Underbridge unit in use during an inspection of Holywell Bridge, Cumbria.
Cumbria County Council recently awarded ROD, in alliance with JBA-Bentley, the contract to restore Holywell Bridge, a masonry arch bridge built c. 1860, to full capacity through the design and construction of a proposed concrete saddle over the bridge.
During our initial visual inspection of the bridge, we found insufficient evidence of structural distress to merit the installation of a concrete saddle to increase its structural capacity. We scoped intrusive investigations, observed these on site and carried out an assessment for inspection.
After coring through the intrados of the arch to confirm the ring thickness, we found reinforced concrete in all three cores, which suggested a concrete saddle had previously been installed. Meanwhile, trial pits progressed on top of the bridge found concrete below the existing surfacing.
While our investigations concluded that no major strengthening works were required, sections of the existing parapet walls had to be rebuilt due to significant bulging, leaning and misalignment. Drawings and specifications for the rebuilding of these sections of parapet walls were therefore produced.
This project demonstrates the value of questioning proposed works and carrying out initial analysis alongside intrusive investigations before undertaking invasive remedial works with the potential to damage aging structures. In this instance, the benefits of this approach were two-fold: the client’s objectives were met, with reduced works for the contractor and, from a sustainability perspective, the reduced work resulted in less time spent on site, less materials used and less associated carbon.
