| The development trend of high-efficiency&intelligent fully mechanized longwall mining is to lengthen the working face length,which changes the mine pressure significantly and makes it much more difficult to control the roof and hydraulic support and hydraulic support group of the working face.In comparison to other analyses,this paper systematically investigates the characteristics of ultra-long working face mining induced stress and the coupling relation between hydraulic support group and surrounding rock from the perspectives of mine pressure behavior regularity,hydraulic support response characteristics,coupling relation between hydraulic support and surrounding rock,and cooperative control of hydraulic support group in ultra-long working faces.It also offers theoretical and technical support for the application and generalization of ultra-long working faces.The following are the major accomplishments in this study:(1)According to mine compaction data,as the working face length increases,the support stress gradually shifts from a single peak to multiple peaks and expands to both terminals;when the pressure is applied first in the middle area of the fully mechanized mining face,the two terminals lag behind.As a result,the high peak area of support stress is clearly increasing.It turns out that the pressure applied to various parts of the working face has distinct temporal characteristics and a wide range of strength.(2)According to a similar simulation experiment of overburden strata movement on various working face lengths,increasing face length contributes to several corresponding identities,including rising strata in the collapse zone and an increasing overall number of fractures and porosity.The collapse strata in the Xiaobaodang No.2 Coal Mine 450 m ultra-long working face will then extend upward at 45°,forming a ladder-shaped form with a narrow top and wide bottom and an "O" shaped feature of the distribution of fracture field and porosity.The increase of the length of the lowest end of the falling zone and the increase of cracks make the plate size of the overlying top decrease and it is not easy to form a stable structure,resulting in the increase of the pressure frequency;The high peak value distribution area of vertical stress in the middle area of the working face is large and presents "m" type distribution,making more areas of the roof in a high stress state.The compressive strength in the middle area of the working face along the face length direction is high,showing a trend of slowly increasing at first and then gradually decreasing towards both ends of the working face.(3)In light of the three-dimensional numerical simulation mining model,this paper thoroughly analyzes the three field evolution regularities of overburden in different layers of an ultra-long working face under both full and insufficient mining conditions.The mining model reveals the temporal and spatial evolution characteristics of mining stress in the overburden of an ultra-long working face,as well as the variation regularity of mining stress in different mining periods,different layers,and different working face positions.This paper also proposes the mining disturbance intensity coefficient of stress and strain to characterize the periodic pressure intensity in front of a super long working face based on the characteristics of ground pressure behavior in an ultra-long working face.(4)Based on the bearing characteristics of hydraulic support and elastic support models,this study reveals the distribution regularity of hydraulic support group supporting stress in an ultra-long working face.The support stress distribution characteristics of a super long working face are also investigated under different roadway stiffness,roof lithology,and basic roof thickness conditions.The working face support stress has three peaks with M-shaped forms,which can be used in the ultra-long working face criterion.Furthermore,the multi-peak distribution trend will be exacerbated by the characteristics of surrounding rock deterioration(low strength roof)and mining height soaring up in deep wells.When the face length is between300～350 meters,the multi-peak characteristics of an ultra-long working face appear.These are the criteria for ultra-long working faces and how they might affect them,as well as reasonable working face lengths that were determined in this study by taking into account coal seam occurrence conditions,working face parameters,and the capacity of the equipment that would be used.(5)The M-shaped distribution characteristics of three peak values of support stress in the face according to the different properties of hydraulic support in space and function are outlined in this paper,which contributes to the group zoning method and positioning technology of hydraulic support in the super long face.This paper outlines the principle of cooperative control in group zoning of super long faces,combined with the regional pressure and frequent pressure in long faces,and the M-shaped distribution characteristics of three peak values of support stress in each face according to the different properties of hydraulic support in space and function.Furthermore,based on the information acquisition module,this study proposes a cooperative control method for the working face equipment group based on state error and cost function,and some information has been obtained for analysis and decision-making to obtain the working face pushing progress,roof pressing step,pressing frequency,support shrinkage,column pressure,roof beam inclination,and other information.As a result,the "single frame control → group control → group control" three-level cooperative control strategy and implementation method can be systematically formulated,which can effectively and successfully instruct the hydraulic support group of an ultra-long fully mechanized mining face to achieve optimal cooperative control.(6)Finally,through the production practice of a 450 m ultra-long fully mechanized mining face in "Xiao Bao Dang" No.2 coal mine,the first model in China with an advancing length of more than 1000m((the advancing length of the working face is 4002m),this study manifests the characteristics of the working face such as high incoming pressure frequency,low incoming pressure uniformity,and large dynamic load coefficient,and the roof collapses and presses asynchronously along the long direction of the working face.For the first time,high reliability,stable support,and collaborative propulsion of the hydraulic support in the ultra-long working face are realized,and stable control of the roof of the super-long working face is currently ensured thanks to hydraulic support group collaborative control technology.The 2～2.5m coal seam has now reached its annual capacity of 10 Mt for the first time.There are 99 drawings,13 tables,and 164 references in total in this paper. |
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