Soil-Foundation Friction Angle (Friction Angle for Foundation Surface)

[CWEngineer]

I am trying to get some clarification regarding the Soil-Friction Angle (Friction Angle for Foundation Surface). Have seen different calculations from the different sources, for example NavFac 7.2 - Table 1 (and other sources) uses a friction factor of tan (delta), with no Safety Factor. Coduto, uses mu_allowable = mu/F, where F = 1.5 or 2 and mu = tan (0.7*phi). Have seen suggestions to use (tan(dela))/2, where 2 is the safety factor.

Appreciate your guidance in trying to clarify the friction angle for foundation surface.

Thanks

 

[Ron]

Others might disagree, but I would use the angle of internal friction (phi) as it is and apply a safety factor to the system of its use. For instance, if you are doing slope stability, use an overall safety factor for the stability of the slope, with consideration of other factors, not just the phi angle used in your calcs.

 

[CWEngineer]

I am looking into this in terms of the soil-foundation friction underneath the footing of a concrete retaining wall or concrete U-channel.

 

[DaveAtkins]

For the coefficient of friction to resist sliding, I use the tangent of the angle of internal friction, divided by 1.5.

DaveAtkins

 

[GeoPaveTraffic]

I use tan(2/3*phi) as the friction angle between the foundation and the soil. If you are looking at plane in the soil, such as with a shear key, then I would use tan(phi).

With either analysis, an appropriate factor of safety should be used.

Mike Lambert