I am a geologist and need some engi

[huey6367]

I am a geologist and need some engineering assistance regarding granular soil and their depth. I know fine grained soils (clay) becomes hard (increased consistency) with an increase in depth due to a process called gravitational compaction. What I am interested in knowing is there something that tells me what happens to granular soil with an increase in depth. I know I reside in a karst area (Florida) so I don't need to know that the effects of karst on soil will cause the granular soil to become loose. What I am getting at is, do granular soils, in the absence of karstic effects, become more dense/compact with an increase in depth. Is there a technical paper that would support this? The purpose of this is for potential litigation events that are possible. I am not an engineer, I am a geologist. It would appear sensible that granular soils would become more dense/compact with an increase in depth due to the load of the overlying soil but like all things in litigation, if it's not written down, it doesn't exist. Also, do the shape of the granular particles have an effect on the compaction (angular v. rounded)?

Any information you may provide is appreciated.

 

[dik]

To me, fine grained soils are generally sand. Silt and clays particle size will pass through a 200 mesh seive and are 'smaller than fine'. In these environs, clay particles can have a thickness of a few angstroms, only a few molecules thick. They typically have an electrical charge on the surfaces that 'bind' the polar water molecule. Other than the top few inches, they do not 'dry' out. Soils of a particular type vary all over the world.

If litigation is pending, you really need a good geotekkie familiar with the area. If it's a soil issue, you need to be 'more up to speed'. If not, you could really 'get hurt' in court. Some engineers on this site are from the Florida area and may be able to offer their services or recommendations.

Dik

 

[oldestguy]

dik provides some insight. However, if there is legal action needed, I'd bring an experienced licensed geotech. While an increase in density (not compaction by the way) does happen, but there are other factors that generally are present, such as how the material was placed, etc. As to a reference verifying this greater density effect with depth, I'd place that "statement" in the same common knowledge category as "why is air denser near the earth as compared to 3,000 feet up?" That's not in a book either.

 

[dik]

because it has 3000' of air 'on top of it'? Thanks OG...

Dik

 

[fattdad]

what do you mean by, "Depth?" In the upper 100 ft or so, I would not rule out having loose sands, even if they are under confinement. Inter-granular contact may be all that's needed to support the grains, even though they are loose. Not so much with clay.

What does happen with coarse-grained soils is their elastic properties (i.e., modulus) increase with depth. So, they may remain loose, but the stiffness increases.

One problem in identifying loose soils at depth is the soils are influenced by the drilling/sampling. So, if they are auger holes below the water table, you may actually have a distorted view of the density - or lack thereof.

(After working 8 years as a field geologist, I went to graduate school and became an engineer. Best thing I ever did, professionally.)

f-d

ípapß gordo ainÆt no madre flaca!

 

[PEinc]

dik, according to Terzaghi & Peck's Soil Mechanics in Engineering Practice, 2nd edition, 1967, page 40, fine grained soils are considered to be silts and clays where the soil particles pass the No. 200 sieve (0.074 mm). Fine-grained soils are divided into three groups: inorganic silts (M), inorganic clays (CL), and organic silts and clays (O).

http://www.PeirceEngineering.com

 

[dik]

PEinc... thanks, didn't know that... my error. I thought fine grains were sands...

Dik