Long-term environmental impact of an artificial island of solidified dredged marine silt

Abstract

Marine dredging silt that has been solidified is commonly used as a filler material for inland reclamation and artificial island construction. However, determining the long-term environmental safety of artificial islands made of solidified silt is a challenge. A bridge–tunnel conversion artificial island made of solidified silt was the research location of this study. Laboratory tests were conducted to study the effect of cement content on the pollutant pore-water concentration and hydraulic conductivity of solidified silt. The results showed that after solidification treatment, the heavy-metal concentration in the pore water of dredged silt reduced by 60–85%, whereas the concentration of hydroxide (OH−) ions increased 106–1070 times, and the hydraulic conductivity decreased by approximately three orders of magnitude. On the basis of the test results, the finite-element method was used for simulating the long-term transport of heavy metal nickel (II) (Ni2+) and hydroxide in artificial islands. When the cement content increased from 60 to 100 kg/m3, the nickel (II) concentration in the dam around the solidified silt decreased by approximately 68%, whereas the hydroxide concentration increased approximately tenfold. However, none of them exceeded the seawater water quality standard. This indicates that the long-term environmental safety of the artificial island could be ensured.