What sort of rock has a bearing capacity of 8000psf? Leonards gives presumptive bearing capacities for "Soft Rock, Sedimentary Layered rock (hard shale, Sandstone and Siltstone)20,000-30,000 psf. That being said, the soft rocks described are subject to frost heave if located above the...
Of course the depth of excavation is important. You may consider benching or sloping the excavation back. Ensure that the top of the excavation sides are not loaded with the spoil. Cover the excavation walls with tarps. Here in Ontario I believe the maximum depth of excavation without...
The proposal is fraught with danger. The floor was not designed to impose the continuos loads by way of a beam. I suggest that you design your truss/beam with two point loads at the locations where the columns presently are, that is to maintain the status quo. Your next problem is to get rid...
Mixing the foundation types, piles and spread footings over soils that you describe is asking for trouble. Unless the peat has been preloaded for an extensive time differential movement will occur, even with preloading peats are subject to secondary consolidation. Provisions for jacking up the...
If, as I read this, you have one or two hair line cracks at center span and you have rechecked your calculations, I would not be unduly worried. Keep the beams(s) under observation, if the cracks develope or multiply, then perhaps a load test will be necessary.
INBCPE Here, Here to your first sentence. Rushman, if you invite me to your structure, I will run the other way! This is the best advice that I have ever given 'Hire a structural engineer!'
I agree with the coments of JAE and Ron, I personally would be inclined to reject the slab as defective work. An epoxy topping may accomodate your imediate problem.
nicholi, is the statement in your second to last paragraph correct? The bulb of pressue of the new footings may well exert influence under the existing footings and thus causing further settlement under the existing footing. It's worth checking.
As I read the original question, there are some footings to be cast over old footings and there are others to be cast on previosly unloaded ground. If this is the case, and the soil is clay you may well have a problem with differential settlement.
In Ottawa, Canada we routinely build on Leda clay for residential structures. Remember there should be no major fills on slopes and ensue proper drainage of cuts. If you are dealing with a genuine Leda clay,it can flow like water once it becomes disturbed, so treat it with respect.
