Study On Macroscopic And Meso-Mechanical Properties Of A Metal Mine Tailings Under Drywetting Cycles

Due to the changes of the natural environment such as rain and snow,the position of the phreatic line of the tailings dam is changed constantly,which makes some parts of the dam repeatedly alternate between dry and wet.Generally,the deformation of the tailing structure is mainly determined by its structural strength and modulus,which are mainly determined by the size,shape and arrangement structure of its particles.In other words,the macroscopic deformation and failure of the tailings structure is the result of the change of its fine and microscopic fabric.Therefore,it is particularly important to study the macro and micro mechanical properties of tailings under the action of dry-wet circulations.In this paper,based on the results of triaxial test of tailings samples in laboratory,the numerical models of triaxial consolidation undrained compression tests of tailing samples with different water content and different dry-wet circulations were established respectively by using particle flow numerical simulation software(PFC^3D).By comparing the results of numerical simulation test and laboratory test,the high degree of coincidence between stress-strain curve,peak strength and elastic modulus is taken as the standard to determine the meso-parameters of numerical simulation of particle flow.By continuously adjusting the parameters,the meso-parameters of numerical simulation of particle flow are finally obtained.The macro and micro mechanical properties of tailings were investigated from the perspectives of stress-strain curve,axial strain-volumetric strain,coordination number,particle velocity vector,particle position when the sample was destroyed,and contact force chain between particles.The main research work and achievements are as follows:(1)Based on the results of undrained triaxial consolidation tests,a numerical model is established,and through a large number of numerical simulation tests,the numerical test parameters which are in good agreement with the mechanical properties of laboratory tests are finally obtained.(2)In the numerical test,the samples with low porosity and confining pressure are more prone to dilatancy.The radial expansion of the model reduces the number of contacts between particles.(3)Compared with the high porosity model,when the axial strain is the same,the particles velocity field of the low porosity model has a higher degree of disorder and particles nearing the lateral wall particles move outward more obviously in the radial direction.From the microscopic perspective,it is proved again that the low porosity has a certain promotion effect on the dilatancy characteristics of the sample.(4)As the sustainment of loading process,the uniformity of the contact force between particles with different porosity models decreases at first and then increases.However,when the axial strain is larger,the contact force between particles tends to be homogenized.