弱感潮河段抛石漂移距现场试验研究

Field experiment study on throwing distance of riprap in weak tidal reach

长江南京以下12.5 m深水航道口岸直水道整治工程位于扬中河段,工程离岸远、水深大、水流实时变化、轴线长,潜堤施工抛石落点预测尚存在难题。在扬中河段开展涨、落潮条件下的抛石漂移距现场试验,获得涨、落潮条件下现场抛石漂移距公式,并应用于口岸直水道鳗鱼沙潜堤施工中。结果表明,抛石漂移距受潮流加速度影响,加速时段的漂移距大于匀速时段,减速时段的漂移距小于稳定时段,潮流加速度小于1.5×10^-3m/s^2时,全潮流过程可采用统一漂移距系数0.892;施工过程中群体抛石中值粒径单块石漂移距小于4.5 m时,可采用群体抛石中值粒径来估算群体抛投平均漂移距,实测群抛抛石成堤断面与设计断面吻合较好。为弱感潮河段水上抛石落点精准预测提供依据。

The Kouanzhi 12.5 meter-deep-water channel regulation project is located in the left branch of the Yangzhong River and the main construction work consists of ripraps.The project area is characterized by long distance offshore,deep water depth,changing flow velocity range,etc.It is difficult to accurately predict the riprap throwing point at the construction site.Thus we carry out a field experiment for riprap throwing distance,and obtain a formula for predicting the throwing distance at the period of the rising and falling tide,which is further used in Manyu-Shoal submerged-dike construction.The results show that the riprap throwing distance is influenced by the tidal current acceleration,which becomes larger during current velocity increasing period while smaller during current velocity decreasing period.Overall,when the current acceleration is smaller than 1.5 × 10^-3m/s^2,the throwing distance prediction formula coefficient can be taken as a uniform value of 0.892 for the whole tidal process.When the throwing distance of the group’s median riprap is smaller than 4.5 m,the averaged throwing distance of riprap group can be estimated by proposed formula with a median diameter of the group chosen.The measured dike section profile agrees well with the designed one.This work provides a good method for accurate throwing distance prediction in tidal river.