Sheet Pile Retaining Wall 3

[dik]

Doing a prelim design for a sheet pile wall with walers and approx 10' embedment in highly plastic clay (firm)... A real geotekkie will be involved with the final design. The excavation is about 35' deep...Looking at using a friction angle of 5 degrees and a c value of 2500 psf... do these values look way out of whack? Thanks in advance...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[GeoPaveTraffic]

How long with the excavation be in place? If the excvation is open very long, then the cohesion value could be a little high. Also, I would just use the 2,500 and ignore the phi as it really isn't going to make much difference over that depth.

Mike Lambert

 

[dik]

a few months... can try using 2000 psf and zero degrees... just writing up an SMath program, now...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[GeoPaveTraffic]

For one or two months, that cohesion may be ok. But with time the material will drain and the cohesion will decrease and the drained phi angel will start to control the design. I expect you will end up with three levels of wales, should be fairly straight foward.

Mike Lambert

 

[dik]

thanks... I don't think you could get this clay to drain with a vacuum cleaner... extremely tight, highly plastic. Even in a drought year, the top 1/2" desiccates. For prelim work, I'll assume c=2000 psf... first waler is up about 8' and embedment is 10' tentatively. Pit is roughly 17'x22'... yup... 3 levels of wales, with about a 3' cantilever at the top... so far great educated guess...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[GeoPaveTraffic]

At that size pit, I expect that you can do it with just walers, no cross or corner baces. Gives the contractor a nice open area to work. Assuming you are working for the contractor, you might want to check with them about where they want their vertical construction joints. Might save you some rework later on possitioning the wales.

Mike Lambert

 

[dik]

Good call... use full moment end connections and +ve and -ve moments are within 'spittin distance' of eachother... The metal cage is the easy part... The walers are W24 size...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[PEinc]

I would also check the design using drained soil properties where c = 0 psf. You never know when the soil will get "tired" and decides it's time to relax.

http://www.PeirceEngineering.com

 

[dik]

Thanks... I don't think our highly plastic clays ever drain... water is held so tightly that you can have it as a supercooled liquid at -40C. I'll take a gander to see what the outcome using 1000 psf.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[EireChch]

Why consider 5 degrees of phi in the undrained condition?

Additionally, ff the CLAY is loaded then there will be an increase in pore pressure which is the undrained condition, it will eventually dissipate to the drained condition.

 

[dik]

I'll take a gander at it with phi=0... I'll check with a local geotekkie, but I don't think our clays ever reach a drained condition; they are just too impervious.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[fattdad]

the drained friction angle is more likely in the 20's - phi'
The undrained friction angle is likely zero - phi
The drained cohesion (for design) should be taken as zero - c'
The undrained cohesion is the more critical strength value for short-term conditions. Seems you are using 2,500 pdf - Su

Check both.
Whether water can flow out of it does not relate to drained or undrained strength.

When walers are used, convention would increase the Rankine earth pressure by 30 percent and convert the triangle to a rectangle.

f-d

ípapß gordo ainÆt no madre flaca!

 

[dik]

Thanks Fattdad... didn't know that, I didn't figure our clays would ever be in a drained condition. Will check both criteria and will be vetted by a geotekkie, anyway.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik