中文摘要：

为了经济、有效地处理软土层位于中间的成层软弱地基,提出了变径搅拌桩加固方法,在高压缩性土层中采用较高的桩体面积置换率,在中等压缩性土层中采用较低的桩体面积置换率,从而形成桩体面积置换率随土层性质变化的成层复合地基。在同一场地建立了变径搅拌桩和常规搅拌桩处理区,通过现场试验对比分析了路堤荷载作用下变径搅拌桩和常规搅拌桩复合地基的工作性状,包括桩土应力、超静孔隙水压力、地表沉降和坡脚深层水平位移。现场试验结果表明：在处理区面积和填土高度相近的情况下,变径搅拌桩处理区比常规搅拌桩处理区节省了14.6%的水泥用量,并取得了与常规搅拌桩处理区相同的加固效果,具有更好的经济效益。

英文摘要：

The variable diameter deep mixing method was proposed so as to economically and efficiently treat a layered soft ground where the soft layer is at the middle depth.A relatively high column area replacement ratio was used for the high compressive soil layer and a relatively low column area replacement ratio was used for the medium compressive soil layer,which could result in a layered composite foundation where the column replacement ratio varied with soil layers.Two testing sections of variable diameter deep mixed column and common mixed column were established on the same site.Field tests were conducted to analyze their engineering performance under embankment load,including stress of column and soil,excessive pore water pressure,ground settlement and lateral displacement under the embankment toe.Field test results show that when the treated site in the areas and embankment heights are similar,the treated section of variable diameter deep mixed column which gets the same consolidation effect can save 14.6% cement than that of the conventional one,and it can be more economically effective than that of the conventional deep mixing method for layered soft ground improvement.