Reduce realization costs for wind farms

Wind turbines have been an integral part of the Dutch landscape for some years now. Some polders - such as Flevoland and Wieringermeer - are almost full of them. The turbines are built higher and higher for better efficiency. Speaking is Paul ter Horst of Tensar, inventors of the geogrid and the Stratum granular mattress. "To install the machine housing and blades at this height, extremely large cranes are needed. However, these cranes must be able to stand stably and safely. A challenge for Dutch wind projects, because most wind blows in areas where the subsoil is not load-bearing."

"The simplest solution for constructing access roads, storage areas and crane stands for wind farms consists of a layer of granular material," Ter Horst begins. "If the bearing capacity is not sufficient, the (mixed) granulate can be mechanically stabilized with TriAx geogrids. Due to the best performance of all types of foundation geogrids, the TriAx mixed aggregate can give a much higher load spread and/or strength. Clear guidelines for the application of geogrids have been established in the CROW1001 and the STOWA Handbook "Crane sidings" (2019-02a), so that in accordance with these guidelines one can
can design."

No poles required

"If soil improvement is too expensive or too invasive and/or the settlements too high, a concrete pile on piles is quickly chosen for crane emplacements," Ter Horst continues. "A concrete pile must - because of the high cost - be exactly matched to the crane that will come to lift. In practice, however, a contractor does not know until the last moment exactly which crane will actually come because of scarcity of such large cranes. An alternative then is a pile mattress. It is a mattress consisting of granules wrapped in multiple layers of high-strength geotextile on piles. This makes a pile mattress much more expensive but provides all the flexibility for applying any taps. However, the best and most beneficial solution is a TensarTech Stratum^® Geocell Mattress. This solution offers equal flexibility to a pile mattress or soil improvement, but does not require piles. On the other hand, minor settlement must be acceptable. Fortunately, settlements are rarely a limitation for crane embankments. In the STOWA Handbook 2019-02a, the above is also confirmed." 

Verification test

For construction of the work roads and crane stands of the Wieringermeer wind farm, consisting of 50 and 32 turbines respectively, the stability of the crane stands was ensured by several Stratum systems. Ter Horst: "The client - Vattenfall - commissioned, among other things, that contractor Van Gelder perform a verification test to test the suitability of the sidings. And with success. This confirmed that the siding meets all the client's requirements and is suitable for facilitating the crane loads." 

The introduction of the Stratum^® granular mattress prevents, among other things, the construction of pile foundations for crane emplacements. "The application of Tensar TriAx and TensarTech Stratum thus contributes directly to reducing the realization costs of wind farms and indirectly to the energy transition as a whole, without compromising on safety," Ter Horst summarizes. "In addition, the CO₂-emissions from project realization because reusable materials can be applied, no concrete production and less transportation is required."