The use of dynamic probing tests and cone penetration tests to verify the effectiveness of expanding polyurethane resin injections for ground improvement

Injection of expanding polyurethane resins is a popular method to improve both the stiffness and the shear strength of the ground below existing foundations. The effect of the polyurethane resin expansion is to increase the soil confining stress and density around the injection holes. An estimation of the horizontal stress and volumetric strain changes that are induced within the ground is derived from the theory of cavity expansion in elasto-plastic materials. A series of case-histories is presented to document the feasibility of different in-situ tests to evaluate the achieved ground improvement. The tests have been performed before and after the injection of polyurethane resins and the obtained results have been compared with theoretical predictions. The considered investigation methods include the dynamic probing tests and the cone penetration tests. The preliminary results that have been achieved using an experimental miniature cone penetration test are also illustrated. The advantages and limitations of different test methods are discussed and practical indications for conducting such verifications of polyurethane resin injection effectiveness are provided.