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Foundation Engineering PYQ – TN TRB Lecturer

      

21. A 600 mm square bearing plate settles by 15 mm in plate load test on a cohesionless soil under an intensity of loading 0.2 N/mm2. The settlement of a prototype shallow footing 1 m square under the same intensity of loading is _____ .

[TN TRB 2017: 2 Marks]

  1. 15 mm
  2. Between 15 and 25 mm
  3. 25 mm
  4. Greater than 25 mm
Answer: Option B
Explanation:
The relationship between settlement of plate (Sp), settlement of foundation (Sf), width of the plate (Bp) and width of the foundation (Bf) in cohesionless soil is,

Sf

Sp

= {

Bf (Bp + 0.3)

Bp (Bf + 0.3)

}2

⇒

Sf

15

= {

1 x (0.6 + 0.3)

0.6 x (1 + 0.3)

}2

⇒ Sf = 19.97 mm ∈ (15,25)
Hence, the correct option is between 15 and 25 mm.

22. A wooden pile is being driven with a drop hammer weighing 20 kN and having a free fall of 1.0 m. The penetration in the last blow is 5 mm. The load carrying capacity of the pile as per engineering news formula is _____ .

[TN TRB 2017: 2 Marks]

  1. 33.33 kN
  2. 66.66 kN
  3. 222.2 kN
  4. 111.1 kN
Answer: Option D
Explanation:
The ultimate load carrying capacity as per Engineering News formula is

Qup =

WH

S + C


Where,
W – Weight of drop hammer = 20 kN
H – Free fall height of hammer = 1.0 m
C – Constant. For drop hammer, C = 2.5 cm
S – Final set = 5 mm

Qup =

WH

S + C

=

20 x 1

0.005 + 0.025

⇒ Qup = 666.67 kN

Thus, safe load carrying capacity, Qap =

Qup

FOS

=

666.67

6

⇒ Qap = 111.11 kN

23.  An excavation is to be made up to a depth of 6 m in cohesive soil having an unit weight of 20 kN/m3, what is the required cohesive strength of clay to keep the sides of earth remains vertical without any support ?

[TN TRB 2017: 2 Marks]

  1. 29.3 kN/m2
  2. 28.9 kN/m2
  3. 30.0 kN/m2
  4. 31.0 kN/m2
Answer: Option C

Explanation:
In a purely cohesive soil, the critical height of an unsupported vertical cut is

hc =

4C

γ

⇒ 6 =

4C

20

⇒ C = 30 kN/m2

24.  Which of the following methods is adopted for drilling bore holes in rocky strata ?

[TN TRB 2021: 1 Mark]

  1. Wash boring
  2. Hand auger
  3. Percussion drilling
  4. Mechanical auger
Answer: Option C
Explanation:
As per IS 1892 (1979),

  • Auger boring – suitable for soft soil and gravelly soil, in which the sides of bore holes can stand unsupported. (Clause 3.6.1)
  • Percussion drilling – suitable for drilling bore holes in boulderous and gravelly strata but not suitable for soil and soft rocks. (Clause 3.6.3)

25.  The soil sampler used to collect undisturbed sample in soft clay is _____ .

[TN TRB 2021: 1 Mark]

  1. Split-spoon sampler
  2. Thin walled sampler
  3. Scraper bucket sampler
  4. Piston sampler
Answer: Option D
Explanation:

  • Thin walled samplers are used to collect undisturbed soil samples. Examples of thin walled samplers are Open-tube sampler, Standard split-spoon sampler, Stationary piston sampler, Rotary sampler, Scraper bucket sampler.
  • As per IS 1892 (1979) Clause 4.2.1.2, split spoon samplers may be used in foundation investigations to collect samples for visual identification and preliminary laboratory tests. This penetration results may be utilized to correlate in-situ properties like density, shear strength and bearing capacity. The sample collected is a disturbed sample.
  • As per IS 1892 (1979) Clause 4.2.1.3, in piston sampler, the piston prevents water and dirt from entering the tube during the lowering operation. It also serves to keep the recovery ratio constant during the punch. Hence the sample collected is an undisturbed sample.

26.  The height of fall of the SPT hammer is _____ .

[TN TRB 2021: 1 Mark]

  1. 750 mm
  2. 600 mm
  3. 650 mm
  4. 800 mm
Answer: Option A
Explanation:

As per IS 2131 (1981) Clause 2.3.1, the height of free fall of hammer in Standard Penetration Test is 75 cm.

27.  The minimum diameter of the test plate used in plate load test is _____ .

[TN TRB 2021: 1 Mark]

  1. 450 mm
  2. 300 mm
  3. 600 mm
  4. 750 mm
Answer: Option B
Explanation:
As per IS 1888 (1982) Clause 3.3, square or circular bearing plates of size ranging from 300 mm to 750 mm are to be used in plate load test.

28.  The value of the coefficient of active earth pressure for pure clay is _____ .

[TN TRB 2021: 1 Mark]

  1. 0
  2. 3
  3. 1/3
  4. 1
Answer: Option D
Explanation:
For pure clay, angle of internal friction, φ = 0

Active earth pressure coefficient, Ka =

1 – sin φ

1 + sin φ

⇒ Ka =

1 – sin 0°

1 + sin 0°


⇒ Ka = 1

29.  The maximum and minimum values of water table correction factors respectively are _____ .

[TN TRB 2021: 1 Mark]

  1. 5 and 0
  2. 1 and 0.75
  3. 1 and 0.5
  4. 1 and 0
Answer: Option C
Explanation:
As per IS 6403 (1981) Clause 5.1.2.4, the value of water table correction factor lies between 0.5 and 1.0.

30.  As per Indian code of practice, the minimum depth of foundation in soil, is _____ .

[TN TRB 2021: 1 Mark]

  1. 1.0 m
  2. 0.5 m
  3. 1.5 m
  4. 0.75 m
Answer: Option B
Explanation:

As per IS 1904 (1986) Clause 7.2, all foundations shall extend to a depth of at least 50 cm below natural ground level.
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