Research On Seepage Failure Mechanism And Simulation Method Of A Landslide Dam

In order to study the mechanism of seepage failure and collapse of landslide dams,an experimental study on seepage failure of landslide dams is carried out.The control variable method is used to study the influence mechanisms of particle size distribution of dam material,position of initial seepage passage,and compactness on seepage failure of a landslide dam.The weight of the residual dam body,flow process through the seepage channel and breach,development process of the seepage channel and breach,and final form of dam failure under different conditions are studied.The main research work and conclusions are as follows:(1)In the pre-test preparation stage,3 groups of dam material gradation,4 initial penetration channels,and 3 dam body compactness are designed.A sufficient amount of test materials was prepared,the test water tank and flow control system were debugged,and auxiliary instruments were set up.During the test phase,10 groups of seepage failure tests were carried out,and the flow development process,passage and break development process,weight of residual dam body,and final failure form of the dam body were measured under each working condition.In the stage of test result analysis,the whole process of seepage failure development of the landslide dam is analyzed in depth according to the test data.In the theoretical research stage,based on the seepage failure mechanism of a landslide dam,the mathematical model of seepage failure is established and the corresponding calculation method is put forward.(2)At the initial stage of seepage failure,the expansion speed of the seepage channel is slow,which prolongs the duration of the dam break to a certain extent.With the continuous expansion of the seepage channel,the scouring effect of seepage water on the soil mass of the seepage channel becomes stronger,resulting in cracks and intermittent collapse of the soil mass above the channel.Due to its looseness,the collapsed soil body is easily washed downstream by dam-break water flow.At this stage,the seepage channel develops rapidly,mainly with intermittent expansion.In a short time,the dam break mode changes from seepage failure to overtopping failure,and the flow decreases gradually after the peak value is quickly reached.During the process of gradually decreasing flow,there is a small increase in flow caused by the intermittent collapse of the collapse slope.(3)The position of the initial seepage channel has an obvious influence on the peak flow rate of dam breaks,especially the horizontal position(middle part of the landslide dam or abutment),which is more obvious than the vertical position.The closer the initial seepage channel is to the dam abutment,the slower the development of dam break and the smaller the width of residual dam break.With the increased compactness of the landslide dam,the duration of dam break is prolonged,the time of peak flow is delayed,and the final width of dam break is reduced.With the increase in gradation width,the width of the residual breach of a landslide dam decreases gradually.(4)A mathematical model that can reflect the mechanism of seepage failure and collapse of the landslide dam is established to simulate the whole process of the evolution of the weir body from the seepage channel to the collapse of the channel and finally to the overtopping.The mathematical model deduces the critical starting flow rate of soil particles through stress analysis of soil particles in penetration channels and breaches.A formula for simulating the evolution of seepage channels and the evolution of overtopping break-out is proposed that takes into account the effects of the inclination angle of seepage channels(slope angle of the dam),friction flow velocity,water flow velocity,and soil particle gradation and intensity on the amount of scouring.The model is used to calculate and analyze the Rio Toro landslide dam in Costa Rica,South America,and a test dam that collapsed due to seepage failure.The rationality of the model is verified.(5)Using the mathematical model established in this paper,the parameter sensitivity analysis of the Rio Toro landslide dam is carried out.The analysis results show that the particle size of the dam material has a great influence on the development of break flow rate and width,and the position of the initial penetration channel has a significant influence on the development law of break,especially the break flow rate and the break crest width.The sensitivity of the output parameters of the dam to the internal friction angle is low.The mathematical model of seepage failure of a landslide dam can provide support for a more accurate evaluation of disaster consequences caused by dam break,mitigation of losses caused by dam break,and the formulation of an emergency plan for flood control.