# Soil Mechanics Questions and Answers – Secondary Consolidation and Three Dimensional Consolidation – 1

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This set of Soil Mechanics Multiple Choice Questions & Answers (MCQs) focuses on “Secondary Consolidation and Three Dimensional Consolidation – 1”.

1. Even after the excess pore pressure due to consolidation is dissipated, change in void ratio continues and this phenomenon is known as _____________
a) secondary consolidation
b) pre-consolidation
c) under- consolidation
d) normal- consolidation

Explanation: The secondary consolidation occurs at a very slow rate. Even after the excess pore pressure due to consolidation is dissipated, change in void ratio continues and this phenomenon is known as secondary consolidation.

2. Secondary consolidation is also known as __________
a) pre-consolidation
b) secondary compression
c) under- consolidation
d) normal- consolidation

Explanation: Secondary consolidation is also known as secondary compression. During the secondary compression, some of the highly viscous fluids between the point of contact, is forced out from between the grains.

3. There is plastic readjustment of soil particles during _____________
a) pre-consolidation
b) secondary consolidation
c) under- consolidation
d) normal- consolidation

Explanation: During the secondary consolidation, there is relative plastic readjustment of soil particles and of the absorbed water due to the continued stress and progressive fracture of some soil particles.

4. In many soil deposits, the secondary consolidation is neglected.
a) True
b) False

Explanation: In many soil deposits, the secondary consolidation is so small and insignificant that it can be neglected. Also for the secondary consolidation to occur, it takes a lot of time.

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5. Terzaghi’s theory of consolidation is invalid for ________
a) pre-consolidation
b) under- consolidation
c) secondary consolidation
d) normal- consolidation

Explanation: Since the dissipation of the excess hydrostatic pressure does not govern the secondary consolidation, the Terzaghi’s theory of consolidation is in valid as it cannot be used to find the rate of secondary consolidation.

6. Secondary consolidation starts in the range of primary consolidation itself.
a) True
b) False

Explanation: Secondary consolidation starts in the range of primary consolidation itself, although ots magnitude is very small. This is one of the reason why the experimental curve is in agreement with the Terzaghi’s theory up to U=60%.

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7. Secondary compression proceeds linearly with ________
a) root of time
b) square of time
c) logarithm of time
d) cube of time

Explanation: It is often assumed that the secondary compression proceeds linearly with the logarithm of time. It appears as a straight line in the graph in the plot of voids ratio as a function of logarithm of time.

8. Secondary consolidation may not constitute a substantial percentage of total settlement for __________
a) highly organic soils
b) inorganic soil
c) highly micaceous soils
d) gyttja

Explanation: For highly organic soils, highly micaceous soils and some loosely deposited clays, secondary consolidation may constitute a substantial percentage of total settlement.

9. The secondary consolidation is represented by __________
a) $$∆e = -α *⁡\frac{t_1}{t_2}$$
b) $$∆e = -α log_{10}⁡\frac{t_2}{t_1}$$
c) $$∆e = -log_{10}⁡\frac{t_1}{t_2}$$
d) ∆e = α log10⁡t1

Explanation: The secondary consolidation is represented by the equation of,
$$∆e = -α log_{10}⁡\frac{t_2}{t_1}$$
Where α = coefficient representing the rate of secondary compression
t1 and t2 = total elapsed time since load was applied to the soil.

10. For a soil at a given void ratio, the coefficient of compressibility _____________
a) increases with increase in magnitude of consolidating pressure
b) increases with decreases in magnitude of consolidating pressure
c) decreases with increase in magnitude of consolidating pressure
d) decreases with increase in magnitude of hydrostatic pressure

Explanation: For a soil at a given void ratio, the coefficient of compressibility increases with increase in magnitude of consolidating pressure, and hence it should be determined in the laboratory consolidation test for the range of pressure that would be encountered in practice.