soils identify basic soils properties
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SOILS Identify Basic Soils Properties. TEC C03-A01. Why is Soil important ?. It is the foundation for all types of pavement systems and building structures. What is Soil ... is the entire unconsolidated earthen material that overlies and excludes bedrock; plus - PowerPoint PPT PresentationTRANSCRIPT
SOILSIdentify Basic Soils Properties
TEC C03-A01
Why is Soil important ?
It is the foundation forall types of pavementsystems and building
structures.
What is Soil ...is the entire unconsolidated earthen material that overliesand excludes bedrock; plusthe water, air, organic matter, and other substancesthat may be contained therein.
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
Engineers evaluate soils by the following Basic Physical Properties:
An engineer will also consider the effect of water on various types of soil for the project.
PHYSICAL PROPERTIES GRAIN SIZE PARTICAL SHAPE GRADATION DENSITY SPECIFIC GRAVITY MOISTURE CONSISTENCY ORGANIC SOIL
….a soil’s properties help determine the engineering characteristic
s.
GRAIN / PARTICLE SIZE
COBBLES
GRAVELS
SANDS
FINES (CLAY OR SILT)
}+ 3”- 3”+ #4- #4+ #200- #200
}
The shape of soil particles influencesthe strength and stability of a soil.
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.
Particles of clay exhibit a platy shape ... onedimension is very small compared to the othertwo.
BULKY
PLATY
GRAIN/PARTICLE SHAPE
WHAT ARE THE 2 TYPES?
The shape of soil particles influencesthe strength and stability of a soil.
bulky shapes
angular subangular subrounded rounded
platy shape
The distribution of the different sizeparticles in a soil mass is the gradation.
Well-graded soils have a good range of allrepresentative particle sizes between the largest and the smallest.
Poorly-graded soils contain either a narrow rangeof 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 wellrepresented.
GRADATION
WHAT ARE THE 2 TYPES?
Well-graded
Uniformly graded
Gap, step, or skip graded
GRADATION
• Density is how closely packedor loose the soil structure is.
• A density structure provides interlocking of larger particleswith smaller particles filling thevoids between larger particles.
DENSITY
• Ratio between the weight-per-unit volume ofa given soil sample and the weight-per-unit volume of a similar volume of water at a statedtemperature.
• 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.
SPECIFIC GRAVITY
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.
MOISTURE
Moisture has its greatest effect on the behavior offine-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
MOISTURE
Soil Moisture occurs in five types:1) SURFACE WATER … water from
precipitation or runoff.… collected or held in pools or layers beneath surface by a restricting layer of soil or rock.
2) SUBSURFACE WATER
3) GRAVITATIONAL PULL
4) CAPILLARY ACTION
5) ABSORBED WATER& HYGROSCOPIC MOISTURE
… voids in soil may form tunnels & tubes and cause water to rise in the tubes
… seeks lower layer & moves through voids until it reaches a restriction.
… water that may be present as thin films.
• Plasticity is a property of fine-grainedsoils that allows it to be deformed withoutcracking or breaking.
• The Plasticity Index (PI) is used to determine weather soil is cohesive. Not allplastic soils are cohesive. (PURE SILT)
• Soil plasticity is determined by observingthe different physical states a soil passes through as the moisture content changes.
PLASTICITY & COHESION
Physical States and Atterberg Limits
In 1911, a Swedish soil scientist, Albert Atterberg described the effects of changing water content on the consistency of fine-grained soil. He also proposed a series of tests to determine soil properties, which define the water content ranges of soil states or phases. The change from one phase to the next is not observable as a precise boundary, but takes place as a gradual transition. Nevertheless arbitrary but specific boundaries have been established empirically and are universally recognized. The moisture contents at these boundaries are known as the Atterberg limits or consistency limits. In 1932, A. Casagrande designed a device, the cup in use today, to standardize the liquid limit test. He incorporated Atterberg limits in a procedure, the Unified Soil Classification System (USCS), to identify the soils used in construction.
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).
SOIL MOISTURE STATES
SOLID STATE
SEMI-SOLID STATE
PLASTIC STATE
LIQUIDSTATE
%W INCREASING%W %W
PL LL
PI
PI = LL - PL
LOW %W HIGH %W
PLASTICITY CHART
0
10
20
30
40
50
60
74
10 20 30 40 50 60 70 80 90LIQUID LIMIT (LL)
PLAS
TICI
TY IN
DEX
(PI
)
“A” L
INE
“U” L
INE
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
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.
Why classify Soil ...purpose of a soil classificationsystem is to be able to predict the engineering properties of the soil.
WHAT SYSTEM DO WE USE?
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
Soil Classification gives agood indication of …
•Strength•Drainage•Resistance to Frost Action•Compressibility(Volume Change)
•Compaction(Constructability)
USCS Letter Symbols
Soils are divided into major groups and further subdivided by characteristics.
Soil Groups Soil CharacteristicsG Gravel W Well gradedS Sand P Poorly gradedM Silt H High compressibilityC Clay L Low compressibility
Pt Organic (Peat)O Organic (Silts and clays)L Liquid limit under 50H Liquid limit over 50
PI > 7 &Plots onor aboveA Line
PI < 4or PlotsbelowA Line
PIPlots onor aboveA Line
PIPlotsbelowA Line
LimitsPlot in
HatchedArea
USCSSoil Classification Chart
Determine %Passing #200
If 50 % or More of Total SampleIt is a Fine-grained Soil
If Less than 50 % of Total SampleIt is a Coarse-grained Soil
Determine %Passing #4
Plot AtterbergTest Data
Determine %Passing #200
Determine %Passing #200
Plot AtterbergTest Data
DetermineCu & Cc
Plot AtterbergTest Data
DetermineCu & Cc
If 50 % or More of Coarse Fraction
It is a Sand
If Less than 50 % of Coarse FractionIt is a Gravel
If Less than 5%of Total Sample
If Between 5% & 12%of Total Sample
If More than 12%of Total Sample
If Less than 5%of Total Sample
If Between 5% & 12%of Total Sample
If More than 12%of Total Sample
Classify withDual Symbol
DetermineCu & Cc
Classify withDual Symbol
DetermineCu & Cc
Cu > 4&
1 < Cc < 3
Cu > 6&
1 < Cc < 3
Cu > 4&
1 < Cc < 3
YES NO
Classifyas
GW
ClassifyasGP
Cu > 6&
1 < Cc < 3
YES NO
Classifyas
SW
ClassifyasSP
Classifyas
GM
Classifyas
GC
Classifyas
GM-GC
Classifyas
SM
ClassifyasSC
Classifyas
SM-SC
Plot AtterbergTest Data
Plot AtterbergTest Data
Plot AtterbergTest Data
Plot AtterbergTest Data
Classifyas
GW-GM-GC
Classifyas
GW-GM
Classifyas
GW-GC
Classifyas
GP-GM
Classifyas
GP-GC
Classifyas
GP-GM-GC
Classifyas
SW-SM-SC
Classifyas
SW-SM
Classifyas
SW-SC
Classifyas
SP-SM
Classifyas
SP-SC
Classifyas
SP-SM-SC
ML or MHFines
ML or MHFines
ML or MHFines
CL or CHFines
CL or CHFines
CL or CHFines
ML or MHFines
CL or CHFines
CL-MLFines
CL-MLFines
CL-MLFines
CL-MLFines
YES NO YES NO
ML or MHFines
CL or CHFines
CL-MLFines
ML or MHFines
CL or CHFines
CL-MLFines
Classifyas
ML
Classifyas
CL-ML
Classifyas
CH
Classifyas
MH
Classifyas
CL
Liquid Limit< 50
Liquid Limit> 50
Classifyas
OH
Classifyas
OL
Liquid Limit (oven dried)Liquid Limit (not dried)
< 0.75If
or
PLASTICITY CHART
0
10
20
30
40
50
60
74
LIQUID LIMIT (LL)
PLA
STIC
ITY
IND
EX (P
I)
“A” L
INE
“U” L
INE
MH OR OH
ML OR OL
CH OR OH
CL OR OL
CL - ML
10 20 30 40 50 60 70 80 9016
PI = 0.9 (L
L - 8)
PI = 0.73 (LL - 20)
Any Questions?