As part of the drainage scheme, a large DN1200 on-line attenuation tank has been installed to manage the excess stormwater from the site. Consideration by the Redrow Homes engineering team and their designer Banners Gate was given to a number of tank design options, including a fully flexible plastic system, but following discussion with FP McCann who were able to demonstrate significant cost savings as well as performance benefits, a reinforced precast concrete StormHold™ pipe tank was the chosen design.
The tank measuring 100 metres in length has been installed under the site’s main access road and consists of 33 standard DN1200 2.5-metre long spigot and socket pipes, one with end cap, a DN1200 rocker pipe and socket butt pipe. There are also 5 bespoke pipe sections in the tank, each having a prefabricated precast concrete side entry manhole access point and integral steps for ease of man entry for inspection. This feature eliminates the requirement for costly manhole builds. The bespoke sections are three bends and two straight units, one of which is complete with end cap. Both end caps have been cored for pipe connections into the main drainage network.
The StormHold™ precast pipe system part of FP McCann’s extensive StormStore™ range of tanks, is the first to be installed as a trial under a highway under the monitoring auspices of north-west water authority, United Utilities and will provide the necessary stormwater storage and controlled drainage run-off with the added capacity to handle a 1 in 30 year and 1 in 100-year storm event.
Additionally, FP McCann has supplied an online box culvert attenuation tank measuring 90 metres long x 1.5 metres wide x 1.275 metres high. In total, 44 individual sections have been supplied each with a dry weather flow channel. There are three main access points along the line of the tank and end wall units have boxed-out pipe inlet and outlet points.
Stuart Hough, Senior Engineer for Redrow Homes North West says of the precast pipe tank design, “We have worked very closely with the FP McCann drainage designers at their Ellistown production facility to establish the most efficient and cost-effective attenuation system to match the site’s drainage requirements. Precast concrete pipes and culverts are simple to install and offer a durable, low maintenance solution for below ground drainage and storm attenuation structures.”
FP McCann’s StormStore™ precast concrete storm and wastewater management systems offer the following benefits:
- The flexibility of design – Off-site adaptations to meet client specification
- Products can be used in space restrictive on-line or off-line sewer or storm drainage systems, providing the required storage volume
- Sustainable systems with a design life in excess of 100 years
- Ease of access for maintenance via built-in access points
- Reduces costly individual manhole construction
- Reduction in imported pipe bedding
- Can be linked to SUDS related systems such as rainwater capture and re-use