Experimental Study On Mechanical Properties Of Soils Reinforced By Carbon Fiber And Nano-silica

Obtaining the engineering properties such as shear strength,compressibility,permeability and liquefaction characteristics of soil is a key factor for geological hazard analysis evaluation,earthquake prevention and disaster reduction.Therefore,many experimental studies on improving the engineering properties of soils have been conducted by researchers.Although some soil reinforcement methods can effectively improve the mechanical properties of the soil to reduce the impact of geological disasters,there are some resulting disadvantages such as great negative influence on the environment,high cost,construction difficulty and unsustainable development.Based on the existing research progress of soil reinforcement methods and combined with the development of new materials,the mechanical properties and related mechanisms of three typical soils which is silty sand,clay and sand reinforced by carbon fiber and nano-silica were scientifically studied.The effects of carbon fiber length and content,nano-silica content on the mechanical properties of the reinforced soil were scientifically analyzed by direct shear test,material microstructure test,unconfined compressive strength test,compaction test and triaxial test.Based on the experimental results of this study,the main conclusions can be draw as follows:(1)The 3mm carbon fiber forms mutually interlocking network structure between the soil particles,which increases the mutual friction of the fiber and the soil,so that it could be effectively improve the internal friction angle and cohesion of the soil.Under the condition of soil water,the nanoparticles can form viscous gel which can fill adequately the pores of the soil between the soil particles.Just for this reason,adding nano-silica has no effect on the internal friction angle of the soil,while the effect of improving the cohesion of the soil is remarkable.When 2wt% of carbon fiber and nanosilica worked together,the shear strength of the soil increases continuously as the content of nano-silica increases,the peak of soil cohesion has been further improved.(2)The shear strength of the sample increases firstly and then decreases with the increase of carbon fiber content when 3mm carbon fiber reinforced clay.And the shear strength of the reinforced clay continues to increase for 6mm and 10 mm carbon fiber reinforced clay.Under different vertical pressures,the shear strength growth rate of reinforced clay with 10 mm carbon fiber is less than corresponding growth rate of reinforced soil with 6mm carbon fiber.Compared with the untreated clay,the cohesion and internal friction angle increased by 380% and 25.5%,respectively.The peak strength of the unconfined compressive strength of clay for 6mm carbon fiber increased from 142.47 kPa to 317.41 kPa,an increase of 122.79%.The modulus of elasticity(E50)increased from 2.54 MPa to 5.29 MPa,an increase of 108.3%.The cohesive force of clay with nano-silica increased by 264.5%,the change of internal friction angle was not obvious.(3)In the triaxial consolidation undrained shear test,with the increase of the length and content of the carbon fibers,the pore water pressure growth of sand can be effectively limited.The ability to resist liquefaction is also constantly increasing,the liquefaction potential is reduced from 0.95 to 0.In the triaxial consolidation drainage shear test,the shear strength and internal friction angle of the sample increased as the length and content of carbon fiber increased.When the pressure is 50 kPa,the volumetric strain of the carbon fiber-doped sample is smaller than that of the unreinforced sand.The volumetric strain of the 3 mm carbon fiber reinforced sand is firstly contraction and then dilatation.For the 6mm and 10 mm carbon fiber reinforced sand,the sample is basically kept contraction,the volumetric strain of the reinforced sand increases continuously,and eventually exceeds the unreinforced sand with the increase of confining pressure.