Question

The ratio of effective stress to total stress at point ‘A’ given in the figure is ............ 

• A. 0.46
• B. 0.35
• C. 0.52
• D. 0.32

Hint:

Effective stress is the portion of total stress carried by the soil skeleton. It's always calculated as total stress minus pore water pressure.

Answer 1

The Correct Option is A

From the figure, total depth from top to point A = 0.6 m (water) + 0.8 m (soil) = 1.4 m
Saturated unit weight of soil \( \gamma_{sat} = 2.5 \text{ g/cc} = 25 \text{ kN/m}^3 \)
Unit weight of water \( \gamma_w = 9.81 \text{ kN/m}^3 \)
Total Stress at A:
\[ \sigma = \gamma_w \times 0.6 + \gamma_{sat} \times 0.8 = 9.81 \times 0.6 + 25 \times 0.8 = 5.886 + 20 = 25.886 \text{ kPa} \]
Pore Water Pressure at A:
\[ u = \gamma_w \times 1.4 = 9.81 \times 1.4 = 13.734 \text{ kPa} \]
Effective Stress at A:
\[ \sigma' = \sigma - u = 25.886 - 13.734 = 12.152 \text{ kPa} \]
Required Ratio:
\[ \frac{\sigma'}{\sigma} = \frac{12.152}{25.886} \approx 0.46 \]