Hi Rene, thought I'd chip in here, although this might not be relevant to your situation...
I've gone a different route with my pier - used a plate and micropiles, and it's worked a treat. Very stable, and I've been able to move the pier by myself to a better location in the yard, leaving behind no trace.
http://www.iceinspace.com.au/forum/s...light=surefoot
I cut down the micro-piles to about 700mm in length, and it's very stable