Injection of expanding polyurethane resins

In recent years, polyurethane resins have frequently been used to reinforce the soil and to recover building foundation structures after subsidence. Such resins are characterized by a swelling capacity during the chemical reaction that determines their formation. As a consequence, in the presence of a confinement, such as that which occurs after injection of the subsoil, the expansive capacity of the resin produces the compaction of the surrounding soil or triggers a fracture. In order to supply design tools for this type of intervention, the physico-chemical, mechanical and hydraulic properties of polyurethane resins are here described and the injection modalities, for different types of soil, are illustrated, through basic experimental tests. Simple theoretical models are then presented in order to evaluate the effects induced by the injection of polyurethane resins on the stress and stain state of the soils. Some examples are given in order to illustrate the results that can be obtained from the application of the theoretical models. Finally, the possibility of using polyurethane resins for the treatment of expansive soils is described.