Effect of carbon fiber and nanosilica on shear properties of silty soil and the mechanisms

In this study, the effects of carbon fiber and nanosilica on properties of silty soil including physical, microstructural characteristics and shear resistance were investigated. Soil samples treated with different contents of carbon fiber and nanosilica were prepared and studied. The samples were tested by direct shear method under different normal pressure levels. Besides, SEM (scanning electron microscopy) tests were performed to examine the microstructural changes. The test results indicated that the shear strength of treated soil samples was significantly improved compared with the untreated soil samples. Carbon fiber was found effective in improving internal friction angle and cohesion thanked to the interface friction between fiber and soil. On the other hand, nanosilica could improve cohesion effectively due to full filling of the pores between soil particles. The results also showed that the combination of 2 wt% carbon fiber and 3 wt% nanosilica could improve the shear stiffness and particularly the residual shear strength, which was increased significantly by 128.3% compared with the untreated soil sample at a normal stress of 100 kPa. The results demonstrated that the use of carbon fibers and nanosilica can be an effective method to improve silty soil in lieu of traditional cement grouting in mitigating geotechnical engineering disasters.