### Soil Mechanics - Seepage of Soils

1. An upward hydraulic gradient I of a certain magnitude will initiate the phenomenon of boiling in granular soils. The magnitude of this gradient is

(a) 0 ≤ i ≤ 0.5

(b) 0.5 < i < 1.0

(c) i ≈ 1

(d) 1 < i < 2 (IES 1996)

2. For a soil, given that porosity(n) = 45% and G = 2.65. Critical gradient will be equal to

(a) 1

(b) 2.01

(c) 1.11

(d) 0.9

3. The specific gravity and insitu void ratio of a soil deposit are 2.71 and 0.85 respectively. The value of the critical hydraulic gradient is

(a) 0.82

(b) 0.85

(c) 0.92

(d) 0.95 (GATE 2002)

Hint:

4. In loose deposit of cohesionless soil with void ratio e = 0.67 and specific gravity of soil solids as 2.67, the critical hydraulic gradient would be

(a) 0.1

(b) 0.5

(c) 1.0

(d) 1.5 (AMIE Summer 98)

5. A coarse grained soil has void ratio = 0.70 and specific gravity = 2.69. The critical hydraulic gradient for quick sand condition is

(a) 0.85

(b) 0.89

(c) 0.94

(d) none of these (AMIE Winter99)

6. For a soil void ratio = 0.7 and specific gravity of solids 2.7, the head required to cause quick sand over a column of 5 m high sand will be

(a) 3.5

(b) 4.5

(c) 5.0

(d) 9.0 (IES 1992, 2000 type)

Hint:

7. If the critical hydraulic gradient of a soil is 1 and its specific gravity is 2.7, then the void ratio will be

(a) 0.58

(b) 0.7

(c) 1.7

(d) 2.7 (IES 1993)

8. Consider the following statements

1. Hydraulic gradient required to initiate quick sand condition is independent of the ratio of volume of voids to volume of solids in a soil mass.

2. Initiation of piping under hydraulic structures can be prevented by increasing the length of flow path of water

3. Seepage pressure is independent of the coefficient of permeability.

(a) 1,2 and 3 are correct

(b) 1 and 2 are correct

(c) 1 and 3 are correct

(d) 2 and 3 are correct (IES 1993)

9. A uniform sand stratum 2.5 m thick has a specific gravity of 2.62 and a natural void ratio of 0.62. The hydraulic head required to cause quick sand condition in the sand stratum is

(a) 0.5 m

(b) 1.5 m

(c) 2.5 m

(d) 3.5 m (IES 1995)

10. Which one of the following equations correctly gives the relationship between the specific gravity of soil grains(G) and the hydraulic gradient(i) to initiate “quick” condition in a sand having a void ratio of 0.5?

(a) G = 0.5i + 1

(b) G = i + 0.5

(c) G = 1.5i + 1

(d) G = 1.5i – 1 (IES 1997)

**Answers**

1. (c) 2. (d) 3. (c) 4. (c) 5. (d)

6. (c) 7. (b) 8. (d) 9. (c) 10. (c)

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