| Based on the related theoretical achievements of mine engineering mechanics,rock mechanics and coal mining,this paper makes use of theoretical analysis,laboratory experiment,numerical simulation,similar simulation,field measurement and other research methods to in-depth study the temporal and spatial evolution characteristics of surrounding rock stress shell.The dynamic re-distribution law of stress field of floor surrounding rock after the initial mining of the working face is carried out.The mechanical essence of floor surrounding rock stress shell is revealed,and the stope division method based on the principal stress is established.The temporal and spatial evolution characteristics of the three-dimensional stress field of surrounding rock for coal seam group mining are revealed by studying the spatial distribution pattern and stress concentration degree of the three-dimensional stress field of surrounding rock in the initial mining and repeated mining.In consideration of the stress field and its temporal and spatial evolution laws of surrounding rock stress shell.The three-dimensional stress field,displacement field and failure field of surrounding rock are taken as the object.The mechanical properties and the interaction of surrounding rock stress shell are studied.The evolution mechanism of surrounding rock force system in the deep coal seam group is carried out.In view of the difficult problems for the coal seam group mining which is easy to induce dynamic disaster,the coordination and integration of management and maintenance measures for the coal seam group mining based on the criterion of "time-space-strength" is proposed,It aimed to provide theoretical support for scientific and reasonable prevention and control of mine pressure disaster.This paper has obtained the following main research results:1.The dynamic re-distribution laws of stress field of floor surrounding rock after the initial mining of the working face are studied.The mechanical essence of floor surrounding rock stress shell is revealed.Based on the stress shell theory,the mechanics model of floor rock mass which is transversely isotropic under the condition of coal measure strata is constructed.The dynamic re-distribution laws of stress field of floor surrounding rock after the initial mining of the working face are studied,and the distribution of stress field of floor surrounding rock in the upper coal seam is obtained,and the stope division method based on the principal stress is established finally.The main conclusions are as follows:(1)The distribution law of dynamic stress of floor surrounding rock is: mining horizontal stress and mining vertical stress have regional characteristics,and the influence depth of horizontal stress is far less than that of the vertical stress.(2)Under the action of stress shell base,the floor surrounding rock in the area near the coal wall or open-cut position is the maximum principal stress increasing area.With the increase of the depth of coal seam,the peak of maximum principal stress decreases gradually,away from the coal wall and transfer to the side of gob.The results show that gob floor surrounding rock occur the obvious stress concentration phenomenon,which forms the stress shell composed of high stress beam,and further reveals the mechanical essence of floor surrounding rock stress shell.(3)Based on the difference of mining stress distribution and mechanical environment in the floor surrounding rock of stope,the formation of "four zones and three zones" of floor rock mass are put forward,which is divided horizontally into four stress zones of the original zone,transition zone,stress increasing zone and pressure relief zone,divided vertically into the pressure relief zone,stress increasing zone and original zone.2.The spatial distribution pattern and temporal-spatial evolution characteristics of the three-dimensional stress field of surrounding rock for coal seam group mining are revealedBased on the numerical simulation and similar simulation methods,the spatial distribution pattern and stress concentration degree of the three-dimensional stress field of surrounding rock under different stope conditions of initial mining and repeated mining are analyzed,and the temporal-spatial evolution characteristics of the three-dimensional stress field of surrounding rock for coal seam group mining are revealed.The main conclusions are as follows:(1)When the repeated exploitation of the lower coal seam is carried out subsequently,stope surrounding rock still exists the stress shell composed of high stress beam,which forms The principal stress value of the inner and outer of stress shell is relatively small,and the inner of stress shell is the lower stress area.(2)Under the initial mining stage of lower coal seam,the macroscopic stress field of stope surrounding rock has changed greatly,that is,the "lower stress shell" and the "upper stress shell" exist at the same time.The "lower stress shell" is located between the upper and lower coal seams.The stress shell base is located in the coal body of the lower coal seam in the front and behind of the working face.The "lower stress shell" is the most important bearing capacity of working face in the initial mining stage,and its shape is related to the structure parameters of stope.(3)During the process of repeated mining in the coal seam group,the working face of the lower coal seam has experienced the process of appearance,evolution and disappearance of the "lower stress shell",and the position and size of shell base are constantly changing.In addition,the stress concentration degree and range of the "upper stress shell" are gradually increased,and the shell base of "upper stress shell" in the rear of the open-cut is gradually shifted obliquely downward,until forming a larger macro stress shell eventually.(4)When the "lower stress shell" and "upper stress shell" merge together,the height of the macro stress shell is further increased,so that the working face will bear larger mining stress in a moment.3.The mechanical properties and the interaction of surrounding rock stress shell are studied.In consideration of the stress field and its temporal and spatial evolution laws of surrounding rock stress shell.The three-dimensional stress field,displacement field and failure field of surrounding rock are taken as the object.The mechanical properties and the interaction of surrounding rock stress shell are studied.The evolution mechanism of surrounding rock force system in the deep coal seam group is carried out.The main conclusions are as follows:(1)Under the initial mining stage of lower coal seam,the horizontal stress in the rock layer which is located between the upper and lower coal seams is much larger than that of the vertical stress,and the peak of horizontal stress appears in the front of working face.The maximum principal stress vector is controlled by the horizontal stress,the stress is concentrated and the direction is gradually deflected,and then the "lower stress shell" is formed.(2)Under the initial mining stage of lower coal seam,with the advance of the working face,the influence area of the stope surrounding rock failure field and displacement field are expanding,but it is only disturbed to the interlayer rock.The "lower stress shell" and the "upper stress shell" exist at the same time,while The "lower stress shell" is the most important bearing capacity of 11316 working face in the initial mining stage,and the failure and displacement are mainly developed in this area,the failure field and displacement field of surrounding rock in the two working faces are not affected each other.4.The coordination and integration of management and maintenance measures for the coal seam group mining is proposed based on the criterion of "time-space-strength"Taken coordinated mining of the Huainan mining area for close distance coal seams as engineering background,based on the research on the mechanical properties and its temporal and spatial evolution laws of surrounding rock stress shell.In view of the difficult problems for the coal seam group mining which is easy to induce dynamic disaster,and further reveal the evolution mechanism of surrounding rock force system in the deep coal seam group,which aims to provide theoretical support for scientific and reasonable prevention and control of mine pressure disaster.The main conclusions are as follows:(1)With the advance of the working face,the effect of shell base of 11318 E working face on the 11316 working face is gradually increased,especially when the upper and lower stress shells are merged into an integral macro stress shell,the maximum principal stress on the shell base reaches the peak,resulting in a rapid increase of support resistance.At the same time,the stress field,displacement field,fissure field,failure field and energy field of surrounding rock are significantly changed,and the abutment pressure of 11316 working face is peaked,and the horizontal stress is always maintained at state of pressure relief,the vertical stress concentration is more obvious.The vertical displacement field and the fissure field of 11316 and 11318 E working faces are overlapped with each other,so that the upper part of gob area which has been disturbed by mining is re-activated,The failure height of roof increases suddenly,the height growth rate of the two zones increases obviously,and the energy field of surrounding rock is drastically changed,To a certain extent,it will cause the increase of mining pressure,then cause the coal wall rib spalling,support crushing and other accidents,so it should be the key prevention area.(2)Based on the research on the mechanical properties and its temporal and spatial evolution laws of surrounding rock stress shell,the coordination and integration of management and maintenance measures for the coal seam group mining is proposed based on the criterion of "time-space-strength" according to the principle of appropriate time,reasonable space and appropriate mining intensity. |
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