coefficient of consolidation Cv 1

[jsf442]

Does anyone have an opinion on which way is a better way to obtain the coeifficent of Consolidation? The lab reported the coefficient of consolidation using both Taylor's square root of time fitting method and Casagrande's logarithm of time fitting method. Plugging the two different numbers into my settlement calculations gives me rather large differences in the time rate of settlement.

 

[MRM]

Are you using the same time factor for each way? Were the Taylors and Casagrande charts based on the same stress increment on the same specimen?

 

[GeoPaveTraffic]

My suggestion is to look at the data plots for both methods. Typically the data "fits" one plot much better than the other, in which case I would use the better fit.

Additionally, Taylor's method tends to work better soils with more silt/sand, i.e. those that drain/consolidate quicker.

 

[tectonator]

Generally, the root time method requires compression reading covering a much shorter period of time compared. On the contrary the log time method requires longer period of times as it is important to define accurately the second linear part of the curve well into the secondary compression range.

For the root-time method is not always possible to obtain a straight-line portion. In such cases the log time method is more useful.

Both methods should give similar results. So, I suggest checking again your data for possible omissions.
If you have values for the in-situ coefficient of permeability (k), you can estimate the mv from the oedometer and then use the following equation:

Cv= k[in-situ]/(mv[lab] *?w)

 

[tectonator]

Cv= k[in-situ]/(mv[lab] *gw)

gw=unit weigth of water

 

[BigH]

Suggest you might find the following web site of interest.

http://www.cv.nctu.edu.tw/english/faculty/Ppt-pdf/AGTwk5Consolidation1.pdf

 

[jsf442]

Thanks for the help everyone!!!