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CROSS Safety Report

Concerns over unreinforced lighting column foundation

Report ID: 652 Published: 1 July 2017 Region: CROSS-UK

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Overview

Concerns were raised on a major highway project after it was noticed that the contractor was casting a pad foundation with no reinforcement in the base.

The contractor stated that this was an innovative design which allowed for fast track construction.

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 intent and the client requirements

  • Works that require approval from the client should be agreed with them prior to undertaking any works on site

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A reporter says that on a major highway project it was noticed that the contractor was casting a pad foundation approximately 1.6m long x 0.9m wide x 0.9m thick to support a lighting column. However, there was no reinforcement in the base. The contractor stated that this was an innovative design which allowed for fast track construction.

However, unreinforced foundations were not permitted without agreement from the client and none had been sought. The lighting column was located at the ‘third point’ along the base and the section showed services running through the middle and a vehicle restraint barrier on one edge of the base (Figure 1).

Image
Figure 1: cross section through pad foundation base

Concerns raised by the client

The client expressed concern that inclusion of services and vehicle restraint would not distribute the loads through the whole foundation without reinforcement, and that cable ducts so close to the HD bolts would induce local failure. As part of the justification for the design, the designer had provided a report that included calculations to several different standards and technical papers, including temporary works standards.

Unapproved design leads to costly remedial works

The design was not accepted by the client and the upshot was that almost 100 bases had to be removed and replaced with conventionally reinforced units. It was later discovered that the contractor had submitted a design check certificate stating that the design complied with client standards. This design check certificate was signed by two Chartered Engineers but all information submitted indicated that the contractor did not design to the standards that they certified.

The design was not accepted by the client and the upshot was that almost 100 bases had to be removed and replaced with conventionally reinforced units

Expert Panel Comments

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In principle, it might be acceptable to use mass concrete bases for certain applications. However, the issue here appears to be one of management control and the recurring theme of all parties being clear about the design intent.

 In some cases, the desire for innovation to allow reduced construction time manifests itself as poor or inadequately thought through design. This can lead to additional costs and delays. When there is the opportunity to add value though innovation there must be adequate time available to ensure that the innovation is technically sound.

In this case the design was not robust, and the assurance failed. As ever it is essential that competent designers are engaged.

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