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MINISTRY OF EDUCATION MINISTRY OF AGRICULTURE AND TRAINING AND RURAL DEVELOPMENT This scientific work has been accomplished at: ThuyLoi University THUYLOI UNIVERSITY Advisor 1: Assoc.Prof.Dr Nguyen Quang Cuong Advisor 2: Assoc.Prof.Dr Le Van Hung MAI LAM TUAN RESEARCHING ON SELECTING SCALE OF DIVERSION WORKS ON DAM BUILDING AND HYDROPOWER IN VIETNAM Review No.1: Prof.Dr Ho Si Minh - Vietnam Water Resources Development Association Review No.2: Assoc.Prof.Dr Vu Huu Hai - National University of Civil Engineering Review No.3: Assoc.Prof.Dr Nguyen Thu Hien - Thuyloi University Specialization: Hydraulic Engineering Code No: 58 02 02 This Doctoral Thesis will be defended at the meeting of the University Doctoral Committee at ThuyLoi University, 175 Tayson str., Dongda, Hanoi, Vietnam on May, 03rd, 2019 SUMMARY OF DOCTORAL DISSERTATION HANOI, 2019 This dissertation is available at: - The National Library - The Library of ThuyLoi University INTRODUCTION diversion works This study does not delve into the effects of turbulence, dynamic Problem statement circuits and downstream energy dissipation When designing a diversion works, the choice of flow rate, especially when the Contents of the research main structure is involved in diversion, still has many issues to discuss Overview of the diversion works on dam building and hydropower projects; Flow diversion through the dam under construction help to save the cost of Scientific and practical foundations for selecting design flow discharge; Building diversion works in the flood season, how to select the scale of the diversion algorithms and flow diversion calculation program; Selecting the scale of the works, how the reinforcement of the dam is being built must have various options diversion works to divert through the coffer dam that are under construction for calculation, and choose the most effective economic and technical options Research methods The dissertation "Researching on selecting scale of diversion works on dam Reviewing the methods of diversion works; Inheritance and practical research on building and hydropower in Vietnam" is essential and important for the design choosing the flow design discharge; Collect information and synthesize analysis; and construction of dams and hydropower projects Application of informatics technology in computing and analysis Aim of the research Scientific and practical significance Reviewing the diversion works on dam building and hydropower; Add perfect Synthesis method of analysis and hydraulic calculation for diversion plan; methods of selecting the flow rate and the design discharge of the diversion Contribute to the scientific foundations to select the reasonable scale of the works; Analysis of constructive elements to serve a reasonable selection the scale diversion works of diversion works through the dams that are under construction; Completing calculation methods and algorithms for designing and selecting the scale of diversion works Selecting the flow rate of the diversion works in accordance with the working conditions of the structures; Proposing the order of calculation and selection of the scale of the diversion works, determining the scale of the diversion works Object and scope of the research with the most effective in economic and technical options 3.1 Objects of the research Thesis contents The main objective of this research is the diversion works on dams building and The dissertation consists of main chapters: hydropower projects, with a focus on determining the scale of the diversion works Chapter 1: Research overviews on flow diversion on dam building and hydropower Chapter 2: Scientific foundations for selecting the design discharge of the diversion 3.2 Scope of the research works and hydraulic calculation The diversion works include two or more functioning structures at the same time; Selecting design discharge, hydraulic calculations, and selecting the scale of Chapter 3: Researching, analyzing and selecting the scale of diversion works Chapter 4: Application of the research for dam building and hydropower in Vietnam CHAPTER RESEARCH OVERVIEWS ON FLOW DIVERSION ON DAM BUILDING AND HYDROPOWER 1.1 The importance of flow diversion Selecting the method of diversion works will affect the construction progress, the time of river prevention, overflowing dams, expenses for diversion Choosing a reasonable diversion method will help save costs, reduce construction time while still ensure construction quality When designing a diversion work, it is necessary to analyze specific conditions and propose some of the most feasible options, through the economic and technical calculations of each option then compare and choose the most optimal plan 1.2.3 Hydraulic calculation Hydraulic calculation software, hydraulic calculation materials are only calculated for independent diversion works, not specifically mentioning the hydraulic conductivity calculation when using two or more structures simultaneously This dissertation researches the setting up of a hydraulic calculation program to guide the simultaneous flow through a dam under construction and a culvert gate, to build a flow chart along the length of the flow through the dam that is under construction, as a basis for determining scale of diversion works and measures to reinforce the flow through the dam that is under construction 1.3 River diversion through culvert and tunnel 1.2 Selecting the design discharge and calculating the hydraulic parameters 1.3.1 River diversion through culvert 1.2.1 Flow rate of the diversion works Engineers should take advantage of long-term culvert to carry water for construction, this makes the construction of the diversion works easier, avoiding the difficulties and complexities of the culvert closure, while reducing the cost for diversion works In the design codes and regulations in Vietnam, choosing the flow rate of diversion works depends only on the level of construction, not mentioning specifically the height of the water column, reservoir capacity when conducting the flow, the recommendation to upgrade or downgrade on selection of the flow rate is not clear This makes it not only difficult for engineers to design the diversion works as well as for the authorities to approve them but also difficult to determine the flow rate In the case of many structures that carry the flow at the same time, the scale of each structure to ensure technical and economic conditions is a common problem for large discharge and construction during many years The choice of the flow rate in Vietnam needs to be adjusted to make it more clear and suitable with the actual construction The diversion culvert is used to carry large floods under high water discharge such as Son La project (2.568 m3/s), Lai Chau project (1.837 m3/s) and Bac Ha project (1.134 m3/s) 1.3.2 River diversion through tunnel The diversion tunnel can be used to conduct flow during both flood and dry seasons such as Hoa Binh and Cua Dat works in Vietnam China has a project of Long Duong Hiep hydropower station, O Giang Do, Dong Giang, in India, there is Si-li-sa-lam project, in the US there is Devosik, Paoerth 1.2.2 The period of diversion works To reduce costs, we often take advantage of the long-term tunnel to carry out the diversion flow such as Hoa Binh (Vietnam), Mao Gia Thon (China) The selection of the flow rate and the period of diversion works will decide the design discharge, this directly affects the scale of the diversion works 1.4 River diversion through dam that is under construction This dissertation analyzes the flow characteristics related to the selection of the diversion periods, measures to handle special cases related to the regional flows in Vietnam Flowing through a rockfill dam is a form of cost savings for diversion in the flood 1.4.1 River diversion through rockfill dam that is under construction season due to the ability to carry large flows It is possible to apply this form to the rockfill dams with the notation to the selection of the height of the overflow and 1.5 Conclusions of chapter the width of the overflowing water to satisfy the conditions of each project, thereby Diversion work is an important task, throughout the construction process, it is having a plan to reinforce the overflow surface, ensuring safety and effectiveness important to the success or failure of a project In order to select the diversion 1.4.2 River diversion through concrete dam that is under construction plan as well as the scale of the diversion work, it must comply with the basic Flowing through the concrete dam under construction is usually applied to gravity concrete dam due to the characteristics of concrete is high abrasion resistance under principles, suitable to natural conditions, people's life and economy and meet the tasks of the project high velocity of the water flow The flow through a concrete dam under Large projects, long construction time, often use many types of diversion works construction is often combined with a culvert located in the dam body and combine many disassembly works together In the world and in Vietnam, 1.4.3 River diversion through earth dam that is under construction there have been many successes as well as lessons learned about this issue When the flow is carried through the earth dam that is under construction with a The researches of authors mainly focus on optimal parameters of hydraulic works large flow, it can be applied to the base of the construction tray In the last dry and energy dissipation solutions, reinforcement of water drainage works but there season, the foundation of the trench were excavated and waterproofing was applied has not been a methodical proposal to solve decided the hydraulic problem to the dam At the end of the dry season, it is necessary to fill the foot of the finished leading the general construction flow tray and reinforce the surface to carry the flow on the flood season At the end of River diversion through culverts, tunnels to help the construction of the dam site the flood season, remove soil mud and surface cover, continue to build dams smoothly Culverts in concrete dams and tunnels can use diversion River diversion through dam and culvert, tunnel simultaneously with other flood removal facilities to lead large flows in the flood When there are many structures participating in the diversion, it is necessary to season determine the design discharge for each project, this is a problem that requires a lot The flow diversion through the dam that is under construction is a solution to of calculation for each different diversion plan Besides, it is necessary to determine carry the large flow, the determination of hydraulic regime and measures to the flow velocity at different locations in order to propose appropriate reinforce the construction of the dam when the water overflow needs to be reinforcement measures Further research is needed on the evolutions on the studied in more detail, serving the selection of the scale of diversion works surface of diversion works when conducting the combined flow through a The model of river hydrodynamic calculation, irrigation canal system is not construction dam and sewer, tunnel suitable for diversion hydraulic calculation, commercial calculation programs have In addition to the hydraulic parameters of diversion works, conduction surface not solved the calculation of hydraulic for diversion works and flow regulation It reinforcement for using dams to be built for diversion, attention should be paid to is required to set up a hydraulic flow calculation program to serve the selection of the volume and intensity of construction between the previous period and after the the scale of the diversion works quickly and efficiently flow through the dam is under construction CHAPTER SCIENTIFIC FOUNDATIONS FOR SELECTING THE DESIGN DISCHARGE OF THE DIVERSION WORKS AND HYDRAULIC CALCULATION 2.1 Analyzing and selecting the flow rate of the diversion works 2.1.1 Basis to select the flow rate of the diversion works When using the main building as a diversion structure, it is necessary to select the flow rate as the same level of the temporary structure or as the main buildings will affect the cost of diversion works When proposing a diversion plan for some projects in the mountainous areas, rapid flood concentration, high water column, in the event that dams cannot be The choice of the flow rate, diversion period and diversion works are closely overtaken, the embankment in this case will be very high It is acceptable for related These three factors are the basis to decide the design discharge, the embankment overflow and foundation overflow in the flood season working time of each diversion work and the hydraulic calculation diagram as well as the determination of discharge flow through each structure The above comparison results also serve as a basis for the acceptance of flood over the embankment and foundation pit When it is acceptable for water to The fact shows that the economic analysis is difficult, corresponding to each overflow the pit, the ability to select small flow may reduce the cost of diversion project will be different, so take the working time of the diversion works, the work with low risk height of water barrier works, the largest capacity of the reservoir with each phase of diversion as a basic indicator of the choice of the flow rate will be convenient for use when conducting current design and convenient for risk analysis of 2.2 Determining the diversion period 2.2.1 Factors influencing the selection of diversion period The diversion period is the working time of a water prevention structure such as diversion plan 2.1.2 Scientific foundations for upgrading or downgrading the flow rate For the diversion works which are used only during construction, cost savings issues are always in conflict with the possibility of risks Choose a specific flow rate that means accepting risk when the discharge exceeds the design value The flow rate selection method gives us a series of problems to determine the flood damage beyond design: dam breaking, embankment overflow/foundation overflow, damaging of the main or temporary buildings, influence on the downstream areas if there are incidents The upgrading or downgrading of flow rate should have a technical and economic feasibility research to decide Thus, there will never be a specific increase or decrease but must be based on specific analysis for each project and ultimately a embankment or main dam and a water diversion such as a channel, drain or spillway The selection of the diversion period directly affects the design flow discharge The period of flow diversion depends on hydrological conditions, structural characteristics, diversion works, and the possibility of overcoming floods It is necessary to comprehensively analyze the above factors, from which to select the appropriate diversion period 2.2.2 Climate conditions and regional flows of Vietnam In Vietnam, due to hydrological conditions in different regions, the dry season of the regions is also different, divided into areas: Northern Midlands and Mountains, North Central, South Central and Tay Nguyen, Southeast the investor's decision To what extent risk taking and the most difficult issue Climate and hydrological factors affect the selection of the diversion periods when making decisions according to regions of Vietnam In particular, there should be a plan to cope with unseasonal flooding at the end of the dry season 2.3 Basis theory of hydraulic calculation for diversion works and flood regulation 2.3.1 Hydraulic calculations through the dam that is under construction Conducting the flow through the spillway in practice is very diverse Hydraulically it is equivalent to a practical spillway or a large spillway Flow regime includes submerged and unsubmerged Figure 2.9 Diagram of hydraulic calculation through a rockfill dam that is under construction 2.3.2 Hydraulic calculations through the culvert Flow modes include open flow when H0 ≤ (1,2÷1,4)Hc; semi-pressure or pressure with H0 > (1,2÷1,4)Hc, depending on the water surface The value (1,2÷1,4)Hc is selected as follows: The entrance is very convenient, then select 1,4Hc; Do not convenient 1,2Hc 2.3.3 Hydraulic calculations through two or more structures simultaneously When calculating, it is necessary to determine the boundary conditions: - The discharge through each structure must have the same upstream (Ztl) and downstream (Zhl) boundary conditions Vmax is determined by the method of drawing the water surface according to the equation (2-16) ∆E =i− j ∆l (2-16) From the velocity and water column at the top of the slope, draw the water surface and find the maximum velocity Vmax on the slop 2.5 Conclusions of chapter The selection of the design discharge closely related to the flow rate selection and the selection of the diversion plan in which the diversion period is chosen - The total discharge at the downstream is equal to the sum of all discharge through each structure Binding to them is the scale, structure of the main building and the natural 2.3.4 Flood regulation in river diversion calculation to determine the scale of diversion works When the water level is low, the reservoir is very small or not yet formed, the calculation of the diversion works does not consider the flood regulation But when the water barrier is high and the reservoir is large enough, it will have the effect of regulating the flood The dissertation uses the method of iteration analysis to solve the problem The scale of diversion works is determined depending on the combination of 2.4 Calculating the maximum velocity when divert overflow rockfill dams When the flow is carried over a rockfill dam, the parameters that greatly affect the maximum flow Vmax are the unit discharge through the building dam (q), the slope length (L) after the overflow threshold, slope of the spillway (m), difference in height at the end of the slope compared to downstream water level (H2) Calculation diagram as shown in Figure 2.9 conditions of the construction site Along with the above work is hydraulic many factors: the scale of the main project, natural conditions, socio-economic conditions, construction capacity, construction duration, and diversion plan It is necessary to compare the technical and economic calculations in accordance with the specific conditions of each plan to select the appropriate diversion work One of the difficult contents in the calculation of diversion works is hydraulic problems This content needs to be specific and detailed in steps to help engineers to avoid mistakes and calculate quickly In particular, the focus is on hydraulic parameters including: flow, water level, flow rate, geometric parameters for structures that are involved in the diversion works 10 CHAPTER RESEARCHING, ANALYZING AND SELECTING THE SCALE OF DIVERSION WORKS 3.1 Research to select the flow rate and the period of the diversion works 3.1.1 Selecting flow rate of the diversion works according to the national standards QCVN 04-05: 2012 has the following disadvantages: The selection of flow rate of diversion works does not mention whether or not the main dam is involved in water barrier, does not specify the effect of reservoir capacity corresponding to dam height is under construction; Increasing or decreasing of the flow rate does not specify how it makes it difficult for designers and approvers of design; When using under construction dam for diversion, it is necessary to use the designed design flow rate to be too safe, not yet reflect the working status of the diversion works when conducting the flow through the embankment dam being built low elevation, not large reservoir capacity Figure 3.2 Applying the main dam according to the economic section 3.2 Producing hydraulic calculation program for diversion work and flood regulation In the process of setting up the hydraulic calculation program, in accordance with the different flow modes of the release works, the calculation formula changes according to the boundary conditions However, the baseball current does not change the sudden mode from open flow to pressure flow Meanwhile, semiexperimental formulas applied at water column transition points will give two different results in terms of discharge Therefore, it is necessary to deal with algorithms at these locations in order to facilitate the calculation but not to make big difference to the results 3.1.2 Selecting the period of diversion in the Vietnamese climatic conditions For constructions with time building greater than year, it should be divided into dry season and flood season When choosing the periods, pay attention to select the dry season period accordingly, the rest of the year will be the flood season There are two options to handle sub-flood at the end of the dry season: - Option 1: Select the maximum flow of the dry season with the flow rate of design as flow design flow for the dry season Figure 3.3 Correlation Q ~ H0 when Figure 3.4 Correlation Q ~ H0 the flow change from submerged to when the flow change from unsubmerged unpressured to pressure - Option 2: Divide the dry season into periods before and after the sub-flood Phase 1: From the beginning of the dry season to the end of the sub-period, select the design flow which is the largest in those months, used to design diversion works Phase 2: From the month of sub-flood to the end of the dry season, choose the largest flow of the month with the sub-flow, using the other phase-1 diversion works, can release larger discharge When applying this option, it is possible to use the main dam with an economic section to reduce the construction intensity of the construction phase beyond flooding (Figure 3.2) The dissertation establishes a block diagram for hydraulic calculation through culverts, hydraulic calculation combined with under construction dams and culverts, calculating flood regulation Calculation results show that the discharge through the culverts and dam is under construction, the flow that is accumulated in the reservoir From the flow through the dam is under construction, calculating the construction of water surface, hydraulic regime on the slope corresponding to the different options The hydraulic calculation program has been tested against the experimental results of Lai Chau hydropower project 11 12 3.3 Selecting the parameters when diverting flow through the under construction rockfill dam 3.3.1 Research the effect of construction parameters to the maximum velocity 3.3.1.1 Effect of parameters to the maximum velocity When changing the slope of the spillway (Figure 3.12), the maximum velocity increases and increases rapidly when m = With such a strong upward trend, for a large length of slope, it is necessary to keep the slope of the spillway (m) small to limit the maximum velocity appearing on the slope Figure 3.8 Water surface and velocity movements When difference in height at the end of the slope compared to downstream water level increases (Figure 3.14), maximum velocity increases with a similar level at both the small unit discharge and the large unit discharge level Difference in height at the end of the slope compared to downstream water level should be minimized to limit the increase of maximum velocity 3.3.1.2 General comment With the same length of slope, the unit discharge and velocity Vmax depends on the slope of the spillway (m) The smaller the slope of the spillway (m), the greater the maximum velocity Figure 3.15 (a), (b) When m