1. SOILS Identify Basic Soils Properties
TEC C03-A01

2. It is the foundation for
Why is Soil important ?
It is the foundation for
all types of pavement
systems and building
structures.

3. What is Soil ... is the entire unconsolidated
earthen material that overlies
and excludes bedrock; plus
the water, air, organic
matter, and other substances
that may be contained therein.

4. What is Soil ... }
Air
Voids
Water
Soil Particles
(Solids)

5. BASIC PHYSICAL PROPERTIES
Engineers evaluate soils by the following Basic Physical Properties:
GRADATION of sizes of the different particles
BEARING CAPACITY as reflected by soils density
PARTICLE SHAPES interlock according to shapes; this affects strength
An engineer will also consider the effect of water on various types of soil for the project.

6. ….a soil’s properties help determine the engineering characteristics.
PHYSICAL PROPERTIES
….a soil’s properties help determine the engineering characteristics.
GRAIN SIZE
PARTICAL SHAPE
GRADATION
DENSITY
SPECIFIC GRAVITY
MOISTURE
CONSISTENCY
ORGANIC SOIL

7. } } GRAIN / PARTICLE SIZE + 3” - 3” + #4 #4 + #200 - #200 COBBLES
GRAVELS
SANDS
FINES (CLAY OR SILT) } }

8. Soils are divided into groups based
upon the size of the particles within
the soil mass.
Size Group Passing Retained on Example
Boulders No Max. Size 12 Inch
Cobbles 12 Inch 3 Inch
Gravel 3 Inch No 4 Lemon to Pea
(Coarse ) 3 Inch 3/4 Inch Lemon to Walnut
(Fine) 3/4 Inch No. 4 Walnut to Pea
Sands No. 4 No Pea to Powdered Sugar
(Coarse) No. 4 No. 10 Pea to Rock Salt
(Medium) No. 10 No. 40 Rock Salt to Table Salt
(Fine) No No Table Salt to P. Sugar
Fines No No Min. Size (Not discernible to eye)
(Silt) No (0.005)mm
(Clay) (0.005)mm No Min. Size

9. GRAIN/PARTICLE SHAPE WHAT ARE THE 2 TYPES?
The shape of soil particles influences
the strength and stability of a soil.
BULKY
Gravels, sands and silt fall into the bulky
shape ...relatively equal in all three dimensions.
Bulky shapes are further subdivided based
upon the effects of weathering. They may be
angular, subangular, subrounded, or rounded.
WHAT ARE THE 2 TYPES?
PLATY
Particles of clay exhibit a platy shape ... one
dimension is very small compared to the other
two.

10. The shape of soil particles influences
the strength and stability of a soil.
bulky shapes
angular subangular subrounded rounded
platy shape

11. GRADATION WHAT ARE THE 2 TYPES?
The distribution of the different size
particles in a soil mass is the gradation.
Well-graded soils have a good range of all
representative particle sizes between the largest
and the smallest.
Poorly-graded soils contain either a narrow range
of particle sizes or lack some intermediate sizes.
Uniformly graded have a narrow range of sizes.
Gap, step, or skip graded have some
intermediate sizes missing or not well
represented.
WHAT ARE THE 2 TYPES?

12. GRADATION
Well-graded
Uniformly graded
Gap, step, or skip graded

13. DENSITY Density is how closely packed or loose the soil structure is.
A density structure provides
interlocking of larger particles
with smaller particles filling the
voids between larger particles.

14. SPECIFIC GRAVITY Ratio between the weight-per-unit volume of
a given soil sample and the weight-per-unit
volume of a similar volume of water at a stated
temperature.
Specific Gravity of water is 1, Gold is 18.
If a soil has a Specific Gravity of 2.72, then
it is 2.72 times heavier than water.

15. MOISTURE Moisture Content is often the most important factor affecting
a soils behavior.
It is the proportion of the weight
of water to the weight of the solid
(dry) mineral grains in the soil.

16. MOISTURE Moisture has its greatest effect on the behavior of
fine-grained soils such as silts and clays.
Coarse-grained soils with larger voids
Are less susceptible to capillary action
Hold less water
Tend to drain more freely
Clay soil particles retard movement of water
Vary from liquid to brick hard
Impervious to passage of free moisture

17. Soil Moisture occurs in five types:
SURFACE WATER
… water from precipitation or runoff.
SUBSURFACE WATER
… collected or held in pools or layers beneath surface by a restricting layer of soil or rock.
GRAVITATIONAL PULL
… seeks lower layer & moves through voids until it reaches a restriction.
… voids in soil may form tunnels & tubes and cause water to rise in the tubes
CAPILLARY ACTION
… water that may be present as thin films.
ABSORBED WATER
& HYGROSCOPIC MOISTURE

18. Moisture Movement through Soil
Capillarity is the ability of a fine-grained
soil to absorb water and transmit it in all
directions. The water softens and expands
the soil.
Permeability refers to the rate at which
gravitational water will flow through soil.
Granular soils offer little resistance to the
flow and are most permeable. Fine-grained
soils, particularly clay, are least permeable.

19. PLASTICITY & COHESION Plasticity is a property of fine-grained
soils that allows it to be deformed without
cracking or breaking.
The Plasticity Index (PI) is used to
determine weather soil is cohesive. Not all
plastic soils are cohesive. (PURE SILT)
Soil plasticity is determined by observing
the different physical states a soil passes
through as the moisture content changes.

20. Physical States and Atterberg Limits

21. CONSISTANCY
Consistency- four states of consistency for fined grained soils (liquid, plastic, semisolid and solid).
The dividing line between these states of consistency are called the Liquid Limit (LL) and the Plastic Limit (PL). All are quantified in terms of water content (w).

22. SOIL MOISTURE STATES PLASTIC STATE %W INCREASING %W %W PI PL LL
LOW %W
HIGH %W
PLASTIC
STATE
SOLID
STATE
SEMI-SOLID
STATE
LIQUID
STATE PI PL LL
PI = LL - PL

23. Between the liquid and plastic limits is the
Physical States and Atterberg Limits
Liquid State ... soil will flow freely under its
own weight
The liquid limit (LL)
Plastic State ... soil will deform under pressure
without crumbling
The plastic limit (PL)
Semisolid or Solid State ... soil is no longer pliable
and will crumble under pressure
Between the liquid and plastic limits is the
plastic range.
PI = LL - PL

24. PLASTICITY CHART MH OR OH ML OR OL CH OR OH CL OR OL10 20 30 40 50 60 7 4 70 80 90
LIQUID LIMIT (LL)
PLASTICITY INDEX (PI)
“A” LINE
“U” LINE
MH OR OH
ML OR OL
CH OR OH
CL OR OL
CL - ML 16
PI = 0.9 (LL - 8)
PI = 0.73 (LL - 20)
LL-PL = PI

25. ORGANICS
Soil having a high content of organic material is described as organic soil.
Organics are typically very compressible and has poor load-maintaining properties.

26. Unified Soil Classification System
Field Classification
Major Divisions
Symbol
Field Identification Procedures
(Base fractions on estimated weights) GW GP GM GC SW SP SM SC ML CL OL MH CH OH Pt
Gravels
<5%
Fines
Sands
>12%
Silts & Clays
LL <50
LL >50
Highly Organic Soils
Fine-grained Soils
Coarse-grained Soils
More than half of
coarse fraction is
larger than
No. 4 sieve
smaller than
More than half of material is larger than
No. 200 sieve
More than half of material is smaller than
Readily identified by color, odor, spongy feel,
and frequently by fibrous texture
Wide range in grain sizes, all intermediate sizes substantially represented
Nonplastic fines or fines with little plasticity (see ML below)
Plastic fines (see CL below)
Predominantly one size or some intermediate sizes missing
Identification Procedures
on Fractions smaller than No. 40 sieve
Dry Strength
Wet Shake
Thread or
Ribbon
None to slight
Medium to high
Slight to medium
High to very high
Quick to slow
None to very slow
Slow
Slow to none
None
Medium
Slight
High

27. WHAT SYSTEM DO WE USE? Why classify Soil ...
purpose of a soil classification
system is to be able to predict
the engineering properties of
the soil.
WHAT SYSTEM DO
WE USE?

28. Unified Soil Classification System
The USCS looks at properties such as:
Percentages of gravel, sand, and fines.
Shape of the grain-size-distribution curve.
Plasticity and compressibility characteristics

29. Soil Classification gives a
good indication of …
Strength
Drainage
Resistance to Frost Action
Compressibility
(Volume Change)
Compaction
(Constructability)

30. USCS Letter Symbols Soils are divided into major groups and
further subdivided by characteristics.
Soil Groups Soil Characteristics
G Gravel W Well graded
S Sand P Poorly graded
M Silt H High compressibility
C Clay L Low compressibility
Pt Organic (Peat)
O Organic (Silts and clays)
L Liquid limit under 50
H Liquid limit over 50

31. USCS Soil Classification Chart
PI > 7 &
Plots on
or above
A Line
PI < 4
or Plots
below PI
Plots
Limits
Plot in
Hatched
Area
USCS
Soil Classification Chart
Determine %
Passing #200
If 50 % or More of Total Sample
It is a Fine-grained Soil
If Less than 50 % of Total Sample
It is a Coarse-grained Soil
Passing #4
Plot Atterberg
Test Data
Determine
Cu & Cc
If 50 % or More of Coarse Fraction
It is a Sand
If Less than 50 % of Coarse Fraction
It is a Gravel
If Less than 5%
of Total Sample
If Between 5% & 12%
If More than 12%
Classify with
Dual Symbol
Cu > 4
&
1 < Cc < 3
Cu > 6
YES NO
Classify as GW GP SW SP GM GC
GM-GC SM SC
SM-SC
GW-GM-GC
GW-GM
GW-GC
GP-GM
GP-GC
GP-GM-GC
SW-SM-SC
SW-SM
SW-SC
SP-SM
SP-SC
SP-SM-SC
ML or MH
Fines
CL or CH
CL-ML ML CH MH CL
Liquid Limit
< 50
> 50 OH OL
Liquid Limit (oven dried)
Liquid Limit (not dried)
< 0.75 If or
PLASTICITY CHART 10 20 30 40 50 60 7 4
LIQUID LIMIT (LL)
PLASTICITY INDEX (PI)
“A” LINE
“U” LINE
MH OR OH
ML OR OL
CH OR OH
CL OR OL
CL - ML 70 80 90 16
PI = 0.9 (LL - 8)
PI = 0.73 (LL - 20)

32. Any Questions?