Study On Mechanical Properties And Slope Stability Of Coir Fiber Reinforced Red Clay

Red clay is a kind of regional special soil,which is mainly distributed in South China,Southwest China and some areas of the two lakes.It has the characteristics of high natural water content,high void ratio,dehydration shrinkage,water ex pansion and so on.It is easy to produce a series of engineering problems such as uneven settlement of foundation,collapse of houses,slope instability and ground collapse.As a kind of green natural biomass material,coir fiber has high tensile strength,and has the advantages of water resistance,mildew resistance,insect resistance,not easy to break and not easy to rot.It is a good red clay reinforcement material.The coir fiber reinforced soil-live tree pile slope support structure developed by the research group uses coir fiber reinforced soil to ensure the short-term stability of the slope.In this case,the reinforcement of red clay with coir fiber has more engineering application prospects.In this thesis,the strength characteristics and microstructure of coir fiber reinforced soil were studied by means of triaxial test,electron microscope scanning and numerical simulation.The mechanism of strength enhancement was discussed.The DuncanChang constitutive model of coir fiber reinforced soil was constructed.A threedimensional numerical calculation method of slope based on Duncan-Chang constitutive model was proposed,and the stability of coir fiber reinforced soil slope was evaluated.The main research contents and innovations are as follows.(1)The triaxial shear tests of coir fiber reinforced red clay under different reinforcement ratios and different confining pressures were carried out by automatic triaxial apparatus.The variation law of stress-strain relationship of coir fiber reinforced red clay and the failure mode of samples were studied.The Duncan-Chang constitutive model of coir fiber reinforced red clay was constructed.The results show that under the same strain,the stress-strain curve of fiber reinforced soil is significantly higher than that of plain soil,indicating that the addition of coir fiber significantly improves the strength characteristics of red clay,and there is an optimal fiber content of 0.3%.The failure modes of the specimens are all bulging failure.Under the same fiber content,the larger the confining pressure,the smaller the lateral bulging deformation of the specimen.Under the same confining pressure,the lateral deformation of the plain red clay specimen is the largest,and the lateral deformation of the fiber reinforced soil specimen decreases first and then increases with the increase of the fiber content.The stress-strain curve of the sample shows typical strain hardening characteristics,which conforms to the hyperbolic hypothesis of the nonlinear elastic model Duncan-Chang model.The established Duncan-Chang model of coir fiber reinforced red clay conforms to the triaxial test results.(2)The microstructure characteristics of plain red clay and coir fiber reinforced red clay were studied by scanning electron microscope.The relationship between fiber content and strength characteristics of reinforced soil was explored,and the reinforcement mechanism of coir fiber reinforced red clay was revealed from the microscopic point of view.The results show that the microstructure of the red clay is mainly laminated structure,and the internal units are mainly surface-surface contact,and there are large pores.The pore distribution shows obvious anisotropy.With the addition of coir fiber,the fiber is tightly wrapped by the soil,and its surface is attached by a large number of soil particles in the form of floccules,which are filled in the pores between the fiber and the soil,increasing the friction force of the interface between the reinforcement and the soil.The movement of soil particles is limited and the shear strength of the whole soil is improved by the gripping,bending and interweaving between the fiber and the soil.However,if the fiber content is too much,it is easy to form penetrating cracks along the fiber cluster and increase the potential failure surface of the soil.(3)Using Midas GTS/NX finite element software,a numerical calculation model of coir fiber reinforced red clay slope based on Duncan-Chang model was established.The data obtained from the triaxial test were used as the parameters of the reinforced soil.The horizontal displacement,vertical displacement,maximum shear stress,maximum shear strain and safety factor of the slope under different conditions were studied,and the stability of the slope was evaluated.The results show that the horizontal displacement of the slope mainly occurs at 1/3 to 2/3 from the top of the slope,and the vertical displacement mainly occurs at the top of the slope.The slope toe area is the shear stress concentration area,and the maximum shear strain also mainly occurs at the toe of the slope.With the addition of coir fiber,the maximum shear strain distribution range of the slope and the horizontal and vertical displacements of the slope decrease to varying degrees,and the safety factor of the fiber reinforced soil slope with 0.3%content is the highest.The larger the angle of the slope,the steeper the slope,the greater the shear stress at the foot of the slope,the larger the horizontal and vertical displacement and the maximum shear strain distribution area of the slope.The higher the height of the slope,the wider the distribution range of the maximum shear strain of the slope,the larger the displacement of the slope,the lower the safety factor,and the more unfavorable to the overall stability of the slope.Therefore,in the design and construction of the slope,the slope angle and slope height of the slope should be reasonably selected.The relevant research results obtained in this thesis can provide some theoretical basis and technical reference for the application of coir fiber in slope engineering.