Soil &

Foundation
CIV 213
L2
Dr. Randa Fouad
 Soil classifications
● Clay is the smallest solid component. These tiny flat particles fit closely
together to create the greatest surface area of all soil types. Clay soil
contains needed nutrients also stores water well. So, well in fact, that
drainage is slow in clay soil.

● Silt represents the middle size pieces. It is made up of rock and mineral
particles that are larger than clay but smaller than sand. Individual silt
particles are so small that they are difficult to see. To be classified as
silt, a particle must be less than 0.06 mm.

● Sand makes up the largest particles in soil structure. These are rounded,
rather than flat and allows for larger space between the particles.
Water drains quickly from the soil that has a lot of sand and the
nutrients drain faster too.

● Gravel soil is a type of soil that contains a significant proportion of

gravel particles. Gravel particles are larger than sand but smaller than
pebbles, ranging from 2 to 64 millimeters in diameter. Gravel soil tends
to have good drainage due to the space between the particles, but it
may have limited water retention and fertility
 Classification of soil
Cohesive soils (e.g. silts and clays)
● Cohesive soils have shear strength. It is possible to make a
vertical cut in silts and clays and it remain standing,
unsupported, for some time. This cannot be done in dry sand. In
clay and silts, therefore, some other factor must contribute to
shear strength. This factor is called cohesion. It results from the
mutual attraction, which exist between fine particles and tends
to hold them together in a solid mass without the application of
external forces.
• Clay consist of very fine microscopic
particles which hold water to increase their
volume, and release moisture to decrease
their volume.

• Special precaution needs to be taken in the

design of footings to resist or avoid the
forces caused by shrinking and swelling.
 Classification of soil
Cohesionless soils (non-cohesive soils) e.g. sand.
• Sand and gravel have no shear strength. An apparent cohesion in
sand can be noticed when water is present. Sand grains stick
together due to negative pore pressure (building sandcastles is an
example). Sand stand in slopes when wet but will not stand when
dry or saturated.

• Strength, bearing capacity and slope stability all derived from

internal friction (Phi). for granular soils (sand & gravel) range
from 30° to 45°. increases due to grading, packing density and
grain angularity.
• Courser grained soils are more permeable to water and, unless
➢ Gravity force > attraction force
saturated, may have very little water in their voids.
Then the soil id non-cohesive.
➢ If attraction force > gravity force
• If well consolidated and confined, they form a foundation that is
Then the soil is cohesive
almost as stable as rock.

• If loosely consolidated or with high percentage of organic matter,

the site must be classified as a problem site
Soil classification
● Soils are generally divided based on their particle size into coarse grained
and fine-grained soils.
● Coarse-grained soils are of particle size greater than 0.075 mm (Sieve 200
mm) or 75 micron and particles smaller than this make up fine-grained soils.
● Further coarse grains are divided into gravel and sand, and fine grains are
divided into silt and clay sized.
Classification of soil Soil

● This classification system helps

engineers and geologists In-organic Organic
Soil Soil
understand the behavior and
properties of different soils, aiding
in the selection of appropriate
Cohesive Cohesionless
construction techniques, Soil Soil
foundation design, and soil
stabilization methods. Small bearing capacity
High settlement
Clay Silt Sand Gravel
Black color
Not suitable for
foundation
F: Fine F M C F M C F M C
M: Medium
C: Course 0.006 0.02 0.2 0.6 6 20
mm mm mm mm mm mm Boulders
0.002 mm 0.06 mm 2.0 mm 60 mm
 Soil classification

Approximate
Manual testing
testing

Textural
Unified Sedimentation
Filed test MIT classification (triangular) Sieve analysis
classification test
classification
Soil Identification- Approximate Field Procedure
Field test: Visual inspection test
● Differentiate clay, sand and gravel through visual inspection.
Soil Identification- Approximate Field Procedure
Field test: Feel test
● Put some soil in your hand with your palm facing upwards. Mix in some water until the
soil is moldable, like putty. With your other hand, firmly pat the edge of the hand,
holding the soil for 5 to 10 seconds. If the surface of the soil starts shining and the water
rises to the surface, it’s silt. If the water does not rise, then it’s clay. This is because water
penetrates silt more easily than clay. Also, clay feels stickier than silt when it’s wet.
Soil Identification- Approximate Field Procedure
Field test: Odor test
If your soil smells like decaying plant
matter, it’s probably organic. Organic soils
also tend to be darker in color (use
an organic impurities plate to compare the
color of your soil to the colors on the plate.
If it is very dark, it could potentially contain
organic material). If it was dug out near the
surface of a natural fill, it is very likely to
contain humus (decomposed plant matter).
Remember that you can only know if a soil
is truly organic if you do an Atterburg limits
test on a dried-out sample and on a normal
sample, and their liquid limits are vastly
different.
Soil Identification- Approximate Field Procedure

Hand texturing
● Add enough water to make a bolus
or ball (Figure 1). Knead the
bolus for 1–2 minutes, adding more
water or soil until it just stops sticking
to your fingers. Note how the soil
feels when kneading it:
○ Gritty (sandy),
○ Silky (silty) or
○ Plastic/sticky (clay).
○ If you can’t make a bolus, the
soil is very sandy
Soil Identification- Approximate Field

Soil ribbon:
Gently press out the soil between your thumb and index finger to form a
hanging ribbon. The ribbon should only be 2–3mm thick. The more clay you have
in your soil, the longer your ribbon will be.
 Soil Identification- Approximate Field Procedure

Field test: Dry strength test

 Soil Identification- Approximate Field Procedure
● After identifying soil as coarse and fine-grained we can further separate them as gravel, sand,
silt or clay.
● From our soil sample if we pick up a soil particle clearly visible like a pebble, roughly larger than
5 mm, then it is gravel particle and if it appears smaller it is sand particle.
● Particles smaller than sand are microscopic and are either silt or clay. We need to perform a
couple of tests to distinguish between them.
● Let’s begin with
Field test: Sedimentation test
1. For sedimentation we take a spoonful of soil sample and mix it in a jar full
of water. We shake the jar to make the soil suspension.
2. Now the jar is placed on the flat surface and the suspension material is
allowed to settle.
3. We will notice that suspended particles settle in layers. The gravel and
coarse sand will settle almost immediately to the bottom and fine sand will
take around 1 to 2 minutes to settle. The silt will take about an hour and
the clay will remain suspended for even longer period of times.
4. We can estimate the relative quantity of each component (sand, silt, and
clay) by comparing the relative thickness of each of the layer at the
bottom of the jar.
Soil Identification- Approximate Field Procedure
Field test: Sedimentation test
● The bottom layer will be the heavier
particles, sand, and rocks.
● The next layer will be the silt particles.
● Above that there’re the clay particles.
● Organic matter may be floating on the
surface of the water.
● The color of the soil gives a clue to its
character – light colors usually have less
organic content than dark soil and dark
soil warms faster in the spring.
Sieve analysis
● Sieving is performed by arranging the various sieves one over the other, the largest
aperture sieve is placed at the top and the smallest aperture sieve is placed at the
bottom. A receiver is placed at the bottom, and a cover is placed at the top. The
soil sample is put on the top sieve and the sieves are put on a sieve shaker, for
about 10 minutes.
 Sieve analysis
Both the position and the shape of the grading curve for a soil can aid its identity
and description.
Some typical grading curves are shown in the figure:
A - a poorly-graded medium sand
B - a well-graded gravel - sand (i.e. equal amounts of gravel and sand)
C - a gap-graded cobbles-sand
D - a sandy silt with little amount of sand
E - a silty clay with little amount of sand
 Sieve analysis
● Sieve number 200 (200 openings per
square inch / opening side length 0.075
mm) is the sieve that separates the
reserved material of gravel and sand
from the passing material of silt and
clay.

● Passing more than 10% of the sample

weight through sieve number 200
indicates a high percentage of fine U.S Standard Sieve No. Sieve Opening (mm)
materials in the soil. Therefore, another 4 4.75
test should be conducted to plot the 10 2.00
20 0.85
grain size distribution curve of the fine 40 0.425
materials, which is Sedimentation 60 0.25
Analysis (Hydrometer). 100 0.15
140 0.106
Sieve analysis
Sieve 4 (4.75 mm) Sieve 200 (0.075 mm)
1. Sieve #4 is used to separate coarse- 1. Sieve #200 is used to separate fine-grained
grained particles from fine-grained particles (silt and clay) from the sand fraction
particles in soil samples. in soil samples.
2. It helps classify soil into coarse-grained 2. It helps identify the amount of fine-grained
(e.g., gravel and sand) and fine-grained material present in the soil, which is important
for assessing soil fertility, water retention
(e.g., silt and clay) fractions.
capacity, and engineering behavior.
3. Coarse-grained particles retained on
3. The percentage of material passing through
this sieve are typically further analyzed the #200 sieve (silt and clay fraction) is often
for their size distribution using other used to classify soils based on their grain size
sieves with smaller openings. distribution according to various soil
4. The presence of significant amounts of classification systems, such as the Unified Soil
material retained on the #4 sieve may Classification System (USCS).
indicate the predominance of coarse- 4. The fineness of the material passing through
grained the #200 sieve also affects soil properties such
as plasticity, compressibility, and shear
strength, which are crucial considerations in
geotechnical engineering and construction.
Sieve analysis
Uniformity coefficient (u)
𝐷60
𝑈=
𝐷10
● Where:

o D60: Particle diameter at which 60% of the soil is finer.

o D10: Particle diameter at which 10% of the soil is finer (Called effective
diameter)
o 𝑈 = 1 ∴ 𝑈𝑛𝑖𝑓𝑟𝑜𝑚 𝑆𝑜𝑖𝑙
o 𝑈 𝑏𝑒𝑡𝑤𝑒𝑒𝑛 (1 − 4) ∴ 𝑃𝑜𝑜𝑟 𝑔𝑟𝑎𝑑𝑒𝑑 𝑆𝑜𝑖𝑙
o 𝑈 > 4 ∴ 𝑊𝑒𝑙𝑙 𝑔𝑟𝑎𝑑𝑒𝑑 𝑠𝑜𝑖𝑙

o U= 4 For Sand
o U = 6 For gravel
Sieve analysis

Curvature coefficient (C)

𝐷302
𝐶=
𝐷10𝑥𝐷60
● Where:

o D30: Particle diameter at which 30% of the soil is finer

o C between (1 – 3) Well graded
o C any thing else poor graded soil
 Soil classification

Well-graded soil.

Uniform-graded soil

Gap-graded soil
Solved Examples

Results of particle size distribution analysis of a soil

sample weighing 2.77 kg are given. Draw the grading
curve.

Sieve size (mm) 9.52 4.80 2.40 1.2 0.6 0.42 0.21 0.15 0.075
Weight retained (gm) 0 56 189 421 778 444 417 361 55
 Solution
Sieve size Weight retained Cum. Weight
% retained % finer
(mm) (gm) retained
9.52 0 0 0 100
56 (𝑊𝐶𝑢𝑚. )
4.80 56 (0+56) = 56 = 𝑥100 = 2% 100 - 2= 98
2770 (𝑊𝑡𝑜𝑡𝑎𝑙 )
2.40 189 (56+189) = 245 8.8 100 – 8.8 = 91.2
1.2 421 (245+421) = 666 24 76
0.6 778 1444 52.1 47.9
0.42 444 1888 68.2 31.8
0.21 417 2305 83.2 16.8
0.15 361 2666 96.2 3.8
0.075 55 2721 98.2 1.8
Pan 𝑊𝑇𝑜𝑡𝑎𝑙 − 𝑊𝐴𝑙𝑙 𝑠𝑖𝑒𝑣𝑒 = 49 2770 100 0
Solution

𝐷10 = 0.18
𝐷30 = 0.4

𝐷60 = 0.83
𝐷30
𝐷60 0.83
𝑈= = = 6.5
𝐷10 0.18
𝐷302 0.42
𝐶= = = 1.07 (𝑊𝑒𝑙𝑙 𝑔𝑟𝑎𝑑𝑒𝑑)
𝐷10𝑥𝐷60 0.18𝑥0.83
MIT classification
Massachusetts Institute of Technology System (MIT)
The MIT Classification System is similar to other soil classification systems, such as the Unified Soil
Classification System (USCS), but it focuses specifically on engineering properties relevant to
geotechnical engineering applications.
Gravel (G):
■ Gravel consists of coarse particles with diameters greater than 2 millimeters (mm).
■ It typically includes materials such as gravel, cobble, and boulders.
Sand (S):
■ Sand comprises particles with diameters ranging from 0.06 mm to 2 mm.
■ It includes materials such as fine sand, medium sand, and coarse sand.
Silt (M):
■ Silt consists of fine particles with diameters ranging from 0.002 mm to 0.06 mm.
■ It has properties intermediate between sand and clay.
Clay (C):
■ Clay comprises particles with diameters smaller than 0.002 mm.
■ It includes materials such as silts, clays, and organic soils.
 Classification of soil (MIT)
1. Boulder ( Particle size greater than 200 mm ). .4. Sand (soil with particle size from 0.06mm to 2mm).
o Coarse Sand: 0.6 mm to 2 mm
2. Cobble ( Particle size between 60 mm to 200 mm). o Medium Sand: 0.2 mm to 0.6 mm
o Fine Sand: 0.06 mm to 0.2 mm
3.Gravel (soil with particle size greater than 2mm).
o Coarse Gravel: 20 mm to 60 mm 5. Silt (soil with particle size from 0.002mm to 0.06mm).
o Medium Gravel: 6 mm to 20 mm o Coarse Silt: 0.02 mm to 0.06 mm
o Fine Gravel: 2 mm to 6 mm o Medium Silt: 0.006 mm to 0.02 mm
o Fine Silt: 0.002 mm to 0.006 mm
6. Clay (soil with particle size less than 0.002mm).
0.002

0.006

0.02

0.06

0.2

0.6

2.0
Clay Fine Medium Coarse Fine Medium Coarse
Gravel
(Size) Silt (Size) Sand

Sieve Sieve
No.(200) No.(4)
Example
Tool Percentage of component

And (‫)و‬ 35-50

----ly (‫)صفة‬ 35-15

Some (‫)بعض‬ 15-5

Traces of (‫)أثار‬ 5-1

Soil Gravel Sand Silt Clay

A 0 68 18 14

B 12 56 24 8

Soil (A) Silty sand, some clay

Soil (B) Silty Sand, some gravel and some clay

 Textural (triangular) classification
• The triangular classification, also known as the textural Silt
triangle or soil texture triangle, is a graphical method
used in soil science to classify soil based on its particle Clay
size distribution.
• It is a simple and widely used tool that helps
characterize soil texture by plotting the percentages of Sand
sand, silt, and clay content on a triangular graph.
• The triangular classification provides a quick and visual
method for assessing soil texture based on its particle
size distribution.
• The triangle is divided into various zones, each
representing a different texture class.

To classify a soil, plot the percentage of sand on the

horizontal axis, the percentage of clay on the left vertical
axis, and the percentage of silt on the right vertical axis. The
intersection of these three lines indicates the soil's texture
class.
Example: Clay: 32%, Sand: 40% & Silt: 28% Clay loam
 Textural (triangular) classification
● The USDA (United States Department of Agriculture) system classifies soil into 12 primary texture
classes based on the percentages of sand, silt, and clay. These texture classes are a standard for
understanding and communicating soil composition. Here are the different texture classes:

1.Sand: Contains 85-100% sand, and the percentage of silt plus 1.5 times the percentage of clay is not more than 15.
2.Loamy Sand: Contains 70-90% sand, and the percentage of silt plus twice the percentage of clay is 15-30.
3.Sandy Loam: Contains less than 30% clay, 50-70% sand, and the remainder is silt.
4.Loam: Contains 7-27% clay, less than 52% sand, and 28-50% silt.
5.Silt Loam: Contains 50-88% silt, 12-27% clay, and less than 20% sand.
6.Silt: Contains 80% or more silt and less than 12% clay.
7.Sandy Clay Loam: Contains 20-35% clay, less than 28% silt, and more than 45% sand.
8.Clay Loam: Contains 27-40% clay, 20-45% sand, and the remainder is silt.
9.Silty Clay Loam: Contains 27-40% clay and 40-73% silt.
10.Sandy Clay: Contains 35% or more clay and 45% or more sand.
11.Silty Clay: Contains 40% or more clay and 40% or more silt.
12.Clay: Contains 40% or more clay, less than 45% sand, and less than 40% silt.
Example
● Classify according to triangular classification system.

Gravel Sand Silt Clay

6% 68% 10% 16%

● The sum of soil contents is 68%+10%+16%= 94%

● To apply the triangular classification system
100
○ Sand content = 68𝑥 = 72.34%
94
100
○ Silt content = 10𝑥 94 = 10.64%
100
○ Clay content = 16𝑥 94 = 17.02%

The point corresponding to the adjusted contents is sandy loam

Adding the effect of gravel content is classified ad sandy loam, some gravel
Textural (triangular) classification
Loam is soil composed
mostly of sand, silt and a
smaller amount of clay By
weight
Example
For the shown particle size distribution, find the effective diameter,
uniformity coefficient and coefficient of curvature. Describe the soil
according to the M.I.T.
Sand Gravel
Solution

𝐷10 = 0.14 𝐷30 = 0.28 𝐷60 = 0.57

𝐷60 0.57 𝐷302 0.282

𝑈= = = 4.1 𝐶= = = 0.98
𝐷10 0.14 𝐷10𝑥𝐷60 0.14𝑥0.57

Sand Gravel

Fine Medium Coarse Fine Medium Coarse

20 50 22 10 --- ---

92 8

Sand, some gravel

USCS: Unified Soil Classification System:

● The Unified Soil Classification System uses a two-letter system to name

different soil types.

● The first letter in the naming describes the major constituents of the soil
(Gravel, S-sand, M-silt, C-clay, O-organic).

● The second letter describes characteristics of the soil.

● For coarse-grained, the second letters are:

○ P-poorly graded (uniform particle sizes),
○ W-well-graded (diversified particle sizes),
○ M-silty fines
○ C-clayey fines.
Soil classification based on the USCS:
USCS: Unified Soil Classification System
● The USCS categorizes soils into three primary groups: coarse-grained soils, fine-grained soils
and organic soil.

● Each group is further subdivided into several classifications based on particle size distribution,
Atterberg limits (liquid limit, plastic limit, and plasticity index), and other engineering properties.

● The first letter in the naming describes the major constituents of the soil (G-gravel, S-sand, M-
silt, C-clay, O-organic).

● The second letter describes characteristics of the soil.

○ Well-graded (W): Indicates a wide range of particle sizes within a soil.
○ Poorly graded (P): Indicates a narrow range of particle sizes within a soil.
○ High plasticity (H): Indicates high clay content and high plasticity.
○ Low plasticity (L): Indicates low clay content and low plasticity.
○ Elastic (E): Indicates that the soil behaves elastically under loading.
○ Inorganic (I): Indicates that the soil is predominantly composed of inorganic materials.
Soil classification based on the USCS:
• Coarse-Grained Soils:
○ Gravels (GW): Well-graded gravels.
○ Gravels with silty fines (GP): Poorly graded gravels with fines.
○ Sands (SW): Well-graded sands.
○ Sands with silty fines (SP): Poorly graded sands with fines.
○ Sands with clayey fines (SC): Sands with significant amounts of clayey fines.
○ Sands with gravelly fines (SW-GM, SP-GM, SC-GM): Sands with significant amounts of
gravelly fines.

• Gravels (GW): Coarse-grained soils with more than 50% of the soil particles retained on the
No. 4 sieve (4.75 mm) and with little to no fines (silt and clay).
• Sands (SW): Coarse-grained soils with more than 50% of the soil particles passing the No. 4
sieve and with little to no fines.
• Silty Sands (SM): Sands with significant amounts of silt (particles between 0.06 mm and 0.002
mm) present.
• Clayey Sands (SC): Sands with significant amounts of clay (particles smaller than 0.002 mm)
present.
 Soil classification based on the USCS:
2. Fine-Grained Soils:
Fine-grained soils primarily consist of
particles smaller than 0.075 mm in diameter.
They are further classified based on their
plasticity and liquid limit:
○ Clays (CL): Fine-grained soils with high
plasticity and cohesion, characterized by
their ability to undergo significant volume
changes with changes in moisture content.
○ Silt (ML): Fine-grained soils with
moderate plasticity, consisting mainly of
silt particles.
○ Silty Clays (CL-ML): Soils with significant
amounts of both clay and silt.
○ Organic Soils (OL, OH): Soils containing
significant amounts of organic matter,
such as peat or muck.
Classification and symbols
 Basic definitions:
● Below A – line is silt – Use symbol M L.L > 50 → 𝐻𝑖𝑔ℎ 𝑝𝑙𝑎𝑠𝑡𝑖𝑐𝑖𝑡𝑦
● Above A – line is clay – Use symbol c L.L < 50 → 𝐿𝑜𝑤 𝑝𝑙𝑎𝑠𝑡𝑖𝑐𝑖𝑡𝑦

No. No. Liquid Plasticity

Soil
4 200 limit Index
A 80 52 30 8

B 79 45 26 4

For soil (A)

➢ 50 ∴ 𝐹𝑖𝑛𝑒 − 𝑔𝑟𝑎𝑖𝑛𝑒𝑑 𝑠𝑜𝑖𝑙
➢ L.L < 50 ∴ 𝐿𝑜𝑤 𝑝𝑙𝑎𝑠𝑡𝑖𝑐𝑖𝑡𝑦

∴ Soil (A) is CL ( Low plasticity clay)

Soil classification
Soil symbols:
Gradation symbols:
G: Gravel
Liquid limit symbols: W: Well - graded
S: Sand
H: High L.L> 50 1 < 𝑐𝑐 < 3 𝑎𝑛𝑑 𝑐𝑢 ≥ 4 𝑓𝑜𝑟 𝑔𝑟𝑎𝑣𝑒𝑙
M: Silt
L: Low if L.L < 50 1 < 𝑐𝑐 < 3 𝑎𝑛𝑑 𝑐𝑢 ≥ 6 𝑓𝑜𝑟 𝑠𝑎𝑛𝑑
C: Clay
P: Poorly – graded
O: Organic

Passing Sieve 200

(0.075 mm)

SM: Silty sand

SW: Well – graded sand
SC: Clayey sand
CL: Low plasticity clay > 50% < 50%
MH: High plasticity silt Fine - grained Coarse - grained
Example
Soil Type Grain Size Distribution Consistency Plasticity Organic Content

Gravel >50% gravel Non-cohesive N/A Low

Sand >50% sand Non-cohesive N/A Low
Silt >50% silt Cohesive Low Low
Clay >50% clay Cohesive High Low
Silty Gravel Gravel + silt Non-cohesive Low Low
Silty Sand Sand + silt Non-cohesive Low Low
Silty Clay Clay + silt Cohesive Medium Low
Sandy Silt Sand + silt Cohesive Low Low
Sandy Clay Clay + sand Cohesive High Low
Organic Clay >50% clay Cohesive High High
Organic Silt >50% silt Cohesive Medium High
Organic Sand >50% sand Non-cohesive N/A High

Organic Gravel >50% gravel Non-cohesive N/A High

Consistency Of Soil And
Atterberg Limits
Consistency is the term used to describe the ability of the soil to resist rupture and deformation. It
is commonly described as soft, stiff or firm, and hard.

● This term is used for fine

grained soils and is related to
the water content.
● If soil is mixed with a large
quantity of water, it forms a
suspension.
● If water is evaporated, the soil
passes through various "states
of consistency".
● These states are Liquid state,
Plastic state, Semi–solid state
and Solid state.
Atterberg Limits
 Consistency Of Soil
● Solid: Soil behaves as a solid when it is dry
or compacted and can resist deformation
under normal stress. Solid soil is typically
stable and can support structures and
loads effectively (Brittle behavior).

● Semi-Solid: Soil exhibits semi-solid

consistency when it is moist or partially
saturated. It has some cohesion and can
retain its shape to some extent but may
deform or flow under moderate stress.
 Consistency Of Soil
● Plastic: Plastic soil is moldable and can be Lower strength
deformed under relatively low stress. It has
some cohesion and can be shaped into
various forms without breaking. Plastic soils
typically exhibit plasticity and can be
molded into different shapes when moist.

● Liquid: Fluid soil behaves like a liquid and

flows freely under its weight or applied
stress. It has no cohesive strength and
takes the shape of its container. Fluid soils
include slurries, mud, and other highly
saturated materials.
 Consistency Of Soil

Liquid Limit, LL
● Liquid limit is the water content of
soil in which soil grains are
separated by water just enough for
the soil mass to loss shear strength.
𝐿. 𝐿 = 1
● A little higher than this water
𝐿. 𝐿 = 0
content will tend the soil to flow like
viscous fluid while a little lower will
cause the soil to behave as plastic.
 Casagrande Cup Method for Liquid Limit Test
● Place a soil paste in the cup.
● Cut a groove at the center of the soil paste
with the standard grooving tool.
● Lift the cup and drop it from a height of 10mm,
using the crank-operated cam. Measure the
water content required to close to distance of
12.7mm along the bottom of the groove and
note down the number of blows.
● Repeat the procedure at least three times for
the same soil at varying moisture contents.
● Plot the moisture content of the soil, in percent,
and the corresponding number of blows on
semi-logarithmic graph.
● Draw the best-fit straight line through the
plotted points.
● The moisture content corresponding to N 25,
determined from the curve, is the liquid limit of
the soil.
 Liquid Limit Test
● The graph is approximated by the
best fit straight line, usually called
the flow line and sometimes called
liquid state line.

● The moisture content that

corresponds to 25 blows is the liquid
limit of the soil.

where w1 and w2 are the water content corresponding to number of blows N1 and N2, respectively.
 Consistency Of Soil
Plastic Limit, PL
● Plastic limit is the water content in which
the soil will pass from plastic state to semi-
solid state. Soil can no longer behave as
plastic; any change in shape will cause the
soil to show visible cracks.

The Plastic limit test is performed by repeated rolling of an

ellipsoidal-sized soil mass by hand on a non-porous surface.
Casagrande defined the plastic limit as the water content at which a
thread of soil just crumbles when it is carefully rolled out to a
diameter of 3 mm (1/8”). If the thread crumbles at diameter smaller
than 3 mm, the soil is too wet. If the thread crumbles at a diameter
greater than 3 mm, the soil is drier than the plastic limit. The sample
can then be remolded, and the test repeated. Once the appropriate
size rolls are made, their moisture content is assessed using the
procedure described previously.
Consistency Of Soil
The shrinkage limit is an important
parameter in soil mechanics as it helps
understand the behavior of soil under
Shrinkage Limit, SL different moisture conditions, particularly
during compaction and drying processes.
● Shrinkage limit is the water content in
which the soil no longer changes in volume
regardless of further drying. It is the
lowest water content possible for the soil
to be completely saturated. Any lower
than the shrinkage limit will cause the
water to be partially saturated. This is the
point in which soil will pass from semi-solid
to solid state.

The shrinkage limit is determined as follows. A mass of wet soil, M1, is placed in a porcelain
dish 44.5 mm in diameter and 12.5 mm high and then oven-dried. The volume of oven-
dried soil is determined by using mercury to occupy the vacant spaces caused by
shrinkage. The mass of mercury is determined, and the volume decrease caused by
shrinkage can be calculated from the known the density of mercury.
Basic definitions:
● P𝑙𝑎𝑠𝑡𝑖𝑐𝑖𝑡𝑦 𝑖𝑛𝑑𝑒𝑥 (𝑃𝐼) = 𝐿. 𝐿 − 𝑃. 𝐿

𝐿.𝐿−𝑊𝐶
● Consistency 𝑖𝑛𝑑𝑒𝑥 (𝐶𝐼) = 𝐿.𝐿−𝑃.𝐿

𝑊𝐶 −𝑃.𝐿
● Liquidity 𝑖𝑛𝑑𝑒𝑥 (𝐿𝐼) = 𝐿.𝐿−𝑃.𝐿

PI Description
0 Non-plastic
1–5 Slightly plastic
5 – 10 Low plasticity
10 – 20 Medium plasticity
20 – 40 High plasticity
> 40 Very high plasticity