The large-diameter very long piles are usually constructed by air-lift reverse circula-tion method and the submergence ratio is an important drilling parameter .In order to control the law of submergence ratio variation during the air-lift reverse construction of large diameter very long piles ,the air-lift reverse construction of the 132 .5 m long bored piles with a diameter of 3 .0 m of the left bridge of Yongjiang River Bridge was taken as the study background .Based on the principle of air-lift reverse circulation ,the burying depth of wind package was calculated ,and com-bined with the results of the trial drilling ,the rearrangement scheme for the wind package was made ,according to w hich the drilling construction conducted and the relations among the submer-gence ratio ,burying depth of the wind package ,air pressure and drilling depths were gained .The results indicate that to make the slurry produced during the air-lift reverse circulation flow up-wards ,the wind pressure must reach a certain value under the condition that the burying depth of the wind package is fixed ,or the burying depth of the wind package must be smaller than a certain value under the relevant wind pressure .The initiation of the air-lift reverse circulation was dictated by the submergence ratio ,only when the submergence ratio is greater than 0 .4 can the air-lift re-verse circulation construction start .As the drilling depth increases ,the submergence ratio steadily rises ,but w hen reaching a certain degree ,the submergence ratio does not continue to increase but tends to be stable .And the application of hob drill showed no effect on the submergence ratio .%桥梁大直径超长桩通常采用气举反循环钻进施工，沉没比是重要的钻进参数。为了解大直径超长桩气举反循环施工沉没比的变化规律，以甬江左线特大桥矱3．0m、长132．5m的钻孔灌注桩气举反循环施工为背景进行分析。根据气举反循环原理，计算风包埋深，并结合试钻结果制定风包倒换方案，采用该方案进行钻进施工，获得沉没比、风包埋深、风压、钻进深度之间的关系。结果表明：为实现气举反循环泥浆上返，在风包埋深确定的情况下风压必须达到一定值，或在相应风压下风包埋深必须小于一定值；气举反循环开始时间由沉没比决定，沉没比大于0．4时才有可能进行；随钻进深度的增加，沉没比持续增大，但到一定程度后沉没比不再增加而是趋于稳定；换滚刀钻头对于沉没比并无太大的影响。
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