Mechanical properties and microstructure evolution of two ecological slope-protection materials under dry-wet cycles

Abstract

Owing to the occurrence of rain and heat during the same period in the Loess Plateau, the strong dry–wet cycle results in shallow damage such as erosion. As a result, applying new ecological protection technologies has become important in solving this problem. In this study, polypropylene fiber and guar gum were mixed with loess in a certain proportion to form two kinds of slope ecological protection materials, i.e., polypropylene fiber reinforced soil (PFS) and guar gum mixed soil (GGS). Sixteen dry-wet cycle tests were carried out on the two slope protection materials, and the shear mechanical tests were conducted on the samples after cycling. On this basis, the microstructure evolution characteristics of the samples were observed by scanning electron microscope. Results showed that the mechanical properties of the two slope protection materials deteriorated after 16 dry-wet cycles. Among them, the c and φ of PFS under the three levels of water content decreased by an average of 21.3% and 8.9%, respectively, whereas GGS decreased by 55.8% and 21.7%, respectively. Moreover, the mechanical deterioration characteristics of the two slope materials showed strong unity with their internal microstructure. The field tests of the two slope protection materials both performed good ecological protection effect, and the deterioration process was in good agreement with the laboratory phenomena. The microscopic action mechanism inside the material was closely related to the macroscopic performance. Polypropylene fiber can act as a “bridge” among soil particles to prevent the development of cracks, and guar gum and its hydration products can enhance the cementation among soil particles. This study could provide reference for further combining the two materials reasonably, using their respective advantages and improving the ecological protection effect of loess slopes.