Semnan University Press Journal of Transportation Infrastructure Engineering 2423-5350 10 3 2024 11 21 Experimental Study of the Effect of Polypropylene Fiber and Nano-silica on the Physical and Mechanical Properties of Silty Sand Soil Experimental Study of the Effect of Polypropylene Fiber and Nano-silica on the Physical and Mechanical Properties of Silty Sand Soil 67 88 9161 10.22075/jtie.2024.35895.1699 FA Mahmoud Malakouti Oloun Abadi Assistant Professor, Department of Civil Engineering, Persian Gulf University, Bushehr, Iran Khosro Salehi MSc, Department of Civil Engineering, Persian Gulf University, Bushehr, Iran Abdoreza Fazeli Assistant Professor, Department of Civil Engineering, Persian Gulf University, Bushehr, Iran Babak Golchin Assistant Professor, Department of Civil Engineering, University of Mohaghegh Ardabili, Ardabil, Iran Ramin Meshkabadi Faculty of Advanced Technologies, University of Mohaghegh Ardabili, Ardabil, I. R. Iran. Journal Article 2024 11 12 This research investigated the effect of using polypropylene fibers and nano-silica on the mechanical properties (such as California Bearing Ratio (CBR) and shear strength) of silty sandy soil. Different laboratory samples were prepared with varying percentages of nano-silica (1%, 2%, and 3%) and polypropylene fibers of different lengths (6 mm and 12 mm). The fibers were mixed with 0.1%, 0.5%, and 1% of soil weight. The microscopic characteristics of soils were examined using SEM. Results showed that addition of polypropylene fibers significantly increased the CBR value, and using 1% of fibers improved the interlocking and bonding of soil particles, creating a more unified soil texture. Increasing the length of polypropylene fibers from 6mm to 12 mm also increased the CBR. Addition of 1%, 2%, and 3% nano-silica increased the CBR value by 2.2, 3.3, and 4.2 times, respectively. The highest load-bearing and shear strength was observed with the use of 1% polypropylene fibers and 3% nano-silica. The shear strength test revealed that polypropylene fibers did not change the soil cohesion, but increased the angle of internal friction, while nano-silica improved the soil cohesion, but did not affect the internal friction angle. The combination of these two materials significantly increased the shear strength of the studied soil. This research investigated the effect of using polypropylene fibers and nano-silica on the mechanical properties (such as California Bearing Ratio (CBR) and shear strength) of silty sandy soil. Different laboratory samples were prepared with varying percentages of nano-silica (1%, 2%, and 3%) and polypropylene fibers of different lengths (6 mm and 12 mm). The fibers were mixed with 0.1%, 0.5%, and 1% of soil weight. The microscopic characteristics of soils were examined using SEM. Results showed that addition of polypropylene fibers significantly increased the CBR value, and using 1% of fibers improved the interlocking and bonding of soil particles, creating a more unified soil texture. Increasing the length of polypropylene fibers from 6mm to 12 mm also increased the CBR. Addition of 1%, 2%, and 3% nano-silica increased the CBR value by 2.2, 3.3, and 4.2 times, respectively. The highest load-bearing and shear strength was observed with the use of 1% polypropylene fibers and 3% nano-silica. The shear strength test revealed that polypropylene fibers did not change the soil cohesion, but increased the angle of internal friction, while nano-silica improved the soil cohesion, but did not affect the internal friction angle. The combination of these two materials significantly increased the shear strength of the studied soil. https://jtie.semnan.ac.ir/article_9161_b98eada144b9b843a56a1b070751ef45.pdf