Solutions

The SOFT-SPOT® was developed by CTE Wind’s engineering team and is implemented in various countries around the world. This foundation design optimizes the bill of quantities as it saves concrete, reinforcement bars and reduces the foundation diameter. It is easy to be built and does not change the construction of the gravity foundation. A patent has been issued.

CTE Wind has already developed and implemented some projects since the launch of the SOFT-SPOT®. Several hundreds of the new foundation design are built around the world : Brazil, France, Lithuania, Indonesia, Mexico, Netherland, Russia, Serbia, Sweden and Thailand to name a few. As a result of his astonishing design the projects allow savings in concrete volume up to 15%, reduction of foundation diameter and total weight of reinforcement bars of 2-5%. In some cases what is even more important than the material costs is the available space : with SOFT-SPOT® you need less surface for the foundation. This reduces the time and excavation costs.

Layer of soft material

CTE WIND Civil Engineering presents to the market a new foundation system for wind turbines, a WTG shallow gravity foundation with SOFT-SPOT®. Through placing a layer of soft material below the central part of the foundation, the slab will effectively act as a ring foundation with respect to the soil-structure interaction. The bearing pressure of the WTG is concentrated at the annular contact surface closer to the edge of the slab. This increases the lever arm of the stabilizing moment. Therefore, the foundation diameter can be reduced in comparison to a standard foundation solution.

Simply the most economical foundation

Thanks to SOFT-SPOT® intelligent design less excavation work is needed. This reduces the machine costs. A major point is that no additional training of site workers is required for the construction of the soft layer. The construction is very easy and the material for the soft layer can be purchased cheaply all over the world. Or as CTE Wind’s client H4a Windenergie B.V pointed out: It is simply the most economical foundation you can choose.

Please contact us if you are interested in knowing more about CTE Wind’s SOFT-SPOT®

The rock anchor is a complex but efficient foundation solution. It reduces the volume of concrete and steel tonnage by using rock as the principal foundation. The rock anchor is highly cost efficient, feasible and has proven to be very reliable in many projects.

This solution uses the rock masses as a WTG foundation. Basically, the tower rests on the top of a small reinforced concrete block.
Two approaches are available:

• Concrete cap anchored into the rock: WTG tower sits on an (customized) anchor cage and the larger concrete cap is anchored to the rock.
• The turbine is fastened to an adaptor-plate and the last one to the ground with multiple post-tensioned anchors.

The anchors counteract uplift forces acting on foundations and post-tension the concrete structures against the rock. The anchors are often about several meters long.

Wind park owner are able to take advantage of the earth crust instead of building a gravity foundation for their wind turbines. The costs for the reinforced concrete and the construction work can be saved.

Soil anchors and rock anchors provide a high load capacity and the bond length can simply be increased to accommodate the required load.  Anchors do not involve large excavation areas as required by alternative methods and are a particularly attractive option when space is limited and when low impact or the environment is a priority.

This solution is specially challenging as the engineers have to adapt the foundation, with an interface, between the towers and the rock anchors. Not to forget the special design work of these anchors that needs to be done.

About anchors

Rock anchors are made of high tensile steel, and typically they are anchored in sound bedrock by means of high strength grouting. Ducts are placed in the concrete and holes will be drilled into the rock for post-tensioning application.

The anchors may be bolts or cables. For most applications the rock anchors are tensioned to a force higher than what is necessary to resist the foundation uplift force. They are eventually grouted on a part of their length to allow for a certain free tensioning length.

Please contact us if you are interested in knowing more about CTE Wind’s rock-anchor solution

The ribbed foundation solution consists of a thin slab, a pedestal/plinth in the center of the foundation and six to twelve arms that strengthen the slab. The saving is estimated up to 40% of the concrete volume.

The ribbed foundation is a variant to the classic gravity foundation. Important parts of the concrete volume are replaced by backfill.

As promising as the benefits of this interesting design may seem at a first glance: the complicated shatter works stands against the savings in concrete. That is why this solution shows his major advantages particularly when the costs for concrete are much higher than the labor costs. Technically, this solution work on grounds with poor soil stresses.

Patented solution

This solution might be protected by various patents in and from certain countries. Often, the patent concerns pre-casted parts of the walls.

Therefore, it should be checked which approach is the most adequate.

Please contact us if you are interested in knowing more about CTE Wind’s ribbed foundation.

High plinth / pedestal foundation allows to reach higher hub heights when the tower is too short.This allows to increase the productivity of the wind turbine.

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». The tower does not experience any modification and the construction of the foundation does not require bigger cranes.

Ideally, this solution is combined with a longer anchor cage so that pedestal and slab are well connected in order to avoid cracking.

CTE Wind’s engineering team can provide the design for the anchor cage and also prepare the detailed anchor cage drawing.

The high plinth foundation is already tested and implemented in multiple projects in Europe and Latin America.

Catch faster and stable wind

Wind velocity at higher altitudes can be higher than at the soil. That’s why it is more beneficial to put the turbine high in the sky where there is more energy to extract.

The high plinth solution allows with his higher hub heights to catch faster and more stable wind speeds. But no only. By increasing the hub heights the wind turbine is able to carry larger and longer turbine blades. Wich mean greater aerodynamic efficiency for the same machine by keeping the same tower lenght.

Please contact us if you are interested in knowing more about CTE Wind’s high plinth foundation.

The anchor cage design solution allows to optimize the foundation design and so the bill of concrete and steel quantities.

In the US a mandatory service from the structural engineer, in Europe delivered by the OEM: the anchor cage design. A well-designed anchor cage, or bolt cage, optimizes the bill of quantities of a wind turbine foundation (WTG) foundation. This special knowhow – or in French «savoir-faire» – of inhouse cage design leads CTE Wind to sophisticated foundation solutions such as the rock adaptor or the high plinth. The last mentioned helps to reach higher hub heights thanks his high pedestal. The tower stands 3 to 6 meters above the «ground level». The solution ideally provides also the design of the anchor cage. CTE Wind’s engineering team develops the cage and determines the bolt length, the pre-stress loads, the steel quality and all other necessary parameters.

Finite element method

CTE Wind uses for the design of anchor cages the finite element method (FEM) which allows to analyze the behavior of structures with complex geometries and strong loads. The picture above shows the stress distribution in a tower base flange connection to the cage. Models like that help to verify structural integrity. FEM in combination with CTE Winds «savoir-faire», allows – in case something goes wrong during construction phase – to find repair solutions. Several clients have saved money and time thanks to CTE Wind’s pathology experience and FEM-skills.

Please contact us if you are interested in knowing more about CTE Wind’s anchor cage design.

Pile foundation transfer the load coming from the wind turbine foundation to the lower-lying ground thereby providing overall support to the structure. A pile foundation solution takes into account any type of piles (driven, precast, etc.).

A pile is basically a long cylinder or prism of reinforced concrete or a tube of steel that is placed in the ground to transfer the loads coming from top structure by friction or cap resistance.

Pile foundations are used in wind parks where the soil cannot bear the compression or tensile loads applied by the wind turbine.

The piles have to carry concentrated loads and are subject to fatigue loads, too. That is why piles must be designed carefully by study the soil reports drilling logs.

Some geotechnical experience is a must to be able to understand and interpret correctly!

Every pile has an area of influence in the ground around it which can also vary from one soil layer to the next.

About the piles

Piles are long, slender columns. They can be determined as single elements but also as pile groups.

Once their dimensions vary under the same foundation cap – length or diameter – their stiffness will also change and then the design becomes a new dimension due to possible differential settlements.

A pile reinforcement drawing will be prepared.

In our current projects, piles length was found from 10 m to 70 m.

Please contact us if you are interested in knowing more about CTE Wind’s pile foundation.

The Hollow Foundation Solution allows for anchoring of the concrete tower to the foundation using pre-stressing or post-tensioning cables.

While there are variants where the concrete tower sits directly on a classic slab foundation, the most common foundation scenario features a cellar where cables are anchored and cable tensioning tools are placed.

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 the design of the anchoring bulkheads where concentrated loads are applied to the concrete in very limited spaces.

Cellar sealing is important

The lower surface of the foundation acts as a bearing ring while the higher weight of the concete tower helps to stabilize the entire structure. The lid overing of the foundation cellar requires special attention to prevent water ingress.

Please contact us if you are interested in knowing more about CTE Wind’s hollow foundation solutions.

The nearshore foundation is a proven solution in intertidal regions. During the low tide the foundation is exposed to the air and submerged in seawater at high tide. On sandy beaches with muddy underground the foundations can require piles up to 70 meters length.

CTE Wind’s special solution allows to save about 30 percent of the construction costs due to the astonishing design and compared to similar projects from third parties.

The solution provides a circular, cone like foundation on top of piles which are designed in-house. To tackle the challenging environmental criteria for geotechnics, tides, waves and ship movements close to the platforms, the patented foundation takes also the feasibility into account

CTV, the Asiaese office of CTE Wind, has already designed five wind farm projects with its patented solution.

Nearshore and Intertidal zone

As nearshore is the area from the swash zone to the position marking the start of the offshore zone defined. Typically, the water depths in nearshore areas are up to of 20 meters. In intertidal zones the water level can change massively between 5 – 15 meters during high and low tide. It is located on marine coastlines, including rocky shores and sandy beaches.

Please contact us if you are interested in knowing more about CTE Wind’s nearshore foundation.

The design of this solution consists of a slab foundation for a steel or a concrete tower. It is the most common form of a foundation for wind turbines but yet remains a complex structure.

Wind turbine generators (WTG) are becoming more and more powerful and the hub heights are increasing by the day. As a result, the concrete volume can reach these days to more than 1000 cubic metres per foundation.

CTE Wind has optimized the bill of quantities massively over the last decades. And still is continuing by means of research to work on effectful improvements with the main objective to deliver resource-savings but reliable design solutions.

The significant advantages of CTE Winds gravity foundation are:

• Easy readable drawings.
• Easy transportable reinforcement bars.
• Easy buildable reinforcement and shape for concrete pourring.
• Life time extension by changing the assumptions of the fatigue loads.

Continuous improvements

CTE Wind continuously improves this standard solution. On one side by taking into account the developments of the turbine manufacturers (size and performance) and on the other hand through close cooperation in research and developments projects (Tower manufacturer, universities, standardization bodies etc.). The major purpose is to cut down the minimal concrete resistance class and to reduce the required amount of steel and concrete. Also improvements trough non-linear calculations.

CTE Wind addapt his gravity foundation to the existing soil conditions. Thus several variants of this standard slab solution exists. Furthermore it can be combined with other CTE Wind design solutions, such as the SOFT-SPOT®. The customer is not spoilt for choice. He will be supported and advised throughout the entire project by experienced geotech and civil engineers.

Please contact us if you are interested in knowing more about CTE Wind’s gravity solution