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Foundation Design for Different Soil Structures

Dependent upon national regulations, wind turbine foundations are inspected and approved by an independent third party on behalf of the manufacturer during the certification process. Proof of stability is issued for one particular soil profile. Seeking support in erecting a wind farm on a soil structure different to that described in the manufacturer proof of stability certification, a wind farm operator turned to TÜV Rheinland.

Basic Facts
Client: Wind farm operator/investor
Project Location: Germany
Main services:• Soil analyses and evaluation
• Geotechnical and structural foundation design

Initial situation and requirements

Because the soil on site was different from the one assumed in certification process, a new soil analysis and evaluation as well as a revision of the foundation were needed. Our experts, already familiar with the turbine and the foundation, easily provided consultation services for the re-design of the foundation according to the soil conditions on-site considering both geotechnical and structural design compliant with the relevant standards and regulations.

Solutions, results

The geological survey indicated that the soil structure (clayey silt in the upper layers) was of low load capacity. Therefore, a flat foundation was not suitable. Instead, a pile foundation transferring loads to deeper viable soil was laid. This type of foundation is typically used for onshore wind farms when soil structures with low bearing capacity do not appear near the surface (~< 5m).

Flat and pile foundations generally differ in how loads are carried. A flat foundation carries load over ground contact pressure and friction, while a pile foundation bears load via friction and pile point pressure.

Although a flat foundation is usually the most economical, it does require a sufficiently loadbearing soil such as cohesive soil with dense packing or rock.

Today, most land-based wind turbines are built on strong and stiff soils, but wind turbines will most likely have to also be built on soils with weaker properties in the future. The standard method with a large spread foundation may then be cast aside for foundation methods more suitable for these inferior soil conditions.

Benefits for the client

• Quality assurance and expertise to secure the investment.

• One-stop-shop for soil analyses and foundation design.

• International accreditations and deep understanding of different national and international standards to be considered.

Did you know?

According to the IEA Medium-Term Renewable Energy Market Report 2014, global renewable generation is expected to rise by 45% and account for up to nearly 26% of overall global electricity generation by the year 2020.

About TÜV Rheinland

Founded 140 years ago, TÜV Rheinland is a global leader in independent inspection services, ensuring quality and safety for people, the environment and technology in nearly all aspects of life.

We can support wind energy projects with a wide range of services covering all project phases – from development and design to construction and operation. We are accredited by the German Accreditation Body (DAkkS) as a Certification Body for type and component certification of wind turbines in accordance with the international standard IEC 61400-22.