Engineering Questions with Answers - Multiple Choice Questions

# Seepage Pressure and Upward Flow – 2

1 - Question

The critical hydraulic gradient ic in terms of specific gravity G and voids ratio e is given by ______
a) Ge
b) G/e
c) G−11+e
d) G+11−e
Explanation: The critical hydraulic gradient ic is given by, ic=γ′γw γ′=G−11+eγw ∴ ic=G−11+e.

2 - Question

The critical hydraulic gradient ic is unity when the specific gravity G=2.67 and voids ratio e is ______
a) 0.67
b) 0.33
c) 0.43
d) 0.80
Explanation: Given, specific gravity G=2.67 critical hydraulic gradient ic=1 The critical hydraulic gradient ic is given by, ic=G−11+e 1=2.67−11+e ∴ e=0.67.

3 - Question

A coarse-grained soil has a voids ratio of 0.66 and specific gravity G of 2.65. What will be its critical hydraulic gradient?
a) 0.99
b) 0.88
c) 0.77
d) 0.66
Explanation: The critical hydraulic gradient ic is given by, ic=G−11+e ic=2.65−11+0.66=0.99.

4 - Question

If a soil has a submerged unit weight of 10.69 kN/m3, what will be its critical hydraulic gradient?
a) 1.09
b) 0.88
c) 1.77
d) 1.66
Explanation: Given, γ’=10.69 kN/m3 The critical hydraulic gradient ic is given by, ic=γ′γw ic=10.699.81 ∴ ic=1.09.

5 - Question

Calculate the height of water table rise in soil mass from a sand stratum of 12m deep from ground level, at which the effective pressure is zero. The water percolates through a soil mass of thickness 5m. The γsat=18.6 kN/m3 and γw=9.81 kN/m3. a) 7.68m
b) 9.48m
c) 5.24m
d) 10m
Explanation: Given, Thickness of soil mass=12m water percolates through a soil mass of thickness 5m γsat=18.6 kN/m3 γw=9.81 kN/m3 the effective pressure at sand stratum becomes aero, σ’=zγsat-hwγw ∴hw= zγsat/γw hw=5*18.6/9.81=9.48m.

6 - Question

Water is flowing at a rate of 0.04 m3/s in a soil sample of 12m thick and cross section of 50m2. The coefficient of permeability is 1.6*10-3m/s. What will be the seepage pressure?
a) 50.76 kN/m2
b) 52.34 kN/m2
c) 55.34 kN/m2
d) 58.86 kN/m2
Explanation: Given, Discharge q=0.04 m3/s z=12m Area A=50 m2 coefficient of permeability k=1.6*10-3m/s the hydraulic gradient i is given by, i=q/(kA) i=0.04/(50*1.6*10-3) i=0.5 ∴ ps =iγwz ps =0.5*12*9.81 ∴ ps =58.86 kN/m2.

7 - Question

Water is flowing at a rate of 0.04 m3/s in a soil sample of 12m thick and cross section of 50m2. The coefficient of permeability is 1.6*10-3m/s. What will be the seepage force?
a) 2943kN
b) 3453kN
c) 2454kN
d) 2443kN
Explanation: Given, Discharge q=0.04 m3/s z=12m Area A=50 m2 coefficient of permeability k=1.6*10-3m/s the hydraulic gradient i is given by, i=q/(kA) i=0.04/(50*1.6*10-3) i=0.5 The seepage force J is given by, J= iγwzA J=0.5*12*9.81*50 ∴ J=2943kN.

8 - Question

Water is flowing at a rate of 0.04 m3/s in a soil sample of 12m thick and cross section of 50m2. The coefficient of permeability is 1.6*10-3m/s. What will be the seepage force per unit volume?
a) 4.9 kN/m3
b) 3.9 kN/m3
c) 4.1 kN/m3
d) 3.2 kN/m3
Explanation: Given, Discharge q=0.04 m3/s z=12m Area A=50 m2 coefficient of permeability k=1.6*10-3m/s the hydraulic gradient i is given by, i=q/(kA) i=0.04/(50*1.6*10-3) i=0.5 The seepage force per unit volume j is given by, j=iγw j=0.5*9.81

9 - Question

Water is flowing at a rate of 0.04 m3/s in a soil sample of 12m thick and cross section of 50m2. The coefficient of permeability is 1.6*10-3m/s. The submerged unit weight γ’=9.59 kN/m3. Calculate the effective pressure if flow is in upward direction. a) 50.76 kN/m2
b) 52.34 kN/m2
c) 55.34 kN/m2
d) 56.22 kN/m2
Explanation: Given, Discharge q=0.04 m3/s z=12m Area A=50 m2 coefficient of permeability k=1.6*10-3m/s the hydraulic gradient i is given by, i=q/(kA) i=0.04/(50*1.6*10-3) i=0.5 ∴ The effective pressure is given by σ’=zγ’-izγw σ’=12*9.59-0.5*12*9.81 σ’=56.22 kN/m2.

10 - Question

A soil has voids ratio of 0.78 and critical gradient at which quick sand condition occurs is 0.94. Calculate the specific gravity.
a) 2
b) 2.5
c) 2.67
d) 2.71
Explanation: Given, Voids ratio e=0.78 critical gradient ic=0.94 ic=G−11+e 0.94=G−11+0.78 ∴ G=2.67.

11 - Question

If a soil has a voids ratio of 0.68 and water percolating through it has a discharge velocity of 1.35*10-2cm/s. Calculate its seepage velocity.
a) 1.35*10-2cm/s
b) 2.35*10-2cm/s
c) 3.34*10-2cm/s
d) 1.05*10-2cm/s
Explanation: Given, Voids ratio e=0.68 discharge velocity of 1.35*10-2cm/s seepage velocity vp=(1+e)ev ∴ vp=(1+0.68)/0.68 * 1.35*10-2 ∴ vp=3.34*10-2cm/s.

12 - Question

If the discharge velocity is 1.35*10-2cm/s and seepage velocity is 3.95*10-2cm/s of water through a soil, then what will be its voids ratio?
a) 0.32
b) 0.43
c) 0.52
d) 0.66
Explanation: Given, discharge velocity v=1.35*10-2cm/s seepage velocity vp=(1+e)ev ∴ vp=(1+e)/ev 3.95*10-2=(1+e)e1.35*10-2 2.6e=1.35 ∴ e=0.52.

13 - Question

Water is flowing at a rate of 0.04 m3/s in a soil sample of 12m thick and cross section of 50m2. The coefficient of permeability is 1.6*10-3m/s. The submerged unit weight γ’=9.59 kN/m3. Calculate the effective pressure if flow is in downward direction.
a) 73.94 kN/m2
b) 152.34 kN/m2
c) 155.34 kN/m2
d) 173.94 kN/m2