Research On Evolution Mechanism Of Tailings Dam Overtopping And Breach And Simulation Of Tailings Discharg

Tailings pond is one of the three major control projects in mines,and its safety not only affects the economic benefits of mining enterprises,but also affects the safety of life and property of downstream residents in the reservoir area and the health of the surrounding ecological environment.There are a large number of tailings dams in China,covering a wide range of areas.In recent years,the country has carried out special renovations on tailings ponds.However,due to the special nature of tailings dams and the gradual deterioration of operating conditions,normal dams have transformed into dangerous,dangerous,and diseased dams.Once the diseased dam body collapses,it will bring extremely serious economic losses and casualties of life and property to the downstream.This article takes the Wanlongshan tailings dam as the engineering background.Firstly,the empirical formula for calculating the dam breach is modified,and its rationality is verified using a tailings dam breach example;Then,model experiments and numerical simulation methods are used to study the development law of tailings dam failure;Finally,the revised empirical formula and numerical simulation methods for dam failure research are applied to the analysis of the Wanlongshan tailings dam failure.The research content and main conclusions of this article are divided into the following four aspects:(1)In response to the empirical formula for calculating the width and depth of dam breach established by Zhong Qiming and others,combined with the large calculation error and the characteristics of narrower particle size distribution and more fine particle content of tailings dams,it was revised.Then,data from existing literature on tailings dam breach examples were used for verification.The results showed that the relative error between the revised empirical formula and the values in the literature was within 20%,the revised empirical formula can be applied to the analysis of tailings dam failure.(2)Establish an indoor tailings dam overtopping breach model experiment to explore the changes in the form,width,depth,sand breaking rate,dam breaking flow rate,and sand breaking volume of overtopping breaches under five operating conditions of inflow flow rates of200L/h,300L/h,400L/h,500L/h,and 600L/h.Through model experiments,it was found that the morphology of the dam’s breach went through four stages from the beginning to the breach,namely the formation stage of the fine gully,the development stage of the gully,the sudden increase stage of the width,and the stable stage of the breach.The final size of the breach increased with the increase of the inflow flow;the experiment shows that there is a linear relationship between the sand breaking rate and the dam breaking flow rate,and the sand breaking amount and dam breaking rate increase with the increase of inflow flow rate.Finally,the modified empirical formula was applied to the analysis of the breach in the model test,and the error of the depth of the breach obtained from the modified empirical formula was within 20%under all operating conditions;In most cases,the relative error of the width of the breach is less than 20%,and in a few cases,the relative error is greater than 50%.The reason is that the strong cohesion of the tailings themselves was not fully considered when establishing the formula.The comparative analysis results indicate that the revised empirical formula is basically reasonable.(3)Using the computational fluid software FLOW-3D for numerical simulation of dam failure,the model was first established and reasonable parameters and boundary conditions were selected.Then,the five working conditions of the model test were simulated for dam failure.The results showed that the error between the simulated values of the depth of the dam failure and the measured values of the model was less than 20% under each working condition,and the relative error of the simulated values of the width of the dam failure was only 14.5% under working condition two,while the other working conditions exceeded 20%.The reason for this is that:,The instability and collapse process of the breach slope in the model test,as well as the particle size distribution of the test sand and other model properties,cannot be fully simulated in numerical simulation,and the tailings sand has strong cohesion.Numerical simulation cannot simulate the instability of the breach slope sliding towards the center of the breach.(4)Using CATIA software to establish a three-dimensional model and downstream terrain model of the Wanlongshan tailings dam,and importing them into FLOW-3D for numerical simulation of dam failure.The results showed that the relative error of the dam failure width value was-16.89%,while the relative error of the dam failure depth value was 25.96%.The reason is that the flow parameters in the two methods were calculated using different empirical formulas for dam failure flow and inflow flow,this leads to inconsistent arrival times of peak flow during numerical simulation of dam failure,resulting in an increase in the depth of the numerical simulation breach greater than the depth calculated by empirical formulas.The numerical simulation of tailings flow shows that the depths of tailings at Zhongzhai,Laozhai,and Xinzhai monitoring points downstream of the Wanlongshan tailings dam reach the corresponding maximum depths of 8.74 m,5.66 m,and 0.92 m at 2200 s,5500s,and 8500 s,respectively.The discharged tailings did not reach the elevation of the three villages,but would threaten the safety of downstream traffic,farmland,and river channels.