Settlement of Existing Fill
Settlement of Existing Fill
(OP)
I have a site with an existing fill between 4 and 17 feet thick over a firm, residual soil. The area of the existing fill is about 4 acres. I need an intelligent method for calculating long-term settlement of the existing fill layer. The fill consists of sandy elastic SILT and micaceous silty SAND. SPT N values range from 2 to 10. The fill is clean with little debris or organics. Moisture contents around 20 to 30 percent. Existing compation about 80 to 85 percent of modified proctor. No additional surcharge is proposed. Site area will be used as a cemetery. Desire to limit future ground surface distortion. I understand that any method is probably a calculated guess at future settlement behaviour.





RE: Settlement of Existing Fill
if it were me, i'd bypass lots of fancy testing and guesstimated analysis and tell them to compact the top and grow some nice grass and call it good. maybe do a favor and not charge them lots in the hope for future work or the client having a good word to pass along to other future clients.
how long has the fill been there and was it placed or "dumped"?
RE: Settlement of Existing Fill
RE: Settlement of Existing Fill
RE: Settlement of Existing Fill
RE: Settlement of Existing Fill
Best guess about the age of fill is that it was placed incrementally over the last 5 to 15 years. New area was a former dump area for soil diplaced by "tenants" in other portions of the site.
I went ahead with Schertmann's method as suggested by Dave600. The selection of the modulus is basically a guess from the SPT data. This seems to work better if I had CPT data. For delta P, I divided fill into sublayers and assumed surcharge as weight of fill above each sublayer. I am coming up with about a max of about 3 inches. I actually used what I think is a watered-down Schmertmann's from NAVFAC. I am going to look around for the other reference to see if it has more content.
If the answer is up to 3 inches, then I think all can live with this. I will suggest to scarify and beat the site site with something big like CAT825.
Thanks all.
RE: Settlement of Existing Fill
I would say you are safe in assuming that the minimum settlement will be less than 3 inches. The only concern I have is with the micaceous sand. Have not worked with it, but I understand it does some odd things.
RE: Settlement of Existing Fill
RE: Settlement of Existing Fill
Regarding the construction of roads, I'd agree to scarifying, recompaction (to 95 percent compaction) and then construction of the appropriate pavement section.
Good luck.
f-d
¡papá gordo ain’t no madre flaca!
RE: Settlement of Existing Fill
Thanks Fattdad
You ain't no flaca?
RE: Settlement of Existing Fill
Hope this helps.
f-d
¡papá gordo ain’t no madre flaca!
RE: Settlement of Existing Fill
f-d
¡papá gordo ain’t no madre flaca!
RE: Settlement of Existing Fill
RE: Settlement of Existing Fill
If you are dealing with sands, then the long term compression is given by a scaler Ct. Duncan's settlement manual lists values of Ct ranging from 1.0 (for one month after initial elastic compression occurs) to 1.5 (for 30 years after initial elastic compression occurs).
Now that I've taken the time to type this, I would agree with BigH - this is not likely a problem. If there is no additional loading and the fill has been in place for several years, the remaining settlement potential is likely to be negligable (sp).
Good luck.
f-d
¡papá gordo ain’t no madre flaca!
RE: Settlement of Existing Fill
are you sure about the correctness of your statement:
"Assuming that the natural moisture content is noticably less than the liquid limit, there is a degree of pre-consolidation that has occurred since the fill was place"
It is the plasticity limit that , upon cpmarison with moisture content, can give you indication on the preconsolidation state of the soil and not the liquid limit (LL). The plasticity index is calculated (LL-PL) and that can give indication on the compressibility of the soil before loosing its matrix structure.
RE: Settlement of Existing Fill
Now that I've said all of this, if it's a critical project, I'd do an odometer test.
f-d
¡papá gordo ain’t no madre flaca!