Shear behavior of polyurethane foam adhesive improved calcareous sand under large-scale triaxial test

The mechanical properties of calcareous sands are very different from those of terrestrial sands as the particle crushing occurs under low confining pressure. If the calcareous sand is used as the foundation materials, engineering problems such as the uneven settlement of the foundation are prone to occur. In this paper, the Polyurethane foam adhesive (PFA) is used to improve the calcareous sand through the unconsolidated undrained (UU) large-scale triaxial test. The shear strength of PFA solidified calcareous sand under different PFA content and confining pressure was studied. In order to facilitate engineering design, this paper evaluates the strength parameters of PFA solidified calcareous sand, including peak strength, internal friction angle and cohesive force, followed by the SEM microstructure test to reveal the micro-mechanism of PFA improved curing. The experimental results show that the shear strength and deformation resistance of the solidified calcareous sand improved significantly by addition of PFA. Furthermore, SEM studies revealed that the PFA is mainly wrapped around the surface of the sand particles or filled between the sand particles, which manifests in the form of improved cohesion which ultimately results in overall improvement in strength of soil PFA mixture