Farndon-Holt Bridge repairs
Works to repair the Farndon-Holt Bridge will be on site from 16 July until the end of October. The aim of the work is to reduce the speed of erosion of the sandstone faces of the bridge by improving the drainage and waterproofing systems.
Road and footway surfacing will be removed as well as the kerbs. The bridge will be waterproofed and new cast iron drainage kerbs installed to take the rainwater away from the bridge. At the same time the parapets will be repaired where they have been damaged by collision and by erosion over many years. New traffic lights will replace the current system, which is coming to the end of its working life, and then the road and footway will be resurfaced.
Farndon - Holt Bridge is designated Scheduled Monument by both Historic England and CADW, and is Grade I listed.
A full closure to vehicles is required throughout the project to repair this important structure. However, access for pedestrians and cyclists will be maintained for the majority of the works. There will be periods during safety critical work that the bridge will need to be closed to all users. However, these periods will only be between 9:30am and 2:30pm on week days.
Current estimates indicate that the full closures for all vehicles, cyclists and pedestrians will be in the region of 10 days.
Why is it necessary?
Council engineers have noticed that erosion of the historic sandstone has increased significantly. Investigation work has shown that rain water is not draining away properly but is seeping into historic fabric of the bridge. When the bridge was originally built a lime-based mortar was used which was softer than the surrounding sandstone. The soft mortar was designed to allow water to escape and slowly erode in the process. Unfortunately, previous repairs have used a hard cement-based mortar which has forced water into the stone blocks, eroding the stone instead of the mortar. The rate of erosion is made even worse here because the sandstone is constantly wet, making it more vulnerable to the erosion effects of the weather. Since the mid-1990s, changing weather patterns have caused the river to flood much more often than before. This means that the masonry stays wet for longer. Flood waters also carry a great deal of debris and fallen trees which rub against and damage parts of the bridge.
Although the bridge structure is strong and secure, some of the sandstone will eventually wear away if action is not taken to improve the drainage system and repair the most damaged stone blocks.
When the drainage and waterproofing is complete, the bridge will be left to dry out properly. Work will then start on a ten year plan to repair and replace the most severely eroded sandstone on the river faces of the bridge and to the underside of the arches. Also, all of the existing hard cement mortar that holds the blocks together will be removed and replaced with a softer lime-based material. It is hoped that this will secure the future of this historic bridge for generations to come.