Undrained Shear Strength - Granular Soils

Question

Undrained Shear Strength - Granular Soils

nbr1 (Geotechnical)

(OP)

1 Oct 14 07:53

For the purposes of a slope stability analysis (static case only), would a free draining material (eg. clean gravel and/or sand)
have an undrained strength? I often see in reports that the undrained strength is equal to the drained strength.
For example, the following values may be reported:

Drained Phi = 30
Drained C = 0
Undrained Phi = 30
Drained C = 0

Would reporting a value of undrained shear strength be appropriate for this type of material, or should
the drained strength be reported only?

tallguru (Geotechnical) · Answer 1 · 2014-10-01 08:14:04

Use drained. Freely draining ignores the fact that interstitial waters would persist.

dgillette (Geotechnical) · Answer 2 · 2014-10-01 10:09:34

Any soil can have both drained and undrained strength. However, for clean gravel and sand, undrained strength is generally irrelevant to anything but a seismic problem.

nbr1 (Geotechnical) · Answer 3 · 2014-10-01 14:16:05

I understand which value would be used in the analysis. I'm just trying to figure out the proper protocol for reporting strength values.
So, if you reported an undrained strength the same as the drained strength.....would that technically be correct?

Or should you just not report an undrained strength at all?

dgillette (Geotechnical) · Answer 4 · 2014-10-01 14:17:51

I think I would report the undrained strength as "n/a."

GeoPaveTraffic (Geotechnical) · Answer 5 · 2014-10-02 17:06:46

I have always reported the undrained strength as equal to the drained strength for free draining materials.

Mike Lambert

BigH (Geotechnical) · Answer 6 · 2014-10-02 23:04:48

Other than seismic, why is anyone reporting undrained shear strengths of granualar soils (say, k<10-04 m/s)?

Mccoy (Geotechnical) · Answer 7 · 2014-10-05 17:05:57

In Italy, SOP is to use something like Dgillette's n/a.

www.mccoy.it

ebenozen (Geotechnical) · Answer 8 · 2014-10-08 20:20:18

RE: Undrained Shear Strength - Granular Soils

ebenozen (Geotechnical) 8 Oct 14 20:20

BigH did you mean k>10-04 m/s?

BigH (Geotechnical) · Answer 9 · 2014-10-09 06:33:02

Yeah - I guess - always get mixed up when dealing with decimals - I am looking at numbers bigger than 10-4 (or so . . .)

Come Join Us!

Posting Guidelines

Related Projects

Jobs

Undrained Shear Strength - Granular Soils