What is the specific content of the discussion on seepage control and reinforcement technology of reservoir dam? The following consultation will answer your questions.

introduce

Dam is the most important hydraulic structure in hydraulic engineering construction, and it is an irreplaceable important water conservancy facility for controlling water flow, flood control, irrigation and hydropower generation. In particular, the reinforcement of reservoir dams is the top priority of reservoir dam safety management. Like other engineering structures, reservoir dams are also likely to have accidents. Therefore, in the long-term use of water conservancy projects, dam safety must be monitored at any time and reinforced in time to prevent problems before they occur, ensure the safe operation of reservoir dams and protect people's lives and property. Waterproofing of water engineering is more complicated, more difficult and more demanding than other engineering technologies. Combined with the construction experience of dam reinforcement in recent years, this paper introduces several anti-seepage reinforcement technologies for reservoir dams, and discusses them with colleagues, hoping to play a role in attracting jade.

1, section reinforcement of reservoir dam

The engineering measures for the reservoir dam to reach the flood control standard are:

(1) Heighten the dam to increase the flood storage capacity of the reservoir;

(two) reconstruction, expansion or addition of spillway, tunnel or culvert and other flood discharge structures. Technical and economic comparison is needed to determine whether to raise the dam or increase the flood discharge capacity. Sometimes it is technically and economically feasible to use both at the same time. If the upstream and downstream slopes of the dam do not meet the stability requirements, it is also necessary to thicken and strengthen the dam section. Appropriate heightening of dams usually takes the following forms:

(1) "wearing a hat" is aggravated. That is to say, if the dam crest is directly raised, the front water surface can be vertically raised by the breakwater, and the upper slope of the rear water surface is steep, which can be determined through stability analysis, for example, the heightening height is not large (for example, 1 ~ 2 m). This method is usually economical.

(2) Thickening and heightening from the back of dam. When the "capping" heightening does not meet the requirements, it is necessary to increase the thickness from the backwater slope of the dam to meet the stable seepage conditions of the dam. There are also a few engineering conditions that allow thickening and heightening from the water surface. For earth-rock dams, it is generally required to use permeable materials such as weathered materials on the back and clay and loam materials on the front.

2, reservoir seepage control engineering quality and safeguard measures

Regarding the engineering quality, earth-rock dams are mainly leakage, landslide and cracks, and some of them are also related to leakage. Therefore, the key to deal with the quality of earth-rock dams is seepage control. This paper mainly puts forward some common anti-seepage engineering measures. The general principle of seepage control is "plug up and drain down". The measures for plugging are horizontal seepage control and vertical seepage control. Horizontal anti-seepage includes the following aspects: digging anti-seepage diversion ditch, decompression well, re-seepage horizontal cover and so on. Vertical seepage control includes concrete seepage control wall, high-pressure jet grouting seepage control, split grouting seepage control, punching and casing grabbing, firewood backfilling and geosynthetics seepage control.

In the seepage control and reinforcement of dangerous reservoirs, some dam foundations need seepage control and reinforcement, and some dam foundations and dams need seepage control and reinforcement. When engineering measures are taken, vertical seepage control measures are often taken. This is because taking this measure usually does not require emptying the container. On the other hand, if horizontal seepage control measures are taken, the reservoir must be emptied before it can be completely carried out. However, after long-term storage, there will always be some siltation, which will bring certain difficulties to horizontal seepage control; Horizontal seepage control is not as thorough as vertical seepage control in maintaining seepage stability and intercepting seepage of dam foundation. At the same time, in the north of China, there is a shortage of water resources, so it is generally prudent to empty the reservoir.

2. 1 Vertical seepage control measures

Take concrete cutoff wall as an example. The main advantage of concrete cutoff wall is that it can adapt to different dam bodies and complex foundation, hydrological and engineering geological conditions. If the dam body and dam foundation are treated as a whole, the cutoff wall can be built from the top of the dam to the bedrock. The two ends of the wall are connected with the anti-seepage facilities on the bank slope or the bedrock on the bank, and the bottom of the wall can be embedded with fresh rock or weakly weathered bedrock to a certain depth. If only the dam foundation is impervious, the upper part of the impervious wall should be connected with the impervious body of the dam body and go deep to a certain depth. As long as the quality is strictly controlled in the treatment, the purpose of completely intercepting seepage water can be achieved. This is a common measure for seepage control and reinforcement of dangerous reservoirs.

In the construction of concrete cutoff wall, we must ensure the construction quality, especially pay attention to the connection between two slotted concrete walls, which is the key to ensure seepage control. At the joint, the wall thickness at any height from the orifice to the bottom of the hole must reach the design thickness, and the concrete wall must be closely connected without mud layer to prevent seepage damage. For example, the earth-rock dam of a reservoir is an inclined-wall gravel dam with a gravel layer depth of 48m and a concrete cutoff wall. During the construction, due to lax quality control, the mud at the joint of the two walls of the tank is thick, and some of it is eroded by seepage, resulting in water leakage and dam surface collapse. After drilling holes in the joints, concrete is poured to block the gaps, and the reservoir can operate normally.

2.2 Horizontal seepage control measures

Horizontal seepage control is divided into horizontal cushion and drainage and decompression facilities.

(1) horizontal bedding reinforcement

To reinforce horizontal impervious blanket, it is necessary to check the engineering and hydrogeological conditions of the area and dam site, which is the premise of impervious reinforcement. Through investigation, we can understand the plane and spatial distribution, hierarchical nature and distribution law of gravel in dam foundation, as well as the dynamic characteristics and seepage path of groundwater, so as to determine the specific size and scope of reinforced cushion, whether it is necessary to add a filter layer under the cushion and whether there is a soft foundation to be treated according to different specific conditions, possible problems, nature and degree, and completed cushion. At the same time, it is necessary to investigate the material source, quantity, gradation, maximum dry bulk density, optimum water content, permeability coefficient and allowable slope of reinforced cushion soil.

During the horizontal blanket reinforcement, according to the supplementary detailed survey test data, the geological section map covering the alluvium is made to further find out the particle gradation, permeability coefficient and allowable permeability gradient of each layer. Generally speaking, the following conditions should be met: ① The seepage gradient in the underlying alluvium should not exceed the allowable seepage gradient of alluvium soil and sand, so as to achieve the seepage stability of the foundation; ② The seepage gradient through the blanket should not exceed the allowable gradient of the blanket soil, so as to achieve the seepage stability of the blanket fill; (3) The residual water head at the downstream seepage outlet will not cause seepage damage, thus realizing seepage stability at the seepage outlet; ④ The seepage flow is less than the allowable loss, so as to achieve the minimum seepage loss. Of these four, the first one is the most important. In order to meet the above four requirements, the correct reinforcement design is mainly to determine the length, thickness, compactness and permeability of reinforcement. The length of cushion should be kept at a certain horizontal seepage diameter to prevent contact erosion and internal piping. Combined with the downstream drainage and decompression facilities, the escape slope should be less than the allowable value. The effective length of the blanket means that increasing the length of the blanket can reduce the seepage from the front end of the blanket to the dam foundation, but the seepage through the blanket itself increases accordingly. After reaching the effective length, increasing the length cannot reduce the leakage. The effective length of blanket decreases with the increase of impermeability of blanket, and increases with the increase of blanket thickness, dam foundation depth, dam foundation permeability and water head. The bottom of homogeneous dam is impermeable, and the length of blanket can be shortened appropriately. For complex geological layers, it is best to determine them according to electrical simulation tests. The thickness and density of the blanket should meet the requirements of the permeability stability of the blanket itself and will not be worn out by the seepage force of the water head. Generally, when rolling construction is adopted, the thickness of the front end of the blanket is 0.5 ~ 1.0m, and the thickness of the joint between the end and the dam body is1/6 ~1/0 head, so the homogeneous dam body can be slightly thinner. If the soil has high water permeability and low density, it will be thickened. The smaller the permeability of the blanket, the greater the thickness, and the better the anti-seepage effect. Generally, it should be several hundred percent or even one thousandth of the base. Quality should be strictly controlled, especially the contact parts, to ensure quality. Where the subgrade bed is in contact with the foundation, such as gravel layer with high permeability and poor grading, a filter layer should be added to avoid repeated cracks and pits in the reinforced subgrade bed after the reservoir is filled with water. When the cushion is reinforced, the rolling method should be adopted. Under special circumstances, if the reservoir cannot be emptied, methods such as throwing soil in water, throwing soil in deep water, drilling soil in ice and artificial siltation can also be used, but they can only be used as auxiliary means of reinforcement.

② Reinforce drainage and decompression facilities.

Drainage and decompression facilities generally use seepage guide ditches, decompression wells and horizontal cover plates for severe leakage. For the reinforcement of the seepage guide ditch, the interlayer relationship should be strictly controlled according to the design requirements to prevent the seepage guide ditch from silting up.

If there is siltation or local damage, it should be removed and repaired in time. The cross section of the seepage guide ditch should meet the requirements of normal drainage due to seepage, and it should be enlarged when it is insufficient. The seepage guide ditch should also have a certain longitudinal slope and drainage outlet. If water is found, it should be repaired in time to eliminate water seepage in time. The reinforcement of relief well is mainly to solve the problem of blockage in the well, and it cannot be decompressed. It should be cleaned with water in time, but the filter layer of the shaft wall should not be damaged, so as not to lose the filtering effect. It is also necessary to prevent pebbles from being thrown into the well artificially. If found, try to clear it in time and strengthen wellhead protection to prevent it from happening again. For the reinforcement of horizontal infiltration capping facilities, if the filter layer fails or the infiltration thickness is not enough, it will be renovated in time to reach the design thickness.

3. Design and analysis of reservoir reinforcement.

3. 1 Design according to relevant specifications.

On the one hand, the design of reservoir reinforcement should ensure the elimination of hidden dangers, on the other hand, it should also ensure the economy and rationality, and designers should refer to relevant specifications for design.

3.2 Strengthen responsibility management and improve design quality.

For the design projects of reservoir reinforcement, the number of projects is generally large, and the required time is short. However, local designers often have to complete several small-scale reservoir reinforcement designs at the same time in a limited time, and designers are prone to negligence.

Therefore, the design department is required to strengthen responsibility management and establish a reasonable and effective incentive mechanism, so that designers can strive to reduce design mistakes and improve design quality.

3.3 Continue to strengthen study and education.

As engineers and technicians, we must persist in conscious learning, constantly update our knowledge and keep up with the pace of the times. Organize training, so that the designers of reservoir reinforcement can understand the guiding ideology of reservoir reinforcement project construction, deeply understand the specific requirements of relevant specifications, master the technical development direction, and popularize and apply new technologies. The design department should carry out professional ethics education for designers. On the one hand, the reservoir reinforcement project uses provincial subsidy funds, on the other hand, it is related to the safety of people's lives and property. It is the sacred duty of every designer to emphasize that the limited funds are used where they are most needed and ask each designer not to make big mistakes in the projects he designs.

4. Concluding remarks

In this project, a variety of dam seepage control technologies are adopted for dam seepage control treatment, and ideal results have been achieved. The project has passed the unit project acceptance organized by a water affairs bureau, and the acceptance conclusion is excellent. After the anti-seepage reinforcement of the reservoir, the operation test of high water level storage proves that the anti-seepage effect is better than expected. The back slope of the original dam was wetted in a large area, and the concentrated leakage of the left abutment disappeared, and the saturation line of the dam body was obviously reduced, and the leakage was obviously reduced. After anti-seepage treatment, the dam is in a stable state, which meets the requirements of safe operation of the reservoir, indicating that the comprehensive application of anti-seepage technologies of high-pressure jet grouting, split grouting and curtain grouting in this project is successful.

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