Stone to Underside Wind Turbine Foundations.
Stone to Underside Wind Turbine Foundations.
(OP)
We have been designing wind turbine foundations for some time now. I have seen some design of late, say in the last 12 months, where a 4-12 inch layer of Type 3 hardcore has been specified under the base of the wind turbine. This confuses me as I don't want to allow rocking to occur across my foundations. I can only imagine that placing stone with a bearing capacity of 50kN/m² over a ground with bearing capacity >100kN/m² would be foolish. There must be a reason however as I am seeing more and more competitors doing this stone detail. Is it at the behest of the turbine manufacturer so that less stress is developed in the turbine structure and more rocking/flexibility allowed in the foundation??? I would think that in wet conditions, the stone would penetrate the ground and eventually cause rocking and ultimately instability. I don't like it, but I also need to know what I am missing? If something was to fail, I would want the tower to fail, and not my foundations. Can someone explain the logic behind a layer of stone under the foundation for these towers?? I would greatly appreciate this.





RE: Stone to Underside Wind Turbine Foundations.
RE: Stone to Underside Wind Turbine Foundations.
RE: Stone to Underside Wind Turbine Foundations.
You have not defined "hardcore - type 3" so I have no idea what it is but I would presume it is a crushed gravel or rock that is likely being used to "level" the foundation as the foundation would be quite wide. This would be as protection against precipitation/construction damage to an approved foundation and facilitate the placement of the steel mat for the reinforced footing; likely in lieu of using a mud mat (blinding concrete). As for "rocking" effects - if the "hardcore" is suitably compacted to 100% Modified MDD (which is what I would specify under an important foundation), I would be very doubtful that this thin layer of well compacted stone would have any detrimental effect.
My thoughts . . .
RE: Stone to Underside Wind Turbine Foundations.
RE: Stone to Underside Wind Turbine Foundations.
Also, I never specify hardcore under foundations. I either have founds cast on hard ground and dead build up, or lean mix of hard up to foundation formation level. I would specify compacted hardcore (max 800mm dp) up to u/s floor slabs. Maybe I'm over-cautious.
Thanks.
RE: Stone to Underside Wind Turbine Foundations.
RE: Stone to Underside Wind Turbine Foundations.
RE: Stone to Underside Wind Turbine Foundations.
the following materials usually have a code allowable foundation pressure of 2,000 psf and they are generally considered to be well drained granular material:
RE: Stone to Underside Wind Turbine Foundations.
RE: Stone to Underside Wind Turbine Foundations.
ICC - 3,000 psf
new york city building code - 8,000 psf
http://publicecodes.cyberregs.com/st/ca/st/b200v07...
http://www.nyc.gov/html/dob/downloads/bldgs_code/b...