International Journal of Science, Engineering and Technology Research (IJSETR)
Volume 1, Issue 1, July 2012
Investigation into Soil Stabilization with Enzyme
Nway Nway Nilar Myint, Than Mar Swe

Abstract–This research paper presents stabilization of soil treated
with enzyme. The objective of the paper is to investigate the
properties of enzyme. Soil samples are taken at about 3 ft depth
from five different locations. They are Laeau village in Wonetho
Township, Chanmyatharzi Township, Basic Education High
School, Shwesaryan and Kyarnikan villages in Patheingyi
Township which are denoted by Soil A, Soil B, Soil C, Soil D and
Soil E respectively. In order to identify and classify the studied
soils, specific gravity test, grain-size analysis test, atterberg limit
test, free swell test, compaction test, unconfined compression
strength (UCS) test and California bearing ratio (CBR) test are
performed. According to Unified Soil Classification System
(USCS), soil A is in MH group, soil E in CL group and other three
types are in CH groups. Selected Enzyme dosages are 500 and
1000 mililitres per 33 m 3 of soil. The studied soils are mixed with
enzyme and cured for one and four weeks. The strength values of
soils treated with enzyme are increased when the amounts of
enzyme dosages are increased. According to the test results, the
strength values of enzyme-treated soils are higher than that of
natural soil. Among the samples of enzyme-treated soils, soil E hasB.
the highest value of strength. Therefore, there are more enzyme
effects on soil E than other four types of soil.
Index Terms –Unconfined compression strength, CBR, Enzyme
dosages
I. INTRODUCTION
Soil is a construction material used in various civil
engineering projects and it supports structural foundation.
Soil is a very important material for the stability of buildings,
dams and roads. Therefore, it is very necessary to know
various properties of soil such as specific gravity, grain size
distribution, consistency limits, compressibility and shear
strength.
Soil can be stabilized by chemically or mechanically. The
chemical stabilizers are substances that can enter in the
natural reactions of the soil and control the moisture getting
to the clay particles. Chemical stabilizers are divided into
three groups. They are traditional stabilizers (hydrated lime,
Portland cement and fly ash), non-traditional stabilizers
(sulfonated oils, ammonium chloride, enzymes, polymers
and potassium compounds) and by-product stabilizers
(cement kiln dust, lime kiln duct). The most basic form of
mechanical stabilization is compaction, which increases the
performance of a natural material.
Soil stabilization refers to the process of changing soil
properties to improve engineering properties of soil. An
enzyme can be used to stabilize a wide variety of soils. The
enzyme stabilizer is a natural organic compound, similar to
proteins, which acts as a catalyst. When enzyme is added to
soils, the strength behavior and the bearing capacity of soil
can be improved. The enzyme allows soil materials to
Manuscript received Oct 15, 2011.
Nway Nway Nilar Myint, Civil Department, Mandalay Technological
University. Mandalay, Myanmar, 09-428119481 (nwaynilar@gamil.com).
Than Mar Swe, Civil Department, Mandalay Technological University.
Mandalay, Myanmar, 09-402589569, (thanmarswe@ gmail.com).
become more easily wet and more densely compacted. In this
study, enzyme is used as a stabilizer for soil stabilization.
II. EXPERIMENTAL WORKS
Before identification and classification of soils, soil
sampling is carried out as follows.
A. Soil Sampling
Soil sample are taken from the interval of 1000 ft in very
Uniform ground, or as little as 50 ft in quickly changing
ground. Undisturbed samples are obtained by driving hollow
cylindrical tube and sealed with wax at the bottom and top of
the sample tube to prevent changes in water content and
chemical composition after the sample is obtained. Disturbed
samples are obtained by boring around the place. In order to
determine the properties of natural soil before adding enzyme,
the following tests are performed.
B. Specific Gravity Test
Specific gravity is defined as the ratio of the unit weight of
a given material to the unit weight of water. For clay and silty
soils, the specific gravity of soil ranges from 2.6 to 2.9. As
shown in Table I, the specific gravities of all studied soils are
within the limits. The test results of specific gravity are
shown in Table I. The equation (1) is used to find the specific
gravity of soil.
Gs 
Where,
G t Ws
Ws  W2 - W1
(1)
Gs = Specific gravity of soil
Gt = Specific gravity of water at t; temperature
Ws = Weight of dry soil (g)
W1 = Weight of bottle plus water plus soil (g)
W2 = Weight of bottle plus water (g)
C. Atterberg Limit Test
The water content levels at which the soil change from one
state to the other are the Atterberg limits. They are the plastic
limit (PL), liquid limit (LL), and shrinkage limit (SL). These
limits are referred to as Atterberg Limits. Atterberg limit test
results are described in Table I.
TABLE I
SPECIFIC GRAVITY AND ATTERBERG LIMIT TEST RESULTS OF
SOILS
Specific
Atterberg Limits (%)
Samples
Gravity
Plastic
Liquid Plasticity
(Gs)
Limit
Limit
Index
Soil A
2.72
65.6
43.2
22.4
Soil B
2.72
18.9
59.2
40.3
Soil C
2.71
57.3
19.0
38.3
Soil D
2.73
22
50.1
28.1
Soil E
2.64
14.3
25.1
10.8
The plasticity index is the difference of liquid limit and
plastic limit. The following equation is used to find the
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International Journal of Science, Engineering and Technology Research (IJSETR)
Volume 1, Issue 1, July 2012
plasticity index.
PI = LL – PL
(2)
D. Grain-Size Analysis of Soil
Grain size analysis is the determination of the size range
of particles present in a soil, expressed as a percentage of the
total dry weight. The following methods are generally used to
find the particle size distribution of soil.
(i) Sieve Analysis is used for particle sizes larger
than 0.075 mm in diameter.
(ii) Hydrometer Analysis is used for particle sizes
smaller than 0.075 mm in diameter.
The grain size analysis of soil results are shown in Table
II. As described in Table II, soil A has the highest percentage
of clay and soil E has the lowest percentage.
Samples
Gravel (%)
Sand (%)
Silt (%)
Clay (%)
F
53.8
200
R
200
F
4
R (GF)
4
SF=R
200
TABLE II
GRAIN SIZE ANALYSIS RESULTS
Soil
Soil
Soil
Soil
A
B
C
D
0
4.6
0
10.4
13.0
12.6
21.7
32.1
33.2
49.8
58.1
45.2
-R
4
SF/GF
87.0
33
82.84
13
20.2
Soil
E
1.4
59
31.8
78.31
12.3
57.49
7.8
39.58
17.16
21.69
42.51
60.42
100
95.43
100
89.62
98.6
0.0
4.57
0.0
10.38
1.4
13
12.59
21.69
32.13
59.02
<1
>1
<1
>1
>1
E. Free Swell Test
Ten grams of oven-dried soil specimens passing No.40
sieve (0.425 mm openings) is placed in the graduated
cylinders containing distilled water and kerosene. Sediment
volumes are measured after complete sedimentation of
specimens in respective fluid. It takes about 24 hours to 120
hours in distilled water. Kerosene is used instead of carbon
tetrachloride since it is easily available in Myanmar. Table III
shows classification of clays on the basis of free swell ratio.
Free swell ratios results of soils are shown in Table IV. To
calculate the free swell ratio, the equation (3) is used.
TABLE III
CLASSIFICATION OF CLAYS ON THE BASIS OF THEIR FREE
SWELL RATIO
Free Swell
Ratio
≤ 1.0
1.0 – 1.5
1.5 – 2.0
2.0 – 4.0
> 4.0
Clay Type
Soil Expansion
Non- swelling
Mixture of
swelling and
non-swelling
Swelling
Swelling
Swelling
Negligible
FSR 
Vw
Vk
Low
Moderate
High
Very High
(3)
Where, FSR = Free Swell Ratio
Vw = Sediment volume of soil in distilled water
(cm3)
Vk = Sediment volume of soil in kerosene
(cm3)
Samples
Soil A
Soil B
Soil C
Soil D
Soil E
TABLE IV
FREE SWELL RATIO RESULTS OF SOILS
Free Swell
Clay Type
Soil
Ratio
Expansion
0.93 (≤ 1.0)
Non- swelling Negligible
1.70 (1.5 – 2.0)
Swelling
Moderate
1.63 (1.5 – 2.0)
Swelling
Moderate
1.50 (1.5 – 2.0)
Swelling
Moderate
1.70 (1.5 – 2.0)
Swelling
Moderate
F. Modified Free Swell Index Test
The free swell test is one of the most commonly used
simple tests in the field of geotechnical engineering for
getting an estimation of soil swelling potential . This is
performed by pouring 10 cm3 of dry soil into a 100 cm3
graduated jar filled with distilled water, noting the swelled
volume of the soil after it comes to rest. Table V shows the
soil classification on modified free swell index and Table VI
shows the modified free swell index values. It is calculated by
the following equation.
Modified free swell index =
VV
s
V
s
(4)
Where, V= Soil volume after swelling (cm3)
Vs= Volume of soil solid (cm3)
TABLE V
SOIL CLASSIFICATION SCHEME BASED ON MODIFIED FREE
SWELL INDEX
Modified Free Swell
Swelling Index
Index
< 2.5
Negligible
2.5 to 10
Moderate
10 to 20
High
>20
Very High
TABLE VI
MODIFIED FREE SWELL INDEX VALUES
Samples
Modified Free Swell
Swelling Index
Index
Soil A
2.53 (2.5 to 10)
Moderate
Soil B
2.94 (2.5 to 10)
Moderate
Soil C
2.86 (2.5 to 10)
Moderate
Soil D
2.75 (2.5 to 10)
Moderate
Soil E
2.10 (< 2.5)
Negligible
G. Classification of Soil
The results obtained from specific gravity test, atterberg
limit test, and grain-size analysis of soil are used to classify
the soil types. According to Unified Soil Classification
System, the studied soils are classified as shown in Table
VII.
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All Rights Reserved © 2012 IJSETR
International Journal of Science, Engineering and Technology Research (IJSETR)
Volume 1, Issue 1, July 2012
TABLE VII
GROUP NAME AND SUB-GROUP NAME OF SOILS
Samples
Group name
Sub-group name
Soil A
MH
elastic silt
Soil B
CH
lean clay
Soil C
CH
fat clay with gravel
Soil D
CH
sandy fat clay
Soil E
CL
sandy lean clay
III. TEST RESULTS FOR NATURAL SOILS
Soil samples are tested in Soil, Concrete Laboratory and
Irrigation Technology Centre, Patheingyi Township,
Mandalay.
A. Compaction Test
Compaction is the densification of soil by removal of air,
which requires mechanical energy. The degree of compaction
of a soil is measured in terms of its dry unit weight. In this
research, standard proctor compaction test is used to
determine optimum moisture content and maximum dry
density. They are used to obtain the values of UCS and CBR.
Compaction test results are described in the following Table
VIII. Soil A has maximum moisture content and minimum
dry density.
TABLE VIII
COMPACTION TEST RESULTS OF SOILS
Samples
Optimum Moisture
Maximum Dry
Content (%)
Density (lb/ft3)
Soil A
34.5
84.5
Soil B
19.56
105
Soil C
22.3
102
Soil D
18.9
108.9
Soil E
12.9
123.14
B. Unconfined Compression Strength Test
The unconfined compression strength test is a special case
of the unconsolidated undrained triaxial test. In this case no
confining pressure to the specimen is applied (i.e, σ 3 = 0). At
failure, σ3 = 0 and qu value can be calculated the following
equation.
σ1= σ3+Δ σf = Δ σf = qu
(5)
Where, qu = Unconfined compression strength (kN /m2)
σ3 = Confining pressure
Δσf = Deviator stress at failure
The relation between consistency and unconfined
compression strength of clays is given in Table IX.
Unconfined compression strength values of soils are shown
in Table X.
TABLE IX
CONSISTENCY AND UNCONFINED COMPRESSION STRENGTH
OF CLAYS
Consistency
qu (kN /m2)
Very soft
0-24
Soft
24-48
Medium
48-96
Stiff
96-192
Very stiff
192-383
Hard
>383
TABLE X
UNCONFINED COMPRESSION STRENGTH VALUES OF SOILS
Samples
qu (kN/m2)
Consistency
Soil A
115 (96-192)
Stiff
Soil B
127.5 (96-192)
Stiff
Soil C
71 (48-96)
Medium
Soil D
153 (96-192)
Stiff
Soil E
150 (96-192)
Stiff
C. California Bearing Ratio (CBR) Test
The California bearing ratio (CBR) is defined as the rate
of the force per unit area required to penetrate a soil mass
with a standard circular plunger of 50 mm diameter at the rate
of 1.25 mm/min to that required for the corresponding
penetration of a standard material. Classification system on
the basis of CBR number is described Table XI. Unsoaked
and Soaked CBR values are described in the following Table
XII.
TABLE XI
CLASSIFICATION SYSTEM ON THE BASIS OF CBR NUMBER
CBR No
General Rating
Uses
0-3
Very Poor
Subgrade
3-7
Poor to Fair
Subgrade
7-20
Fair
Subbase
20-50
Good
Base, Subbase
>50
Excellent
Base
TABLE XII
CALIFORNIA BEARING RATIO (CBR) TEST RESULTS OF SOILS
Samples
CBR No
General
Uses
Rating
Unsoaked Soaked
Soil A
10
5
Poor to Fair Subgrade
Soil B
10
5
Poor to Fair Subgrade
Soil C
7
3
Poor to Fair Subgrade
Soil D
23
9
Fair
Subbase
Soil E
11
6
Poor to Fair Subgrade
IV. TEST RESULTS FOR ENZYME-TREATED SOILS
A. Atterberg Limit Tests Results for enzyme-treated soils
The soil- enzyme mixtures are tested after one and four
weeks of curing period. Results of plasticity index are shown
in Table XIII and figure 1.
TABLE XIII
PLASTICITY INDEX VALUES FOR ENZYME-TREATED SOIL
Dosage 1
Dosage 2
Samples Untreated
1
4
1
4
week
weeks
week weeks
Soil A
22.4
19.6
22.4
29.2
18.7
Soil B
40.3
36.5
34.8
33.1
32
Soil C
38.2
37.7
36.3
36.6
42
Soil D
28.1
22
20
21.8
19.5
Soil E
10.8
6.2
4.5
5.7
4.4
As shown in figure 1, the PI values of natural soils are
greater than enzyme-treated soils for soil B, soil D and soil E.
Dosage 2 of soil A (1week) and soil C (4 week) are greater
than that of natural soils.
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International Journal of Science, Engineering and Technology Research (IJSETR)
Volume 1, Issue 1, July 2012
45
40
Untreated
CBR values of soils treated with enzyme are described in
figure 3.
50
Dosage 1
(1 week)
30
45
Dosage 1
(4 weeks)
20
15
Dosage 2
(1 week)
10
Dosage 2
(4 weeks)
5
35
Dosage 1
(1 week)
30
25
Dosage 1
(4 weeks)
20
15
0
Dosage 2
(1 week)
10
soil A
Soil B
Soil C
Soil D
Soil E
5
TABLE XIV
UCS TEST RESULTS OF ENZYME-TREATED SOILS
Dosage 1
Dosage 2
Samples Untreated
1
4
1
4
week
weeks
week weeks
Soil A
115
118
136.4
125
203
Soil B
127.5
141.2
173
148
180.4
Soil C
71
73
90.2
79.4
123
Soil D
153
165
212
172
226
Soil E
150
167
234.4
180.4
252
300
Soil A
Soil B
Soil C
Soil D
Soil E
Figure 3. Unsoaked CBR values of enzyme-treated soils
In figure 3, unsoaked values of CBR for enzyme-treated
soils are described. As shown in figure 3, dosage 2 of all soils
are greater than that of dosage 1 and natural soil except soil C.
CBR values are increased when the amount of enzyme
dosages are increased for soil B, soil D and soil E.
30
Untreated
25
CBR Values (%)
B. Unconfined Compression Strength Test Results for
Enzyme-Treated Soils
Optimum moisture content and maximum dry density
from compaction of soil treated with enzyme are used to test
unconfined compression strength values. Table XIV
describes the UCS test results of soils treated with enzyme
and figure 2 shows the UCS values (qu) of enzyme-treated
soils.
Dosage 2
(4 weeks)
0
Figure 1. Plasticity Index for enzyme-treated soils
20
Dosage 1
(1 week)
15
Dosage 1
(4 weeks)
10
Dosage 2
(1 week)
5
Dosage 2
(4 weeks)
0
Untreated
250
qu values (kN/m2)
Untreated
40
25
CBR Values (%)
Plasticity Index (%)
35
200
Dosage 1
(1 week)
150
Dosage 1
(4 weeks)
100
Dosage 2
(1 week)
50
Dosage 2
(4 weeks)
0
soil A
Soil B
Soil C
Soil D
Soil E
Figure 2. qu values of enzyme-treated soils
According for the figure 2, qu values of soils are increased
when the enzyme dosages are increased for one and four
weeks.
C. California Bearing Ratio (CBR) Test Results for
Enzyme-Treated Soils
Soils are treated with enzyme dosages for curing one and
four weeks at optimum moisture content. The soaked values
are obtained to keep in water for four days tested for CBR.
Soil A
Soil B
Soil C
Soil D
Soil E
Figure 4. Soaked CBR values of enzyme-treated soils
From the figure 4 results, soaked CBR values are increased
when the amount of enzyme dosages are increased except soil
C after curing one and four weeks.
V. DISCUSSIONS AND CONCLUSION
In this research, different soils are tested in the soil
laboratory. Physical properties tests are firstly carried out to
identify and classify different types of soil. In studied soils,
specific gravity of Soils are 2.72 for soil A and soil B, 2.71
for soil C, 2.73 for soil D and 2.64 for soil E. According to
Unified Soil Classification System, it is found that they are in
MH group, CH group and CL group. Their sub-group names
are elastic silt, lean clay, fat clay with gravel, sandy fat clay
and sandy lean clay. Free swell ratios of soils are negligible
and moderate. Then, modified free swell index for different
types of soil are moderate and negligible. The unconfined
compression strengths of different soils are increased when
the enzyme dosages are increased for curing period one and
four weeks. According to the CBR results, enzyme-treated
soils have higher values than natural soils. Atterberg limit test,
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All Rights Reserved © 2012 IJSETR
International Journal of Science, Engineering and Technology Research (IJSETR)
Volume 1, Issue 1, July 2012
compaction test, UCS test and CBR test are performed after
adding various enzyme dosages to the studied soils.
In this paper, the soil samples with different enzyme
dosages are carried out to study the strength behaviour of
soils by using UCS test and CBR test. The strengths of
studied soils are improved when the various enzyme dosages
are added to the soils. From the results of UCS and CBR tests,
the strength values of soil E are higher than other types of
soils. Thus, it can be concluded that enzyme is more effect on
CL group than MH and CH groups.
ACKNOWLEDGMENT
The author is most deeply indebted to Dr. Kyaw Moe
Aung, Associate Professor and Head, Civil Engineering
Department of Mandalay Technological University, for his
accomplished guidance and helpful suggestions.
Especially, the author wishes her special thanks to
supervisor, Daw Than Mar Swe, Demonstrator, Civil
Engineering Department of Mandalay Technological
University, for her valuable suggestions, true-line guidance,
great supervision and encouragement throughout the thesis
period.
The author thanks all of her teachers from Department of
Civil Engineering for their patient guidance and suggestions.
The author would like to thank Daw Nu Nu Htwe and her
staff members of Soil, Concrete Laboratory and Irrigation
Technology Center, Chaung Win, Patheingyi Township, for
their kind help during the study of this paper.
Finally, the author deeply great thanks to my family
especially my parents, for their supports and encouragements
to attain our destination without any trouble.
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[3] Braja M. Das, : Advanced Soil Mechanics,Third Edition. (2008)
[4] Sivapullaiah,P.V., Sitharam, T.G. and Rao,K.S.Subba.: Modified Free
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[5] Raul Velasquez, Mihai O. Marasteanu, Ray Hozalski, Tim Clyne,:
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