浅覆盖层钢围堰区域泥面冲刷模型试验及防护措施

Model Test of Mud Scour in Steel Cofferdam Region with Shallow Overburden

沌口长江公路大桥主桥为主跨760m的双塔双索面钢箱梁斜拉桥,3号墩处上部覆盖层多为易冲刷的细沙,有效覆盖层浅,加之钢围堰尺寸巨大,围堰区域泥面存在局部冲刷问题。采用系列模型延伸法,在40m(长)×5.0m(宽)水槽中进行冲刷模型试验,发现钢围堰沉放到位后,遇到较大水流时在围堰周围会产生明显的局部冲刷(前冲后淤形态)。提出了堆码4圈沙袋的冲刷防护方案,通过冲刷防护模型试验验证了该方案的有效性。根据试验结果并结合施工期水深、地质等不确定因素,现场采取在围堰四周抛填厚70~80cm的碎石层,在碎石层上堆码4圈沙袋进行冲刷防护,同时设置支撑桩防止围堰超沉。

Themain bridge of Zhuankou Changjiang River Highway Bridge is a two-pylon steel box girder cable-stayed bridge with amain span of 760m. The stay cables are fanned out in double cable planes. The overburden on the top of the pier No.3 is composedmostly of the fine sands, the effective overburden is shallow and the steel cofferdam has a giant body, as a result, there exits localmud scour in the region of the steel cofferdam. The extensionmethod of serialmodels was adopted, and the scourmodel test was carried out in the water flume with a dimension of 40m(length)×5.0m(width). When the steel cofferdam was lowered into position, obvious local scours(in themode of front scouring and rear silting) were observed around the cofferdam with big water flows. The scour protection scheme of piling four circles of sand bags was proposed, and the effectiveness of the scheme was verified by the scour protectionmodel test. According to the test results and the uncertain factors during the construction, like water depth and geological conditions, a 70 to 80 cm thick rip-rap layer was formed around the steel cofferdam, on which four circles of sand bags were piled for scour protection, at the same time, supporting piles were driven to prevent the cofferdam from over sinking.