Shear strength of soil at plastic limit 1

[gesi]

the shear strength of soil at liquid limit is 1.67 kPa and its penetration is 20 mm. It is alleged that the shear strength of soil at plastic limit is about 167 kPa. Why is the penetration of the soil at plastic limit is very variable?

 

[BigH]

Can you rephrase the second question - it doesn't read quite right and want to respond succinctly (for once!!)

 

[fattdad]

I have to agree, there's not enough information to answer this question. The soil type has to be defined (i.e., what's the sand content), the method of a "penetration" test has to be defined, who is alleging what and what is the basis for the allegation, what is the PI, and what is the confining stress? These are just what comes to mind, but as it stands, it's hard to put your question into context. . . .

f-d

¡papá gordo ain’t no madre flaca!

 

[iandig]

One question, who is saying the soils shear strength is 167kPa. I have just been having a conversation [over a completly seperate project] with another engineer in our office over the likley shear strength of a soil at it's plastic limit, and he showed me a figure based on the liquidity index of a soil. This suggests that a soil at its plastic limit would have a shear strength of around 100 kPa [80 to 120 ish. I don't have a copy of the figure to hand, but the relationship forms a parabolic curve, which compares well to historical data of the drop in shear strength with increasing moisture above the plastic limit.

 

[BigH]

iandig: I have seen the 170 kPa (or 200 kPa) before - see the abstract of a paper in the ASCE Geotech and Geoenvironmental Journal by Sharma(2003):

http://scitation.aip.org/getabs/ser...00129000008000774000001&idtype=cvips&gifs=yes

The actual paper gives pretty good background references with Skempton being involved early along with Wroth. Of course, in 2005, there was some dissent and closure by the authors.

 

[dgillette]

1.67 kPa is only 35 psf. I suspect a decimal got slipped.

 

[BigH]

1.67 kPa is the "Su" value at liquid limit - most suggest that at plastic limit is is 100*Su(LL). How the 1.7 and 170 have come up. The paper by Sharma explains pretty well.