Construction of earth-rock dams in water conservancy projects?

What exactly does the construction of earth-rock dams in water conservancy projects include? The following Zhongda Consulting Bidding Teacher will answer your questions for your reference.

Earth-rock dam is currently the most widely used and fastest-growing dam type in dam construction projects in the world. Compared with other dam types, earth-rock dams have absolute advantages both in terms of economy and construction. According to incomplete statistics, earth-rock dams account for 82.9% of the total number of dams in the world, and the number of earth-rock dams in China accounts for 50% of the total number of dams. 93%.

Because the materials used in the construction of earth-rock dams are generally mined on site, and various excavated materials are fully utilized during construction, including local soil materials, stones or mixed materials, the construction of earth-rock dams is It is a water-retaining dam built by dumping, rolling and other methods. Therefore, the earth-rock dam is also called a local material dam. When the dam material is mainly soil and gravel, it is called an earth dam; when the dam material is mainly soil and gravel, it is called an earth dam; , when blasted stone is the main material, it is called a rockfill dam; when both types of local materials account for a considerable proportion, it is called an earth-rock mixed dam.

According to different construction methods, earth-rock dams can be divided into: rolling earth-rock dams, flush-fill earth-rock dams, water-filled earth-fill dams and directional blasting rockfill dams. Among them, the most widely used is the roller compacted earth-rock dam, which is mainly characterized by low foundation requirements and strong adaptability to foundation deformation.

Earth-rock dams can be divided into low dams, medium dams and high dams according to dam height. The technology of building high dams was only developed in modern times.

Rolling compacted earth-rock dams can be divided into homogeneous dams, soil core wall dams, soil inclined wall dams, and various soil quality dams according to the configuration of soil materials in the dam body and the types of materials used in the anti-seepage body. Dam, artificial material core dam, artificial material face dam, etc.

Earth-rock dam is the oldest dam type. Its advantages include: using local materials, saving important construction materials such as steel, cement, and wood, and reducing long-distance transportation during dam construction; the structure is simple and easy to maintain, heighten, and expand; the dam body of the earth-rock dam is made of loose earth and rock particles The solid structure has good performance in adapting to deformation, so the requirements for the foundation are low; the construction technology is simple and the process is few, which facilitates rapid construction by combined machinery. Its disadvantages are that the dam body generally cannot overflow, construction diversion is not as convenient as a concrete dam, and the filling of sticky soil materials is greatly affected by climatic conditions.

The biggest problem in earth-rock dam construction is seepage. How to control and prevent seepage is one of the most important tasks in the construction of earth-rock dam projects.

The so-called seepage refers to the fact that the soil filling the earth-rock dam and the gravel of the dam foundation have a granular structure, and there are a large number of pores between the particles, so they have a certain degree of water permeability. When the reservoir is impounded, under the action of water pressure, the water flow will inevitably seep downstream along the pores in the soil material of the dam body, the soil of the dam foundation and the foundations on both sides of the dam end, causing leakage in the dam body, dam foundation and around the dam. If this kind of seepage is under design control, the soil in any part of the dam will not cause seepage damage, and it will be normal seepage. At this time, the seepage volume is generally small, the water quality is clear and transparent, and does not contain soil particles, which has a negative impact on the dam body. and the dam foundation will not cause seepage damage; on the contrary, it can cause seepage damage to the soil, or the seepage flow will be too large and concentrated, the water quality will be turbid, and the transparency will be low, causing the dam body or dam foundation to produce piping damage, soil flow, contact erosion and other seepage damage. This effect The seepage that benefits from water storage is abnormal seepage.

According to statistics on early earth-rock dam projects in my country, the damage accident rate caused by seepage accounts for about 31.7%. Among them, large reservoirs account for 11, and for small and medium-sized reservoirs, those who overflow the dam and collapse The largest number, accounting for 51.5%, followed by dam collapse caused by leakage, accounting for 29.1%. This shows that the dam collapse problem caused by leakage is quite serious. Therefore, ensuring seepage control of the dam body and dam foundation is an important measure to ensure the safety of earth-rock dams.

The control theory of seepage control is developed and applied in engineering practice and is the result of practical feedback. It includes three parts: the basic principle of seepage, the analysis method of seepage field, and the stability of soil seepage. , which is the basis of seepage control theory. Seepage control technology is an implementation measure of the basic theory of seepage. It mainly includes grouting technology, filter dam technology, earth-rock dam slope sliding failure reinforcement technology, earth-rock dam dam body pouring clay slurry reinforcement technology, and density reinforcement technology of the dam body and dam foundation. , geosynthetic material reinforcement technology and anti-seepage wall and dam body and dam foundation reinforcement technology, etc.

In summary, the reasons for abnormal seepage are as follows: ① The design of the filter layer between the dam fill and the drainage body is incorrect, the interlayer coefficient is too large, or there are staggered breaks during construction. Mixed layer phenomenon, or the filling soil is not dense enough, and excessive seepage causes the filling soil to drain into the drainage body, which will cause the damage and failure of the filter layer. The filter layer is a particularly critical link in the entire anti-seepage system. Even if there are cracks or leakage channels in the front anti-seepage body, as long as the filter layer works normally and the drainage is reduced, the leakage damage will not expand. ② The anti-seepage body does not reach directly to the bedrock or a continuous and reliable clay layer at the bottom. When excavation of the interception channel was completed, it was abandoned halfway due to construction difficulties, thus leaving hidden dangers. ③The bank slopes on both sides of the earth-rock dam are stepped. It should be dug into a smoother slope. To reduce excavation, the slope can be changed. At the turning point of the upper and lower slopes, the difference between the two slope angles should not be greater than 15° to 20°. If there is a platform, the filling height of the platform should be the same as the platform. The filling height at both ends is very different, and the amount of settlement changes suddenly, which can easily cause cracks and lead to seepage damage.

How to organize scientific and orderly construction, improve project quality, and control seepage are the keys to the success of the entire process.

I think the earth-rock dam process should be controlled from the following aspects during construction:

① The foundation treatment must be done in a foolproof manner. For many large-scale earth-rock dams, filling construction can only be carried out after the foundation treatment is stable and the bearing capacity of the dam foundation and foundation anti-seepage must be met. Especially when construction projects are built on deep overburdens, the foundation treatment work is large and cannot be carried out. There are many foreseeable factors, and it is often necessary to use anti-seepage walls, vibrating, curtain grouting, consolidation grouting, etc. to comprehensively treat the foundation.

② Master the local geology, hydrometeorological data, and control the construction period. Seasonal earth-rock dams are extremely sensitive to hydrometeorological factors. In the rainy season, the moisture content of the soil material has a great influence, which directly restricts the dam. During filling, the construction intensity will be affected; in winter, the soil material freezes, and filling cannot be carried out if no active measures are taken. Moreover, filling construction in winter rainy season has the dilemma of high investment and low output. For construction during the flood season, a targeted construction plan should be prepared. Earth-rock dam projects are generally not allowed to overflow. Therefore, the "peak construction period" of earth-rock dam projects should be controlled to reach the stage of flood control and flood section water retention before the first flood after the closure of the project. After the closure, it must be accelerated. The construction progress is to ensure that the entire section of the dam body or the small section for flood relief is filled to the flood relief elevation before the flood. Therefore, the construction period for filling the dam body is limited. When winter construction is carried out in the northern region, the average monthly temperature is below 0°C. In some areas, rivers freeze and the soil layers freeze. Excavation projects, concrete projects, grouting projects and filling projects are difficult to complete. All projects have adverse impacts, so the monthly filling intensity must be increased to reach the river barrage elevation on schedule according to the requirements for safe flood crossing.

③Ensure the material quality of the earth and stone quarried in the quarry used in the project. The importance of the quarry to the earth-rock dam is self-evident, but it is also the weakest point that is most likely to affect the smooth filling of the dam. According to engineering practice, generally speaking, the depth of geological exploration work in the material field is far less than that of the dam site. Especially for the rockfill material with the largest filling volume, geological description is often based on only a few caves or topographic surveys. After entering the site, it is closely related to the bidding process. There is a high possibility that the file will change and conditions for large-scale mining (or bench mining) cannot be formed, which directly affects whether the dam filling gradation can be guaranteed. In terms of anti-seepage soil materials, the water content has also become the key to whether the dam can be filled quickly. Therefore, it is particularly important to conduct a complete and careful review and re-exploration of the material yard. Do a good job in the material yard review and reserve calculation, Be aware of it.

In addition, the rolling test of materials is also a very important task. For earth-rock dams, the rolling compaction test is the most important technical parameter demonstration work before filling. It is also an important step in determining whether the dam can be filled smoothly and ensuring the safety of the dam. The quality of the rolling compaction test directly affects the filling of the dam body.

In the rolling compaction test, it is also necessary to determine and adjust the moisture content of the anti-seepage soil material, and at the same time, the amount of water sprinkled on the rockfill material should also be determined. In addition, in order to ensure the filling quality of the earth-rock dam, the construction of the earth-rock dam project must require test pit sampling. Only after the filling surface has passed the rolling and acceptance inspection can the upper layer of filling be carried out.

④ Determining reasonable dam surface zoning is the key to filling construction. Because the earth-rock dam is large in size, it provides the necessary scene for the dam surface zoning flow operation. Earth-rock dam projects generally start during the filling process. It is divided into paving, paving, watering, compaction, quality inspection and other tasks. In the dam surface zoning flow operation, the construction of anti-seepage soil materials should be based on the needs of filling, the filling area should be reasonably divided and the flow operation should be carried out according to the actual situation, and the mechanical equipment used and the filling situation should be adjusted. For earth-rock dam projects that use flat filling and temporary section filling, the normal construction of large machinery must not be affected by blindly reducing the amount of temporary section filling, and the filling quality must be ensured.

⑤ Determine and adopt the dam body and dam foundation reinforcement technology based on the actual conditions of the project, which mainly refers to the clay slurry reinforcement technology used for the earth-rock dam body, including grouting design, grouting technology adoption, etc.

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