India is the seventh largest country in the world, with a land area of 2,974,700 square kilometers and a population of nearly 654.38 billion. It consists of 22 states and 9 territories, with arable land accounting for 55% of the total area and agricultural output accounting for 50% of the gross national income. The average annual precipitation in China is 1 100mm, the total precipitation is 370,000 m3, the evaporation accounts for about 1/3 of the precipitation, the annual runoff of surface water is about170,000 m3, and 79,000 m3 seeps into groundwater, of which the available amount is about 27,000 m3. Rainfall in India is unevenly distributed. The maximum annual precipitation in the eastern and western Himalayas is 4000mm, Assam in the eastern part is 65438 0,000mm, and the leeward slope of Kochi Mountains in the central and southern parts is less than 600mm. The annual rainfall in Rajasthan and thar desert in the driest northwest and Gujarat in the north of Mumbai is insufficient 100 mm. There are two kinds of rivers in India: one is snow water supply, which often causes floods in the north and west; The other is the replenishment of monsoon rainfall (90% of Indian rainfall is concentrated in the rainy season from June to September), resulting in short-term floods in central and southern China. These rivers dry up in the dry season and skyrocket in the rainy season, which is very regular.
The existing irrigation area in India is 22 million hm2, accounting for 15% of the arable land, which is only half of the estimated potential irrigation capacity. According to a rough estimate, there is more water in India 1/3 area. 1/3 area is short of water, and 1/3 area is short of water. Therefore, the best and most reliable way to develop water resources in India is to store monsoon rainfall runoff in reservoirs and use it for irrigation during crop water demand. Compared with the annual runoff, the reservoir capacity can not be effectively controlled and optimized, so long-distance inter-basin water transfer has become a suitable and important way to develop water resources in India.
Long-distance and large-flow water transfer in India has a history of five centuries, such as the West Jumuna Canal and the Agra Canal, which transfer water from the Himalayas to remote Punjab, Utaparadi and Rajasthan. Since the 20th century, especially since India's independence, water diversion projects have developed rapidly and achieved great economic benefits. For example, the Salda-Sahayak water transfer project in Uttar Pradesh transports water from Kakla River to Hengxi Plain, with a water supply canal length of 260km, a design flow of 650m3/s, an irrigation area of about 6.5438+0.6 million hm2, and an irrigation area of about 600,000 hm2 for Lamugang River water supply project. Bakla-Qianggar water transfer project, with an irrigation area of about1333,300 hm2；; Junashana Water Supply Project, with an irrigation area of about 800,000 hm2；; The water supply project in badra in Tang Dynasty, with an irrigation area of about 400,000 hm2, and the Rajasthan Canal Project under construction, transported water from the Himalayas to the desert areas of Rajasthan. The water supply canal length is 1.78km, the design flow is 685m3/s, and the irrigation area is about1.2000 hm2.
See table 1 for the national water demand forecast in 2000 and 2025 put forward by Indian National Hydrological Institute in 1990s.
Table 1 India Water Demand Forecast Table in 2000 and 2025
It can be seen from the table that the annual water demand in India will increase from 552 billion m3 in 1990 to105 billion m3 in 2025, an increase of190%; Irrigation water consumption increased from 460 billion cubic meters to 770 billion cubic meters, an increase of 167%. Its growth rate is amazing.
Despite the large-scale development of irrigation water sources in recent decades, the Indian government and state governments are still seriously planning and investigating the problem of long-distance and large-flow water transfer. These water transfer plans include: the GoDavalli River-Krishna River-Pune River water transfer plan; High-water canal of Namade River; West-to-East Gas Transmission Project; Ganges high dam water storage plan; Yarlung Zangbo-Ganges water transfer plan and Rajasthan desert development plan. The Indian government has recognized the importance of large-scale water transfer for developing water resources and improving the environment. It can be predicted that in another decade or two, most of these plans will come true, and the social economy, people's life and ecological environment in most parts of India will be completely new.
2 Design, operation and management of Salda-Sahayak water transfer project
Salda-Sahayak water transfer project was built in the middle and late 1970s, and has been running normally for more than 20 years. The water transfer project is located in Uttar Pradesh, India. It takes water from Kakla River and Salda River, which originated in the southern foothills of Himalayas in Nepal, and is rich in water resources. Build a diversion hub consisting of a low dam and a water intake gate on each of the two rivers. Building a connecting canal between the two rivers, with a length of 14.5km and a design flow of 480m3/s, is the first water intake project. The main water conveyance canal is led from Salda River, with a total length of 260km (including 26km to 104km for double-line parallel water conveyance and the rest for single-line water conveyance), with a designed water diversion capacity of 650m3/s and an irrigation area of 160hm2. The main crops in the irrigation area are sugarcane, rice, wheat, vegetables and fruit trees, and the main irrigation period is from June to 1 1. 165438+10-March uses less water, which is generally maintained at around 400m3/s; March to June is the non-irrigation period. The main canal is basically located in the plain area, with flat terrain, sparse villages and towns and relatively straight canal lines. The canals are mostly filled or semi-excavated and semi-filled, with a design water depth of 7.0m~6.8m, a channel bottom width of 48m~23m, a design slope of 1/2.0 and a longitudinal slope of11000. The water conveyance part of the main canal adopts mixed lining. The lining structure is plain concrete cushion (thickness 10cm)- brick (thickness 12cm)- plastic film impervious layer-brick (thickness 12cm) from bottom to top, and the total length of lining section is 130km. The main canal is equipped with 4 inspection gates and 12 branch gates. In order to ensure the safety of water conveyance, a sluice is set every 40km~60km, and the backwater flow is 1/2 of the design flow of the corresponding main canal. There are two large buildings at the intersection of the main canal and the existing river channel, including 1 river aqueduct and 1 river culvert. Due to the sparse villages on both sides of the main canal, the distance between road and bridge is about 2 km ~ 4 km.
The water transfer project still implements the government administrative management system. The general management organization is Uttar Pradesh Irrigation Administration, and management offices are set up in key projects and important buildings. Irrigation quota of crops in irrigation area is 1m water depth (equivalent to 10005m3/hm2). Irrigation water fee is calculated in hm2 according to crop type, such as: 287 rupees/hm2 for wheat; Sugarcane 474 rupees //hm2. The water fee is collected by the local government, and the project management, operation and maintenance costs are allocated by the government. The application method of the project is also relatively simple. Generally, the canal does not deliver water according to the irrigation water demand, but maintains a large flow all the year round, and the excess water is sent to the downstream river.
3 Design, construction and management of Gometi aqueduct
Gomaiti aqueduct is one of the largest aqueducts built in the world at present. Located at the main canal 163km of Salda-Sahayak water transfer project, it is a large-scale main canal crossing project across Gomaiti River. The design flow of the main canal is 357m3/s, the design flood flow of the Gometi River is 4530m3/s, and the total length of the aqueduct is 473.6m, of which, the inlet gradual change section is 37m, the box body is 38 1.6m, and the outlet gradual change section is 55m. The flume is12.8m wide and 7.45m high. It is supported by a frame system consisting of prestressed concrete longitudinal beams, stiffening ribs, cross beams and upper connecting rods with a height of 9.9m.. At the top of the left and right longitudinal beams, there is a 5-meter-wide highway bridge connecting the traffic on both sides of the Gometi River. Hollow pier and foundation caisson of aqueduct substructure, pier length 18m, width 3m and height 9m; The open caisson is 27m long, 12m wide and 35m deep.
The engineering design and construction features of Gomaiti aqueduct mainly include the following points.
3. 1 Increase blind span and reduce the open caisson depth of pier.
The design flood discharge of Gomaiti River is 4530m3/s, and the aqueduct is set with a span of 10, with a span of 3 1.8m, which can meet the flood discharge requirements. However, according to this scouring calculation, the depth of open caisson in river channel is 35m, and the depth of open caisson on both banks is 58m, which is not only too expensive, but also too difficult to construct. Therefore, blind spans of 1 span and 3 1.8m span were added on both banks in the design, and the wells on both banks were designed as buried wells, regardless of the influence of scouring. The total design length of aqueduct is 12 span, each span is 3 1.8m, and * * * is 381.6m.
3.2 The water delivery tank is independent from the load-bearing frame, which solves the problem of crack resistance of the box.
The upper structure of Gomaiti aqueduct adopts the arrangement form of prestressed load-bearing frame supporting non-prestressed aqueduct body. This structure has definite stress, and the load-bearing frame with a span of 3 1.8m does not directly block water, so it is not necessary to calculate the crack resistance. On the other hand, the water tank is supported on three sides by beams and ribs with the spacing of 1.95m, which is a multi-ribbed structure and easy to meet the safety requirements of crack resistance. Due to the adoption of this structure, the water tank can be arranged in sections, and it is designed as three sections per span, each section is10.6m, so as to enhance the adaptability of the tank to changes such as settlement, displacement, temperature and earthquake.
3.3 The bearing structure adopts prestressed box frame, which has strong bearing capacity.
The load-bearing structure of Gomaiti aqueduct adopts prestressed box frame, which consists of longitudinal beams, transverse beams, vertical ribs and pull rods. In order to enhance the rigidity of the frame, a cross tie beam is also set between the bottom longitudinal beam and the cross beam. All parts of the frame are prestressed concrete structures, each longitudinal beam is equipped with 38 longitudinal prestressed steel strands, each transverse beam is equipped with 12 transverse prestressed steel strands, each vertical rib is equipped with 3 vertical prestressed steel strands, and each strut is equipped with 4 transverse prestressed steel strands. This box-shaped frame, which is composed of three-dimensional prestress, is 9.9m high, 14.6m wide and 3 1.8m long, and has high bearing capacity. After more than 20 years of high water level operation, there has been no problem.
3.4 Two sections of steel trough connection section are adopted, and reasonable supports and splicing water-stop structures are selected to adapt to earthquake, temperature, expansion and settlement deformation.
In order to eliminate the influence of pier subsidence and longitudinal displacement on structure and water sealing during earthquake, Gomaiti aqueduct adopts unconventional connecting sections, supports, joints and water sealing forms. Through calculation and field test, the settlement of the pier is 7.2 cm ~ 13.4 cm, and the displacement of the top of the side wall in the corresponding gradual change section can reach 30cm. Therefore, a simply supported sliding steel trough with a span of 1.2m is set between the pier and the gradual transition section. The steel trough is supported on the fixed and sliding cylindrical hinge support and the rolling cylindrical hinge support, and can bear the sliding displacement of one side of the rolling hinge support by 30cm. In order to facilitate sliding and ensure sealing and water stopping, a stack of lead plates with the thickness of 10mm is added to the bearing pad, and corrugated copper sheets for water stopping are welded to the steel trough and the bearing steel plate, so that they can adapt to the displacement of the aqueduct and ensure the water tightness of the aqueduct. In the gradual change section, the flume section is adapted to the open caisson layout, that is, each flume section is placed on one open caisson, and the smaller flume section is arranged between open caissons. The water tank support adopts special tangent rubber support, and 30cm flat-fell seam is set between adjacent water tanks, and V-shaped rubber is used for water stop. This waterstop is covered with steel plates, one side of which is fixed on one water-saving tank and the other side is overlapped on another water-saving tank. Laying aluminum plate under the steel plate, installing P-type sealing rubber to stop water to prevent sediment from entering. The transition section is the most serious part of the aqueduct, and the above measures are taken to ensure the safe operation of the aqueduct.
3.5 Open caisson foundation is adopted in the gradual transition section to reduce uneven settlement with the main channel section.
The upper part of Gomaiti aqueduct has a large load, and the main aqueduct adopts open caisson foundation. The open caisson is a double D-shaped section, with a length of 27m, a width of 12m, a wall thickness of 2.25m and a partition wall thickness of1.5m. The transition sections are located on both banks, and the tank body is located on undisturbed soil. If it is not treated, it will cause great uneven settlement between the main trough and the gradual change section, resulting in structural damage and water leakage of the aqueduct. Therefore, in the design, special attention is paid to the foundation treatment of the gradual transition section on both banks, and the tank of the gradual transition section also adopts open caisson foundation. The length and width of the foundation open caisson in the gradual change section are 26m 14m, which is larger than the size of the open caisson in the main channel. There are three open caissons in the upstream gradual change section and four open caissons in the downstream gradual change section. Except for two double D-shaped sections adjacent to the pier, the other five sections are rectangular, and the wall thickness of rectangular open caisson is1.7mm. In order to make the design more practical, a test well with a diameter of 5m and a wall thickness of 1.25m was built on the left bank of Gometi River. After detailed observation, it is found that the shaft lining friction is1.9t/㎡; The total average settlement when the allowable bearing capacity of the bottom hole is 4.5 kg/cm2 and the load intensity is 5 kg/cm2. These measured data provide a reliable basis for open caisson design.
3.6 The beam system structure adopts I-section, and the stress condition is good.
I-shaped section is adopted as the main stress component of Gomaiti aqueduct. The longitudinal beam is 9.9m high; The upper flange is 5m wide; The mid-span web is 350mm thick, the lower flange is 600mm wide and the height is1.5m; The web thickness of the 5.55m long part at both ends is 600mm, the width of the lower flange is 1650mm, and the height is1.5 m; A 600mm long transition section is set between the mid-span part and both ends. The beam height is1.5m; ; The thickness of the web is 350 mm; ; The flange width is 1m, the upper flange thickness is 150mm, and 45 beam shafts are 90mm high. Thickness of lower flange 150mm, and axil height of 30 beams150 mm. The tie rod is also an I-shaped section, with a section height of 600mm, a web thickness of 350mm, upper and lower flanges of 450mm and a thickness of150 mm. Although the I-shaped section is used as the main stress member, it brings certain difficulties to the construction, and it has the advantages of economical and reasonable section and convenient reinforcement, and is especially suitable for prestressed concrete structures.
3.7 Number of Gometi Aqueducts
Gomaiti aqueduct was started in June 1973 and completed in June 1978, with a total construction period of 5 years. The main quantities are: 35000m3 earth and stone works, open caisson earthwork excavation180,000m3, concrete and ordinary reinforced concrete140,000m3, 8000m3 prestressed concrete, 7500t steel bars, and 3500t steel formwork and steel support. Open caisson excavation adopts 10t crane and 1.5m3 grab, two for each well. Because of the heavy weight of open caisson, it usually sinks by itself, and no additional weighting is needed, but concrete weighting blocks are also prepared at the construction site. During the construction, one open caisson did not sink after using the weighting block for one month, but suddenly sank 10m under unexpected circumstances. Fortunately, it did not cause any damage. The construction sequence of superstructure is: longitudinal beams, each longitudinal beam is poured in three times; Cross beam; Inner and outer ribs; Pull rod; Water transmission tank and other minor works, such as guardrail, wear-resistant layer, connecting device, etc. Because of the low bearing capacity of riverbed soil, it is impossible to install scaffolding and formwork on the ground during the construction of longitudinal beam. Therefore, a special steel arch beam with rollers is made and erected on the pier, which can be constructed for 4 spans at a time. The longitudinal beam adopts shaped steel formwork, and the concrete is poured in three layers. Once the longitudinal beam is poured, 1 prestress is applied, and the steel arch beam can be moved to the rear four spans, and the rear four spans of the longitudinal beam are poured. The formwork of beam, rib, tie rod and water delivery box are supported on scaffolding suspended from the upper edge of longitudinal beam. Because the side wall of the water conveyance tank is very thin, the concrete on the side wall is poured in four layers, and compacted by formwork vibrator. In order to prevent water leakage, the bottom plate and side wall of the water transmission tank are coated with two layers of epoxy resin. The application procedure of prestress is longitudinal beam (first vertical and then longitudinal); Cross beam; Five days after the pouring of the tie-rod longitudinal beam is completed, the vertical prestress is symmetrically applied from the middle of the longitudinal beam to both ends, the top of the longitudinal beam is loaded, and the hole is sealed by grouting at the bottom. Longitudinal prestress is applied in two stages. 1 stage, after 7 days of concrete pouring, 26 steel strands are prestressed, and the prestress of 6 steel strands at the bottom of the beam is enough to bear the weight of the longitudinal beam. At this time, the steel formwork at the bottom can be removed; In the second stage, the prestress is applied 2 1 day after the concrete pouring of the longitudinal beam, and each longitudinal steel strand is prestressed from both ends of the longitudinal beam. The prestress of the longitudinal beam is symmetrically applied from the longitudinal beam to the midspan. In order to reduce the influence of additional stress on the longitudinal beam, it is carried out in three steps: step 1, first prestress the two steel strands of each beam; Secondly, prestressing the other two steel strands; Step 3, jack up the whole span frame, support the longitudinal beam on rolling bearings that only allow lateral displacement, and then prestress other steel strands in the beam. The prestress of all beams is applied from one end, and the construction is carried out in a symmetrical way. Prestressing of tie rods starts from the span of 1/4 at both ends of the longitudinal beam, and is carried out symmetrically at the middle and both ends of the span. The prestress of each tie rod is applied once. All prestressed steel strand channels are grouted by concrete pump to ensure that the slurry fills the whole channel. The rest of the aqueduct was built by traditional methods.
Gomaiti aqueduct has a management office, which is responsible for operation management and maintenance. For more than 20 years, aqueduct has been running under high water level without any accident. After testing, no obvious displacement and settlement were found in the project, and no common water leakage was found in the aqueduct. All these fully show that the design, construction and management level of Gometi aqueduct is very high.