大跨度飞燕式系杆拱桥桩基础施工工法研究——以合江长江公路大桥为例

Foundation Construction Method for a Long-Span Feiyan Tied Arch Bridge-Using Hejiang Changjiang Highway Bridge as an Example

以四川合江长江公路大桥桩基工程为研究对象,开展了大跨径飞燕式系杆拱桥桩基础施工工艺研究,并就施工过程中的重难点进行了分析。结果发现:(1)钻进过程中应根据土层的坚硬程度确定合适的冲程,软土地层宜选用1~2m冲程,中密土选择2~3m冲程,密实土应设置3~5m冲程,但是最高不能超过6m;(2)软硬互层地层或者存在明显层理角度的地层钻进应低垂快打,并且在孔内投入坚硬片石形成稳定平台;(3)清孔验收应确保孔内循环抽出的泥浆均匀无杂质,用手揉搓无2~3mm大的固体颗粒;泥浆比重1.03~1.10;泥浆含砂率<2%;泥浆粘度17~20s,沉渣厚度<80mm,同时灌注前应进行二次验孔和清孔;(4)由于大桥所处的水文环境特殊,应结合水文条件动态调整排水施工工艺,当地下水位深,补给量不大时,采用单桩桩内抽水;当地下水补给来源丰沛,水位较浅时,应多桩同时抽排来降低地下水位;若桩基深度不大,可以考虑在场地四周设置排水措施。

The case history of foundation construction methods for the long-span Feiyan tied arch bridge for Hejiang-Changjiang highway project is presented in this paper.The key aspects during the caisson installations are also evaluatedin the paper.The following results are found:1)For the striking drilling method,the appropriate stroke should be determined based on the stiffness of various soils.The stroke setting for the soft or loose soils should be 1.0to 2.0meters;2.0to 3.0meters for medium soils and 3.0to 5.0meters for the dense or hard soils.However,the maximum stroke should not be higher than 6.0meters.2)The low stroke and fast striking method should be used for alternating of soft and hard soil stratigraphy,hard stone pieces can be dumped into the borehole to form a firm platform in the hole.3)for the quality acceptance,the circulated slurry pumped from the borehole should be uniform and without debris;No solid particles with dimension 2to 3mm by using the hand touch;the specific gravity of the slurry should be between 1.03and 1.10;sand content in the slurry should be less than 2%;the viscosity should be between 17and 20s;the thickness accumulated at the bottom of borehole should be less than 80mm.At the same time,borehole cleanness examination and cleaning should be performed immediately before the concreting work.4)due to the special hydrological conditions at the bridge site,the disposal of the drilling fluid should be arranged with the variation of the hydrological conditions dynamically:When the groundwater level is deep and the groundwater recharge to the borehole is not high,single borehole pump disposal can be used,however,when the groundwater recharge to the borehole is large,and the groundwater water level is shallow,multiple borehole pump disposal method can be used.If the caisson length is not large,drainage ditches can be used around the caisson locations.