Asymmetric Deformation Characteristics And Failure Mechanism Of The Gob-Side Coal-Rock Roadway And Its Control Techniques In Gently Inclined Coal Seam

As the main component of the only base located in South China among 14 large coal bases of China,Guizhou province,AKA the coal sea in the south of the Yangtze river,is rich in coal resources,yet the mining conditions are also very complicated.For instance,the typical gob-side coal-rock roadway in gently inclined coal seam(GSCRRGIC)shows obvious asymmetric large deformation during its service period due to the asymmetry and anisotropy of the surrounding rock structures and the effect of the coal-rock interface of ribs.It is difficult for the traditional supporting schemes such as the "bolt + mesh + anchor cable" and the U-shaped steel support to adapt to the deformation of surrounding rock and the control effect is poor,which seriously slows down the process of coal industry transformation and the upgrading of intelligent mechanization in Guizhou province.Taking the 1511 air return roadway of a mine in Guizhou province as the engineering background,this paper carries on a systematic research on the asymmetric deformation and failure mechanism and its control techniques of this kind of roadway by the comprehensive research method combining the field measurement,indoor test,theoretical analysis,similar simulation,numerical simulation and industrial test.Important findings are listed below:(1)Based on the field investigation and mechanical tests,the asymmetric deformation of the GSCRRGIC and the failure of the support bodies are analyzed.It shows that the continuous floor heave,coal-rock interface slip-fault and the difference of deformation positions of ribs are the main characteristics of the surrounding rock asymmetric deformation of this kind of roadway.The maximum uniaxial compressive strength of roadway surrounding rock is 24.95 MPa.The content of clay minerals is as high as 57%,and the disintegration resistance index is as low as 8.70%,therefore the mechanical strength is generally low,which can be identified as the typical soft surrounding rock.The main causes of support failures of the "bolt + mesh + anchor cable" and U-shaped steel are the poor boltability due to the soft and broken surrounding rock,lack of scientific design of restriction position structure of the clamp,the poor contact relationship between support and surrounding rock and the asymmetric failure caused by the heterogeneous load distribution.(2)Aiming at the disadvantages of the conventional two-dimensional physical modeling test rig,the similar simulation test rig was improved by designing the vertical and lateral force transferring devices,making the model size and loading position adjustable according to the test requirements.In order to solve the difficulties of laying model and excavating the coal-rock roadway precisely in the inclined coal and rock strata,the test method of "label location,line drawing and preset roadway model" is proposed.(3)By using the improved two-dimensional physical similarity simulation test rig and test method,the asymmetric deformation and failure test of the GSCRRGIC during driving and mining was carried out.The fractures and stress distribution characteristics of surrounding rock under the influence of driving and mining disturbance are obtained.The driving mechanism which causes the asymmetric deformation and failure by the fracture and stress are revealed: during the driving disturbance stage,the stress concentration mainly occurs in coal pillar side,the fractures of roadway surrounding rock mainly develop in the arc triangle coal of ribs and the roof of the coal pillar,presenting an obvious asymmetric distribution characteristics in space.With the increase of mining disturbance intensity,the coal pillar gradually yields and becomes unstable.The stress concentration area of surrounding rock gradually changes from the initial coal pillar side area to the lower solid coal side.The area where new fractures of roadway surrounding rock are developing changes from the area which are initially in roof and narrow coal pillar to the lower solid coal side.The characteristics of asymmetric deformation and failures are further highlighted.(4)Based on the limit equilibrium theory,the shear-slip-fault mechanical model of coal-rock interface of the GSCRRGIC's ribs is established,revealing the asymmetric deformation and failure mechanism of the GSCRRGIC.Considering the asymmetric deformation and failure test of the GSCRRGIC which is under the influence of driving and mining disturbance,the main roof fracture positions are divided into two types: the caving side above the coal pillar and the roadway side above the coal pillar.It is concluded that the shear-slip-fault deformation of coal-rock interfaces are the main deformation parts of ribs and becomes the main channels of releasing the stress and deformation energy.During driving,the stress concentration of the surrounding rock is mainly located at the side of the coal pillar of the upper side,coupling with the influence of the downward component of gravity stress along the coal-rock interface.The shear-slip-fault deformation of the upper side is larger than that of the lower side,and the asymmetric deformation gradually appears.During mining,with the increase of mining disturbance intensity and the slip-fault deformation,the narrow coal pillar gradually yields and becomes unstable,and the stress concentration transfers to the lower solid coal side,leading the shear-slip-fault deformation of the lower coal-rock interface intensified.Due to the space difference of the coal deformation positions of the ribs,the asymmetric deformation and failure characteristics are further highlighted.The fracture position of the main roof is linearly positively correlated with the thickness of the coal seam,and negatively correlated with the dip angle of the coal seam.The shear-slip-fault deformation of coal-rock interface is most severe when the fracture position of the main roof is above the coal pillar.(5)Based on the relative difference degree of deformation quantity on both sides of the roadway,the "asymmetric deformation rate" of the GSCRRGIC is defined,and its asymmetric deformation characteristics are quantitatively characterized.The larger the asymmetric deformation rate is,the more obvious the asymmetric deformation characteristics of the roadway are,which is also related to the difference of deformation spatial position on both sides of the roadway.Based on three-dimensional numerical modeling analysis,the asymmetric deformation and failure evolution law of the GSCRRGIC under different mining conditions is obtained: with the increase of the coal pillar width during driving disturbance,mining disturbance intensity,dip angle of coal seam,coal-rock ratio and mining depth,the asymmetric deformation rate of the GSCRRGIC takes on the changes of oblique "S" type,fluctuation descending type,"V" type,unimodal type and stationary type.The asymmetric deformation rate is relatively small when the coal pillar width is 3?5m and the dip angle of coal seam is 10 degrees.The more the mining disturbance,coal-rock ratio and mining depth,the more the deformation of arc triangle coal of the lower and upper side of surrounding rock is,and the more obvious the asymmetric deformation characteristic is.The plastic zone of surrounding rock mainly extends in the area of roof and coal pillar side.(6)In order to realize the high resistance and pressure relief support of the U-shaped shed,the position limiting structure of the U-shaped shed' clamp was improved,and its splint anti-slip and anti-collapse safety clamp set was designed.Based on the changing of the coal-rock interface position in the field,a kind of structure of locking U-shaped steel by anchor cable was developed,which is mainly used to improve the cooperative control effect.A method of cable anchoring enhancement of soft surrounding rock based on "cross" type stirring device was introduced,and the test to verify the anchoring enhancement effect was carried out.Based on this,the coordinated control technical system of anchor and support by U-shaped shed and cable is proposed,which takes the determination of reasonable coal pillar width as the main control method and the "asymmetric prestressed cross-layer locking shed cable" as the core.(7)A fast and nondestructive supporting quality checking and evaluation system for the coal-rock roadway's asymmetric deformation is proposed and established which takes the laser roadway section detector and cable nondestructive detector as the main detection methods.The industrial test was carried out,showing that during the driving and mining,the biggest roadway section shrinkage rate was about 23%,the biggest asymmetric deformation rate was 5.2%,and the cable bearing reliably and acting timely,the roadway took on an uniform and coordinated deformation,satisfying the requirements of safe production.