At the time piles were being installed and this probably softened the ground which did not help.

Expert Panel Comments

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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.

CROSS have had previous examples of failures in basements (including simple domestic basement work) where excavation below the toe line has allowed walls to kick in. Anyone excavating a new basement 1.8m below an existing basement should clearly have had a competent plan and competent temporary works.

The point has been made several times that there are dangers at the interfaces of contractors and for anything complicated, there should be one party in overall charge of stability. Basement works are recognised as a problem issue in domestic construction, particularly in London.

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