SOIL CLASSIFICATION

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SOIL CLASSIFICATION
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According to their particle sizes, soils are
divided into two

• Coarse grained soils Gravel
• Sand
• Fine grained soils Silt
• Clay

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• Cohesionless soils
• Sand
• Silt
• Cohesive soil
• Clay
• Cohesion sticking together of like materials

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Plasticity of Fine-Grained Soils

• Plasticity is an important characteristic in
  Fine-Grained Soils.
• Plasticity is the ability of a soil to undergo
  unrecoverable deformation at constant volume
  without cracking and crumbling.
• Plasticity is due to the presence of clay
  minerals or organic material.

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PARTICLE SIZE DISTRIBUTION

• It is a screening process in which coarse
  fractions of soil are separated by means of
  series of sieves.
• Particle sizes larger than 0.074 mm (U.S. No. 200
  sieve) are usually analyzed by means of sieving.
• Soil materials finer than 0.074 mm
• (-200 material) are analyzed by means of
• sedimentation of soil particles
• by gravity (hydrometer analysis).

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SIEVE ANALYSES
4                                             
10                                             
20                                             
40                                             
100                                             
200                                             
PAN                                             

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Hydrometer Analysis
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Hydrometer Analysis
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General Particle Sizes

• Particle Average Diameter (mm) Average
  Diameter (mm)
• According to MIT According to ASTM
• Boulders ? 200 ? 300
• Cobbles 200-60 300-75
• Gravel 60.0 2.0 75- 4.75
• Sand 2.0 0.06 4.75- 0.075
• Silt 0.06 0.002 0.075- 0.002
• Clay ? 0.002 ? 0.002
• MIT(Massachusetts Institute of Technology)
• ASTM (American Society for Testing and
  Materials)

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Classification Systems

• The most widely used classification systems are
• the American Association of State Highway and
  Transportation Officials (AASHTO) and
• the Unified Soil Classification System (USCS).
• In this class, we will mainly discuss the USCS
  system that is used by engineering consulting
  companies and soil-testing laboratories.

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Well graded soil

• Well graded a coarse grained soil is described
  as well graded if there is no excess of particles
  in any size range and if no intermediate sizes
  are lacking. Almost all particle sizes are
  present.
• In general a well-graded soil is represented by a
  smooth concave distribution curve.

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Poorly graded soil

• UNIFORM SOIL A high proportion of the particles
  have sizes within narrow limits.
• GAP GRADED SOIL Particles of both large and
  small sizes are present but with a relatively low
  proportion of particles of intermediate size.
• Example
• mixture of coarse sand and clay with no silt.
• mixture of gravel and silt with no sand.

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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 E - a typical silty CLAY
(e.g. London clay, Oxford clay)
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For Cohesionless Soil (Gravel and Sand)

• the soil can be
• Poorly Graded or
• Well Graded
• Poorly Graded P
• Well Graded W

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There are certain parameters used in the
classification of soils.

• Effective size, D10 The size such that 10 of
  the particles are smaller than that size.
• D60 The size such that 60 of the particles are
  smaller than that size.
• D30 The size such that 30 of the particles are
  smaller than that size.

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• Parameters Obtained From Grain Size Distribution
  Curve
• 1- Uniformity Coefficient Cu (measure of the
  particle size range)
• Cu D60/D10
• Cu lt 5 ----- Very Uniform
• Cu 5 ----- Medium Uniform
• Cu gt 5 ----- Nonuniform

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2- Coefficient of Curvature Cz (Cc)

• (measure of the shape of the particle size curve)
  
• Cz from 1 to 3 ------- well graded

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• Unified Soil Classification System (USCS)

• Note  The amount of Fines in a soil sample is
  the percent by weight that passes a number 200
  sieve.