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The most common foundation scenario for concrete towers features a cellar. Since 2010, CTE Wind has provided foundation solutions for concrete towers in different variants. One such foundation solution is the hollow foundation solution.

One critical factor to be considered in a wind farm project is the type of wind turbine tower.  There are primarily two categories of wind turbine towers available in the market: tubular steel and concrete tower. The mix of both types is a hybrid tower. Independent from the selected tower system, the increased prevalence of higher hub heights leads to larger tower bases which challenges the tower manufacturers to develop new solutions or systems.

In addition to the various pros and cons of tubular steel versus concrete to be considered, the choice of the tower has an impact on the foundation. A steel tower nowadays almost always comes with an anchor cage. On the other hand, concrete towers need a tensioning system usually using cables anchored in the foundation. CTE Wind Civil Engineering has provided solutions for concrete towers in different variants for the last 11 years and counting.

Let us take a closer look at the different parts of the concrete tower foundation:

Foundation design of the outer shape

Like the toes and the ball of your feet, the outer shape prevents the wind turbine from tipping over. The foundation for concrete towers can be designed as standard gravity or deep foundation with piles. To save resources, CTE Winds Soft-Spot® solution (patent pending) or a ribbed (star) foundation could also be applied. Moreover, working with different tower manufacturers requires consideration for further variable construction criteria. CTE Wind is specialized in its knowledge and experience in factoring in said variables, such as the pre-stressed or post-tensioned cable system.

The foundation from inside

The most common concrete tower foundation scenario from the inside point of view features a cellar where cables are anchored and cable tensioning tools are placed. This kind of solution is often referred to as a “Hollow Foundation Solution” as shown in the picture. This design has a cellar to allow for access into the foundation and to tension the anchor cables of the tower. The reinforcement design for the hollow foundation solution is also substantially different from that of standard gravity foundations. Besides the customized interior formwork, special attention has to be paid to the design of the anchoring bulkheads where concentrated loads are applied to the concrete in very limited spaces.

Another option to anchor the tower to the foundation is to install protruding bolts out of the pedestal and into the tower where the cables can be connected. In this solution, the cellar is not necessary. The bolts are easy to access for tensioning. Lastly, and more seldomly used, is the combination of the concrete tower and foundation into a monolithic structure where only classic reinforcements are used but no tensioning elements are needed.  This type of solution can unfortunately lead to concrete cracks at the bottom tower section.

If you want to learn more about CTE Wind International and CTE Winds CONCRETE TOWER FOUNDATIONS SOLUTION please visite OUR-PROJECTS & OUR-NEWS – sections. For more Information about OUR-SERVICES please CONTACT US.

Since 2019 CTE Wind provides geotechnical engineering services to their clients. Over the last six months, Ana Bielza, Senior Engineer at CTE Wind Iberica has taken part in over 45 projects. We have asked her what she actually does and why her role is crucial for the foundation design of wind turbine generators (WTG).

Can you briefly explain to us what a specialist in geotechnical engineering like you does?
Ana Bielza: Geotechnicians apply scientific methods and engineering principles to predict the response of the ground to the foundation requirements. They then deliver this information to the civil engineers so they can design foundations accordingly.

What is the difference between common geotechnical engineering for bridges or building compared to the WTG-geotechnics?
Ana Bielza: There are not many differences. The ground has to be investigated with similar methods (drillings, geophysics, lab tests, etc.) and the same kind of parameters are needed. But the ground capacity is usually not what determines the foundation size, because most of the time the soil strength transmitted by a turbine foundation is not high. Besides, settlements in general are not important in this type of structures. But rotational stiffness can rather be the main ground parameter to manage and sometimes it can even set the foundation size.

CTE Wind offers his services worldwide

You worked on over 45 projects in six months, which is quite a lot. In which countries did you take a look at the ground?
Ana Bielza: Yes, there were many. It looks like our services are very appreciated by the customers (She smiles delighted). I worked for projects in Argentina, Australia, Belgium, Brazil, Chile, India, Indonesia, Israel, Lithuania, Mexico, Netherlands, Peru, Russia, Spain, Tanzania, Tonga, Turkey, and Ukraine. Of course, every country has its peculiarities. And I not only mean the different ground types you can find but also how the different investigations that are conducted and how the results are delivered.

Looking back on these last months, what were the challenges? Can you maybe share one or two projects with us?
Ana Bielza: Challenging projects are usually the ones located on recent soils in seismic areas and near to the shore (high water table). For example, we have done several basic designs for a huge project in India with 1000 wind turbines, located on a saline desertic zone most of the year. But during the monsoon season the landscape becomes a swamp, with water at ground level. It is a region with an extreme seismic risks, on a recent granular soil (potentially liquefiable) and very aggressive to the concrete. We had to analyze the ground with just four boreholes in an area for 1000 turbines!

Sounds like fun. As far as we know, there are no known cases of significant damage from liquefaction in wind farms. So, how did you solve this problem?
Ana Bielza: Well, with only four drillings for such a huge area, it was mandatory to be conservative, therefore, and according to the client, we worked with two possible scenarios. We hope they were representative for the situation in most of the future turbine positions. The civil engineer then follows our specifications and designs the foundations accordingly with piles.

Trust is an important key factor

Could you tell us about another project?
Ana Bielza: Another challenging project has been the one in a country in South America, a wind farm with over 40 turbines. This was a constructive design where we had also drafted the geotechnical study from a factual report given by the customer, with 45 boreholes, 80 trial pits and 46 geophysical tests as well as an important amount of laboratory tests. The ground was good, a consolidated gravely soil -a conglomerate-, but seemed to be prone to suffer some dissolution because it had salt in its matrix.

What does it mean exactly?
Ana Bielza: The matrix describes the different layers a soil can have. The salt in the matrix can be dissolved by heavy rain or ground water. But even if the ground suffers an hypothetical dissolution, the remaining gravely soil would show enough strength and rigidity to carry the WTG. Besides, there was no water at all in the area, it was in a desert area.

Good conditions. What was the problem then?
Ana Bielza: Yes, but the client was pressuring us to set down categorically that there was no risk of dissolution, and there was no possibility at all for buoyancy. The geotechnics of the project showed good conditions for our SOFT-SPOT® foundation, but the wind farm owner seemed to have unfounded fears and wanted us to affirm that there was zero risk in this area. But zero risk does not exist. It was tricky to explain why there are no risk but we had to write about an hypothetical dissolution. Luckily, we finally came to an understanding. (ctewind)

CTE Wind’s engineering team is working on different wind projects in Ethiopia, Egypt, South Africa and Saudi-Arabia. And not for the first time ! The WTG foundation experts can look back on 15 years of project history in these regions.

La Richardais FRA – Wind projects all over Africa and Middle East are ramping up. The Global Wind Energy Council foresees wind energy capacity reaching over 3GW by the end of 2023 in South Africa, but according to the IEA, Sub-Saharan Africa alone offers a wind energy potential of 1,300 GW.

Foundation Expertise

As a matter of fact, CTE Wind has been requested to support different European and Arabian customers for their wind projects in Africa and the Middle East. Projects in South-Africa, Ethiopia, Egypt and Saudi-Arabia are currently in CTE Wind’s pipeline. The engineering office provided many times its wind turbine foundation expertise over the last 15 years in North and South Africa. As of 2021, CTE Wind designed, value-engineered or peer-reviewed foundations of 2700 wind turbines within 76 projects. The services vary from geotechnical consulting, to preliminary and detailed foundation design, as well as forensic engineering for existing wind farms, without forgetting the third-party verification (CAT3) task.

First African Project

CTE Wind has worked regularly in Morocco but also in other countries of Africa and the Middle East.

In 2008 CTE Wind had its first wind project for a project in North-Africa. The expert in foundation design for wind turbine foundations designed gravity bases for 131 Siemens machines in the Tarfaya wind park, located in Southern Morocco. Then came the Ashegoda wind farm in Ethiopia, the Kabertene wind park project in Algeria, the Balikesir wind farm in Turkey and the Nojoli wind park in South Africa

Bigger Wind Parks

In 2016 CTE Wind has been awarded the wind park in Ras Ghareb, Egypt, with 125 wind turbines.

The Ombepo wind farm in Namibia came later. In Saudi Arabia, the trouble shooting work was done successfully for the Dumat Al Jandal wind park with 99 positions. A new project in the country has just been awarded to CTE Wind.

This short list gives a quick overview as to where CTE Wind’s expertise in wind turbine foundation in Africa and the Middle East has been requested.

CTE wind is more confident than ever to work on any wind projects from South-Africa to the Middle East region. Get in touch if you need further information about foundation expertise and services.

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About CTE Wind

About CTE Wind – Experts in Foundation Design World Wide:We serve since 2003 the wind industry as civil / structural engineers for wind park owner, developers and EPC/BoP-contractors. Often also directly for the OEMs. 25000 wind turbines in 73 countries. We provide geotechnical services, preliminary and final designs for wind turbine foundations, repowering and life time extension services.

A pile foundation transfers the WTG loads to the lower-lying ground, thereby providing an overall support to the structure. Geotechnical experience is a must for designing wind turbine foundation pile. CTE Wind designed piles with length varying from 10 to 70 meters.

Foundation piles transfer loads from the wind turbine foundation to lower-lying ground, thereby providing overall support to the structure. These piles carry concentrated loads and are subject to fatigue. As such, careful assessment of geotechnical conditions and proper interpretation of the soil reports’ drilling logs and laboratory data are critical, which is why CTE Wind has senior geotechnical engineers working on wind farm projects worldwide.

CTE Wind’s pile foundation designs solutions consider driven, bored and drilled piles as well as vibro piles and Franki piles. Once the pile solution has been chosen, the length and diameters, as well as the stiffness of the pile and the loads on top of it have to be determined. The compression, the tensile and the fatigue loads are taken into account to establish the calculation report and the final drawings stating the rebars and concrete volumes.

Piles for intertidal nearshore foundations

In current projects CTE Wind has designed pile foundations with lengths varying from 10 to 70 meters which is exceptional. The latter was designed and built in Asia in different nearshore projects on an intertidal sea-zone. CTE Wind also provided pile designs in Belgium, France, Germany, The Netherlands, Brazil, Serbia, Ukraine, Russia, and Finland to name a few.

If you want to learn more about CTE Wind International and CTE Winds PILE FOUNDATIONS please visite OUR-PROJECTS & OUR-NEWS – sections. For more Information about OUR-SERVICES please CONTACT US.