Numerical Simulation On Formation And Evolution Process Of Wangxia Rock Mass And Rockfall Trajectory Prediction

Two thirds of the land area is mountainous and hilly areas in our country,especially in the western region of high topographic relief, complex geologicalstructure, crushing rocks, significant disastrous meteorological conditions, making thedangerous rock collapse, landslides, debris flow and other geological disasters verydeveloped. As a typical representative of the geological disasters, dangerous rockstability problems have the characteristics of distribution breadth, collapse instabilitysudden, rapid movement, strong hazard. However, the present study of perilous rockis weak. The premise of theoretical research, prevention and control measures ofdangerous rock mass is clear deformation mode and failure mode. Usually it can bedivided into: sliding failure, dumping and falling. Dangerous rock mass formation,instability, collapse and movement of the whole evolution process, are affected by theinternal and external causes. The internal causes could be topography andgeomorphology, formation lithology and rock mass structure. External causes couldbe weathering, human engineering activities, heavy rainfall.This paper regards unstable rock Wangxia as the object of study by collectingdata on the theoretical research and control methods, summarizing the deformationfailure mode and classification method at home and abroad, stability analysis methodsof dangerous rock collapse and the research on rockfall movement characteristics.What’s more, another task is analyzing natural geography and regional geologicalconditions in the study area, Wangxia dangerous rock mass history and recentdeformation and failure situation monitoring data, as well as the dangerous rock massof basic features. By using discrete element numerical simulation method, simulatingthe evolution of Wangxia rock mass at four different status of deformation and failure:Firstly, subjected to weathering, steep cliff front weakening rock mechanics propertiescause stress redistribution;Secondly, due to the influence of the cliff coal mining, andlocal stress concentration, the deformation and failure development; Thirdly, Fromfurther unloading and weathering rock mass due to mining, the mechanical propertiesof a further weakening;Finally, analyzing the impact of rainfall on the stability of rock body. Further to October21,2010, morphology of collapse deposits on the basis oforthogonal test method, carries on the method of rock and soil mass to the recoverycoefficient, tangential restitution coefficient and friction Angle of back analysis.Finally, the achievement parameters of rockfall are used to predict probable rockfalltrajectory of the Wangxia rock mass in the future. The main conclusions of this paperare as follows:(1) Through the analysis of the dangerous rock body of historical and recentdeformation monitoring data, realizing the rainy season is the period of increaseddeformation of WangXia rock mass. Furthermore, the effect of rainfall on October13-21,2010is the induction of severe deformation of the main reason for theinstability and collapse. The deformation and destruction lag law of rainfall is in1-3days.(2) The analysis of geology about Wangxia rock formation mechanism, realizesthat Wang-Xia rock is the result of coal excavation. Excavation makes crackpropagation, which contacts the two groups of joints under the original folds. It makesthe whole dangerous rock mass move down. As a result, the collapse pit becomesdeeper and larger. The mined-out area continues to influence the overlying strata.Thus, rainfall could intensify deformation and failure of the dangerous rock mass.Later, according to the results of numerical simulation, this paper analyzes thedangerous rock mass mainly affected by mining. The genetic mechanism for thewhole dangerous rock mass is sinking and tilting. The deformation and failure modeis going down and plastic flow-tensile fissure collapse.(3) The simulation model of discrete element numerical simulation in UDEC,could simulate on formation and evolution process of Wangxia dangerous rock massunder the following4stages: weathering, excavation, unloading and weatheringweakening mechanical index and the role of water. The numerical simulation analyzesthe displacement field, stress field adjustment and changes in the whole stage fromformation to deformation, and then to collapse. Thus, dangerous rock deformation andfailure is mainly caused by excavation. Finally, heavy rainfall could intensify deformation and even induce instability.(4) The process of formatin and evolution is as following: Sedimentary, Uplift Ofthe Three Gorges Reservoir Area, River Incisionâ†'Early Joints Cutting Rock Massâ†'Coal Mining, Coal Pillar Crushing, Compaction Of Backfill Material and StressConcentrationâ†'Weak Base Rock Mass Stress Concentration, Plastic Extrusion FlowDirection to the Free Surface, Rock Mass Collapse at the Foot of Cliffâ†'The UpperRock Mass Going Down, and the Lower Rock Mass Collapse Developing, PlasticExtrusion Flow Increasingâ†'Processive Going Down and Plastic ExtrusionFlow-Tension Crack Collapse.(5) Excavation influences the deformation and failure of lower dangerous rockmass. In which, intercalated sliding and interlaminar separation play an important rolein the interlayer. Damage of deep fissures control the deformation of the upperdangerous rock mass.(6) Reference of typical engineering examples at home and abroad researchresults given recovery coefficient （normal and tangential）and looking to Wangxiarock mass movement for calculating target position as far as2010, using orthogonalexperiment method, back analysis get the recovery coefficient and the friction Anglein the study area. And found that the main factors influencing the rock fall stopposition as far as initial velocity, which has nothing to do with the rock fall weight.(7) Deposits stay farthest position range from844m to848m, when Wangxiadangerous rock probably collapses in the future.