Soil report recommendation
Soil report recommendation
(OP)
I have this soil report that says "The structure to be constructed can be supported by shallow spread footings embedded at least 1.80 m below existing ground surface". It goes on to say that the foundation "can be designed with an allowable soil bearing capacity of 200 kPa for gravity loads". Yet, the soil report also says that "The site is prone to liquefaction".
Can I follow the soil report's recommendation?
Can I follow the soil report's recommendation?





RE: Soil report recommendation
Ask the geot for a more clear assessment of liquefaction potential and whether it is isolated, localized, what depth it occurs, etc.
It appears from the recommended bearing depth that the geotech might be expecting a mat foundation, which would also be one way to bridge localized liquefaction zones.
RE: Soil report recommendation
I wonder if the Geotech read his report...
Something's not right in... well... wherever the project is.
Mike McCann, PE, SE (WA)
RE: Soil report recommendation
Mike, I think spread footings founded at 1800 below the surface are quite common, and I would call that a shallow footing as opposed to deep, which usually means piles of some sort.
RE: Soil report recommendation
Mike McCann, PE, SE (WA)
RE: Soil report recommendation
RE: Soil report recommendation
RE: Soil report recommendation
As Ron pointed out, the liquefaction statement may be a general comment to protect liability. Sort of like groundwater comments where no groundwater was encountered in the borings. Maybe it's boiler plate that got left in by accident, maybe not. Probably better to speak the engineer who prepared the report rather than just assume it's wrong.
RE: Soil report recommendation
RE: Soil report recommendation
RE: Soil report recommendation
Understood. Mike stated that he considered the frost depth as an indicator of the definition between shallow and deep. I could be getting out of my depth here (no pun intended), but I believe the most absolutely technical difference between shallow and deep is whether the theoretical slip surface intersects the ground surface or not. So, a spread footing could be considered a deep foundation if it was deep and narrow enough. Likewise a pier can behave as a shallow foundation if it is short enough. In a full clay profile, as Nc approaches (arrives at) 9, the foundation becomes a "deep" foundation.
RE: Soil report recommendation