Research On Deformation And Failure Mechanism Of Slope Induced By Underground Mining In Mountainous Gently Inclined Coal Strata

Slopes with gently inclined coal Strata are widely distributed in Southwest mountainous areas,and there are some common characteristics.such slopes usually with long time mining activities beneath the slope,high and steep terrain,and well-developed jointswith high dip angle,“hard on the soft” slope structures.Superimposed by special geological condition and underground mining activities,the forming mechanism of process is more complex,and slope stability evaluation and early detect becomes very difficult.Therefore,the study is very important for the analysis of slope deformation and failure mechanism induced by underground mining with gently strata,also for stability evaluation and early identification characteristics.This article takes the case of Meidongpo deformation bodies in Duyun city of Guizhou province.Based on several means of field investigation,geophysical and process simulation,it is identified by mined-out area distribution and development rule of slope fracture system.It recreates movement and deformation process of overburden rock in multi-coal Strata under repeated mining conditions.It analyses mechanism and rule of slope deformation induced by repeated mining and free face.The mechanism of slope deformation and failure and the characteristics of instability identification are put forward.There has been some progress in the study about investigation of the mined-out area distribution,construction of deformation crack system,slope deformation rules in multi-coal Strata under repeated mining conditions and geological mechanical model.The results have references to mechanism of deformation and failure of mining slopes.The results are as follows:(1)The mined-out distribution modelin multi-coal Stratais established.Based on high-density resistivity method and transient electromagnetic method,the distribution and failure of the mined out areas are surveyed by collecting the materialand coal mine survey results.Thereby,the mined-out distribution modelin complex and multi-coal Stratais established in the slope.The mined-out area can be broadly divided into nine blocks according different periods.(2)It expounds that the crack system of Meidongpo deformation body is corresponding to the mined-out area,and establishes a conceptual model of deformation mechanism of Meidongpo slope.It identifies the development rules of Lishanpo deformation body and Jieniangpingdeformation body.The relationship between cracks induced by the long wall method,the mined-out area and the joint surface is analyzed.There is a corresponding relationship between the mined-out area boundary and the fracturesboundary in coal mines on the top of slope.The formation of wide cracks has a relationship with repeated mining activities in large extent.(3)The rule and mechanism of deformation and failure of overburden rock in multi-coal Strata under repeated mining conditions are revealed.Physical model testing revealed there is a corresponding relationship between the deformation crack and the underground mined-out area.Cracks are distributed at the boundary and the middle part of the underground mined-out area.The V-shaped tensile cracks at the mined-out area boundary are formed,thatis,wide at the top and narrow at the bottom.The direction of crack propagation is roughly perpendicular to the working face of coal mining.The central part of the mined-out area is subjected to bending and subsidence,which can broke.No obvious cracks were found in the remaining area of the mined out area,andoverburden rock separations were often found.The overburdenrock on the outerboundary of the mined-out area is pushed outwards by mining pressure arch.Subsidence of overburden rock has asymmetry of non-normal relationship with the excavation sequence.Horizontal movement of overburden rock has wave-shapedor parabolic relationship with the excavation sequence.Repeated mining has great impact on slope deformation and failure.(4)It reveals that free face has “amplification effect” on mining slope with high and steep terrain.Numerical simulation experiments withdiscrete element method show that slopeswith free face have not only toppling deformation toward mined-out area,but also toward free surface.Free face obviously increases the horizontal movement value and range.Along with the increasing angle of free surface,the gradually increase of movement of overburden rock willclose to the free surface.(5)The regularity of the influence on the slope deformation induced by repeated mining is revealed.Under the primary and secondary repeated mining conditions,slope will form moving Basin.Along with the repeated mining,the slope will produce discontinuous deformation.Slope surface cracking deformation continues to expand,and both sides of the mined out area will formfractured zone.The overburden and slope surface willproduce a larger subsidence by the effects of repeated mining,and the horizontal movement value appears to be less affected by repeated mining.Combination of repeat mining and free surface enlarges fractured zone,and intensifies the deformation.Slope deformation due to repeated mining in multi-coal Strata has experienced four stages,namely initial deformation stage,constant deformation stage and accelerated deformation stage and stable deformation(creep).The monitoring data show thatthe slope is in the steady deformation(creep)phase.(6)It establishes a geological and mechanical model for the deformation and failure of the mining slope in gently inclined coal Strata.It proposes that slope deformation process includes four stages: mining disturbance,the tension at the crest,deformationincrease,creep deformation throughnumerical simulation and physical model test.Slopedeformation and failure mechanism can be summarized as tension-creep-lateral shear failure type.Thereby,a geological and mechanical model for the deformation and failure of the mining slope in gently inclined coal Strata is established.Based on geological model of slope,displacement vector graph,crack evolutiongraph and sliding sketch are drawn.Itproposes that five characteristics can identify mining slope failure type and landslides direction in Southwest Mountain.which are high and steep terrain,favorablefree surface,well-developed jointswith high dip angle,undergroundmining condition,“hard on the soft”slope structures.It is proposed that free surface has implications for slope failure identification.