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saikiran gone General Sponsor
Joined: 22 Apr 2016 Posts: 217
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Posted: Sat Nov 12, 2016 6:31 am Post subject: Angle of internal friction |
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Dear Engineers,
Please explain what exactly angle of internal friction means with practical examples, if possible with images . I can visualize in my mind what is cohesion (c) . But I unable to visualize what is the angle of internal friction (phi).
I know it is related to shear strength property of cohesionless soil . How it will help in resisting the skin friction forces (i.e uplift).I know that cohesion value is more in sands but how it will help in resisting the uplift by skin friction I am not understanding.
Thanks,
Regards,
Saikiran. |
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saikiran gone General Sponsor
Joined: 22 Apr 2016 Posts: 217
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Posted: Tue Nov 15, 2016 6:51 am Post subject: |
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Dear Engineer,
Waiting for experts to comment on the above query.
Thanks,
Regards,
Saikiran. |
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mallan SEFI Regulars
Joined: 17 Mar 2016 Posts: 21
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Posted: Wed Nov 16, 2016 6:06 pm Post subject: |
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Dear Er. Gone,
Im in no way an expert, but would like to contribute to this discussion.
The physical phenomenon involved is basically micro-level interlock between particles of soil.
When two surfaces slide over each other, the friction between them is a function of a co-efficient of friction and the normal force b/w them. In case shear in soils also it is similar, wherein the normal force is replaced by the effective stress in the soil. This is evident from the failure envelope of a triaxial shear graph. http://www.geocities.ws/dominic_trani/paper4j.jpg
This coefficient of friction can be expressed in terms of an angle such that Tan-1 θ = coefficient of friction. This θ is the angle of internal friction.
Angle of internal friction is also equal to angle of repose. The angle of repose of a soil is the steepest angle of descent to which a soil can be heaped without collapsing/slumping. https://en.wikipedia.org/wiki/Angle_of_repose
Now, when the two sliding surfaces are both soil, such as the case of Terzhagi's derivation of shear strength of a soil, then the friction between the surfaces is a function of angle of internal friction, which is cohesive in nature. When the sliding surfaces are of different material such as concrete piles and soil, then angle of adhesive friction should be investigated. In the absence of investigation, it is taken as (2/3) times the angle of internal friction of soil. |
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