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Grain Size Analysis

This document provides an overview of grain size analysis techniques for soil mechanics. It discusses the purposes of grain size analysis, including its importance for concrete structures, roads construction, agriculture, and the environment. It covers sieve analysis and hydrometer analysis. Sieve analysis involves using a set of standard sieves to separate particles by size. Hydrometer analysis uses the principle of sedimentation to measure the fraction of particles smaller than 0.075 mm. The document defines key terms like effective size, uniformity coefficient, and coefficient of gradation used to characterize particle size distributions. It provides examples of interpreting particle size distribution curves and criteria for well-graded soils.

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132 views36 pages

Grain Size Analysis

This document provides an overview of grain size analysis techniques for soil mechanics. It discusses the purposes of grain size analysis, including its importance for concrete structures, roads construction, agriculture, and the environment. It covers sieve analysis and hydrometer analysis. Sieve analysis involves using a set of standard sieves to separate particles by size. Hydrometer analysis uses the principle of sedimentation to measure the fraction of particles smaller than 0.075 mm. The document defines key terms like effective size, uniformity coefficient, and coefficient of gradation used to characterize particle size distributions. It provides examples of interpreting particle size distribution curves and criteria for well-graded soils.

Uploaded by

JQ
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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College of Engineering

Civil Engineering Department

Soil Mechanics
NCE 412

Grain Size
Analysis

Lecture 2
Week 2
Content

• Purposes of Grain Size Analysis


• Sieve Analysis
• Hydrometer Analysis
• Particle Distribution
• Shape of Soil Particles
Purposes of Grain Size Analysis

The size distribution is often of critical


importance to the way the material performs
in use.

Examples

• Concrete Structures Economical Filler

• Roads Construction Bearing Base

• Agriculture Infiltration Rate

• Environment Filters
Grain Size Analysis

S2 < d < S 1 S1 < d

M2% M1%

d < S3 S3 < d < S2


M4% M3%
Sieve Analysis
Sieve Analysis
Standard Sieves

Sieve Opening
Sieve No.
(mm)
4 4.750
10 2.000
20 0.850
40 0.425
60 0.250
100 0.150
200 0.075

See text book (table 2.5)


Cohesiveness

• Soils can also be divided into:


cohesive and non-cohesive

• Non-cohesive means the soil has no shear strength if no


confinement.

• Cohesive soil contains clay minerals and posses


plasticity

• Clay is cohesive and plastic.

• Sand is non-cohesive and non-plastic.


Hydrometer Analysis

Based on the principle of sedimentation of soil


grains in water and bouncy principle.

Bouncy Force Stock’s Law

V1 < V2
F=Vρg
Hydrometer Analysis
Questions?!

30:00 min
Percent Finer

Finer (Passing)
76.2 mm 100 %

Gravel 100 – 93 = 7% Gravel

4.75 mm 93 %

Sand 93 – 62 = 31% Sand

0.075 mm 62 %
Silt and Clay 62 – 0 = 62% Silt and Clay
Pan 0%
Example: Sieve Analysis
Example: Sieve Analysis
Example: Sieve Analysis

100

90

80

70

Percent Finer %
60

50

40

30

20

10

0
5 4 3 2 1 0
Particle Size (mm)
Example: Sieve Analysis

Log-Scale
Group Work
Particle-Size Distribution Curve
Particle-Size Distribution Curve

1. Effective Size (D10)


10% Finer Hydraulic Conductivity

2. Uniformity Coefficient (Cu)


D60
Cu 
D10

3. Coefficient of Gradation (Cz)


D230
Cz 
D60  D10
Particle-Size Distribution Curve

1. Effective Size (D10)


10% Finer Hydraulic Conductivity

2. Uniformity Coefficient (Cu)


D60
Cu 
D10

3. Coefficient of Gradation (Cz)


D230
Cz 
D60  D10
Particle-Size Distribution Curve

Question
What is the Cu for a soil with only one
grain size?
Particle-Size Distribution Curve

Uniformity Coefficient (Cu)

Coefficien t of uniformity
Finer

D
Cu  60  1
D10

D
Grain size distribution
Particle-Size Distribution Curve

Criteria for Well-Graded Soil

1  C z  3 and Cu  4
(for gravels)

1  C z  3 and Cu  6
(for sands)
Particle-Size Distribution Curve
Questions?!

90:00 min
Hydrometer Analysis

Stokes’ Law
ρs  ρ w 2
v D
18 η

L 18 η
D
t ρs  ρ w

L
DK
t
Hydrometer Analysis
Hydrometer Analysis

L = 16.29 – 0.164 R

L
Corrections: Hydrometer Analysis

1. Temperature (FT)
FT = - 4.85 + 0.25 T

2. Meniscus Correction (Fm)

3. Zero Correction (Fz)


Questions?!

105:00 min
Example: Sieve Analysis
Example: Sieve Analysis

Rounded

Angular
Questions?!

120:00 min

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