广佛肇高速公路北江大桥施工关键技术

Key Construction Techniques for Beijiang River Bridge of Guangzhou-Foshan-Zhaoqing Expressway

广佛肇高速公路北江大桥主桥为(115+215+115)m连续刚构桥。主梁为单箱单室箱梁,顶板宽16.25 m,底板宽8.15 m,梁高4.2~12.8 m,设计采用C60混凝土。基础均采用钻孔灌注桩和分离式承台,主墩为双薄壁墩,过渡墩为花瓶墩。针对桥址处河床无覆盖层,且存在串珠状溶洞地质条件,主墩钻孔桩位处的溶洞采用钢护筒跟进、片石黏土回填及混凝土回填等方式组合处理。针对裸岩地质条件,33号主墩分离式承台采用连体式错位型钢板桩围堰配合旋挖钻铣槽法进行施工;32号过渡墩采用钢板桩打入强风化岩一定深度,对基底岩溶裂隙进行注浆处理后,并以岩石作为支撑结构进行施工。为减小混凝土箱梁开裂风险,通过多种参数配合比试验,研制低收缩、低徐变C60混凝土,大幅提升混凝土工作性能、力学性能及耐久性能,且经济效益明显。

The main bridge of Beijiang River Bridge carrying a section of the Guangzhou-Foshan-Zhaoqing Expressway is a continuous rigid-frame bridge with a main span of 215 m and two side spans of 115 m.The superstructure consists of single-cell box girders made from C60 concrete.The top,bottom and depth of the box girder are 16.25 m,8.15 m,and 4.2-12.8 m,respectively.The main piers are double-thin-walled piers,while the transition piers are vase-shaped piers,and both the main and transition piers are mounted on separated pile caps that are supported by bored pile foundations.To address the challenging geological conditions,including the riverbed with no overburden and beaded karst caves,steel casings together with riprapping,and backfilling with clay and concrete were applied to treat the karst caves for the pile foundations.To construct the separated pile cap of main pier No.33,the tandem and staggering type steel sheet pile cofferdam was built up for shoring and rotary drilling rigs were employed for slotting.During the construction of the transition pier No.32,the steel sheet piles were driven into a depth of the severely-weathered rock,the crevices in the bed rocks were grouted,and the remedied rock then acted as supporting structure for the subsequent construction.To reduce the cracking risk of the concrete box girders,multiple mix proportions were tested and compared,and a type of C60 concrete featuring low shrinkage and creep was developed,which improved the workability of the concrete as well as the mechanical property and durability of the box girders,achieving good economy.