12-14-2014, 02:06 PM
You would have to drill pretty deep for a 15 to 20 foot "pole" anchorage to work, as your anchorage would be transferred to tensile strength on the rebar, and "frictional" strength of the depth, keeping in mind the fracture strength of the surrounding pahoehoe without lateral bracing of the poles. The "general rule" of pier depth is one third of length of pole is buried ( 20 ft pole above ground, 6 to 7 feet of burial) on "freestanding" no lateral bracing. Poured footings are a different breed, as lateral bracing is required if the "pole" does not have an integral "mounting flange" for bolts to fasten "pole" to footing. Footing would have to be "engineered" for proper sizing to type of soil/wind load, etc.. Look at metal street light poles, cellphone towers, and the like to get an idea.
Community begins with Aloha
Community begins with Aloha