Clay stratum N SPT > 50 settlement
Clay stratum N SPT > 50 settlement
(OP)
Hello, I am new to the forum, but I've had my geotechnical lab for several years now. I have a doubt which I hope someone can solve: Can a clay stratum with N SPT > 50 be considered incompressible regarding to consolidation settlement? Thanx beforehand.





RE: Clay stratum N SPT > 50 settlement
Mike Lambert
RE: Clay stratum N SPT > 50 settlement
RE: Clay stratum N SPT > 50 settlement
Unless you are dealing with a large areal load, it's not likely to be to compressible though.
f-d
¡papá gordo ain’t no madre flaca!
RE: Clay stratum N SPT > 50 settlement
RE: Clay stratum N SPT > 50 settlement
Answering to morelat221, a road bridge in northeast Mexico is going to be replaced with a new one (I didn't ask why, most probably is to increase hidraulic area) and the strata with N SPT > 50 are at about 10 meters deep, and after that, they increase. So I am proposing piles embeded in these stratum to support the new abutments. The liquid limits on the support strata are OK, from 20 to 35 and void ratios of about 0.5. The water level is about 6 meter deep. I am also proposing an optional shallow foundation, because the upper strata have lesser N SPT values but are low compressibility clays and sands, too.
I also made my original question because it has happened to me that the N SPT > 50 strata, is made of CH clays. So we have an stratum of a material with a very high cohesion (sometimes with rejection to the SPT head) but also high liquid limits.
Thanks everyone for your comments.
RE: Clay stratum N SPT > 50 settlement
RE: Clay stratum N SPT > 50 settlement
f-d
¡papá gordo ain’t no madre flaca!
RE: Clay stratum N SPT > 50 settlement
RE: Clay stratum N SPT > 50 settlement
Due the high SPT values, consolidation settlements are not a concern. If you treat this as elastic settlement, settlement values will be very low as moduli of elasticity (E) for SPT>50 is way too high.
roadrunner13 said the strata above these SPT-N>50 layer "have lesser N SPT values but are low compressibility clays and sands, too". "have lesser N SPT values" is very vague comparison.
You might have SPT-N between 20 and 30 for sands (considered medium dense) and they might be subject to liquefaction potential. So that something you need to clearfy.
Other than that, having low compressibility soils above this "clay layer", I don't see the use of deep foundations. Probably shallow footings will be the best option.
RE: Clay stratum N SPT > 50 settlement