Tóm tắt Luận án Research proposed design mothod and construction to improve the quality of small drainage works on the road in Lao People's Democratic Republic

INSTRODUCTION 1. Reason of research selecting Lao People’s Democratic Republic is on the way of modernization. The road networks is being renovated, upgraded and construction to serve the development needed of the country. In recent years, Lao Party and the State attach importance to the construction of infrastructure. Which they have focused on constructing and developing road network, especially roads. When constructing road, we have special attention on small drainage works across it, although it is not large proportion compared with others, but the possibility of flood drainage of small drainage works and influence are directly related to the life of the pavement, roadbed and other structures on the road. Laos is located in the tropical monsoon climate, rainfall and climate conditioning in the year, but some areas have large and irregular rainfall. Laos has hilly terrain with high cliffs and network traffic from north to south through the mountainous route, because of high slope, the volume of water flow on the peak of the mountain flow down quickly lead to damage the samall drainage works and make the quality of roads is not stable over the seasons. One of the important reasons is the method of hydraulic calculation for small drainage works and a large selection of the dangerous state of the the road construction is irrational. To improve drainage capability across roads need to study some hydraulic computational problems such as: hydraulic calculation of water level and water slopes, estimating hydraulic of step cascade and steep slope, scour at culvert outlets and calculated velocity of soil scouring at culvert outlets. All these issues that involve to the research methods to designed and increase possibility of flood drainage for small drainage works. In Laos, do not have the design method of hydraulic calculations of drainage works yet, we currently use foreign methods such as (Europe, America, Vietnam) for natural environment conditions and climate in Laos. In fact we need further research on this issue. With qualification and experience of the scientists - Vietnamese techniques can help me a lot on my research. So that, Government Lao send me to research this topic: “Research proposed design mothod and construction to improve the quality of small drainage works on the road in Lao People's Democratic Republic”. 2. Purpose of the research The thesis is focused on hydraulic calculation of small drainage works across of road such as: (step cascades, steep slope, velocity of soil scouring at culvert outlets and scour at culvert outlets). So that, Proposed solutions and selection methods to reinforced or choose the mitigating energy method relevant with downstream culverts on the roads. And find solutions for small drainage works across the road with terrain characteristics matching the natural environment conditions and climate in Laos. 3. scope of the reseach The scope of the research is the calculate the hydraulic for small drainage works across the road in Laos. 4. Research Methodology Research methodology combines empirical theory. 5. Structure of the thesis Thesis presented in 166 pages and 04 chapters, Conclusions, Recommendations subsequent research, References and Appendixs. CHAPTER 1: OVERVIEW THE CHARACTERISTICS NATURAL CONDITIONS, ROAD NETWORKS AND THE DESTRUCTION OF SMALL DRAINAGE SYSTEMS ON THE ROAD IN LAO P.D.R 1.1. Features of terrain conditions and climate in Laos Lao People’s Democratic Republic is a country with relatively area of 236,800 km2. The terrain of Laos mainly rolling terrain with 70% and 30% of flat terrain. - Topography: mountains and highlands make over 3/4 of the natural area, the rest are flat terrain. Generally the mountains in Laos with an average elevation on the north and east, the highest peak is Mount Bịa (2820m), and some other high peaks such as Mount Xao (2690m), Hunting mountain (2218m) mountain Huat (2452m). Mountain in Northeast Provinces Xieng Khouang Laos - Tattooing Nua, which begins north of the Truong Son mountain range. Their general direction is northeast - southwest lies the entire West, not consecutive long and flat as in Mekong Delta. - Climate: tropical monsoon climate, with two seasons: + Rainy season: starting from May to November, The temperature is about 30oC, rain fall quite often, and there are some flooded overflow the Mekong river after several years. + Dry season: from November to April, less rain and temperature is about 15oC, Mountains sometime is 0°C. 1.2. Introduction of the road network systems in Laos 1.2.1. Period before 1975 1.2.2. Period 1975-1985 1.2.3. Period 1985-2000 1.2.4. Period 2000-2015 In Laos there is not yet have a complete road network systems to connecting between provinces and districts. The Internal transport to some provinces still cannot let the car drive smoothly to the provincial capital, and between districts, and to the villages are more difficult. Now, the road network systems in Laos is only have grade III, IV and V. 1.3. Depravity of small drainage works on the roads in Lao P.D.R Laos has the tropical monsoon climate, cause of rainfall and climate in year, mainly some areas with lots of rain and some areas with irregular rainfall over the year. Laos has hilly terrain with high cliffs and road network systems from north to south through the mountainous route, due to the high slopes, volume of water on the peak of the mountain flow down quickly, resulting to damaged drainage system on roads and makes the quality is not stable over the seasons. Drainage systems on the roads in Laos have designed with low technical, and need maintenance infrequently, with the management and maintenance fee are limited, so it may not yet maintenance in time for roads in Laos. 1.3.1. Common failures of drainage systems on the roads and cause of failures Phenomenon damaged small drainage works on the roads in Lao P.D.R occurred on all the routes are exploited. Consequently, as they so often cause large losses, costs, repair. To serve thesis explored many roads and servey in Lao P.D.R: road No.1D, 1J, 2E, 4A, 7, 8, 12...The survey results were presented detailed in thematic reports: The destructive small drainage works on roads in Lao People's Democratic Republic and the cause. In here summarize some typical damages directly related to the issues in the content of the thesis. 1. Damaged drains (hình 1.2A và 1.2B); 2. Damage upstream and downstream of culvert (hình 1.3A, 13B, 13C và 13D); 3. Damage erosion of culvert body (hình 1.4); 4. Damaged joints of culvert (hình 1.5); 5. Deposition soil, sand in culvert (hình 1.6A và 1.6B). 1.3.2. The situation applies structural drainage works in Laos During the construction and development of transportation network systems, we research for shapes of culverts structures and small bridges on the roads, and also make new research to improve the quality of construction, easy to maintenances, lower fee, and ensuring the quality and safety for cars driving on the mountain roads. Generally these small drainage structures (culverts and small bridges) have been applied on the roads in Laos, such as: reinforced concrete pipe culvert, reinforced concrete box culverts, steel culverts, ditch on 2 side of roads, reinforced concrete bridge etc... Currently, we not yet have research and technical solutions to handle the drainage structures in Laos. When the damaged roads sections occur, we will have organization to repairs, and choose a certain solutions suitable to the actual damages and depending on the professional competencies and experience of construction unit. 1.4. Conclusion chapter 1 After studying, the researcher have some necessary problem and some important conclusions below related the objectives of the thesis: 1. Develop and maintain road network systems to serve the develop economy of Laos, the Lao Party and State were identified as a key task, lots of roads will be built and renovated in future. For the construction road works effectively need to improve the quality of construction. Tasks to improve quality of road construction should start at the planning stage to design. This thesis wants to participate in the first stage above with the aim of improving the quality of construction to extend the level service life of the project and ensure the quality. 2. Together with colleagues, the researcher have reviewed some main roads systems as mentioned above with a very common failure on the destructive road at positions of drainage structures like small bridges and culverts. Depending on varied of destructive forms but the most common failures are road-bed, pavements at the location of erosion, scour at the culvert outlets. This destructive pattern is absolutely cause of forecast hydrological work and hydraulic modeling calculation are not suitable, resulting the water speed, water pressure on the pavement is too strong that can damage road construction and reduced security of safety traffic. These predictions explain the thesis that focused on hydraulic calculation for small drainage systems. Thus, hope that later road less swept away by water, less culverts damage, and less bridges damage after flood season. This destructive pattern is different from bridges collapsed or culverts failures under the impact of vehicle weight and embankment weight itself. These types of failures are caused by poor construction quality, this thesis does not solve that problem. 3. Climatic conditions, temperature, rain and wind are very harsh. Later when applying the general formula for hydraulic calculation for small drainage systems across the road needed attention to this characteristic. But this is a very complex problem requires more research, and more construction experience. So my thesis wanted to have the general granted theory and experience of scientists, technicians to achieved with desire problems are resolved more quickly. To response the objectives and contents of the thesis, the following issues will be studied in the next chapter: a. The main contents of hydraulic calculation of pooled step cascade, hydraulic resistance at steep slope, scouring of the downstream river bed and scour at culvert outlets of small drainage works across the road; b. Research proposed design method of hydraulic calculation for small drainage structures across the roads in Lao People’s Democratic Republic. c. Construction solution for small drainage works across specific terrain in Lao People’s Democratic Republic. CHAPTER 2: OVERVIEW OF HYDRAULIC PROPERTIES WITH POOLED STEP CASCADES, HYDRAULIC RESISTANCE AT STEEP SLOP SCOURING OF THE DOWNSTREAM RIVER BED AND SCOUR AT CULVERT OUTLETS OF SMALL DRAINAGE WORKS ACROSS THE ROAD 2.1. Overview of hydraulic properties with pooled step cascades in hydraulic type stilling basin 2.1.1. The studies hydraulic property of pooled step cascades Pooled step cascades were studied by lots of authors with different approach like: Velocity coefficient for rectangular cross-sections of the water layer of (Alekxeev IU.S, 1965), the forms of flow current through the step cascades of (IU.M Konstantinov, 1966, 1969), the speed and depth of flow on upstream of (Popov VN, 1957)... Pooled step cascades include many step cascades link together in serial with cascade types are applied for the rolling terrain, to reduce volume of earthworks, less environmental destruction. Thus, each step cascade must be calculated for the minimum length of hydraulic properties, while ensuring the specific terrain conditions that is the average local slope must be satisfied: Scb=∑Pi/∑Li [5]. When calculate pooled step cascades, we often only calculate first cascade and second cascade, the next cascade is calculated as second cascade, the last cascade we calculate include the influence of water current on downstream flow, usually in hydraulic type stilling basin. 2.1.2. The formulas for hydraulic pooled step cascades in basin type 2.1.2.1. Determine the length of the water fall in the step cascade inlets [5] Length of water fall in the rectangular channel can be calculated by the formula [5]. 2.1.2.2. Length of water fall along the water current at stepped weir [5] Water current flow on stepped weir when the cascades are not flooded include two parts are the free fall part in the air and nother submerged on stepped weir can be determined according the research of (Kostantinov IU.M, 1988) [80]. - For the rectangular section: Pavlovski N.N (2.9) Chertouxov M.D (trung bình) (2.10) or (2.10a) Bradley and Peterka (2.11) Ohtsu et al (2.12) 2.1.2.3. Experimental study on the inlet cascades hydraulic jump [5] Figures measure pressure changes along the depth at inlets, according to research (Rajaratnam and Muralidha, 1968) [54]. Excess pressure at the top and bottom water flow is zero, in the scope which value of curvature is greater than atmospheric pressure, but always less than the statically hydrostatic pressure. Research and semi experimental indicated hb / hc = 0715 for rectangular sections. 2.1.2.4. Determine the depth on narrowing sectional [2], [5] Depth on narrowing sectional on stepped weir determined by the equation of (Bernoulli) for the cross upstream channel and narrowed section on stepped weir for rectangular sections. Eo=hch+(q2/2gj2h2ch) (2.14) 1). Research of (Agroskin I.I, 1964) [2], [5]: q=jhch(2g(Eo-hch))0.5 (2.18) For: tch=hch/Eo and t2ch=h2ch/Eo F(tch)=q/(jE3/2o) (2.19) Through the relations of function F(tch)=q/(jE3/2o) corresponding to the coefficients ratio value of different speed (Appendix 1) we can calculate and corresponding coefficients ratio . 2). Research of (Rakhamanov A.N) [5]: Using equation (2.14) write the equation in the form of ratio relative to the critical depth : Eo/hc=(hch/hc)+(1/2j2)(hc/hch)3 (2.20) For: xEo=Eo/hc; xch=hch/hc and x2ch=h2ch/hc Relationship curve between , with corresponding coefficients ratio (Appendix 2). 2.1.2.5. Calculated depth of stilling basin [5] Determine depth of stilling basin can follow the diagrams of (Chertouxov M.D, 1962) that diagrams have built through relations between xz=f(xEo,j) (Appendix 3). The graph shows the value d corresponding to the hydraulic jump in place determined by the formula (2.32) as follows: d=xEohc-Eo (2.32) Research of (Detlef Aigner) [23]: Calculated the pooled step cascades at hydraulic type stilling basin [23] by known flow unit and step cascade height can find tga=P/L, after that find the relation between pt/P with hc/P and can calculate the size of pooled step cascade such as: height of stilling wall, length of step cascade ... 2.1.3. Evaluation of hydraulic type stilling basin This study, authors focused on solving equations to find depth of narrow section on the stepped weir, large combines depth of hydraulic jump with the depth of narrow section on stepped weir is, calculate wall height of pooled step cascade and depth of stilling basin on final cascade follow the analysis method and numerical method, charting to define the relationship between pt/hc with P/hc and Lbc/hc with P/hc define pt and Lbc. 2.2. Overview of research on hydraulic resistance at steep slope 2.2.1. The studies related to hydraulic resistance at steep slope [5] Calculated hydraulic at steep slope, are divided into three sections: culvert inlets, steep slope and culvert outlets sections (Figure 2.7). 2.2.1.1. Calculate culvert inlets hydraulic at stepped chutes bb=Q/(m(2g)0.5(Ho3/2)) (2.40) 2.2.1.2. Calculate steeped slopes hydraulic Slopes length: Ld=(P2+L2)0.5 (2.41) Slopes of water slopes: id=P/Ld (2.42) Flow modulus of channel: Ko=Q/(id)0.5 (2.43) 2.2.1.3. Calculate culvert outlets hydraulic at steep slope h2=(h21+2h3c(1/h1-1/hcr))0.5 (2.44) 2.2.2. The issue of hydraulic resistance calculation of steep slope To determine the flow ability of drainage structures across the road such as culverts, steep slope, step cascades are also important to determine the correct average speed of water current and correspondent of flow volume, speed and volume of water current depends on defining resistance friction coefficient f , (Darcy-Weisbach) [79]. 1). Research of (Pavlovski N.N) [79]: Define Sedi factor used for 0.1<R<(35) and n<0.04. C=(1/n)Ry (2.49) Exponent In fact, sometimes calculate with values y in constant, often taking y=1/6. 2). Research of (Aivazian, 1977, 1984, 1985, 1987, 1992, 1996, 2001) [73], [74], [75], [76], [77] f=a+bixRy (2.51) Analysis results for calculating the coefficient f in concrete bed (Kosichenko IU.M, 08/1993) [81]: a) For uniform flow (Fr<1): fe=0.245/Re0.158 (2.52) b) For tumbling flow (Fr>1): fx=0.0187Re0.0384 (2.53) 2.2.3. The Issues should be studied This research focused on analysis of f coefficient in concrete bed through the use of real data [73], [74], [75], [76], [77], in (appendix 5) [89]. 2.3. Overview of oil scouring at bottom of flow current 2.3.1. The gained issue Now, have 4 research ways of startup soil scouring: 1. Velocity of soil scouring, which puts relations between soil diameter d and velocity of soil scouring or medium velocity at bottom of flow current to make the soil elements moved. 2. Lift force, which lift the soil elements excess of itself-weight of the soil in water current. 3. Critical stress, which is based on the perception of tangential force applied to the soil elements at the bottom of the flow current, is the main cause the soil elements moved. 4. Probability method is applied to solve problems. 2.3.1.1. Velocity of soil elements 2.3.1.2. Perceptions about lift force impact on soil elements Py 2.3.1.3. Tangential stress of flow current 2.3.1.4. Probability method 2.3.2. Reviews In this study, the authors want to show out a simple model for uniform sand elements are impact with hydrodynamic forces and move by sliding along the flow, account to the turbulent regime and pulsating flow velocity under law of and using the results of recent studies. 2.4. Overview of researches on scour at culvert outlets on small drainage works across the road 2.4.1. Studies concerning the scour at culvert outlets and scour at small bridge Research of (Andreev O.V, 1963): (2.74) 2.4.2. The issue should be studied Authors studied the issue using equation for momentum change to settle the theoretical calculation formula for scour at culvert outlets, small bridges to compare and check the results of experiments over. 2.5. Conclusion Chapter 2 Chapter 2 has overview of research on the pooled step cascades, hydraulic resistance on the steep slope, scouring of the downstream river bed and scour at culvert outlets of small drainage structures across the road, research to choose the formula for hydraulic calculation of small drainage works across the road. CHAPTER 3: RESEARCH PROPOSED DESIGN METHOD AND CONSTRUCTED TO IMPROVE THE QUALITY OF SMALL DRAINAGE WORKS ON ROADS IN LAO PEOPLE’S DEMOCRATIC REPUBLIC 3.1. Theoretical hydraulic calculation for drainage works across the road As described in Chapter 2 we have the following theory to calculate hydraulic for small drainage structures across the road: 3.1.1. Calculate pooled step cascades 3.3.1.1. Determining the depth of pooled step cascades (3.1) 3.1.1.2. Determining the narrowing length of stepped weir Write the Bernoulli equation through two sections (1-1) and (c-c) Compare section and write equation like (Figure 3.3). (3.2) 3.1.1.3. Calculated the height of stilling wall of stepped chutes pt=sh2ch-H1 (3.8) 3.1.1.4. Combined stilling basin To have hydraulic jump submerged in basin (Figure 3.5), stilling basin depth should add from 5% to 10% (), we have: (3.11) 3.1.1.5. Các bước chi tiết tính bậc nước nhiều cấp dạng bể tiêu năng 3.1.2. Steep slope Hydraulic Calculations of steep slope as outlined in Chapter 2. So hydraulic resistance coefficient ca