Unit weight of silty sand with gravel

[GeoGrouting]

For till like materials (23% sub-rounded gravel, 43% sand of mainly fine grained and 33% fines) with SPT of about 50, how could one estimate the typical unit weight values.

 

[YannisChasiotis]

Why not use ?=18 kN/m3 ???

 

[fattdad]

I'm going for 21. Seriously, I'd bet a well-compacted, well graded "till" like soil would easily have a moist unit weight in the neighborhood of 135 pcf.

To the OP, local experience and judgement is the best method, if you don't have a bulk sample. Then again, you can always take your nuke gauge on a field trip.

f-d

¡papá gordo ain’t no madre flaca!

 

[PEinc]

I'm with fattdad on this one.

http://www.PeirceEngineering.com

 

[Ron]

I agree with FD that the unit weight could be that, just keep in mind that your SPT in this material might be a bit misleading (on the high side) because of the high gravel content.

 

[BigH]

Well, one could always take the "core" from the split spoon and so a unit weight determination . . . . No more crude that guesstimating. I'd say that you are probably talking more like 140 pcf.

 

[dgillette]

Just remember to distinguish between dry unit weight and moist unit weight (you didn't specify which one you are talking about). A dense broadly graded soil like that could have a DRY unit weight as high as 130 pcf, with MOIST unit weight over 140.

 

[fattdad]

O.K. I'll go to 22. No problem.

f-d

¡papá gordo ain’t no madre flaca!

 

[GeoGrouting]

Would appreciate a reference with regards to

fattdad (Geotechnical) 27 May 10 8:43
I just want to clear up the passive pressure "calculation" presented by "fixedearth."

Given Kp, the "potential" passive pressure is determined by Kp*Gamma*A*Cp (citing Brinch-Hansen), where
Kp=tan^2(45+phi/2)
Gamma=unit weight (you get to determine whether to use moist or bouyant)
A=surface area of the embedded pier
Cp= arching coefficient, typically taken as phi/10

 

[fattdad]

I think this is the correct citation.

Brinch Hansen, J., The Ultimate Resistance of Rigid Piles Against Transversal Forces, Geoteknish Institute Bulletin No. 12, Copenhagen, 1961.

The B-H citation provides for a value that you can use to increase the passive reaction. This value is related to the friction angle. J. M. Duncan noticed that this value is about equal to phi/10 and that's what he taught me in grad school. I don't have a copy of the orignal B-H citation so I'm going from notes.

Good luck in your search. Interlibrary loan can be your friend!

f-d

¡papá gordo ain’t no madre flaca!

 

[PEinc]

Why not just use a Coulomb passive earth pressure coefficient with some wall friction? It's easier than searching for a obscure, 1961 reference. There's been a lot of wall research done since 1961.

http://www.PeirceEngineering.com

 

[fattdad]

(not sure if this is directed at me. . . I use the Brinch-Hansen passive pressure coefficient on laterially loaded piles because it's correct, makes sense, consistent with my education and as advised by J. Michael Duncan. Not sure how wall friction has anything to do with the subject of laterially loaded single piles, but I have methods to account for wall friction also. That said, this whole sidebar has nothing to do with the OP.)

f-d

¡papá gordo ain’t no madre flaca!

 

[PEinc]

In his last response, the OP (GeoGrouting) did bring up passive pressure and Kp. Therefore, the sidebar is his. However, to me, it is a bit unclear whether his sidebar is about foundation piles, drilled piers, or soldier beams. Based on the mention of Kp, I assume the sidebar is about soldier beams.

When I mentioned "wall friction," I was referring to friction between the ground and the embedded portion of the soldier beam or sheet piling (which is part of the wall). I often use a "wall friction" angle of phi/2 when calculating Coulomb earth pressure coefficients. Rankine coefficients are too conservative. Some think Coulomb coefficients are unconservative. However, in designing and building a few thousand excavation support walls and sheet pile bulkheads using Coulomb earth pressure coefficients, I've never had a problem with passive resistance. I'm not saying anyone or any method is incorrect.

http://www.PeirceEngineering.com