新近吹填淤泥现行真空预压技术加固效果不佳原因分析

Cause of conventional vacuum consolidation technology failure to newly filled reclamation mud foundation

为探讨现行真空预压技术加固新近吹填淤泥地基时效果不理想的原因,首先分析新近吹填淤泥的工程特性,然后开展不同含水率下新近吹填淤泥的室内真空固结足尺单井模型试验研究。研究结果表明:1)新近吹填淤泥主要由较细颗粒物质和极细颗粒物质组成,其中黏粒含量(黏粒+胶粒)和强亲水矿物含量(伊利石+蒙脱石)均较高;孔隙特征主要以孤立孔隙和粒间孔隙为主;含水率基本在100%以上、均大于1.5倍的液限,孔隙比均大于2.5,塑性指数基本在20以上,液性指数基本大于2.0。2)新近吹填淤泥采用现行真空预压技术加固时,膜下真空度损失程度可高达20%以上;真空度从排水板向周围土体中传递时的径向损失程度严重,真空压力的径向作用范围仅局限于直径约为40 cm的土柱范围内:土柱范围内土体的无侧限抗压强度值不超过35 kPa;土体的有效加固深度和强度增长幅度均较小。这两方面是新近吹填淤泥采用现行真空预压技术进行处理时效果不理想的主要原因,因此,有必要结合新近吹填淤泥的工程特性研发出一种新型加固技术或对现行真空预压技术加以改进。

It is proved that the improvement effects cannot meet the use requirements for conventional vacuum preloading techniques improving new hydraulic reclamation mud foundation. To investigate the reasons, we analyze firstly the engineering properties of new hydraulic reclamation mud, and then carry out a full-scare single- well indoor model experiment considering different initial moisture contents. It is shown that： （1） the new hydraulic reclamation mud mainly consists of fine and very fine soil particles with high content of clay soil particles（ clay ＆ rubber） and strong hydrophilic minerals （illite ＆ smectite）; its pores mainly consist of isolated pores and intergranular pores; its moisture content is usually larger than 100% and more than 1.5 times greater than the liquid limit; its void ratio is larger than 2. 5; its plasticity index is larger than 20; its liquid index is larger than 2.0. （2） when it is improved by no-sand vacumm preloading for new hydraulic reclamation mud, the vacuum degree loss can be up to 20% under the membrane, and the radial loss extent of vacuum degree is severe from vertical drains to soils; the radial range of vacuum degree is limited to the soil column with the diameter of around 40 cm; the unconfined compressive strength does not exceed 35 kPa in the range of soil column; it is small for the effective improvement depth and intensity of the soil strength growth. The above two reasons both result in the unsatisfiedimprovement effects. Therefore, it is very necessary to optimize the conventional vacuum preloading techniques or develop a new improvement technology for new hydraulic reclamation mud.