Situated on the once-sloped grounds of the Welsh Spinal Cord Injury and Neuro Rehabilitation Centre in University Hospital Llandough, Cardiff, this project involved significant groundwork and drainage engineering design before the garden pavilion build could begin.

Historically, the hospital made the garden space useable by levelling the ground, bringing it higher with the use of fill, and erecting a retaining wall with the use of a geo-grid system.

While this solution is suitable for landscaped ground, the fill does not allow for the direct support of a building. AWA were provided with some information regarding below the ground services and structures, but extra scanning and investigative digging were needed on site to confirm this data prior to commencing groundworks.

To create appropriate support for the garden pavilion, helical screw piles were inserted into the ground, connected with a grid of reinforced concrete ground beams, supporting a suspended concrete slab. The pile positions needed to be coordinated in order not to clash with the geo-grid system, and some of the ground beams had to cantilever to avoid any important hospital pipework services.

Once the groundworks were completed work started on the exposed timber pavilion, fabricated and supplied by the Timber Workshop. They created a beautiful full-timber structure with timber cross bracing.

From a drainage perspective, the fill and heavy clay virgin ground made soakways unworkable. The site already had a wider drainage strategy in place, with the surface water run-off from the buildings flowing into a large attenuation tank, so this was utlised. Our engineers worked closely with the team who designed the original drainage to make sure the system was not overloaded.

There was a requirement not to have any ponding or puddles on the paths or surfaces for the safety and comfort and tracking of the wheelchair users. Usually, paths have a slope that allows the surface water to drain to a gully or channel, but this wasn’t possible as flat surfaces were required. Rather than the rain hitting the path and flowing to a low point, it had to hit the surface and soak through.

Unfortunately, the fill and clay soil meant permeable surfaces weren’t an option, so our solution was to place an impermeable polythene liner underneath the permeable pavement. This helped the water seep through the path before it was directed to outlets connected to the main drainage. This created a flat, dry surface that met the client’s requirements without compromising the drainage.