Use of expanding polyurethane resin to remediate expansive soil foundations

Injection of expansive polyurethane resin can be used to remediate differential settlement issues. The resin is injected incrementally under a structure to achieve a desired foundation level, forming a composite resin–clay material. This solution is not well documented in the literature and some questions arise on the long-term performance of this solution. As injection is usually carried out in a settled soil mass that is dry and dessicated, rehydration of the soil after injection may lead to swelling of the leveled foundation and overlifting of the structure. Experimental research undertaken to investigate this rehydration issue and determine if there is a risk of overlifting in the long term is presented here. In situ and laboratory testing was performed to investigate the most fundamental aspects of the problems. This included the in situ injection of resin, study of resin propagation in the soil mass, influence of resin on the hydraulic conductivity of the soil mass, and large-scale swelling tests. The results suggest that, even though the resin cannot prevent the rehydration of the soil mass, the risk of overlifting in the long term is limited.