Soil Improvement by Expanding Polyurethane Resins-Paper

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The paper examines the use of expanding polyurethane resins to strengthen soils and remediate foundation settlements, and proposes a theoretical framework to improve on largely empirical design methods.<br /><br />The resin forms through an exothermic reaction between polyol and isocyanate, producing carbon dioxide and expanding before hardening. Laboratory data show that its swelling pressure depends strongly on its final density; under unconfined conditions, it can expand to roughly 30 times its initial volume.<br /><br />Injection behavior varies with soil grain size. In coarse-grained soils, the liquid resin penetrates the pores and forms a bulb that expands as it solidifies, compacting the surrounding soil. In fine-grained soils, it cannot enter the pores and instead propagates through fractures, generating displacement and temporary pore-pressure increases.<br /><br />For coarse-grained soils, the authors model bulb expansion using cavity-expansion theory for an elastic-plastic medium. Equilibrium is reached when the resin’s swelling pressure matches the radial confining stress of the soil. A calculation example compares small- and large-deformation formulations. The large-deformation model predicts an equilibrium pressure of 375 kPa and a swelling ratio of 6, compared with 450 kPa and 5.3 under the small-deformation assumption. Thus, the small-deformation approach overestimates equilibrium pressure by about 20% and underestimates the swelling ratio by about 12%.<br /><br />The proposed model offers a basis for estimating expansion in coarse soils, but further development is needed to predict changes in surrounding soil stresses and strains. The authors also note that fine-soil behavior and time-dependent pore-pressure effects require separate consideration.

Keywords

polyurethane resin

soil stabilization

foundation settlement

cavity expansion theory

swelling pressure

expanding resin

coarse-grained soil

fine-grained soil

injection grouting

pore pressure