1, the basic characteristics of water conservancy projects:
① Very systematic and comprehensive. A single water conservancy project is an organic part of various water conservancy projects in the same basin and region, which complement and restrict each other; A single water conservancy project itself is often comprehensive, and its service objectives are closely related and contradictory. Water conservancy projects are also closely related to other sectors of the national economy. The planning and design of water conservancy projects must proceed from the overall situation, systematically and comprehensively analyze and study, in order to get the most economical and reasonable optimization scheme.
② Great impact on the environment. Water conservancy projects will not only affect the economy and society in this area through their construction tasks, but also affect the natural features, ecological environment and natural landscape of rivers, lakes and nearby areas, and even the regional climate to varying degrees. This kind of influence has both advantages and disadvantages, so it must be fully estimated in the planning and design, give full play to the positive role of water conservancy projects and eliminate its negative influence.
③ The working conditions are complicated. All kinds of hydraulic structures in water conservancy projects are constructed and operated under natural conditions such as meteorology, hydrology and geology, so it is difficult to accurately grasp them. They bear the thrust, buoyancy, permeability and scouring force of water, and their working conditions are more complicated than other buildings.
(4) The benefits of water conservancy projects are random and vary according to different hydrological conditions every year. Irrigation and water conservancy projects are also closely related to changes in meteorological conditions. Have a wide influence.
⑤ Water conservancy projects are generally large in scale, complex in technology, long in construction period and large in investment, and must be constructed in accordance with the basic construction procedures and relevant standards.
2, the basic composition of water conservancy project:
No matter how to control water disasters or develop water conservancy, it needs to be realized through a certain number of hydraulic structures. Hydraulic structures can be roughly divided into three categories according to their functions: ① water retaining structures; (2) drainage structure; ③ Specialized hydraulic structures. The collection of several hydraulic structures is called a water conservancy project.
Water-retaining structure
Buildings that block or block water flow, hold high or adjust the upstream water level are generally called dikes, and those built on both sides of the river along the direction of water flow are called dikes. Dam is the key project to form reservoir. Most of the dams built in modern times are earth-rock dams filled with local earth and stone or gravity dams filled with concrete, which rely on the weight of the dam itself to maintain its stability. When the valley is narrow, the arch dam with curved plane can be used. In the case of insufficient dam material, reinforced concrete light dam (commonly known as buttress dam) can be used, but its ability to resist earthquake action and durability are poor. Masonry dam is an ancient dam, which is not easy to be mechanized and is mainly used in small and medium-sized projects. The main problems to be solved in dam design are the anti-sliding or anti-overturning stability of the dam body and the prevention of the dam body's own rupture and leakage. Earth-rock dams or sandy soil foundations play a more important role in preventing the movement and destruction of soil particles caused by seepage (so-called "piping" and "flowing soil"). When building a dam in an earthquake area, we should also pay attention to the possibility that the cohesive sand saturated with water in the dam body or foundation suddenly loses strength in the earthquake. This phenomenon is called "liquefaction phenomenon" (see sand liquefaction).
export structure
A building that can safely and reliably discharge excess or needed water from a reservoir. There are many earth-rock dams in history, all of which burst because the flood exceeded the reservoir capacity. In order to ensure the safety of earth-rock dams, river spillway must be set up in water control projects. Once the reservoir water level exceeds the specified water level, the excess water will be discharged through the spillway. Concrete dam has strong scour resistance and can discharge flood through the dam body, which is called overflow dam. The key of building drainage structure is to solve the problems of energy dissipation, corrosion resistance and wear resistance. The discharged water generally has great kinetic energy and scouring force. In order to ensure the downstream safety, the internal impact and friction of water flow are often used to eliminate energy, such as hydraulic jump or jet energy dissipation. When the velocity is greater than10 ~15m/s, the so-called cavitation damage may occur in some irregular sections of the overflow part of the spillway structure, that is, the damage of the vacuum cavity near the side wall caused by high-speed water flow. The main methods to prevent cavitation erosion are to streamline as much as possible, increase pressure or reduce flow rate, use high-strength materials and ventilate local areas. Wear resistance must also be solved in rivers with high sediment concentration or in the case of stone slag in water.
Professional hydraulic structure
In addition to the above two common general buildings, buildings built for special purposes or tasks. Channels are water conveyance structures, which are mostly used for irrigation and water diversion projects. When the mountain is in the way, you can bypass the winding mountain or dig a water tunnel to pass (see hydraulic tunnel); If it intersects with rivers and ditches, it is necessary to set aqueducts or inverted siphons, as well as buildings that intersect with bridges and culverts. According to the location of the power station and the diversion mode, there are river bed type, behind dam type, diversion channel type and underground type. The hydropower station buildings mainly include the water diversion system with centralized water level drop, the pressure regulating system to prevent the surge pressure from being too large when suddenly stopped, the hydropower station buildings and the tailrace system. Generally, the flow through hydropower station buildings is small, but these buildings often bear large water pressure, so steel structures are used in many parts. After the completion of the reservoir, the dam blocked the original channels of ships, rafts, bamboo rafts and fish, which had a great impact on shipping and aquaculture. Therefore, ship locks, rafts and fishways should be specially built for ships, rafts and fish to cross. These buildings have strong local characteristics and should be specially studied before construction.
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