| Waste dump is usually composed of a large number of loose geotechnical materials,in which geological disasters such as landslides and debris flow(water-rock flow)may occur under action of self-weight,rainfall,freeze-thaw cycle,vibration and vehicle load.These disasters may seriously not only threaten the human beings living in the downstream,but also influence the safe operation of open-pit mine.Taking the landslides in 2014 and the water-rock flow in 2010 occurred at the Nanfen high waste dump as cases,the thesis systematically studies the occurrence mechanism and dynamic process of landslides and water-rock flow by using field investigation,meteorological and hydrological data,satellite map data,the smoothed particle hydrodynamics(SPH)numerical simulation and physical model tests.The main contents and results of this thesis are as follows:(1)The precursors,failure forms and characteristics of landslides and water-rock flow in the waste dump are described,and the start-up mechanism of landslides and waterrock flow is revealed.Continuous and intensive dumping leads to an increase of the selfweight of the waste dump and a decrease of its stability.Under the action of multiple factors such as soil moisture content,freeze-thaw cycles,pore pressure,external loads and gradation,the shear strength of the soil decreases,and landslides eventually occurred in the waste dump.The antecedent rainfall and daily rainfall are the most direct inducements to cause water-rock flow in the waste dump.The loose shallow gravel soils and the U-shaped valley with a certain slope provide the necessary conditions for the occurrence of water-rock flow.Through the analysis of historical rainfall data,the probability criterion of the occurrence of water-rock flow(debris flow)is given.(2)A numerical method for generating real three-dimensional terrain is proposed,which can build different geological disaster models on the terrain.This method generates a real three-dimensional surface,while the bedrock with a certain depth under the surface is ignored.At the same time,the thin three-dimensional terrain is used as the calculation boundary condition of the numerical model.This numerical method can reduce the computational cost and improve the computational efficiency,and the numerical results are closer to reality.(3)To obtain the movement characteristics and morphological evolution of geological disasters of the dump,the SPH method combined with Mohr-Coulomb theory and Mie-Grüneisen state of equation were employed to reproduce their dynamic process.The SPH simulation results of landslides and water-rock flow in the dump show that their sliding(flow)velocity,distance,deposition profile and influence range are consistent with the field investigation results.The SPH method can vividly reproduce the dynamic process of landslides and water-rock flow in the dump.(4)To understand the deformation characteristics of the Nanfen waste dump under composite loads,a physical model test of waste dump without support and reinforcement was conducted under the action of 0-75 kg graded external loads.With the thawing of ice-snow layer and the increase of external loads,the model dump has successively experienced settlement,local collapse,clastic flow and landslides.To study the support effect of different anchor cables and the deformation and failure characteristics of waste dump,the reinforcement model tests were performed with the graded external loads of 0-100 kg,under action of constant resistance,large deformation NPR(negative Poisson’s ratio)anchor cables and conventional PR(Poisson’s ratio)anchor cables combined with flexible anchor net.With the thawing of snow-ice layer and the increase of external loads,the model dump supported by NPR anchor cables has successively experienced settlement,local collapse and debris flow,while the model dump supported by PR anchor cables has experienced shallow landslides with the increase of external loads.(5)With the increase of external load,the NPR anchor cables did not fail due to the sliding of the constant resistance body,while the PR anchor cables were partially broken.The failure characteristics of the model dump supported by NPR are weaker than those of the dump supported by PR.The NPR anchor cables can continue to play the role of support and reinforcement,effectively control the deformation of the dump,and has a good reinforcement effect.In addition,in the physical model test,distributed optical fibers,thermometers,and tension meters were employed to monitor the strain,temperature,and anchor cable force,respectively,and an ice-snow layer was laid to simulate the thawing process.Finally,some disaster prevention and mitigation measures for the waste dump are given.The analysis of the dynamic process and occurrence mechanism of landslides and water-rock flow in the waste dump and the assessment of the risk range can provide key parameters and a basis for the prevention and control of dump disasters.The physical model test and NPR anchor cable support can provide an optional ideal solution for the slope support and reinforcement of the dump to promote the long-term safe production and operation of the open-pit mine. |
