Abstract: The vibrofloation method without gravel backfill was only thought to be proper for treatment of medium and coarse sand with less than 10 % fine particles. Almost no project case available is concerning vibrofloation without backfill treatment of silty and fine sand. A laboratory test was then carried out to achieve the relating characteristics of the hydraulic silty and fine sand .In this test a reduced scale prototype model was set up, in which pressure gauges were embedded. From the data acquired during and after vibroflotation, the pore water pressure development and dissipation functions are established. The spatial distribution of pore pressure among soil was also studied. The cone penetration test(CPT) was made after each vibroflotation to discover the relationships among CPT, relative density and water pressure. Furthermore, the conclusions obtained from test were then used in guiding a ground improvement project in Shanghai.

Key words: vibrofloation without backfill, silty and fine sand, pore water pressure, relative density, cone penetration test