Rock Anchor Solution

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

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

Concrete cap anchored in the rock: The WTG tower sits on a (customised) anchor cage and the larger concrete cap is anchored to the rock.
The turbine is anchored to an adapter plate and the final anchor to the ground using multiple prestressed anchors.

rock anchored solution wind turbine foundation design

Advantages

Ground and rock anchors have a high load capacity and the bond length can easily be increased to accommodate the required load. Anchors do not require the large excavation areas of alternative methods and are a particularly attractive option where space is limited and low impact or environmental considerations are a priority.

Wind farm owners can take advantage of the earth’s crust instead of blowing into the rock with explosives in order to build a gravity foundation. The cost of reinforced concrete and construction work will be reduced.

Technic

The anchors counteract the uplift forces acting on the foundations and pre-stress the concrete structures against the rock. The anchors are several metres long.

This solution is particularly challenging as engineers have to create an interface between the towers and the rock anchors. Not to mention the special design work that needs to be done on these anchors.

rock anchored solution wind turbine foundation design 2

rock anchor solution wtg foundation design 2

rock anchor solution wtg foundation design

About anchors

Rock anchors are made from high tensile steel and are typically anchored in sound rock using high strength grouting. Ducts are placed in the concrete and holes are drilled in the rock for post-tensioning.

Anchors can be bolts or cables. The bolts are tensioned to a force greater than the one required to resist the uplift force of the foundation. They are grouted a part of their length to provide a certain free tensioning length.