郑州黄河公铁两用桥主桥长大钻孔桩施工技术

Construction Techniques for Long and Large Bored Piles of Main Bridge of Zhengzhou Huanghe River Rail-cum-Road Bridge

郑州黄河公铁两用桥主桥为两联钢桁梁结构,主桥2号~5号墩位于黄河主河槽中,均采用24根直径为2.0 m的钻孔灌注桩群桩基础。施工中钢护筒在工厂制造后运至墩位,吊装到定位导向架中下沉到位;钻孔施工采用PHP泥浆,减压钻进,保持重锤导向作用,严格控制泥浆比重在1.08~1.10,保持护筒内泥浆面高于黄河水位2~3 m,以防止塌孔;通过清孔、检孔后,进行钢筋笼施工,钢筋笼在工厂采用长线法制造,用专用的扁担梁起吊下沉;桩基采用C40水下混凝土,采用单根垂直导管法灌注。通过合理的施工方法、严格的施工控制,在桩基直径大、地质条件差的情况下,主桥Ⅰ类桩比例为99.6%。

The main bridge of Zhengzhou Huanghe River Rail-cum-Road Bridge is a continuous steel truss girder structure arranged in two continuous units.The piers No.2～No.5 of the bridge stand in the main channel in the river and are all supported on the group pile foundations,each made up of 24 nos.of 2 m bored piles.In the construction,the steel casings for the piles were fabricated in shop,delivered to the pier sites where the casings were then lifted to the positioning and guiding frames and sunk down in place.To prevent collapse of the bored holes,the boring construction was carried out by a series of measures of utilizing the PHP slurry and pressure-reduction boring,maintaining the guiding effect of heavy hammer,strictly controlling the specific weight of the slurry within 1.08~1.10 and keeping the slurry top inside a casing 2~3 m above the water levels of the river.The installation of reinforcement cages came after the bored holes were cleared off and inspected.The cages were fabricated in shop by the long line match method and then lifted into the bored holes by the special spreading beams.The C40 tremie concrete was used for the bored pile foundations,which was cast by the individual vertical tremie duct.By the application of the rational construction methods and strict construction control,the ratio of type I piles for the main bridge reached 99.6% even under the construction conditions that diameters of the piles were great and the geology was poor.