A granular soil possesses saturated density of 20KN-m3- Its effective angle of Internal friction is 35- If the desired factor of safety is 1-5- the safe angle of slope for this soil- when seepage occurs at and parallel to the slope surface- will be

Effective angle of internal friction nbsp; ϕ ' = 35^∘ FOS = γ _sub z cos^2β tanϕγ _sat z cosβ sinβ ⇒ 1.5 = (20 10) z cos^2β tan35^∘20 z cosβ sinβ ⇒ ...

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Foundation Engineering

Infinite Slopes -Dry Cohesionless Soil

A granular so...

Question

A granular soil possesses saturated density of $20 K N / m^{3}$ . Its effective angle of Internal friction is $35^{\circ}$ . If the desired factor of safety is 1.5, the safe angle of slope for this soil, when seepage occurs at and parallel to the slope surface, will be

25^{\circ}

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23^{\circ}

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20^{\circ}

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13^{\circ}

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Solution

The correct option is D $13^{\circ}$
Effective angle of internal friction

$ϕ^{'} = 35^{\circ}$

$F O S = \frac{γ_{s u b} z c o s^{2} β t a n ϕ}{γ_{s a t} z c o s β s i n β}$

$\Rightarrow 1.5 = \frac{(20 - 10) z c o s^{2} β t a n 35^{\circ}}{20 z c o s β s i n β}$

$\Rightarrow 1.5 = \frac{1 t a n 35^{\circ}}{2 t a n β}$

$t a n β = \frac{t a n 35^{\circ}}{3}$

$\Rightarrow β = {13.138}^{\circ} = 13^{\circ}$

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A granular soil possesses saturated density of 20KN/m3. Its effective angle of Internal friction is 35∘. If the desired factor of safety is 1.5, the safe angle of slope for this soil, when seepage occurs at and parallel to the slope surface, will be

The correct option is D 13∘Effective angle of internal friction ϕ′=35∘ FOS = γsub z cos2β tanϕγsat z cosβ sinβ ⇒1.5=(20−10) z cos2β tan35∘20 z cosβ sinβ ⇒1.5=1 tan35∘2 tanβ tanβ=tan35∘3 ⇒β=13.138∘=13∘

A granular soil possesses saturated density of $20 K N / m^{3}$ . Its effective angle of Internal friction is $35^{\circ}$ . If the desired factor of safety is 1.5, the safe angle of slope for this soil, when seepage occurs at and parallel to the slope surface, will be