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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 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 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” 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 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 Research methodology - Theoritical research; - Experimental research; - Expert research; - Applied research 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 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 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 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 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 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 (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 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 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 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 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 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 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 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 and chapter 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 The result of percolation test with cement proportion changed and 2% lime content The mix of soild and admixture 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 (%) The content of lime (%) The factor of percolation k (cm/s) 2 2 9.0710-05 6.3110-05 4.3110-05 2.7210-05 1.2410-05 10 0 The content of cement (%) Figure 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 The result of percolation test with lime proportion changed and 2% cement content No The content of cement (%) 2 2 Coefficient of permeability k (10-5 cm/s) 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 (%) 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 0 The content of lime (%) Figure 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% 9% The test is carried to identify the disintegrated time of the soil Table 3 The result of the test identifying the disintegration characteristic of the soil No Name of samples MB-0 MB-1 MB-2 MB-3 MB-4 MB-5 MB-7 MB-9 Cement content % 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 The content of cement (%) 10 Figure 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 40 35 30 1.6 Wop (%) c (g/cm3) 1.8 1.4 25 20 1.2 15 10 15 20 25 30 35 40 45 50 10 55 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 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 10 10 15 20 25 30 35 40 45 50 55 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 10 15 20 25 30 35 40 45 50 55 ms (%) 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 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 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 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 Basic parameters of the earth-dam of Buon Sa reservoir No 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 0.2 439 436 -65 -60 -55 -50 -45 -40 -35 -30 -25 -20 -15 -10 -5 10 15 20 25 442 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 Khoảng cách Figure 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 10 15 20 25 30 35 40 45 50 55 60 65 70 Khoảng cách Figure 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 0.1 442 0.1 0.2 445 0.1 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 10 15 20 25 30 35 40 45 50 55 60 65 70 Khoảng cách Figure 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 10 15 20 25 30 35 40 45 50 55 60 65 70 Khoảng cách Figure 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 10 15 20 25 30 35 40 45 50 55 60 65 70 Khoảng cách Figure 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 10 15 20 25 30 35 40 45 50 55 60 65 70 Khoảng cách Figure 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 10 15 20 25 30 35 40 45 50 55 60 65 70 Khoảng cách Figure 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 10 15 20 25 30 35 40 45 50 55 60 65 70 Khoảng cách Figure 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 10 15 20 25 30 35 40 45 50 55 60 65 70 Khoảng cách Figure The result of stability calculation for the downstream face with dam crown’s width B = 5.0m 4.2.3 Discussion on results Table The calculation’s result of stability coefficient of the dam face No Dam crown’s width B = 4.0 B = 4.5 m = 5.0 Jmax 0.405 0.351 0.322 Kmin in upstream face 2.799 2.790 2.767 Kmin 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 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 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 Limitations 1) Due to the limitations of budget and time, the author has only taken soil samples from 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 3) Some research results have been conducted based on the two old standards, which are TCVN 8297-2009 and TCVN 8216-2009 The research has not yet studied in corresponding with a new standards TCVN 8297-2018 and TCVN 8216-2018, which is the replacement of the two old standards used in the research Development direction 1) Within research in this thesis, the author has only studied to propose the solutions for improving some physico-mechanical properties as well as particular factors of the soil In particular, they are the soils that have a light dry density; have a significant coefficient of permeability k, or have a remarked disaggregation Therefore, it is recommended to research with other alluvial soils containing other physico-mechanical properties as well as particular factors that not meet the requirements of applicable standards in order to have a proper approach to improve them for using in earth-dam construction 2) With the swelling soil, the solution to improve the characteristic of the soils can be referred to some previous studies [29] or [45] 3) It is necessary to carry the application study to have the procedure of the execution process in making the final material mix as well as to evaluate the result of this study 4) It might research with other PCB 30 types of cement to compare the gained results 24 PUBLICATIONS OF THE AUTHOR Mai Thi Hong, Pham Huy Dung “A research of using the local material to reinforce the Buon Sa Earth-Dam” Journal of Water Resources and Environmental Engineering, ISSN1859 – 3941, Issue 63-2018 Mai Thi Hong, Nguyen Trong Tu “Effect of gravel content on properties of the rhodic ferralsols used for earth dams in Tay Nguyen” Vietnam Geotechnial Journal, ISSN – 0868-279X, Volume 22, Number 1-2018 Nguyen Trong Tu, Mai Thi Hong, Pham Huy Dung “Solutions to Improve Permeability and Disintegration of Earth Dam in Central Highlands, Vietnam” The 8th International Conference on Fluid Mechanics, September 25-28,2018, Sendal, Japan Mai Thi Hong, Pham Huy Dung, Nguyen Trong Tu “The research on the solutions to improve the local soils, which has particular physico-mechanical properties, to use as filled material for dam banking in the Central Highlands” Proceedings of the annual conference of Thuyloi University 2017, ISBN: 978604-822274-1 Nguyen Trong Tu, Nguyen Thi Thanh Binh, Mai Thi Hong “The present conditions of some small and medium-size earth-dams in the Central Highlands” Proceedings of the annual conference on Water Resources 2016, ISBN: 978-60482-1980-2 ... 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... 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... 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