The Floor Heave Mechanism And Control Of Weak Cementation Soft Rock Mining Roadway

With the increasing depletion of coal resources in the central and eastern regions of China,the exploitation of coal resources moves northward and westward.Shaanxi and Inner Mongolia have gradually become the coal m ining centers,while most of the coal resources in the eastern region of Inner Mongolia are hosted in Mesozoic.The cementation degree of surrounding rock is poor,the interlayer adhesion is poor,and the water is easy to expand,the parameters are deteriorated,and the creep of surrounding rock is prominent.Especially,the stability of roadways excavated in this kind of strata is poor.The conventional support method is not ideal for the stability of roadway surrounding rock,and the bottom drum problem is particularly serious,which seriously restricts the safe and efficient production of the mine.In this paper,taking the 16-306 weakly cemented soft rock return airway in Mindong No.1 Mine as the working background,the physical and mechanical properties of weakly cemented soft rock and the deformation and failure characteristics of roadway floor are explored by using comprehensive research schemes such as field monitoring,laboratory test,theoretical analysis and numerical simulation.Based on the deflection of principal stress direction,the evolution characteristics of plastic zone of roadway surrounding rock are studied,the,mechanism of floor heave in weakly cemented soft rock roadway is revealed,and the targeted control countermeasures are put forward.The main research contents and results are as follows:(1)By evaluating the physical and mechanical properties of the rock samples collected from the roof and floor of the 16-306 return air roadway,it is concluded that the main components of the surrounding rock of the roof and floor of the roadway are quartz and kaolinite,and the strength of the surrounding rock is generally low,especially the floor.The compressive strength is only 5.45 MPa,and the tensile strength is only 1.16 MPa.The bearing capacity is weak,and the water is easy to expand and argillate,which belongs to the typical weak cemented soft rock roadway.(2)The field measurement of roadway floor deformation and failure shows that the floor deformation of 16-306 return airway is relatively severe in the early stage of roadway completion,and the deformation rate has been reduced to a certain extent with the passage of time,but it has never reached a stable state.Affected by the advance stress in the mining stage,the deformation rate and deformation increased significantly,and the maximum cumulative floor heave reached 480 mm.Combined with the bottom hole peeping,it is found that the rock stratum under the floor of the roadway is seriously damaged,and the maximum damage depth is about 3 m,which is accompanied by slag and separation,and there is water accumulation at the bottom of the borehole.(3)The FLAC3D numerical model that can reflect the mining activities of 16-306 return airway is established to study the evolution law of stress direction and the distribution pattern of plastic zone in the three sections at the two stages of roadway excavation and working face mining.In the roadway excavation stage,the angle between the maximum principal stress and X axis of the roof and floor of the roadway transits from vertical to sharp angle,the stress direction of the roof deflects to the right as a whole,and the floor deflects to the left as a whole.The plastic zone of the surrounding rock evolves from asymmetric ’Butterfly Leaf’ distribution to ’Water Droplet’ distribution.In the mining stage,the angle between the maximum principal stress of roof and floor of roadway surrounding rock and the X axis gradually tends to be horizontal,the direction of roof stress continues to deflect to the right,the floor continues to deflect to the left,and the plastic zone of surrounding rock expands from the ’Bulb’ type to the asymmetric ’Butterfly Leaf’ type.The stress deflection zone of roadway surrounding rock is basically consistent with the plastic zone contour.(4)Based on the pressure arch theory and the principal stress trace earth pressure theory,the mechanical model of floor heave considering the deflection of stress direction is established,and the formula of floor failure depth and force source of floor heave is derived.It is concluded that the floor heave of weak cemented soft rock roadway is the result of multiple factors coupling of initial stress field,roadway surrounding rock properties,mining disturbance,support form and section shape,and the floor heave form of roadway is determined to be the shear dislocation expansion type floor heave.The formation process of the floor heave was analyzed:the initial maximum horizontal stress and roadway skew→ the initial argillization of the floor caused by roadway driving→the deflection of the principal stress direction disturbed by the mining stress→ the extrusion of the damaged floor→the floor heave.(5)According to the mechanism of floor heave,this paper puts forward the targeted scheme of bottom fixation and water separation-overbreak anchorage backfill control scheme,and carries out numerical simulation analysis on the scheme.The feasibility of the scheme is proved from the aspects of stress,displacement and plastic zone,which effectively controls the stability of roadway and achieves good results.