Grain size distribution in Soil Mechanics, Soil classification of soil on the basis of grain size. Soil mechanics, Distribution curve on the basis of grain size in soil mechanics

2. Grain Size
Soil Mechanics CT-233
Department of Civil Technology
Course In charge: Engr. Ameer Murad Khan.
Mir Chakar Khan Rind University of Technology, DGK.

3.  Grain size is a fundamental physical property of sedimentary rocks and, as
such, is a useful descriptive property.
 Grain size affects the porosity and permeability and porosity of the rocks
and thus is of considerable interest to petroleum geologists.
 Grain size data reflects sedimentation mechanisms, transportation and
depositional conditions
Importance Of Grain Size Data

4. Manual measurement of the clasts
 Sieve Analysis
 Settling tube analysis
 Pipette analysis
 Sedi graph
 Laser diffractometer
 Coulter Counter
 Image Analysis
 Photo hydrometer
 Thin section measurement
 Electron microscope
Techniques for measuring grain size

5.  This method is used to measure unconsolidated
sediments by sieving them through a set of nested wire mesh screens.
 Particles having size smaller than the mesh pass through while the smaller
ones remain.
 Size of mesh is standardized and is identified using mesh number.
 The mesh number denotes the number of squares present in 1sq.inch of
area
Sieve Analysis

7.  The settling velocity of particles falling through a fluid medium depends on the
size, shape, and density of the particle, and the density and viscosity of the fluid.
 In this technique, grains are allowed to settle through a column of water at a
specified temperature in a settling tube. It is based on Stoke’s law:
where;
V= settling velocity
C= constant
D= diameter of the particle
Settling Tube Analysis

8.  A laser-diffractor size analyzer operates on the principle that particles of a given size
diffract light through a given angle, which increase with decreasing particle size.
 This technique use T.V cameras to capture and digitize grain images from which, with the
aid of appropriate computer software, grain size diameters can be calculated.
 A photohydrometer is a settling tube that relates the changes in the intensity of the beam
of light passed through a column of suspended sediment to particles settling velocities
and thus to particle size
Laser Diffractometer

9. 1.Histogram-a bar graph
2.Frequency curves Show the variation of
wt.% as a continuous function of grain size.
3.Cumulative curves-an Sshaped curve on
the arithmetic ordinate scale
GRAPHICAL PRESENTATION OF GRAIN SIZE DATA

10. 1.Mode-most frequency
occuring particle diameter
2.Median-midpoint of
grain Size distribution
3.Mean-arithmatic mean
can be Arrived at by
picking selected Percentile
value and averaging them
STATISTICAL PARAMETERS OF GRAIN
SIZE

11. 4.Standard
Deviation-measures
the ‘sorting’
(uniformity of
particle size
distribution)
5. Skewness-
measures of
The asymmetry of the
distribution
STATISTICAL PARAMETERS OF GRAIN
SIZE

12. 6.Kurtosis-degree of “peakedness”
- If the central portion is better sorted=excessively
Peaked or “leptokurtic”
- If the tails is better sorted =flat peaked or “platy-kurtic”
STATISTICAL PARAMETERS OF GRAIN
SIZE

15. Lets Learn
Together…
 Any Question