Author(s): Zelong Liang, Liquan Xie, Peng Jin

Linked Author(s): Peng Jin

Keywords: Coastal engineering; Drainage improvement; Soft clay; Pressed air bubbles; Model test;

Abstract: Vacuum preloading technique is widely used to improve the geotechnical properties of dredged slurry that are hydraulically placed in seawater for land reclamation in east and southeast of China. Although the performance of vacuum drainage has been improved when combined with other techniques, soil columns usually form on the drainage boundary which induce the decrease of permeability around the boundary, thereby limiting the further development of vacuum preloading technique. To improve the vacuum drainage efficiency, a method combined with pressed air bubbles is proposed to increase the seepage gradient around the drainage boundary. A self-developed model test device was applied to investigate the efficiency of drainage under different pressures of pressed air bubbles. According to the actual situation in the treatment of deep soft clay in coastal engineering, two conditions whether there are micro-cracks on the surface with a thin layer of water or not were considered in the test. The results show that 1) the vacuum drainage technique has a better efficiency when combined the pressed air bubbles under a proper range of pressure condition; 2) the drainage efficiency is higher with increase of air pressure (less than 35 kPa in the tests), and the water content in soil can be effectively reduced; 3) when there are no micro-cracks on the soil surface, the soil failure of soft clay is in the form of honeycomb coal at the contact with the cylinder wall under the effect of pressed air bubbles, while the initial micro-cracks on the soil surface may expand to macro-cracks until drainage failure; 4) when the soil is broken through by the pressed air bubbles, the pore water in the soil will be difficult to be drawn out, and the effect of air pressure drainage will be greatly reduced.

DOI: https://doi.org/10.3850/38WC092019-0514

Year: 2019