Permeability of Soils – Part 3
6 questions. Tap an option to check it instantly, then read the solution.
Question 1Medium
The expression for the discharge (Q) through a flow net for isotropic soil is given by:
Answer: A. Q = K · H × (Nf)/(ND)
Discharge through a flow net (isotropic soil): Q = K x H x (Nf/Nd).
Question 2Easy
The force per unit area that must be exerted in order to extract water from the soil is known as:
Answer: C. capillary potential
Capillary (matric) potential = force per unit area to extract water from soil (same as Q12).
Question 3Medium
For a granular soil, with increasing void ratio, the critical hydraulic gradient:
Answer: A. Decreases
Critical hydraulic gradient decreases as void ratio increases.
Question 4Medium
If the specific gravity of the soil is represented by G and the void ratio is e, the hydraulic gradient i is expressed as:
Answer: A. (G-1)/(1+e)
Critical hydraulic gradient ic = (G-1)/(1+e).
Question 5Hard
The viscosity and unit weight of the percolating fluid are reduced to 65% and 95% respectively due to rise in temperature. If other things remain constant the coefficient of permeability will be:
Answer: A. increased by 46%
k2/k1 = 0.95/0.65 = 19/13 -> permeability increases by about 46%.
Question 6Medium
Based on Allen-Hazens experiments, the co-efficient of permeability k (cm/s) is related to the effective size of soil D10 (cm) as (where C is a constant with a value between 100 and 150):
Answer: B. k = C D10²
Hazen's formula: k = C x D10^2, with C between 100 and 150.