Engineering Questions with Answers - Multiple Choice Questions

# Permeability – Validity of Darcy’s Law

1 - Question

The coefficient of permeability is equal to velocity of flow when _________
a) hydraulic gradient is equal to one
b) hydraulic gradient is less than one
c) hydraulic gradient is greater than one
d) hydraulic gradient is equal to zero
Explanation: According to Darcy’s law, we have, V=ki When i=1 V=k.

2 - Question

Darcy’s law of linear dependency is valid for only _______ flow conditions in soil.
a) laminar and turbulent
b) laminar
c) turbulent
d) intermediate
Explanation: The linear dependency between velocity of flow and hydraulic gradient is valid only for laminar conditions in the soil.

3 - Question

For Darcy’s law to be valid, the Reynolds number should be ________
a) greater than one
b) less than one
c) equal to one
d) greater than five
Explanation: The Darcy’s law is valid if flow through soils is laminar. The flow will be laminar only if the Reynolds number is less than one.

4 - Question

For flow through soils, the characteristic length in Reynolds number is taken as ________
a) uniformity coefficient
b) coefficient of curvature
c) coefficient of percolation
d) average diameter of the particles
Explanation: The validity if the Darcy’s law is expressed by the Reynolds number in the form, vDaρwηg≤1 Where, Da is the average diameter of the particles.

5 - Question

Darcy’s law in some cases is not valid in ______
a) clay
b) silt
c) fine sand
d) coarse-gravel
Explanation: The flow conditions in clay, sit and fine sand will be laminar, but whereas in the voids of the coarse gravel it will be a turbulent flow.

6 - Question

The critical Reynolds number varies from ________ for validity of Darcy’s law.
a) 0.1-75
b) 75-100
c) 100-175
d) 175-200
Explanation: The Reynolds number is the ratio of inertia to viscous forces. For the validity of Darcy’s law, the critical Reynolds number varies from 0.1-75. The critical Reynolds number is the condition when the flow changes from laminar to turbulent flow.

7 - Question

The linear dependency between velocity of flow and hydraulic gradient exists if effective size of soil _______
a) does not exceed 3mm
b) exceeds 3mm
c) equal to 3mm
d) equal to 5mm
Explanation: In 1892, Allen Hazen concluded that the linear dependency between velocity of flow and hydraulic gradient exists if effective size of soil did not exceed 3mm.

8 - Question

The drainage property of silty clay is ________
a) very good
b) good
c) fair
d) very poor