Lateral earth pressures from drained cohesive materials

[JCGS]

Hi

I had a graduate engineer come to me earlier with a query that I didnt immediately know the answer to.

The problem refers to an existing cut slope standing up at 85 degrees i.e. near vertical over a 2m high section, flattening off to around 35 degree after this. Doing some pseudo backanalysis/common sense checks we came up with some drained parameters of c'=5 and phi =27 degrees. Its crappy silty gravelly fill most likley uncontrolled.

So. The client wishes to put a retaining wall half way up the slope at about 2-2.5m.

If you try and use the normal coulomb equations for ka, the equation falls over as the slope above the proposed wall is steeper than the angle of friction assumed, and subsequently you cant therefore use ka in the formula 2sqrt[ka*(1+cw/c')] to add the effects of the cohesion in the soil....

Does anyone have any design charts, papers, comments on this seemingly simple problem ??.

Please keep it practical - I know the temptation to delve into unsaturated soil mechanics will be difficult to resist !!!

Cheers

 

[Arizona3106]

Similar thread here:

http://www.eng-tips.com/viewthread.cfm?qid=202767

 

[fattdad]

for long-term performance, use the drained friction angle and ignore cohesion.

That's the only approach I take. There are too many wetting and drying cycles that will occur over the next 50 years that will fatiegue the cohesion.

f-d

¡papá gordo ain’t no madre flaca!