Building a deck on extremely soft ground.

by John
(Illinois)

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?



Editor's Comments:

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.

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May 10, 2021
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Building a deck on soft ground NEW
by: Ron

Whether deck, shed or above ground pool support is needed at certain intervals. normally for small structures like these its about every 4 to 6 feet. In cases where a big tree stump was removed and a rut was left behind or a cesspool was in that area on the property you can build one of the structures one the spot. Care has to be taken to ensure the weight is dispersed pass the point where the ground can't support it.
This is done by creating footings slightly past the outer perimeter the the structure being built "let's assume a 14ft diameter pool 4 ft deep.The weight of this pool full of water will be about 12 tons. This equates to ruffly 160lbs/sqft. You'd start by placing footing blocks around the perimeter every 4 ft after digging escavating 12 to 24ins. Next do the same along the centerline north, south and east west axis' come in 4ft from the perimeter edge and creat footings. From this point you'd have a proper structure to work footing wise. Depended on the structure let's say pool in this case I would use 2x6 treated lumber sitting on edge and add treated plywood sheets creating a platform the the pool would rest on. This will last you about 8 to 10 years about the life spavn of the pool. This use to be a common practice when I was younger. I must include this level your footings before building up.

Mar 28, 2019
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Help me
by: Anonymous

I need to put decking on soft garden to hold a hot tub on how do I stop it from sinking

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