Study On The Mechanical Effect Of Vegetation Roots On Soil Consolidation In Ecological Restoration Of Abandoned Rare Earth Mines

In the process of ecological restoration treatment of abandoned rare earth mines,ionic rare earth tailings as an anisotropic,weakly cemented special geological body.The problems of low survival rate of ecological restoration vegetation,serious shallow soil erosion and frequent occurrence of small-scale landslides exist when relying solely on conventional soil slope reinforcement or vegetation ecological restoration techniques,and the mechanical properties of vegetation root system and its soil consolidation mechanics are often ignored.In response to the above problems,this paper systematically analyzed the root system characteristic parameters and tensile strength characteristics of typical abandoned rare earth mine ecological restoration vegetation,and also characterized the change law of composite shear strength of ionic rare earth tailings under different root system characteristic parameters,different tilt angles and different water content,finally revealed the mechanism of different root systems on composite shear strength of ionic rare earth tailings,and clarified the mechanism of ecological restoration vegetation in abandoned rare earth mine.The effect of root system on the composite shear strength of ionic rare earth tailings was finally revealed.The main conclusions are as follows:(1)The root system characteristics RLD,RSAD,RAR and RAI were exponentially decreasing downward along the rare earth tailing layer;the shallow clustering effect of the root system was obvious and the root system morphology was inverted triangular,the root system of vetiver and paspalum notatum was mainly distributed in vertical direction and the caudal root was well developed,the root system of cynodon dactylon and setarria viridis was mainly distributed in horizontal direction and the upper root system was well developed in fibrous roots.(2)The average maximum tensile strength and tensile strength of four typical vegetation root systems were: vetiver(1.278 N,12.878MPa),paspalum notatum(1.029 N,10.315MPa),cynodon dactylon(0.82 N,8.623MPa),and setarria viridis(0.718 N,7.626MPa).The maximum tensile strength of single root increased as a quadratic function of root diameter while the tensile strength decreased as a quadratic function of root diameter.The role of fine roots in root consolidation should not be neglected because of their stronger tensile strength and waterholding properties and their larger surface area compared with coarse roots of the same mass.Root system indexes had a significant effect on the maximum tensile strength of single roots,with RAR and RAI having the most significant positive correlation coefficients and RAI/RAR having the most significant negative correlation coefficients with the maximum tensile strength of single roots.(3)The shear strength,cohesion and internal friction angle of the same type of rootcontaining specimens increased with increasing RAR and decreased with increasing water content,and the gain of inclined root system on the shear strength of rare earth tailings was smaller than that of vertical root system.The gain of RAR on the shear strength of rare earth tailings showed a trend of rapid increase and then leveled off,and the angle of root system showed a trend of slow increase and then surge.The gain of root system on the shear strength of rare earth tailings was the greatest at RAR of 0.655.The root system had the greatest effect on the gain of cohesion and internal friction angle,with the average values of 12.901 k Pa and6.272°,respectively.The increase in cohesion was greater than the increase in internal friction angle,and the role of cohesion in root consolidation was more significant.(4)The results of principal component analysis showed that the factors influencing the effect of soil consolidation mechanics were RAR,internal friction angle,cohesion and root angle with the greatest weights.The results of the gray correlation model showed that the effects of root angle and RAR on the incremental cohesion of rare earth tailings were higher than the effects of water content on them,and the effect of root angle was the largest,the effect of water content on the incremental internal friction angle of rare earth tailings was higher than the effects of root angle and RAR on the internal friction angle,and the effect of water on the incremental internal friction angle of the specimens containing roots was the largest.