Foundation Settlement for Embankments

[ONENGINEER]

I am designing a waste rockfill (10m high) on compact sand and gravelly sand foundation (Average corrected SPT = 24). Looking for a methodology to measure the settlement under the foundation and then check that the membrane would not be stretched excessivley under differential movements. I would appreciate your feedback.

 

[fattdad]

horizontal inclinometers or settlement cells.

http://www.slopeindicator.com/instruments/contents.html

f-d

¡papá gordo ain’t no madre flaca!

 

[ONENGINEER]

Thank you fattdad

I correct my question that I am looking a methodoloy to calculate settlement and then choose the appropriate membrane. Sorry for the wrong use of word "measure"

 

[BigH]

As a first go, do an elastic analysis - the rockfill is the load - can get the elastic solutions in Poulos and Davis among other references. You have indicated compact sand (must be Canadian!! yeah!!) so the 'N' value is likely about 20 (10 to 30). Estimate the E value (as per Bowles correlations - or others) - then do a sensitivity analaysis. Vary the E value and see what the immediate settlements will be - use 'very low' E to 'high E'. As your waste rock will be flexible, the solutions will also be able to give you the settlement at many points and you can then estimate if the strains are too much for the geomembrane. Do any of these give worrisome settlements? If not, then, ok - if yes, what can you do to reduce the settlements? Maybe load the site for a few meters, then remove and then reload?? (likely not a good scenario). You could consider then methods of densifying further your soil to a higher state of relative density.

 

[ONENGINEER]

Many thanks BigH. I have also seen calculating the settlement of the above by a software that uses coefficient of consolidation, Cv and Cvr and T90 etc.Are these parameters applicable to sand or only for clays? Is it correct to assume that sand and gravel are subject to immediate settlement while clays are subject to consolidation settlements too.

 

[fattdad]

you may also want to consider CGPR #41, "Settlement of Vally Fills," which is shown in the following link:

http://matrix.vtrc.virginia.edu/gra... Publications Chronological List 01-19-10.pdf

CGPR is the "Center for Geotechnical Practice and Research at Virginia Tech. The thrust of this publication pertains to the actual settlement of the rock fill itself rather than the foundation soils supporting the rock fill.

If you are dealing with N-values of 25 or so, I'd use elastic theory to evaluatate the settlemet of the foundation soils. Now, what's the best method to evaluate elastic modulus? Right now you just have N-values. You could use a dilatometer. You could just take 7N (or 11N) and return a value of 175 to 275 tsf. Then it's just a matter of determining the change in stress from the embankment and integrating the stress change and dividing out the modulus.

At least I think I got that right. . .

f-d

¡papá gordo ain’t no madre flaca!