I put in a lot of high tension pasture fence posts using a 4" auger and then pounding them in 20 years ago and they are still fine today. I started out trying to just pound them in but rocks and tree roots soon sent me to buy a 4" auger to finish the job.I recently bought a hydraulic auger in preparation to putting in a horse arena fence. I got 9" and 14" auger bits to be sure I could make holes bigger than the posts (6" PT fence posts and larger diameter corner posts). However, a friend suggested an alternative approach that might avoid a lot of work tamping around the posts and also make the posts more securely set. He suggested I drill a 4" hole then use a post driver to drive the 6" posts into the holes. They'd go in a lot better than pounding with no pre-drilled holes and yet be very securely set in place without any backfilling/tamping.
Has anybody else tried this approach? Do you think it would work as hypothesized?
BOB
In those days the posts were black pressure treated creosote and tar. The posts were tapered a little so the fat end goes in the ground. That keeps them from trying to get back out of the holes over time from the winter freeze and thawing. They still will if precautions like putting the fat end in are not followed even driven 3 feet in the ground. Depending on the soil, clay here, some folks even put cross pins through the bottom of the posts to hold them in place.
You should check with local folks to find out what works best in your area and soil type.
You will get too many opinions that don't fit your area from this forum based on our experiences and how we all did it.