| Large open pit coal mine slope stability is the key technical issues related to the production of safety,is also an important subject and long-term research in geotech-nical engineering.This paper made a servery of Moatize open pit coal mine,and found out the stratum structure and the physical and mechanical parameters of differ-ent lithology and the water occurrence situation of slope.And conducted a compre-hensive evaluation of engineering geological conditions,according to the Moatize open pit slope structure and physical and mechanical parameters of different lithology.Combined with geological conditions,for the end slope of Moatize Open-pit Coal Mine,slope shape and exposure time are the external factors affecting its stabil-ity,and rock mechanics properties are the internal factors affecting the slope.The precondition of analyzing the stability of End-Slope is to judge the potential landslide mode of the slope,and then select the appropriate method of slope stability analysis.Moatize Open-pit Coal Mine mining to the first mining area of the current position of the south side slope basement is anti-dip,the north side slope basement is near the level.Through the analysis of the engineering geological condition of the mine,it is found that the main constituents of the end slope are coal,mudstone and sandstone,which have large thickness,many layers,good permeability and high strength.The potential landslide mode is preliminarily judged to be arc sliding.Generally speaking,slope deformation is usually the precursor of slope failure.Slope failure does not occur instantaneously,only when the slope deformation accu-mulates to a certain extent,it will lead to the ultimate failure.Deformation and failure of open-pit coal mine slope mainly includes spalling,caving,sliding,settlement and flow according to the specific form of occurrence.Deformation and failure of the same slope may be one or several of them,and there will be a certain degree of trans-formation between failure modes.Sliding deformation is one of the most frequent and serious failure modes of open-pit mine slope.According to the type of formation five geotechnical boreholes enabled soil me-chanics testing by taking undisturbed samples using Shelby tubes.SK-1,SK-3,SK-5,SK-6,SK-11 are the names of these five boreholes.The 1-7 section slopes of permanent slopes in southwest and northwest China are analyzed.A factor of safety value of 1.50 for permanent slopes was decided to be sat-isfied for planned water table level.7 sections with 21°overall slope angle having 5benches were analyzed.The slip surface having lowest factor of safety was detected and the section#3 had the lowest factor of safety 1.47.Flac3D was used to explicit finite-difference for analyzing Moatize failure,Temporary and Permanent slopes were designed in the safe range of safety factor as steep as possible.Finite Difference Analysis and Limit Equilibrium Analysis in Temporary Slopes were carried out in order to observe displacements and confirmation of the stability of the slope and the production slopes were analyzed and considered as safe,and was obtained the factor of safety analysis of slopes with different water level and different angles by limit analysis,the factor of safety of the weakest part was analyzed by Flac3D software of the model was 1.73.In fact,factor of safety value is higher for an overall instability condition.The strength reduction method for determining factor of safety was implemented in Flac3D by SOLVE FS command.Flac3D found 1.22 factor of safety value for permanent slopes having 21°overall slope angle which is the same value(1.20).Fi-nite difference model was modified for different overall slope angles and the effect was investigated when the overall slope angle is steepened.Overall slope angles of21°,27°,35°and 36°were modeled.When the model had overall slope angle of 35°,was still stable and 36°was found as a boundary for stability.When the angle was raised to 36°instabilities drastically increased and a collapse could be predicted.It was understood that factor of safety was 1.00 when the overall slope angle is between35°and 36°.When deciding the stability-instability boundary,some graphical outputs are considered as beneficial.Factor of safety analysis of slopes having 35°and 36°overall slope angles were computed by using Flac3D software.Flac3D computed 1.13 for 35°and 0.96 factor of safety for 36°overall slope angle.Factor of safety values for 21°,35°and 36°slope angles are summarized on the Figure 4-39 by using Flac3D factor of safety calculation property.A drastic change is also take attention between the overall slope angles of35°and 36°.Results of Flac3D/Slide for factor of safety results ratio is 1.26.It is observed that the results calculated by Slide is lower than the Flac3D results.In permanent slopes the factor of safety was analyzed with three different water levels by Limit Equilibrium Analysis and Finite Difference Analysis.from the shear strain rate contour of the finite difference analysis and Janbu Simplified method was used in the analysis as follow:(1)For conditions constituting local weaker parts like benches,shear strength re-duction principles on Flac3D will result in finding a factor of safety dedicated to overall stability.Moreover,Flac3D may be upgraded for different options for finding factor of safety for this kind of particular conditions as considered.(2)If an overall slope having 21~°angle is established and dewatering target is not satisfied,the situation must be foreseen.Thus,a water table level which was 50 m deep from the surface and a water table on the surface was constructed on to the mod-els and circular failure analyses were conducted.The slip surfaces having lowest fac-tor of safety was detected for two distinct dewatering conditions.Limit equilibrium analyses are presented in the Slide Software Graphical Outputs for permanent slopes having ground water level 50m below the surface.(3)When the ground water level was raised to the 85m and maintaining the slope angle,the Factor of safety instability drastically increased and a collapse could be predicted.It was understood that factor of safety was 1.474 when the overall slope.(4)The stability of end slope is closely related to slope angle,and the stability co-efficient of each section decreases linearly with the increase of slope angle.When the slope angle of S section is steeper to 28°,the slope stability coefficient is 1.127,and that of N section is steeper to 26°,the slope stability coefficient is 1.109.Both of them can meet the requirement of safety reserve factor 1.1 before pressing,and take into account the safety and economy of the end-to-end steep slope mining.There are 74 figures,21 tables and 100 references. |
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