Experimental Study On The Influence Of Railway Piers On The River Flow In Jiangning Center And The Improvement Measures

The construction of railway bridge and other wading infrastructure is bound to cause the change of river level and flow pattern in the section of the project,which will reduce the river flow capacity and adversely affect the flood discharge and river regime.Due to the action of bridge piers,the water level of the river is raised,and vortex and local scour are generated around the bridge piers,which makes the flow field of the upstream and downstream of the bridge piers very complicated.In this paper,the influence of bridge piers on river flow in jiangning central river and improvement measures were studied by using model test method and DPIV surface flow field measurement system based on the research background of the new inter-city railway crossing the central river along the southern Yangtze river in jiangsu province.The influence of various improvement measures on river flow pattern,water level change and velocity near the bridge piers were emphatically analyzed.The main research contents and results are as follows:(1)From the model test range,similarity criteria,model materials and layout,measuring instruments and measuring methods,the physical model of the south river railway crossing the central river project was designed,and the DPIV surface flow field measurement system was used to collect the data of the model plane flow field(2)Simulate the current river course through physical model test,determine the test conditions and test methods,and study the river flow characteristics under the current condition.The single-hole arch bridge in the present river channel has a great influence on overflow and river regime.Under the confluence condition,the flow state is basically stable except that the downstream flow of single-hole arch bridge has short deflection.After the water flows through the single-hole arch bridge in the diversion condition,multiple vortex zones are formed in the central river 2.(3)In the current situation,three new railway piers are built in the river.Measures should be taken to improve the flood discharge capacity of the river and the flow pattern of the river.The section compensation method should be adopted to increase the flood discharge area of the river.The results show that the overcurrent plane compensation is satisfied in central river 1 and central river 3,but the water level in central river 2 is slightly higher than the current river level,and the design scheme of central river 2 needs to be further optimized.The main stream in central river 2 bends and swings,and circular choke zone is generated near the bridge pier,and the direction of downstream flow changes(4)On the basis of the compensation design test scheme,the optimized design scheme was proposed for cutting and straightening the river channel at 2 central river and changing the bank slope to an upright wall,and the experimental study on the river flow characteristics of the scheme model was carried out,and the experimental results of the two schemes were compared and analyzed.The results show that the optimized design scheme can solve the flood control problem caused by the newly built piers.The main flow in central river 2 is relatively straight,the circular choke area generated by the bridge pier is reduced,and the downstream flow direction is optimized,which is close to the current channel shape.(5)The span adjustment and shoreline adjustment measures were adopted to study the flow pattern at 2 central rivers and analyze the river surface layer flow field.In this paper,the transverse-adjusting scheme adopted in central river 2 has no obvious effect on the improvement of flow pattern,and the influence of single-hole bridge and the channel boundary convection pattern behind the single-hole bridge is great.The shore-line adjustment scheme can obviously improve the flow regime,weaken the phenomenon of the original river bank and disappear the phenomenon of the secondary river bank.The research on the influence of railway bridge piers on the river flow in jiangning central river and the improvement measures carried out in this paper can provide improvement measures and Suggestions for the design and maintenance of the railway crossing the central river along the south river,which is of great significance to the improvement of flood control capacity and flow pattern of the central river.At the same time,it can provide reference for similar projects that need to take improvement measures when water flow is affected by buildings in the water.