Laboratory test on dredger fill reinforced by hierarchical vacuum preloading

According to the problems of long time self consolidation and the drain pipes are easy to block of high viscous dredger fill in the actual engineering projects, this paper firstly puts forward the idea of self-weight consolidation method which hydraulic filling and drainage consolidate at the same time and the method of hierarchical vacuum preloading which applies vacuum pressure step-by-step, and carries out laboratory test, at the meanwhile, takes physical and chemical tests and mercury intrusion porosimetry of dredger fill after each consolidation stage. The test results show that: the two curves of settlement and pore water pressure all show downward trend, in the late hierarchical vacuum preloading stage, the two curves all tend to horizontal due to the accomplishment of consolidation of dredger fill; the moisture content and the soluble salt content decreases gradually, the strength increases gradually in the consolidation process of dredger fill. The physical and chemical properties of dredger fill have been improved after the hierarchical vacuum preloading, and doesn´t appear the phenomenon of blocking drain pipe, the reinforce effect is uniformity; the total pore volume, porosity and the average pore diameter of dredger fill are all gradually reducing, and the larger pores are first compressed into smaller, and then the smaller pores are compressed; the pore distribution of dredger fill develops from large size pore to small size pore; The nearer to the drain pipe, the smaller settlement of dredger fill is, the faster pore water pressure dissipates, and the smaller porosity is; in contrary, the farther to the drain pipe, the greater settlement of dredger fill is, the slower pore water pressure dissipates, and the bigger porosity is.