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Re: Wind Turbine Foundations

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The following guideline may help in designing a wind turbine foundation.

First try designing a circular or octagonal mat footing.  This should
comply to the following equations:

		e = M/W

		F.S. = R/e

  where    M = Overturning moment.
	   R = Radius of footing.
	   W = Vertical load + weight of footing + overburden.
	  F.S. = Factor of Safety against overturning.

This will allow you to find the minimum foundation consistent with
safety against overturning.

Check soil stress.

If soil stresses are more than allowable you need a larger foundation
and rock anchors will not help.

If soil stresses are much less than allowable you can use rock anchors
to reduce the foundation size and maintain the desired factor of safety
against overturning.  This will also have the effect of increasing soil

The use of rock anchors is a cost optimization.

The above equations are valid with rock anchors providing the
stabilizing effect of the rock anchors being mobilized is properly taken
into account.


				H. D. Richardson, P.Eng

Steven Mallett wrote:
> I am looking for information on design guidelines for foundations for wind
> turbines, i.e. big overturning moment. This proposed wind turbine has a
> 200 foot high steel tubular post, 150 foot diameter rotor. Approximate
> forces are vertical load of 150 kips, horizontal load of 120 kips, and
> overturning moment of 15,000 ft.kips.
> Foundation material will be sandstone (about 5 ksf allowable bearing)
> with 8 feet overburden. I would appreciate some reference to where I
> could find foundation design information for something of this magnitude
> and dynamic load implications.
> Thanks,
> Steven A. Mallett, P.Eng.
> Dillon Consulting Ltd.
> 137 Chain Lake Drive
> Halifax, NS  B3S 1B3
> Ph.  902-450-4000, Ext.234
> Fax. 902-450-2008