Soil Mechanics Questions and Answers – Consolidation Process – 3

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This set of Soil Mechanics online quiz focuses on “Consolidation Process – 3”.

1. For an ordinary clay of medium to low sensitivity, the value of Cc corresponding to the field consolidation line is roughly equal to __________ the compression index of remolded sample.
a) 1.3
b) 2.3
c) 3.3
d) 4.3

Explanation: For an ordinary clay of medium to low sensitivity, the value of Cc corresponding to the field consolidation line is roughly equal to 1.3 times the compression index of remolded sample.

2. The Cc for ordinary clay of medium to low sensitivity, the value of Cc corresponding to the field consolidation line is given by ______
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%)
For an ordinary clay of medium to low sensitivity, the value of Cc corresponding to the field consolidation line is roughly equal to 1.3 times the compression index of remolded sample.
∴Cc=0.009(wL-10%) for ordinary soil sample.

3. The equation for pre-compressed soil given by Hough (1957) is ______
a) Cc=0.009(wL-10%)
b) Cc=0.007(wL-10%)
c) Cc=0.3(e0-0.27)
d) Cc=0.007(wL-30%)

Explanation: The equation for pre-compressed soil given by Hough (1957) is,
Cc=0.3(e0-0.27) where e0= in-situ voids ratio.
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4. The coefficient of compressibility av is given by _____________
a) $$a_v=-\frac{e_0}{∆σ’}$$
b) $$a_v=-\frac{∆σ’}{∆e}$$
c) av=-∆e
d) $$a_v=-\frac{∆e}{∆σ^{‘}}$$

Explanation: The coefficient of compressibility av is defined as the decrease in voids ratio per unit increase of pressure.
∴ $$a_v=-\frac{∆e}{∆σ^{‘}}.$$.

5. For a given difference in pressure, the value of av _______ as pressure increases.
a) increases
b) decreases
c) is same
d) becomes unity

Explanation: The coefficient of compressibility av is defined as the decrease in voids ratio per unit increase of pressure. Therefore, for a given difference in pressure, the value of av decreases as pressure increases.

6. The coefficient of volume change mv is also known as ______________
a) coefficient of compressibility
b) coefficient of volume compressibility
c) compression index
d) expansion index

Explanation: The coefficient of volume change mv is also known as coefficient of volume compressibility. The compression index is denoted by Cc and the expansion index is denoted by Cs.

7. The coefficient of volume change mv is given by ______
a) $$m_v= \frac{1}{∆σ’}$$
b) $$m_v= \frac{-∆e}{1+e_o}$$
c) $$m_v= \frac{-∆e}{1+e_o} \frac{1}{∆σ}$$
d) $$m_v= \frac{-∆e}{1+e_o} \frac{1}{∆σ’}$$

Explanation: The coefficient of volume change mv is defined as the change in volume of a soil per unit of initial volume due to a given increase in unit pressure.
∴ $$m_v= \frac{-∆e}{1+e_o} \frac{1}{∆σ’}.$$

8. The relation between mv and av is __________
a) $$m_v=\frac{a_v}{e_0}$$
b) $$m_v=\frac{a_v}{1+∆σ’}$$
c) $$m_v=\frac{a_v}{1+e_0}$$
d) $$m_v=\frac{1}{e_0}\frac{a_v}{1+e_0}$$

Explanation: The coefficient of volume change mv is given by,
$$m_v= \frac{-∆e}{1+e_o} \frac{1}{∆σ’}$$ now substituting $$a_v=\frac{-∆e}{∆σ’},$$
we get $$m_v=\frac{a_v}{1+e_0}.$$

9. When the soil is laterally confined, the changes in volume is ______
a) proportional to change in thickness ∆H
b) inversely proportional to change in thickness ∆H
c) equal to change in thickness ∆H
d) does not depend upon the thickness

Explanation: When the soil is laterally confined, there is decrease in the volume. Since the soil is laterally confined, there will be change of volume only due to the decrease in the thickness which implies to the changes in volume is proportional to change in thickness ∆H.

10. The coefficient of volume change with respect to thickness is given by ______
a) $$m_v= H\frac{1}{∆σ’}$$
b) $$m_v= \frac{-∆H}{H_0}$$
c) $$m_v= \frac{-∆H}{H_0}\frac{1}{e}$$
d) $$m_v= \frac{-∆H}{H_0}\frac{1}{∆σ’}$$

Explanation: When the soil is laterally confined, there is decrease in volume due to the decrease in the thickness of the sample.
∴ $$m_v= \frac{-∆e}{1+e_o} \frac{1}{∆σ’} =\frac{-∆H}{H_0}\frac{1}{∆σ’}$$
Hence $$m_v= \frac{-∆H}{H_0}\frac{1}{∆σ’}$$.

11. The change in thickness due to pressure increment is given by ______
a) ∆H = -mv Ho ∆σ’
b) ∆H = -mv ∆σ’
c) ∆H = -mv Ho
d) ∆H = -Ho ∆σ’

Explanation: The coefficient of volume change with respect to thickness is given by,
$$m_v= \frac{-∆H}{H_0} \frac{1}{∆σ’}$$
therefore, the The change in thickness due to pressure increment is given by,
∆H = -mv Ho ∆σ’.

12. The minus sign in the change expression for change in thickness ∆H = -mv Ho ∆σ’ denotes ______
a) thickness decreases with increase in pressure
b) thickness decreases with decrease in pressure
c) thickness increases with increase in pressure
d) thickness does not changewith increase in pressure

Explanation: The minus sign in the change expression for change in thickness ∆H = -mvHo∆σ’ denotes that with the applied load, the thickness of the soil layer decreases. Thus, in the expression minus sign denotes that thickness decreases with increase in pressure.

13. The consolidation settlement can be computed by ______
a) using coefficient of volume change only
b) using voids ratio only
c) using both Using coefficient of volume change and voids ratio
d) using compression index only

Explanation: The consolidation settlement can be computed by the following methods:

• using coefficient of volume change
• using voids ratio.

14. The consolidation settlement ρf for a soil stature of thickness H that has fully consolidated index, a pressure increment ∆σ’ with respect to mv is given by ____________
a) ρf=mv H
b) ρf=H∆σ’
c) ρf=mv H∆σ’
d) ρf=mv ∆σ’

Explanation: Since the change in thickness is given by,
∆H= -mvHo∆σ’,
The consolidation settlement ρf for a soil stature of thickness H that has fully consolidated index, a pressure increment ∆σ’ with respect to mv is given by,
ρf=mv H∆σ’.

15. In practical case under a finite surface loading the intensity σ’ ______ with depth of layer.
a) decreases
b) increases
c) remains constant
d) has negligible effect

Explanation: In practical case under a finite surface loading the intensity σ’ decreases with depth of layer. In theoretical case, the pressure increment is transmitted uniformly over a thickness H of the soil layer.

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