N values of densified soils
N values of densified soils
(OP)
I use N-values to estimate settlement in shallow foundations in sand by correlating N with soil moduli. I use a linear relationship, higher N=higher Es. The approach is somewhat conservative, but it is as accurate as any cheap method to my knowledge. My problem is that often I am estimating an N-value of a densified fill subgrade. Structural fill in this area is usually SP sand, 95% modified Proctor, unit weight about 115 pcf. I have been using N=15 for densified sand subgrade. For most loads and bearing pressures this value is conservative but calculated settlement estimates are within tolerable parameters (i.e. 1"total 1/2"differential). I would like to use a higher N-value for estimating settlement on some projects but cannot find anything in the literature which justifies the higher value. Does anyone have any information concerning relationships of N-values to densified sands, silty sands, clayey sands, etc? I recently did some SPT borings on 5 feet of densified fill and averaged N-values in the 30's, although I think this number is not conservative enough to be used on a regular basis.





RE: N values of densified soils
RE: N values of densified soils
Looks like "D'Appolonia" method wins. Like your method, D'Appolonia uses E as a function N, and also adds footing width, influence factor etc. So try to get hold of D'Appolonia's 1970 paper, or ASCE's Geotechnical puiblication #5.
A Member of
www.civilvillage.com
RE: N values of densified soils
You can also do a consolidation test on these sands to develop the modulus as well.
RE: N values of densified soils
RE: N values of densified soils
Appreciate all your comments. Thank
RE: N values of densified soils
RE: N values of densified soils
"Measured Performance of Shallow Foundations", ASCE Geotechnical Special Publication No. 15
"Predicted and Measured Behavior of Five Spread Footings on Sand", ASCE Geotechnical Special Publication No. 41