The Influence of Vacuum Location and the Spacing of Drain Well on the Effect of Preloading Improvement

As a mathod of improvement of soft foundation, the vacuum, preloading method has been widely used, However, the traditional method that vacuum is applicated on the ground surface is not perfect for the dredged marine clay fill. It costs too expeneive and lasts long period. It is considered that the vacuum surface moves down to the deeper level would be better than that on the ground surface, the model tests performed in laboratory with the samo materials and testing condition are introduced in this paper, The improving effect of different vacuum levels and the influence of the spacing of drain well on are compared. The vacuum value in the sandmat and the negative pressure, the settlement and the volume of water output in the peat were measured. The variation of water content, the distribution of the vane strength aloag the depth of clay fill and the triaxiai compression strength after testing are also measured so as to clarify the changes of soil behaviours, according to the fundamental of soil mechanics, some parameters, including the coefficient of consolidation degree, the coefficient of effective stress increment and the coefficient of excess pore pressure are introduced. The results are presented that it would more reasonable when the vacuum surface moves down to the lower level. To shorten the spacing of drain well would have an efficient improvement of soft clay fill.