Study of factors affecting the remediation of contaminated soil through pneumatic fracturing and soil vapor extraction

In low-permeability soils, the effectiveness of soil vapor extraction (SVE) is often constrained, resulting in increased time and operational expenses. In this study, pneumatic fracturing and the SVE were combined to remediate lowpermeability clay contaminated with ammonia gas. The soil parameters, pneumatic fracturing parameters, extraction mode, and other influencing factors were investigated via laboratory testing. The results indicated that: (1) Pneumatically induced fracturing disrupts soil structure, forming cracks and providing new pathways for ammonium gas migration; (2) the soil crack area exhibits a quadratic function relationship with both the fracturing pressure and frequency, and the soil crack area increases with higher pneumatic frequencies, leading to a faster pneumatic pressure decline; (3) a denser network of pathways emerges within the soil due to the reduced distance between the two pneumatic fracturing points, consequently enhancing soil permeability and increasing pollutant elimination efficiency; (4) the ammonium gas removal efficiency gradually increases with an increase in the extracted vapor flow rate, but there is an optimal extraction flow rate (9 L/min); (5) continuous extraction combined with gas injection effectively ameliorates the issue of prolonged fluctuations in ammonium gas concentration during the later stages of extraction. (6) Fracturing and extraction reduce the moisture content of the surrounding soil. The results demonstrated the feasibility and superiority of pneumatic pre-fracturing extraction in low-permeability soils.