1. The study of seepage of water through soil is important for, which of the following purpose?
a) Drainage of soils
b) Stability of slopes
c) Ground water flow towards well
d) All of the mentioned
Explanation: The study of seepage of water through soil is important for the following engineering problem
i. Ground water towards soil and drainage of soil
ii. Calculation of seepage through the body of earth dams, and stability of slopes.
2. Darcy’s law describes the state of flow within individual pores.
a) True
b) false
Explanation: Darcy’s law in no way describes the state of flow within individual pores. Darcy’s law represents the statistical macroscopic equivalent of the Navier-Strokes equations of motion for various viscous flow of ground water.
3. In the definition of the seepage velocity, the cross-sectional area of the voids is taken as _______ to the direction of flow.
a) parallel
b) opposite
c) perpendicular
d) tangential
Explanation: The seepage velocity is defined as the rate of discharge of percolating water per unit cross-sectional area of voids perpendicular to the direction of the flow.
4. The relation between discharge velocity and seepage velocity is ________
a) Vs=Ve
b) Vs=Vn
c) Vs=V/e
d) Vs=V/n
Explanation: Since the discharge is equal,
Q=VA=VsAV
Vs=VA/AV
Since AV/A=VV/V=n
∴ Vs=V/n.
5. Seepage velocity is inversely proportional to hydraulic gradient.
a) true
b) false
Explanation: From Darcy’s law, the discharge velocity is proportional to the hydraulic gradient. Since discharge velocity is also proportional to seepage velocity, we have seepage velocity proportional to the hydraulic gradient.
6. The coefficient of permeability of clean gravel is _________
a) 1*10-6 and smaller
b) 5*10-4 – 1*10-5
c) 1 – 1*10-2
d) 1 and greater
Explanation: The coefficient of permeability of clay, silt and clean coarse sand are 1*10-6 and smaller, 5*10-4 – 1*10-5 and 1 – 1*10-2 respectively.
7. The unit coefficient of permeability is ______
a) cm
b) s
c) cm/s
d) cm/s2
Explanation: Consider velocity in cm/s,
The hydraulic gradient i=(h/L), where both h and L are in cm.
By Darcy’s law,
V=ki
K=v/i
Considering its units,
K=(cm/s)/(cm/cm)
∴ K=(cm/s)
Hence, coefficient of permeability has same units as velocity.
8. If the discharge velocity is 4*10-7cm/s and the porosity is 33%, then the seepage velocity will be _______
a) 18*10-7cm/s
b) 12*10-7cm/s
c) 6*10-7cm/s
d) 3*10-7cm/s
Explanation: Given,
discharge velocity V=4*10-7cm/s
porosity n=33%=0.33
seepage velocity Vs=V/n=(4*10-7)/0.33
∴ Vs=12*10-7cm/s.
9. If the soil has discharge velocity is 9*10-7cm/s and the voids ratio of 0.5, then the seepage velocity will be _______
a) 18*10-7cm/s
b) 27*10-7cm/s
c) 16*10-7cm/s
d) 13*10-7cm/s
Explanation: Given,
discharge velocity V=9*10-7cm/s
voids ratio e= 0.5
n=e/(1+e)=0.5/(1+0.5)=0.33
Vs=V/n=(9*10-7)/0.33
∴ Vs=27*10-7cm/s.
10. The velocity of flow is proportional to _________ according to Darcy’s law.
a) effective stress
b) hydraulic gradient
c) cohesion
d) adhesion
Explanation: The Darcy’s law states that the rate of flow is proportional to the hydraulic gradient.
V=q/A=ki
where, V=velocity
i=hydraulic gradient
K= coefficient of permeability.