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SOIL CLASSIFICATION

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SOIL CLASSIFICATION According to their particle sizes, soils are divided into two: Coarse grained soils: Gravel Sand Fine grained soils ... – PowerPoint PPT presentation

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Title: SOIL CLASSIFICATION


1
SOIL CLASSIFICATION
2
According to their particle sizes, soils are
divided into two
  • Coarse grained soils Gravel
  • Sand
  • Fine grained soils Silt
  • Clay

3
  • Cohesionless soils
  • Sand
  • Silt
  • Cohesive soil
  • Clay
  • Cohesion sticking together of like materials

4
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.

5
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).

6
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7
SIEVE ANALYSES
4                                             
10                                             
20                                             
40                                             
100                                             
200                                             
PAN                                             

8
Hydrometer Analysis
9
Hydrometer Analysis
10
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)

11
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12
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.

13
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.

14
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.

15
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)
16
For Cohesionless Soil (Gravel and Sand)
  • the soil can be
  • Poorly Graded or
  • Well Graded
  • Poorly Graded P
  • Well Graded W

17
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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19
  • 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

20
2- Coefficient of Curvature Cz (Cc)
  • (measure of the shape of the particle size curve)
  • Cz from 1 to 3 ------- well graded

21
  • 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.
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