Engineering Questions with Answers - Multiple Choice Questions

# Shallow Foundations – Mat or Raft Footing

1 - Question

The foundation that is used when the soil mass is sufficiently erratic?
a) Strap footing
b) Combined footing
c) Mat footing
d) Rectangular combined footing

Explanation: Mat footing is used where the soil contains compressible lenses or the soil is sufficiently erratic so that the differential settlement would be difficult to control.

2 - Question

Usually, rafts are designed as _________
a) Reinforced slabs
b) Reinforced concrete flat slabs
c) Ordinary concrete slab
d) Inverted flat slabs

Explanation: Ordinarily, rafts are designed as reinforced concrete flat slabs using heavy beams.

3 - Question

The weight of the raft is not considered in the structural design, because ___________
a) Weight is carried by subsoil
b) Raft does not remain contact with soil
c) The weight is transferred to column
d) All of the mentioned

Explanation: The weight of the raft is not considered in the structural design because it is assumed to be carried by directly by the subsoil.

4 - Question

If a maximum settlement of 50 mm is permitted for a raft, the differential settlement must not exceed ___________
a) 30 mm
b) 10 mm
c) 20 mm
d) 25 mm

Explanation: A raft may undergo large settlement without causing harmful differential settlement. For this reason, almost double settlement of that permitted for footing is acceptable for raft. Therefore if a maximum settlement of 50 mm (2 in) is permitted for a raft, the differential settlement is not likely to exceed 20 mm (0.75 in).

5 - Question

The net ultimate bearing capacity for raft may be determined by __________
a) Skempton’s equation and Terzaghi’s equation
b) Darcy’s equation
c) None of the mentioned
d) All of the mentioned

Explanation: The net ultimate bearing capacity may be determined from both Skempton and Terzaghi’s equation as given below:
i) Skempton’s equation: q nf = 5 [1 + 0.2D/B ] [1 + 0.2B/L]c
ii) Terzaghi’s equation: q nf = 5.7[ 1 + 0.3B/L]c.

6 - Question

In raft footing, if the C.G of the load coincide with the centroid of the raft, the upward load is considered as ___________
a) Non uniform pressure
b) Uniform pressure
c) Excess pressure
d) None of the mentioned

Explanation: If the Center of gravity of the load coincides with the centroid of the raft, the upward load is regarded as a uniform pressure, which will be equal to the downward load divided by the area of the raft.

7 - Question

Raft is subdivided in to series of beams to establish __________
a) Shear failure and Moment diagrams
b) Pressure distribution
c) None of the mentioned
d) All of the mentioned

Explanation: The raft is subdivided into a series of continuous beams (strips) centered on the appropriate column rows to establish shear failure and moment diagram.

8 - Question

The penetration resistance N for designing of raft should be taken at ___________ intervals.
a) 50 cm
b) 60 cm
c) 75 cm
d) 20 cm

Explanation: The penetration resistance N values should be taken at 75 cm intervals for a depth equal to width of the raft, below the base of the raft.

9 - Question

If the penetration resistance N is less than 5, which of the following measures can be adopted?
a) Using piles and piers and Compacting sand
b) Using inverted flat slab
c) None of the mentioned
d) All of the mentioned

Explanation: If N is less than 5, sand should be compacted by artificial means to rise N above 10, or else piles or piers should be used.

10 - Question

The net pressure can be calculated for raft having width greater than ___________
a) 6 m
b) 20 cm
c) 30 cm
d) 4 m