Question

If dry density, water density and specific gravity of solids of a given soil sample are 1.6 g/cc, 1.84 g/cc and 2.56 respectively, the porosity of the soil sample, is.

Answer 1

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Rankine’s Earth Pressure in Cohesive Soil for Active Case

AUGUST 29, 2013 BY ENGINEEERING PROJECTS 0 COMMENTS

Figure 1 shows the Mohr’s circle in which point B indicates the vertical stress and point E represents the active pressure. The circle is tangent to the failure envelope. For this case the relation between Pa and \sigma_v is given by:

 

P_a=K_a\sigma_v-2c\sqrt{K_a}———-(1)

P_a=K_a\gamma z-2c\sqrt{K_a}  ———-(2)  

Where, K_a=\dfrac{1-sin\phi}{1+sin\phi}=tan^245^0-\dfrac{\phi}{2}

In the above equation (2) where z = 0

P_a=-2c\sqrt{K_a}

The negative sign indicates that the pressure is negative and tensile, As a result there would be gap between backfill and wall. The tensile stress decreases with the increasing value of z. When z = zc say Pa=0. Then,

0=K_a\gamma z_c-2c\sqrt{K_a}

Or, 0=\gamma z_c\sqrt{K_a}-2c

2c=\gamma z_c\sqrt{K_a}

Z_c=\dfrac{2c}{\gamma\sqrt{K_a}}———-(3)