Study On The Mechanism Of Ecological Slope Protection In Ion-type Rare Earth Mines

The mining of ion-absorbed rare earth ore has gone through three stages: pool leaching,heap leaching and in-situ leaching since the 1980 s.The mining area with in-situ leaching process covers an area of 2534 square kilometers,and the slope of in-situ leaching stope is prone to landslide,collapse and soil erosion under the action of external forces such as rainfall.To protect the stope slope with in-situ leaching technology and restore the ecological environment of mining area,ecological slope protection is an effective measure.Taking an abandoned rare earth mine in Zudong River Basin,Longnan County,Jiangxi Province as the research object,the failure forms and characteristics of stope slope with in-situ leaching technology has been summarized through field geological survey,the reinforcement effect and slope reinforcement effect of plant roots on stope slope with in-situ leaching technology has been studied by direct shear test and finite element analysis,and the binary multiple equation of the added value of cohesion varies with water content and root content also has been obtained by least square method.On this basis,an ecological slope protection model of "bamboo lattice + bermudagrass roots" was proposed,in which bermudagrass roots was used as ecological slope protection means and bamboo lattice was used as engineering measure material,the increasing effect of slope stability of ecological slope protection model of "bamboo lattice + bermudagrass roots" were analyzed with two-dimensional finite element method,and the support parameters of spacing,length and diameter of bamboo piles were optimized by visual analysis method of orthogonal experiment.Combining the research results with the engineering geology and hydrogeology conditions of rare earth mine slope,the ecological slope protection design of in-situ leaching stope slope was carried out.The main research results and conclusions are as follows:(1)The density,water content,specific gravity of the soil,liquid-plastic limit and shear strength under different water content conditions of the rare earth mineral sandy clay were obtained,the cohesion and internal friction angle of sandy clay decrease with the increase of water content and have strong water sensitivity.(2)The cohesion and internal friction angle of root-soil composite increase with the increase of root content,and the reinforcement effect of root of the Cynodon dactylon(L.)Pers on cohesion was stronger than that of internal friction angle;When the root content reaches 0.8% or more,the increase of cohesion decreases significantly,and then the cohesion of root soil will not be enhanced significantly by increasing the root content;When soil moisture content approaches plastic limit(28.6%)or is greater than plastic limit,the reinforcing effect of roots on soil cohesion tends to decrease.(3)The results of finite element analysis show that the existence of root system can improve the safety factor of slope to a certain extent,when the root content increased from 0% to 1.1%,the safety factor increased from 1.473 to 1.532.;The stress field of the slope changes with the existence of roots,but this change mainly concentrates on the reinforced layer of roots and the shallow soil near the reinforced layer.Therefore,for the slope with poor self-stability ability can not only rely on herbs to improve the stability of the slope.(4)The reasonable parameters of the bamboo pile in the "bamboo lattice" ecological slope protection structure are as follows: the length of the bamboo pile is 3m,the spacing of the bamboo pile is 2.5m,and the diameter of the bamboo pile is 8cm.When the optimized " bamboo lattice + bermudagrass roots " ecological slope protection mode is adopted to protect the slope,the stability safety factor of the slope is significantly improved compared with the plain soil slope,and the plastic slip zone appears in deeper soil layer.It shows that the " bamboo lattice + bermudagrass roots " ecological slope protection mode can limit the shear deformation of the slope surface and effectively prevent the slip of the surface soil of the slope.The " bamboo lattice " ecological slope protection structure has the characteristics of improving the overall stability of the slope,slowing down the erosion of the slope surface,conducive to plant growth,simple construction and low cost,and has certain application value.