By using lava instead of Grauwacke to build a subbase, the new synthetic turf football field in Lelystad, Netherlands, will first clean drained water before it is temporarily stored underneath the pitch.
Dutch cities like Lelystad are increasingly experiencing changing precipitation patterns. This has forced municipalities to consider new innovations to manage the vast amount of water that falls in a short period of time during torrential rain. Preferably, water is stored on the premises before it is discharged into a river, lake, or the sewer system. This reduces the burden on the system by discharging it in a controlled manner. Storing water on site also helps to cover extensive hot and dry periods. Water present in the subbase prevents the nearby area from drying out and, as such, experiencing soil problems.
When Leystad tendered a synthetic turf football field, prospects were asked to submit proposals in which the subbase would provide buffer capacity.
Out of all the bids received, the municipality awarded the bid to installation company TopGrass, who installed a Polytan synthetic turf system. This third-generation synthetic turf football field with polymeric infill will be built on top of a Waber subbase. It is anticipated that this subbase will provide enough storage capacity to store all the water that lands on the pitch through rainfall, as well as the surrounding areas and the adjacent parking.
Lava instead of Grauwacke
The Waber (Water Retaining) system is usually built from Grauwacke pebbles to deliver a subbase in areas prone to settlement. This type of sandstone from Germany, hooks well, thus providing a stable subbase. In a standard 50 cm high subbase, the open spaces between the pebbles provides enough capacity to store 160-200 liters of water per square meter. For a full-size synthetic turf football field, this translates to 1.25 million litres of water.
However, as the new field in Lelystad will use SBR infill, Dutch construction regulations for synthetic turf fields stipulate the use of lava in the subbase. The porous lava has the advantage of cleaning the water of any material that might leach from the infill granules before discharge.
TopGrass have used lava of 16/32mm fraction to build the bottom part of the subbase. The structure was finished with a layer of lava pebbles of 0/16mm fraction to achieve the required density and levelness. The total height of the subbase is 25 cm and the subbase is built on top of a water-permeable geo-textile. Thanks to this approach, the field doesn’t need an additional drainage system.
To monitor the sensitivity to frost of the entire subbase, testing institute, Kiwa Isa Sport, has installed six temperature sensors. These sensors will be monitored for the coming 18 months to be sure the replacement of Grauwacke with lava doesn’t cause any problems. As the air in between the pebbles also acts as a thermal layer, the expectation is that the innovative subbase will remain fully functional and intact during the winter season.