Contribution of the fiber reinforcement on the fatigue behavior of two cement-modified soils

Abstract Soil modification with cement is a well-established practice in the field of geotechnical engineering. The addition of cement is an eco-friendly process to increase mechanical performances of fine grained soils. This practice is commonly used to rationalize the cost of land transport infrastructures. The mechanical fatigue, which results from repeated loadings, is one of the main failure modes of these layered structures. These repeated loadings generate repeated tensile stresses at the bottom of the layers. To overcome these stresses on cement-modified soils, it seems relevant to add fibers in the materials as it is usually used in the field of concrete. The objectives of the study are to investigate the influence of the reinforcement with a small amount of natural fibers on the fatigue behavior of two cement-modified soils. The first soil can be defined as a sandy clay material, while the second can be defined as a coarse grained material with a small clay content. Fatigue performances of the two cement-modified soils without fibers and reinforced with several amount of fibers are measured using the two-point bending test. Results highlight that the reinforcement has positive effects on the stabilized sandy clay material while the fibers addition seems to slightly decrease the performances of the stabilized coarse grained material. Microscopic observations coupled with a statistical analysis on gammadensimetry measurements show in both cases that a fiber-balls phenomenon limits the homogenous distribution of the fibers in the soils. In the first case, this phenomenon is not detrimental. The natural matrix is intimately related with the fibers, and fibers prevent microcracking process. In the second case, because of the size of the grains, the links between the matrix and the fibers are isolated and fibers are not stressed during microcracking process. This study highlights that the failure processes of cement-modified soils are clearly related to the mineralogical nature of the matrixes. It also highlights that the failure processes for those materials are different than for highly cemented materials.