Study On The Variation Law Of Tailing Sand Strength Under Freeze-thaw Cycles

The tailings dam is a dam body formed by the accumulation of tailings sand,which plays a great role in the protection and management of the mine environment.Accidents that occur in tailings dams are often the result of long-term accumulation of weak damage or a combination of other factors.When the temperature changes periodically with the seasons,the moisture inside the tailings undergoes a constant phase change,which will lead to changes in the structure,moisture field and stress field of the tailings.Therefore,this paper takes the tailings sand of a tailings pond in Fuxin,Liaoning Province as the research object.The effect of freeze-thaw cycle times and moisture content on the stress-strain of tailings sand was studied by the combined method of macro and micro.Combined with the change characteristics of the microstructure of the tailings sand under the action of freeze-thaw cycles,the strength change law of the tailings sand was explored.And a constitutive model of freeze-thaw damage is proposed.The main research results of the paper include:(1)A series of freeze-thaw cycle tests and triaxial compression tests were performed on tailings sands with different moisture contents.The results show that the stress-strain curve characteristics of tailings sand are similar to those of ordinary soil.It consists of three stages:elastic stage,elastic-plastic stage and failure stage.However,the peak intensity appears late,and the softening phenomenon is not obvious.The shear strength of tailings sand decreases with the increase of freeze-thaw cycles.In addition,increasing the moisture contents.of the tailings sand to a certain extent is beneficial to improve the interface mechanical properties of the tailings sand.When the moisture content exceeds the optimal moisture content,it is not conducive to the stability of the tailings sand.(2)Obtain the mesoscopic structure images of tailings sand after freeze-thaw cycles by electron microscope,and use software to compare and observe the internal structure of tailings sand samples.The results show that with the increase of the number of freeze-thaw cycles,the frost heave will cause irreversible deformation inside the tailings sand,and the structure of the sample will be damaged.The overall level of the pore size of the pores becomes larger,the internal structure of the sample is loose,and the macroscopic mechanical strength decreases,specifically,the shear strength decreases.(3)Based on damage mechanics and tailings sand macro and mesoscopic test results,a damage constitutive model of tailings sand meso-structure damage during freeze-thaw process was established.The model is verified by experimental data,and the correlation coefficients of the fitting results are all over 0.920,indicating that the fitting effect is good.Freeze-thaw damage variables of tailings sand gradually increase with the number of freeze-thaw cycles.When the number of melting cycles is the same,the damage variable of tailings sand decreases with the increase of confining pressure.The increase of moisture content will also aggravate the degree of freeze-thaw damage of tailings sand.Through the above research,the mechanical properties of tailings sand under the action of freeze-thaw cycles were explored,and the strength damage of tailings sand by freeze-thaw cycles was studied,which has important scientific value and guiding significance for the safety and stability of tailings dams.