中文摘要：

提出了以变径水泥土搅拌桩加固软土层位于中间的多层软弱地基的方法.通过现场试验介绍了变径搅拌桩的施工方法、桩身质量检测,并通过单桩荷载试验研究了变径搅拌桩的单桩承载力特性.现场试桩开挖表明,该方法能够施工形成中间截面扩大的变径搅拌桩.由于采用了双向搅拌工艺,保证了水泥掺量,提高了搅拌均匀性,变径搅拌桩的桩身强度大大高于常规搅拌桩.单桩荷载试验结果表明,变径搅拌桩的单桩极限承载力是常规搅拌桩的3-5倍.基于变径搅拌桩的单桩破坏模式,提出了变径搅拌桩的单桩极限承载力计算方法,其计算结果与荷载试验结果比较吻合.

英文摘要：

The diameter-varied soil-cement deep mixed column is developed to improve multi-layered soft ground with the soft layer in the middle.The column installation and column quality measurement are introduced,and the bearing behavior of single diameter-varied deep mixed column is investigated through field loading tests.The excavation of testing column indicates that the proposed method for diameter-varied deep mixed column installation is effective.As the double mixing technology is used,the cement content mixed in the column is ensured and the mixing uniformity is improved;thus the column strength of diameter-varied deep mixed column is much higher than that of conventional deep mixed column.The results of loading tests on single column indicate that the ultimate bearing capacity of single diameter-varied deep mixed column is 3 to 5 times that of conventional deep mixed column.Based on the failure model of single diameter-varied deep mixed column,the calculation method of its bearing capacity is presented,and then the calculation method is verified by the results of loading tests.