刚柔性桩复合地基加固双层软弱地基现场试验研究

为研究路堤荷载下刚柔性桩对深厚双层软弱地基的加固效果及其桩土荷载传递规律，结合连云港港某铁路软基处理工程，采用带帽预制方桩和带扩大头的双向搅拌粉喷桩联合加固，对路堤填筑过程及预压期内地表沉降、桩土差异沉降、深层水平位移、超静孔隙水压力、桩土应力比以及桩土荷载分担的变化规律进行了分析。结果表明：载荷试验中复合地基桩土应力比随外荷载增加而增加；地基变形发生在填土期，预压期内沉降变形继续并逐渐趋于稳定；填土荷载向刚性桩及搅拌桩桩顶集中，刚性桩桩顶应力增长较快；面积置换率为22.2%的预制方桩（含桩帽）承担了56.2%的荷载，但其承载力只发挥了不到18%；面积置换率和土质条件是桩土荷载分担比的主要影响因素。

Field test of double-layered soft ground improved by rigid-flexible composite pile foundation

To limit the settlement of double-layered soft ground formed by the dredging blow filled soft soil and the natural deposited soft soil, precast square pile and deep mixing column with expanded head are combined to improve the ground. A field test was carried out in Lianyungang port railway project. The ground settlement, differential settlement between pile and soil, layered soil settlement, deep horizontal displacement, pore water pressure and loading ratios between pile, soil and column were studied. The test results show that the column-soil stress ratio of composite foundation increases with the external loadings. The foundation deformation occurs in the filling stage, and the settlement in the preloading period continues and tends to be stable. Filling load transfers to the precast square pile and T-shape deep mixing column by 56.2% and 20.4% of the total loadings, respectively, the replacement ratio and soil condition is the main influential factor for the proportion of loadings.