# Soil Mechanics Questions and Answers – Consolidation Process – 2

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This set of Soil Mechanics Question Bank focuses on “Consolidation Process – 2”.

1. The delay caused in consolidation by the slow drainage of water out of a saturated soil mass is called as __________
a) hydrodynamic lag
b) hydrodynamic pressure
c) hydrostatic pressure
d) pore pressure

Explanation: The hydrodynamic pressure, hydrostatic pressure and pore pressure are all the same and they represent the pressure that builds up in pore water due to load. The hydrodynamic lag is the delay caused in consolidation by the slow drainage of water out of a saturated soil mass.

2. The reduction in volume of soil which is due to squeezing out of water from the voids is __________
a) effective pressure
c) primary consolidation
d) secondary consolidation

Explanation: The reduction in volume of soil which is due to squeezing out of water from the voids is primary consolidation. Even after the hydrostatic pressure is reduced to zero, some compression of soil takes place and this is known as secondary consolidation.

3. After the hydrostatic pressure is reduced to zero, some compression of soil takes place by the process of _________
a) effective pressure
c) primary consolidation
d) secondary consolidation

Explanation: Even after the hydrostatic pressure is reduced to zero, some compression of soil takes place and this is known as secondary consolidation. During secondary consolidation, some of the highly The effective pressure is the pressure between the soil grains.
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4. Secondary consolidation is also known as __________
a) effective pressure
c) compaction
d) secondary time effect

Explanation: Even after the hydrostatic pressure is reduced to zero, some compression of soil takes place and this is known as secondary consolidation. Secondary consolidation is also known as secondary time effect or secondary compression.

5. If a soil is confined in a consolidometer, then at equilibrium stage, the applied pressure is equal to ____________
a) zero
b) effective pressure
c) total pressure
d) pore pressure

Explanation: If a soil is confined in a consolidometer, under an applied pressure, a final settlement and a voids ratio is reached. At equilibrium stage, the applied pressure is equal to the effective pressure.

6. The virgin compression curve is the curve between _______________
a) voids ratio and effective pressure
b) effective pressure and total pressure
c) effective pressure and pore pressure
d) total pressure and total pressure

Explanation: The virgin compression curve is the curve between voids ratio and effective pressure. 7. The straight portion of the virgin compression curve is given by the empirical formula _______________
a) $$e = e_0*\frac{C_c log_{10} σ’}{σ’_0}$$
b) $$e = \frac{e_0}{\frac{C_c log_{10} σ’}{σ’_0}}$$
c) $$e = e_0-\frac{C_c log_{10} σ’}{σ’_0}$$
d) $$e = e_0+\frac{C_c log_{10} σ’}{σ’_0}$$
Explanation: The straight portion of the virgin compression curve is given by the empirical formula given by Terzaghi is,
$$e = e_0-\frac{C_c log_{10} σ’}{σ’_0}$$ where, e0= initial voids ratio corresponding to the initial pressure σ’0.
e=vids ratio at increased pressure σ’
Cc=compression index.

8. In a semi logarithmic plot, the virgin compression curve becomes
a) straight line
b) parabolic curve
c) hyperbolic curve
d) elliptical curve

Explanation: In a semi logarithmic plot, the virgin compression curve becomes a straight line if the curve is plotted with effective pressure σ’as abscissa and the voids ratio e as ordinate on an arithmetic scale.

9. The compression index is a dimensionless quantity.
a) True
b) False

Explanation: The compression index is a dimensionless quantity. The compression index represents the slope of the linear portion of the pressure-voids ratio curve. It remains constant within a fairly large range of pressure.

10. The compression index is given by _________
a) $$C_c=\frac{e_0-e}{log_{10} \frac{σ’}{σ’_0}}$$
b) $$C_c=\frac{e}{log_{10} \frac{σ’}{σ’_0}}$$
c) $$C_c=\frac{e_0-e}{\frac{σ’}{σ’_0}}$$
d) $$C_c=\frac{e_0}{log_{10} \frac{σ’}{σ’_0}}$$

Explanation: The compression index is given by the expression,
$$C_c=\frac{e_0-e}{log_{10} \frac{σ’}{σ’_0}}$$ ,where e0= initial voids ratio corresponding to the initial pressure σ’0.
e=vids ratio at increased pressure σ’
Cc=compression index.

11. The difference in voids ratio ∆e of initial and increased pressure is given by __________
a) $$∆e=log_{10}\frac{σ’_0+∆σ’}{σ’_0}$$
b) $$∆e=C_c \frac{σ’_0+∆σ’}{σ’_0}$$
c) $$∆e=C_c log_{10} \frac{σ’_0+∆σ’}{σ’_0}$$
d) $$∆e=C_c log_{10} \frac{σ’_0}{σ’_0}$$

Explanation: The difference in voids ratio ∆e of initial and increased pressure is given by,
$$∆e=C_c log_{10}\frac{σ’_0+∆σ’}{σ’_0}, here ∆e=e_0-e.$$

12. The expansion index is a ‘curve’ on semi log plot.
a) True
b) False

Explanation: The expansion index is a fairly straight line on semi log plot. The expansion index is a measure of volume increase due to the removal of pressure. The expansion index is also a dimensionless quantity like the compression index.

13. The expansion index is also known as ___________
a) compressibility index
b) compression index
c) swelling index
d) consolidation index

Explanation: The expansion index is also known as swelling index and is represented by Cs. The expansion curve is a fairly straight line on semi log plot. The expansion index is a measure of volume increase due to the removal of pressure.

14. The expansion curve is given by the expression ___________
a) $$e_0=elog_{10} \frac{σ’_0+∆σ’}{σ’_0}$$
b) $$e_0=e/C_s \frac{σ’_0+∆σ’}{σ’_0}$$
c) $$e_0=e-C_s log_{10}\frac{σ’_0+∆σ’}{σ’_0}$$
d) $$e_0=e+C_s log_{10} \frac{σ’}{σ’_0}$$

Explanation: The expansion curve is a fairly straight line on semi log plot and its expression is given by,
$$e_0=e+C_s log_{10} \frac{σ’}{σ’_0}$$
Where Cs=expansion or swelling index.

15. The equation given by Skempton for compression index for a remoulded sample is ___________
a) Cc=0.009(wL-10%)
b) Cc=0.007(wL-10%)
c) Cc=0.007(wL-20%)
d) Cc=0.007(wL-30%)

Explanation: Skempton conducted consolidation tests on a number of clays from different parts of the world and gave the following expression for the compression index for remoulded sample,
Cc=0.007(wL-10%)
Where Cc=compression index
wL=liquid limit.

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