Mechanical Characteristics Of Robinia Pseudoacacia Root System And Its Effect On Loess Slope Stability

Plant roots can reinforce slope soil and effectively improve slope stability.It is of great theoretical and practical value to study the mechanical properties of plant roots and their effect on slope reinforcement.This study based on botany,soil mechanics and geotechnical mechanics,the principles and methods of test and analysis the locust tree roots and the friction between the soil and the mechanics characteristics of using large direct shear apparatus to test the different growth duration of the same root-composite soil shear strength,geotechnical engineering numerical calculation software is used to analyze the acacia root of loess slope reinforcement effect.The main research achievements are as follows:(1)The tensile property index of robinia pseudoacacia root has significant effect with the change of root diameter.The tensile strength index increases with the increase of root diameter,and the longitudinal limit elongation,tensile strength and elastic modulus index decrease with the increase of root diameter.The root diameter is in the range of 0.8-14.5mm,and the tensile strength is in the range of 36-3867 N.The values of longitudinal ultimate elongation range from 10.6% to 29.3%.The tensile strength range is 17.54-89.57mpa;The elastic modulus ranges from 147.27 MPa to 343.18 MPa.(2)According to the friction characteristics test,the friction characteristics of root-soil interface change with the change of root diameter,soil dry density and soil moisture content.The frictional resistance between root and soil has a strong correlation with the root diameter of robinia pseudoacacia,loess soil dry density and loess soil moisture content.The root-soil interface friction coefficient has a strong correlation only with soil dry density and soil moisture content of loess,but not with root diameter.The friction coefficient increases with the increase of dry density,while in the process of soil moisture content increasing,the friction coefficient first increases and then decreases.(3)Robinia pseudoacacia root has a good reinforcing and anchoring effect on the surface soil.Under the same vertical load,the root with the larger growth years,the higher the shear strength.The shear strength of soil without roots under normal stress of 50 k Pa,100 k Pa and 150 k Pa is 49.48 kpa,67.54 kpa and 89.92 kpa,respectively.The shear strength of root-soil complex increased linearly in the range of 66.25-117.02 k Pa,89.49-142.83 k Pa and 110.57-172.09 k Pa,respectively.Plant roots mainly influence the shear strength by enhancing the cohesion of the root-soil complex.The cohesion index of 7a soil is 211.53% higher than that of the soil without root,while the influence of the internal friction Angle index of 7a soil is only 31.14% higher than that of the soil without root.Therefore,with the increase of root growth years,the cohesion increased significantly,while the internal friction Angle index remained unchanged.(4)Using FLAC3 D software strength reduction method to simulate the stability of loess slope with different years of robinia pseudoacacia root system,it is believed that robinia pseudoacacia root system has a certain influence on the stability of loess slope,slope ratio of 1:1,1:0.5 respectively,after the consolidation of robinia pseudoacacia root system,The safety factor increased from 2.59 and 2.12 to 2.78 and2.31,respectively,with an increase of 7.34% and 8.96%.The reinforcement scope is mainly shallow slope soil.The lower the safety factor of the loess slope,the greater the shear stress at the foot of the slope,the more prone to sliding failure,engineering practice,should pay attention to the overall reinforcement at the foot of the loess slope.