Lecture (4)
Mechanical Analysis of Soil
Sieve Analysis
Mechanical Analysis of Soil is the determination of the
size range of soil particles, expressed as a percentage of
total dry weight.
The particle size distribution of soil can be fined by two
methods.
• The sieve analysis technique is applicable for soil
grains larger than No. 200 (0.075 mm) sieve size.
• For fine-grained soils the procedure used for
determination of the grain-size distribution is
hydrometer analysis. This is based on the principle of
sedimentation of soil grains.
• Particle Size Classification. (Amercian Association –
(AASHTO )
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CLAY&SILT SAND %
GRAVEL
%PASSING
SIEVE 200
< (0.075 mm)
SAND %
GRAVEL
%
FINE
0.075-0.42
mm
MEDIUM
COARSE
0.42-2.0 mm
2.0-4.75 mm
4.75-75 mm
For a basic understanding of the nature of soil, the
distribution
of the grain size present in a given soil mass must be known.
The grain-size distribution of coarse-grained soils (gravelly
and / or sandy) is determined by sieve analysis. the opening
size of some U.S. sieves. Below,
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U.S. standard sieves
Sieve no. Opening size (mm)
4 4.75
8 2.38
10 2.00
20 0.84
30 0.59
40 0.425
50 0.297
60 0.25
70 0.21
100 0.149
140 0.105
200 0.075
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Sieve Analysis consists of shaking the dried soil sample
through a set of sieves having progressively smaller openings.
• First the soil sample is oven dried.
• All lumps are broken into small particles
• The standard sets of sieves is placed in the sieve
shaker and the sample is passed through the sieves.
( the duration of sieve shaker is about 10 minutes).
• The portion of soil sample retained on each sieve is
weighted.
• Percentage passing are calculated, the resulting
values are plotted on a semi-log. Scale.
• The cumulative percent by Dry weight of a soil passing a
given sieve is referred to as the percent finer
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Figure below shows the results of a sieve analysis for a sandy
soil. The grain-size distribution can be used to determine
some
of the basic soil parameters, such as the effective size, the
uniformity coefficient, and the coefficient of gradation.
Grain-size distribution of a sandy soil.
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• The effective size of a soil is the diameter through
which 10% of the total soil mass is passing and is
referred to as D10.
Effective Diameter = D10
Cu Uniformity coeff. = D60 / D10
Cc Gradation coeff. = (D30 )2/ (D60 * D10 )
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A soil is called a well-graded soil if the distribution of
the grain sizes extends over a rather large range. In that
case, the value of the uniformity
coefficient is large. Generally, a soil is referred to as well
graded if Cu is larger than about 4–6 and Cc is between 1
and 3.
When most of the grains in a soil mass are of
approximately the same size—i.e., Cu is close to 1—the
soil is called poorly graded.
A soil might have a combination of two or more well graded
soil fractions, and this type of soil is referred to as a
gap-graded soil.
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I. Poor graded Soil – Most of the soil grains are the Same
Size
II. Well graded Soil - Soil particle sizes are distributed
over a wide range.
III. Gap graded Soil – Soil might have a combination of
two or more uniformly graded fractions.
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PARTICLE-SIZE ANALYSIS
ASTM D 422
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D10% = 0.101
D30% = 0.266
D60% = 0.555
Effective Diameter = 0.101
cu uniformity coeff. = 5.471
Cc gradation coeff. = 1.260
Effective Diameter = D10
Cu Uniformity coeff. = D60 / D10
Cc Gradation coeff. = (D30 )2/ (D60 * D10 )
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PARTICLE-SIZE ANALYSIS
ASTM D 422
12/16
13/16
Pharos University
Faculty of Engineering
CV 256: Soil Mechanics
Architectural Dept.
Dr. Hassan Abd Ellatif
Sheet (2)
Grain Size Analysis
Sieve analysis was made for four soil samples and the results are
as shown in the following table:
Sample (A)
Sample (B)
Sample (C)
Sample (D)
(W retained) in gm
(W retained) in gm
(W retained) in gm
(W retained) in gm
4.75
0.00
28
0
0
2.00
21.60
42
44
0
0.840
49.50
48
56
0
0.425
102.6
128
82
249.1
0.250
89.10
221
91
179.8
0.149
95.60
86
136
22.7
0.075
60.40
40
92
15.5
Pan
31.2
24
45
23.5
Sieve (D) in mm
* Determine the percent finer than each sieve
and plot a
Grain -Size Distribution Curve for all the
samples.
* Calculate D10, D30 & D60 form the Grain Size Distribution
Curve for all the samples
* Calculate the uniformity coefficient, Cu
* Calculate the coefficient of gradation, Cc.
* Comment about each sample gradation.
* Classify each sample.