Research Of Damage Characteristics And Control Technology Of Composite Floor In Coal Roadway

With the mining of coal resources from shallow to deep,the surrounding rock support of deep roadway becomes one of the most difficult problems in coal mining.The theory and engineering practice show that the floor of deep mining roadway is easy to be destroyed,especially the composite floor with "strong-weak-strong" structure composed of gangue,coal body and rock mass in the composite structure coal seam.In the complex situation of deep mining,the coal seam of composite floor becomes a gap of roadway floor stable.If not treated and controlled,the destruction of roadway floor coal seam will promote the destruction of parting above the coal,thus causing the destruction of roadway floor.This paper studies the failure modes of floor parting and coals by establishing mechanical models are based on the theory of mine pressure,elastic-plastic mechanics theory and the theory of slip line field in soil mechanics,clarifies that the damage characteristics of composite floor can be divided into two stages.The first stage,the floor parting is the buckling instability of the pressure bar under the effect of horizontal stress.At this point,the horizontal stress become the key to the failure of the floor.If the horizontal stress exceeds the minimum axial force of the parting failure,the parting will be failure.The second stage is that when the parting is buckling instability,the free space is formed with the overlying coal seam.Under the high supporting pressure and overlying high load,the broken coal of floor will slip along the primary joints and new cracks of the coal body,so that the coal body will be squeezed into the free space,which will produce the extrusion pressure on the parting of floor,thus promote the destruction of the parting.At this point,the vertical stress plays a key role in floor failure and the horizontal stress only increases the confining pressure of coal is no longer the most important factor of floor failure.The criterion for the failure of the parting in the floor and the expression of the maximum bearing capacity of the floor coal is derived.The main influencing factors of composite floor failure are also analyzed with numerical simulation.It is believed that the greater the mining depth,the larger the lateral pressure coefficient,the greater the support pressure,the greater the thickness of the floor coal seam,and the thinner the floor clamp,the more unfavorable the stability of the composite floor.Based on the analysis of the failure characteristics of composite floor and its influencing factors,this paper studies the techniques of unloading pressure by large diameter boreholes in roadway sides,cut off floor and blast,bolt support of floor,preventing slide of floor coal by drilling.The control effect of different supporting schemes of composite floor is simulated by using FLAC3D5.0 and UDEC4.0 simulation software,which is based on the mining roadway in the 10_upcoal seam of Da'anshan.It is propose that cut off floor when the thickness of the bottom plate is less than lm,and the drilling in the corner of floor to cut off slip path of floor coal seam.When the thickness of parting is between 1m and 1.5m,the corner bolt is applied in the floor to prevent the active force zone of the floor seam slid along the crack,and the bolt is applied in the middle of floor to strengthen parting and control the passive slip zone of the floor seam.Finally,Monitor mining roadway with two support schemes taking the mining roadway of first west coal face as project instance.The monitoring results show that the failure of composite floor can be effectively controlled by use unloading pressure large diameter boreholes in roadway sides,cut off floor and blast,preventing slide of floor coal by drilling,bolt support in bottom corner of floor,and strengthen parting by bolt.