Construction technology of earth-rock dam in water conservancy project?

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

Because the materials used in the construction of earth-rock dams are generally mined on the spot, all kinds of excavated materials, including local soil, stone or mixture, are fully utilized in the construction, so the construction of earth-rock dams is a retaining dam formed by throwing and rolling these materials, so earth-rock dams are also called local material dams. When the dam materials are mainly soil and gravel, they are called earth dams. When stone slag, pebbles and blasting stones are the main materials, they are called rockfill dams. When the two 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, water-filled earth-rock dams and directional blasting rock-fill dams. Among them, the roller compacted earth-rock dam is the most widely used, and its main characteristics are low requirements for foundation and strong adaptability to foundation deformation.

Earth-rock dams can be divided into low dams, middle dams and high dams according to dam height. However, the technology of high dam construction only developed in modern times.

According to the configuration of soil materials and the types of materials used for seepage control, RCC dams can be divided into homogeneous dams, soil core dams, soil inclined wall dams, various soil dams, artificial material core dams and artificial material face dams.

Earth-rock dam is the oldest dam type. Its advantages include: using local materials, saving important building materials such as steel, cement and wood, and reducing long-distance transportation during dam construction; Simple structure, convenient maintenance, heightening and expansion; The dam body of earth-rock dam is a granular structure of earth and rock, which has good adaptability to deformation, so the requirements for foundation are low; The construction technology is simple, with few working procedures, which is convenient for the rapid construction of combined machinery. Its disadvantages are that the dam can not overflow generally, the construction diversion is not as convenient as that of concrete dam, and the filling of cohesive soil is greatly affected by climatic conditions.

The biggest disease of earth-rock dam construction is leakage. How to control and prevent leakage is one of the most important tasks in the construction of earth-rock dams.

The so-called seepage means that the earth material filled by earth-rock dam and the gravel of dam foundation are granular structures, and there are a lot of pores between particles, so they have certain water permeability. When the reservoir is filled with water, under the action of water pressure, water will inevitably penetrate downstream along the pores in the dam body soil, dam foundation soil and foundation on both sides of the dam, resulting in leakage around the dam body, dam foundation and dam. If this seepage is under the design control, the soil in any part of the dam will not be damaged by seepage, which belongs to normal seepage. At this time, the seepage flow is generally small, the water quality is clear and transparent, and there are no soil particles, which will not cause seepage damage to the dam body and dam foundation. On the contrary, abnormal seepage can cause seepage damage of soil, or the seepage work is too concentrated, the water quality is turbid and the transparency is low, resulting in seepage damage such as piping, soil flow, dam body or dam foundation contact erosion.

According to the statistics of early earth-rock dams in China, the dam-break accident rate caused by seepage accounts for about 3 1.7%, of which 1 1 is for large reservoirs, with overflow dams accounting for the most, accounting for 5 1.5%, followed by dam-break caused by seepage, accounting for 29.6438+0. Therefore, it is an important measure to ensure the seepage prevention of dam body and dam foundation.

The control theory of seepage control has been developed and applied in engineering practice, which is the result of practical feedback. Among them, the basic principle of seepage, the analysis method of seepage field and the seepage stability of soil are the basis of seepage control theory. Seepage prevention technology is the implementation measure of seepage basic theory, which mainly includes grouting technology, filter dam technology, slope sliding failure reinforcement technology of earth-rock dam, grouting clay slurry reinforcement technology of earth-rock dam body, dense reinforcement technology of dam body and dam foundation, geosynthetics reinforcement technology, cutoff wall and its dam foundation reinforcement technology.

To sum up, the causes of abnormal seepage are as follows: ① The design of the filter layer between the dam material and the drainage body is incorrect, the interlayer coefficient is too large, or the mixed layers are staggered during construction, or the filler is not dense enough. Excessive seepage causes the filler to drain into the drainage body, which will cause the damage and failure of the filter layer. The filter layer is the key link of the whole seepage control system. Even if there is seepage fluid in the front crack or leakage channel, as long as the filter layer works normally and the drainage is depressurized, the leakage damage will not expand. (2) The impervious body does not reach the bedrock or the continuous and reliable clay layer at the bottom. When excavating and cutting the trench, it is abandoned halfway due to construction difficulties, leaving hidden dangers. ③ The bank slopes on both banks of the earth-rock dam are stepped. It should be dug into a smooth slope. In order to reduce excavation, the slope can be changed. At the corner of the upper and lower slopes, the difference between the two slope angles should not be greater than15 ~ 20. If there is a platform, the height of fill at the platform is different from that at both ends of the platform, and the settlement changes suddenly, which is easy to produce cracks and lead to seepage failure.

How to organize construction scientifically and orderly, improve project quality and control leakage is the key to the success of the whole process. I think the construction process of earth-rock dam should be controlled in the following aspects:

(1) To do a good job in basic treatment, we must be foolproof. Many large earth-rock dams can only be filled after the foundation treatment is stable under the conditions of meeting the bearing capacity of the dam foundation and foundation seepage prevention, especially when the foundation treatment project is built on deep overburden. Because of the large amount of engineering and many unforeseen factors, it is often necessary to adopt comprehensive treatment of foundation such as cutoff wall, vibroflotation, curtain grouting and consolidation grouting.

(2) Seasonal earth-rock dams with local geological and hydrometeorological data and well-controlled construction period are extremely sensitive to hydrometeorological factors. In rainy season, the water content of soil has a great influence, which directly restricts the dam filling and affects the construction strength; In winter, the soil is frozen, so it can't be filled without taking active measures. In winter and rainy season, there is a dilemma of high input and low output in filling construction. For the construction in flood season, a targeted construction plan should be made. Earth-rock dam projects are generally not allowed to overflow. Therefore, the "construction peak period" of earth-rock dam project should be controlled to reach the flood prevention stage before the first flood season after river closure, and the construction progress should be accelerated after river closure to ensure that the whole section or small section of dam body is filled to the flood prevention elevation before flood season. Therefore, the construction period of dam filling is limited. During winter construction in northern China, the monthly average temperature is below 0℃, and rivers and soil layers freeze in some areas, which has adverse effects on excavation, concrete engineering, grouting engineering and filling engineering. Therefore, in order to meet the requirements of safe flood control and reach the river blocking elevation on schedule, it is necessary to improve the monthly filling strength.

(3) Ensure the material of earthwork mined in the engineering yard. The importance of the material yard to the earth-rock dam is self-evident, but it is also the soft spot that most easily affects the smooth filling of the dam. According to the engineering practice, generally speaking, the geological exploration depth of the material yard is far less than that of the dam site, especially the rockfill with the largest filling amount, which is often described by only a few exploration holes or topographic exploration. After entering the site, it is likely to change with the tender documents, and the conditions for large-scale mining (or bench mining) will not be formed, which will directly affect whether the dam filling gradation is guaranteed. In terms of impervious soil, water content has also become the key to whether the dam can be filled quickly. Therefore, it is particularly important to review and re-explore the quarry with a perfect and prudent attitude, do a good job in reviewing and calculating the reserves of the quarry, and be aware of it.

In addition, the rolling test of materials is also a very important work. For earth-rock dams, rolling test is the most important technical parameter demonstration work before filling, and it is also an important link to determine whether the dam can be filled smoothly and ensure dam safety. The quality of rolling test directly affects the filling of dam body.

In the rolling test, it is necessary to determine and adjust the water content of impervious soil materials, and at the same time, it is necessary to determine the water spraying amount of rockfill materials. In addition, in order to ensure the filling quality of earth-rock dam, the construction of earth-rock dam must require trial pit sampling, and the next layer of filling can only be carried out after the compaction of the filling surface is qualified and can pass the acceptance.

(4) Determining reasonable dam surface zoning is the key to the construction of filling project. Because of the large size of earth-rock dam, it provides a necessary scene for the partition flow operation of dam surface. Earth-rock dam engineering in the filling process is generally divided into paving, paving, sprinkling, compaction, quality inspection and other work. In the partition flow operation of dam surface, the construction of impervious soil materials should be based on the needs of filling, reasonable division of filling areas and flow operation according to the actual situation, and adjustment of mechanical equipment and filling conditions. For earth-rock dams with horizontal filling and temporary filling, the normal construction of large machinery cannot be affected by blindly reducing the filling amount of temporary filling, and the filling quality must be guaranteed.

⑤ According to the actual situation of the project, the dam foundation reinforcement technology is determined and adopted, mainly the grouting reinforcement technology for earth-rock dams, including the grouting design and the adoption of grouting technology.

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