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Civil EngineeringCivil Engineering
Soil MechanicsSoil Mechanics
Flow MeasurementsFlow Measurements
SurveyingSurveying
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SOIL MECHANICSSOIL MECHANICS
y Soil Classificati
on
y S
ieve Analysis
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INTRODUCTIONINTRODUCTION
Soils:
All naturally occurring relatively unconsolidated earth
material (organic or inorganic) that lies above bedrock.
They can be broken down into constituent particles
relatively easily (distinct from rocks, hard soil at the
boundary).
Soil mechanics:
Concerns the application of principles of mechanics,
hydraulics & chemistry to engineering problems related
to soils & to under stand soil behavior.
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INTRODUCTIONINTRODUCTION
In most of the civil engineering applications, soil is
subjected to stress due to external loading.The external
loading is caused by buildings (residential, commercial,
industrial), highways, dams, embankments etc.
In the present course, soil is studied as engineering
material and it is classified (gravel, sand, silt, clay) based
on certain experimental parameters. Based on this
classification proper use of soil as civil engineering
material is determined (in foundation, dam, highway,
embankment construction etc.)
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CLASSIFICATION OF SOILSCLASSIFICATION OF SOILS
y article Size Classification
y Textural Classification
y Public Roads Administration Classification
System
y Unified Soil Classification System
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Different types of soil classification:
(i) Particle size classification: Soil is classified as gravel, sand, silt &
clay based on particle size.
Grain size distribution of soil is determined.
(ii) Textural classification:
(a) IS:1498-1970 system: Grain size distribution of soil is obtained.
Weight of soil grain within each size group is computed.
% of soil in each size group is obtained (as per this system, mixed soilmight contain 10% gravel, 52% sand, 38% silt & clay).
(b) US bureau of soils & chemistry system: First % of sand, silt and
clay is found.
CLASSIFICATION OF SOILSCLASSIFICATION OF SOILS
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y Based on this a point is located on the triangular chart which indicates soil
type (Fig. 1 on page 14).
CLASSIFICATION OF SOILSCLASSIFICATION OF SOILS
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(iii) Public roads administration classification system [AASHTO
(1978) system]:Classification is based on particle size composition
as well as on plasticity characteristics.
Group index of soil is determined and soil is rated as subgrade material.
Higher value of group index indicates poor quality of material.
(iv) Unified soil classification system (USC): This method is based
on grain size distribution and plastic properties. It is applicable for
any use.
Modified USC has been adopted in IS:1498-1970.
Plasticity chart for classifying fine grained soil is given in Fig. 2 (Page 14)
Soils belowA line are inorganic silt, organic silt or organic clay.
CLASSIFICATION OF SOILSCLASSIFICATION OF SOILS
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CLASSIFICATION OF SOILSCLASSIFICATION OF SOILS
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y Coarse grained: gravel has 80mm to 4.75mm particle size.
sand has 4.75mm to 0.075mm size.
y Fine grained: silt has 0.075mm to 0.002mm particle size.
clay has less than 0.002mm particle size.
y Organic fine grained soil has appreciable amount of
organic matter in soil. It has dark brown colour and
odour of decaying vegetation.
y Inorganic fine grained soil is classified based on dry
strength, shaking, plasticity and dispersion test.
FIELD IDENTIFICATION OF SOILSFIELD IDENTIFICATION OF SOILS
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In dry strength test, 3mm size dry lump of fine grained
soil is broken between thumb and forefinger. Silt breaks
with little effort and clay requires lot of effort.
In shaking test, fine grained soil of very soft consistency
with smoothened top surface is kept in hand. It is shaked
in hand by tapping. If shiny appearance comes at top, then
it is silt. If dull appearance comes at top, then it is clay.
FIELD IDENTIFICATION OF SOILSFIELD IDENTIFICATION OF SOILS
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y In plasticity test, small fine grained soil paste is rolled
into 3mm thread. Clay can easily be rolled into thread,
whereas silt can·t be.y In dispersion test, small soil sample is dispersed in 10cm
water depth. Sand settles in 30sec, silt in 0.5 to 240
minutes and clay takes several hours to several days.
FIELD IDENTIFICATION OF SOILSFIELD IDENTIFICATION OF SOILS
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SieveAnalysis
WetAnalysis (HydrometerAnalysis)
Pipette Method
GRAIN SIZE ANALYSISGRAIN SIZE ANALYSIS
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SIEVE ANALYSIS
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SIEVE ANALYSIS
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SIEVE DESIGNATIONSIEVE DESIGNATION -- LARGELARGE
Sieves larger
than the #4
(4.75mm) sieve
are designated
by the size of the
openings in the
sieve
(Example:
31.5mm Size)
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SIEVE DESIGNATIONSIEVE DESIGNATION -- SMALLERSMALLER
10
openings
per inch
# 10 sieve
1-
inch
Smaller sieves are numbered according to the number of openings per inch
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SIEVE ANALYSIS
y Write down the weight of each sieve as well as the
pan to be used in the analysis.
y Record the weight of the given dry soil sample.
y Make sure that all the sieves are clean, and assemble
them in the ascending order of sieve numbers. Placethe pan below the smallest sieve. Carefully pour thesoil sample into the top sieve and place the cap over it.
yPlace the sieve stack in the mechanical shaker andshake f or 10 minutes
y Remove the stack fr om the shaker and carefully weigh and record the weight of each sieve including
the pan with its retained soil.
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SIEVES AS PER IS CODE OF PRACTICE
4.75mm
2.36mm
1.18mm
0.6mm
0.425mm
0.3mm0.15mm
0.075mm
PAN
(Weight of the Sample ± Depends on the Nominalsize of the Mix and the Sieve Aperture (For thecurrent Experiment ± 1200Gm)
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