Rock-anchored and High Plinth Foundations

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Two simply but effective foundation solutions are the rock anchor, designed for a wind park in Mexico and the high plinth solution for a wind farm in Chile. They are highly cost efficient, feasible and have proven to be very reliable in many projects.

Bilbao (ESP) – Special requests often demand tailormade solutions. But tailormade needs an high specialization and a lot of knowhow from the engineers in the specific field. In foundation design for wind turbine generator (WTG), this specific knowledge is not that common, except for CTE Wind International. Their senior engineers are often asked to find new design solutions. For this purpose, they resort to tried and tested instead of reinventing the wheel. Two simply but effective solutions are the rock anchor and the high plinth solution. They aren’t NEW solutions but are highly cost efficient, feasible and their reliability has been proved in many projects. This article features two project cases, among many others, where CTE Wind International designed rock-anchored foundations for a wind park in Mexico and a high plinth foundation for a wind farm in Chile.

Cost savings thanks to rock anchors

In Mexico, CTE Wind Ibérica was selected as WTG foundation designer by the EPC company. The project consisted of more than 20 concrete tower WTGs. The project analysis conducted by the foundation design expert has led to the recommendation to deploy two different solutions in order to optimize the costs of project. In fact, the soil conditions showed that over a third of the wind turbines were planned on rocky ground. Rather than equipping all wind turbine with standard slab foundations, CTE Wind’s engineering team decided together with the customer to implement rock anchors. This solution uses the rock mass as a WTG foundation. In that way the construction company is able take advantage of the earth crust instead of building a slab foundation. The costs for the reinforced concrete and the construction work can be saved. But this solution is specially challenging as the engineers have to adapt the foundation, with an interface, between the concrete towers and the rock anchors. Not to forget the special design work of these anchors that needs to be done. Finally, the client was impressed and satisfied about the result. But more important: the project costs were below the initial budget.

High plinth for extra height

In another case, CTE Wind was approached by a global construction company and explained the challenge for its project in Chile, with over 35 WTGs. The customer needed an hub height of 4 meters more to increase the energy production and ensure the yield and so its income. They weren’t totally satisfied with a complex solution by one of CTE Wind’s competitors. That is why the construction company asked CTE Wind to find a simple, reliable, feasible and cost-effective solution. That is how the high plinth foundation was chosen: a solution already tested and implemented in multiple projects in Europe. The idea of this foundation is to reach higher hub height with a high pedestal. The tower stands 3 to 6 meters above the «ground level», keeping the gravity foundation independent from the tower system. Ideally, the solution provides a longer anchor cage. CTE Wind’s engineering team designed the anchor cage for this project and determined the bolt length and steel quality. If needed, CTE Wind can also prepare detailed anchor cage drawings. After comparing the results of CTE Wind’s predesigns to the competitor’s solutions, the customer decided to go ahead with CTE Wind’s high plinth foundation. No difficulties in regards the construction have been reported. On the contrary, the Spanish expert of WTG foundation design was congratulated.