1. Main problems in sediment deposition and dike reinforcement in the lower Yellow River
The foundation has strong permeability and is difficult to treat; There are many breaches in history. When plugging breaches, many sundries such as straw materials will be left behind, causing hidden dangers. After several heightening, the quality of the dike body is uneven. Especially in history, most dams were repaired by mobilizing migrant workers, and the quality was difficult to guarantee. Due to historical reasons, there are many hidden dangers such as bunkers and military ditches in the dike. Embankment soil is poor, mostly sandy soil, with poor impermeability and erosion resistance, and there are many joints, cracks and caves inside the embankment.
2. The role of sediment deposition in dike reinforcement in the lower reaches of the Yellow River The basic principle of mechanical sedimentation in dike reinforcement.
The effective measure of dike reinforcement is to increase the section of dike, which requires a lot of earthwork and solves the problem of soil source. There is a large amount of sediment deposition in the Yellow River every year, and it is an effective way to harness the lower reaches of the Yellow River by rationally using river sediment to strengthen dikes. Mechanical dredging in the lower reaches of the Yellow River is to transport the silt deposited in the Yellow River channel to the back of the levee for dredging, which not only strengthens the levee, but also solves the problem for the silt deposited in the Yellow River.
3. The role of sediment deposition in dike reinforcement in the lower Yellow River: the production link of mechanical dredging in dike reinforcement.
Mechanical siltation is to dig sand in the Yellow River channel and transport it to the back of the levee through hydraulic pipeline for sand settling. Since the 1970s, workers in the Yellow River have made a simple dredger according to the sandy characteristics of the Yellow River, which uses high-pressure water flow to destroy the riverbed soil to form mud, and uses hydraulic pipes to transport the mud containing a lot of sediment to the back river of the Yellow River levee for sediment settling. The siltation and dike reinforcement of the Yellow River started with a simple dredger. Through years of practice, it has developed into a variety of machinery such as dredgers, hydraulic washing units and combined pumps. The main production links include pulping, sediment transport and sediment deposition. These three links constitute the whole production process of mechanical siltation and dike consolidation, and any one of them plays a decisive role in the production efficiency and production cost of the system.
(1) pulping
It mixes the deposited solid sediment with water to form flowing mud, which creates conditions for the hydraulic transportation of sediment, thus achieving the purpose of pumping mud and taking soil. Slurry making is one of the most important links in the reinforcement of mechanical embankment. Engineering construction needs soil, and the water in the mud is not important to the project itself. Water is only the carrier of soil, and it needs to be discharged after the soil material is precipitated. Therefore, when pumping mud for the purpose of taking soil, it is hoped that the less water contained in the mud per unit volume, the better, and at the same time, the pumped mud should have enough quantity.
In actual production, there are many pulping methods, and different machines and means can be used. According to the different principles of mud formation, the basic ways of mud formation can be divided into: water carrying, water flushing and mechanical disturbance.
(2) Transportation
Transportation is to transport the manufactured mud to the design site. Mud pumps and hydraulic pipelines are mainly used for transporting river embankments by mechanical siltation under pressure in the lower Yellow River, and mud flows under pressure. When the transportation distance is close, the single-stage pump is generally used for transportation. When the row distance is far and the single-stage pump is difficult to transport, relay transportation is needed.
(3) Sinking
It is to settle the sediment in the designated place according to the design, so as to achieve the effect of strengthening the Yellow River levee, which is the ultimate goal of mechanical siltation and dike reinforcement. Mud is transported to the back side of the levee through hydraulic pipeline. Sedimentation needs to separate the water and sediment in the mud according to the engineering design, drain the water and accumulate sediment. In addition, because the sand excavated in the river course is coarse, mostly silty sand and fine powder sand, it is easy to cause sandstorms and soil erosion in rainstorm weather. Therefore, the sand settling step also includes silt back protection, that is, after the sand has settled to a certain extent, necessary measures are taken to ensure the integrity and durability of the project and meet the design requirements.
The basic method of sediment settlement and discharge is basically the same as that of general hydraulic fill, and the main working procedures include: (1) construction of construction cofferdam. (2) sedimentation and drainage. (3) plastic surgery. (4) Surface protection.
4. The role of sediment deposition in dike reinforcement in the lower reaches of the Yellow River Advantages of mechanical sedimentation in dike reinforcement
Long-term practice has proved that mechanical dredging has incomparable advantages over other schemes:
(1) Due to mechanical siltation, soil is usually taken from the Yellow River to reduce the excavation and destruction of farmland. Calculated according to the average digging depth 1.0m, each digging 1.0 hm2 soil will destroy farmland1.0hm2.. Compared with digging a pit to borrow soil, the earthwork for embankment consolidation by machine silting in the lower reaches of the Yellow River is reduced by nearly 60,000 hm2, which is equivalent to the cultivated land of nearly one million farmers. At present, solving the "three rural issues" proposed by the state is very beneficial to supporting grain production, protecting farmers' interests and promoting agricultural income.
(2) It can reduce the national construction investment, and because of the adoption of hydraulic transportation, the compensation for excavation loss is reduced, and the project cost is relatively reduced. Compared with manual or mechanical construction, under the same construction conditions, the unit earthwork cost can be reduced by 20% ~ 40%, saving a lot of engineering investment.
(3) The mechanical silt filling embankment will deal with the seepage stability of the embankment body and foundation, as well as hidden dangers such as poor filling, poor soil quality and badger-fox hole, which can significantly improve the overall stability of the embankment and effectively solve the quality problems of the embankment body and hidden dangers of the embankment foundation.
(4) The wider silt back area can use its land resources to develop silt back area and develop the Yellow River economy. A large number of trees can be planted on the slope in the silt area, which provides a lot of materials for flood fighting and emergency rescue of the Yellow River and improves the ecological environment along the Yellow River.
(5) Sand can be dug from the river, which has a certain effect of dredging and silting reduction, making the Yellow River sediment turn harm into benefit. Therefore, long-term implementation of silting and dike reinforcement, using the Yellow River silt to raise the back river surface, while strengthening the dike, silting up a "relative underground river", making the "suspended river" on the ground look like groundwater, and realizing the long-term stability of the Yellow River.
5. The role of sediment deposition in dike reinforcement in the lower Yellow River: the practical effect of mechanical siltation in dike reinforcement.
In order to improve the strength of dikes, from the early 1970s, Yellow River workers made their own simple dredgers to dredge the sediment in the Yellow River channel, and used hydraulic pipes to transport the sediment to the back of the dike for settlement, which widened the Yellow River dike by 50- 100 meters and achieved remarkable results. According to statistics, by 2000, 600 million cubic meters of earthwork in the lower reaches of the Yellow River had been mechanically silted and consolidated. By filling the low-lying pit and pond on the back river side, the width of the dike is increased, the seepage diameter is prolonged, and the stability of the dike is enhanced. It has a remarkable effect on solving the dangerous situations such as leakage, seepage and piping, and effectively improves the flood control ability of the dike. Practice has proved that there is no danger to the back river when there is a big flood in the embankment section that has been reinforced by silt and reached the reinforcement standard. In addition, because the sand is taken from the river bed, it conforms to the policy of treating the Yellow River with Yellow River, and also has great economic and social benefits.
6. The role of siltation in dike reinforcement in the lower reaches of the Yellow River. Problems that should be paid attention to in dike reinforcement construction by mechanical siltation.
(1) Choose a responsible and enterprising captain and host engineer. As the saying goes, the quality of work depends on the monitor. The captain and the host are the squad leaders of this class. If you choose a monitor, you can take this class well and do it well.
(2) Pay attention to leave a certain distance outside the toe of the slope in the silt area when excavating the intercepting ditch and the backwater channel, so as to avoid the cofferdam collapsing and blocking the intercepting ditch during construction. The intercepting ditch should be excavated according to the design standard, so as to avoid cutting corners, digging not deep enough and not wide enough to reduce the service life of the intercepting ditch.
(3) Pay close attention to the three elements of mechanically consolidated silt: sediment concentration, water yield and operation time. Always move the ship's position, flexibly grasp the law that the big water is close to the slippery edge and the small water is willing to be tender, so that the sediment concentration is always in the best state.
(4) In order to reduce the sediment loss in the silt area, the silt content of the discharged water flow at the outlet should be controlled below 3 kg/m3.
(5) The most important problem of earthwork siltation is to take good care of the dam, especially in rainy season. It is best to spread a layer of plastic cloth from top to bottom on the dam to prevent the dam from bursting and scouring the nearby fields and buildings. In order to ensure the flood control safety of the Yellow River, provide guarantee for the social and economic development along the Yellow River, and eliminate the weak links of dike projects as soon as possible, the Yellow River Water Resources Commission decided to build standardized dikes, flood control safety lines, emergency traffic lines and ecological landscape lines in 2002 according to the Yellow River regulation goal put forward by Wang Shucheng, Minister of Water Resources. It is required that the width of silt area should reach 100 m, the elevation of silt area should be based on the fortification standard in 2000, and the flood control guarantee line should be built. In the silt back area of 100 meters, suitable forests should be planted at the spacing of 2 meters and the row spacing of 3 meters. It can be seen that mechanical siltation plays an important role in the construction of standardized dikes and gives full play to its irreplaceable role.
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