Research On The Mechanical Properties Of Soil Reinforced With Basalt And Straw Fiber And Its Application On Slope

Silt in Beijing has the properties of poor graded,bad viscosity,low plasticity index,difficult to compaction and poor water stability,as a consequence,when the soil was used alone as subgrade filler,it will cause soil erosion,seepage failure,Excessive deformation and other roadbed diseases.In order to improve the above situation combined with the subgrade of a section of Beijing-Taiwan express way,basalt fiber and corn straw fiber were used to improve the properties of the soil.The effects of fiber content,length and other factors on the strength of soil and the stress-strain were studied by the basic mechanical test and the three axis test.Based on the experimental results,the model of fiber reinforced soil subgrade slope is modeled by Geo-Studio,and the stability analysis of slope under the condition of rainfall is discussed by the coupling analysis of software.The main research results of this paper can be summarized as follows:(1)The properties of the BFRS in shear strength,compressibility,permeability were improved;when fiber length was set as constant,the improvement in each respects of the basalt fiber-reinforced silt were increasing attenuation when the mixing ratio were less than 4‰,3‰ was the best mixing ratio for shear strength and compressibility,well 2‰ was the best for permeability;for fiber length,when the mixing ratio was constant,3cm was the best length for the shear strength and compressibility,and 2cm had the best effect for permeability.(2)Basalt fiber can increase shear strength of silt in the cohesion mainly,the model equation between shear strength parameters and two-fiber-factor is built,and the best mixing scheme is given;the curves of stress-strain relationship exhibits it exhibits a softening character under a lower cell pressure,while a hardening feature under the higher cell pressure.A soften formulation was adopted to describe the softening curves under low cell pressure,while the Duncan-Chang model was used for the hardening curves under high cell pressure.Combining the two models mentioned above,the stress-strain relationship of BFRS could be depicted well.(3)In order to verify the feasibility of SFRS,three kinds of antiseptic solutions were selected and polyvinyl alcohol is best,and the fiber reached saturation after three days of immersion in Polyvinyl alcohol.The increase of the cohesion of the silt is about 100% as much as pure soil,which contribute to water stability of silt,the curves of stress-strain relationship of reinforced soil exhibit a hardening character,which is different to softening character of pure soil,while the failure mode of reinforced soil was comparatively complete,which was different to shear failure modes of pure soil(4)According to the triaxial tests results,the best mixing ratio of SFRS is 2%,and the optimum fiber length is 2cm.Three factor orthogonal triaxial test under freeze-thaw cycle showed that SFRS can stabilize its strength in a certain point after freeze-thaw cycle,the variation of the intensity is affected by the large-to-small amount of fiber content,cycle period and freezing temperature;The increase of the number of freeze-thaw cycles can make the soil and low maxing ratio of SFRS change from strain softening to strain hardening.The stress-strain curves of the high mixing ratio of SFRS under different cyclic showed similar trend,and the peak stress decreased with the increase of cycle period,and the phenomenon was more obvious under high cell pressure.(5)Numerical simulation showed that both the BFRS and SFRS can strengthen the subgrade slope effectively and the behavior of the slope reinforced by fibers are better than the engineering scheme under rainfall.The failure mode of slope reinforced with BFRS are similar under different rainfall patterns and the potential risk slip surface is concentrated in a small range.Pore water pressure of different positions in the slope are different,it decreases as the height and distance increase in general.The relationship between safety factor and rainfall time is fitted with exponential function and the results show that the function can fit all the three rainfall patterns well.