Bath Quays South – Masterplan
Bath, UK
Project details
Client
Bath and North East Somerset Council
Architect
Penoyre & Prasad
Services provided by Buro Happold
Bridge engineering and civil structures, Ground engineering, Water
Bath Quays is a flagship regeneration project that will establish a thriving commercial quarter at the heart of this UNESCO World Heritage Centre.
Overlooking the River Avon, Bath Quays South is a focal element of this transformative initiative. Conceived to address the city’s shortage of grade A office facilities, this development mixes historic and modern architecture to produce an inspiring environment for creative minds.
The site encompasses a new office building, No.1 Bath Quays, alongside a second phase (Bath Quays 2) and the refurbished industrial Newark Works. A river bridge for pedestrians and cyclists will connect to a sister development, Bath Quays North, and provide easy access to the city centre.
With the context of the masterplan, Buro Happold was engaged to address sitewide infrastructure, enabling works, flood risk assessment and river permits.
Challenge
Given the past industrial use of the site, it was anticipated that there would be significant obstructions below ground level. Some of these obstructions were known – such as a large box underneath the remnants of a weighbridge – but our geotechnical experts also had to contend with the unexpected.
Mitigating the risk posed by the river rising is a hugely important part of this project. The flood defence wall is part of a protective scheme that covers a long stretch of the river; the wall to the west had already been constructed so our scheme had to coordinate with this.
Solution
An enabling package of works was undertaken to find ground obstructions ahead of any substructure works; the below-ground drainage was installed as part of the package. During this installation, a drainage pipe was discovered that could not be seen on any survey drawings. It was proven to be receiving surface water and so had to be diverted around the footprint of the office building – No.1 Bath Quays – and out to the river.
The flood defence wall runs along the river edge on the eastern part of the site, providing support to the new pedestrian bridge. It then turns inland in line with the buildings’ facades, creating a wider landscaped river bank.
The design conditions for the inland flood wall are relatively straightforward. Performance specified by Buro Happold’s water engineers and designed by the sheet piling subcontractor, the design – which allows for a 100-year flood event, climate change and surface fluctuations – has been dominated by the deflections that occur in a flood loading scenario. In this case, the wall could deflect inwards by up to 50mm.
Matters become more complicated for the stretch of wall at the river’s edge. This sheet-piled wall is installed 2m into the river to avoid clashing with the foundations of the existing river wall, which is in poor condition. It involves a much more onerous design condition, with riverbed level on one side and approximately 6m of retained earth on the other. Carried out before development of the Bath Quays South scheme, the initial design proposed a series of ground anchors at close centres tying the sheet-piled wall to the land. The Buro Happold team quickly realised that these anchors, which pass beneath the footprint of the Bath Quays 2 building footprint, would have to be avoided while installing the piles. This would be like threading a succession of weighty needles with unyielding thread.
Having explored numerous options – including ground anchors, concrete dead weight, ties back to anchor piles and reusing the existing wall – our team conceived a two-part solution. For the stretch of wall adjacent to the residential building footprint, the retained level of ground is minimised. For the section that does not interact with the residential footprint, the wall is tied to a piled anchor block.
These flood works are not limited to the wall itself. The reprofiled bank becomes a conveyance zone for the river, providing extra width for the water to spread into and a straighter path when levels are high. In clearing the bank, a resident otter was discovered and carefully rehomed. To lower the river edge, the existing masonry wall to the west of the site is reduced in height and a gabion solution was devised for the upstream end to provide scour protection.
An additional early concern was the risk of river water travelling through the permeable ground layers under a head of water in a flood scenario. It was recognised that there was a need to cut off this route, which is achieved by ensuring that the wall penetrates the ground layer of impermeable clay alluvial deposits.
Our water engineering specialists are also assisting BAM in obtaining the necessary Environment Agency permits as they take the design for No.1 Bath Quays through to construction.
Buro Happold is now working on the landside elements of the pedestrian bridge to both the north and south. The south ramp must take account of changes in levels, the flood wall anchor blocks and the existing curtilage listed arches that sit adjacent.
Value
Buro Happold’s expertise, ingenuity and imagination ensures that this picturesque riverside location is sound below ground and thoroughly protected from the threat of flood.
It is worth noting that site access is limited, both in temporary and permanent situations. There is only one route in and out for all construction traffic, which also provides the only way in for all buried utilities. Throughout our work – for No.1 Bath Quays, the Newark Works and across the site – Buro Happold makes sure that the interfaces between neighbouring projects, such as the Bath Quays 2 plot, are understood while liaising with all stakeholders to ensure coordination. This helps several teams operating in constrained surroundings to smoothly deliver the constituent elements of Bath Quays South.
