A27 Chichester Drainage Scheme

Whole Project Award

Excellent (80.5%)

Project Team

Client: Highways Agency
Designer: Balfour Beatty Mott MacDonald JV
Contractor: Balfour Beatty Mott MacDonald JV

Project summary

The works are located on the A27 Chichester Bypass between the A259 Fishbourne Road roundabout and the A285 Portisfield Way roundabout. The A27 in this location consists of a Dual All Purpose 2 lane Carriageway with roundabout junctions except for the B2144 Oving Road which is a signal junction.

The works involve the renewal of the existing drainage linear soakaways to relieve the re-occurant flooding along the bypass. The existing drainage is by drainage channels to short lengths of carrier drains to linear soakaways. Primarily the drainage renewal is of the soakaways to bring them back to full operation. The works will also include the construction of a pumping station and the repair of category 3-5 defects following surveys in 2010.

Waste was designed out of this scheme by incorporation of geocelluar units for soakaways reducing the need for trench excavation and therefore waste from cut and fill.

Trenchless technology also reduced the need for excavation and therefore waste during the installation of the link to the pumping station at Whyke Roundabout, successfully achieved in 2014 following a delay due to problems in the initial exercise.

It was assumed that 100% recycling rates could be achieved for all waste streams listed.

Key CEEQUAL Achievements

Energy Assessment Results: LifeCYCLE assessment identified the following savings.

The majority of the additional carbon in the traditional soakaway is within the concrete drainage pipes that are required, which accounts for the large difference. Over 1,840m of concrete piping was needed, which accounted for 83% of its total capital carbon for the soakaway.

The difference between the Standard total carbon in 2012 to the Geocellular total carbon in 2013 and 2015 is the result of the change to the design and as it evolved the associated carbon was reduced still further.

When comparing the Geocellular total carbon at inception with the geocellular at construction we see that there was an overall percentage drop of 4%. This equates to 17.6 tonnes CO2e. This shows that efforts were made to reduce the total carbon by reducing the construction materials required.

The basic lifecycle analysis for the Geocellular block design indicated that 53% of the carbon emitted was during the initial works over a 50 year life span and it was found that 22% carbon saving could be achieved with the geocellular blocks design.