Mackenzie Construction recently completed the construction of a new access bridge into Glenburn School, Greenock valued at £343,000.

Inverclyde Transportation and Roads had engaged Fairhurst in 2000 to assess a number of bridges in Inverclyde in accordance with a wider national bridge assessment programme.

Their report concluded that the Glenburn School Bridge, although not in a poor physical condition, failed the technical requirements of a 40 Tonne Assessment Live Load Analysis at a low level and concluded that the bridge should be replaced as strengthening was not a viable option.

Since the existing bridge was the only vehicular and pedestrian access to both Glenburn Primary and Greenock High School, a temporary road and pedestrian footbridge was required during construction of the new on-line bridge.

The existing bridge deck contained main service crossings serving the Schools and these required diversion in the temporary period and re-aligned through new service ducts within the new bridge construction.

The site investigation boreholes identified bedrock at approximately 14m depth and existing ground conditions led to the choice of a piled foundation for the new bridge structure. It was anticipated that the choice of rotary bored mini-piles would reduce the effects of vibration and possible damage to services and facilitate penetration of the dense gravel layer.

The existing bridge abutments were retained and the twin-cell culverts are supported on a piled concrete raft constructed between the existing abutment walls. The resultant gap between the new and existing structure was filled with lean mix concrete providing sufficient resistance to horizontal loading.