A major new warehouse in Milton Keynes

Posted on 1/Jan/2008

Winvic Construction commissioned to build a major new warehouse in Milton Keynes

Following a successful tender Winvic Construction were commissioned by Prologis to build a major new warehouse in Milton Keynes. But before the construction work could start in earnest several key challenges had to be met…

What were the design requirements?

One of the main requirements was the need for surface water run-off from the new warehouse and yard to match the run-off from a Greenfield site. At the same time the design needed to provide enough stormwater attenuation to cope with the kind of rainfall that might only be seen once every 100 years.

Were there any site-specific problems?

The main problem was the lack of a suitable space for underground storage. The ideal location was under the car park but the fact that it was on two levels meant two separate tanks would be needed.

In addition the building programme required the stormwater tanks to be installed before the main structure was erected. This meant that any solution would need to have sufficient strength to withstand heavy construction traffic. Winvic chose Stormwater Management Ltd for their experience in this field to help them design and install a system to meet these punishing conditions.

What was the solution?

Two tanks using Flowblock units with a total volume of 2750m³ were designed with a thrust relief wall. This helped to reduce lateral load pressure as the confined space meant that the installation depth would be limited.

Using Stormwater Management’s own specialist Installation Team, the tanks were installed to a tight schedule in April 2006. Using Fibertex F4M protection fleece and a tough and durable PVC membrane, the specialist team installed the tanks in sections on a ‘dig-install-and-backfill’ basis. As soon as each section was completed the area was opened up for construction traffic and material storage. Choosing this method helped Winvic Construction to fast track the overall construction process and maintain its programme.

What are the technical properties of the system?

Flowblock units each 1.00m x 0.5m x 0.4m with a vertical loading of 440 Kn/m² and a lateral loading of 63 Kn/m² were used to create two tanks:

Tank One: 61 x 14 x 1.6m

Tank Two: 74 x 14 x 1.2m and 13 x 9 x 1.2m

The tanks take rainwater from a symphonic system on the roof of the warehouse and surface water from the service yard and car park. The total installed depth of Tank One was 4.5m and Tank Two was 4.0m.

Each tank excavation was levelled using type 1 MOT, compacted and then lined with 3.2mm thick Fibertex F4M protection fleece. 0.8mm thick PVC membrane was then welded to form the tank liner and the Flowblock stormwater crates were placed and clipped together to create the tank.

The PVC membrane was then welded and sealed around all pipe inlet and outlet connections and enveloped around the Flowblock units and sealed using welded joints. Once the Fibertex protection fleece had been wrapped around the tank the sides were then backfilled using dry mix concrete on three sides to create the thrust relief wall, while the remaining sides were backfilled using clean aggregate.

Was any warranty given with the system?

FlowBlock modules already come with a 50 year guarantee and in cases like this where Stormwater Management carries out the installation, they’re able to provide a 30 year warranty on the system and its construction.

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