Highly organic silts and clays as defined by seismic code.

[CashCabby]

I understand the quantitive definition of organic silt/clay (OL OH) using ASTM 2487-06, but can anybody direct me to a resource that describes what a "HIGHLY organic silt/clay" is vs "organic silt/clay"? IBC 2006, ASCE-7 2005, and FEMA 450 all use the term "highly organic" for seismic site class "F".

 

[jdonville]

http://books.google.com/books?id=1C...=X&oi=book_result&resnum=1&ct=result#PPA68,M1

The reference at the above link suggests that OL/OH/PT soils are "Highly Organic". Perhaps the term "highly organic" means that the behavior of the soil is largely determined by the organic fraction rather than by soil particles (if any), to distinguish from soils that may contain measureable amounts of organics by mass, but behave largely like "normal" silts and clays in terms of limits and phi-c properties.

Jeff

 

[CashCabby]

Thanks Jeff,
The reference in the link is similar to the current ASTM D 2487 (USCS). However, ASTM D 2487 does not distinguish OL and OH as "highly organic", just organic. I recently found a table in DM 7.01 (Table 5)that published properties of orgaic soils with different concentrations of organics. Unfortunately I am having trouble uploading that table for you... It is also published in the Geotechnical Engineers Pocket Handbook. I am just not sure if this is a widely accepted table or not. I haven't had much luck in finding any published properties to compare with, atleast nothing as inclusive as the DM 7.01 table 5.

Scott

 

[jdonville]

CashCabby,

I have a PDF copy of DM7-1, so no worries. Apparently the reference listed in the text is an unpublished (at the time) paper by Ayers and Plum. Perhaps it is in the literature now?

As for how widely it is accepted is an open question. Does the IBC, ASCE and FEMA guidance list DM7.1 or the Ayers/Plum paper as a reference? (Don't know, as I don't have copies of any at my disposal).

It would seem that whomever wrote the guidance into IBC, ASCE-7 and FEMA 450 should be able to provide a reference to where the tem is defined, or provide an explicit definition themselves! You may wish to cite Table 5 as your reference when making the determination of organic vs. highly organic.

Jeff