| In recent years,deep roadway control problem is a hot research issue in roadway support engineering. Due to the increase of mining depth, the failure characteristics and mechanism in deep rock roadway is significantly different with that in shallow surrounding rock. The further deterioration of roadway stability leads to that the existing roadway support theory and techniques are not well adapted to deep roadway, which results in deep roadway maintenance difficulties, a sharp increase in support costs, while causing deep mining roadway roof fall accident increase. Roadway deformation and destruction is essentially caused by the formation and development of plastic zones. Currently, the plastic zone theory holds that the shape of surrounding rock roadway plastic zone is mainly round or oval or other more uniform shapes, which is mainly applied to the middle level or shallow tunnel in small stress field. For deep roadway, especially deep roadway along gob, due to increased depth of roadway surrounding rock stress field is no longer uniform, and the rock plastic zone is no longer round or oval regular shape as the traditional theory holds, leading to the emergence of new roadway support problems. Therefore, the search for suitable deep roadway surrounding rock control theory and control technology is a serious issue.Henan Jiaozuo Coal Seams Zhaogu 2# mine is an high yield and efficient modern mine, the annual production is 2.4Mt, and the main coal layer is 2-1 coal and seam average depth of 700 m, coal seam thickness is 6.0m ~ 6.59 m, average in 6.32 m, the width roadway excavation roadway during the cross-sectional dimensions is 4.8m, the height is 3.3m.In order to ensure the stability of the roadway, Zhaogu second mine has been using a large pillar to protect road about 30 m, only the loss of coal pillar amounted to 520 000 t, the direct economic loss is 620 million yuan. Although the big pillar played certain role to protect the roadway stability, caused huge economic waste. In order to improve resource recovery, mine 11030 working face transportation lane used 8m narrow pillars gob-side entry driving, caused the roadway’s non-uniform driving top down during the occurrence, the deformation of coal sides is prominent, supporting body support such as the failure phenomenon, have an important influence on the safety of mine roadway excavation.Therefore, this doctoral dissertation takes Zhaogu second mine which uses deep narrow pillar entry as engineering background, using theoretical analysis, numerical simulation, field testing, laboratory experiments and field tests and other methods. Taking the distribution pattern of deep roadway butterfly plastic zone as the main line, mechanical mechanism of deep roadway butterfly plastic zone formation was systematically studied, the deep roadway butterfly plastic zone theory was established. Numerical simulation researched the effects of coal pillar size of roadway principal stress directions and non-uniform deformation mechanism of deep narrow pillar entry form on butterfly distribution on the plastic zone, revealed the principal stress directions. On this basis, we explored the deep roadway butterfly plastic zone forms of "low resistance constant" characteristic, proposed roof caving control technology based on flexible plastic zone butterfly bolt patterns, formed the following main conclusions and innovative achievements.1. The mechanical mechanism of deep roadway butterfly plastic zone formation was illustrated.(1) When the higher the degree of non-uniform stress field of deep roadway in which that side of the pressure coefficient farther away from 1, the maximum principal stress and surrounding rock partial minimum principal stress the absolute value of the greater of the two partial formed between the larger stress difference;(2) According to the circular hole in the elastic-plastic mechanics stress solution, using Mohr-Coulomb strength criterion, according to the circular hole in the elastic-plastic mechanics stress solution using Mohr-Coulomb strength criterion, obtained under conditions of force field surrounding rock should characterize non partial stress circular roadway radius relation plastic zones and expression:(3) The formation of deep roadway butterfly plastic zone is due to the presence of high partial wall rock stress difference, the greater the difference between a high bias stress deep roadway more easily formed butterfly plastic zone. Environmental stress and surrounding rock mechanics parameters are two conditions in deep roadway butterfly plastic zone formed regardless of the roadway cross-sectional shape. Surrounding rock cohesion and angle of internal friction and the plastic zone size butterfly inverse relationship, while the size of the roadway and butterfly plastic zone size is proportional to the relationship;(4) Deep tectonic stress field of surrounding rock plastic zone was erected butterfly distribution, plastic radius of the largest roadway shoulder position, the top position, followed by plastic zone radius, and help position the Department of plastic zone radius of the smallest. Deep mining stress field of surrounding rock plastic zone leads to a horizontal butterfly distribution of plastic zone radius of the largest roadway shoulder position, the position of the Ministry of help followed by plastic radius, and the radius of the smallest roof strata plastic zone.2. The non uniform deformation and failure mechanism of roadway in deep narrow coal pillar was revealed.(1) Butterfly shaped plastic zone of surrounding rock in deep tunnel has a certain direction, when the maximum and minimum principal stress is in the horizontal vertical direction, the deviation angle of the butterfly is in the vicinity of 45 degree(the deviation is within 5 degrees).When the direction of the principal stress changes, the direction of the butterfly plastic zone changes with the angle of the principal stress rotation, and the four butterfly leaves in the plastic zone are located at different locations of the surrounding rock of the tunnel;(2) Coal pillar size will have an important influence on the maximum principal stress and the direction of the minimum principal stress of surrounding rock. When the roadway coal pillar size is smaller, the main stress direction of roadway surrounding rock will be larger, while the coal pillar size is larger, the main stress direction of roadway surrounding rock will be smaller. Therefore, the narrow coal pillar roadway will cause a large deflection of the main stress direction of the roadway surrounding rock;(3) In the direction of the main stress direction of surrounding rock, the distribution shape of the plastic zone will be changed, which leads to the different position of the butterfly in the surrounding rock of the tunnel:(1) When the main stress deflection angle of roadway surrounding rock is less than 40 degree, the four butterfly plastic zone of the surrounding rock of roadway is located on the left side of the roadway, the left side wall rock, the right side wall rock and the right bottom rock stratum;(2) When the main stress deflection angle of roadway surrounding rock is between 50 degrees to 80 degrees, two of the surrounding rock butterfly plastic zone is located in the roadway roof rock strata, and the remaining two butterfly leaves are located in the right side of the lower wall rock and the right side of the rock stratum;(3) When the main stress deflection angle of roadway surrounding rock is between 100 degrees to 130 degrees, the two butterfly shaped plastic zone of the surrounding rock is located in the roof rock strata, the remaining two butterfly leaves are located in the left side of the left side of the surrounding rock and the left bottom rock strata;(4) When the main stress deflection angle of roadway surrounding rock is more than 140 degrees, the four butterfly plastic zone of the surrounding rock of roadway is located in the right side of the roadway, the surrounding rock of the left side, the right side of the surrounding rock and the left bottom rock strata.(4) There is a positive correlation between the size of surrounding rock and the deformation of surrounding rock, the size of plastic zone is larger, the deformation of surrounding rock is larger, the distribution shape of butterfly shape plastic zone of surrounding rock and the deformation of surrounding rock are basically the same;(5) Reveals the zhaogu second coal mine 11030 haulage gateway non uniform deformation and failure mechanism, supporting the roadway 8m of narrow coal pillar will enable roadway locations of surrounding rocks of the principal stress appeared obvious stress concentration, forming high deviatoric stress environment, the rock formation butterfly plastic zone. At the same time, 8m coal pillar will make the rock main stress direction of deflection of about 160 degrees, thus resulting in roadway surrounding rock butterfly shaped area of four butterflies leaves are located in the roadway coal pillar side of roof strata and coal pillar for coal, coal wall side bottom slate layer coal wall and help in coal body, the leaf disc plastic zone the location of the surrounding rock deformation compared to the other position of surrounding rock deformation amount is larger, eventually leading to the present obviously inhomogeneous deformation and failure characteristics of 11030 transportation roadway surrounding rock.3. The flexible bolt roof control technology of plastic zone based on the morphology of the butterfly.(1) Due to the existing engineering technology can provide supporting resistance and deep roadway surrounding rock by stress field in the same order of magnitude, which belongs to the lower support resistance, resulting in deep roadways butterfly shaped area is mainly affected by the original rock should force field and mining stress field superposition of stress field control, the existing branch support technology can provide support resistance of rock butterfly shaped the influence has little effect. So it can be considered that the butterfly shaped plastic zone of the surrounding rock of deep tunnel has the "low resistance and the same" under the existing technical level;(2) For the deep narrow coal pillar roadways, as a result of the roadway surrounding rock butterfly shaped the butterfly leaves in different positions of the surrounding rock of roadway, and make of roadway surrounding rock not only non uniformly varying characteristics. At the same time will make the roadway surrounding rock large deformation, resulting in roadway roof sinking severely and anchor cable is unable to adapt the large deformation of surrounding rock and roof collapse;(3) As a result of the butterfly shaped region of the "low resistivity change", so in supporting design should be supporting key from the control of surrounding rock deformation "go to" prevent roof caving ", supporting to plastic zone of rock mass deformation, plastic zone in rock mass stability of leaf disc was improved, to prevent the occurrence of roof fall accident;(4) Formed to rock butterfly shaped plastic zone distribution for the flexibility of the foundation bolt- common bolt collaborative roof control technology with high elongation of flexible anchor rod instead of conventional cable roof control plastic zone damage depth of strata, give full play to the anchor flexible deformation capacity, in the process of deformation of the surrounding rock does not break off failure, increase the roof of the elastic stability of rock damage, prevent roof falling accident;(5) The industrial field tests of anchor flexible control technology of roof falling,which based on the butterfly plastic shape, was taken in 11030 transportation roadway. The experimental results show that flexible anchoring bolt can be very good to adapt to the roof of the continued to sink, and prevent the roof top. Although the roof is made of flexible anchor bolt supporting coordination deformation support for supporting the roof subsidence amount is still large, but during the mining of narrow coal pillar mining roadway based on deformation will continue to increase, using flexible bolt elongation can ensure roadway safety, reduce the risk of roadway roof fall. |
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