桥墩振动对其局部冲刷的影响

为了探究桥墩振动对其局部冲刷的影响,以圆柱型桥墩为例,开展了不同泥沙底床条件下的振动桥墩局部冲刷水槽试验。结果表明,在振动载荷下,对于中值粒径分别为14.42μm、31.75μm和85.92μm的细颗粒底床,当振动强度从0增大至3.72,最大冲刷深度和最大冲刷半径均随之增大;中值粒径为14.42μm的泥沙底床最大冲刷深度增幅最大达910%,且粒径越大,增幅越小。对于中值粒径为260μm的粗颗粒底床,当振动强度从0增至2.31,最大冲刷深度降低了37.50%,而最大冲刷半径增加了38.37%。因此,桥墩的振动对其局部冲刷有着重要影响,且对细颗粒底床和粗颗粒底床的影响不同。桥墩振动导致有黏性的细颗粒泥沙发生流变从而加剧了其局部冲刷;而无黏性的粗颗粒泥沙受到振动作用而加密,其局部冲刷削弱。提出了考虑桥墩振动的局部冲刷深度计算公式,其理论计算值与实测值相对误差在±20%的数据达87.5%,能够为涉水桥梁基础埋深的设计提供更合理的计算依据。

Effect of pier vibration on the local scour

To explore the influence of pier vibration on its local scour，a series of experiments of local scour around the vibrating cylindrical pier on different sediment beds are conducted in a flume. The result shows that for fine sediment beds with the median diameters of 14. 42 μm， 31. 75 μm and 85. 92 μm， the maximum scour radius depth and scour radius increase when the vibration strength increases from 0 to 3. 72，the amplification of the maximum scour depth is up to 910% on the 14. 42 μm-median diameter sediment bed and the larger the sediment particle size， the smaller the amplification of the maximum scour radius depth. For coarse sediment bed with the median diameter of 260 μm， the maximum depth reduces by 37. 50% and the maximum scour increases by 38. 37% when the vibration strength increases from 0 to 2. 31. Therefore， the vibration of pier has an important influence on its local scour，and the effect on cohesive fine sediment bed is different from that on non-cohesive coarse sediment bed. The local scour of pier on fine sediment bed is intensified as a result of sediment rheology while it is weakened on coarse sediment bed by vibration compaction. In addition，a formula to calculate local scour depth considering the vibration of the pier is proposed. The data is up to 87. 5%，which relative error between the theoretical calculation and the measured data is ±20%. It can provide a more reasonable calculation basis for the design of pier buried depth.