Study On The Effect Of Plant Roots On Soil Strength And Creep

Vegetation slope protection is one of the main measures used to control the geological environment in closed pit mines and abandoned outcrops.The intensity and creep properties of soil reinforced by plant roots directly affect the aesthetics and stability of the ecological landscape after treatment.In this paper,the triaxial composite soil samples were prepared by consolidation method using bermuda grass,Ophipogon and ryegrass as experimental materials.Through tensile test,triaxial shear test and triaxial creep test,the tensile properties of root system,shear strength and creep deformation of composite soil under different root content and water content were discussed.The main conclusions are as follows:(1)The shear failure of composite soils with plant roots still satisfies the Mohr-Coulomb strength theory.Under the same confining pressure,the shear strength of the same type of composite soil increases gradually with the increase of root content.Under the condition of low root content,cohesion was positively correlated with root content.With the increase of root content,the growth rate of cohesion slowed down and reached the peak gradually.When the root content exceeded the critical value,the cohesion did not increase.The internal friction angle was not significantly affected by root content.The cohesion of soil strengthened by roots changed significantly.The shear strength of soil can be improved by adding plant roots,mainly through improving cohesion.The order of cohesion is ryegrass > Ophipogon > bermuda grass,which is consistent with the order of single root tensile strength.(2)Within the test water content range,the cohesion and friction angle of composite soil and rootless soil are negatively correlated with the increase of water content,and the change trend of internal friction angle of composite soil is linearly negatively correlated.The change of cohesion caused by the change of water content is larger,and the change of composite soil is larger than that of rootless soil,and the change of ryegrass composite soil is the largest;the change of internal friction angle caused by the change of water content is smaller,and the change of composite soil is similar to that of rootless soil.(3)Under the action of lower deviatoric stress,both composite soil and rootless soil are in stable creep stage.The difference is that after instantaneous deformation,the creep rate of rootless soil decreases sharply to 0,and composite soil decreases slowly to 0.Finally,both of them tend to be stable.Under the action of medium deviating stress,there is a big difference between them.Rootless plain soil is the first to destroy,showing unstable deformation,and composite soil is stable deformation.However,with the increase of time,step-like deformation may occur due to root breaking.Under higher deviator stress,unsteady creep occurs in both composite soil and rootless soil until the specimen is destroyed.(4)The creep deformation of rootless plain soil is obviously larger than that of composite soil in a certain time range.The higher the root content,the smaller the creep deformation.The creep rate of composite soil is relatively small.Within the range of root content,the higher the root content,the smaller the creep rate,and the better the effect of delaying creep deformation of soil.(5)Water content does not affect the creep form of composite soil,but has a great influence on the axial deformation of composite soil.Within the experimental water content range,the creep deformation increases with the increase of water content under the same deviating stress.Within the experimental water content range,the smaller the initial water content is,the smaller the creep deformation rate of composite soil is,and the longer the deformation reaches stability.