Integrated infrastructure

Dora Carr is an award-winning social housing and community centre scheme in Oxford. SOLID was appointed as civil and structural engineers. The civils side of this project was particularly challenging. SOLID completed the external and highway design, foul and surface water drainage design.

Surface Water

The site is in an area of Oxford clay. Infiltration values were very poor, and our design had to ensure we separate site water from the underlying clay due to risk of heaving. We also had to consider the impact that the Northway and Marston flood alleviation scheme could have on the site.

A sustainable drainage system (SuDS) approach was decided upon to align side wide surface water drainage requirements with natural water processes. Due to the scale of the project and the footprint size of non-permeable buildings, a staged approach was designed to attenuate surface water flows.

First stage was to attenuate water in the sub-base of the roads. This was done through permeable paving systems which allowed water to be collected in the tanked sub-bases. The road system was a site-wide shallow tank with a capacity of 860m3.

From this sub-base, a network of pipes directed the water to two attenuation ponds located in a field next to the community centre and mansion block.

One pond enhanced the natural habitat of newts found in the proximity to the site. This pond has shallow areas that allowed newts to enter the pond and a deeper section (1.2m deep) which provided shelter during winter time as deeper water maintained the same temperature through the year. The pond is fully lined using a combination of clays to avoid any water loss. Water entering this pond was from the roofs of the Mansion Block. Once the pond was full, it overflows to the main attenuation pond.

The main attenuation pond provided storage of 800m3. This pond was designed to collect all the flows produced by the development.  It consists of two interconnected inlet soil detention areas and a channel. The pond was lined using local clays.

The design of the ponds was completed in 3D using ALLPlan terrain and micro-drainage. 

Foul Water

On the foul water side, one of the main challenges was obtaining the Thames Water permits for the adoption of the new sewer and the new connection into their sewer network. These applications were particularly challenging as a new storage tank was required as part of the foul water design and the public sewer pipework was very close to the new buildings.

We engaged with Thames Water and presented our storage volume calculations, our calculated volumes were substantially smaller than those calculated by Thames Water. We instigated multiple meetings with the Thames Water’s engineers to get agreement on the minimum storage volume that the development can provide. Our approach was based on sound engineering principles and a complete understanding of the legislation regarding water companies and their roles and responsibilities. Our detailed calculations supported the argument for a small storage tank within the network. The outcome of the challenge was an agreement on a small tank with a different flow control device. This approval produced a saving to the project in the region of £25k.

Road design and external

This site was very flat which allowed us to easily and fully comply with access to buildings are per Building Regulations approved document M. However this caused that cross falls and slopes across surfaces were very tight. Our response was to incorporated permeable surface were possible. Along roads, kerbs were flat and a combination of colours between kerbs and paving block allowed the road to be demarcated with further planting along the kerbing.