Class 2 Grain Size Analysis ( Geotechnical Engineering )

1. Civil Engineering - Texas Tech University
CE 3121: Geotechnical Engineering Laboratory
Class 2
Grain Size Analysis
Sources:
Soil Mechanics – Laboratory Manual,B.M. DAS (Chapters 4 & 5)
Soil Properties, Testing, Measurement, and Evaluation, C. Liu, J. Evett

2. Civil Engineering - Texas Tech University
 Grain size Analysis
 Chapter 4: Mechanical Method (Sieve Analysis)
 Chapter 5: Hydrometer Method
Class Outlines

3. Civil Engineering - Texas Tech University
2- Grain size Analysis
 The knowledge of sizes of solid particles
comprising a certain soil type and their
relative proportion is useful because it is used
in;
 Soils classification
 Soil filter design
 Predictions the behavior of a soil with respect
to shear strength, settlement and permeability

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Grain size Analysis (Continue)
 Two types of grain size analyses are typically
performed
 Mechanical analysis also know as sieve
analysis
 Hydrometer analysis

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Sieve Analysis
 ASTM D 421
 Applicable for soils that are mostly granular
with some or no fines
 The U.S. No. 200 sieve (0.074mm or
0.0029in) is the smallest sieve size typically
used in practice
 Small size is 500g (why?)

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Sieve Analysis (Cont.)

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Sieve Analysis (Cont.)
 3/8”, ¼” sieves is the size
of the opening
 No.10 sieve …. has 10
apertures per linear inch
 Use sieves No.3/8”, No.4,
No.10, No.40, No.140 &
No.200

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Grain Size Distribution Curves
D60
D30
D10
0.8 mm
0.4 mm
0.15 mm
0.15 mm
0.8 mm
5.3
0.4
0.15 0.8
1.33

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Sieve Analysis (Cont.)
 D60 - the diameter corresponding to 60% finer in the
particle-size distribution curve
 D10 – effective size
 Cu – coefficient of gradation,
 Cc – coefficient of curvature,
10
60
D
D
cu 
 
1060
2
30
DD
D
cc


Note:
If cu is relatively large, it indicates a well graded soil. Cu = 1 indicates
that the soil grains are of approximately equal sizes.

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Hydrometer Analysis
 ASTM D422
 This method is generally used to determine the particle-
size distribution for soils with small grain sizes < 0.075
mm (No. 200)
 The lower limit of the particle size determined by this
procedure is about 0.001mm
 In the lab we will use ASTM 152-H Hydrometer (?)
 This method is based on Stoke’s law “The larger the
grain size, the greater its settling velocity in a fluid”
 The sample size is 50g passing #10 (why?)
waterofityvisDv ws
cos:;
18
)( 2


 


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Hydrometer Analysis (Cont.)
L =30

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Hydrometer Test (Cont.)
 A Hydrometer reading of 30 means that there
are 30 g of soil solids in suspension per
1000cc of soil-water mixture at a temperature
of 200C
 Take reading at 15, 30, 60 seconds then at 2,
5, 15, 30 and 60 minutes

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Composite Corrections
 Fm – Meniscus Correction
 Zero Correction, Fz
Accounts for the effect of using a deflocculating agent
 Temperature Correction, FT
FT = - 4.85 + 0.25T (T between 15 – 280C)
 Composite Correction = Fm + Fz + FT
Fm

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Hydrometer Test (Procedure)
1. Prepare a deflocculating (dispersing) agent
 Use a 4% solution of Sodium
hexametaphophate (Calgon)
 Add the 40g of Calgon in 1000cc of distilled
water and mix thoroughly
2. Use 45±5g of soil passing #10
3. Take 125cc of the mixture prepared in (1)
and add it to the soil in (2) and let it soak for
about 8 – 12hours

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Hydrometer Test (Calculation - pp 30)
 R – Hydrometer reading (col 2)
 Rcp – corrected hydrometer reading for calculation of
percent finer (col 3)
Rcp = R + FT – Fz
 Percent finer (col 4) =
 RcL - Corrected reading for determination of effective
length (col 5) & Find L from Table 5-1 pp 26
RcL = R + Fm
 Determine D =
s
cp
W
Ra a = correction for Gs see
Table 5-3 pp 30
Assume Gs = 2.65
(min)
)(
t
cmL
A