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Unformatted text preview: 202 *Mohr01: Find the angle of internal friction & of a soil. (Revision: Jan09) The horizontal stress on a soil particle at a depth of 130 ft is & of its vertical stress. If the average unit weight of the intervening soil mass above is 116.4 pcf, and the shear stress on the soil particle’s failure plane is 30 psi, what is the soil’s average angle of friction? Solution: The vertical stress is the major principal stress & 1 and the horizontal stress is the minor principal stress & 3 . The shear stress is related to these two principal stresses via the angle ¡ , which is the angle to the failure plane with respect to the principal stress & 1 . These are related by the equation, 1 3 2 2 sin σ σ σ σ σ σ σ σ τ θ τ θ τ θ τ θ = From this relation, the angle of internal friction is found from ¡ , 2 90 ϕ θ ϕ θ ϕ θ ϕ θ = ° Therefore, ( ) ( )( ) ( ) 2 1 3 2 3 1 1 3 1 0 116 4 130 105 144 1 0 33 105 35 3 105 35 2 30 2 2 2 2 120 2 90 120 90 30 lb ft h . . ft psi ft in...
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 Summer '10
 STAFF
 Force, Stress

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