| This paper takes outer stagger arrangement roadway driving along goaf of thick coal seam in Xiegou coal as practical engineering background, carrying out research from the aspects of recovery rate, the stability and the stress distribution of roadway surrounding rock,position of roadway and roadway supporting technology of goaf, comprehensively using the theoretical analysis, indoor similar simulation, the computer numerical simulation, field observation and other research methods in the whole research.This paper first analyzed the existing problems in the coal industry from the importance of coal for our country energy. On this basis, combining with the main content of the paper to collect and analyze the research status at home and abroad on the technology of gob-side roadway and full high mining of thick coal seam. Stagger arrangement roadway layout mining method can realize the real meaning mining without coal pillar, but for a long time the research mainly focuses on inner stagger arrangement roadway layout, since it has the characteristics of slicing mining and inner roadway layout, the way of supporting can only be in the form of passive support, thus affected the roadway driving speed and connection between mining and tunneling. Therefore, in order to solve the problems of inner stagger arrangement roadway layout, this paper based on outer stagger arrangement roadway layout combined with the technology of gob-side roadway to determine the research content, method and technical route.1. 13# coal seam of Xiegou adopted outer stagger arrangement mining method, which leaving 13 m coal pillar, through the field measurement of surrounding rock deformation of roadway and pillar stress, which can get the following conclusions:(1) Through drilling peep of the roadway roof and the side of coal where away from working face 50 m and 60 m, we found when adopted leaving 13 m coal pillar, the structure of roadway surrounding rock was very complex and the roadway support became very difficulty, on the basis of borehole peep, we proceed to reinforcing supporting of roadway surrounding rock.(2) Through the field measurement of roadway surrounding rock of outer stagger arrangement after strengthening the supporting, we found deformation of roadway surrounding rock is still serious and strongly influenced by mining.(3) Through the field measurement of outer stagger arrangement of coal pillar abutment pressure distribution, we found that coal pillar was greatly influenced by mining, mining influence scope up to 40 m or so, within the scope of the coal pillar was in plastic zone.Through analyze and research of the field measurement, we found that Xiegou coal mine adopt outer stagger arrangement mining method leaving 13 m coal pillar had certain irrationality, therefore we need to rethink its optimization design plan.2. In order to determine the location of gob-side entry of outer stagger arrangement roadway layout, the paper first studied the stability of triangle coal pillar which below the slope section of outer stagger arrangement roadway layout.(1) Analyzed the influence of the slope section on recovery rate and identified the necessity of the different slope sections. On this basis, established mechanical model of the triangle coal below slope section, using the limit equilibrium theory to research the relationship between width and height of triangle coal, obtained the bearing expression of slope section in the limit equilibrium state:At the same time got the relationship between the width of limit equilibrium section and height of the triangle coal:From the formula, we can find that with the increase of height of the triangle coal, the width of coal pillar which satisfied the limit equilibrium stress also rise. Only from the point of mechanical characteristics of triangle coal, lateral dimension of the triangle coal pillar of slope section which can meet the requirements of limit equilibrium. Thus, triangle coal can divide into broken zone, plastic zone and elastic zone, which can provide lateral stress for section coal pillar.But during the period of actual mining, suffering from the influence of the bearing stress, the floor at a certain depth may be damaged, so we should further study the destructiveness of triangle coal.(2) In order to determine the damage depth of triangle coal, the paper first studied floor failure mechanism and built the mechanics model, derived floor damage depth h1 under limit state by using fracture mechanics and Griffith criterion:Due to the main factors of destruction of floor including stress, therefore which need to determine the stress value in the process of working face advancing.(3) Taking the key layer of overlying as a thin plate model, combining with using elastic thin plate mechanics theory, Hooke’s law and the reciprocal theorem, studying the influence of the main roof on the coal in the process of working face advancing cause the main roof fracture, determined the bending moment distribution and application of load. At the same time, considering the relationships between the basic roof, immediate roof and coal, and then studied the depth of floor damage and got its expression:On this basis, determined the principle of stability of triangle bottom coal, that is to say, compared h1 with height of the slope section, triangle coal was in a state of destruction within the scope of [3.5m, h1], which can’t provide lateral bearing stress, triangle coal was elastic within the scope of [h1, 10.5 m], which can provide lateral bearing stress to section coal pillar.3. Based on the study mentioned above, the paper emphasis research the key technology of outer stagger arrangement roadway driving along goaf, including mechanics of the stability of section coal pillar, roadway location and supporting technology, the specific conclusion is as follows,(1) First analyzed on the stability of entity coal of outer stagger arrangement roadway driving along goaf, found that:(1) scheme 1, due to the triangle coal was in the state of destruction, so which can’t provide lateral bearing stress to the side of entity coal, only can provide lateral support resistance Px; scheme 2 and scheme 3, due to the increase of slope section height, the triangle coal provide certain amount of lateral bearing stress for the entity coal, mining roadway of scheme 3 completely arrangement along the roof, in the theory regard as the scope of lateral bearing stress which the triangle coal provided is the biggest, which is beneficial to keep the stability of the section coal pillar during the successive working face mining.(2) Combined with the effects of different triangle coal on abutment stress of entity coal, by using the limit equilibrium theory, we can solve the distance from the laneway’s side to the coal pillar where reach the limit strength,Combined with different slope schemes to analyze, we can obtain the conclusion that the stability of the entity coal which the mining roadway layout along the roof is best.(2) On the basis of the research on the stability of the entity coal, combined with the surrounding rock and the stress distribution of the roadway, we find that outer stagger arrangement roadway can achieve completely driving along the goaf without coal pillar, the main features include,(1) Although the roadway layout along the floor, the surrounding rock was in the state of integrity and stability, which is good for excavation and maintenance of the roadway.(2) Affected by high coal seam, the high coal seam was in the scope of damage, and the distance from successive working face adjacent roadway is 4 ~ 5m, the successive working face adjacent roadway was in the range of low stress, which also conducive to the excavation and maintenance of roadway.(3) The overburden of successive working face exists elastic region, although the high coal seam belongs to the failure zone, we can strengthen supporting in the working face adjacent roadway to offer conditions for anchor-cable to actively supporting of successive working face.(3) On the basis of the position selection of gob-side entry, combining the “ultimate self steady equilibrium arch theory” to study on supporting technology, which got the following conclusions:(1) We derive the maximum height of the ultimate self steady equilibrium arch:And put forward that the stability of roadway has great influence on the height of ultimate self steady equilibrium arch of roof. There are differences among different triangle coal for the roof of roadway supporting.(2) This paper proposed that adjacent roadway joint supporting technology of outer stagger arrangement roadway layout.Compared with the intake airflow roadway of first working face layout along roof and floor, we found that the height of ultimate self steady equilibrium arch of the former is less, which is considered beneficial for supporting from the point of theory.Considered successive adjacent face roadway arrange along the right side of the intake airflow roadway, between two roadways don’t exist pillar and there is a thick coal seam in the vertical direction. Therefore, we can help to enhance entity coal supporting of intake airflow roadway which arrange along roof, so as to provide suspension point for the cable of successive face adjacent roadway when determining that entity coal supporting of intake airflow roadway by using anchor – cable, which adopt entire section anchoring bolts and cables, and at the same time digging two rows of 4 m deep hole to grout which make the shallow coal seam into a whole.(4) Lastly, combined with engineering background of Xiegou coal to analyze the roadway supporting technology, conclusions are as follows:(1) Using outer stagger arrangement roadway driving along goaf technology, the difficulties of roadway supporting is still in situ stress area of full coal roadway, because the coal seam is soft and subject to suffer in-situ stress, the ultimate self steady equilibrium arch is high which can reach 1.83m;(2) The roadway of stagger arrangement which arrange along the coal seam roof, due to the direct support of the object is roof strata, which has large mechanical strength and good stability, and the ultimate self steady equilibrium arch is low which can only reach 1m;(3) Although outer staggered arrangement roadway driving along the goaf without pillar is still full coal roadway, which is arranged in the elastic entity coal below the ultimate equilibrium zone, therefore the bearing of surrounding rock is low and ultimate self steady equilibrium arch is 1.48 m, it is beneficial for adopting the initiative supporting scheme.For comparison, we add the scheme of roadway driving along goaf with adopting traditional roadway layout along the coal seam floor, its ultimate self steady equilibrium arch is 5m.Comparative analysis found that using conventional bolting supporting is unable to meet the height of equilibrium arch when we adopt scheme of roadway driving along goaf with adopting traditional roadway layout along the coal seam floor, so which only rely on passive supporting or increase supporting density of anchor to ensure the stability of the roadway.4. Similar simulation experiment research on outer stagger arrangement roadway driving along the goaf in Xiegou coal mine(1) When mining the first working face, with the increase of the inclined length, the height of the overlying rock, the peak of the lateral supporting stress and the influence range also increase. But the experimental results show that although the stress concentration coefficient of the strain gauges which were arranged the scope of roadway driving along the goaf was increased, the extent was very small and its numerical value was lower than the original rock stress value, which is considered to be less affected by the first mining face;(2) With the increase of the inclined length of successive working face, the characteristic of overburden strata movement was similar to the first working face, and coal pillar gradually becomes unstable from steady state owing to increasing length of working face, a large number of fracture generated in the coal pillar when the width of coal pillar from 15 m reduce to 10 m, and the coal pillar occurs instability of overall failure when the size of coal pillar reduce to 8m.(3) During the period of successive working face extraction, by collecting and systemizing the data of strain gauges of roadway completely driving along goaf of the first working face, we found that the stress had the tendency of further increasing but the stress value less increase, the maximum stress concentration factor was only 0.45.5. Numerical simulation study of outer stagger arrangement roadway in Xie Gou mine(1) By comprehensively analysis the stability of different height of triangle coal pillar below the slope section, we found that with the increasing of the height of slope section, the stability of triangle coal became better, and the whole triangle coal was in stress relaxed area.(2) By the comprehensive analysis the stability of the entity coal with different height of triangle coal pillar below the slope section, which can find that with the increasing of height of the slope section, the range of limited equilibrium area is reduced and the range of the elastic region is increased of the side of entity coal.(3) Under optimal prerequisite of entity coal stability determining the slope section the height of 10.5m, studying further the stability of different sizes of coal pillar, which found that the damage range of triangle coal pillar side was minimum by digging completely along goaf, it can achieve effective controlled roadway surrounding rock stress, and the stress concentration factor was minimum which require minimum support strength, while driving completely along goaf can improve the state of surrounding rock by strengthen supporting of intake airflow roadway side of the adjacent working face, thus achieving active supporting program of anchor and bolt.6. The study of joint supporting technology in Xiegou mineCombined with the above theoretical analysis, analog simulation and numerical simulation analysis to optimize the scheme of stagger roadway outer arrangement in Xiegou mine, proposed that the height of slope section increase to 10.5m, using outer stagger arrangement roadway completely driving along goaf and roadway joint support technology, the effect of scheme verified by numerical simulation. Optimization scheme improves the coal recovery rate, while stress of surrounding rock roadway and the amount of deformation has dropped drastically, which reaching optimization purposes.This paper achieved the following innovations:(1) Studied the relationship between width and height of triangle coal by using limited equilibrium theory, and obtained the bearing expression of slope section in the limit equilibrium state:At the same time got the relationship between the width of limit equilibrium section and height of the triangle coal.(2) Considering the relationships between the basic roof, immediate roof and coal, and then studied the depth of floor damage and got its expression:(3) Using outer stagger arrangement roadway layout, if the roadway driving along the seam roof, the entity coal is lateral supported by the triangle coal pillar, successive working face is arranged along goaf without coal pillar, the side of triangle coal belongs to the elastic region, the integrity of the roadway surrounding rock is good and carrying small.(4) Proposed "joint adjacent roadway support technology" for the outer stagger arrangement roadway, which uses anchor bolt + 7.5m, adopt entire section anchoring bolts and cables, and at the same time digging two rows of 4 m deep hole to grout which make the shallow coal seam into a whole, thus entity coal side of the roadway initiative to strengthen support for the successive working face roadway along the roadway roof bolt using cord suspension provide a basis. |
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