Permanent Pile Docks
The permanent pile dock is a heavyweight, long-term version of the pipe dock - still a ramp on long legs, but definitely not portable. Instead of resting on the surface of submerged lands (as the legs of pipe docks do), long poles of wood or tubes of steel or plastic - all referred to as piles - are sunk into the earth, either by force or by being set in pre-drilled holes. Either way, because of the heavy-duty equipment required, a pile dock is not the stuff of home workshop projects.
Piles should always be braced to prevent sway, and although there are no theoretical limits to depth, if the exposed portion of the pile extends 7.5 metres (approximately 25 feet) or more above supportive soil, construction costs will skyrocket.
The permanent pile dock shares many of the environmental advantages of the pipe dock - minimal contact with submerged lands, free flow of water underneath, and the ability to build a relatively narrow dock that is still quite stable. 
Sunk deep in the ground, piles made of wood, steel, or plastic make a great base for a stable dock.
Sunk deep in the ground, piles made of wood, steel, or plastic make a great base for a stable dock.http://customboardwalks.com/dock-primer/176.html
