Site Event/Activity record ECH6916 - Chester City Walls: Pre-Works Inspection

In 2021, a desk based assessment and visual inspection was undertaken for the south-western section of Chester City Walls along Nun’s Road and above Castle Drive. The City Walls are both a scheduled monument and a Grade I Listed structure. The aim of the study was to identify alterations to the wall throughout its lifetime to better understand its condition and construction. The work was undertaken as part of the Northgate development project, for which a new surface water run off drainage route is required to the river. This was originally proposed to follow Grosvenor Road and then down Castle Drive, avoiding clashes with Chester City Walls, however, an alternative is to divert the proposed route of the water tunnel beneath the City Walls adjacent to the arched opening on Castle Drive, and then along Castle Drive to the river in an open-cut excavation. It is understood that the new route largely runs through the layer of rock situated under the City Walls. The proposed tunnelling is to be low vibration and new drainage access points will be created using underpinned excavation to minimise impact on the Walls The aim of the visual structural and condition inspection of the walls was to record all visible defects by photograph and drawn record. Key objectives were to identify areas that may suggest a structural weakness or imperfection in the walls, these key identifiers include: - Erosion of the stone - Vegetation and/or organic material - Algae and/or salt leaching - Changes in wall geometry - Visible repairs, patches or historical infills - Cementitious mortar repairs The study recommends mitigation should include that tunnelling activity beneath the walls should occur at a depth of approximately 6m. Tunnelling should be completed using low-vibration methods. Monitoring throughout construction work should be undertaken to assess any change to the condition of the walls. (1)