Select Design Undrained Shear strength in clay with varied Su for strip footings
Select Design Undrained Shear strength in clay with varied Su for strip footings
(OP)
I had a bunch of in-situ testing that gave me varied Su for clay soil, with values from 1000 psf to 4000 psf. If I am using strip footing, it seems to be really conservative to simply use the lowest value. I think strip footing should be able to bridge over the weak spots, but I couldn't find any reference to back up my thought. Any suggestions?





RE: Select Design Undrained Shear strength in clay with varied Su for strip footings
Once you have this, then by placing your footing at various depths you can make an estimate of the allowable bearing capacity; then, carry out analyses for estimated settlement and adjust the allowable bearing pressure from the two values.
RE: Select Design Undrained Shear strength in clay with varied Su for strip footings
RE: Select Design Undrained Shear strength in clay with varied Su for strip footings
The solution might avoid the trend and involve multiple layers, and this is what is done sometimes when the structural engineer uses directly his geotechnical analysis add-ins which are linked to the structural routines of the software.
At least, this is the SOP now in seismic projects in my place.
The question if a strip footing can bridge over weak spots (weaker random fluctuations of the shear strenght of the soil) is not an easy one. It depends on the strip size, especially its width, and the size of the random fluctuations of the soil properties. If strip footings are connected into a rigid foundation framework, than the foundation is likely to behave as a large unit and it is not sensitive to weak flucuations (that is: the values which govern are not the minimum ones, rather the average ones).
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