This document discusses soil engineering topics including formation of soils, index properties, classification, and compaction behavior. It begins with an overview of three types of weathering - mechanical, chemical, and biological - that form soils. Index properties such as water content, void ratio, density, and degree of saturation are explained. Common soil classification systems including textural, USCS, and ISCS are covered. The document concludes with a discussion of compaction, including concepts such as optimum moisture content, maximum dry density, standard and modified Proctor tests, and factors affecting compaction such as soil type and compaction effort.

1. D.Mythili
Assistant Professor
Department of Civil Engineering
Excel Engineering College

2. Formation of Soils
Index Properties of Soils
Classification of Soils
Compaction behaviour of soils

3. Formation of Soils
Index Properties of Soils
Classification of Soils
Compaction behaviour of soils

6.  Mechanical weathering
 Chemical weathering
 Biological weathering

7.  Temperature
 Frost action
 Organic activity
 Gravity
 Abrasion

8. Expansion and contraction of rock surface during
day and night causes disintegration of rock

9.  Water freezes in
cracks, expands,
making the crack
larger.
 With time, this causes
the rock to break into
pieces.

10. A plant growing in a crack
can make the crack larger
as the root spread out.
Root Wedging

11.  Sometimes gravity pulls loosened rocks down
mountain cliffs in a landslide.
 As the rocks fall, they collide with one
another and break into smaller pieces.

12. - airborne or waterborne particles chip
off small fragments of other rocks.

14. Action of Water
Oxidation
Carbonation
Sulfuric acid
Plant acids

16. Rounded Subrounded
Subangular Angular
Sand & gravel- Generally formed by
mechanical weathering- bulky particles
Clay particles are like sheets!

19. Residual Soils Transported Soils

20.  Water – smallest particles to small boulders
 Wind – smallest particles to sand size
 Glacier – smallest particles to boulders as big
as a house.

21. Mode of Transportation Classification
Wind Aeolian soils
Sea (salt water) Marine soils
Lake (fresh water) Lacustrine soils
River Alluvial soils
Ice Glacial soils
Gravity Colluvial soils

22. Formation of Soils
Index Properties of Soils
Classification of Soils
Compaction behaviour of soils

23. INDEX PROPERTIES
The properties, which are used for classification
and identification of soil
ENGINEERING PROPERTIES
 Permeability: Property of a soil mass to allow water
to pass through it.
 Compressibility: Deformation produced in soil
when they are subjected to compressive loads.
 Shear strength: Ability to resist shear stress

24. S : Solid Soil particle
W: Liquid Water (electrolytes)
A: Air Air

25. Water content (usually expressed in percentage)
 Water content w = (Ww/Ws)*100
Oven drying method (IS: 2720 (Part II)
Sand bath method
Alcohol method
Pycnometer method

26. Void ratio: (decimal, no units)
 Void Ratio e = Vv/Vs = Vv/(V-Vv)
Porosity :(usually expressed in percentage)
 Porosity n = Vv/V = Vv/ (Vv+Vs)
Relation between n and e
e =n/(1-n)
n = e/(1+e)

27. Degree of saturation (usually percent):
 Degree of Saturation S = Vw/Vv
 For a fully saturated sample, Vw = Vv and
hence S=1
 For perfectly dry sample, Vw = 0 and hence
S=0

28. Percentage air voids (expressed in percentage):
 na = (Va/V) x 100
 na = (Va/V) x (Vv/Vv) = ac . n
Air content:
 ac = (Va/Vv)
 Va = Vv – Vw  ac = 1 – (Vw/Vv) = 1 – S

29. Density of soil mass
 Bulk density  = M/V
 Dry density d = Md/V
 Density of solids s = Md/Vs
 Saturated density sat = Msat/V
 Submerged density ’ = (Md)sub/V
’ = sat – w
Where w is the density of water and may be taken
as 1g/cm3 for calculation purposes.

30. Unit weight of soil mass
 Bulk Unit Weight  = W/V
 Dry unit weight d = Wd/V
 Unit weight of solids s = Wd/Vs
 Saturated unit weight sat = Wsat/V
 Submerged unit weight ’ = (Wd)sub/V
’ =  sat – w
Where w is the unit weight of water and may be
taken as 9.81 kN/m3 for calculation purposes.

31.  Core cutter method
 Sand replacement method

32.  Specific gravity
G= γs / γw
 Density bottle method
 Pycnometer method
 Measuring flask

33. Assumptions
 Sectional area is assumed as unity, hence the height is taken
as volume.
 The volume of solids is assumed as unity (i.e Vs=1)
 When the soil is fully saturated, the voids are completely filled
with water

34.  Case 1: When soil is partially saturated (S<100%)
S=Vw/Vv = Vw/e
But Vw=Ww/w = w Ws/w = = w G
or
 Case 2: When soil is saturated (S=100% i.e S=1)
 e = w G

35. Relationship between e, G, w & 
 The weight of water is Ww = w Ws =
So the moist unit weight is given by
 The dry unit weight is
 The degree of saturation is given by
◦ For saturated soil, Sr=1 hence e = w.Gs
 Saturated unit weight of soil is given by

36.  Grain size distribution
 Atterberg limits
 Relative density
 Free swell

37. Sieve analysis Hydrometer analysis

38. D30 D60
D10

39. Very useful for coarse-gained soils:
 Classification
 Coefficeient of permeability can be approximately calculated
 Used for design of filters
 Provides an index to the shear strength of soils
◦ Example: Well graded sand has high strength
 Uniform soil is more compressible than well-grades soil
 Indicates mode of deposition
◦ Example: Gap graded soils: indicates two different agencies for deposition

40. 0
20
40
60
80
100
0.01 0.1 1 10 100
Percent
finer
(%)
Particle size, mm
Guiding envelopes

41. (%)
100
)
(
)
(
min
max
max




e
e
e
e
Dr
0-15 Very loose
15-35 Loose
35-65 Medium dense
65-85 Dense
85-100 Very Dense

42. Liquid state
Plastic state
Semi-solid state
Solid state
Increasing
water
content
Liquid limit
Plastic limit
Shrinkage limit

44. Casagrande’s Apparatus Fall cone

47. )
(
)
(
P
L
P
L
w
w
w
w
I



cu = 2 kPa cu = 200 kPa
IL = 1.0 IL = 0
Soil A wL = 35% wP = 20%
Soil B wL = 120% wP = 40%

48. Activity
Clay
particle
Water
Card house structure!
Leda Clay, Canada

49. (Soil volume in water-Soil volume in kerosene) x100
DFI (%) = -----------------------------------------------
Soil volume in kerosene

50. Formation of Soils
Index Properties of Soils
Classification of Soils
Compaction behaviour of soils

51.  Textural classification
 Highway Research Board (HRB) Classification
 Unified Soil Classifications (USCS)
 Indian Standard Classification System (ISCS)

52. Soil particles mainly consist of following four size
fractions
 Gravel : 80 – 4.75 mm
 Sand : 4.75mm – 0.075mm (75 micron)
 Silt : 75 – 2 micron
 Clay : less than 2 micron

55.  Conduct Sieve analysis and Hydrometer analysis on soil sample
and plot particle size gradation curve and determine Cu and Cc.
 Conduct liquid limit and plastic limit test on soil samples as per
procedure
 The classification should be done in conjunction with the
Plasticity Chart.

58. Formation of Soils
Index Properties of Soils
Classification of Soils
Compaction behaviour of soils

59.  Compaction is the process of increasing the
Bulk Density of a soil or aggregate by driving
out air.
 The densification of soil is achieved by
reducing air void space.

61.  Increases density
 Increases strength characteristics
 Increases load-bearing capacity
 Decreases undesirable settlement
 Increases stability of slopes and embankments
 Decreases permeability
 Reduces water seepage
 Reduces Swelling & Shrinkage
 Reduces frost damage
 Reduces erosion damage

62.  Compaction of foundation soil for house
construction.
 Compaction of soil/gravel/crushed rock/asphalt
in road & pavement construction.
 Compaction of soil in earth embankments.
 Compaction of soil behind retaining walls.
 Compaction of soil backfill in trenches.
 Dam construction
 Construction of clay liners for waste storage areas
 Ground improvement

64.  Optimum Moisture Content (OMC) is the moisture
content at which the maximum possible dry
density is achieved for a particular compaction
energy or compaction method. The corresponding
dry density is called Maximum Dry Density (MDD).
 Water is added to lubricate the contact surfaces
of soil particles and improve the compressibility
of the soil matrix. It should be noted that increase
in water content increases the dry density in most
soils up to one stage (Dry side). Water acts as
lubrication.
 Beyond this level, any further increase in water
(Wet side)will only add more void space, there by
reducing the dry density.

65.  Standard Proctor’s Test
 Modified Proctor’s Test
Objectives of Laboratory Compaction Tests
 To simulate field condition
 To provide data for placement conditions in
field
 To determine proper amount of mixing water
 To determine the density in field

66.  Refer IS 2720 –
Part VII – 1987
Apparatus
 Cylindrical metal mould with detachable base plate
(having internal diameter 101.6 mm, internal height
116.8 mm and internal volume 945000 mm3)
 Collar of 50 mm effective height
 Rammer of weight 2.5 kgf (25 N) with a height of fall
of 304.8 mm

67.  The theoretical maximum
compaction for any given
water content corresponds
to zero air voids condition
(na = 0)
 The line showing the dry
density as a function of
water content for soil
containing no air voids is
called zero air void line or
saturation line.

68. Compaction energy =

69. Compaction energy in Modified Proctor’s Test is 4.5
times greater than in Standard Proctor’s Test
Compaction Energy in Modified Proctor’s Test
Compaction Energy in Standard Proctor’s Test

70.  A laboratory compaction test on soil having
specific gravity of 2.7 gave a maximum dry
density of 18 kN/m3 and a water content of
15 %. Determine the degree of saturation, air
content and percentage air void at the
maximum dry density. What would be the
theoretical maximum dry density
corresponding to zero air voids at the
optimum water content?

71.  A cohesive soil yields a MDD of 18 kN/m3 at
an OMC of 16 % during standard Proctor’s
Test. If G = 2.65, what is the degree of
saturation? What is the MDD it can further be
compacted to?

73. ◦ Water Content
◦ Amount of Compaction
◦ Method of Compaction
◦ Type of Soil
◦ Addition of Admixtures

74.  With increase in water content, compacted density increases up to a
stage, beyond which compacted density decreases.
 At lower water contents than OMC, soil particles are held by electrical
forces that prevents the development of diffused double layer leading
to low inter-particle repulsion.
 Increase in water results in expansion of double layer and reduction
in net attractive force between particles. Water replaces air in void
space.
 Particles slide over each other easily increasing lubrication, helping in
dense packing.
 After OMC is reached, further increase in water, increases the void
space, thereby decreasing dry density.

75.  Effect of increasing
compaction effort is to
increase MDD and reduce
OMC (Evident from Standard
& Modified Proctor’s Tests).
 However, there is no linear
relationship between
compaction effort and MDD

76.  Weight of compacting equipment
 Type of compaction - Impact, Kneading, Rolling, Static
Pressure
 Area of contact of compacting equipment with soil
 Time of exposure
 Each of these approaches will yield different compaction
effort. Further, suitability of a particular method depends
on type of soil and application

77.  Maximum density
achieved depends on
type of soil.
 Coarse grained soil
achieves higher
density at lower water
content and fine
grained soil achieves
lesser density, but at
higher water content.

78.  Stabilizing agents are the admixtures added
to soil.
 The effect of adding these admixtures is to
stabilize the soil.
 In many cases they accelerate the process of
densification.

79.  Density
 Soil Structure
 Shear strength
 Permeability
 Bearing Capacity
 Settlement
 Swelling & Shrinkage

80.  Effect of compaction is to reduce the voids by
expelling out air. This results in increasing
the dry density of soil mass.

81. In fine grained soil
 On dry side of
optimum, the structure
is flocculated. The
particles repel and
density is less.
 Addition of water
increases lubrication
and transforms the
structure into
dispersed structure

82.  In general, effect of compaction is
to increase the number of
contacts resulting in increased
shear strength, especially in
granular soils.
 In clays, shear strength depends
on dry density, moulding water
content, soil structure, method of
compaction, strain level, drainage
condition etc.
 Shear strength of cohesive soils
compacted dry of optimum
(flocculated structure) will be
higher than those compacted wet
of optimum (dispersed structure).

83.  Increased dry density, reduces the void space,
thereby reducing permeability.
 At same density, soil compacted dry of
optimum is more permeable.
 At same void ratio , soil with bigger particle
size is more permeable.
 Increased compaction effort reduces
permeability.

84.  Increase in compaction increases the density
and number of contacts between soil
particles.
 This results in increased .
 Hence bearing capacity increases which is a
function of density and 

85.  Compaction increases
density and decreases
void ratio.
 This results in reduced
settlement.
 Both elastic settlement
and consolidation
settlement are
reduced. At low pressure, soil compacted wet of
optimum shows more compressibility than
that on dry side. But at higher pressure,
behaviour is opposite.

86.  The effect of compaction is to reduce the void
space. Hence the swelling and shrinkage are
enormously reduced.
 Further, soil compacted dry of optimum
exhibits greater swell and swell pressure than
that compacted on wet side because of
random orientation and deficiency in water.

88. (i) Placement water content,
(ii) Type of equipment for compaction
(iii) Lift thickness and
(iv) Number of passes based on soil type &
degree of compaction desired

92.  Used for rapid determination of water content of soil in field.
 Proctor’s needle consists of a point, attached to graduated
needle shank and spring loaded plunger.
 Varying cross sections of needle points are available.
 The penetration force is read on stem at top.
 To use the needle in field, Calibration in done on the specific
soil in lab and calibration curve is prepared and the curve is
used in the field to determine placement water content.

93.  Characteristics of the compactor:
 Mass, size
 Operating frequency and frequency range
 Characteristics of the soil:
 Initial density
 Grain size and shape
 Water content

94. Construction procedures:
◦ Number of passes of the roller
◦ Lift thickness
◦ Frequency of operation vibrator
◦ Towing speed
Degree of Compaction
Relative compaction or degree of compaction
Correlation between relative compaction & relative
density R.C. = 80 + 0.2Dr
Typical required R.C. >= 95%

95.  Smooth Wheeled Steel Drum Rollers
 Pneumatic Tyred Rollers
 Sheepsfoot Rollers
 Impact Rollers
 Vibrating Rollers
 Hand Operated Vibrating plate & rammer
compactors

96.  Capacity 20 kN to 200 kN
 Self propelled or towed
 Suitable for well graded sand, gravel, silt of low
plasticity
 Unsuitable for uniform sand, silty sand and soft clay

97.  Usually two axles carrying rubber tyred wheels for
full width of track.
 Dead load (water) is added to give a weight of 100
to 400 kN.
 Suitable for most coarse & fine soils
 Unsuitable for very soft clay and highly variable
soil.

98.  Self propelled or towed
 Drum fitted with projecting club shaped feet
to provide kneading action.
 Weight of 50 to 80 kN
 Suitable for fine grained soil, sand & gravel
with considerable fines.

99.  Compaction by static pressure combined with
impact of pentagonal roller.
 Higher impact energy breaks soil lump and
provides kneading action

100.  Roller drum fitted with vibratory motion.
 Levels and smoothens ruts

101.  It is used for backfilling trenches, smaller
constructions and less accessible locations

103.  Holtz, Kovacs & Sheahan (2011), An
Introduction to Geotechnical Engineering, 2nd
Edition, Pearson
 V.N.S.Murthy, Geotechnical Engineering
Principles and Practices of Soil Mechanics and
Foundation Engineering, MARCEL DEKKER,
INC, NEW YORK
 B. C. Punmia and A.K. Jain, Soil Mechanics &
Foundations, 16th Edition, Laxmi Publications,
New Delhi, 2005