The reclamation project of Jiushang Shunba in Zheshan Bay of Qiantang River covers an area of 466 1.7 hm ~ 2. It is located at the peak of strong tidal bore in Qiantang River, near Qianjiang Farm in Xiaoshan, 5 kilometers away from Hangzhou International Airport, 3 kilometers away from the population of the Second Qianjiang Bridge, and 6 Qianjiang Bridge 1 km away. It is a golden zone for the future economic development of Xiaoshan District. The overall regulation planning of Zheshan Bay started from 1958, and the first phase of the project was completed in 1970. The dam was dumped and filled in 1 1km, and the embankment was constructed 15 17km, so that the seawall between Baihushan and No.9 dam could meet the river course. There is also land 3333 13hm2 around, which belongs to the farms of Xiaoshan Hongken and Hongshan. The second phase of the project ends at 1982, and the seawall between Dam No.9 and Dongfeng Corner is 8km. The third phase of the project started at 1984 and was completed at 1989, and 34617hm2 was reclaimed. The rest is 5 12km from the upstream of No.9 dam to Dongfeng corner, and the beach can be fenced 466 17hm2 ~ 2, commonly known as "reclamation along No.9 dam". This dike line is arranged according to the Qiantang River regulation planning line, which is the last phase of reclamation in Zheshan Bay. It is closest to the main river and has the strongest destructive power to the tidal current. Rockfill dams have been thrown and washed away many times, but they have not been blocked, so it is very difficult to reclaim them.
2 Research and Practice of Reclamation Project
2. 1 Characteristics of reclamation in this period The reclamation project in this period was a difficult one in the history of Xiaoshan District. Compared with other reclamation projects, it has three characteristics. (1) Low altitude. The length of reclamation dike line in this period is 5 12km (which has reached the planning line of Qiantang River), and the average elevation of dike line is 4 103m, which is lower than the average suitable elevation of 5 18m 177m, in which the easterly angle ranges from 0+000 to 2+2800m. The section from 3+200 to 4+800 is 1600m long, with the highest elevation of 2 165m, the lowest elevation of 0 104m and the average elevation of1kloc-0/22 m, which is the first phase of reclamation with the lowest bid height. (2) The beach is soft. Because the beach belongs to new silt, the surface silt is thick, the beach surface is soft and easy to sink, and pedestrians are difficult, which brings great difficulties to the erection, transportation and transformer installation of high and low voltage lines. (3) Engineering insurance. This reclamation project started in February 2000 and belongs to spring reclamation. During the construction period, there is more rain, and the water level of the outer river changes greatly and rapidly. Moreover, due to the soft overburden, a large number of stones in the original riprap dam were washed away by tidal bore, which made it difficult to clean the foundation of the dike pond and prevent seepage and closure of the dike body. Because of the high silt content, long silt settling time and slow consolidation speed, it is difficult to stabilize the embankment. After the dike is formed, it will be threatened by rainy season flood and autumn spring tide, which is the biggest engineering risk in Xiaoshan's previous reclamation.
2.2 The implementation plan of reclamation in this period is based on the characteristics of low tidal flat elevation, deep and wide tidal current ditch, weak overburden and dangerous engineering position, and in line with the principle of combining reclamation with river regulation, a two-phase reclamation plan is formulated in this period. Specifically, the whole line adopts mechanized riprap at the same time upstream and downstream to promote siltation; In the low elevation section, mud pump is used to borrow soil from outside the river to fill silt; In the deep trough of Longkou, temporarily and appropriately retreat the dike line, build a temporary transition cofferdam to form internal closure, speed up the siltation of Longkou, and then complete the dike enclosing task according to the designed dike line. Among them, the first phase of the project plans to build dikes of 41247km (including fixed dikes of 21262km and transitional inclined dikes of1.654,38+0.985km), and the second phase of the project has an enclosed area of 280hm2. Transition embankment 1 1 1km, enclosed area 186 17hm2.
2.3 Research and practice on the layout of reclamation project (1). According to the original topography and the actual situation of promoting siltation, the arrangement of dike axis should not only enclose and fix the dike line as soon as possible according to the planned route, but also draw up the first-stage enclosure scope considering the appropriate elevation of the tidal flat, enclose the original control gate of 1 dam as much as possible, build inland waterway, solve the necessary water source and temporary drainage channels, achieve the purpose of enclosing and promoting siltation, and strive for time to strengthen the new enclosure pond.
(2) Design criteria. The dikes and ponds along the reclamation line are designed according to the flood level standard of 100. At the same time, considering that the riprap dam has experienced tidal bore impact for many times, some genes in the dike pond contain stones, so it is difficult to clean up. In order to meet the needs of seepage control, besides digging ditches and clearing stones and intercepting water as much as possible, an intermediate platform with a width of 5m was added to the inner slope of the dike with an elevation of 9 10m, which raised the elevation of the pond protection ground to 7 10m, increased the seepage length of the dike body and improved the seepage control effect. According to the amount of earthwork required for embankment construction, the Tanghe River is excavated to achieve the purpose of connecting the embankment with the river (Figure 2).
(3) Construction practice of reclamation project. Generally speaking, the construction methods of reclamation in this period can be divided into two types: the first phase of the project adopts the construction method of small section sealing and filling and large section follow-up; The second phase of the project adopts the construction method of reserving longkou and advancing the whole line. Selection of methods to promote siltation by throwing dams. Because this project is located in the special section of bend and breach, the tidal bore is very destructive to the project, and there are two methods to block the mouth by throwing stones: the conventional method of throwing stones to promote siltation, that is, it is easy first and then difficult, first blocking the upstream 3000m dam to promote siltation, and then blocking the deepest and largest gap in the downstream; Advancing upstream and downstream at the same time can reduce the scouring degree of the upstream dam body after the tidal bore enters from the downstream, speed up the river closure progress and improve the siltation promotion effect. After theoretical analysis and practical comparison, the second method was adopted and promoted at both ends on June 25, 2008 with +065438, and satisfactory results were achieved. Determination of section of riprap dam. The design of riprap dam section should not only consider the safety needs of the dam body and save the investment of engineering quantity, but also consider the needs of the working face when the project is implemented. Therefore, the width of dam face is 8m (two lanes), and the elevation is about 1m above the average high tide level, that is, the elevation is 8 10m. Slope1:115—112. 70% rubble and 30% ballast are mixed and thrown, which not only achieves the effect of dam compaction and reverse filtration, but also completes the construction of traffic pavement, ensuring the operation time and project progress. Experience and exploration of throwing dams to promote siltation. At the beginning, in order to speed up the requirement of promoting siltation, the tidal inlet was temporarily kept at 400m, and the riprap dam was closed after the upstream siltation increased by 280hm2. However, it is found that the remaining 1, 336, 5438+0.3 hm2 tidal flats are only allowed to seep into the tidal flats through riprap dams, and the progress of promoting siltation is slow. After research, we chose the section with good downstream dam body and easy to repair, and the tidal bore of 80m was opened above the elevation of 6 10m, which accelerated the process of siltation promotion. In this way, in less than 1 month, the other 186 17hm2 beaches basically reached the appropriate elevation except for the gap of more than 200m, which created the foundation for the second phase of reclamation. Construction sequence and principles. In order to seize the favorable opportunity of low tide level in the small flood season, a short section is built first, and the two tides of 1d are shut out, and then the tidal increase speed is faster than (0 15 ~ 0 18m)/d for heightening and strengthening. At the same time, in order to solve the difficulty of taking soil, soil is taken from water and underwater, inside and outside the dike at the same time. After the small section is closed, all the soil will be transferred to the dike to speed up the progress and reduce the investment. Longkou is blocked At the tidal inlet, it is very difficult to block the mouth and build a dike because of the high velocity and low elevation. Temporary crescent weirs should be built at 200 ~ 300 m to reduce the import and export water, reduce the erosion of Longkou by water flow at low tide, and make the gap naturally promote siltation. Practice has proved that within half a month after the completion of the cofferdam, the gap has been basically silted up, and then the embankment was built according to the planned route, and the second phase of reclamation was successfully completed. 186 17hm2. Riprap slope protection. Immediately after the earth embankment is completed and accepted, organize forces to build mud-rock pavement on the pond surface and lay geotextile on the outer slope. The riprap filter layer is 50cm thick, and the riprap 1 ~ 1 15 m thick is used to protect the slope from moisture and flood, which lays the foundation for building a permanent standard seawall in winter after the flood.
3 Conclusion
After careful research and design, scientific and reasonable construction, the riprap dam construction of Jiushang Shunba Reclamation Project began on 20001October 301999 ~ 10, and the riprap dam construction was basically closed (except for the gap of 400m), from February 26 to March 2000/kloc-0. Then, various measures were taken to promote siltation, fill siltation and return siltation, and tidal gullies and low-lying beaches were quickly filled. From April 27th to early May, the Moon-shaped sub-dike in Longkou was completed first, forming a closed circle for the second phase of reclamation. From June 7th to June 3rd/KLOC-0, the closure of Longkou River was completed according to the requirements of the design dike axis. At this point, the 250hm2 reclamation project of Jiushang Shunba has been fully completed. Actually * * * completed 2.4 million m3 of earthwork and 650,000 m3 of riprap (including 400,000 m3 of dam reinforcement and dam retaining riprap and 250,000 m3 of riprap for slope protection), invested 35,505 workers and 5,880 mud pumps, and * * * invested about 50 million yuan. With flat terrain, deep strata, reliable fresh water resources, closed sewage outlets and convenient transportation, it is an excellent commodity base for developing fresh and high-grade agricultural products and non-staple foods. The plot is close to Qiantang River, with beautiful scenery and convenient transportation. It is a good place for tide watching, recuperation, vacation, sightseeing in agricultural parks and real estate development. It is also a prime location to attract foreign investment to build factories. It is very important to estimate the benefit of its investment and development. At the same time, through reclamation and dike pulling along the dike line, the water flow conditions of the channel in the bay have been improved, the river surface has narrowed and the main channel has deepened, which is beneficial to the development of shipping. The river regulation task of Jiushang Shunba section of Zheshan Bay has been completed for 38 years, and the engineering economic and social benefits are remarkable.
I believe that after the above introduction, everyone has a certain understanding of the research and practice of the construction scheme of reclamation project in the strong tidal bore area of Qiantang River. Welcome to Zhong Da for more information.
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