Research On Freeze-thaw Damage Mechanism Of Mudstone Slope And Seasonal Control Mining Method In Open-pit Mines Of Cold Regions

The damage and deterioration of rocks in cold regions under the action of seasonal replacement and day night cycle of freezing and thawing has led to a series of engineering geological problems,which seriously affect the engineering construction and mineral resources development in cold regions.The macroscopic mechanical properties and microscopic damage mechanism of rock under freezing and thawing have always been the frontier direction in the application field of rock mechanics and cold area engineering.Studying and mastering the mechanism and evolution law of rock freeze-thaw damage can provide theoretical basis and engineering guidance for engineering construction and safe mining of mineral resources in cold regions.Combined with the actual needs of open-pit mine engineering in cold area,based on indoor test,theoretical analysis and numerical simulation,this thesis focuses on the change characteristics of macro mechanical properties of mudstone under freeze-thaw and freezing conditions,the freeze-thaw damage mechanism of mudstone,the influence of freeze-thaw on the whole life cycle stability of open-pit slope and the control mining method.The main research work is as follows:(1)Taking the mudstone of open-pit mine in cold area as rock sample,the freeze-thaw cycle test and uniaxial compression test considering slope water replenishment conditions are carried out,the relationship curves between uniaxial compression strength,elastic modulus,peak strain and freeze-thaw cycle times of mudstone are obtained,the relationship curve between macro mechanical parameters of frozen mudstone and freezing temperature is obtained,and the freeze-thaw damage evolution equation of cement replenished rock is established,The strengthening mechanism of freezing strength of mudstone is analyzed,and the freeze-thaw damage mechanism of mudstone is revealed.(2)The effects of freeze-thaw cycle on the fracture structure and micro morphology of mudstone were analyzed by electron microscope scanning technology(SEM);Using nuclear magnetic resonance(NMR)technology,the pore structure and pore size of mudstone are measured,and the NMR characteristics such as T₂distribution,total spectral area and pore size distribution of mudstone are obtained.The changes of NMR characteristics and pore structure of mudstone under different freeze-thaw cycles are revealed.(3)The transformation model between macro damage factor(elastic modulus)and micro damage factor(porosity)under different freeze-thaw cycles is established,and the freeze-thaw damage evolution equation and constitutive model of mudstone based on elastic modulus as damage factor are deduced.(4)This thesis analyzes the influencing factors of slope stability of open-pit mine in cold area,expounds the theoretical connotation of time-dependent slope of open-pit mine,reveals the temporal and spatial evolution law of shape and stable state of end slope in the whole life cycle of near horizontal internal drainage open-pit mine,and defines the three-stage characteristics of end slope stability in the process of open-pit mine from trenching to periodic internal drainage,The engineering time point of the worst stability state of the end slope is defined.(5)Combined with the characteristics of seasonal climate change in cold region,the influence of freezing and thawing on the stability coefficient and failure mode of end slope is analyzed;Based on the strength strengthening characteristics of frozen mudstone,the landslide mode of frozen slope is studied,the seasonal control mining method and safety guarantee measures of open-pit mine in cold area are put forward,and the window period of side mining is defined.(6)Taking Xinjiang Tianchi energy south open pit mine as an application case,the step parameters,pressure and drainage parameters and time of seasonal side slope mining in the south side are determined.Considering the economic benefits of different development and transportation systems in the south open pit mine,the optimal side slope mining scheme is determined,the slope monitoring scheme is formulated,and the slope radar monitoring data before,during and after side slope mining are analyzed.This dissertation includes 100 figures,26 tables,and 122 references.