Friction Angle and EFP for Caly soil 1

[rlewistx]

I was trying to determine lateral earth pressure for the soil. I have some pocket penetrometer readings in the logs. I know I need to talk to the geotech to get the lateral earth pressure recommendation but I was wondering for my own education, how does the geotech determine these values? What information from the logs helps establish the value? Is it possible to determine the friction angle of the soil? I am going to use "at rest" values because the wall will be rigid. Would the equivalent fluid pressure be Ko*D where Ko=1-sin(phi)? How does the pocket penetrometer reading help determine the value?

I have searched through my geotech books but haven't found a good discussion on this for clay material.

Thanks for any insight.

 

[jdonville]

rlewistx,

1) Not all test results make it to the logs.

2) Lateral earth pressure depends on unit weight of soil, groundwater conditions and additional loadings. Depending on soil layering and groundwater conditions, the plot of lateral earth pressure may not be linear with depth below the crest of the wall. Additional loadings (say from foundations or live load allowances) may also cause significant nonlinearities in the pressure envelope.

3) Ko is usually simplified to 1-sin(phi), however, this relation can be somewhat low for overconsolidated clays and densified sands. Phi can be determined experimentally from triaxial testing of (relatively) undisturbed samples. Phi can also be estimated based on other index properties of the soil.

4) Assuming a rigid wall, flat backslope and no surcharge loads, the equivalent fluid pressure would be Ko*W, where W is the moist unit weight of the soil.

The following link (

http://www.keystonewalls.com/media/technote.pdfs/eq_fld_prs.pdf)

has a discussion of how the equivalent fluid pressure changes with wall geometry and discusses the limitations of use.

Hope this was helpful,

Jeff


Jeffrey T. Donville, PE
TTL Associates, Inc.

http://www.ttlassoc.com