Controlling Mechanism And Technology For Anchoring Layer Stability Of Roof In Deep Large Section Roadway

The roof stability control of large section mining roadway is a universal problem in western mining area.At present,most of the mines tend to use high-density combined support technology of bolt and cable,but the problems of roof control have not been fundamentally solved.High-density support restricts the speed of driving,which makes the contradiction between mining and drivinng more remarkable.It is usually difficult for the combination of bolt and cable to achieve coupling support and easy to be crushed one by one during large deformation period.It has great meaning both in theory and reality to research a new support theory.Based on the strata structure analysis and the nature of roof caving,a structural model of continuous roof beam is established in this paper.And the mechanical and bearing characteristics of continuous roof beam are obtained.The support effect of continuous beam is compared and analyzed by means of physical simulation experiment.The stress and displacement evolution law and the circle distribution characteristics of the large section coal roadway are expounded by 3D numerical calculation.Based on above analysis,a new type support technology of high pretension and long anchorage length is proposed.At last,an example of support design is given in an industrial test and the maintenance effect is evaluated.The main achievements are as follows:Based on the strata structure analysis and the nature of roof caving,the control theory of continuous roof beam of mining roadway is established.The classification of layered roof structure is summarized.Three kinds of roof caving forms,including loose caving,extrusion caving and monolithic caving are expounded.It is considered that the lack of roof rigidity will lead to uncoordinated deformation and that the separation deterioration of the layer and the roof instability will ensue.The definition of continuous roof beam is put forward and the mechanical model is established.It is considered that the thick anchoring layer constructed by the high efficiency support can resist stress disturbance and avoid the stress transmission of separation barrier.Thus the two-way and continuous transfer of roof stress is realized and the stability control of roof is achieved.Through theoretical analysis and mechanical calculation,the pretension of bolt and the thickness of anchoring layer play a decisive role in forming the continuous roof beam.The law of roadway surrounding rock movement is obtained by three-dimensional numerical calculation.The control effect of layered continuous roof beam is analyzed by physical simulation experiment.The zone characteristics and formation mechanism of stress,displacement,energy field and destruction of the large section coal roadway are studied during driving and mining disturbance period.Based on the strata characteristics of experimental site,a simulation model is established.The stress distribution and deformation failure state of the roof are compared and analyzed in the case of support and without support.The roof bearing capacity is improved remarkably under the condition of continuous beam,including that the stress of surrounding rock is optimized and the damage degree of superficial rock mass is reduced.Temporal and spatial evolution law and formation mechanism of rock failure around roadway are expounded.According to the distribution state of plastic zone during driving and extraction period,the temporal and spatial expansion regularity of plastic zone of surrounding rock is obtained.The distribution characteristics of stress and deformation in the surrounding rock of roadway are analyzed,and the relation between the distribution zone of surrounding rock and the depth of roadway is concluded.Thus the relation between the radius of fracture area and the length of anchorage is defined.A new type support technology of high pretension and long anchorage length is put forward based on the cross boundary support principle.It is pointed out that the bolt support should pass through the key circle of the surrounding rock and the shallow large displacement sphere should be restrained by deep small displacement sphere to make the two circles move closely together,thus forming the idea and principle of the cross boundary support.By increasing the pretension and raising the anchorage length,the continuous roof beam with thick anchoring layer is constructed to control the deformation failure and eliminate the delamination instability.This paper systematically expounds the concept,the material structure and technical characteristics of high pretension and long anchorage length support technology.The anchoring effect and group anchoring effect of common technology and the high pretension and long anchorage length support technology are compared and analyzed.Numerical simulation demonstrates that the support efficiency of single bolt is 2-6 times of common bolt and the group support efficiency of high pretension and long anchorage length is 3.5?5 times as common support.The research results was applied to the field industrial test,and the rationality of the continuous roof beam theory and the high pretension and long anchorage length support technology are verified preliminarily.The experiment was conducted in the 21204 main return airway of Hulusu mine.Through technical evaluation and feasibility analysis,a new support scheme of high pretension and long anchorage length was put forward.Comparison of mine pressure monitoring and benefit analysis showed that the roof interior crack and the surface displacement were well controlled as the roof anchoring layer thickness was increased.The advantages were obvious that the number of bolt in new support scheme was reduced by 48.5%and the supporting strength was increased by 24.1%.Western mining area,such as Meng-Shan,widely use large section mining roadway.The preliminary exploration of the roof anchoring mechanism and supporting technology can provide reference for the roof stability control of such roadways.The technology with low support density,single support mode and small damage and deformation of surrounding rock can improve the quality of roadway support and guarantee the safe and efficient production of large modern mines.