Innovative drainage system supplied to The Royal Oldham Hospital in Manchester 

The Background

In 2014, Pennine Acute Hospitals NHS Trust, which runs The Royal Oldham Hospital, announced plans to create a new purpose built car park at Westwood Park for hospital staff.  The car park would provide 562 spaces located much closer to the hospital and would also feature improved security, including CCTV monitoring, a new controlled pedestrian entrance allowing access for staff 24 hours a day and improved lighting.

Manchester based national contractor, Bethell Construction, were successful in securing the £1.8m contract following a competitive tender process and they were employed on a 'design and construct' basis to develop the initial planning design for not just the new car park, but also footpaths, external works and an adoptable access road.

The Problem

As the site was within close proximity to the hospital, noise, dust and traffic movements needed careful consideration.  The options for the surface water design were compounded by the fact that the local statutory water company, United Utilities, had specified a 5l/s flowrate for the outfall of surface water from the 13,000m2 car park into the public sewer.  An essential component for the successful delivery of this complex project was finding the right materials supplier to work with to produce a workable solution for the car park drainage.  The ability to deliver both technical advice and an innovative solution was key.

The Solution

Aggregate Industries recommended an innovative system using Drainasphalt, a permeable asphalt that allows water to pass freely through the underlying structure, specifically developed for use as an asphalt porous surface and binder course component in a Sustainable Urban Drainage System (SUDS) pavement. This material also reduces surface water spray and headlight glare in wet weather, and its inverted texture allows for high capacity acoustic absorption.

Aggregate Industries’ technical team worked alongside Manchester-based, national contractor, Bethell Construction to install the system which comprised a 100mm layer of 63-10mm aggregate over an impervious membrane, with a 50mm layer of Type-3 sub-base on top.  Water would drain into an attenuation tank with an underground soakaway, while a drainage channel running along the middle of the car park was also incorporated into the design.  Finally, the surface of the car park was laid in layers of asphalt approximately 90mm of 20mm Drainasphalt Binder Course and 40mm of 10mm Drainasphalt Surface Course.

Aggregate Industries technical department ensured that the mixes were available at a number of its mainstream asphalt plants in the area to ensure it could supply from more than one source if necessary. This meant that there would be minimal disruption when supplying in excess of 300t of asphalt per day.

A 20mm Dense Binder Course and 6mm Dense Surface Course were also used for the footpaths, and 30/14 Hot Rolled Asphalt was used for the new access road.