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MINISTRY OF EDUCATION AND
TRAINING

MINISTRY OF AGRICULTURE
AND RURAL DEVELOPMENT

THUYLOI UNIVERSITY

MAI THI HONG

RESEARCH ON THE IMPROVEMENT OF THE
ALLUVIAL SOIL IN ORDER TO BUILD, TO UPGRADE
THE EARTH-DAMS IN THE CENTRAL HIGHLANDS

Specialization:
Code No:

Hydraulic Engineering
958 02 02

SUMMARY OF DOCTORAL DISSERTATION

HA NOI, 2019


This scientific work has been accomplished at Thuyloi Univeristy

Supervisor:

Assoc. Prof. Nguyen Trong Tu

Reviewer No. 1:

Prof. Le Kim Truyen

Reviewer No. 2:

Assoc.Prof. Le Xuan Roanh

Reviewer No. 3:

Assoc.Prof. Hoang Viet Hung

This Doctoral Thesis will be defended at the meeting of the University
Doctoral Committee in room No………… on …….

This dissertation is available at:
- The National Library
- The Library of Water Resources University


INTRODUCTION
1. The rationale of thesis
The Central Highlands area has a dense river network. It is the beginning place
of four main river systems, which are the Po Ko - Se San river system in Kon
Tum that pours into Me Kong river; Ba - Ayun river system in Gia Lai that pours
into Da Rang river; Serepok river system ub Dak Lak that pours into Me Kong;
and Dong Nai river system in Dak Nong and Lam Đong that pours into East Sea.
In fact, the water demand the Central Highlands area is much lesser than the
potential reserves, but the shortage of water for agricultural production and others
economic activities is still frequently happening. It means there is a huge amount

of potential water that has not been used for living or manufacturing yet. There
are more than 1000 reservoirs in the Central Highlands. Most of them are earthdams, which was built by the compacted soil since the 80’s - 90’s with the
limitation in construction technology back then. By now, many of the earth-dams
has deteriorated such as the body of the dam is deformed, cracked, sliding, or
infiltration. Moreover, due to the scocial-econimic developing of the Central
Highlands area, it requires a larger comsumption of water. According to, the
water needs for agricutural production will increase 1112%; the water for
industrial use is 1.71.8 times bigger; and the water of human comsumption is
1.92.0 times bigger, in comparison with the present. Although the demand for
water is increasing, the necessary conditions for constructing new reservoirs is
hard. Therefore, the necessity of the repair or upgrade for the earth-dams in the
Central Highland is an urgent need to ensure the capacity of the reservoirs in
order to supply for bigger water consumption.
There are some features that affect the mean of repairing or upgrading those
earth-dams. Firstly, most of the reservoirs are allocated separately in many
places, and the amount of soil needed for upgrading the dams is quite small.
Therefore, the transportation of the soil from a long-distance would be an
uneconomical option. Secondly, the Central Highlands area has been categorized
for some specific uses, such as the area for industrial trees or the area for fruit
trees. It leads to the difficulty in finding the approprioate material source for
reinforcing the earth-dams.

1


In fact, there are some researches that were carried with the aim of using the the
soil in the Central Highlands to construct an earth-dam. However, there is no
study that focuses on using the alluvial soil from reservoirs or rivers to use for
upgrading or repairing the body of earth-dams.
From the above points, research of using local material that can be found in the

area closed to the in-repair dams in order to reinforce the dam body is having
great meaningful in both economic and technique perspective. Therefore, the
choosing of the author for the topic of her PhD research is “Research on the
improvement of the alluvial soil in order to build, to upgrade the earth-dams
in the Central Highlands”.
2. Research purposes
- To identify the content of fine gravel to improve the density of the soil to meet
the standard of upgrading and repairing the earth-dam.
- To identify the proper content of cement to reduce the disintegration of the soil
that contains a significant amount of fine gravel to meet the standard of upgrading
and repairing the earth-dam.
- To identify the proper content of cement and lime to reduce the permeability of
the soil that that contains a significant amount of fine gravel to meet the standard
of upgrading and repairing the earth-dam.
3. The objects of research and research scope
3.1. The objects of research
- The medium and small earth-dams in the Central Highlands;
- The soil in the research: The alluvial soil that has a light dry density, and a
significant permeability or a remarked disintegration;
- The fine gravel’s size is not bigger than 10mm;
- The bidding materials are cement and lime.
3.2. Research scope
- The reseach area: the provinces in the Central Highlands;
- Use the cement - Vicem Hoàng Thạch PCB 30
4. Research methodology
2


- Theoritical research; - Experimental research; - Expert research; - Applied
research.

5. Scientific and practical significance of thesis
- Scientific significance: The thesis has provided a deeper academical knowledge
about the alluvial soil in the Central Highlands, which is used to improve the
quality of the alluvial soil as the local material for upgrading and constructing
the earth-dams in the Central Highlands area.
- Practical significance: The results from this thesis can be used as a scientific
basis for repairing the old one and constructing the new earth-dams in the Central
Highlands.
CHAPTER 1 OVERVIEW OF DAM USING LOCAL MATERIAL AND
THE EARTH DAMS IN THE CENTRAL HIGHLANDS
1.1

Earth-dam and the requirements in design and construction

Earth-dams is built by the local soil that is near to the location of dams. This type
of dams doesn’t allow the overflow of the water. Its mission is collecting and
keeping the water in the reservoir.
The earth-dams has been used for long-time to reserve the water for human
consumption and agricultural production. In Egypt, the earth-dam has been built
since 4400 BC, and in China, it has been built since 2280 BC. At that time, the
earth-dams was built mainly by hand; using bidding material; construction time
would be quite long (10 15 years); the height of the dam is not over 15m.
1.1.1

The requirements in the dam design

The requirements that has to be followed in designing a earth-dam: The body and
the foundation of the dam must be steady in both construction and utilization
time; The infiltration through the dam’s body and foundation is not significant in
term of losing the water as well as creating the inside erosion; Not allow the water

overflow the dam’s body; Having necessary equipments to protect the dam under
the effects of environment…..; Choosing the appropriate alternative for the type
of dam; the configuration of dam’s structure; the construction time and
construction method; the utilization and maintenance.

3


1.1.2

The requirements in the dam materials

The chosen material for constructing the dam with compaction method needs to
be satisfied the following criteria:
The filled soil for the dam should have those characteristics: Shear resistance
(C,) is high; Coefficient of permeability (k) is small; Organic content, admixture
is less than 5%; The content of soluble salt is smaller than 0,3%; Plasticity
index IP = WL- WP = (720)%;
Grain composition Cc = d60/ d10 < (30100), and the boundary of the allowed
aggregate is provided in the design. The soil is not going to degenerate,
weathering, or significantly deformed after compacting process; The content of
clay is not more than (50 60)%, and the desirable value is (10 25)%; When the
dam’s body has a core wall that is for infiltration resistance, then the coefficient
of permeability of the core wall must be smaller than the other parts’s soild about
(2050) times; According to TCVN 4447-87, the deviation of the dry weight (or
dry density) (c) in comparison to the design must be lesser than 0,03T/m3, and
the number of failed specimens is not more than 5% total of the tested specimens.
1.2
1.2.1

The characteristics of the reservoirs and the water consumption in the
coming years in the Cetral Highlands
The characteristics of the reservoirs and earth-dams in the Cental
Highlands

At present, there are 2352 irrigation structures in the Cetral Highlands. In which
the reservoirs are 1190, the water-raising dams are 970, pump houses are 130,
other types are 62. The irrigation area in the plan is 289604 ha, while the
irrigation area in real is 215765 ha, and the area that needs to be irrigated is
772189 ha. It means the area of agricultural production that has been provided
with the water is only 27.94%.
Most of the reservoirs in the Cental Highlands are medium and small size, their
volume is amost less than 3 milion m3. Those reserviors are allocated separately
in a huge area where the infrastructure has not yet developed, which would make
transportation is a huge difficulty. The reservoirs were built for 30-40 years.
Therefore the quality of them have been degraded, and they are not capable of
either watering purpose or safety requirements in the flooding case. Since most
of the small and medium-size reserviors are earth-dams, the common
4


degradations are the infiltration through the dam’s foundation or dam’s body, and
breakdown at road-bed slope or dam’s face…etc.
1.2.2

The water consumption in the coming years

According to statistical data from Institute of Water Resources Planning, the total
water demand for the economic-social development of the whole Central
Highlands area are about 11 billion m3 in 2015, and it will increase up to

approximately 12 billion m3 in 2030. The present water consumption is only 23%
yearly coming water in the Central Highlands. However, the distribution of the
coming water is hugely different in a year. It leads to remarkable lacking water
in dry season and flooding in the rainy season. Hence, at the moment the amount
of lacking water in the Central Highlands is about 5.5 billion m3, which would
be up to 5.5 billion m3 in 2030 due to the increase of water consumption from all
sectors.
1.3
1.3.1

Previous research on eath-dam using local material
Previous international research on eath-dam using local material

According to Nhichiporovich, the type of soild using for constructing dam
includes Sedimentary soil – Aluvi; Sesidual soil; Loose soil. To reduce the
disaggregation of the soil Shearard, J.L., Decker R.S., and Ryker, N.L., proposed
to mixe pulverized lime into the soil that would have an immediate effect. The
research made by Nelson, J.D., & Miller, D.J. (1992) reveals that the swelling
capability of soil depends mainly on the content of colloids in the soild. The
research on quality of the compacting process showed that it depends on
following factors: i) grain composition of filled soil; ii) soil moisture; iii) the
thickness of the compacted layer; iv) type of compactor and number of
compaction times.
1.3.2

Previous national research on eath-dam using local material in the
Vietnam

Nguyen Cong Man, Nguyen Van Tho and Pham Van Thin did the research on
the red basaltic soil, which is the product of weathering process from basalt rock

and it is allocated widely over the Central Highlands area as well as the Southeast
area. The Pham Van Thin’s research showed that the red basaltic soil in the
Central Highlands area has different characteristics. The basaltic soil without
laterite has a maximum dry density in the range 1.281.41 (g/cm3), while the
basaltic soil with laterite has a maximum dry density in the range 1.551.94
5


(g/cm3) that is heavier than first type 2137.8%. Nguyen Van Tho, Tran Thi
Thanh studied the red basaltic soil in the Central Highlands that has a high
content of silty clay, which has a small dry density of 1.01.2 T/m3, and after
standard compaction test its dry density can be increased to 1.31.4 T/m3, and its
maximum dry density is only 1.6 T/m3 by giving more compacting process. The
results from previous studies indicated that if the soil’s dry density has increased
then its shearing resistance is also improved and its compressibility reaches to
medium range, which allows for using this red basaltic soil as filled material. The
resaerch of Nguyen Van Tho, Pham Van Thin and others authors on the
compacting process of red basaltic soil, they found that if the soil moisture is
keeping in proper level during compacting process then it dry density will
increase and the saturated soil has a high shearing resistance; Nguyen Van Tho,
Pham Van Thin, Nguyen Van Chien, Nguyen Cong Man study on the
mineralizable ability, the physico-mechanical properties of basaltic soil that
containt lateritic to use its as filled material. Their research also considered the
effect of the content of coarse grain on the physico-mechanical properties of soil.
They came to the conclusion that the content of coarse grain, the physical
properties of soil, the shape and struture of grain has a remarkable effect on the
constructive ability of the soil; The study of Nguyen Van Tho showed that the
content of coarse grain (N) changed leads to the change of dry density, shearing
resistance, coefficient of permeability. The coefficient of permeability almost
remains when the content of coarse grain N = (0  50)%, but the content of coarse

grain is more than 50% will lead to the increase in the coefficient of permeability.
Pham Van Thin has established some formulas in order to define the mechanical
factors and the coefficient of permeability of basaltic soil that containt the solid
lateritic. Those formulas allow to calculate the needed factors without using the
huge machine to test the soil, therefore it is useful for construction in the actual
conditions. Pham Van Co and Nguyen Huu Ky had an initial reaserch on the soils
that are from diffirent sources. The research reveals that the content of coarse
grain increased leads to the improvement of the shearing resistance , C, but the
coefficient of permeability will be declined; Le Thanh Binh studied the relation
between changing the the content of coarse grain and the physico-mechanical
properties of the soil.

6


1.4
1.4.1

The previous research on using cement and lime to consolidate the soil
The international research on using cement and lime to consolidate
the soil

Mitchell and Freitag research on the soild with low flexibility, or sandy soil. The
proportion of cement using in consolidating soil is 5÷14% of soil’s weight. The
proportion of cement needed depends on the type of soil, state of the soil; Hisaa
Aboshi và Nashahiko Kuwabara (Japan) study to consolidate for different types
of soils. Their research’s result points out that the improvement of soil’s intensity
for the muddy soil and clay is not high as for sandy soil and gravel. Shiells studies
on the wet mixing method, which uses more percentage of cement in comparison
with the dry mixing method. To be specific, the amount of cement needed is

180÷400kg for one m3 soil in the wet mixing method, while it needs only
90÷180kg cement for for one m3 soil in the dry mixing method. It means the
amount of cement needed in the dry mixing method is only about 50% in
comparison to the wet mixing method. The Law’s research in the Asian
Enigeering Insititute, by mixing 5% cement with low quality clay in Bangkok
(Thailand) has improved the lateral deformation of the soil in 10 times, the
consolidation coefficient of the soil in 10÷40 times; Meei-Hoan Ho và CheeMing Chan has researched the clay that is taken from the Centre of research of
the soft soil at Tun Hussein university in Malaysia (UTHM) from the depth level
from 1.52.0m. After adding the cement, the physical factors of soil has been
improved. Nguyễn Duy Quang studies the muddy ground collected from the
estuarine region of Ariake (Japan) to use as local filled soil.
Hence, the results from the international researchers indicate that the
consolidation of soil by using lime, or lime-cement mix has certainly enhanced
the physical factors of the soil.
1.4.2

The previous research on using cement and lime to consolidate the soil
in Vietnam

There were many studies on using cement and lime to consolidate soil from many
researchers such as Pham Van Huynh; Le Xuan Roanh; Nguyen Quoc Dung. In
conclusion, The national studies on using the inorganic bidding material in
consolidating soil have a common indication that when the increase of cement
proprotion leads to the change in the physico-mechanical properties of the soil,
particularly in term of intensity improvement. The soils that are suitable for
7


consolidating by adding cement are gravel soil, sandy soil, clay sand, clay loam.
When the lime has been added, it helps to reduce the disaggregation of the soil.

However, all the mentioned studies only focus on improving the soil’s intensity.
While the study on adding cement in order to reduce the soil’s permeability
and disaggregation has not been researched yet. Finally, the type of soil in the
previous studies are aeolian soil that has stable physico-mechanical properties.
1.5

The content of the research

1/ To study the physico-mechanical properties and particular characteristics of
some alluvial soils in the Central Highlands in perspective of using for earth-dam
construction.
2/ To suggest the solutions to improve the quality of alluvial soil to meet the
applicable standards in order to use it for upgrading, building the earth-dam in
the Central Highlands area.
3/ Choosing the proper ration of each material in the final miture in order to
improve the particular factors, as well as reduce the drawback factors of alluvial
soil that does not meet the capplicable standards.
4/ To apply the result of the research to improve the quality of local material that
is used for Buon Sa dam.
1.6

The conclusion of chapter 1

There was a number of studies on using the local material to build the dam in the
Central Highlands area. However, those studies are only forcusing on utilizing
the weathered soil from the basement rock that exists for very long times, as well
as looking for the solution in designing and in the construction process for each
type of that soil. Whereas, this type of soild is now mainly used for agricultural
production. Beside, the relevant research can be devided in two groups. i) The
research on using the binding material such as cement and lime to consolidate

the original soil. They are mostly in perspective of using in infrastructure
construction. Therefore, they forcused on enhancing the intensity of the soil,
while using the the binding material to reduce the permeability and
disaggregation of the the alluvial soil has not mentioned yet. ii) The common
construction method used is soil compaction, which aims to improve the dry
density of the soild. However, the effect of soil compaction method depends

8


highly on the grain composition and the soil moisture. Hence, all of the
mentioned issues are going to be considered in this thesis.
CHAPTER 2 SCIENTIFIC BASIS OF THE IMPROVEMENT OF THE
ALLUVIAL SOIL TO MEET THE NEED IN UPGRADING, BUILDING
THE ERATH-DAM IN THE CENTRAL HIGHLANDS AREA
2.1

The filled soild in the Central Highlands area

The soil in the Central Highlands is created from basaltic rock, sedimentary rock,
metamorphosed rock, plutonic rock. Based on the source in creation, the soils in
the Central Highlands can be devided in 2 groups: alluvial soil and residual soil
that is residue on the rock base created from different sources.
2.2

The technical approaches to improve the filled soil

The improvement made to the filled soil to reduce its weak factors, which is in
order to meet the requirement in design, such as: enhancing the bearing capacity;
to reduce the penetrability; to reduce the disintegration; improving the dry

density; to resuce the void ratio; enhancing the compression coefficient;
enhancing the compactness; to improve the deformation module; enhancing
shearing strength of the soil;…etc. The goal of all technical approaches is
improving the binding strength between the soil’s grains as well as the
compactness of the soil to meet the necessary improvement for the original soil.
At present, there are many methods to improve the quality of the soil such as: i)
To improve the soil by mechanical approach: The soild is consolidated by
rammer, compactor, vibrant compactor; ii) To improve the soil by adding the
new grain composition; iii) To improve the soil by adding the inorganic binder
or organic binder such as cement, lime, bitumen,...
2.3

The scientific basis of choosing the binding material to improve the
soil having a high penetrability and remarkable disintegration

The soils that are high permeability and a remarkable disintegration are normaly
contaning a huge content of Na, Mg. When the content of ion Na+ is big enough,
then ion Na+ can be replaced for ion Ca++. When the concentration of ion Na+ is
closed to the surface of the clay minerals, it involves directly into the double
diffuse field and makes this field is thicker. Therefore, an efficient approach is to
replace the ion Na++ by others similar one. The author chooses the replaced ion

9


is Ca++. The solution is to add the rich calcium compound into original soil. The
two common materials for that are lime or cement.
If the thickness of the double diffuse field can be reduced, it means the Van der
Waals adhesion will improve and hence the clay grains are coming closer. When
the proportion of ion Ca++ is increased meaning the proportion of ion Na++ is

decreased, it is the process of replacing the ion in the soil. Therefore, the efficient
way is to add one of following compoud into the soil: CaO, Ca(OH) 2 or others
material that has a rich Ca content, which basically change the penetrability and
the disintegration of the soil. The amount of adding material depends on the type
of soil, compaction density, the water soluble-salt, the construction
method,…etc. Before choosing the ration of mixing, it is necessary to have a test
to identify the proper mixing ratio. That is the basis for the author’s experiment
study in chapter 3.
2.4

The scientific basis to choose the coarse grain to improve the dry
density of the soil

There are many studies on improving the dry density of the soil by the method
of soil compaction. This method is simple and economical efficiency. However,
the effective of soil compaction is highly depening on the moisture of the soil,
the grain composition of the soil, and compacting equipment. According to
previous research, the method of soil compaction is effective with the soil that
contains the clay content is smaller than 15%. In addition, in the clay (cohesive
soil) is usually existting the air bag, which affects the process of compacting the
soil under the press of external force. To this iusse, it is important to eliminate
the existing of the air bags and to improve the air venting of the soil that depends
on soil’s grain composition and soil porosity.
In particular, the soil’s dry density is calculated by the following equation:


2.5

tm
c

 tc . cm
 t
 c (1  N )  N  cm

The conclusion of chapter 2

Based on the research objective, the author chooses the approaches to improve
some physico-mechanical properties, as well as some particular factors of the soil
as follow: i) To choose the approach using binding materials to reduce soil’s
enetrability and disintegration; ii) To choose the approach changing the grain
10


composition, particularly adding more coarse grain in order to enhance the dry
density of soil. That is the scientific basis for the author to carry the experimental
study in the following chapters.
CHAPTER 3 RESEARCH ON IMPROVING THE PHYSICOMECHANICAL PROPERTIES OF THE ALLUVIAL SOIL TO
UPGRADE THE ERATH-DAM IN THE CENTRAL HIGHLANDS AREA
3.1

Introduction

The analysis in chapter 1 and chapter 2 showd that the earth-dams in the Central
Highlands are at small- and medium-size; they were built for a long time; hence
many of them have been degraded and not be able to work as original design.
Beside, the irrigation structures in the Central Highlands spread in a large area
with the amount of the material needed for ungrading is quite small. It leads to
the demand for using the local materials for ungrading the dams is quite urgent.
Moreover, the source of soil that can be used as filled materials for upgrading the

dams, which has been researched by many authors, has been planned for growing
the agricultural production and insutrial plants. Therefore, it is necessary to
research to find the new source of the materials that, in this thesis, is the alluvial
soil. However, this type of soil is normally having some physico-mechanical
properties, as well as some particular factors those are not meet to the
requirement for using in ungrading the earth-dams.
3.2

Choose the soil samples for research

- The soil sample MA, which has been taken in the material yard A near the Tân
Sơn (Gia Lai) water reservoir, is representative for the soil group I that containts
mainly small dimension grains.
- The soil samples MB and MC, which has been taken in the material yard B and
C near the Eamlô and Buôn Sa (Đắk Lăk) reservoir respectively, are
representative for the soil group II that the grains are mainly bigger than 2mm.
3.3

The consolidation of experimental results

The results of the test on soil samples MA, MB, MC revealed that some physicomechanical properties and particular factors of the soils meet the requirements
for constructing, upgrading, repairing the earth-dams, according to TCVN 82162009 and TCVN 8297-2009. However, there are some criteria that the soils have
not yet met the standard as such:
11


- MA soil sample: The dry density is small and the optimum moisture is high,
according to TCVN 8297-2009;
- MB soil sample: the disintegrated time is very short, after 500 seconds the
sample has been completely disintegrated.

-MC: The soil has a significant coefficient of permeability, which does not meet
the requirements of filled soils in embankment construction. according to TCVN
8216-2009.
Therefore, it is necessary to propose an approach to improve some physicomechanical properties and particular factors in order to meet the requirements of
filled soils in embankment construction.
The research on improving the soil’s percolation resistance

3.4

1/ The first scenario: the proportion of cement content are changed by
1%,2%,3%,5%,7% and the lime content is fixed by 2%
Table 3. 1 The result of percolation test with cement proportion changed and 2% lime
content.
The mix of soild
and admixture

1
2
3
4
5

MC-1-2
MC-2-2
MC-3-2
MC-5-2
MC-7-2
Coefficient of permeability k (10-5 cm/s)

No

The content
of cement
(%)
1
2
3
5
7

The content
of lime (%)

The factor of
percolation k (cm/s)

2
2
2
2
2

9.0710-05
6.3110-05
4.3110-05
2.7210-05
1.2410-05

10
8

6
4
2
0
0

1

2
3
4
5
6
The content of cement (%)

7

8

Figure 3. 1 The effect of cement content and 2% lime on the factor of percolation

When the content of cement increased, it leads to a significant decrease in the
factor of percolation k. It is because both cement and lime contains a fine grain
composition that easily fulfills the soil’s voids. In addition, mixing cement and
12


lime into the soil will lead to hydration reaction with the existing water in the
soil, which crystallizes the soil’s grains that resuces the penetrability of the soil.
With the cement content is 3% in cooperation with 2% content of lime, the factor

of percolation k = 4.3110-05 cm/s.
2/ The second scenario: the proportion of lime content are changed by
1%,2%,3%,5%,7% and the cement content is fixed by 2%
Table 3. 2 The result of percolation test with lime proportion changed and 2% cement
content.
No

The content of
cement (%)
2
2
2
2
2
Coefficient of permeability k (10-5 cm/s)

1
2
3
4
5

The mix of soild
and admixture
MC-2-1
MC-2-2
MC-2-3
MC-2-5
MC-2-7

The content of
lime (%)
1
2
3
5
7

The factor of
percolation k (cm/s)
9.3810-05
6.3110-05
2.0510-05
0.81910-05
0.42710-05

10
8
6
4
2
0

0

1

2

3

4

5

6

7

8

The content of lime (%)

Figure 3. 2 The effect of lime content and 2% cement on the factor of percolation

The test’s result indicates that the factor of percolation decrease when the content
of cement and lime increase, as well as lime, is mor effectively in comparison
with cement. The factor of percolation decreases quickly when the content of
lime increase from 13%. With the content of lime is more than 3%, the factor
of percolation keeps going down but with slower speed. Therefore, to enhance
the efficiency of reducing the factor of percolation in regard to the economical
issue, the proposal is using 3% content of lime and 2% content of cement. With
that choice, the factor of percolation of the soil is 2.0510-05cm/s, which is
satisfied TCVN 8216-2009 for using as filled material for constructing or
upgrading the earth-dams.

13


After choosing the content of cement and lime to reduce the soil’s penetrability

is 2% and 3% respectively, it is necessary to recheck the shearing and deforming
resistance of the soil in order to avaluate the effect of additive cement and lime.
The test’s results show that using the content of binding material with 2% cement
and 3% lime leads to the improvement of the shearing and deforming resistance
factors, only specific soil cohesive strength C is insignificantly decreased. Hence,
the author proposes the ration of binding material are 2% cement and 3% lime in
order to improve the soil’s penetrability.
3.5

Research on reducing the soil’s disintegration

3.5.1

Research on choosing the cement content to extend the disintegrated
time of the soil

The soild sample has been prepared for the content of cement at 0%, 1%, 2%,
3%, 4%, 5%, 7% và 9%. The test is carried to identify the disintegrated time of
the soil.
Table 3. 3 The result of the test identifying the disintegration characteristic of the soil
No

Name of
samples

1
2
3
4
5

6
7
8

MB-0
MB-1
MB-2
MB-3
MB-4
MB-5
MB-7
MB-9

Cement
content
%
0
1
2
3
4
5
7
9

The disintegrated
volume of soil
%
100
100

100
100
100
100
100
100

Disintegrated
time
phút
8.3
12.6
22.7
35.5
46.4
64.3
75.6
116.2

120

time t (minute)

100
80
60
40
20
0
0

2

4
6
The content of cement (%)

8

10

Figure 3. 3 The effect of cement content on the disintegrated time of the soil

To be aware that when the content of cement increased the disintegrated time of
the soil significantly increases. In particular, with content of cement is 1% the
disintegrated time of the soil is longer than 1.5 times, with content of cement is
14


3% the disintegrated time of the soil is longer than 4.3 times, and with content
of cement is 9% the disintegrated time of the soil is longer than 14 times.
The disintegrated time increased along with the increase of cement content
because the fine-grain composition in the cement makes the unit surface between
grains increasingly, which lead the surface of reaction between grains also
increasingly. However, in concern to economical factors, it should be noticed
that the disintegrated time of the soil with 5% cement content is quicker than 7.75
times in comparison with no cement content, similarly with 9% cement content
the time for disintegration is 14 times quicker without cement. To this end, the
initial choice of cement content is 5% in regard to both the efficiency of technical
and economical aspects.

3.5.2

Research on the physico-mechanical properties of soil mix with 5%
cement content

The test’s results show that adding 5% cement content leads to a reduction of
soil’s angle of internal friction. It becauses the addictive cement increases the
proportion of rounded grains that reduce the angle of internal friction , whereas
soil adhesion is increasing; the soil defromability is increasing; and soil’s
penetrability is decreasing, which makes the properties of the mix is to meet
TCVN 8216-2009. The increase of shearing resistance of the soil and the
decrease of soil deformability are the result of the ion-exchange reaction between
soil and cement, which is similar to the pozzolanic reaction. The cation Ca 2+,
Mg2+ replace to Na+ and H+ in the double electricity field on the surface of clay
grains. In conclusion, to extend the disintegrated time of the soil, the author
proposes to add 5% cement content in comparison to soil’s dry density into the
soil that has a strong disintegration.
3.6

Research on enhancing the dry density of the soil

The alluvial soils (MA soil sample) that have been taken in the area near to Tân
Sơn reservoir have light dry density. The author proposes the approach that is
changing the size of the grain composition of the soil, particularly the author
chooses to add fine gravel into the soil sample. The reason for doing that is the
fine gravel has not water-retaining ability and it reduces the optimum moisture
content of the mix. Moreover, the existing of bigger size grain (fine gravel) will
help smaller size grain (soil grain) esialy to occupy the voids in the mix, which
increases the efficiency of the compaction process.
15

3.6.1

The effects of the content of fine gravel on the dry density and the
optimum moisture content

When adding the fine gravel with soil sample will improve the dry density and
reduce the optimum moisture content of original soil. That change is calculaed
by TCVN 4201:2012.
2

40
35
30

1.6

Wop (%)

c (g/cm3)

1.8

1.4

25
20

1.2

15
1
0

5

10

15

20

25

30

35

40

45

50

10

55

0

mS (%)

10

15

20

25

30

35

40

45

50

55

mS (%)

The effects of the content of fine gravel
on the dry density

3.6.2

5

The effects of the content of fine gravel
on the optimum moisture content

The effects of the content of fine gravel on the shearing resistance of
the soil
45

0.5

40
0.4

C (kG/cm2)

 (o)

35
30
25

0.3

0.2

20
0.1

15

0

10
0

5

10

15

20

25

30

35

40

45

50

0

55

5

10

15

20

The effects of the content of fine gravel on
the angle of internal friction of the soil

3.6.3

25

30

35

40

45

50

55

mS (%)

mS (%)

The effects of the content of fine
gravel on the soil adhesion

The effects of the content of fine gravel on soil deformation and soil
permeability
400

700

350

600

k (10-6 cm/s)

E1-2 (kG/cm2)

300
250
200
150

500
400
300
200

100

100

50
0
0

5

10

15

20

25

30

35

40

45

50

0

55

0

ms (%)

5

10

15

20

25

30

35

40

45

50

55

ms (%)

The effects of the content of fine gravel
on the modulus of soil deformation

The effects of the content of fine gravel
on the lên soil permeability

16


3.6.4

Analysis to choose the proper proportion of the fine gravel

For the MA soil sample, the physico-mechanical properties and particular factors
are all satisfied with the requirement for filled materials. Before changing the
size of grain composition in order to improve the dry density c, the soil has a
medium bearing capacity and medium deformability. In particular, the modulus
of soil deformation E1-2 = 82.37 kG/cm2; a medium shearing resistance with
internal friction of the soil  = 18.40; the soil adhesion C = 0.278 kG/cm2; the
penetrability is quite small with coefficient of permeability 1,63×10-6 cm/s; all
factors are meet to design requirements. However, the result of standard Proctor
compaction test shows that the dry density of soil is quite small c = 1.42 T/m3
and the optimum moisture content Wop= 30.34%, which are not meet to design
requirement in TCVN 8297-2009 for the requirement on the dry density, and the
optimum moisture content
Based on the research’s results, it proposes adding fine gravel in order to enhance
dry density and reduce the optimum moisture content. The research’s result also
indicates that the increase of fine gravel content leads to improvement of shearing
resistance and reduction of deformability, but the resistant-permeability is
decreased. Especially, with the content of fine gravel is over 25%, the soil
permeability increase quickly over 5x10-5 cm/s. According to TCVN 8216-2009,
the required value of soil permeability k is not bigger 1x10-4 cm/s in the dam
design, and to be safe it should choose the soil permeability k < 5.23x10-5 cm/s,

which is in corresponding with fine gravel content ≤ 25%. Therefore, it is
suggested to add the content of fine gravel from 2025% to mix with fine grain
soil in order to improve the characteristics of original soil, which is going to use
for dam banking.
3.7

The conclusion of chapter 3

The research on original characteristics of some filled soil in the Central
Highlands such as gain composition, physico-mechanical properties, and
particular factors has been made, which is the basis for a proper proposal to
improve some physico-mechanical properties of soil in order to use the final mix
for upgrading and constructing the earth-dams. To be specific, the author has
studied 3 types of soils that intend to use for dam banking in the Central
Highlands. Those soils include:

17


- The soils containt a significant fine gravel content: i) If the soild has a marked
penetrability, then the solution is adding 2% cement and 3% lime to reduce the
penetrability; ii) If the soild has a strong disaggregation, the author suggests
adding 35% cement content into original soil.
- The soils with light dry density: the author suggests mixing the fine grave
content from 2025% to improve the mix’s dry density. It also leads to the
reduction of the optimum moisture content and deformability, the increase of
shearing resistance and penetrability but all of the factors are still meet the
applicable requirements to the filled soil of dam banking.
CHAPTER 4 APPLYING THE RESULTS OF THE RESEARCH TO
UPGRADE, TO REPAIR AN EARTH-DAM IN THE CENTRAL

HIGHLANDS
4.1

Choosing the dam for the application study

4.1.1

Choosing and introducing the dam

The dam that has been chosen is earth-dam Buon Sa in Buon Reng, Ea’bong
village, Krong Ana district. The chosen dam is a homogeneous earth dam that
has the basic parameters as in Table 4.1.
Table 4 1 Basic parameters of the earth-dam of Buon Sa reservoir

No
1
2
3
4
5
6
4.1.2

Basic parameters
Dam level
The level of the top wall breakwater
Retention level
The width of the top of dam’s face
Dam height
The coefficient of the coefficient

battered upstream/downstream face

Value
463.54 m
463.84 m
461.0 m
3.0 m
12.0 m
3.0

The dam’s present condition and to propose the approach for
upgrading

The investigation of the dam shows its clear degradation; the upstream/
downstream faces are not reinforced, there are luxuriant trees; the dam’s face
18


without reinforcement for years has been disintegrated and not enough
dimensions as designed. The downstream face appears many holes and there is
no drainage water equipment. The downstream face appears many strong
permeable areas, especially at the location of the old river channel.
At present, the dam is being percolated. Therefore, the necessity of repairing to
fix the percolation as well as to ensure the safe utilization of this earth-dam is
urgent. The objective of the repair is to fix the percolation of the dam’s body (at
the location of the old river channel); to expand the outline of dam; to embank
the upstream face by using the local material that has been improved; to build a
new drainage prism in downstream side (in order to improve the stability for
downstream face).
4.2

4.2.1

The result of dam upgrading by embanking the upstream face
The results of the percolation calucaltion in different scenarios

The author proposes the scenario with the coefficient of the battered-backfill face
m =3.5 to calculate the permeability and stability of the dam’s body after
upgrading, with the changes in the backfill thickness that leads to the
correspondent values of the dam crown’s width that are B = 4.0; 4.5 and 5.0m.
472
469
466
463

448

0.4

0.3

0.35

5
0.2

439
436
-65

-60

-55

-50

-45

-40

-35

-30

-25

-20

-15

-10

-5

0

5

10

15

20

25

5

442

0.1

0.05

445

0.2

451

0.15

454

0.0

m³/sec
3.5582e-006
0.2

457

0.1

Cao ®é

460

30

35

40

45

50

55

60

65

70

Kho¶ng c¸ch

Figure 4. 1 The result of permeability calculation with dam crown’s width B = 4.0 m
472
469

466
0.6

463

Cao ®é

0.1

454
451

0.4

0.1

445

0.2

448

0.3

457

3.4136e-006 m³/sec
0.2

0.5

0.8
0.40.7

460

442
439
436
-65

-60

-55

-50

-45

-40

-35

-30

-25

-20

-15

-10

-5

0

5

10

15

20

25

30

35

40

45

50

55

60

65

70

Kho¶ng c¸ch

Figure 4. 2 The result of permeability calculation with dam crown’s width B = 4.5m
472
469
466
0.35

463

0.05

451
448

0.3
0.0
5

0.1

442

0.1

0.2

445

0.1
5

3.2902e-006 m³/sec

Cao ®é

457
454

0.25

0.2
0.4

460

439
436
-65

-60

-55

-50

-45

-40

-35

-30

-25

-20

-15

-10

-5

0

5

10

15

20

25

30

35

40

45

50

55

60

65

70

Kho¶ng c¸ch

Figure 4. 3 The result of permeability calculation with dam crown’s width B = 5.0m

19


4.2.2

The results of the stability calculation of dam face

1/ The calculation of stability of upstream face:

2.799

472
469
466
463

Cao ®é

460
457
454
451
448
445
442
439
436
-65

-60

-55

-50

-45

-40

-35

-30

-25

-20

-15

-10

-5

0

5

10

15

20

25

30

35

40

45

50

55

60

65

70

Kho¶ng c¸ch

Figure 4. 4 The result of stability calculation for the upstream face with dam crown’s
width B = 4.0m
2.790

472
469
466
463

Cao ®é

460
457
454

451
448
445
442
439
436
-65

-60

-55

-50

-45

-40

-35

-30

-25

-20

-15

-10

-5

0

5

10

15

20

25

30

35

40

45

50

55

60

65

70

Kho¶ng c¸ch

Figure 4. 5 The result of stability calculation for the upstream face with dam crown’s
width B = 4.5m

2.767

472
469
466
463

Cao ®é

460
457
454
451
448
445
442
439
436
-65

-60

-55

-50

-45

-40

-35

-30

-25

-20

-15

-10

-5

0

5

10

15

20

25

30

35

40

45

50

55

60

65

70

Kho¶ng c¸ch

Figure 4. 6 The result of stability calculation for the upstream face with dam crown’s
width B = 5.0m

2/ The calculation of stability of downstream face:
1.638

472

469
466
463

Cao ®é

460
457
454
451
448
445
442
439
436
-65

-60

-55

-50

-45

-40

-35

-30

-25

-20

-15

-10

-5

0

5

10

15

20

25

30

35

40

45

50

55

60

65

70

Kho¶ng c¸ch

Figure 4. 5 The result of stability calculation for the downstream face with dam
crown’s width B = 4.0m

20


1.643

472
469
466
463

Cao ®é

460
457

454
451
448
445
442
439
436
-65

-60

-55

-50

-45

-40

-35

-30

-25

-20

-15

-10

-5

0

5

10

15

20

25

30

35

40

45

50

55

60

65

70

Kho¶ng c¸ch

Figure 4. 8 The result of stability calculation for the downstream face with dam
crown’s width B = 4.5m

1.648

472
469
466
463

Cao ®é

460
457
454
451
448
445
442
439
436
-65

-60

-55

-50

-45

-40

-35

-30

-25

-20

-15

-10

-5

0

5

10

15

20

25

30

35

40

45

50

55

60

65

70

Kho¶ng c¸ch

Figure 4. 9 The result of stability calculation for the downstream face with dam
crown’s width B = 5.0m

4.2.3.

Discussion on results

Table 4 2 The calculation’s result of stability coefficient of the dam face

No
1
2
3

Dam crown’s
width
B = 4.0
B = 4.5
m = 5.0

Jmax
0.405
0.351
0.322

Kmin min
in upstream face
2.799
2.790
2.767

Kmin min
in downstream face
1.638
1.643
1.648

[K]
1.30
1.30
1.30

With the result of the calculation of permeability and stability of
pstream/downstream face, the author realizes that using the diffirenet coefficents
of the battered-backfill upstream face, TL m =3.5m with the dam crown’s width
B = 4.0; 4.5 and 5.0m are all satisfied the impervious ability and stability of the
dam. However, to ensure the condition for using construction machinery and
equipment in the construction process as well as to enhance the dam safety, the
author recommends the dam crown’s width to emback the battered-backfill
upstream face is TL 4.5m.

21


4.3

The conclusion of chapter 4

The author made an investigation on the present condition of Buon Sa dam.
Based on that, the author proposes the approach for upgrading the dam to meet
the anti-infiltration requirement and suggests using battered-backfill upstream
face to improve the anti-infiltration ability of the dam. From the result of an
experimental study in chapter 3, the author suggests using the improved mix that
is made from soil sample MC with 3% lime, 2% cement to embank the batteredbackfill upstream face. The calculation made by SEEP/GEO-SLOPES program
reveals that with the coefficient of the battered-backfill upstream face m=3.5 and
the dam crown’s width B = 4.5 m, the dam meets all requirement on antiinfiltration ability, the anti-slipping ability of upstream/downstream face, as well
as the condition for using construction machinery in construction process.

CONCLUSION AND RECOMMENDATION
I. The achieved results of this thesis
From the result of research, the main achivements of the thesis are as follow:
The characteristics and the physico-mechanical properties of the soil in the
Central Highlands have been collected and to generalized. Based on that, the
representative soil has been chosen to research, in which the proportion of the
fine-size are the majority as well as containing a marked content of fine-gravel
grain.
Based on the analysis of scientific basis and techincal approaches to improve the
soil characteristics, the author has chosen 3 methods for improving the soil. For
the soil that has s significant permeability, the chosen method is adding cement
and lime to improve the anti-infiltration ability of the soil; For the soil that is
quickly disintegrated, the chosen method is adding cement into the soil; For the
soil that has a light dry density, the chosen method is changing the size grain in
the grain composition, particularly it is adding fine gravel into the soil.
For the soil that has s significant permeability, the solution is adding a proper
content of cement and lime to reduce the permeability. In particular, the author
proposes the content of additives are 3% lime and 2% cement in the thesis.

22


For the soil that is quickly disintegrated, the solution is adding cement to reduce
the soil’s disintegration. In particular, the author suggests using 5% cement to
mix with original soil in this case.
For the soil that has a light dry density, the proposal is to add fine gravel in order
to enhance the dry density of the mix. Together the increase of dry density, the
optimum moisture content decrease and the ability of soil for shearing resistance
and anti-deformability both increase, but the ability in anti-infiltration is quicky

decreased when the content of gravel grain increasing. The author recommends
using the fine-gravel grain with the content 2025% to mix with original soil,
which is the proper proportion to have an optimal result in the dam construction.
To upgrade the earth-dam that the body of the dam is infiltrated. The proposed
solution is the battered-backfill upstream face by using the improved local soil.
The proposal of the coefficient of the battered-backfill upstream face m=3.5 and
the dam crown’s width B = 4.5 m.
II. The new finding in the thesis
To propose a proper content of gravel grain 2025% to mix with alluvial soil that
has a light dry density. It helps to improve the soil’s dry density; to reduce the
optimum moisture content; to enhance the ability of soil for shearing resistance
and anti-deformability. Finally, the improved soil is satisfied with the criteria in
the applicable standard to use as filled material for upgrading and constructing
earth-dam.
To propose using 3% lime and 2% cement with alluvial soil that has a significant
content of gravel grains ( 48%) to reduce the soil’s permeability from 10-4 cm/s
to 10-5 cm/s, which is meet the requirement of anti-infiltration for the dam.
III. Limitations and development direction of the thesis
1.

Limitations

1) Due to the limitations of budget and time, the author has only taken soil
samples from 3 locations in the Central Higlands to have representative samples
in the research.
2) The research just has been conducted in the laboratory. It has not deployed in
real construction yet to evaluate the research results.

23