1. After years of research and development, China's water conservancy and hydropower construction technology and techniques have made great progress, including diversion and cofferdam construction technology has made significant breakthroughs. Due to the water conservancy and hydropower construction is mostly in the environment of the more harsh field, to realize the effective position of water resources to adjust, and does not damage the local natural environment should be implemented effective diversion and cofferdam. In the process of river diversion, to analyze and investigate in detail the local hydrology and water uncertainty, choose the appropriate and accurate calculation and design method for diversion program design and specific diversion technology, so as to ensure that the relevant water conservancy and hydropower construction work is carried out smoothly.
2. Overview of the project
Yancheng City, Yundong set of locks project is located in Huai'an City, Chuzhou District, southern suburbs of the 2.5km of the confluence of the Suzhou-North Irrigation Canal and the Beijing-Hangzhou Grand Canal, the Beijing-Hangzhou Canal and the Suzhou-North Irrigation Canal is the communication of the Beijing-Hangzhou Canal and the Suzhou-North Irrigation Canal of a single set of locks. It is a single-stage set of gates connecting Beijing-Hangzhou Canal and North Jiangsu Irrigation Canal. The gates, together with the Yundong Hydropower Station at Yundong Gate on its left side and the embankment of North Jiangsu Irrigation Canal***, constitute the flood control barrier under the Yundong Gate. The cofferdam during the construction period of the project includes the construction cofferdam on the side of the Beijing-Hangzhou Canal upstream of the set of gates, the construction cofferdam upstream of the Diversion River Slant River and the construction cofferdam on the side of the General Canal downstream of the set of gates, and the secondary cofferdam on the side of the General Canal of the North Jiangsu Irrigation downstream of the set of gates (the repair was completed in April 2015 before the opening of the Diversion River to the water).
3. Engineering geological conditions
3.1 Hydrometeorology
Yundong set of locks is located in the Huaihe River downstream of the Baimahu area, is located in the northern subtropical and warm belt of the overland, by the influence of the monsoon circulation, with the summer and cold changes in the four seasons, rain and heat of the same season of the climate characteristics. The average annual temperature between 14 ~ 16 ℃, frost-free period of 220 ~ 240 days, the average number of sunshine hours for many years for 2300h, the average evaporation for many years for 1350mm, the average precipitation for many years 931mm, rainfall inter-annual differences in rainfall between seasons within the year distribution is not uniform, rainfall in June to September accounted for 60 ~ 70% of the annual rainfall, often occurring after the first drought, drought and flooding, floods and droughts, drought and flooding The weather situation of alternating drought and flood.
3.2 Geological conditions
According to the work area engineering geological survey report and stratigraphic section map, the work area engineering geology is general, specifically divided into seven layers, respectively, for the vegetative filling soil powdery clay sandwiched between light chalky loam light chalky sandy loam light chalky clay heavy chalky sandy loam light chalky sandy loam and chalky clay intercalation of chalky sandy loam sandwiching chalk chalk chalky clay and chalk sand sandwiching loam chalky sand, and its composition is to Chalk particles are dominant.
3.3 Groundwater
Groundwater in the exploration depth range of the exploration area is mainly the air space diving and pore pressure water in the loose sediments, the permeability of the (5th) layer is poor, the groundwater below the (5th) layer has the nature of pressure water, the main water-bearing layers are the (6A) layer and the (7th) and (8th) layer, the recharge mode is mainly lateral, and the connectivity with surface water is poor, the pressure water level is on average at the level of the (6th) layer and the (7th) and (8th) layer, and the water level of the (6th) layer and the (7th) layer are at the average level of the (6th) layer and the (7th) layer. The average water level of pressurized water is about +4.2m.
4. Cofferdam construction program selection and design
According to the hydrological data provided by the bidding documents, the water level in front of the construction cofferdam on the Cuijiang Sloping River is considered at a minimum level of not less than 4.0m water level.
4.1Design of earth cofferdam on the side of the slanting river
Water is blocked by filling and damming in the open water section of the slanting river of the cited river, and the water-blocking cofferdam in this part is filled along the excavation line on the south side of the pit (the right side), with a top width of 7.0m, and a bumping platform with a width of 3.0m is filled in the water surface, with a bumping platform elevation of 4.0m, and 8m-long log piles with a center spacing of 40cm are driven in the bumping platform, which are designed to prevent the water from entering the cited river. According to the standard of defense provided by the bidding document, the water level of the construction dam on the side of the main canal of the slanting river is designed at the highest water level of 6.0m during the non-flood season, and considering the factors of wind and waves and overheight, it is suitable to design the elevation of the top of the dam to be 7.0m, and the slope ratio of the inside and outside of the dam is 1:2.5 and 1:5, respectively.The slopes of the water surface are protected by impermeable geotextile and 30cm-thick bagged soil to enhance the stability and the ability of resistance to shabu-shabu.
4.2Design of cofferdam on downstream side of set of gates
According to the standard of fortification provided in the bidding document, the water level of the construction dam on downstream side of the Yundong set of gates is designed at the highest water level of 6.0m in non-flood season, and taking into consideration of the factors of wind and waves and overheight, the designed elevation of the top of this dam is 7.0m, the ratio of the slopes of inside and outside of the dam is 1:5 and the width of the top of the dam is 6.0m. Meanwhile, 8m-long central center of the weir is added in the weir at the back of the water surface and at the connection point between south side of the weir and the steel pile weir. At the same time, 8m-long log piles with a center distance of 40cm are installed at the backwater of the cofferdam and the south side of the cofferdam with the steel sheet pile.
4.3 Design of steel sheet pile cofferdam
Steel sheet pile cofferdam is used in the narrower river near the lower gate head position, which is an effective method of deep water foundation pit support, and a form of cofferdam with simple construction and clear structural stress. According to the actual situation of the water level of the sloping river, the water depth is about 4m, and the steel sheet pile cofferdam is used, which occupies a small section of the river and has strong anti-scouring ability. The steel sheet pile cofferdam consists of double rows of Ⅳ type Lassen steel sheet piles and 24# channel steel surrounded by Φ18 steel wire rope connection, the middle of the clay filling, the cofferdam width of 7m, the top elevation of 7.0m (1m high bagged soil cofferdam), the top and bottom of the steel sheet piles elevation of 6.0m-3.0m.
4.4 Pit enclosure design after adjusting the cofferdam program
Containment of the inclined river cofferdam from the two cofferdams adjusted to a vertical cofferdam, the lower gate head and the lower gate head will be the same as the lower gate head, the lower gate head and the lower gate head. After the cofferdam, the lower gate head and gate room south (right) pit space is reduced, the cofferdam outside the river water on the pit impact is obvious, in order to ensure that the building construction, need to strengthen the lower gate head construction pit support and drainage. Specific arrangement is as follows: the south side of the lower gate head (right side) pit support adopts 9m Larsen Ⅳ steel sheet pile enclosure, pile bottom elevation -7.5m, pile top elevation 1.5m, the enclosure structure is 20cm away from the gate head and the downstream navigational wall bottom plate distance. at the same time, there are 8 sets of lightweight wells along the weir in order to enhance the interception of river water outside the weir. The construction method is the same as pit enclosure special program.
5. Cofferdam construction process
The total amount of earth filled in the longitudinal retaining cofferdam on the side of the sloping river side of the river diversion is about 15,000 square meters, and the amount of clay filled in the cofferdam of the steel pipe pile is about 5,000 square meters. According to the site conditions, it is planned to gradually take soil from the pit excavation to fill the longitudinal earth cofferdam on the side of the sloping river of the diversion river during the pumping period of the Zhatang River, and the insufficient soil source can be purchased.
5.1 earth cofferdam construction
1) earth cofferdam cofferdam filling construction dam root cleanup → cofferdam earth filling construction → earth filling compaction → slope repair → anti-washout sandbag filling. 2) debris silt cleanup: in order to ensure the quality of the filling cofferdam soil, the soil extraction area using excavator or bulldozer to remove the surface of the about 40cm thick tree roots, sod and other debris. Before filling the cofferdam, excavator and bulldozer are used to clear the surface of the cofferdam dam root area to ensure that the cofferdam is embedded in the river bank and the seepage control effect of the connecting section is guaranteed; the silt in the river bottom position of the weir site is removed by the method of earth extrusion.3) Filling construction of cofferdam: the construction is carried out by the method of entering into the occupied area, and the filler soil is above the level of the river water for 0.5m, and then it will be compacted with bulldozers by layered leveling. The cofferdam filling on the water, adopting the program of laying soil in layers and compaction in layers, the layer thickness is 25cm, bulldozer leveling and compaction, and do the side slope sufficiently. This project construction cofferdam filling using excavator loaded dump trucks to transport soil bulldozer for earth into the occupation of leveling compaction, excavator with the repair. 4) leveling compaction: cofferdam out of the water will be bulldozed in layers of compaction to the design elevation, and timely construction of the backwater slopes, according to the requirements of the construction of other anti-punching or reinforcing measures. 5) log piles and anti-punching filling sandbag construction.
5.2 Steel sheet pile cofferdam construction
Steel sheet pile cofferdam construction procedures are: steel sheet pile sizing → horizontal I-beam steel confinement fixed taut → bamboo raft sheet with geotextile fixing → cofferdam clay heart wall filling construction → top of the weir soil leveling and compaction of stacked bags of soil.
1) Sheet pile construction: Sheet pile is driven by piling ship.
2) Two horizontal I-beams are confined and fixed, and wire ropes are pulled against each other.
3) Bamboo fence sheet geotextile enclosure construction: To prevent soil loss between piles, bamboo fence sheet geotextile enclosure is used, and the bamboo fence sheet can be fixed on steel sheet piles by wire.
4) cofferdam clay heart wall filling construction, the site using excavator directly into the clay barge, shipping to the side of the cofferdam has been good sheet pile cofferdam using dredger (placed fixed in the engineering ship) to dig clay into the cofferdam, steel sheet pile clay filling from the north side of the river bank to start forward construction, the water part of the use of small machinery tamping, tamping backfill to the design of the top of the pile elevation in layers, process Pay attention to the solidification of the pulling wire rope. 5) Bagged soil yard high protection.
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