Interface Mechanical Properties And Engineering Application Of Geogrid-Tailings Complex

Tailing pond is a kind of special industrial structure.Its operation not only affects the economic benefits of a mining enterprise,but also is closely related to the safety of life and property of the residents in the lower reaches of the reservoir area and the surrounding environment.The reinforcement treatment of tailings dam can not only improve the stability of tailings dam,but also enlarge the slope ratio of the dam to increase the storage capacity of tailings dam and save land resources,which is of great practical significance in today's increasingly precious land resources.In this paper,Angang Fengshuigou tailings pond is taken as the research object.The interface mechanical properties and engineering application of geogrid reinforced tailings were studied by means of laboratory test,theoretical analysis,model test and field test.The main achievements are as follows:?1?An experimental instrument for macro-and micro-analysis of interface characteristics of visible reinforced soils were developed,which could be used for direct shear and pull-out tests with different geosynthetics and fillers.The direct shear and pull-out tests of geogrid and geotextile reinforced tailings sand were carried out with the newly developed apparatus.In order to analyze the effect of geogrid reinforced tailings more accurately,the interface frictional effect of geogrid-tailings should be separated from the interface comprehensive frictional effect.The reasonable mesh size of geogrids reinforced tailings should be controlled about 0.4 of the area ratio between geogrid-tailings interface and shear surface.?2?Through triaxial compression test of reinforced tailings with 0,1,2 and 4 layers of geogrid and geotextile,the stress-strain characteristics and reinforcement effect of reinforced tailings with different layers were obtained.The stress-strain curves of geogrids show hardening characteristics,while the stress-strain curves of geotextiles have strain softening properties.With increasing reinforced layers,the hardening or softening characteristics become more prominent.The stress-strain curves of geogrids and geotextile reinforced tailings under different reinforced layers can be fitted by the Duncan-Chang model.?3?An interface pull-out formula which can predict the tension and displacement at any position of reinforcement was proposed.The application and detailed analysis steps of the interface pull-out formula were given,and the predicted results of interface pull-out formula were compared with the experimental results.Aiming at the strain hardening and strain softening phenomena of geosynthetics during pull-out,bilinear shear stress-displacement hardening model and trilinear shear stress-displacement softening model were proposed.Based on the basic control equation of reinforcement-soil interface,the expressions of interface tension,shear stress and displacement at different stages of reinforcement of two kinds plastic deformation,strain hardening and strain softening,under pull-out load were derived respectively,which well reflect the progressive failure of the pull-out interface between reinforcement and soil.?4?A nonlinear,four-parameter viscoelastic model was proposed to characterise the mechanical properties of geogrids under long-term and low-stress load.A simplified rheological model of the viscoelastic plastic geogrid-reinforced tailings was established.The stress analysis of the whole reinforced tailings complex was divided into two stages which were corresponding to elastic and plastic state of tailings respectively.The time of tailings to produce plastic deformation?plastic arrival time?taken as cut-off point of two stages,constitutive relation of reinforced complex in two stages was put forward.?5?Through the single index and multi factor test of orthogonal design,reinforcement modulus?E?,laying length?L?,laying spacing?d?,pseudo-cohesion of reinforcement-tailings interface(c_if)and pseudo friction angle of reinforcement-tailings interface(?_if)were selected,the L₂₅?5⁶?orthogonal table was designed and 25 sets of calculation schemes were carried out.The sensitivity of five factors to the safety factor of reinforced tailings dam was obtained.The order of sensitivity was that laying length?L?>laying spacing?d?>reinforcement modulus?E?>pseudo-cohesion(c_if)>pseudo friction angle(?_if).?6?Through the model test and field prototype test of reinforced tailings dam,the influence laws of different reinforced layers,reinforcement types,overburden pressure,water content and outer slope ratio of the dam body on surface settlement,phreatic line and internal vertical pressure of reinforced tailings dam were obtained;The variation law of pore water pressure and earth pressure of conventional dam,geogrid reinforced dam and geotextile reinforced dam after slurry discharge was obtained.The reinforcement effect and mechanism of the reinforced dam were revealed.