Experimental Study On Local Scour Protection Measures Of Pier Foundation

Local scour of pier foundation is an important cause of bridge flood damage.The hydraulic characteristics and scour evolution process around pier are complex,and there are many influencing factors,but there are few indoor experimental studies on local scour protection measures of pier.In this paper,two protection measures for local erosion protection of rectangular pier and double row cylindrical pier are tested.At the same time,combined with theoretical analysis and numerical simulation,the erosion evolution process,characteristics and protection effect under the protection measures are studied.Aiming at the common rectangular piers and double row cylindrical piers in rivers,this paper selects the retainer protection in active protection and the gabion protection in passive protection for cross test,and carries out model control test by changing the near flow velocity of water in the test tank,the size of retainer and Gabion The influence of protection method and pier type on the local scouring evolution process of pier and the shape of scouring pit.The test takes the maximum scouring pit depth as the index to quantitatively analyze the protection effect of retainer and Gabion when protecting double row cylindrical pier and rectangular pier.The test conclusions mainly include:(1)both retainer and Gabion can effectively reduce the maximum scouring depth of rectangular pier and double row cylindrical pier,and their scouring depth reduction rate will not change greatly with the change of flow velocity.Retainer and Gabion are reliable as local scouring protection measures for rectangular pier and double row cylindrical pier;(2)When the rectangular pier is protected,because the range of horseshoe vortex around the rectangular pier is larger than that of the cylindrical pier,the sediment outside the retainer and Gabion will also be washed by horseshoe vortex,and the protective effect of the retainer and Gabion is not different;(3)When protecting double row cylindrical piers,the most important factor affecting scouring is the wake vortex behind the pier of the upstream pier,and the sediment under the downstream pier retainer is easy to be hollowed out.Because the gabion can produce coordinated deformation with the development of the scouring pit,it always covers the sand bed to enhance the ability of the sand bed to resist the shear stress of water flow.The rough surface of the gabion can also retain sediment and prevent sediment The function of moving downstream,so its protective effect is better than the retainer.It can be seen that gabions should be preferred when protecting local scour of double row cylindrical piers;(4)The size of the retainer and Gabion is an important factor affecting the protection effect.When the size of the retainer and Gabion is increased from 0.5d to D,the protection effect of the retainer and Gabion is significantly improved.When the size of the retainer and Gabion is increased from D to 1.5D,the improvement rate of the protection effect becomes slower.In practical application,setting the size of the retainer and Gabion to D can be the maximum when meeting the actual demand Reduce the maximum scour depth of pier.A three-dimensional flow and sediment model is established by using FLOW-3D software,based on RNG k-ε For the turbulence model,the local nested grid and the favorite grid method unique to the software are used to discretize the geometric model.The variation characteristics of local scour pits of piers with different protection methods are analyzed and compared with the test results.The comparison results show that the numerical simulation is in good agreement with the test results.