# Calculate the shear strength in terms of effective stress soil on a plane within a saturated soil mass at a point where the total normal stress is 295

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Calculate the shear strength in terms of effective stress soil on a plane within a saturated soil mass at a point where the total normal stress is 295 kPa and pore water pressure is 120 kPa when c’ = 12 kPa and angle of internal friction is 30°. (take tan30 = 0.578)

1. 75.68 kPa
2. 113.15 kPa
3. 135.64 kPa
4. 85.06 kPa

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Correct Answer - Option 2 : 113.15 kPa

Concept:

Shear strength of soil:

Shear strength of the soil is the capacity of soil to resist shearing stresses.  It can be defined as the maximum value of shear stress that can be mobilized within a soil mass. If this value exceeded by the shear stress on any plane or a surface at a point, failure will occur in soil because of the movement of a portion of the soil mass along that particular plane. The soil is then said to fail in shear.  Therefore, shear strength generally represented the strength of the soil.

Shear strength of soil is given as:

$\tau$ = C + $\bar \sigma$ tan ɸ

$\tau$ = Shear  strength of the soil

C = Cohesion of the soil

ɸ = Angle of internal friction of the soil

$\bar \sigma$ = Effective stress acting on the soil at a point

Calculation:

$\begin{array}{l} \bar \sigma = \sigma - u\\\bar \sigma = 295 - 120 \end{array}$

$\bar \sigma$  = 175 kN/m2

C = 12 kN/m2

ɸ = 30°

$\tau$ = 12 + 175 tan 30°

$\tau$ =  113.15 kN/m2