Effect of Microreinforcement of Soils from Very Small to Large Shear Strains

Abstract

Previous studies of fiber soil reinforcement have shown significant improvement of the mechanical properties of soils, such as increased peak and postpeak strength, ductility, and tenacity. However, studies of such materials have thus far been restricted to small to intermediate shear strains of approximately 0.1–20%, due to the restrictions of the standard equipment used (e.g., triaxial and direct shear tests). The objective of the present research was to study the behavior of fiber-reinforced soils ranging from very small shear strains to very large displacements, to determine what effect reinforcement would have on the initial stiffness, and also whether the improved strength would eventually deteriorate. Bender element and ring shear tests were carried out, as well as standard triaxial tests, in order to investigate the effect of fiber microreinforcement of three different soils over a wide range of strains and displacements. A silty sand, a uniform sand, and a bottom ash were used as matrixes, in which 0.5% (by weight) polypropylene fibers were inserted that were 24 mm in length and 0.023 mm thick. The results show a marked influence of fiber reinforcement on the ultimate strength, with no loss in shear strength, even at very large horizontal displacements. At very small strains, the introduction of polypropylene fibers did not influence the initial stiffness of the materials studied.