分级施工河堤下高灵敏性黏土的强度增加

软黏土地基由于其含水量高、孔隙比大、强度低、渗透性差,因此,在灵敏度很高的软黏土地基上建造高度较高的路堤,其稳定性很难得到保证.一般采用分级加载的方法使软土地基在路堤荷载的作用下发生固结,强度获得增长.为加速固结,常采用塑料排水板处理地基,使之能在较短的时间内完成固结,加速地基强度增加.针对日本佐贺县高灵敏度的有明黏土地基上修建的分级加载的6.5 m高河堤下软黏土的物理力学性质的变化,说明分级加荷的重要性.现场软土地基为结构性黏土,有很高的灵敏度.而且该软黏土地基的渗透系数极低.因此采用塑料排水板进行了加固处理,施工过程中对地基土的物理与力学性质随固结过程的变化进行了测试.分析了其发展规律,结果表明地基土的单轴强度在250 d内增长了近1倍.

Strength increase of high sensitive clay under stage constructed embankment

For the embankment constructed on soft clayey subsoil, the soft clay generally has large void ratio, high water content, high compressibility, low hydraulic conductivity, low shear strength. Not only large vertical and lateral displacement of soft subsoil will happen during the embankment construction but also sliding failure maybe occurs due to the insufficient bearing resistance of soft subsoil. For this reason, embankment is constructed stage by stage to make subsoil consolidation under embankment loading and to make the soft subsoil acquiring strength from consolidation. This paper presents a case history of a stage constructed embankment on soft high sensitive Ariake clay. In order to speed up the consolidation, prefabricated vertical drain was installed in soft subsoil to increase the vertical hydraulic conductivity of soft subsoil in the macro sense. Field measured results show that during consolidation, water content of soft subsoil decreased and its unit weight increased. The undrained shear strength increased to twice of the original value.