Construction conditions of Sutong Bridge

1. The bridge area has a humid monsoon climate in the north subtropical zone, with complex and changeable weather and frequent bad weather. Bad weather that has a greater impact on the project includes heavy rain, continuous rain, thunderstorms, typhoons, strong winds, heavy snow, fog, etc. . Regarding typhoons, the bridge area is likely to be hit by typhoons from late May to late November, with an average of 2.3 to 2.7 typhoons per year. The period from early July to September is the typhoon-prone period, and August is the month most affected by typhoons, accounting for about 40%. In the design, priority should be given to structural plans and construction plans with strong wind resistance; when arranging the construction schedule, construction states that are greatly affected by typhoons, such as maximum single cantilever, maximum double cantilever, etc., should be avoided as much as possible during typhoon-prone periods to ensure the safety of the bridge. . The annual average rainy days in the bridge area is about 120 days, with a maximum of 150 days; the annual average foggy days and thunderstorm days are about 30 days, with a maximum of 60 days. The above-mentioned bad weather will lead to a reduction in the number of effective construction days, and full consideration must be given when arranging the construction period.

2. The annual average temperature in the bridge area is about 15.4℃, the annual extreme maximum temperature is 42.2℃, and the annual extreme minimum temperature is -12.7℃; the monthly maximum temperature is 30.1℃, and the monthly minimum temperature is -0.2℃. From this, it is determined that the design temperature parameters of the bridge are: the closing temperature of the structure is 10~20℃, the temperature rise and fall of the concrete structure is ±20℃; the temperature rise and cooling of the steel structure are +32℃ and -33℃.

3. By reviewing weather disaster records and visiting local residents on both sides of the bridge, comprehensive analysis and research showed that no tornado occurred at the bridge.

4. By establishing an observation platform on the river and an observation tower on the shore, it was revealed that the wind conditions on the wide water are different from those at nearby weather stations and wind speed measurement stations along the coast, truly reflecting the bridge's The wind conditions of the location. Observation data shows that the wind speed on the river surface at the bridge location is significantly greater than that of the adjacent weather station. The average wind speed is about twice that of the adjacent weather station. The wind speed on the river surface is also greater than that on the river bank.

5. The dominant wind direction on the river is easterly. The rose diagram of wind direction frequency in Nantong City over the years is shown in Figure 3-2.

6. The basic wind speeds in different return periods at the bridge location where the river surface is 10m away from the average water surface are shown in Table 3-1.

1. The proposed Sutong Bridge is located on the downstream side of the Xuliujing mark in the Xuliujing node section. For more than a hundred years, it has experienced the upstream Tongzhou Sand Channel and the Langshan Sand Channel main channel. It fluctuates greatly, but the main stream of the Yangtze River in the Xuliujing node section is always on the line between Hupu and Xuliujing, and the river situation is relatively stable. Since 1958, the planar shape of the deep trough near the bridge has not changed much. In particular, the right side slope of the main trough has better stability. Over the past 40 years, the right side of the deep trough within 1 km upstream and downstream of the bridge has been -10m and -20m. The amplitude of the depth contours is all within 300m. The bridge section is one of the most stable sections of the Yangtze River below Jiangyin.

2. Research on the stability of the riverbed in the bridge area shows that there is a silty clay layer between -10m and -26m in the area near the south bank of the bridge area. The average starting flow velocity of this soil layer is 2.2m/s. , is more than 2 times greater than the starting flow velocity of other layers, and has strong resistance to erosion. In addition, the water flow near the bridge axis is smooth, and the rising and falling tide paths are basically the same. These all play a positive role in the stability of the south bank slope. effect.

3. The moving bed physical model test shows that the riverbed changes caused by the bridge project are only near the bridge axis, with the main deep channel riverbed being eroded and the side beaches being silted. The construction of the bridge will not change the existing river regime and will not have any obvious adverse impact on the existing docks and dedicated waterways on the south bank.

4. Relevant functional departments and research units have unanimously concluded that the river situation at the Xuliujing node section (i.e. the bridge section) is stable, and that the Xuliujing river section will be strengthened in the future. The node function will be beneficial to the construction of the Sutong Bridge, and will be beneficial to the regulation of the Baimaosha River section, the management of three sands, the comprehensive development of the Yangtze River Estuary, and the construction of the deep-water channel of the Yangtze River Estuary.