Research On Failure Mechanism And Support Of Surrounding Rock Of Roadway With Medium-thick Compound Roof Contained Several Soft Interlayers

Medium-thick compound roof contained several soft interlayers contained many soft interlayers which are thinner and have rich joint fissures.And this kind of roof easily occurred with the bed separation and roof instability as its poor heterogeneous property,poor integrity,low strength and stiffness.The roof as a part of the surrounding rock,if the damage occurred,it is easy to affect the stability of the other parts of the surrounding rock,and ultimately the loss of its function roadway.However,there are a lot of researches on the support theory of surrounding rock of roadway with compound roof,which is very little for the research of soft interlayer.So it will bring some blindness and irrationality,and even produce some security risks that the previous theory of surrounding rock controlling of roadway was completely quoted to solve the problem of surrounding rock controlling of roadway with medium-thick compound roof contained several soft interlayers.Therefore,it is necessary for us to study the stability of the compound roof carefully,and find out the deformation mechanism and failure mechanism of surrounding rock of roadway,and then put forward corresponding supporting theory and technology of surrounding rock,so that provides a reasonable andeffective basis for surrounding rock controlling of roadway with similar geological conditions.Based on summarizing the theory and technology of existing roadway support,and according to the typical geological conditions,the coupled model of deformation of roadway surrounding rock is established and the deformation characteristics of surrounding rock of roadway is revealed by means of numerical simulation and derivation of mechanics theory.Meanwhile,The influence of distribution,thickness and thickness ratio of weak intercalation,lateral pressure coefficient and load on deformation and failure of roadway surrounding rock are analyzed.Combined with bolt and cable coupling support theory,the corresponding means of surrounding rock controlling is obtained.At the same time,combined with the mechanical analysis of roadway surrounding rock support structure,the design method of support parameters was obtained.The main contents and results are as follows:(1)The effect of weak interlayer on the roof strength of the roadway was analyzed from the point of view of mechanics.The strength effect of the structural plane of the multi-weak sandwich composite roof was obtained: The lateral expansion and deformation of the composite roof rock mass will occur in the vertical direction due to the maximum principal stress parallel to the bedding plane.The strength of the roof was mainly controlled by the weak interlayer or the tensile strength of the bedding plane between sandwich and hard layer when the lateral confinement in the vertical direction of composite roof have lost;(2)From the point of view of structural mechanics,the conditions of separation of multi-soft sandwich composite roof were analyzed as load condition and deformation condition,and the deformation condition includes bending deformation condition and shear deformation;(3)The mechanical model of roadway surrounding rock was established and the pressure and lateral pressure of the two sides of the roadway and the deflection equation of the floor in the different range were analyzed.At the same time,according to the deformation characteristics of roadway roof,two sidewalls and floor,the coupled model with compound timoshenko beam and elastic foundation beam was built;(4)According to the distribution of weak interlayers,the classification of medium-thick compound roof contained several soft interlayers are as follows: uniform distribution type,upper concentrated type,central concentrated type,lower concentrated type and progressive distribution type.The effect of internal factors such as soft interlayer thickness,thickness ratio of weak interlayer and hard rock on the stability of roadway surrounding rock is analyzed by using FLAC3 D finite difference numerical simulation software.At the same time,the influence of external factors,such as lateral pressure coefficient and load on surrounding rock,on the deformation and failure characteristics of roadway surrounding rock are analyzed.The numerical simulation results show that:(1)The vertical stress is mainly concentrated in the two sidewalls of roadway,horizontal concentrated stress nuclei are generated in the floor and thick and hard strata of immediate roof,and the horizontal stresses at the weak interlayers are lower;the maximum displacement and distribution range of the plastic zone of surrounding rock of roadway are increasing in the order of the upper concentrated type,the central concentrated type,the uniformly distributed type,the gradually distributed type and the lower concentrated type.(2)The vertical deformation of the floor of roadway of compound roof with different weak interlayers distribution is almost the same with the loading time step.With the loading progress,the vertical displacement of the middle position of the floor is increasing.The downward vertical displacement of the roof of the roadway increases rapidly at the initial stage of loading,and then gradually becomes stable;the vertical displacement of the immediate roof of the upper concentrated type and the central concentrated type is relatively small,and the separation of the roof is not obvious,but the roadway of uniformly distributed type,gradually distributed type and lower concentrated type is obvious;(3)The thicker weak interlayer in the immediate roof of the roadway is,the bigger the thickness ratio of the weak interlayer and the hard rock is,and the more the number of the weak interlayer is,the larger the shrinkage of the roadway section is,the wider the distribution range of plastic zone is;(4)The load of roadway surrounding rock is mainly affected by the extent of the plastic zone of surrounding rock,while the lateral pressure coefficient mainly affects the distribution of roadway plastic state.(5)According to the deformation and destabilization characteristics of the surrounding rocks in the roadway with medium-thick compound roof contained several soft interlayers,the arch-beam coupling supporting structure of roof and the thick bolted board supporting structure of sidewalls are established,and the strength of supporting structure is analyzed,and the strength formula of the support body is obtained;(6)Combined with the influence of the difference of distribution characteristics of soft interlayer on the deformation and destabilization characteristics of the roof in the roadway,the support mode of surroundingrock of the uniform distribution type,the upper concentrated type,the central concentrated type,the lower concentrated type and the gradually distributed type roadway are respectively determined.According to the theory of suspension,combined beam theory and timoshenko beam theory,the support parameters of bolts and anchor cables of roof are obtained.At the same time,using thick bolted board theory,the support parameters of sidewalls are obtained.