Download Mechanical Analysis of Soil - Introduction to Sieve Analysis | CIVL 1101 and more Exams Civil Engineering in PDF only on Docsity!
Mechanical Analysis of Soil
] Mechanical analysis is the determination of the size
range of particles present in a soil, expressed as a
percentage of the total dry weight.
] There are two methods generally used to find the
particle–size distribution of soil:
\ 1) sieve analysis – for particle sizes larger than 0.075 mm in
diameter, and
\ (2) hydrometer analysis – for particle sizes smaller than
0.075 mm in diameter. The basic principles of sieve analysis
and hydrometer ever analysis are briefly described in the
following two sections.
Mechanical Analysis of Soil
Sieve analysis Hydrometer analysis
Sieve Analysis
] Sieve analysis consists of shaking the soil sample
through a set of sieves that have progressively smaller
openings.
Sieve Analysis
Sieve Number Opening (mm) 4 4. 6 3. 8 2. 10 2. 16 1. 20 0. 30 0. 40 0. 50 0. 60 0. 80 0. 100 0. 140 0. 170 0. 200 0. 270 0.
Sieve Analysis
] First the soil is oven dried and then all lumps are
broken into small particle before they are passed
through the sieves
] After the completion of
the shaking period the
mass of soil retained on
each sieve is determined
Sieve Analysis
] The results of sieve analysis are generally expressed
in terms of the percentage of the total weight of soil
that passed through different sieves
Sieve
Diameter (mm)
Mass of soil retained on each sieve (g)
Percent of soil retained on each sieve (g)
Percent passing (%)
Pan –– 278.99 62.00 0
Sieve Analysis
Sieve
Diameter (mm)
Mass of soil retained on each sieve (g)
Percent of soil retained on each sieve (g)
Percent passing (%)
Pan –– 278.99 62.00 0
] Sieve Analysis (Mass of Dry Soil Sample = 450 g)
Sieve Analysis
Sieve
Diameter (mm)
Mass of soil retained on each sieve (g)
Percent of soil retained on each sieve (g)
Percent passing (%)
Pan –– 278.99 62.00 0
] Sieve Analysis (Mass of Dry Soil Sample = 450 g)
Particle–Size Distribution Curve
] The results of mechanical analysis (sieve and hydrometer
analyses) are generally presented by semi–logarithmic
plots known as particle–size distribution curves.
] The particle diameters are plotted in log scale, and the
corresponding percent finer in arithmetic scale.
Particle–Size Distribution Curve
Silt and clay Sand
Particle diameter (mm)
Percent finer (%)
1. Weigh to 0.1 g each sieve which is to be used
2. Select with care a test sample which is representative
of the soil to be tested
3. Weigh to 0.1 a specimen of approximately 500 g
of oven–dried soil
4. Sieve the soil through a nest of sieves by hand
shaking. At least 10 minutes of hand sieving is
desirable for soils with small particles.
5. Weigh to 0.1 g each sieve and the pan with the soil retained on
them.
6. Subtract the weights obtained in step 1 from those of step 5 to
give the weight of soil retained on each sieve.
The sum of these retained weights should be checked against the
original soil weight.
Recommended Procedure
] Percentage retained on any sieve:
Calculations
100%
weight of soil retained
total soil weight
= ×
] Cumulative percentage retained on any sieve:
= ∑Percentage retained
] Percentage finer than an sieve size:
100%− ∑Percentage retained
Effective Size, Uniformity Coefficient, and
Coefficient of Gradation
] For the particle-size distribution curve we just used,
the values of D 10 , D 30 , and D 60 are:
D 10 = 0.093 mm D 30 = 0.25 mm D 60 = 0.51 mm
u
D C D
=
mm
mm
= =
c
D C D D
= ×
(0.25 )
0.51 0.
mm
mm mm
= = ×
Effective Size, Uniformity Coefficient, and
Coefficient of Gradation
Particle diameter (mm)
Percent finer (%)
] The particle–size distribution curve shows not only the
range of particle sizes present in a soil but also the
type of distribution of various size particles.
Effective Size, Uniformity Coefficient, and
Coefficient of Gradation
Particle diameter (mm)
Percent finer (%)
] This particle-size distribution represents a soil in
which the particles are distributed over a wide range,
termed well graded
Effective Size, Uniformity Coefficient, and
Coefficient of Gradation
Particle diameter (mm)
Percent finer (%)
] This particle-size distribution represents a type of
soil in which most of the soil grains are the same size.
This is called a uniformly graded soil.
Effective Size, Uniformity Coefficient, and
Coefficient of Gradation
Particle diameter (mm)
Percent finer (%)
] This particle-size distribution represents such a soil.
This type of soil is termed gap graded.
Example Sieve Analysis
] From the results of a sieve analysis, shown below,
determine:
(a) the percent finer than each sieve and plot a grain–size
distribution curve,
(b)D 10 ,D 30 ,D 60 from the grain–size distribution curve,
(c) the uniformity coefficient,Cu, and
(d) the coefficient of gradation,Cc.
Sieve Number
Diameter (mm)
Mass of soil retained on each sieve (g) 4 4.750 28 10 2.000 42 20 0.850 48 40 0.425 128 60 0.250 221 100 0.150 86 200 0.075 40 Pan –– 24
Example Sieve Analysis
Sieve
Number
Diameter
(mm)
Mass of soil retained
on each sieve (g)
Pan –– 24
Sieve Number
Mass of soil retained on each sieve (g)
Percent retained on each sieve (%)
Cumulative percent retained on each sieve (%)
Percent finer (%)
Pan 24 3.89 100.00 0 617
Example Sieve Analysis
Sieve Number
Mass of soil retained on each sieve (g)
Percent retained on each sieve (%)
Cumulative percent retained on each sieve (%)
Percent finer (%)
Pan 24 3.89 100.00 0 617
Example Sieve Analysis
Particle diameter (mm)
Percent finer (%)
Example Sieve Analysis
D 30 = 0.27 mm
D 10 = 0.14 mm
D 60 = 0.42 mm
Example Sieve Analysis
] For the particle-size distribution curve we just used,
the values of D 10 , D 30 , and D 60 are:
D 10 = 0.14 mm D 30 = 0.27 mm D 60 = 0.42 mm
u
D C D
=
mm
mm
= =
c
D C D D
= ×
(0.27 )
0.42 0.
mm
mm mm
= = ×
Group Work - Sieve Analysis
] From the results of a sieve analysis, shown below,
determine:
(a) the percent finer than each sieve and plot a grain–size
distribution curve,
(b)D 10 ,D 30 ,D 60 from the grain–size distribution curve,
(c) the uniformity coefficient,Cu, and
(d) the coefficient of gradation,Cc.
Sieve Number
Mass of soil retained on each sieve (g) 4 0 10 40 20 60 40 89 60 140 80 122 100 210 200 56 Pan 12
