Study on the migration mechanisms of water-soluble agents in high-pressure rotary jetting remediation

High-pressure rotary jetting (HPRJ) remediation is a recent-applied technology for in situ remediation of contaminated soils. The effectiveness of remediation depends upon the migration and distribution of the injected agents in the soil. However, the corresponding migration mechanisms have received little attention. In this study, laboratory HPRJ tests and numerical simulations were performed using chlorine (Cl^-) as a tracer to investigate the transport during HPRJ and the subsequent advection and diffusion. The test results showed that the HPRJ transported Cl^- into the mixing zone by eroding the sand, and the radius of the mixing zone could be reasonably predicted by the erosion model. The Cl^- concentration decreased linearly along the radial direction in the mixing zone. In addition, the Cl^- transport distance increased with the increase in nozzle diameter, jetting times, especially injection pressure, and decreased with an increasing rotation speed. The Cl^- concentration and radial uniformity were correlated positively with rotation speed, particularly nozzle diameter and jetting times. Numerical simulation showed that part of Cl^- migrated from the mixing zone to diffusion zone by advection-diffusion after rotary jetting, which contributed positively to the agent distribution distance and uniformity. The Cl^- migration was dominated by advection in the initial stage (30 days), while diffusion became more important thereafter.