Change of hydraulic conductivity of cohesive soils due to consolidation treatments with expanding resins

Settlements of ground subjected to foundation load are often due to both natural and/or anthropogenic causes, such as differential consolidation, seepage, periods of drought alternating with heavy rainfalls, growth of tree roots, sewer leaks, vibrations induced by vehicle traffic, excavations, or construction defects. Techniques of soil consolidation and stabilization by means of injection of polyurethane expanding resins have been efficiently used to mitigate or even solve this issue. The efficiency of the resin injection treatment has been well documented also thanks to the develop of a procedure of planning and monitoring which combines traditional geotechnical tests with the application of electrical resistivity tomography, which is strongly sensitive to the presence of water or voids. The combination of these survey methodologies allows to recognize the effect of injection in terms of soil compaction and water migration, a key factor for understanding the phenomenon and planning of resolutive interventions. The present study follows a previous work aimed at evaluating the increase in the geotechnical performance of cohesive soils treated by injection of expanding resins (same soil, resin, at the same site) and integrates it by focusing on the quantification of the effects of consolidation treatments, by means of expanding resins injection, on hydrologic properties of cohesive soils, focusing on saturated hydraulic conductivity measurements. Laboratory permeability test, performed in triaxial cell at different stress conditions and hydraulic gradients, were performed on undisturbed samples collected on "natural (non-treated)" and "treated soils", before and after the injection of resin (MAXIMA ® by GEOSEC ® ) in a full-scale test site characterized by the presence of continuous and homogeneous cohesive soils, (clay and silts). The investigated soil is classified as CH or CL soil, very firm and apparently overconsolidated. The study shows how the treatment is able to modify the characteristics of hydraulic conductivity of the soil. The injected resins partly follow pre-existing weaknesses and partly impregnate homogeneous and continuous masses of soil in a capillary way, giving it, in addition to the already documented greater mechanical strength, a lower hydraulic conductivity. The electrical resistivity investigations allow to appreciate the volumes affected by the treatment to which the variations of the measured properties can be attributed.