Consistency on Silty materials 3

[pelelo]

Engineers,

I have noticed in some geotechnical reports that some consultants when they describe silty soils (ML, MH), they do not include the typical consistency as we usually do for sands and clays. Instead they just leave the description with no details.

On the other hand, other consultants, perform UCS tests (either in the lab or using the PP) and based on that, they include in the description the consistency (for example, soft silt or stiff silt). Similar to clay consistency.

I understand silty soils are in a gray area between sands and clays.

What do you think should be the proper way to describe silts in a boring a log?.

Please advise.

 

[GeoEnvGuy]

Consistency of fine grained soils on field logging sheets I have seen from my employers and competitors are based on N or vane shear values. ASTM 2488 describes this as how easily the intact sample is penetrated by thumb or thumbnail.

For silts am I assuming cohesion or not? (Senior engineer says do both analysis anyways)

What I really want to know from my log is if there is low plasticity or no plasticity meaning can they roll a thread and what is the dilatancy reaction if it is rapid or slow.

 

[pelelo]

Thanks for your response.

So if senior engineer said to do analysis both ways, in the logs, would you include the consistency of the silt?, would you include it assuming it as a granular soil (dense, loose, etc) or as a fine grain (clay) soil (soft, hard, medium, etc)?

Or would you just leave it with no consistency at all (just the description e.g very light gray silt)?

 

[MTNClimber]

I've seen engineers use both consistency or relative density. Some say if its non-plastic then relative density should be used. I haven't seen logs that don't say anything to describe the blow counts. I personally just use consistency but could be convinced either way.

 

[geotechguy1]

If it's non plastic, use sand-like terms, if it's plastic, use clay like terms, in my opinion.

ML and MH soils generally plot below the A-Line either because of the mineralogy (i.e. the type of clay particle) or the presence of organics.

The whole terminology we use is honestly very poor and needs to be replaced in my opinion: 'Clays' that plot above the A-Line plot above the A-line because of the mineralogy and likewise with 'Silts' that plot below the A-Line. It's really an indicator of the mineralogy of the particles and the number of them.