Wetland frost foundation
Wetland frost foundation
(OP)
My project requires construction of a boathouse in a wetland. The water table is at 1.5' to 0'. Site is subject to occasional flooding. Dimensional restictions require structures to be at least 10' from shore. Soils are saturated gravel and sand. Local frost depths penetrate 5-6'. Looking for online specifications using granular material and insulating foam to provide stable foundation. Any thoughts?





RE: Wetland frost foundation
RE: Wetland frost foundation
I would be reluctant to attempt borings for cast-in-place piles. They'll slough immediately without casing at this site. A shallow foundation such as a monolithic slab (i.e. slab thickened at the edges and at any interior bearing locations if any) may be appropriate for a boat house. The foundation will have to be protected from frost by insulation.
The following link should get you to some useful information. It is a D.O.W. Chemical product but the paper is good and produced by a powerful research and development team.
http://www.dow.com/webapps/lit/litorder.asp?objid=09002f1380026990&filepath=/noreg
RE: Wetland frost foundation
RE: Wetland frost foundation
Good practical point you bring w.r.t. frost susceptible soils in relation to the type of building considered. The formation of ice lense segregation in clean sands and gravel shouldn't occur as would be expected in silt, varved clays, and fine silty sands. In most cases, however, I find it difficult as a geotechnical engineer to condone the implementation of a shallow foundation without frost protection, however small the facility may be. Maybe I'm overly cautious on this one. I would at least price the insulation option. Alternatively, the foundation could be heavily reinforced and allowed to 'float' seasonally. With overhead doors, etc... some functional difficuties may arise as a result of differential movements across the foundation, requiring periodic adjustments.
RE: Wetland frost foundation
I think it is only prudent to locate footings below frost line, particularly in areas subject to high water tables or flooding during the winter. That's my two cents.
RE: Wetland frost foundation
I'm not an expert on frost penetration and frost heave, but I do have some experience with it (beneath ice cream freezers.) And I have a pretty good handle on boat houses.
As I read the posts in this thread, it seems that BigH acknowledged the sands and gravels would freeze - but didn't expect much heave to result, other than the heave that occurs as the water freezes. After all, Digger57 is dealing with gravels and sands - not silts and very silty fine sands.
Some differential movement can be tolerated by the boat house itself, and the walkway can be designed and built in a manner that is very tolerant of movements.
Sometimes we tend to avoid solutions for some site conditions because we have little or no experience with that foundation type. I've been guilty of this from time to time -
My suggestion? Give the owner the choice - after all, it's his/her money. Clearly lay out the advantages and disadvantages for every foundation system (including costs.) Then get the owner to write you with their decision.
As a side note:
Digger57 - have you given any thought to a pontoon structure? This would have very little impact on the wetlands, and could be moved if necessary. And it shouldn't get flooded out...
RE: Wetland frost foundation
A nice enviornmentally friendly alternative solution!!