Evolutionary Regularity Of Plastic Zone And Stability Control In Repetitive Mining Roadway In Shendong Mining Area

Shendong mining area has the characteristics of high exploitation intensity.In order to ease the tightness of mining and excavation,most of the mining methods of mining roadway are the ways of simultaneously excavating two or even three roadways.As a result,some retained roadways are affected by repeated mining,the mine pressure appears intense and maintenance is time-consuming.This kind of arrangement of double lanes or even three lanes is widespread in Ningxia,Shanxi and Inner Mongolia.Therefore,the damage mechanism and stability mechanism of roadway affected by repeated mining are clarified,and the stability of surrounding rock of roadway is ensured by repeated mining,which has certain theoretical significance and practical value.In this paper,the mining roadway in Shendong mining area is taken as the engineering background,theoretical analysis,on-site observation,numerical simulation and field engineering test are adopted,and the formation and evolution of the plastic zone of roadway surrounding rock is the main line.The distribution law of main stress in surrounding rock of roadway under repeated mining conditions is obtained,the evolution law of the plastic zone of surrounding rock of repetitive mining roadway is obtained,and the mechanism of malignant propagation of roadway surrounding rock plasticity under repeated mining conditions is revealed.A quantitative prediction of the depth of plastic failure of surrounding rock of roadway under repeated mining conditions is obtained.The plastic failure depth of roadway surrounding rock is controlled by optimizing the mining technical parameters.The stability control system for the surrounding rock of the roadway in the plastic zone and the subsequent support is formed to guarantee the safe and efficient production of the mine,and the following main conclusions and innovations are achieved:(1)The distribution of roadway stress and the asymmetry evolution of plastic zone under repeated mining conditions in Shendong mining area have been obtained.The criterion for the morphological parameters of plastic zone has been established,and the mechanism of the malignant extension of the plastic zone of roadway surrounding rock under repeated mining conditions has been revealed.And the occurrence of malignant expansion of plastic zone under repeated mining conditions is clarified.(1)The dynamic distribution law of the axial principal stress during retained roadway is obtained.The non-full mining stress curve showed a single peak distribution,and the peak position is in the middle of the goaf.Under full mining conditions,the stress characteristic curve is ?-shaped,symmetrical about the left and right,the middle is high and gentle,and the left and right sides are low,but the change is large.It is divided into 7 stages.The distribution curve of the angle between the maximum principal stress and the vertical direction is an inverted ?-shaped distribution,which approximates the horizontal,vertical,deflection,stability,and then deflection back to the near-horizontal direction.The rapid change in the magnitude and angle of the principal stress is located in the stage of lag drastically affected,within 200 m behind the working face.(2)The distribution rule of the principal stress during the secondary mining of retained roadway is obtained: the principal stress change curve is decreased on both sides,and the middle stable axisymmetric distribution is divided into three stages.The curve of the angle between the maximum principal stress and the vertical direction is just opposite to that of the principal stress curve.It appears to be deflected,stabilized,and then deflected to near-horizontal opposite direction in the vertical direction.The sharp changes in the size and angle of the principal stress are located in the advance impact phase,within 10 m in front of the working face.(3)The law of evolution of the plastic zone of the surrounding rock of the roadway with repeated mining has been obtained,and the whole process of the evolution of the plastic zone has shown obvious stages.During the first mining period,the evolution of the plastic zone of the surrounding rock is characterized by five phases.The rapid expansion of the plastic zone is located in the stage of severe lag of lag,within 200 m behind the face.During the period of secondary mining,the evolution of the plastic zone of the surrounding rock is characterized by two stages.The rapid expansion of the plastic zone is located in the stage of advanced severe impact,within 10 m in front of the working face.(4)It is found that the plastic zone of roadway surrounding rock exhibits non-uniform expansion under repeated mining conditions.In the stage of lag severely affected and the period of severely advanced influence,it can be found from the extended depth and shape of the plastic zone that the expansion of the roof on the side of the coal wall is greater than on the side of the coal pillar,and the direction of the expansion of the floor is just opposite to that of the roof.Coal pillars show a significant expansion to the roof side.The depth of the middle wall of the coal wall shows a symmetry expansion characteristic.The depth of expansion of the coal pillars is obviously larger than that of the coal wall.(5)It reveals the mechanism of the malignant propagation of the plastic zone in surrounding rock of roadway under repeated mining conditions.By analyzing the morphological characteristics of the plastic zone of roadway surrounding rock,it is concluded that the greater the difference in principal stress and the ratio,the more uneven the plastic zone of the roadway surrounding rock is,the greater the depth of plastic zone damage is.When the direction of principal stress of surrounding rock is deflected,the distribution pattern of the plastic zone of roadway surrounding rock will be deflected.The position of the leaf in the plastic zone has directionality.Under the joint action of the size and angle of the principal stress,the plastic zone will develop unevenly.When the principal stress difference and ratio are constant,the larger the minimum principal stress is,the larger the plastic zone is.When the principal stress difference and ratio and the minimum principal stress are both large,the plastic zone will develop viciously.(6)Changes in the width of coal pillars will result in changes in the position of the roadway,which will change the size and direction of the main stress of the surrounding rock.In the mining area affected by the mining of the goaf,the farther the roadway location is from the goaf,the smaller the main stress of the surrounding rock is.The direction of maximum principal stress is gradually deflected from the vertical direction to the horizontal direction.The smaller the plastic damage range and depth of surrounding rock are,the more uniform the plastic zone morphology is.(2)The nine main controlling factors for the depth of plastic failure in the repetitive mining roadway in Shendong mining area are determined,and the main controlling factors of the depth of plastic failure of the surrounding rock are significantly affected,and a plastic extended depth prediction model is established.A prediction system for the extended depth of the plastic zone of the roadway surrounding rock is developed to realize the quantitative prediction of the depth of plastic failure of the roadway under repeated mining conditions in Shendong mining area.(1)Based on the mining conditions and surrounding rock conditions in Shendong mining area,combined with the recessive equations of the plastic zone boundary of surrounding rock in a round roadway in a non-isostatic stress field,the main control factors of five plastic failure depths of two sides of roadway such as the mining depth,mining height,coal pillar width,working face length,roadway height,etc.are optimized.And the main control factors of nine plastic failure depths in roof and floor such as cohesion,internal friction angle,tensile strength,and elastic modulus are discussed.The sensitivity of the depth of plastic failure in the retained lane is from large to small in the two sides: mining depth,working face length,coal pillar width,mining height and roadway height;in the roof: The top plate is: mining depth,working face length,cohesion,internal friction angle,elastic modulus,coal pillar width,mining height,roadway height,tensile strength.And it is similar basically in the floor and roof,except that the width of the coal column is lower than the mining height.(2)Based on the significant influence degree of main controlling factors of plastic failure depth of surrounding rock of mining roadway,a multivariate non-linear regression analysis is used to analyze the relationship between the depth of plastic failure and the influencing factors of the depths of roofs and floors.A prediction model for the depth of plastic deformation of retained roadway is established,and a prediction system for the depth of plasticity in the surrounding rock of a roadway with repeated mining is developed.The prediction of the depth of plastic failure of roadway under repeated mining conditions in Shendong mining area is realized.(3)Based on the prediction system of plastic failure depth of repetitive mining roadway,by optimizing the technical parameters of mining to control the depth of plastic failure of roadway surrounding rock,a stability control system for the roadway surrounding rock that is “control first-yield second-support last” is formed,which provides foundation for quantitative design of support parameters of repeated mining roadway in Shendong mining area.The study found that the support resistance provided by the existing support technology has little effect on the plastic zone of surrounding rock.Based on the prediction system of plastic failure depth of repetitive mining roadway,the technical parameters of the mining are optimized to fundamentally change the stress and angle of the surrounding rock of the retained roadway so as to achieve the purpose of controlling the plastic failure depth of the surrounding rock.When it is impossible to adjust the mining conditions,the concept of “control first-yield second-support last” is formed,and the reinforcing support technology is applied to obtain the reasonable position and supporting time of the support for retained roadway,and prevent the occurrence of safety accidents such as roof fall and ensure safe production.After applying the roof reinforcement support technology to the 22205 return airway of Buertai Mine,it can effectively control the collapse and fall of the collapsed surrounding rock and ensure the stability of surrounding rock.