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Foundation Engineering PYQ – TN TRB Lecturer

11. When the standard penetration test is carried out in a sandy soil below the water table, the water table in the bore hole is always maintained _____ .

[TN TRB 2017: 1 Mark]

Slightly above the ground water level
Slightly below the ground water level
At a depth of ground water level
None of the above

Answer: Option A
Explanation:

As per IS 2131 (1981) Clause 3.2.2, while boring below water table, the water in the borehole shall be maintained at least 1.5 m above the level of the water table.
Hence, when SPT is carried out in sandy soil below the water table, the water table must in the bore hole must be slightly above the ground water level.

12. The degree of disturbance for a soil sample collected from the sampler is usually expressed by _____ .

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Void ratio
Area ratio
Recovery ratio
Consolidation ratio

Answer: Option B or Option C
Explanation:

The degree of disturbance for a soil sample collected from a sampler is expressed by area ratio and recovery ratio.
Area ratio is defined as the ratio of the volume of soil displaced by the sampler tube in proportion to the volume of the sample. Lesser area ratio implies that the cutting edge is sharp and hence the disturbance in collected soil samples is lesser.

A_r =

D₂² – D₁²

D₁²

x 100%

Where,
D₁ – Inside diameter of cutting edge
D₂ – Outside diameter of cutting edge

Recovery ratio (L_r) is defined as the ratio of actual length of sample in the sampler tube to the total length of the sampling tube driven below the bottom of the bore hole.

Lr = 1 – Good recovery
Lr > 1 – Sample is swelled
Lr < 1 – Sample is shrunk

13. The horizontal strain required to produce passive earth pressure condition in a cohesionless soil is _____ .

[TN TRB 2017: 1 Mark]

More
Less
Very less
Less than zero

Answer: Option A

Explanation:

In case of passive earth pressure, the horizontal stress acting on the soil is more than the vertical stress. Hence, horizontal stress is the major stress and vertical stress is the minor stress.
Thus, the horizontal strain in soil is more than the vertical strain.

14. The total vertical settlement of a rigid foundation under a pressure ‘q’ is taken to be _____ times the total vertical settlement at the centre of the flexible foundation. Choose the correct answer from those listed below.

[TN TRB 2017: 1 Mark]

Answer: Option C
Explanation:

Total vertical settlement, S = S_i + S_c + S_s
Where,
S_i – Initial or immediate settlement due to compaction. S_i depends on the flexibility of footing.
S_c – Primary consolidation settlement
S_s – Secondary consolidation settlement

S_i =

qB (1 – µ²)I

E_s

Where,
q – uniform pressure at the base of footing (or) contact pressure intensity
B – least lateral dimension of footing
µ – Poisson’s ratio of soil mass

I – Influence factor or shape factor, depending on

Length

Width

ratio of footing

Es – Young’s modulus of soil
Considering circular foundation,
Influence factor for flexible footing at center, I_f = 1.0
Influence factor for rigid footing, I_r = 0.8
Thus, the ratio of total vertical settlement of a rigid foundation (S_r) to the total vertical settlement at the centre of the flexible foundation (S_f) is,

S_r

S_f

I_r

I_f

0.8

1.0

⇒

S_r

S_f

= 0.8

15. Relationship between settlement (S_f) of a foundation width (B_f) and settlement (S_p) of test plate width (B_p), as per as Terzaghi and Peck is concerned, is _____ .

[TN TRB 2017: 1 Mark]

S_f S_p
= {
B_p (B_p + 0.3) B_f (B_f + 0.3)
}²
S_f S_p
=
B_p² B_f²
S_f S_p
= {
B_f (B_p + 0.3) B_p (B_f + 0.3)
}²
S_f S_p
= {
B_p + 30 B_f + 30
}²

Answer: Option C
Explanation:
Nominal length of chain, l = 30 m
Actual length of chain, l’ = 29.9 m
Measured distance, L’ = 300 m

Thus, correct distance, L =

l₁

l

x L’

⇒ L =

29.9

30

x 300

⇒ L= 299 m

16. The area ratio of core cutter sampler having inner diameter 150 mm and outer diameter 165 mm respectively is _____ .

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17.35%
12.8%
112%
21%

Answer: Option D
Explanation:

Area ratio, A_r =

D₂² – D₁²

D₁²

x 100%

⇒ A_r =

165² – 150²

150²

x 100%

⇒ A_r = 21%

17. For a base failure of a finite slope the depth factor _____ .

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D_f = 1
D_f < 1
D_f > 1
None of the above

Answer: Option C
Explanation:

Let,
H – Height of the slope
D – Depth of failure surface from the top of slope
Depth factor is the ratio of depth of the failure surface to the height of the slope.

D_f =

D + H

H

Toe failure occurs when D_f = 0 and base failure occurs when D_f > 1.

18. The coefficient of earth pressure at rest for a sand having the Poisson’s ratio value of 0.25 is _____.

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Answer: Option C
Explanation:
Coefficient of Earth pressure at rest,

K₀ =

µ

1 – µ

⇒ K₀ =

0.25

1 – 0.25

⇒ K₀ = 1/3

19. Trapezoidal combined footing is specifically adopted when _____ .

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Two column loads are close
The interior column carries more load
Column are close to property line
The exterior column carries more load than the interior column

Answer: Option D
Explanation:
Trapezoidal combined footing is commonly adopted when the load on one column is more than the load on another column.

20. Pickup the incorrect statement on dynamic pile driving formulae from the following.

[TN TRB 2017: 1 Mark]

In Hiley’s formula a number of constants are involved, which are difficult to determine.
The formula do not take into account the reduced bearing capacity of pile when in group.
Dynamic formulae are best suited to coarse grained soils for which shear strength is independent of rate of loading.
Law of impact used for determining energy loss is strictly valid for piles, subjected to restraining influence of the surrounding soil.

Answer: Option D
Explanation:

Law of impact used for determining energy loss is not strictly valid for piles, subjected to restraining influence of the surrounding soil.

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