Estimating Consolidation in Fine Grained Soils without Oedometer Test 4

[geojosh84]

This is a very broad question, so please go easy on me. I currently work at a geotech firm that mainly uses corrected SPT resistances corresponding with index properties (i.e. atterbergs, moisture contents, gradation, etc.) for giving foundation recommendations. We predominantly practice is the coastal region, so SPT generally will suffice for the coarse grained soils encountered. Sometimes we encounter clays and silts, especially if we venture into the piedmont regions to the west of us. We do not have an oedometer to determine consolidation characteristics of fine grained soils, therefore I generally just look at the atterberg limits and natural moisture contents relative to a structures zone of influence to make judgements. I will also use a pocket penetrometer and a torvane in spoon samples and or test pit walls sometimes as well. Additionally, most clients do not want to pay for consolidation testing for small to medium size commercial projects. I would like to know if there is any way ESTIMATE consolidation without running an oedometer on a shelby sample? Thank you in advance.

J

 

[oldestguy]

The WEB site vulcanhammer.net has a lot of soil mechanics publications free for download. The Navy Manuals NAVFAC DM7 series may help.. In my old version in Section 8, Consolidation tests they quote the Terazghi and Peck and the Nishida estimates based on LL and water content. Estimates of preloading also there.

 

[geojosh84]

oldestguy, thank you!

 

[oldestguy]

In case you have not heard of this paper, I used to work for B.K Hough, a former Cornell prof. This paper had some controversy by Peck and others, but was checked out by California DOT and found to be pretty good most of the time, except under estimating settlements when high water table.

B.K. Hough paper August 1959 ASCE Paper number 2135 of SM 4

“SOIL MECHANICS AND FOUNDATION DIVISION of ASCE”

“COMPRESSIBILITY AS THE BASIS FOR SOIL BEARING CAPACITY”

He set this up based o blow count for most soils. I have used it a lot.

If you can find a copy of the second edition of his text "Basic Soil Engineering", Ronald Press, that has the scoop, but presented more convservatively.

 

[oldestguy]

Hough had a new term he called BEARING CAPACITY INDEX. which is (1+e)/Cc

That then is found by his charts, I did a Google search for BEARING CAPACITY INDEX and many places came up. I down loaded one and I see his method is in it.

http://onlinepubs.trb.org/onlinepubs/nchrp/nchrp_rpt_651Appendixh.pdf

 

[SlideRuleEra]

Here are low-cost copies of the book oldestguy recommended. Be sure to check, not all may the the second edition (published 1969).
Note: I have no connection with either the book or the sellers. Just have a knack for finding things on the internet.

1. "Basic Soils Engineering", B.K. Hough

2. "Basic Soils Engineering", B.K. Hough

3. "Basic Soils Engineering", B.K. Hough

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[fattdad]

if the natural water content is near the liquid limit, the soil is likely close to normally consolidated. If the natural water content is less, then there is some amount of overconsolidation.

Su/P can be estimated from the pocket penetrometer (or torvane) and a good guess on density (or the density from a Shelby tube). If your ratio of Su/P is much different than 0.2 or 0.25 you are dealing with some preconsolidation. When you get to the depth that Su/P is close to 0.2 or 0.25, you are likely normally consolidated.

Cc is obtained through correlations to liquid limit. In-situ void ratio is a bit of a problem, but can be estimated through guessing specific gravity and knowing water content - I mean if you are dealing with consolidation, it's mostly likely that the water content will be close to saturation. So, solve the block diagram.

Cr is often 1/10th of Cc. (recall you just got a sense of Pp-Po.)

C-alpha is correlated to water content.

Run the numbers!

f-d

ípapß gordo ainÆt no madre flaca!

 

[geojosh84]

Thanks everyone. One day years from now I hope to reciprocate the same experience to other green engineers as y'all do for me!

 

[BigH]

Hough's Bearing Capacity Index typically called the compression ratio now . . . perhaps because the word capacity implies shear strength? Recompression Raio, as well. The nice "thing" about the Compression Ratio (Bearing Capacity Index) is that you do not need to know eo. The slope of the "compression" line in a strain-logp plot is Cc/(1+eo).