I’m building a cottage on the shore of a Canadian Shield lake. The granite is 12″ to 30″ under the pine needles and root matt, except for one corner. This corner is closest to the water and we have not hit rock after digging 36″. This hole is also filled with water, the substrate is clay-like and densly packed.
A local builder suggests excavating 30″x30″ (to bedrock) at each post location and filling the holes with clean 2″ crushed granite, then setting a large reinforced concrete slab on the stones and using 8″x8″ posts from there. There would be re-bar through the slabs into the stones and the posts.
My initial plan was to pour concrete in sono tubes with Bigfoot footings up to grade then go with 8″x8″ from there. The local builder says he’s seen too many sono tube systems move, both tilting and heaving.
Any experienced insights?