Study On Deformation Mechanism And Failure Prediction Of Landslide In West Open-Pit Mine In Fushun

Coal extraction in West Open-Pit mine in Fushun,China began in 1901.At present,this mine comprises the largest pit mine in Asia.West Open-Pit mine measures 6.6 km long from east to west and 2.2 km wide from north to south,with a depth of approximately 420 m.Owing to more than one hundred years of high-intensity mining,open-pit slope became unstable.Different scales of landslides,collapses,ground fissures,and other geological disasters occurred numerous times.Over 90 recorded landslides took place in this mine.Currently,signs of dangerous huge landslide appear on southern slope of the West Open-Pit mine.Through engineering geological survey,southern slope of West Open-Pit mine features a deep-seated rock landslide with length of 1.5 km in north–south direction,width of 3.1 km in east–west direction,sliding surface depth of more than 100 m,and volume of approximately 0.3 billion m3.Owing to large distribution area of studied landslide many enterprises and residents situated around this area,occurrence such phenomenon will cause many casualties and property damages.Therefore,a landslide geological model should be developed to enable research on deformation characteristics,mechanism,and failure prediction in southern slope of West Open-Pit mine.This article relies on three topics cover by the following studies on mechanism and prediction of landslide: evaluation on stability of monitoring sections E400,E1200 and medium–short-term prediction of landslide failure time on southern slope of West Open-Pit mine;medium-scale shear on structural plane and acoustic logging test on southern slope of West Open-Pit mine landslide;landslide evaluation on southern slope of West Open-Pit mine.First,in the present paper,landslide investigation,deformation monitoring,and landslide surface survey are used to determine geological conditions of southern slope of West Open-Pit mine.This research determines morphological,structural,and material characteristics of predicted landslide and establishes a landslide geological model.Based on results of integrated monitoring system,landslide deformation characteristics are analyzed,and landslide risk zoning and deformation phase division are carried out.Based on landslide deformation signs,landslide mechanism is discussed.Second,landslide development trend and its failure time are analyzed and studied.The present work also puts forward long-term and medium–short-term prediction models and criteria and establishes a landslide prediction system for the southern slope of West Open-Pit mine.Finally,multi-source data are studied,and an integrated system is established for southern slope of West Open-Pit mine by combining multi-source geological data of the landslide.This system not only provides integration function about the landslide geological conditions,monitoring data and prediction results,but also offers deformation monitoring data,curves and prediction results in the form of dynamic web pages.The main research results are as follows:1.The following are research results on regional geological environment conditions of southern slope of West Open-Pit mine: southern slope of West Open-Pit mine features a large depth.On southern slope of West Open-Pit mine,dips of rock strata and landslide are in the same direction.Exposed strata comprise mainly of tuff and basalt with weak interlayer,and underlying bedrock is granitic gneiss.Weak basalt structural plane and unconformity(ancient weathered crust)between granite gneiss and basalt can be a potential sliding surface.Potential sliding surface inclination is larger than slope angle,representing a “hidden type” bedding slope.Fault F5 and F3–1 form east and west boundaries of the landslide,respectively.Many joints and weak structural plane develop,and groundwater and surface water are in close contact.2.The following are research results on deformation characteristics of landslide on southern slope of West Open-Pit mine: According to deformation characteristics of different parts obtained by landslide survey and results of engineering geological investigation,by combining differences between horizontal displacement and vertical settlement in deformation monitoring and using line E600(mine coordinates)and Fault F5–3 as dividing line,the whole landslide is divided into two regions: eastern and western regions.In eastern region,deformation rate is smaller than that in western area.Spatial deformation characteristics of landslide are obtained by studying 2D displacement vector of monitoring points and 3D displacement vector field of the whole landslide.Based on displacement characteristics and velocity with time curves,evolution of landslide deformation is divided into the following four stages: primary stage(August 2010 to August 6,2012),secondary stage(August 7,2012 to March 17,2013),tertiary stage(March 18,2013 to March 9,2014),and post-failure stage(March 10,2014 until the present).3.The following result is based on the study on landslide mechanism on southern slope of West Open-Pit mine.The failure mode is “sliding–bending–shearing”.The foot of the slope is cut as the rock mass is stripped because the mining activity started at the bottom of the open-pit since 2009,which resulted in a rock layer that was cut.The original rock and arch structure supporting the north and south slopes were destroyed.To obtain rocks in their free state,natural state of original rock is destroyed.Consequently,rock stress is released,and the slope deformation is triggered with the rock mass sliding north.The landslide initiated from the upper part and developed downward with increasing displacement.The sliding surface can be divided into two parts: the upper steeper part in the weak interlayer and the lower flatter part in the basalt.The deformation and failure processes can be described as follows: creep along the upper weak interlayer,tension cracking in the rear,and the lower,flatter part acting as a “locking section” to restrict slope deformation.The stress on the “locking section” accumulates with the development of creeping and cracking.Finally,the “locking section” is broken by the shearing force,and landslide failure occurs.4.This section discusses study on long-term prediction system of landslide on southern slope of West Open-Pit mine: Combined with basic characteristics and deformation characteristics of landslide,VC++,MATLAB programming language,limit equilibrium method(including Sarma,Janbu,and imbalance thrust methods),and analytic hierarchy process-fuzzy comprehensive evaluation(AHP-FCE)are adopted to develop a long-term prediction system for landslides.Results of limit equilibrium method and AHP-FCE method are in good agreement.Predicted landslide is unstable.5.The following discuss the study on medium–short-term prediction system of landslides on southern slope of West Open-Pit mine.Related study proposes two new models of medium–short-term prediction,namely,mathematical and physical models.Medium–short-term prediction system of landslide is developed using VC++ and MATLAB language.This system consists of data pre-processing module and medium–short-term prediction module.Based on displacement monitoring data on tertiary stage of landslides,this prediction system is used to predict landslide failure time,which is March 8,2014,through comprehensive evaluation of results from the two models.Through model evaluation of prediction results and by comparing these results with actual failure time of landslide,prediction results achieve high accuracy with acceptable error.Predicted and actual failure times are very close,indicating that the proposed model successfully predicted landslide.Results of the two methods are very close to actual failure time of the landslide,showing that these models can effectively reflect deformation characteristics and trend of deep-seated rock landslide and possess strong applicability and reliability,which can be used in actual landslide prediction.6.The following describe the study on geological multi-source data integration system of landslides on southern slope of West Open-Pit mine.For prediction results,landslide monitoring data and management platform are completed through system analysis and overall design.Using Google Earth,3D landslide display platform is specially designed.Web management platform and spatial database are integrated.Integrated system is constructed for southern slope of West Open-Pit mine;this system includes multi-source geological data(ISMsGD)about landslides.The system functions in 3D visualization,geological data and landmark correlation,and database connection.This system not only provides comprehensive integration function about location,geological conditions,deformation information,monitoring data,and prediction results of landslide but also offers deformation monitoring and prediction information of landslide in the form of dynamic web pages.This integrated system can provide data query,display,and management functions of landslide ISMsGD,serving as good platform for landslide research professionals and related workers.