Question

In a falling head permeability test the initial head of 1.0 m dropped to 0.35 m in 3 hours, the diameter of the stand pipe being 5mm. The soil specimen was 200 mm long and of 100 mm diameter. The coefficient of permeability of the soil is:

• A. 4.86 $\times$${10}^{-5}cm/s$
• B. 4.86 $\times$${10}^{-6}cm/s$
• C. 4.86 $\times$${10}^{-7}cm/s$
• D. 4.86 $\times$${10}^{-8}cm/s$

Answer 1

The correct option is B 4.86 $\times$${10}^{-6}cm/s$

In falling head test, coefficient of permeability

$K=\frac{aL}{At}ln\frac{h_1}{h_2}$

Where,

a = Area of stand pipe

L = Length of soil specimen

A = Area of soil specimen

t = The time interval during which the head falls from $h_{1}to{h}_2$

Thus,

$K=\frac{\frac{\pi }{4}(0.5{)}^2\times 20}{\frac{\pi }{4}(10{)}^2\times 3\times 3600}\times ln\frac{1}{0.35}$

$=4.86\times {10}^{-6}cm/s$