final classification of soil ppt

8/10/2019 Final Classification of Soil PPT

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Classification Of Soil

Gurdarshan Singh

Roll no 1307Geotechnical Engineering


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1.Purpose

Main soils are ;clay, silt, sand, gravels andboulders etc.

Above type seldomexits separately in the

nature.

Natural soil deposits comprise mixture of

above type in varies proportions.

Soil classification mean to arrange in soil of

groups and label them based on theirproperties and behavior.

Soil classification has been developed by

different organizations .


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. Classifying soil into groups with similar behavior into the termof Simple indices can provide geotechnical a general guidance

about engineering properties of the soil through theaccumulated of experiences .

Communicate

between

Engineers

Simple index Classification Estimate Achieve

system Engineering Engineering

GSD, LL, PL ( Language ) Properties Purposes

Use the

accumulated

experience


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Soil Classification System

Classification system developed by different organization

1 Unified Soil Classification System (USCS).

2 AASHTO ( American Association Of State Highway and

Transportation official ) soil classification .

3 Indian Standard Classification System (ISCS)


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1. Unified Soil Classification

System(USCS)

The Unified Soil Classification System (USC) was first

developed by casagrande in 1948. It is modified by the Bureau of Reclamation and the crops of

Engineers of the Unified State of America.

The system has also been adopted by American Society of

Testing Material (ASTM). The System is the most popular system for use in all types of

engineering problems involving soils .


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There are four major divisions of unified soil classification system

(USCS)

(1) Coarse Grained

(2) Fine-Grained

(3) Organic Soils

(4) Peat


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Definition of Grain Size

8

Boulders Cobbles

Gravel Sand Silt and

Clay

Coarse Fine Coarse FineMedium

300 mm 75 mm

19 mm

No.4

4.75 mm

No.10

2.0 mm

No.40

0.425 mm

No.200

0.075mm

No specific grain

size-use

Atterberg limits


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General Guidance

9

Coarse-grained soils:

Gravel Sand

Fine-grained soils:

Silt Clay

NO.200

0.075

mm

Grain size distribution

Cu

Cc

PL, LL

Plasticity chart

50 %

NO. 44.75 mm

Required tests: Sieve analysis

Atterberg limit

LL>50 LL


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Dry Clay Silt Medium Coarse Sand Fine Gravel Medium Gravel

Sieve Analysis


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Liquid Limit (LL) Test

Plastic Limit Device

PlasticLimit(PL)

Atterberg Limits

(Standard tests methods

for Liquid Limit, Plastic

Limit and Plastic Index of

properties)


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Symbols

12


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Procedures for Classification

15

Coarse-grained

material

Grain size

distribution

Fine-grained

material

LL, PI

Highly


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Organic Soils

Highly organic soils- Peat (Group symbol PT)

A sample composed primarily of vegetable tissue in various stages of

decomposition and has a fibrous to amorphous texture, a dark-

brown to black color, and an organic odor should be designated as a

highly organic soil and shall be classified as peat, PT.

Organic clay or silt( group symbol OL or OH):

Thesoils liquid limit (LL) after oven drying is less than 75 % of its

liquid limit before oven drying.If the above statement is true, then

the first symbol is O.

The second symbol is obtained by locating the values of PI and LL

(not oven dried) in the plasticity chart.

16


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Borderline Cases (Dual Symbols)

For the following three conditions, a dual symbol should be used. Coarse-grained soils with 5% - 12% fine.

About 7 % fines can change the hydraulic conductivity of the

coarse-grained media by orders of magnitude.

The first symbol indicates whether the coarse fraction is well or

poorly graded. The second symbol describe the contained fines. Forexample: SP-SM, poorly graded sand with silt.

Fine-grained soils with limits within the shaded zone. (PI between 4

and 7 and LL between about 12 and 25).

It is hard to distinguish between the silty and more claylike

materials.

CL-ML: Silty clay, SC-SM: Silty, clayed sand.

Soil contain similar fines and coarse-grained fractions.

possible dual symbols GM-ML


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18

Borderline Cases (Summary)

2 A i A i ti Of St t


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2. AmericanAssociation Of StateHighway And Transportation

Official System

This system was originally developed by Hogentogler and

Terzaghi in 1929 as the public roads classification system .

They particle size analysis and the plasticity characteristics

are required to classify a soil .

The classification system is a complete system which classifies

both the coarse grained and fine grained soils.


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The system is based on the following three soil properties:

1.Particle-size distribution .

2.Liquid Limit .

3.Plasticity Index .


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Key Elements:

1.Grain Size:

Gravel: Fraction passing 75mm sieve and retained on #10 (2mm)US sieve

Sand: Fraction passing #10 sieve and retained #200 sieve

Silt and Clay: Fraction passing #200 sieve

2.Plasticity:

Term silty is applied when fine fractions have a PI< 10

Term clayey is applied when fine fractions have PI> 11

3.Groups:

Soilsareclassifiedintoeightgroups,A-1throughA-8.

ThemajorgroupsA-1,A-2,andA-3representthecoarsegrainedsoils.

TheA-4,A-5,A-6,andA-7representfinegrainedsoils.

TheA-8areidentifiedbyvisualinspection.


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The ranges of the LL and PI for groups A-2,A-4,A-5,A-6andA-7:


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General Guidance 8 major groups: A1~ A7 (with several subgroups) and organic

soils A8

The required tests are sieve analysis and Atterberg limits.

The group index, an empirical formula, is used to furtherevaluate soils within a group (subgroups).

The original purpose of this classification system is used for roadconstruction (sub grade rating).

A4 ~ A7A1 ~ A3

Granular Materials

35% pass No. 200 sieve

Silt-clay Materials

36% pass No. 200 sieve

Using LL and PI separates silty

materials from clayey materials

Using LL and PI separates silty

materials from clayey materials(only for A2 group)


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24

Group Index

)10PI)(15F(01.0

)40LL(005.02.0)35F(GI

200

200

)10PI)(15F(01.0GI 200

For Group A-2-6 and A-2-7

The first term is determined by the LL

The second term is determined bythe PI

In general, the rating for a pavement sub grade is

inversely proportional to the group index, GI.

use the second term

only

F200: percentage passing through the No.200 sieve


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It may be noted that:

The higher the value of GI the weaker will be the soil and

vice versa. Thus, quality of performance of a soils a sub grade

material is inversely proportional to GI.

A soil having GI of zero is considered as the best.

If the equation gives negative value for GI, consider it zero.

Always round off the G I to nearest whole number.

GI=0 for soils of groups A-1- a, A-1-b ,A-2- 4, A-2-5, and A-3.

For groups A-2-6 and A-2-7 use partial GI for PI only:


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Classification of Highway Subgrade Materials :


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Classification of Highway Sub grade Materials :


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Indian Standard Classification System

(ISC)

Indian standard classification (ISC) system adopted by bureau

of Indian standards is in many respects similar to the Unified

Soil Classification (UCS) system.

There is one basic difference in the classification of fine

grained soils .

The fine grained soils in ISC system are subdivided into three

categories of low, medium and high compressibility instead of

two categories of low and high compressibility in USC system .


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Soils are divided into three broad divisions :

1. Coarse grained soils, when 50% or more of the total material

by weight is retained on 75 micron IS sieve .

2. Fine grained soils, when more than 50% of the total materialpasses 75 micron IS sieve .

3. If the soil is highly organic and contains a large percentage of

organic matter and particles of decomposed vegetation, it iskept in a separate category marked as peat (Pt).


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Basic Soil Components in ISC System1. Coarse grained soils Coarse grained soils are sub divided

onto gravel and sand. The soil is termed gravel(G) whenthan 50% of coarse fraction (plus 75) is retained on 4.75mm IS sieve , and termed sand (S) more than 50% of thecoarse fraction is smaller than 4.75 mm IS sieve.

2. Fine grained soils the fine grained soils are further dividedinto three subdivisions, depending upon the values of theliquid limit:

a) Silts and clays of low compressibility these soils have aliquid limit less than 35.

b) Silts and clays of medium compressibility these soils have aliquid limit greater than 50.

c) Silts and clays of high compressibility- these soils have aliquid limit greater than 50.


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Basics Soil Components ISC System


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Reminder 0.075 mm(75m) separates coarse and fine grained soils .

Uniformly graded soils are poorly graded .

Grain size distributions are mainly for coarse grained soils;Atterberg limits are for fines.

Clay particles are negatively charged flakes with a high surface

area and are smaller than 2m in size; they are plastic andsticky (cohesive). Silts are non plastic (PI=0)

A fine grained soil is classified as clay or silt based onAtterberg limits not on relative proportions .

The first thing one should know when classifying a soil is the% of fines.

In AASHTO, the general rating as a subgrade decreases fromleft to right, A-1 being the best and A-8 being the worst.


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References

Soil Mechanics And Foundation Engineering ( DR. K.R. Arora).

Geotechnical Engineering ( N Sivakugan / Braja M. Das).

Soil Mechanics and Foundations ( Dr B C Punmia and Ashok

Kumar Jain)

final classification of soil ppt

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