Recent completion of the A63 Castle Street Improvement scheme marks an achievement in successful planning, design and execution of a complex ground engineering challenge.
An underpass and integral bridge now routes heavy mainline traffic below ground while two new ‘gateway’ footbridges improve the safety and experience of pedestrian traffic between the City Centre and Hull Marina. Several new retaining walls and a new 11m diameter pumping station shaft also contribute to the scheme’s significant transformation of Hull’s waterfront space.
Construction of a 400m long underpass up to 7m below ground in the problematic glacial and estuarine deposits of the Humber posed several significant geotechnical risks. Very soft organic clays, running sand, a confined chalk aquifer with 5m tidal range and piezometric surface near to ground level, all presented different challenges to design and construction.
The underpass solution centred around a collection of specialist geotechnical techniques including; deep soil mixing, jet grouting, diaphragm walls and tension piles. The application of innovation and technical excellence was in how these techniques work together as a holistic solution and in how the interfaces were managed at all stages of the delivery.
The scheme presented several unexpected challenges. Through early geotechnical site trials, novel technical governance structures and a truly collaborative project team, challenges were overcome and significant cost and programme impacts were mitigated.
The project was recently announced the Winner of the “projects with geotechnical value over £10m” category in the 2026 Ground Engineering Awards.
This presentation will expand upon and share the major successes, challenges and lessons learned across the delivery of the scheme from the designer’s perspective.
