Building a deck on extremely soft ground.
I am looking to build a ground level deck or raised platform on the shore of a small pond within 10 feet of the water
The ground is soft enough that pylons will most likely shift with the frost. This means that using pylons as a mean of total support would most likely not work.
What is some way I can fix the deck to the ground without relying on pylons for total support?
It is not exactly clear if you are referring to pylons as traditional concrete poured piers with larger footings below or if you are envisioning engineered helical piers.
Either option would probably work but post challenges. Water Table
I wonder how high the water table is and if it is quite high this poses are real challenge for installing poured concrete footings.
What might be best and easiest in this environment is a true engineered helical pier. this is where a contractor comes in with a small tractor or hydraulic drilling unit and drives down long pipes with a single helical blade.
They would drive down as deep as necessary and add additional lengths of pipe to the pier until such time as they strike bedrock or attain a certain torque rating.
In either situation the contractor would be able to provide an engineer's stamp confirming the bearing capacity of the pier.
The deck would never move even if the soil froze all around the piers in this case.A Cheaper Alternative
The engineered route above is the best but most expensive. An alternate choice but one that would not prevent the deck from rising annually as the soil freezes and thaws would but using many concrete blocks. The more that are used, the lighter the bearing load from any given footing imposed on the soil beneath it.
This is simple in concept but would require a lot of them.
So those are the main options I would see for building a ground level deck on soft ground as you describe.