Dynamic properties of polyurethane foam-sand mixtures using cyclic triaxial tests

• Polyurethane foam can be considered as a potential alternative for reduction of seismic earth pressures.
• In mixtures samples, damping ratio is highly affected by the foam mass.
• The damping ratio and the shear modulus of pure foam increases and decreases respectively, with an increase in the initial deviator stress.

Reducing the static and seismic earth pressures on geotechnical structures, such as retaining walls, bridges abutments and buried pipes, using compressible materials is a novel idea which has received increased consideration during recent years. Despite the high compressibility of injectable polyurethane (PU) foams, their performance as a compressible inclusion material has not yet been studied. This paper presents results from a series of cyclic triaxial tests to investigate the dynamic properties of PU foam and PU foam-sand mixtures at intermediate to large strains. Furthermore, the effect of various parameters including initial deviator stress, static confining stress and foam-sand mixing percentage, on damping ratio and shear modulus are identified. The laboratory test results indicated that in pure foam, the damping ratio attenuated in elastic strain amplitudes, which remained constant once the stress was increased to near the yield point. The results of the tests on the foam-sand mixture samples with various mixing ratios demonstrated that the variation in damping ratios is a function of foam mass. So that for specimens with 5% PU foam, after a relative decrease, the damping ratio increased in the cyclic shear strain amplitudes more than 0.03–0.05%. In addition, it was observed that the dynamic behavior of the mixture is significantly affected by the content of injected foam and also confining stresses (proportional to the depth of the treatment zone).