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Wind Turbine Foundations

Due to extremely high overturning moments induced by the height of the tower and the forces acting on the blades, wind turbines founded on spread footings feature very broad footings for the simple fact that a spread footing has no resistance to uplift - all of the overturning moment has to be taken out in compression from one side of the foundation only at any one time. This fact results in large footprint bases, and since the bases are heavily reinforced, the consequence is high volumes of concrete and rebar. The same set of circumstances result in similarly large bases being required for turbines founded on driven piles when those piles have no uplift capacity

It is possible, given beneficial geology at a wind turbine site where the turbines are not founded directly on bedrock, to dramatically reduce the size of the turbine base by applying innovation to the foundation design. For instance, at a site where the soils are too compressible to support a reasonably sized conventional spread footing, but where rock or another suitably hard stratum is present at relatively shallow depth, deep foundations such as micropiles, drilled piles or internally post-tensioned bored piles can be used. The added cost of the piling system is balanced or outweighed by the sizeable reduction in excavation size and concrete and rebar quantities.

For turbine bases founded directly on bedrock, rock anchors can be used to reduce the size of the turbine base. Rock anchored bases work on the exact opposite principle of broad spread footings. In the case of the spread footing, all of the overturning is resisted by compression of the bearing soils at the half of the base under compression while none of the overturning is taken by uplift resistance of the half of the base under uplift. In the rock anchor case, all or practically all of the overturning resistance is taken by the rock anchors at the half of the base under uplift.

Geo-Foundations has installed over 1,750 rock anchors for wind turbine bases.

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