Experimental Study Of Local Scouring Of Tandem Double Bridge Piers Under Ice Cover And Ice Jam Conditions

The presence of bridge piers will cause changes in the water flow structure leading to the generation of local scouring,local scouring will damage the foundation of the bridge piers thus causing damage to the piers,the generation of ice caps ice plugs will exacerbate this phenomenon.Therefore,based on the flume test,an experimental study on the local scouring of tandem double piers under ice cover conditions and the distribution of balanced ice plug thickness of tandem double piers under ice plug conditions was carried out using different flow rates,water depths,pier spacing and other conditions.The main research results and innovative findings are as follows:(1)Under ice cover test conditions,when the pier spacing ratio L/D = 2(where,L= the pier spacing distance,and D = the pier diameter),the rear pier(the downstream one)will intensify the horseshoe vortex process behind the front pier,and the scour depth around the front pier will increase by about 10%.As the pier spacing ratio L/D increases,the scour depth around the front pier will gradually decrease.When the pier spacing ratio L/D = 5,sediment scoured around the front pier begins to deposit between these two piers.Results also showed that the existence of the rear pier will lead to an increase in the length of scour hole but decrease in the depth of scour hole around the front pier.The local scour around the front pier interacts with the local scour of the rear pier.The maximum scour depth of the scour hole around the rear pier increases first,then decreases and increases again afterward.When the pier spacing ratio L/D = 9,the scour depth around the rear pier is the least.With an increase in the pier spacing ratio,the influence of the local scour around the front pier on the local scour around the rear pier gradually decreases.When the pier spacing ratio L/D is more than 17,the scour around the front pier has hardly influence on that around the rear pier.The scour depth around the rear pier is about 90% of that around the front pier.(2)Under ice jam test conditions,unlike straight channel ice jam,which are transported from upstream to downstream along the midline position of the straight channel,curved channel ice jam are transported from upstream to downstream along the convex bank position;Unlike the accumulation of ice plugs in straight troughs,ice jam in curved troughs tend to accumulate and thicken at the entry and exit bends,and when the thickness reaches a certain level,the whole body is transported downstream,after which it continues to accumulate at the entry bend of the curved trough,forming a dynamic equilibrium of ice jam.The same as the results of the straight tank test,in the curved tank test,the greater the flow rate,the smaller the equilibrium ice jam thickness when other conditions are the same.The same as the straight channel test results,in the curved tank test,in other conditions are the same,the greater the water depth,the greater the thickness of the equilibrium ice jam.In the curved channel test,when other conditions are the same,the pier diameter is different,the equilibrium ice jam thickness on the left bank of the curved is affected by the pier diameter,the larger the pier diameter,the equilibrium ice jam thickness is slightly larger;the equilibrium ice jam thickness on the right bank of the curved channel is basically not affected by the pier diameter.