Key Foundation Construction Techniques for South Anchorage of Xianxin Road Changjiang River Bridge in Nanjing
The Xianxin Road Changjiang River Bridge in Nanjing is a two-tower,earth-anchored suspension bridge with a main span of 1 760 m.The south anchorage is supported by a circular diaphragm wall foundation measuring 65 m in the outside diameter,with wall thickness reaching 1.5 m.The foundation measures 60 to 63 m deep,socketed more than 3 m into the slightly decomposed conglomerate.To ensure the formation accuracy and quality of trenches for the diaphragm walls,the sidewalls of trenches were strengthened by the soil mixing cutter(SMC)method before the construction of diaphragm walls,to ensure the alignments and improve waterproofing capacity of the diaphragm walls in soft ground.Afterwards,the diaphragm walls corresponding to phase-Ⅰ and phase-Ⅱ trenches,respectively were constructed in sequence.The inner cells of the diaphragm wall foundation were excavated in layers by a top-down method,parallel with the layer-by-layer implementation of linings,to create an integral shoring system till the pit was excavated to the design elevation.Subsequently,the bottom slabs,in-fill concrete cores and concrete bulkheads of the foundation were cast by a bottom-up method.Three types of cranes were compared,and the mobile grabbing cranes were selected for soil disposal.An integral soil disposal system that consisted of the grabbing cranes,loaders and soil deloading guiding devices were established,which effectively improved the excavation efficiency in deep foundation pit and ensured a clean and organized environment at the construction site.The cast of the bottom slabs,in-fill concrete cores and massive concrete bulkheads were performed using the tower cranes,anti-segregation pipes and concrete pumps,to accelerate the layered casting of mass concrete components of large deep foundations.
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