Primary Consolidation Settlement

Q. A soil deposit has a void ratio of 1.0. if the void ratio is reduced to 0.60 by compaction, the percentage volume loss is

1. 10%
2. 20%
3. 30%
4. 40%

Q. A 6 m thick clay layer beneath a building is overlain by 6 m of sand stratum and is underlain by an impervious rock. Water table is located at a depth of 3 m below ground level. The unit weight of clay and sand are $18kN/m^3$ and $20kN/m^3$ respectively. Consolidation test on clay gave the following relation between void ratio and pressure.
$e=1.5-0.5lo{g}_{10}P$

The Pressure increment due to foundation of building placed at 3 m below ground level at top and bottom of clay is 75 kPa and 25 kPa respectively. Due to excavation for foundation the average pressure release in clay layer is 20 kPa. The amount of settlement expected due to building is ?
(in cm, Assume $\gamma ={\gamma }_{sat}and{\gamma }_w=10kN/m^3$ )

1. 20.78
2. 15.19
3. 10.25
4. 32.17

Q. A clay sample, originally 25 mm thick at a void ratio of 1.22, was subjected to a compressive load. After the clay sample was completely consolidation, its thickness was measured to be 24 mm. What is the final void ratio?

1. 1.322
2. 1.421
3. 1.311
4. 1.050

Q. The natural void ratio of a saturated clay strata, 3 m thick is 0.90. The final void ratio of the clay at the end of consolidation is expected to be 0.71. The total consolidation settlement of the clay strata is

1. 30 cm
2. 25 cm
3. 20 cm
4. 15 cm

Q. The initial and final void ratios of a clay sample in a consolidation test are 1 and 0.5, respectively. If initial thickness of the sample is 2.4 cm, then its final thickness will be

1. 1.3 cm
2. 1.8 cm
3. 1.9 cm
4. 2.2 cm

Q. At a reclamation site for which the soil strata is shown in figure, 3 m thick layer of a fill material is to be laid instantaneously on the top surface.

If the coefficient of volume compressibility $m_v$ for clay is $2.2\times {10}^{-4}{m}^2/kN$ the consolidation settlement of the clay layer due to placing of fill material will be

1. 69.5 mm
2. 139 mm
3. 228 mm
4. 278 mm

Q. The settlement analysis for a clay layer draining from top and bottom shows a settlement of 2.5 cm in 4 years and an ultimate settlement of 10 cm. However detailed subsurface investigation reveals that there is no drainage at the bottom. The ultimate settlement in this condition will be

1. 2.5 cm
2. 5 cm
3. 10 cm
4. 20 cm

Q. In a consolidation test, the thickness of saturated specimen of clay under over burden pressure of $150kN/m^2$ is 30 mm at water content of 20%. On increasing the consolidation pressure to $250kN/m^2$, the sample thickness decreases to 25 mm after consolidation. If specific gravity of clay is 2.7 the compression index of the clay.

1. 1.16
2. 2.32
3. 5.98
4. 0.15

Q. An undisturbed soil sample was taken from the middle of a clay layer (i.e., 1.5 m below GL), as shown in figure. The water table was at the top of clay layer. Laboratory test result are as follows:

Natural water content of clay : 25%

Preconsolidation pressure of clay : 60 kPa

Compression index of clay : 0.50

Recompression index of clay : 0.05

Specific gravity of clay : 2.70

Bulk unit weight of sand : $17kN/m^3$

A compacted fill of 2.5 m height with unit weight of $20kN/m^3$ is placed at the ground level.


Assuming unit weight of water as $10kN/m^3$, the ultimate consolidation settlement (expressed in mm) of the clay layer is .

1. 37.04

Q. A 4 m thick layer normally consolidated clay has average e = 1.3. Its compression index is 0.6 and coefficient of consolidation is $1m^2/yr$. If the increase in vertical pressure due to foundation load on the clay layer is equal to existing effective overburden pressure, the change in the thickness of the clay layer in mm.

1. 314

Q. A footing of size 2m $\times$ 2m transferring a pressure of $200kN/m^2$, is placed at depth of 1.5 m below the ground as shown in the figure (not drawn to the scale). The clay stratum is normally consolidated. The clay has specific gravity of 2.65 and compression index of 0.3.


Consideration 2:1 (vertical to horizontal) method of load distribution and ${\gamma }_w=10kN/m^3$ , the primary consolidation settlement (in mm, round off to two decimal places) of the clay stratum is

1. 74.28

Q. A strip footing of 2.5 m wide located at a depth of 1 m below G.L as shown in figure below is assumed to distribute the load over the soil stratum at 2 V : 1 H dispersion. If the value of ${}^{\prime }{m}_v^{\prime }$ varies over the depth of clay as
$m_v=(20+1.6Z^2)\times {10}^{-5}{m}^2/kN$
where 'Z' is distance from top of clay layer
The consolidation settlement of clay stratum in mm is

1. 46 mm
2. 35 mm
3. 30 mm
4. 50 mm

Q. A water tank is to be constructed on the soil deposit shown in the figure below. A circular footing of diameter 3 m and depth of embankment 1 m has been designed to support the tank. The total vertical load to be taken by the footing is 1500 kN. Assume the unit weight of water as 10$kN/m^3$ and the load dispersion pattern as 2V:1H. The expected settlement of the tank due to primary consolidation of the clay layer in _____ mm.

1. 53.236

Q. In a 7 m thick soil stratum, with its initial void ratio of 0.40, the void ratio decreases to 0.30 when the effective pressure on the stratum is increased by $1.0kg/c{m}^2$. The consolidation settlement of the stratum will be

1. 5 cm
2. 50 cm
3. 100 cm
4. 150 cm

Q. Consider the following statements:
Theory of consolidation predicts settlement due to primary consolidation; it cannot include settlement due to initial compression nor due to secondary consolidation. The happens because of the following assumptions made by the theory:

1. Soil grains and water are incompressible.
2. Soil is fully saturated.
3. Compression takes place in vertical direction only.
4. Time lag in consolidation is entirely due to low permeability soil.

Which of these statements are correct?

1. 1, 2 and 3
2. 2 and 3
3. 3 and 4
4. 1, 2 and 4

Q. A one-dimensional consolidation test is carried out on a standard 19 mm thick clay sample. The oedometer's deflection gauge indicates a reading of 2.1 mm, just before removal of the load, without allowing any swelling. The void ratio is 0.62 at this stage. The initial void ratio (round off to two decimal places) of the standard specimen is

1. 0.82

Q. In a consolidation test the sample tested has height H; water content is w, specific gravity of solids G. After increasing the loading by an increment $\Delta p$, the height decrease is $\Delta H$. Which one of the following expresses the corresponding change in void ratio $\Delta e$?

1. $\Delta e=\frac{\Delta H}{H(1+wG)}$
2. $\Delta e=\frac{\Delta H(1+wG)}{H}$
3. $\Delta e=\frac{H(1+wG)}{\Delta H}$
4. $\Delta e=\frac{H}{\Delta H\left(\right)1+wG}$

Q. In the phase diagrams given the change due to initial state changing into final state is shown due to consolidation. Depth of soil layer undergoing consolidation is H, $e_0$ is initial void ratio; $e_f$ is final void ratio; $\Delta e$ is change in void ratio.

Indicate which of the following expressions gives settlement of the layer

1. $Hlo{g}_{10}\left(\frac{\Delta e}{1+e_0}\right)$
2. $lo{g}_{10}\left(H\frac{\Delta e}{1+e_0}\right)$
3. $\frac{\Delta e}{1+e_0}$
4. $H\frac{\Delta e}{1+e_0}$