Potteries Museum: Geotechnical groundwork design and solutions

Background

We were appointed by Stoke-on Trent City Council to provide multi disciplinary services on the construction of a new £5.4m glass extension to the Potteries Museum and Art Gallery to house the city’s iconic RW388 Spitfire Aircraft.

Challenges around ground conditions

One of the first steps in any project is to undertake investigations to determine the existing ground conditions. Initial borehole site investigations indicated that there was a significant depth of made ground, up to 4m in places, comprising bricks and stone. This prevented the use of shallow foundations, instead requiring deep piled foundations to support the new building.

Stoke On Trent has a history of mining and review of the mining history and the Phase 1 site investigation indicated the presence of abandoned mine workings beneath the proposed building location. Having identified this, we approached Byland Engineering, a geotechnical sub-consultant who we have worked with on several previous projects, to provide their specialist input to this issue.

Resolutions

Working closely with Pick Everard’s structural engineers, and comparing the proposed piled foundation design to the coal mining records, it was clear that the depth of the piles would either be close to, or directly clash with the abandoned mine workings. Therefore, further boreholes were undertaken, to a much greater depth than previously (around 40m), in order to fully understand the relationship between the existing mine workings and the proposed foundations.

The further boreholes showed that mine workings were present in 2 No. coal seams beneath the building. Following this discovery, Byland Engineering put forward an approach to backfill the mine workings by injecting grout via a systematic grid of drillholes. The approach was put to the Coal Authority for their approval, which was duly received prior to the works being undertaken.

The works were successfully carried out prior to the main construction phase.

Working closely with our specialist subcontractor, and our in-house design teams, enabled a viable solution to be generated to address the presence of mine workings beneath the site.