鳊鱼洲长江大桥北汊航道桥N15号墩超长桩施工技术

Construction Techniques for Super-Long Piles of Pier N15 of North-Branch Navigation Channel Bridge of Bianyuzhou Changjiang River Bridge

新建京港高铁安九段鳊鱼洲长江大桥北汊航道桥为(49+2×140+49)m单箱六室预应力混凝土箱梁斜拉桥。桥位地质条件复杂,N15号墩下伏巨型溶腔,设计采用15根2.5 m超长桩基础,桩身穿过溶腔进入溶腔底板持力层,因岩溶复杂,成孔难度大。为确定桩底标高,掌握溶腔发育情况,指导成孔施工、研究并确定岩溶处理方案,在逐桩地质钻探基础上,对巨型溶腔进行三维地质CT物探,建立BIM三维地质模型,确定了超长桩桩底标高,其中5根桩有效桩长超过100 m,最大钻孔深度达152.15 m。施工中,采用重载钻孔平台、KTY5000大型旋转钻机、气举反循环法成孔;应用桩周预注浆稳固、护筒复打跟进、孔内抛填黏土和片石造壁、大直径高强长导管水下混凝土灌注等技术,完成了超长桩基施工。成桩后,经超声波检测发现,桩身质量优良,完整性好,全部为Ⅰ类桩。

The north-branch navigation channel bridge of Bianyuzhou Changjiang River Bridge carrying the Anqing-Jiujiang Section of the newly-built Beijing-Hong Kong High-Speed Railway is a cable-stayed bridge with span arrangement of 49,2×140 and 49 m.The superstructure consists of six-cell prestressed concrete box girders.The pier N15 is supported by 15 piles of 2.5 m diameter.During the construction,the piles had to pass through a karst cave to reach the bearing strata beneath.The complex karst condition made the borehole formation quite challenging.The base elevation of piles and the karst growth condition were surveyed,to direct the borehole formation,study and determine the karst treatment solution.Based on the pile-by-pile geological drilling,the 3D geological CT geophysical prospecting was carried out for the karst cave.The BIM geological model was established to calculate the base elevations of the super-long piles,and the effective lengths of 5 piles exceeded 100 m,and the maximum drilling depth reached up to 152.15 m.During the construction,a heavy-duty drilling platform was built,the KTY5000 rotary drilling rig was employed and the reverse circulation borehole formation method was used.The piles were pre-grouted along the perimeter to ensure stability,the repeated driving of steel casings timely ensued,clay and rip raps were filled into the borehole to create walls,and the tremie concrete was cast using long large-diameter high-strength conduits.After completion,the ultrasonic testing showed that the piles were all intactⅠ-grade piles,with sound quality.