INTRODUCTION A sieve analysis or gradation test is a practice or procedure used used
in civil
engineering
to
assess
the particle
size
commonly
distribution (also
called gradation) of a granular material. The size distribution is often of critical importance to the way the material performs in use. A sieve analysis can be performed on any type of non-organic or organic granular materials including sands, crushed rock, clays, granite, feldspars, coal, soil, a wide range of manufactured powders, grain and seeds, down to a minimum size depending on the exact method. Being such a simple technique of particle sizing, it is probably the most common.
LITERATURE REVIEW There are two soil classification systems in common use for engineering purposes.
The Unified
Soil
Classification
System is
used
for
virtually
all
geotechnical engineering work except highway and road construction, where the AASHTO soil classification system is used. Both systems use the results of grain size analysis and determinations of Atterberg limits to determine soil’s classification. Soil components may be described as gravel, sand, silt, or clay. A soil comprising one or more of these components is given a descriptive name and a designation consisting of letters or letters and numbers which depend on the relative proportions of the components and the plasticity characteristics of the soil.
1. MIT System of soil classification: Clay
Clay is also known as Cohesive Soil, Frictionless Soil or Expansive Soil
Composed of very fine particles (less than 0.002 mm in size)
Flaky in shape, thus having considerable surface area
Have high inter particle attraction and thus having sufficient cohesion
Susceptible to swelling and shrinkage, and possess low permeability
Commonly brown in colour
Silt
Silt particles rang in size from 0.002 mm to 0.06 mm
Have high capillarity and very low dry strength
Since particle size ranges in between that of clay and sand thus possessing properties of both sand and clays i. e. it shows slight cohesion and also friction.
The colour of silty soil is mostly brown
Sand
Sand is also known as Frictional Soil or Cohesionless Soil
Particle size ranging from 0.06 mm to 2 mm.
It may be rounded to angular in shape
Grey in colour
No plasticity
Possess high strength in confined state and has considerable frictional resistance
Angular particles have high frictional resistance than rounded ones
It has high permeability and low capillarity
Gravel
Particle size ranges from 2 mm to 60 mm
Gravel form good foundation material
Shows high frictional resistance
Angular particles have high frictional resistance than rounded ones
The gravels produced by crushing of rocks are angular in shape while those taken from riverbeds are sub-rounded to rounded
2. AASHTO classifications of soils: The AASHTO system classifies soils into seven primary groups, named A-1 through
A-7,
based
on
their
relative
expected
quality
for road
embankments, sub-grades, sub-bases, and bases. Some of the groups are in turn divided into subgroups, such as A-1-a and A-1-b. Furthermore, a Group Index may be calculated to quantify a soil’s expected performance within a group. To determine a soil’s classification in the AASHTO system, one first determines the relative proportions of gravel, coarse sand, fine sand, and silt-clay. ( Refer Figure 1)
Figure 1 Secondly, if any fines are present, Atterberg limits are determined and the plasticity index is calculated. A soil is a granular material if less than 35% of the soil by weight passes the No. 200 sieve (#200). Granular materials are classified into groups A-1 through A-3. Soils having more than 35% passing the No. 200 sieve are silt-clay and fall in groups A-4 through A-7. Having the proportions of the
components
and
the
plasticity
data,
one
enters
one
of
the
two
alternatives AASHTO classification tables and checks from left to right until a classification is found for which the soil meets the criteria. It should be noted that, in this scheme, group A-3 is checked before A-2. Soils classified as A-1 are
typically well-graded mixtures of gravel, coarse sand, and fine sand. Soils in subgroup A-1-a contain more gravel whereas those in A-1-b contain more sand. Soils in group A-3 are typically fine sands that may contain small amounts of non-plastic silt. Group A-2 contains a wide variety of “borderline” granular materials that do not meet the criteria for groups A-1 or A-3. Soils in group A4 are silty soils, whereas those in group A-5 are high-plasticity elastic silt. Soils in group A-6 are typically lean clays, and those in group A-7 are typically highly plastic clays. Within groups containing fines, one may calculate a group index to further evaluate relative quality and supporting value of a material as sub-grade. The group index is calculated according to the following empirical formula: Group index F 35 – ( )0.2 0.005 LL 40 – ( ) + [ ] + 0.01 F 15 – ( )PI 10 – ( ) In the AASHTO system:
gravel is material smaller than 75 mm (3 in.) but retained on a No. 10 sieve;
coarse sand is material passing a No 10 sieve but retained on a No. 40 sieve; and fine sand is material passing a No. 40 sieve but retained on a No. 200 sieve.
Material passing the No. 200 sieve is silt-clay and is classified based on Atterberg limits.
It should be noted that the division between gravel and sand is made at a smaller size (No. 10 sieve) in the AASHTO system than in the unified system (No. 4 sieve).
3. Unified soil classification system (USCS): The Unified Soil Classification System is based on the airfield classification system developed by Casa Grande during World War II. With some modification it was jointly adopted by several U.S. government agencies in 1952. Additional refinements were made and it is currently standardized as ASTM D 2487-93. It is used in the U.S. and much of the world for geotechnical work other than roads and highways. In the unified system soils are designated by a two-letter symbol:
the first identifies the primary component of the soil, and the second describes its grain size or plasticity characteristics. For example, poorly graded sand is designated SP and low plasticity clay is CL. Five first-letter symbols are used: G for gravel S for sand M for silt C for clay O for organic soil Clean sands and gravels (having less than 5% passing the No. 200 sieve) are given a second letter P if poorly graded or W if well graded. Sands and gravels with more than 12% by weight passing the No. 200 sieve are given a second letter M if the fines are silty or C if fines are clayey. Sands and gravels having between 5 and 12% are given dual classifications such as SP-SM. Silts, clays, and organic soils are given the second letter H or L to designate high or low plasticity. The specific rules for classification are summarized as follows and described in detail in ASTM D 2487. For coarse-grained soils, the proportions of sand and gravel in the coarse fraction (not the total sample) determine the first letter of the classification symbol. The coarse fraction is that portion of the total sample retained on a No. 200 sieve. If more than half of the coarse fraction is gravel (retained on the No. 4 sieve), the soil is gravel and the first letter symbol is G. If more than half of the coarse fraction is sand, the soil is sand and the first letter symbol is S. For sands and gravels the second letter of the classification is based on gradation for clean sands and gravels and plasticity of the fines for sands and gravels with fines. For clean sands (less than 5% passing the No. 200 sieve), the classification is well-graded sand (SW) if C ≥ 6 and 1 £ Cc £ 3. Both of these criteria must be met for the soil to be SW, otherwise the classification is poorly graded sand (SP). Clean gravels (less than 5% passing the No. 200 sieve) are classified as wellgraded gravel (GW) if Cu ≥ 4 and 1 £ Cc £ 3. If both criteria are not met, the soil is poorly graded gravel (GP). For sands and gravels where more than 12% of the total sample passes the No. 200 sieve, the soil is a clayey sand (SC), clayey gravel (GC), silty sand (SM), or silty gravel (GM).
METHODOLOGY The result of mechanical analysis 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 . Percentage finer given in the last column can be used to plot the particle size distribution curve with particle size as abscissa on log scale and the percentage finer as ordinate.
Graph semi – log
RESULTS AND DISCUSSION
BOREHOLE
BH1
BH2
BH3
DEPTH ( M )
3.00 – 3.80
4.00 – 4.70
12.00 – 12.80
PARTICLE’S
% PASSING
% PASSING
% PASSING
SIZES 20 mm
100
100
100
10 mm
100
100
100
6 mm
100
99
99
5 mm
100
98
97
3.35 mm
98
97
78
2.36 mm
96
95
52
1.70 mm
85
88
35
0.60 mm
68
67
27
0.335 mm
55
43
24
0.180 mm
47
35
22
0.063 mm
44
30
21
Cu =
d60
d10
Cc
=
d302
d60 x d10
In this experiment, the particulate nature of soil was greatly observed. It was also shown that certain classifications in soil can be done through sieve analysis. One essential thing to do in this experiment is to arrange the sieves properly. The accuracy of this experiment is very much dependent on the sieve arrangement.
The arrangement of sieves must be in decreasing mesh openings from top to bottom. This is very useful in order to separate the particles from coarser to finer. Lastly, It was observed that for particles having sizes larger that the sieve opening to which it will be retained. On the other hand, those with smaller sizes were able to pass through. This phenomenon is the basic reason on how particles were separated.
CONCLUSIONS For conclusion of classification of soil for engineering purposes, we oath to know the distribution of the grain sizes in any given soil mass especially the one obtain from the construction site or burrow pits. Particle size distribution test, also known as sieve analysis test is a method used to determine the grain(granular) size distribution of soil samples. Grain-size analysis is widely used in engineering classifications of soils. The standard grain size analysis test determines the relative proportions of different grain-sizes as they are distributed among certain size ranges. The sieve analysis is a process where the grain size distribution of soil is determined. This test is done by letting a sample of soil pass through a stack of sieves of decreasing mesh opening sizes and by measuring the weight retained on each sieves. The main concept in this process is to retain the large particles not able to pass through the varying sieve sizes. The sieve analysis is primarily applied to soil particles with sizes from 75mm to75microns. Sieve analysis can be classified as dry sieving and wet sieving. Dry sieving is a sieving process that is used for soil with negligible amount of plastic fines like gravels and clean sands. On the other hand, wet sieving is applied to soils with considerable plastic fines.
REFERENCE 1. https://en.wikipedia.org/wiki/Sieve_analysis 2. https://theconstructor.org/geotechnical/particle-size-distribution-of-soil-byseiving/2741/ 3. https://www.google.com/#safe=strict&q=semi+log+graph+example
