International Journal of Science, Engineering and Technology Research (IJSETR)
Volume 1, Issue 1, May 2014
Experimental Research on the Strength Behavior
of Enzyme-Treated Soils
Aye Nyein Thida, Than Mar Swe

Abstract—This research paper presents the evaluation of
strength behavior of enzyme-treated soils. The objective of this
study is to evaluate the strength behavior of soils treated with
enzyme in terms of Unconfined Compression Strength (UCS)
and California Bearing Ratio (CBR). Soil samples are taken at
about 3ft depth from Kyarnikan village in Patheingyi township
and two places of ASEAN Highway (Mandalay-Naypyitaw
portion). The first place of ASEAN Highway is between
milepost 366/1 and 366/2 and the second place is between
milepost 364/5 and 364/6. The soils from these locations are
expressed by location 1, location 2 and location 3. respectively.
To identify and classify the studied soils, atterberg limit test,
specific gravity test, grain size analysis and free swell test are
performed. Compaction test is carried out to determine the
optimum moisture content (OMC) and maximum dry density.
According to Unified Soil Classification System (USCS), all of
the studied soils are found as CL group. Three enzyme dosages
are selected as 0.5 liter, 1 liter and 1.5 liter per 33m3 of soil. The
strength tests are conducted after the curing period of one week
and four weeks. When the soils are stabilized with enzyme, UCS
and CBR values are higher than that of natural soil.
Index Terms — CBR, Enzyme dosages, Plasticity Index,
Unconfined Compression Strength.
I. INTRODUCTION
Soil is defined as the uncemented aggregate of mineral
grains and decayed organic matter with liquid and gas in the
empty spaces between the solid particles. Soil is used as a
construction material in various civil engineering projects,
and its supports structural foundations. Thus, civil engineers
must study the properties of soil, such as its origin, grain-size
distribution, soil classification and so on.
When poor quality soil is available at the construction site,
the best way is to modify the properties of soil by
stabilization. Stabilization is the process of blending and
mixing materials with a soil to improve certain properties of
the soil. Two primary methods of soil stabilization are
mechanical stabilization and chemical stabilization.
Mechanical stabilization means improving the soil properties
by rearrangement of particles and densification by
compaction, or by changing the gradation through addition or
removal of soil particles. Chemical stabilization refers to that
in which the primary additive is a chemical. Chemical
stabilizers are fly ash, cement, lime, bitumen and enzyme etc.
Nowadays Enzymes have emerged as new chemical for soil
stabilization. Enzymes are chemical, organic and liquid
concentrated substances which are used to improve the
strength behaviour of soils.
Manuscript received May 20, 2014.
Aye Nyein Thida, Civil Department, Mandalay Technological
University,Mandalay,Myanmar,09-400539973,(ayenyeinthida13@gmail.co
m).
Than Mar Swe, Civil Department , Mandalay Technological University,
Mandalay, Myanmar, 09-402589569, (thanmarswe@gmail.com).
II. TESTS FOR PHYSICAL PROPERTIES OF SOILS
In order to determine the physical properties of studied
soil, the following tests are performed:
1) Water Content Determination Test
2) Specific Gravity Test
3) Grain Size Analysis Test
4) Atterberg’s Limit Test
5) Free Swell Test
6) Classification of Soil
A. Water Content Determination Test
Water content determination test is a laboratory test to
determine the field moisture content of soil. The water
content, also known as moisture content is properly the most
common and simplest type of laboratory test.
The results of water content for three different types of
soils are 15.56% in location 1, 26.51% in location 2 and
10.7% in location 3.
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. Specific
gravity is dimensionless parameter. Specific gravity test
results for studied soils are shown in Table I.
TABLE I
SPECIFIC GRAVITY TEST RESULTS FOR STUDIED SOILS
Sample
Gs
Type of soil
Location 1
2.74 (2.70-2.8)
Inorganic Clay
Location 2
2.75 (2.70-2.8)
Inorganic Clay
Location 3
2.64~2.65
Sand
C. Grain Size Analysis Test
Soils are generally characterized as gravel, sand, silt, or
clay. 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. Two methods are generally used to
find the particle-size distribution of soil:
(1) Sieve analysis-for particle sizes larger than 0.075 mm in
diameter.
(2) Hydrometer analysis-for particle sizes smaller than 0.075
mm in diameter.
Grain size analysis test results of studied soils are shown in
Table II.
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International Journal of Science, Engineering and Technology Research (IJSETR)
Volume 1, Issue 1, May 2014
TABLE II
GRAIN SIZE ANALYSIS TEST RESULTS FOR STUDIED SOILS
Particle Size
Distribution
Gravel (%)
Sand (%)
Silt (%)
Clay (%)
F200
R200
F4
R4 (GF)
SF=R200-F4
SF/GF
Location1
Location 2
Location 3
18.1
23.8
43.2
15
58.18
41.82
81.95
18.05
23.77
>1
26.7
53.9
19.4
73.3
26.7
100
26.7
>1
1.4
59.0
31.8
7.8
39.58
60.42
98.6
1.4
59.02
>1
FSR =
Vw
Vk
TABLE IV
FREE SWELL TEST RESULTS FOR STUDIED SOILS
(1)
where, PI =plasticity index
LL =liquid limit
PL =plastic limit
Atterberg's limit test results for studied soils are shown in
Table III.
Sample
Free Swell
Ratio
Location 1
1.07(1.0-1.5)
Location 2
0.87(≤1.0)
Location 3
1.14(1.0-1.5)
TABLE III
ATTERBERG’S LIMIT TEST RESULTS FOR STUDIED SOILS
Plasticity Index
(PI) (%)
Location1
Location 2
Location 3
46.6
34.6
25.1
17.5
14.6
14.3
29.2
20.0
10.8
E. Free Swell Test
Free swell tests are commonly used to identifying
expansive clay and to predict the swelling potential. Ten
grams oven dried soil specimens passing ASTM sieve No-40
(0.425 mm openings) was placed in the graduated cylinders
containing distilled water and kerosene. Sediment volumes
are measured after complete sedimentation of specimens in
respective fluid. It looks about 24 hours to 48 hours in
distilled water. Kerosene is used instead of carbon
tetrachloride since it is easily available in Myanmar.
Soil
Expansively
Clay Type
Mixture of
swelling and
non-swelling
Non-swelling
Mixture of
swelling and
non-swelling
Low
Negligible
Low
i) 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 test 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.
The modified free swell index can be calculated from the
following equation.
Modified Free Swell Index=
Atterberg’s
Limit
Liquid limit
(LL) (%)
Plastic limit
(PL) (%)
(2)
where, FSR =Free Swell Ratio
Vw = Sediment volume of soil in distilled water
(cm3)
Vk = Sediment volume of soil in kerosene
(cm3)
Free swell test results for studied soils are shown in Table
IV.
D. Atterberg’s Limit Test
Atterberg’s Limits are liquid limit, plastic limit, shrinkage
limit and plasticity index. Liquid limit is the moisture
content, in percent, at which the soil changes from a liquid
state to a plastic state. Plastic limit is the moisture content, in
percent, at which the soil changes from a plastic state to a
semisolid state. Shrinkage limit is the moisture content, in
percent, at which the soil changes from a semisolid state to a
solid state. Plasticity index is the different between the liquid
limit and plastic limit. The plasticity index is important in
classifying fine-grained soil.
Plasticity index can be calculated from the following
equation.
PI=LL-PL
To calculate the free swell ratio, the following equation is
used.
V V s
Vs
(3)
where, V = Soil volume after swelling (cm3)
Vs = Volume of soil solid (cm3)
Modified free swell index test results of studied soil are
shown in Table V.
TABLE V
MODIFIED FREE SWELL INDEX TEST RESULTS FOR STUDIED
SOILS
Sample
Modified Free Swell
Index
Swelling Index
Location 1
2.84(2.5-10)
Moderate
Location 2
2.43(<2.5)
Negligible
Location 3
2.1(<2.5)
Negligible
F. Classification of Soil
The purpose of soil classification is to divide the soils into
groups so that all the soils in a particular group have similar
characteristics by which they may be identified. The Unified
Soil Classification System (USCS) is commonly used for
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International Journal of Science, Engineering and Technology Research (IJSETR)
Volume 1, Issue 1, May 2014
classification of soils by geotechnical engineers. This system
takes into consideration both particle-size distribution and
Atterberg's limits. According USCS, location 1 soil is sandy
lean clay with gravel in CL group, location 2 soil is lean clay
with sand in CL group and location 3 soil is sandy lean clay in
CL group.
III. TEST FOR MECHANICAL PROPERTIES OF SOILS
In order to determine the mechanical properties of studied
soil, the following test are performed:
1) Compaction Test
2) Unconfined Compression Strength Test
3) California Bearing Ratio (CBR) Test
A. Compaction Test
Compaction is the densification of soil by removal of air,
which requires mechanical energy. In this study, Standard
Proctor Compaction test is used. In the standard proctor test,
the soil is compacted in a mould that has a volume of 1/30 ft3.
The diameter of the mould is 4 inches. The soil is mixed with
various amount of water and then compacted in three equal
layers by a hammer that delivers 25 blows to each layer. The
hammer weight 5.5 lb and has a drop of 12 inches.
Compaction test results for studied soils are shown in
Table VI.
TABLE VI
COMPACTION TEST RESULTS FOR STUDIED SOILS
Type of
soil
Location 1
Location 2
Location 3
Optimum Moisture
Content (%)
15.7
17.0
12.9
Maximum Dry
Density (pcf)
116.9
114.1
123.14
B. Unconfined Compression Strength Test
The unconfined compression test is a special case of the
unconsolidated undrained triaxial test. In this case no
confining pressure to the specimen is applied (i.e., σ3=0). For
such conditions, for saturated clays, the pore water pressure
in the specimen at the beginning of the test is negative
(capillary pressure). Axial stress on the specimen is gradually
increased until the specimen fails. At failure, σ3=0 and so
σ1=σ3+Δσf=Δσf=qu
(4)
Unconfined compression strength of studied soils are
shown in Table VII.
TABLE VII
UNCONFINED COMPRESSION STRENGTH TEST RESULTS FOR
STUDIED SOIL
Sample
Location 1
Location 2
Location 3
2
qu (kN/m )
76.49(48-96)
49.03(48-96)
150(96-192)
Consistency
Medium
Medium
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 1.25mm/min to that required for the corresponding
penetration of a standard material.
The apparatus consists of a cylindrical mould of 150 mm
inside diameter and 175 mm in height. It is provided with a
detachable metal extension collar 50 mm in height and a
detachable perforated base plate 10 mm thick. A circular
metal spacer disc 148 mm in diameter and 47.7 mm in height
is also provided.
Classification system on the basis of CBR number is
described in Table VIII
TABLE VIII
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
CBR test results for studied soils are shown in Table IX.
TABLE IX
CBR TEST RESULTS FOR STUDIED SOILS
Type of soil
CBR (unsoaked)
CBR (soaked)
Location 1
11.5(7-20)
3.1(3-7)
Location 2
4(3-7)
3.5(3-7)
Location 3
10(7-20)
5(3-7)
According to the results, location 1 and location 3 soil is
suitable for subbase and subgrade and location 2 soil is
suitable for subgrade.
IV. STABILIZATION BY USING ENZYME
Three dosages are selected to study the effect of the
variation of the enzyme concentration on the stabilization
mechanism.
1) 500ml/33m3
2) 1000ml/33m3
3) 1500ml/33m3
The required dosages of enzyme for mixing with soil are
given in Table X.
TABLE X
SELECTED ENZYME DOSAGE FOR THE STUDIED SOIL
Required Enzyme Amount/kg of soil
Dosages
Location 1
Location 2
Location 2
0.5l/33m3
0.0081
0.0083
0.007
1l/33m3
0.016
0.017
0.015
1.5l/33m3
0.024
0.025
0.023
3
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International Journal of Science, Engineering and Technology Research (IJSETR)
Volume 1, Issue 1, May 2014
TABLE XI
CONSISTENCY LIMITS OF ENZYME TREATED SOILS
Limit
(%)
Dosage
Location 1
Location 2
Location 2
Curing period
Curing period
Curing period
1st
46.9
16.8
30.1
48.9
17.6
31.4
49.1
17.2
31.9
LL
PL
PI
LL
PL
PI
LL
PL
PI
(1)
(2)
(3)
4th
46.1
16.8
29.3
44.9
16.9
28.0
43.7
16.7
27.0
1st
34.8
17.5
17.3
32.9
16.3
16.6
33.7
14.7
19.0
4th
37.9
16.0
21.9
37.1
16.7
20.4
35.2
18.1
17.1
1st
20.3
14.1
6.2
20.0
14.3
5.7
19.3
14.4
4.9
4th
19.0
14.5
4.5
18.9
14.5
4.4
18.4
14.4
4.0
35
Location 1(one week)
Plasticity Index (%)
30
25
Location 1(four
weeks)
20
Location 2(one week)
600
Location 1(one week)
500
Location 2(one week)
300
200
Location 2(four
weeks)
100
Location 3(one week)
0
Untreated
Dosage 1
Dosage 2
Dosage 3
Location 3(four
weeks)
Figure 2. qu value of enzyme-treated soil
From Figure 2, it can be found that qu values increase with
higher dosage for a higher curing period. The qu values of the
enzyme treated soils are found to be maximum with dosage 3.
C. CBR Test Results for Enzyme Treated Soils
Soils are treated with three dosages of enzyme at optimum
moisture content.CBR moulds were kept in soaked condition
for 4 days and then tested for CBR.CBR values are carried
out after one week and four weeks curing time. CBR values
of enzyme treated soil in various curing days are given in
Table XIII.
15
TABLE XIII
CBR VALUES FOR ENZYME TREATED SOILS
Location 2(four
weeks)
10
Location 1(four
weeks)
400
qu (kN/m2)
A. Consistency Limits of Enzyme-Treated Soil
Liquid limit and plastic limit of soils mixed with selected
dosages of Firmament Enzyme are tested after one and four
weeks of curing. Results of consistency limits tests of
enzyme treated soils are shown in Table XI.
Location 3(one week)
5
0
Untreated
Dosage 1
Dosage 2
Location 3(four
weeks)
Dosage 3
Dosage
CBR (%)
TABLE XII
UNCONFINED COMPRESSION STRENGTH VALUES FOR
ENZYME TREATED SOILS
Location 2
Curing period
Curing period
Curing
period
4th
1st
4th
1st
4th
Unsoaked
23
35.1
16
20
18
30
Soaked
3.2
3.2
10.3
14
19
22
Unsoaked
23.5
35.8
18.6
22.1
19
35
Soaked
3.5
3.6
11.1
15.5
19
26
Unsoaked
24.5
42.7
22.1
24.3
22
37
Soaked
6.3
7.0
15.5
19.2
22
32
(1)
(2)
(3)
45
40
35
CBR (%)
B. Unconfined Compression Strength Test Results for
Enzyme Treated Soil
Unconfined compression strength test of three different
soils was evaluated by stabilization with three dosages of
enzymes for one week and four week curing periods. The test
results of UCS test for soil treated with enzyme in curing
period days describe in Table XII.
Location 2
1st
Figure 1. Plasticity index of enzyme-treated soil
Figure 1 shows that plasticity index of enzyme treated soil
mostly decreased with dosage 3 both in location 1, 2 and 3 in
four weeks curing period. In one week curing period, PI
values of location 1 soil are more than that of natural PI value.
PI value mostly decreased with dosage 2 in location 1 and
dosage 3 in location 3 in one week curing time.
Location 1
Location 1(one
week),unsoaked
30
Location 1(one
week),soaked
25
20
Location 1(four
weeks),unsoaked
15
10
Location 1(four
weeks),soaked
5
0
Untreated
Dosage1
Dosage2
Dosage3
qu values of treated soils in (kN/m2)
Location 1
Location 2
Location 2
Curing period
Curing period
Curing period
1st
4th
1st
4th
1st
4th
77.47
135.33
77.47
195.15
166
234
2
93.16
192.21
104.93
270.66
180
252
3
141.22
304.99
151.02
538.39
193
267
Dosage
1
Figure 3. CBR value of enzyme-treated soil on Location 1
Figure 3 shows the effect of enzyme on CBR value of
location 1 soil. In location 1 soil, there is little improvement
in the CBR values of soaked condition. By comparing CBR
values of soaked and unsoaked condition, enzyme is not
effective for location 1 soil in wet condition.
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International Journal of Science, Engineering and Technology Research (IJSETR)
Volume 1, Issue 1, May 2014
30
CBR (%)
25
20
Location 2(one
week),unsoaked
15
Location 2(one
week),soaked
10
Location 2(four
weeks),unsoaked
5
Location 2(four
weeks),soaked
0
Untreated
Dosage1
Dosage2
Dosage3
Figure 4. CBR value of enzyme-treated soil on Location 2
The effects of enzyme dosages on CBR value of location
2 soil for a period of one to four weeks of curing are shown in
Figure 4. It is evident that there is gradual improvement in the
CBR values of enzyme treated soil as curing period increases.
Results show that highest quantity of enzyme that is dosage 3
improve to a higher range. In location 2 soil, it can be found
that CBR values of enzyme treated soil in unsoaked condition
is more higher than the soaked condition.
40
35
Location 1(one
week),unsoaked
CBR (%)
30
25
ACKNOWLEDGMENT
The author would like to express her gratitude to
Dr. Kyaw Moe Aung, Associate Professor, Head of Civil
Engineering Department in Mandalay Technological
University, for his invaluable support and managements. The
author would be very pleased with her expression of gratitude
of her supervisor, Daw Than Mar Swe, Demonstrator,
Mandalay Technological University, for her kind guidance,
support, suggestions and careful instructions.
The author wishes to record millions of her thanks to all
teachers in Civil Engineering Department in Mandalay
Technological University, for their enthusiastic suggestion
and careful instructions.
The author would like to express million of her thanks to
Daw Khin Thi Dar (Assistant Engineer, Soil Testing,
Irrigation Training Center, Chaung Win), U Myint Swe
(Senior Assistant Engineer, Soil Testing, Irrigation Training
Center, Chaung Win), and staff members (Soil Testing,
Irrigation Training Center, Chaung Win), for their teaching
and guidance the procedure of laboratory tests that are of
great support in her study.
Location 1(one
week),soaked
20
Location 1(four
weeks),unsoaked
15
10
REFERENCES
[1]
Location 1(four
weeks),soaked
5
0
Untreated
5) Based on the UCS test results, it can be noted that
enzyme stabilization of location 2 soil is more effective than
other two types of soils.
6) According to CBR tests results, enzyme is more
effective on location 2 and 3 than on location 1.
[2]
Dosage1
Dosage2
Dosage3
[3]
[4]
Figure5. CBR value of enzyme-treated soil on Location 3
[5]
The effects of enzyme dosages on CBR value of location
3 soil for a period of one to four weeks of curing are shown in
Figure 5. It is evident that there is gradual improvement in the
CBR values of enzyme treated soil as curing period increases.
It can be found that CBR values of location 3 soil have been
much improved with highest enzyme dosage 3. In location 3
soil, it can be found that CBR values of enzyme treated soil
have improved both in soaked and unsoaked condition.
[6]
Lekha B. M ,"Laboratory Studies on Bio-Enzyme Stabilized Lateritic
Soil as a Highwat Material." Department of Civil Engineering
NITK-Surathkal (2010)
David O. Simmons, " Enzyme Stabilization of Low-Volume Gravel
Roads. " Brigham Young University (2009)
Braja M. Das, " Advanced Soil Mechanics. " Third Edition (2007)
Naresh C. Samtani and Edward A. Nowatzki, " Soil Mechanics:
Laboratory Testing." Department of Transporation Federal Highway
Administration (2006)
Braja M. Das, " Principle of Geotechical Engineering." Fourth
Edition. Boston. U.S.A: PWS Publishing Company (1998)
Khaing Maw Shan, Ma. 2013. Study on Stabilization of Soil Treated
with Firmament Enzyme. M.E.(Thesis), Department of Civil
Engineering, Mandalay Technological University.
V. DISCUSSION AND CONCLUSION
In this study, physical property tests are firstly carried out
to identify and classify the types of studied soil. And then,
compaction tests are carried out to determine optimum
moisture content and maximum dry density. According to
USCS, all of the studied soils are found as CL groups. Based
on the test results, the following conclusions can be drawn.
1) Dosage 3 has the lowest PI value with respect to other
dosages for four week curing period in location 1, 2 and 3.
2) When soils are stabilized with enzyme, UCS and CBR
values are higher than that of natural soil.
3) For a higher dosage of 1.5liter/33m3, UCS value of soil
increased by a maximum of 298.73% in location 1, 998.08%
in location 2 and 77.95% in location 3 after four weeks of
curing.
4) In soaking condition, CBR value has improved to a
maximum of 125.81% in location 1, 540% in location 2 and
location 3 after four weeks curing in a maximum dosage 3.
5
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