温州瓯江北口大桥主桥为(215+2×800+275) m的三塔双层钢桁梁悬索桥,中塔采用沉井基础,沉井顶平面尺寸为66.0 m×55.0 m,总高68.0 m.为了解沉井定位着床期间河床的局部冲刷情况,通过封闭水槽试验研究沉井定位着床期间的河床局部冲刷深度及冲刷形态.结果表明,河床局部冲刷非常严重,沉井下沉时会产生倾斜扭转.为确保沉井平稳安全着床,采用抛填防护层的方法对沉井周围20 m范围内的河床进行预防护施工,防护层包括反滤层(厚0.8m,采用级配砂)和护面层(厚2.2m,采用粒径为5 cm的碎石).预防护施工后,经现场检测可知,着床后沉井中心偏差11 cm,平面扭转0.21°,均小于允许值,沉井几何姿态控制良好.说明河床预防护技术可以有效减小局部冲刷,保证了沉井着床精度.%The main bridge of the Oujiang River North Estuary Bridge in Wenzhou is a tripletower and double-deck steel truss girder suspension bridge with span arrangement (215 +2 × 800+ 275) m.The foundation for the middle tower of the bridge is the open caisson that has the plan dimensions of 66.0 × 55.0 m at its top and total height of 68.0 m.To understand the local scouring situations of the riverbed at the time the caisson was landed and positioned there,the local scouring depth and scouring patterns of the riverbed during the landing and positioning of the caisson were researched through the closed water tank tests.The results of the research reveal that the local scouring of the riverbed is very severe and the caisson may title and turn about at the early stage as it is landed onto the riverbed and sinks down.To ensure that the caisson can be landed and can sink down stably and safely,the 20-m range of the riverbed around the caisson is pre-protected by the method of riprapping the protection layers.The protection layers incorporate the reverse filtering layer (the graded sand of 0.8 m thick) and the surface protection layer (the cracked stones of particle size of 5 cm and 2.2 m thick).After the construction of the pre-protection layers,the filed inspection tells that the offsetting of the center of the caisson landed onto the riverbed is 11 cm and the plan turning of the caisson is 0.21°,which are all less than the allowable values and the geometric posture of the caisson is well controlled,showing that the pre-protection techniques herewith can effectively reduce the local scouring and ensure the precision of the landing and positioning of the caisson.
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