psmart
Active member
- Feb 3, 1999
- 1,507
I'm helping a local organization with the erection of a 40x50 foot timber-frame pavilion to be used for outdoor education and events. Basically a timber-frame roof resting on 8 timber posts with open walls. The question is what to use for the foundation under each of the 8 posts. The posts will be in two rows about 30 feet apart, and braced to the roof structure to keep them vertical, so the foundation only needs to provide vertical support for the posts.
The site is very rocky, with rocks and boulders up to 5' diameter (over 10,000 pounds). I've removed half a dozen of the beasts to clear the site so I know there is no easy digging anywhere. The minimal topsoil was removed before digging out the boulders, and the site was been leveled with 1.5" crushed gravel over 1.5" stone. The depth of the stone and gravel ranges from 3" at one end of the pad to 18" at the other. I suspect the water table is near the original surface in the spring, but I encountered no water in 6 foot deep holes in the fall. The surface is extremely firm and well compacted (it was previously a log landing) and there is never any standing water on the surface.
The initial plan was to install sono-tube foundations, but my time on the site tells we that every tube is going to run into rocks we don't really want to move, since each would result in an enormous hole. What are the other foundation options? Would pre-cast concrete bases be appropriate? A shallow foundation would avoid the excavation issue, but might not provide enough frost protection in New Hampshire. (On the other hand, we're not using drywall or other building materials that require an especially rigid foundation.) We could add a certain amount of fill to build up around precast bases, but not too much, since the goal is to maintain full accessibility around most or all of the perimeter. I've even thought about a well driller, that that would probably be too expensive!
Excuse the long question, but I wanted to provide all the background that might be pertinent to your recommendations. Thanks.
The site is very rocky, with rocks and boulders up to 5' diameter (over 10,000 pounds). I've removed half a dozen of the beasts to clear the site so I know there is no easy digging anywhere. The minimal topsoil was removed before digging out the boulders, and the site was been leveled with 1.5" crushed gravel over 1.5" stone. The depth of the stone and gravel ranges from 3" at one end of the pad to 18" at the other. I suspect the water table is near the original surface in the spring, but I encountered no water in 6 foot deep holes in the fall. The surface is extremely firm and well compacted (it was previously a log landing) and there is never any standing water on the surface.
The initial plan was to install sono-tube foundations, but my time on the site tells we that every tube is going to run into rocks we don't really want to move, since each would result in an enormous hole. What are the other foundation options? Would pre-cast concrete bases be appropriate? A shallow foundation would avoid the excavation issue, but might not provide enough frost protection in New Hampshire. (On the other hand, we're not using drywall or other building materials that require an especially rigid foundation.) We could add a certain amount of fill to build up around precast bases, but not too much, since the goal is to maintain full accessibility around most or all of the perimeter. I've even thought about a well driller, that that would probably be too expensive!
Excuse the long question, but I wanted to provide all the background that might be pertinent to your recommendations. Thanks.