ASSESSMENT OF THE EFFECT OF EXPANDING RESIN INJECTIONS ON SOIL AND GROUNDWATER FLOW CONTAINMENT

The present work explores the potential of expanding resin injections as a containment technology for soil and groundwater flow in granular soils, in collaboration with Geosec s.r.l., leading company in resin injection treatments. These treatments, commonly used in geotechnical engineering to address settlement issues in foundations and infrastructure, have been found to also modify soil hydraulic properties, reducing permeability and altering groundwater flow paths both in cohesive and granular soils, opening the possibility for new applications as a containment technology. To this aim, a mesoscale physical model was realized within a saturated sand-filled experimental container (EC) of dimensions 193 x 143 x 232 cm, where resin injections were performed perpendicularly to the imposed water flow. A series of constant head permeability tests were carried out to assess the hydrogeological properties of the soil before and after the resin injections. Throughout the tests, piezometric probes monitored water pressure and level, temperature, and conductivity. Electrical resistivity tomography was also conducted to try evaluating the resin distribution and volume during and after the injection phases, while hydrochemical monitoring was carried out to assess the possible impact of the injection process on water chemistry. Furthermore, after the recovery of the resin barrier from the EC, a detailed 3D model of the barrier was created, providing insights into the continuity and morphology of the resulting barrier, and correlating the obtained volumes and geometries with the injected resin quantities and the hydrogeological results. Lastly, a seismic response analysis was developed on specimens sampled from the barrier, through the execution of cyclic triaxial tests, aimed at evaluating, at a laboratory scale, the improvement induced by the resin injections on the soil resistance to cyclic loading. The results obtained revealed that, although the resin injection setup was unable to achieve a perfectly continuous barrier, the impact of the barrier was visible in both the reduction of water flow rates and hydraulic conductivity, showing higher influence especially in its lower section. The constant-head permeability tests showed a decrease in hydraulic conductivity up to 80%, confirming the resin's significant role in impeding flow and creating low-permeability zones. The subsequent three-dimensional geometrical analysis confirmed how the resin barrier impeded the water flow, achieving a coverage of the flow section ranging from 83% to 94% during the hydraulic tests. The correlation between the reconstructed volumes and the injected quantities showed good agreement, while the morphology analysis highlighted the influence of boundary condition, injection sequence and injected quantities on the resulting shapes. Moreover, the results highlight that the resin’s performance as a permeability barrier is strongly influenced by the injection grid, injection sequence, and prevailing boundary conditions, thus underscoring the importance of carefully planning the resin injection parameters to ensure barrier continuity. Lastly, the preliminary results of the seismic response analysis on resin-treated sand specimens provided strong foundations for supporting the effectiveness of expansive resin treatments in enhancing the resistance to repeated loading cycles. Overall, the positive results position the resin injection treatment as a promising tool for creating a physical barrier to be applied as containment technology, having also the great advantage to be eco-friendly, minimally invasive and applicable in restricted environments.