Soil Classification using lab techniques according to
The Unified Soil Classification System
1.0 Introduction
The objectives of the labs and the application/relevance they have in relation to construction
were as follows:
1.1 Lab 3 Mechanical Method
The purpose of the Mechanical Method Lab was to determine the particle size
distribution of the soil sample collected in Lab 1 by performing a sieve analysis. The
sieve analysis depends upon gravity and agitation to segregate the particles into various
sieves. The particle size distribution of the particles bigger than the No. 50 sieve were
used and a distribution curve was made from the results. This is for the classification of
the soil according to the Unified Soil Classification System (USCS) [1].
1.2 Lab 4 Hydrometer Method
The objective of the Hydrometer Method Lab was to perform a hydrometer analysis and
determine the particle size distribution for those particles passing through the No. 50
sieve from the sample collected in Lab 1. A distribution curve was made from the results
and used for the classification of soil according to the USCS. [2]
1.3 Lab 5 Atterberg Limits
The objective of Atterberg Limits Tests were to determine the plastic limit (PL), liquid
limit (LL) and plasticity index (PI) for the soil collected in Lab 1. This lab along with Labs
3 and 4 will be used to classify the soil according to the USCS. [3]
This final analysis helps to complete the classification and also helps achieve a number
of things including:




Classifying soil in a given identification system.
Determining suitability of a soil for use in road, airfield, and embankment
construction.
Predicting soil-water movement.
Determining the soil’s susceptibility to frost action [1][2].
2.0 Theory
In this section, technical or theoretical background is provided to assist in the
understanding of the report.
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2.1 Grain size analysis
Now that the soil sample has been oven-dried a further analysis of the soil determines
the classification of the soil through different lab based techniques. These lab based
techniques include the following:

Sieve analysis – the particle size distribution is determined through a system that
uses gravity and agitation of the sample to segregate the particles onto various
sieves, (See Fig 2.1). The particles used to make the distribution curve are those
that are larger than the *No. 200 sieve [1].
http://enginemechanics.tpub.com
Fig. 2.1

Hydrometer analysis – the particle size distribution is determined by adding a 4%
sodium hexa-metaphosphate solution to the material which passed through a *No.
200 sieve, adding 1 liter of water, agitating the mixture, and taking hydrometer
readings for approximately 36 hours, (See Fig. 2.2, page 3). A full description of the
test can be found in Lab 4 (See Appendix B, page 20). The particles used to make
the distribution curve are those that are smaller than the *No. 200 sieve [2].
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http://.extension.umn.edu
Fig. 2.2

Atterberg Limits Tests – plastic limit (PL), liquid limit (LL), and plasticity index (PI)
are determined through the following tests:
o Liquid Limit Determination – using a device which has a crank that moves a
brass cup attached to it up and down with a fall height of 10 mm determines
the liquid limit. Water is added to the soil, and then the soil is placed in the
brass cup with a groove incised into the soil. It is then cranked a number of
times until a half inch of the soil is closed along the length of the groove, (See
Fig. 2.3, page 4). The initial number of hits should be between 30 and 40. The
numbers are recorded, 15 g of soil is removed and the process is repeated
with a little more water added to the soil each time. The soil is then oven-dried
and the moisture content for each sample is determined [3].
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https://www.dot.ny.gov
Fig. 2.3
o Plastic Limit Determination – this test includes taking 3 peanut sized samples
from the soil-water mixture which has a stiff putty consistency and rolling
them on a glass plate until they begin to crumble at 1/8” diameter, (See Fig.
2.4). Then the samples are placed into moisture cans and oven dried. The
samples are then measured for moisture content to determine the plastic limit
(PL) [3].
http://collections.infocollections.org
Fig. 2.4
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2.2 Coarse-grained or Fine-grained Soil
Soil types are classified into gravel, sand, silt, and clay, by their particle size. A coarse
grained soil particle is 0.075 mm and larger (depends on classification system used). A
coarse grained soil contains more than 50% particle sizes of 0.075 mm and greater. A
fine grained soil particle is smaller than 0.075 mm (depends on classification system
used, see Appendix D, page 32). A fine grained soil contains more than 50% particle
sizes less than 0.075 mm [4].
2.3 Size ranges for gravel, sand, fine soil particles
Particle size ranges for gravel, sand, silt, clay are different based on the soil
classification systems used. See Table 2.1 below, for an example of Unified Soil
Classification System.
Unified soil clasification system
Clasification
Inches
mm
Boulders
> 12
> 305
Cobbles
≤ 12, > 3
≤ 305, > 75
Coarse Gravel
≤ 3, > 3/4
≤ 75, > 19
Fine Gravel
≤ 3/4, > 0.19
≤ 19, > 4.76
Coarse Sand
≤ 0.19, > 0.08
≤ 4.76, > 2.0
Medium Sand
≤ 0.08, > 0.017
≤ 2.0, > 0.42
Fine Sand
≤ 0.017, > 0.003 ≤ 0.42, > 0.075
Fines (Silt & clay)
≤ 0.003, > 0
≤ 0.075, > 0
Table 2.1 [4:16]
2.4 “Clean” gravel/sand versus a gravel/sand with fines
A “clean” gravel/sand is when less than 5% of the material is smaller than a *No. 200
sieve size (0.075 mm). A gravel/sand with fines is when more than 12% of the material
is smaller than a *No. 200 sieve size (0.075 mm) [5:176].
2.5 Well graded versus a poorly graded gravel/sand
A well graded gravel/sand has a wide range of particle size and substantial amounts of
intermediate particle size. A poorly graded gravel/sand has mostly one size particle or a
range of sizes with missing intermediate particle sizes [5:176].
2.6 Lab based classifications
Lab based classifications start with grain size analysis through the different methods of
particle size distribution including sieve analysis, hydrometer analysis and Atterberg
Limits tests. The sieve analysis initially gives whether the soil is a coarse-grained or
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fine-grained soil by the amount of material which passes through a *No. 200 sieve.
According to USCS the percentage of material which passes through the *No. 200 sieve
determines what the classification is and is further classified through the hydrometer
analysis if more than 50% passes through. The final tests are the Atterberg limit tests
which determine the liquid limit, the plastic limit, and the plasticity index. The results are
determined through using the Plasticity Chart for the USCS [1] [2] [3].
3.0 Procedure
This section will make reference to directions outlined in the resource material, and/or test
standards.
3.1 Lab 3
See Appendix A, page #
3.2 Lab 4
See Appendix B, page #
3.3 Lab 5
See Appendix C, page #
4.0 Observations
This section will detail the observations and results of the labs.
*NOTE: The No. 50 sieve was used, in place of a No. 200 sieve, as the cutoff between the
sieve and hydrometer analysis to minimize possible “soil grinding/declumping errors.” [1]
4.1 Lab 3
The following are the observations made of the sieve analysis on the soil sample (see
Table 4.1, page 7):
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SIEVE GRAIN ANALYSIS CHART
Original Mass of Sample = 350.0 grams
Weight before
Weight after
Weight of
Sieve Size
adding soil
seiving + soil soil retained
(grams)
retained (grams)
(grams)
5/8 "
804.90
804.90
0.00
% of
Material
retained
0.00
Cumulative
Cumulative
% retained
% passing
Cum. %
0.00
100.00
3/8 "
775.00
775.00
0.00
0.00
0.00
100.00
#4
754.10
754.40
0.30
0.09
0.09
99.91
#8
656.30
659.90
3.60
1.02
1.11
98.89
# 16
469.00
483.50
14.50
4.12
5.23
94.77
# 30
437.00
493.50
56.50
16.07
21.30
78.70
# 50
559.60
629.70
70.10
19.94
41.24
58.76
Pan
488.20
694.80
206.60
58.76
100.00
0.00
Total
351.60
Original mass of test material, x
=
350.00
grams
Total of Retained mass of material tested, y
=
351.60
grams
% Loss/Gain (x-y)/x * 100
=
0.46
% (Gain)
Table 4.1 [1]
A “Particle Size Analysis” graph was used to plot the grain-sized distribution curve for
the soil up to the No. 50 sieve. (See appendix A, page 18)
According to the USCS

Less than 50% of the soil is larger than No. 50 sieve, meaning its’ classification
moves to the “Fine-Grained” soil flow chart (See Appendix E).
4.2 Lab 4
The following are the observations made from the hydrometer analysis of the sample
soil (see Table 4.2, page 8):
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Hydrometer Grain Analysis
Specific Gravity of soil solids G:
2.65
α (from Table 1):
1.00
Zero correction:
1.00
Meniscus Correction:
1.00
Weight of soil used, Ws:
50.24 grams
% of total field sample tested *A:
Hydrometer Reading
Corrected
Elapsed
"L"
Temp. Actual, Corrected,
for
time, t
from
°C
Ra
Rc *B
meniscus
(min.)
Table 4
only
0
1
24
40
37.0
41
9.6
2
24
38
35.0
39
9.9
3
24
35
32.0
36
10.4
4
24
32
29.0
33
10.9
8
24
27
24.0
28
11.7
15
24
25
22.0
26
12.0
30
24
23
20.0
24
12.4
56
23
21
17.7
22
12.7
1373
21
15
11.2
16
13.7
1840
22
15
11.4
16
13.7
5.87 %
% Finer
Date
Time of
reading
9/24/13
9/24/13
9/24/13
9/24/13
9/24/13
9/24/13
9/24/13
9/24/13
9/24/13
9/25/13
9/25/13
9:24 AM
9:25 AM
9:26 AM
9:27 AM
9:28 AM
9:32 AM
9:39 AM
9:54 AM
10:20 AM
8:17 AM
4:04 PM
* Notes:
A
B
C
D
E
% of field sample tested =206.6g ÷ 351.6g x 100% (from seive chart)
Rc = Ra - Zero corection + Temp. correction "C T"
D = K*(L /t)^0.5
% Finer of Hyd. Sample = [Rc*α/Ws] x 100%
% Finer of Field Sample =% Finer of Hyd. Sample * % of total field sample tested * 0.01
L/t
9.60000
4.95000
3.46667
2.72500
1.46250
0.80000
0.41333
0.22679
0.00998
0.00745
of Hyd.
"K" from D (mm)
Sample
Table 3
*C
*D
0.0130
0.0130
0.0130
0.0130
0.0130
0.0130
0.0130
0.0132
0.0135
0.0133
0.0403
0.0289
0.0242
0.0215
0.0157
0.0116
0.00836
0.00629
0.00135
0.00115
73.6
69.7
63.7
57.7
47.8
43.8
39.8
35.2
22.3
22.7
of Field
Sample
*E
4.3
4.1
3.7
3.4
2.8
2.6
2.3
2.1
1.3
1.3
Table 4.2 [2]
The soil, water, and sodium hexametaphosphate solution in the Control Cylinder, during
the first 56 minutes of testing, was medium brown in colour and had approximately 1/2”
of foam at the surface. The solution was lighter in colour at the 1373 minute reading,
there was no foam and no foam at the 1840 minute reading.
The following are computations from line 6 (t=8min.), from the hydrometer grain
analysis, Table 4.2 (see Table 4.3, page 9):
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Column 6
Rc=Ra-Zero Correction+CT
CT=1.00 {the temp. correction from Table 2 on page 6 of Lab Handout 4, at 24⁰C (see
Appendix B, page 25 )}
Rc = 27-4+1 = 24.0
Column 7
Hydrometer Reading Corrected Only for Meniscus
27+1 = 28
Column 8
L = 11.7
From Table 4 on page 7, of Lab Handout 4 (see Appendix B, page 26) using
Hydrometer Reading of 28 from column 7
Column 9
L/t = 11.7÷8 = 1.46250
Column 10
K = 0.0130
From Table 3 on page 6 of Lab Handout 4 (see Appendix B, page 25), using
temperature of 24⁰C from column 4 and G of 2.65 which was provided by the instructor.
Column 11
D = K*(L/t)^0.5 = 0.0130*(1.46250)^0.5 = 0.0157 mm
Column 12
% Finer of Hydrometer Sample
(Rc*α)/Ws*100%
α = 1.00 {from Table 1 on page 6 of Lab Handout 4 (see Appendix B, page 25)}
(24.0*1.00)/50.24)*100% = 47.8%
Column 13
% Finer of Field Sample
(%Finer of Hydrometer Sample)*(% of Total Field Sample Tested)*0.01
47.8*58.76*0.01 = 28.1%
Table 4.3
4.3 Lab 5
The following are the observations made from the Atterberg Limits Tests from the
sample soil, including, the Plastic Limit Test (PL) (see Table 4.4) and the Liquid Limit
Test (LL) (see Table 4.5, page 10):
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Plastic Limit Test
Moisture Can (MC) #
2-2
Wgt of MC (g)
22.35
Wgt of Wet Soil + MC (g) 24.80
Wgt of Dry Soil + MC (g)
24.53
Wgt of Dry Soil (g)
2.18
Wgt of Water (g)
0.27
Moisture Content %
12.39
2-4
22.74
26.70
26.09
3.35
0.61
18.21
PL = Avg. of Moisture Content % from 3 tests =
2-6
30.54
33.27
32.78
2.24
0.49
21.88
17.49
Table 4.4 [3]
Liquid Limit Test
# of Blows (N)
30
22
Moisture Can (MC) #
7
2-0
Wgt of MC (g)
22.67
22.40
Wgt of Wet Soil + MC (g) 41.77
40.21
Wgt of Dry Soil + MC (g)
38.12
36.73
Wgt of Dry Soil (g)
15.45
14.33
Wgt of Water (g)
3.65
3.48
Moisture Content %
23.62
24.28
16
98
23.47
41.99
38.34
14.87
3.65
24.55
12
38
22.64
39.35
35.96
13.32
3.39
25.45
Table 4.5 [3]
To determine the Liquid Limit (LL), the Liquid Limit Test results were plotted (see Fig. 4.1).
Fig. 4.1 [3]
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The Plastic Limit and Liquid Limit results are used to determine the Plasticity Index.
PI=LL-PL
PI= 23.87 – 17.49 = 6.38
The PI and LL results are used to classify the soil using the Plasticity Chart for the USCS
(see Fig. 4.2).
Fig. 4.2 [6]
5.0 Discussion of Results
In this section, observations and results from the labs will be discussed.
5.1 Lab Classification of Soils
58.76% of the soil passing through sieve No. 50 after performing the sieve analysis test
resulted in it being a “fine-grained” soil according to the Unified Soil Classification
System (USCS) (see Appendix E). The Particle Size Analysis Graph also shows that
the soil is a “fine-grained” soil (see Appendix A, page 18).
The hydrometer analysis determined the particle size distribution for the particles
passing through the No. 50 sieve and the results showed what the distribution was.
“…According to Stokes’ law, larger spheres will have a higher terminal velocity, and,
thus, in a suspension of particles, will fall to the bottom in suspension at a given
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time.”[2]. The Particle Size Analysis Graph shows the distribution of particles which
passed through sieve No.50 (see Appendix A, page 18).
The Atterberg Limits Tests showed the Plastic Limit being 17.49 and the Liquid Limit
being 23.87 of the sample soil and with these numbers the Plasticity Index was found to
be 6.38. These results showed that it was a ML-CL.
Following the Lab-Based Classification of Soils (USCS) Flow chart (see Appendix E):
Less than 50% of the soil was larger than No. 50 sieve therefore it is a fine grained soil.
The soil had no smell and a dull brown colour therefore not organic.
The LL was less than 0.75LL as found therefore it is (ML, MH, CL, or CH).
The LL was less than 50 therefore it is (ML or CL).
The PI was Greater than 4 and less than 7 therefore the soil is ML-CL.
5.2 Lab based versus Field based Classification
The initial field classification results yielded a CH soil, and the lab based classification
results yielded a ML-CL soil. The difference comes from a more detailed analysis of the
fine grained particles.
6.0 Conclusions
This section contains statements that will give clear answers to the objectives in the
Introduction.
6.1 Lab 3
It was determined, after the calculations were made from the soil sample, that it had the
following engineering properties:
58.76% of the soil sample passed through a No. 50 sieve (according to the USCS it
should be a No. 200 sieve, however, a No. 50 sieve was used as the cutoff between the
sieve and hydrometer analysis to minimize possible “soil grinding/declumping errors”)
determining the sample was a “fine-grained” soil.
6.2 Lab 4
Soil that passed through the No. 50 sieve was analyzed with a hydrometer test to
determine the particle size distribution. The results were plotted on the particle size
analysis graph and subsequently used to classify the soil sample according to the
USCS.
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6.3 Lab 5
The soil was tested with two tests, the Liquid Limit Test and the Plastic Limit Test. The
following results were made and the Plasticity Index was calculated:
Liquid Limit = 23.87
Plastic Limit = 17.49
Plasticity Index = 6.38
This resulted in a double classification of the soil; it was a Silt (M) with Low Plasticity (L)
and a Clay (C) with Low Plasticity (L). The sample soil was a Silty Clay.
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References
[1] Materials II, CIVL 1356, “Lab 3 - Sieve Analysis.” [On-Line]. Available: https://
niagara.blackboard.com/bbcswebdav/pid-1532741-dt-content-rid
3873344_1/courses/1134_CIVL1356_AA/Lab3_Sieve_Analysis%284%29.pdf [Sep., 2013].
[2] Materials II, CIVL 1356, “Lab 4 - Hydrometer Analysis.” [On-line]. Available:
https://niagara.blackboard.com/bbcswebdav/pid-1532748-dt-content-rid3883908_1/courses/1134_CIVL1356_AA/Lab%204%20Hydrometer%20Analysis.pdf1 [Sep.,
2013].
[3] Materials II, CIVL 1356, “Lab 5 - Atterberg Limits.” [On-line]. Available:
https://niagara.blackboard.com/bbcswebdav/pid-1532754-dt-content-rid3923945_1/courses/1134_CIVL1356_AA/Lab_5_Atterberg_Limits%282%29.pdf [Oct., 2013].
[4] Materials II,CIVL 1356 “Week 2 PowerPoint Notes.” [On-line]. Available:
https://niagara.blackboard.com/bbcswebdav/pid-1532732-dt-content-rid-3859450_1/xid3859450_1 [Sep., 2013].
[5] P. F. Boles et al. Pearson Construction Technology – CIVL 1256/1356, Materials I,
Materials II (Soils). Boston, MA: Pearson Learning Solutions, 2011, pp.153-189.
[6] Materials II,CIVL 1356 “Week 4 PowerPoint Notes.” [On-line]. Available:
https://niagara.blackboard.com/bbcswebdav/pid-1532746-dt-content-rid3884234_1/courses/1134_CIVL1356_AA/Week4_Powerpoint%282%29.pdf [Oct., 2013].
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