# Soil Mechanics Viva Questions

**Soil
Mechanics Viva Questions**

**1.
Compare Alluvial Soil and Aeolian Soil?**

The
soils that are transported by running water is known as alluvial soil and the
soil transported by wind is termed as Aeolian soil.

**2. Discuss about Lacustrine Soils?**

These
type of soils are deposited at the bottom of the lakes.

**Note**:
Soils can be derived from igneous rocks, sedimentary rocks and metamorphic
rocks. The chemical weathering of soil is mainly due to oxidation, hydration,
carbonation and leaching. We can say the residual soils are sands, silts and
clays. Sands are the examples of cohesion less soils. A fine grained soil may
or may not be plastic in nature. We know that 0.002 mm is the maximum size of
the particles of a clay.

**The void ratio of
saturated soil = Water content x Specific gravity of solids.**

Montmorillonite
is the clay mineral that gives maximum swelling. We know that Gravel and sand
is a non-cohesive coarse grained soil. The specific gravity of sandy soils is
2.7. The unit weight of soil mall is measured in N/ m^{3}.

In
a normal clay, the sensitivity range is about 2 to 4. In clays, the plastic
limit exists. The clays exhibiting high activity contain montmorillonite and
having high plasticity index. A flow net is used to determine the seepage flow,
seepage pressure and the exit gradient. The critical gradient of all soils is
normally has the value of 1.

**3.
What is a fine grained soil with little or no plasticity?**

Slit

**4.
Discuss about black cotton soil?**

A
black cotton soil is inorganic in nature, it exhibits high compressibility and
it contains large percentage of clay mineral.

**5.
What you know about consolidation?**

Consolidation
can be defined as the property of soil used in finding the settlement of
structures.

**6.
Define dry soil and porosity?**

In
a dry soil, the pores of a soil are completely full of air only. The ratio of
the volume of voids to the total volume of soil mass is termed as porosity.

**7. Define air content?**

Air Content = (Volume of air voids) / (Volume of voids)

**8. Define specific gravity of a soil?**

(Unit
weight of soil solids) / (Unit
weight of water) at 27^{0}C

**9. How will you accurately determine the
water content of soils?**

By using oven drying method.

**10. What types of corrections are
required at the time of hydrometer analysis?**

At
the time of hydrometer analysis, it requires temperature correction, meniscus
correction and dispersing agent correction.

**11. What is the use of uniformity coefficient?**

The range of particle size are measured
by uniformity coefficient.

**12.
What is the peculiarity of well graded soil?**

In this type of soils, the particles are
nearly of same size. This type of soils has uniformity coefficient more than
10.

**13. Discuss about sensitivity and
thixotropy?**

Sensitivity = (Unconfined
compressive strength of undisturbed soil) / (Unconfined compressive strength of
soil in a remoulded state)

Thixotropy
can be defined as the property of a soil
that enables to regain its strength lost on
remoulding in short times, without the change of the moisture content.

**14.
Define shrinkage limit?**

For
a saturated soil, the maximum water content at which a reduction in its
moisture doesn't cause a decrease in volume of soil is termed as the shrinkage
limit. The soil will be in solid state, if the water content in a soil is
reduced beyond the shrinkage limit.

**15.
Define Plasticity Index?**

Plasticity Index = The liquid limit -
The plastic limit

**16. Define the activity of clay?**

Activity of clay = (Plasticity Index) / (Clay
Fraction)

**17. Define relative consistency?**

Relative consistency = (Liquid Limit -
The natural content of a soil) / (Plasticity Index)

**18. When you say a soil has a flocculent
structure?**

If the particles of a soil are oriented
'edge to edge' or 'edge to face' with respect to one another, we can say that
the soil has a flocculent structure.

**19. Define permeability of soil?**

The
permeability of soil can be defined as the property of the soil mass which
permits the seepage of water through its inner connecting voids. The value of permeability
depends on the influence of grain size, void ratio and the degree of
saturation.

**20. What you know about seepage
pressure?**

Seepage pressure is the pressure exerted
by water on the soil through which it percolates. The flow net in the seepage
of water through a soil medium is by the network of flow lines and
equi-potential lines.

**21.
What are the properties of seepage force in soils?**

The seepage force in soils is
proportional to the head loss, proportional to the exit gradient and
perpendicular to the equi-potential lines.

**22. What are the factors affecting the
effective stress on the soil?**

The effective stress on the soil depends
on the external load acting on the soil and the weight of water present in soil
pores.

**23. Give the
equation of coefficient of volume compressibility? **

Coefficient of volume compressibility
can be defined as: (The change in volume of soil) / (Unit of initial volume due
to a given unit increase in pressure)

**24. What you know about the critical
density?**

The critical density is the density of
sand where there has no change in volume under the pressure of shearing
strain produced because of shear stress.

**25. What is the use of density index?**

The density index is used for estimating
the angle of friction of a sandy soil.

**26. What are the types of frictional
resistances offered by sand?**

Sliding friction, Rolling friction and
Resistance due to interlocking.

**27. Define saturation line?**

The saturation line can be defined as a
line, which shows the dry density as a function of water content for soil
contains no air voids.

**28. Which parameter is directly
proportional to the square of the depth of soil?**

Lateral earth pressure

**29. What you know about the safe bearing
capacity?**

The safe bearing capacity is the maximum
unit pressure that a soil can withstand without
rupture in shear or without the excessive settlement of the structure.

**Note:**
the total settlement of isolated footings for cohesive soil should be **65 mm**
as per the I.S code. The contact pressure of flexible footings on
non-cohesive soils is high in centre as compared with the edges. **At 60 ^{0} **the water content of
a highly organic soil is determined. By the oxidation with hydrogen peroxide,
the organic matter is removed in pre-treatment of soil. The particle size
distribution curve is obtained in a gap graded with a hump.

The coefficient of curvature is between **1 and 3** for a well graded sand. The
unified soil classification and the IS classification of soils are similar.
Clays are the soils which are plotted **above
the A line** in the plasticity chart. As
per the IS classification system, soils are classified into 18 groups. The
plasticity characteristics of a clay are because of **adsorbed water**. The bulking of sand is usually between 20% and 30%.
The permeability of soil usually varies with respect to the square of grain
size. **0.2mm** is the maximum particle size for applying Darcy's law.

**30. Discuss the different parameters
affecting the settlement of a footing in sand?**

The settlement of a footing in sand
mainly depends on the width of the footing, the relative density of sand and
the stress deformation characteristics of the sand.

**31. What you understand about soil
compaction and soil stabilization?**

Soil compaction is the process of
obtaining increased density of soil in a fill. This is obtained by the
reduction of its pore space by the expulsion of air.

Soil stabilisation is the process of maintaining
or improving the performance of a soil as a constructional material. This is
done by the use of admixtures.

**32. What type of soils are formed due to
physical disintegration?**

Cohesion less Soils

**33. Which method is used for determining
the water content in sands?**

Pycnometer Method

**34. In which law, the terminal velocity of the particle is
directly proportional to the square of the radius of the particle?**

Stoke's Law

**35. In which analysis, the meniscus
correction is positive and the dispersing agent correction is negative?**

The hydrometer analysis for a soil mass

**36. What is the maximum size of particle
for slit?**

75μ

**37.
If a soil has a liquid limit as30, then what is the corresponding plasticity
index given by the A line?**

7.3

**38.
Give the normal range of coefficient of permeability of clay?**

10^{-5} & 10^{-8}
mm/s

**39.
For coarse grained soils, which type of permeability test are used?**

A
constant head permeability test

**40.
If a soil has a void ratio of 0.5 and a discharge velocity of 6x10 ^{-7}m/s,
Calculate its seepage velocity?**

Seepage
velocity = 18x10^{-7} m/s

**41.
What is the shape of phreatic line in a homogeneous dam?**

Parabolic

**42.
What is the use of flow net?**

A
flow net is used for determining seepage, exit gradient and the uplift
pressure.

**43.
What is a quick sand?**

The
condition in which a cohesion less soil loses its strength due to the upward flow of water is termed as quick
sand.

**44.
Which parameter of a soil increases with decrease in void ratio?**

The
critical hydraulic gradient

**45.
Give the relationship between the specific gravity of solids (G) and the
hydraulic gradient ( i ) for a void ratio of 0.6 for the quick sand condition?**

G = 1.6i + 1

**Note: **The stress
developed at a point in the soil exactly below a point load at the surface is
inversely proportional to the square of the depth of the point. In homogeneous
soils, the Westergaard's analysis for vertical stress is used. As the liquid limit
increases, the compression index of soil also increases. The consolidation time
for a soil sample increases with decrease in
permeability. As the compression index increases, the ultimate
settlement of a soil deposit also increases. The lime stabilisation of clayey
soils leads to **Flocculation of
particles.**

**46.
Name the curve which joints points of
equal vertical stress?**

Isobar

**47.
The vertical stress under any shape of loaded area can be determined by?**

The
Newmark's influence chart

**48.
What is coefficient of compressibility?**

It
is the ratio of change in void ratio to the change in effective stress.

**49.
What is drained test?**

If
a drainage is permitted throughout the tri-axial test, then the test is called
as a drained test.

**50.
The shear strength of which soil is proportional to the tangent of angle of
shearing?**

Cohesion less soil

**51.
What is the angle of failure of plane with the major principal plane?**

45^{0} + Ø/2

**52.
Which one is most suitable for the compaction of clays?**

Vibratory
rollers

**53.
What is the range of the mass and the drop of a hammer in a standard compaction
test?**

2.6
Kg and 310 mm

**54.
The relative compaction is same as relative density? True or False.**

FALSE

**55.
Vibratory rollers are effective in the case of highly cohesive soils? True or False.**

FALSE

**56.
Zero air void line and 100% saturation line are identical? True or False.**

TRUE

**57.
What is the percentage of particles passing 75μ sieve for getting maximum dry
density?**

20%

**58.
What you understand about aquiclude?**

Aquiclude
is the geological formation which contains water but is not able to transmit.

**59.
Which test is used for measuring the shear strength of very soft and sensitive
clays?**

In-situ
vane shear test

**60.
What is the corrected value of the standard penetration number (N), if the
actual value of N is greater than 15 for fine sands?**

15+

**61.
What is the ratio of height to diameter of on-situ vane shear test apparatus?**

2.0

**62.
Which chart is based on the total stresses using the friction circle method?**

Taylor's
stability chart

**63.
What you know about applied shear stress?**

In
stability analysis, the term mobilised shear strength is termed as applied
shear stress.

**64. What is known as effective stress?**

The
active earth pressure coefficient K_{a} is generally refers to
effective stress

**65.
What is the radius of friction circle in the analysis of earth pressure?**

R.SinØ

**66.
In which case, the permissible settlement is maximum?**

Raft on clay

**67.
When a negative skin friction on a pile developed?**

when
the surrounding it settles more than the pile

**NOTE****:**
For a bored pile in sand, the load carrying capacity **is 1/2 to 2/3 times** that of a driven pile. For driven piles in sand
at close spacing, the group efficiency is **greater
than 100%**. The contact pressure beneath a rigid footing resting on a
cohesive soil is **more at edges as
compared to the centre. **

**68.
What is the void ratio of the soil, if in a wet soil mass, air occupies
one-fourth of its volume and water occupies one half of its volume?**

3

**69.
Calculate the value of porosity of a soil sample, if the total volume of soil
grains is equal to twice the total volume of voids?**

33.33%

**70.
Give the correct sequence of parameters of earth pressure intensity in
descending order?**

Passive, at rest, active

**71.
What is the ratio of passive to active lateral earth pressure for a sand having
internal friction of 30 ^{0}?**

9

**72.
What is the inclination of failure plane to horizontal in direct shear test?**

0

**73.
Which factor governs the behavior of a
clay?**

Surface energy

**74.
What is the maximum value of stability number in a stability chart?**

0.26

**75.
Which type of soil is practically incompressible?**

Clay

**76.
Because of large lateral pressure, which type of soils are not good for
backfilling?**

Cohesive
Soils

**77.
What is the value of the depth factor D _{f} for toe failure of slopes?**

1.0

**78.
When a body of soil is said to be in plastic equilibrium?**

On the verge of failure

**79.
As the specific gravity increases, what also increases?**

The
critical hydraulic gradient of seepage water

**80.
When the vertical pressure distribution on a horizontal plane is negligible?**

If the horizontal distance is equal to twice the depth.

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