www.fixitwise.com Use gravity and water to install and sink your dock posts ( pilings ) 3 feet into the mud. Order a higher grade of exterior pressure treated wood from your lumberyard called "Critical Structure" - It's a grade above "Ground Contact". Simply tie into your lawn irrigation pump. These powerful pumps create enough volume and pressure to get the job done. Normal house water pressure is not enough. Sandy soils work best. If you have clay (like we did) plan on spending a little more time. Create a waterjet nozzle (pipe) as long as you need it with standard steel pipe fittings available at the local hardware store. If you don't have an irrigation pump handy, go rent a trash pump at the rental yard. The concept is the same. the professional dock builders use these larger pumps and bigger pipes make the job go easier and faster.
*NOTE: This project demonstrates how to use a dock piling to fix a sagging floor joist in a "NON- PRIMARY AREA OF A SUPPORT BEAM". If you need "primary structural support", you should have it engineered properly.