high mast pole foundation

huangyhg

high mast pole foundation
i am having a problem in designing a foundation for a high mast light pole.  the pole material is concrete and is 135'-0" long.  in analyzing the foundation soils using the hansen method i obtained an embedment depth of 18'-0".  this number agrees with charts i have according to soil type.  the issue i have is that the typical soil type used in the design extends down to to 15'-0" then the soil boring states there is a rock core.  what should be done in order to obtain the correct embedment for the pole?  any help would be appreciated.
csterne  
check out our whitepaper library.
drill and pin the rock face too resist the overturn moment.
rock socket - see pp 7 46-49 of gaylord and gaylord's structural engineering handbook 4th ed. there are interesting equations and nomographs that will help you design the right rock embedment depth.
make sure that the geotech has substantiated the properties and magnitude of the rock...weathered, bedrock, shale????, and things like extents of the formation and blow count.  if you have solid rock, you might consider yourself lucky, oftentimes the rock anchors, or most likely in your case a pile socket, can reduce your foundation construction costs by providing a solid moment resisting connection. i have seen jobs where the formation wasn't thoroughly investigated and it resulted a huge change order.
i am gearing up to work on a very tall sewer aerial that must rest on columns, the presence of good rock on my project is a blessing. primarily because it is close to the surface and i won't have to design a deep foundation.
i concur on the gaylord reference.  the book is quite dry, but i keep going back to it.