BLOG: A design-led approach to solving groundwork challenges on heritage sites

Manchester’s build-to-rent (BTR) property market is booming, as regional city centre locations grow in popularity and developers respond in kind with a wealth of ambitious new projects. This climate of optimism has benefited the entire sector from architects to contractors, and GRAHAM has placed itself at the forefront of the movement in Manchester.

In partnership with developers Glenbrook, GRAHAM is on-site at two major projects in Manchester city centre and Salford Quays. The first, Trilogy at Ellesmere Street, Castlefield, contains 232 apartments and is due to complete in Summer 2018. The second, Erie Basin at Salford Quays, recently began superstructure construction and on completion in 2019 will provide 270 high spec apartments.

Situated adjacent to MediaCity UK, which houses the BBC and other major national broadcasters, Erie Basin will add another batch of quality apartments to the rapidly rising Salford Quays area.

Due to its unique location, the Erie Basin project has presented a variety of challenges throughout the build process, particularly in the assessment of groundworks and the development of the site’s foundations. The area’s industrial heritage and the previous structure present on-site meant that significant hurdles had to be overcome in partnership with engineering consultants and geotechnical specialists Design ID to improve the project’s economic viability.


Site history
The development is situated on what was once Number 9 Dock, opened in 1905 following the land’s purchase by the Manchester Ship Canal Company and conversion from its previous use as part of Manchester Racecourse. On completion the waterway became the largest dock of its kind and formed a critical artery in the canal network, fuelling Manchester’s rise as a city.

Since the decline of the United Kingdom’s heavy industry and Manchester’s subsequent transformation into an economic powerhouse for the region, Salford Quays has garnered attention for its evolution into a self-contained hub for the media sector – which has in turn made it a secondary epicentre for the PRS and BTR boom in the city.

The complex history of the region and this post-industrial area means that the brownfield sites left undeveloped after years of decline present not only huge opportunity to developers, but also significant challenges for contractors, engineers and architects in getting projects off the ground and overcoming the legacy of the site’s previous uses.

The presence of a major industrial goods warehouse on the site as well as gantry cranes for loading cargo onto docked ships, which had been demolished in past decades, presented a complicated issue for GRAHAM and engineering and geotechnical partners Design ID to overcome.

In order to compete with the challenges of building on a canal side site with a geology primarily consisting of alluvium (clay, silt sand and gravel) using the limited construction expertise available in the year 1905, the goods warehouse – which spanned the entire site by the 1950s – was accompanied by substantial foundation work that was not removed on the structure’s demolition in the 1980s to make way for car parking.

This foundation work consisted of existing concrete piles and pilecaps with a thickness of up to 3.5 metres, alongside a precast concrete grain tunnel that had to be considered when deciding on the placement of new piles.

This presented a unique complication that had potential to impact the progression of the project’s construction, as the scheme was set to implement traditional piled foundations to form the groundworks of the structure, the standard approach for a residential build of this nature.

These would have been obstructed by the existing piles that remained from the goods warehouse meaning a suitable solution had to be established – removal or incorporation.

The solution
An early report compiled on the site prior to the development of Glenbrook’s Erie Basin plans suggested that it could be economical for any developer to reuse the existing piles that remained from the sites industrial past, contingent on their condition being good enough for the task.

However, a full evaluation of the strength of the existing piles would not have presented a viable option for the project – and a failure to find a solution to this issue could result in the development not being cost-effective on this particular site.

In consultation with engineering partners Design ID, GRAHAM proceeded with a plan to incorporate the existing piles into the new development using a raft solution that negated the need to remove all of the historic foundations, while not relying on them as a part of the buildings load bearing structure.

The solution involved the removal and reduced levelling of a select number of existing piles, while the majority remained and were incorporated and augmented by the addition of 272 new piles to support the superstructure.

The raft construction developed that bypassed the original piles and weaved in new piles to act as the structures foundations allowed the construction to go ahead without the need for costly investigations into the integrity of the historic piles.

The project was also designed, developed and delivered to a BIM level 3 standard which streamlined the process of implementing the new piling method while maintaining the architect’s vision for the design and preventing compromise on the desirability of the apartments within.

Had a full removal of the historic foundations been required, the demolition and earthworks, additional piles required and increased demand for new structures could have set back the construction schedule and significantly increased the cost of the project.

GRAHAM’s innovative approach to solving the complex issues presented by this site was key to maintaining the viability of the project as a whole. By working closely with engineering partners Design ID the construction team was able to accurately assess the condition of the site and develop a unique solution to maintain the project’s economic viability and construction schedule while maintaining the integrity of the architect’s design.