中性网格对圆桩局部冲刷的水动力弱化及防护效果分析

Protection measure of neutral lattice against local scour around circular pile

针对水下桩墩的局部冲刷问题,提出一种适用范围广、防冲促淤效果显著的防护措施。该防护措施把一种相对密度略大于水、几何特征特殊的中性网格结构完全覆盖在冲刷坑或可能出现冲刷坑的床面上,以减弱冲刷坑内水动力,促进泥沙落淤,达到减轻局部冲刷的目的。通过数值模拟和水槽试验探讨了中性网格结构对圆桩周围冲刷坑内水动力及床面形态的影响,并研究了网孔尺寸对防冲促淤效果的影响规律。结果表明:该中性网格结构能显著减小局部冲刷坑内的流速,有效抑制局部冲刷,且对桩前来流来沙的影响微弱。孔径比7.7的网格防护结构可以使无黏性沙床上圆桩的局部冲刷深度减少92%,已存在的冲刷坑则可被修复73%。这些研究成果为桩墩局部冲刷防护提供一种新的思路。

In order to solve the problem of the local scouring around pile and pier,a protective measure with wide application,remarkable effect of erosion protection and high cost performance was proposed.It uses a neutral lattice with relative density close to water and special geometric characteristics to completely cover the scour pit or the bed surface where the scour pit may appear,so as to weaken the hydrodynamic force in the scour pit,promote sediment deposition,and reduce the local scouring around piles.By carrying out numerical simulations and flume experiments,the influences of the neutral lattice on the hydrodynamic characteristics in the scour pit and the bed surface morphologies around circular piles were analyzed,and the influences of the lattice thickness and lattice size on the anti-scouring and deposition promotion effect were studied.The results show that the neutral lattices can remarkably reduce the flow velocity in the local scour pits,effectively inhibit local scour and hardly affect the approach flow.Furthermore,under the water and sand conditions of the test,when the ratio of mesh size to sediment particle size is 7.7,the local scour depth of the circular piles can be reduced by 92%,and the existing scour pits can be repaired by 73%.These research results provide a new idea for the protection measures of local scouring around piles and piers.