Mechanical Properties And Supporting Mechanism Of Pile At Roadway Floor Corner In Xing’an Coal Mine

The large deformation of deep roadway floor has been affecting the efficient mining of coal resources and the safety and stability of roadway,which is also an important problem to be solved in the safety and efficient production of coal mine.Due to the difference of mechanical environment and geomechanically parameters of deep roadway surrounding rock,there is no reliable,applicable,simple construction and low-cost support structure system applied in the treatment of large deformation of roadway floor surrounding rock.In recent decades,scholars at home and abroad have conducted many studies on the mechanism and prevention technology of large deformation of deep roadway floor,and achieved achievements in theory,numerical analysis and experimental research.However,there are still many problems to be solved.This article relies on the national key research and development program "of roadway roof pile static load al block impingement technology(20170804204)",to utilize modern ore 18 orbital lane four level as the engineering background,put forward a new form of bottom of pile,based on the theory of slip line field and elastic-plastic slab pile mechanics model is established,reveals the bottom horizontal stress of pile blocking mechanism,The design principle of bottom pile is clarified and the calculation formula of key parameters of bottom pile is given.The physical and mechanical properties of early-strength self-compacting concrete filled steel tubular(CFST)and the cooperative performance of bending and shear of floor row piles were studied by combining laboratory test and numerical simulation,and the force transmission path and bearing capacity improvement mechanism of floor row piles were revealed.A full section collaborative support system of roof,two sides and floor roadway based on floor pile support technology was proposed,and the space-time evolution law of surrounding rock stress and deformation in high level horizontal stress roadway was revealed.Combined with the site conditions,the construction technology of integrating bottom Angle into pile is put forward,and the results are applied to the site engineering practice.The main conclusions are as follows:(1)Supporting characteristics of bottom pile and barrier mechanism of high horizontal stress of bottom slab.Based on the slip line field solution of plane strain and the Mohr-Coulomb strength theory,the critical failure depth and minimum length of roadway bottom pile under horizontal stress were deduced,which provided a theoretical basis for the design of bottom pile.The stress barrier mechanics model of floor pile is proposed and the critical criterion of buckling instability of floor surrounding rock is deduced under the condition of floor pile support.Based on the flexural properties of CFST and the principle of virtual work,the expression of ultimate barrier resistance of bottom pile is derived.The cross section geometric parameters and pile spacing of bottom pile are the key parameters to determine the ultimate barrier resistance.The rationality of theoretical analysis was verified by numerical analysis.(2)Mechanical properties and support reaction of early-strength steel tube concrete.Based on the self-compacting early-strength concrete experiment,the core concrete ratio of bottom pile was determined by evaluating the working performance of concrete and the compressive strength of different ages,and the change rule of core concrete ratio of bottom pile and core concrete strength with time was revealed,and the empirical formula of concrete age-strength was given.The hoop effect and failure law of early concrete are determined by analyzing the early strength of core concrete.The supporting reaction force and hoop coefficient of bottom pile at different ages are determined.From the point of view of the whole failure process of CFST,with the increase of age,the elastoplastic section and the strengthening section of concrete are obviously prolonged.Due to the existence of the hoop effect,the concrete is in a state of three-way compression,and the formation and development of internal cracks are inhibited.The essence of concrete filled steel tube failure is the failure of steel tube hoop effect.(3)Study on bending and shear synergistic force of bottom slab row piles.Through laboratory and numerical analysis,the mechanical characteristics of single pile support and the cooperative mechanical properties of bent-shear were studied,and the force transmission path and cooperative mechanical law of bottom pile were revealed.The results show that the bending bearing capacity of a single pile without cooperative support is low,and the pile is prone to buckling failure in the fixed section.Compared with the single pile model of bottom plate pile,the deformation of row pile under yield and failure is very small,and the bearing capacity of different spans is improved to a certain extent.Under the action of joint work,the bearing capacity of single side span pile is increased by 20%,the bearing capacity is obviously improved,and the mid-span bearing capacity is increased by 10%.Compared with single pile,the force of floor row pile is more complicated.The failure state and instability criterion of row pile are determined by numerical analysis.(4)Study on synergistic effect between bottom pile and upper support structure.Based on the natural equilibrium arch theory considering floor heave,the deformation and failure characteristics of surrounding rock roadway affected by high level stress were analyzed.Based on the natural equilibrium arch theory,the collaborative support model considering floor pile support was established.Floor pile improves the ability of floor rock mass to resist horizontal stress by blocking and transferring floor horizontal stress,enhances the supporting effect of two sides of roadway on roof,reduces the generalized span of floor rock mass,and controls the stability of surrounding rock roadway.Theoretical analysis and numerical calculation results show that upper slab pile and retaining structure integrated solutions to control the damage of the surrounding rock,fully mobilize rock bearing capacity of deep surrounding rock,improve the stress state of roadway surrounding rock,to realize "-two-floor roof" bearing,coordinated and integrated with each other,promote each other,make the surrounding rock stress more reasonable,the overall carrying capacity of roadway,The effect of surrounding rock control has been significantly improved.(5)Research on engineering application of bottom pile support.The process of integrating bottom Angle into pile is formed and applied in engineering practice.Through the field industrial test on the four-level 18-storey track roadway in Xing ’an Mine,the field related data are monitored.The field monitoring results show that floor pile accelerates the convergence rate of floor heave,inhibits the growth rate of floor heave in the early stage,and effectively reduces floor heave.The floor pile plays a good supporting effect on the surrounding rock,and the floor rock is relatively intact without penetrating crack.The ability of floor rock to resist horizontal stress is significantly enhanced,the deformation of roadway floor is significantly reduced,the convergence rate of roadway is accelerated,and the energy storage limit of floor is significantly increased.Compared with the non-floor support area,floor micro-seismic events show the characteristics of low frequency and low energy.