| Resource recovery of bound coal is an important part for sustainable development of coal mine, but it’s difficult to mine for its complex geological conditions, it should be programmed to exploit in advance.This article summarized somen failure experiences of exsited roadway. Based on geological conditions of Ganhe Colliery, many rock samples were obtained from worksite. SEM, X-ray diffraction test, uniaxial compression test, point loading test and triaxial compression test were carried out to get data of micro structure, mineral composition,σc,C,φ,E, and so on. In order to research the creep regularity of rock beams, mortar and support similar materials were made according to those properties, a test platform was founded to research bending creep regularity of rock beams, including beams without support, multihore beams and imbedded anchor beams. Based on those test datas and curves, some regularity were summarized. The functions,the relationship of stress and time, were fitted by Origin, control mechanism of rock creep was put foward. Two mechanical model, roadway without support and roadway with side support, were analysed using beam theory, shearing force and moment of roof were solved. We come to a conclusion that the roof thickness and roadway parameters meet hyperbolic connection. Four types of support designs were analysed by FLAC, also different timings of support design were contrasted. Support parameters were optimized by contrast length, number, row space of bolt and anchor effect. Finally reasonable support designs for main and branch roadway were proposed.1. Sampling of surrounding rock and basal mechanical parameters testThe geological conditions and parameters of surrounding rock are playing an important part for stability and support design of coal roadway, it’s preconditions of mining and support design. It is necessary to test basal parameters of rock for the lack of mechanical parameters in Ganhe Colliery. Sampling of rock and analysing of RQD must be done to make an assessment of rock integrality. The diameter of drill is 75mm, its length is 800mm. The worksite is in two roadways of NO.l mining area. From this area, we get the roof rock and floor rock. According to sampling work and results, some experiences are obtained as follows.(1) The integrality of surrounding rock is poor for both roof and floor RQD are lower than 30%, the fractures and joints are well developed. (2)The quality and revolving speed, operation level of workers have big effect of sampling quality. (3) It really hard to process rock samples, whose joint were well developed.Mechanical parameters of surrounding rock have big effect on roadway stability, while the micro structure and mineral composition are determinants of its property, so test of mechanical parameters is of great significance. Five rock samples were chose to do SEM and X-ray diffraction test in the key laboratory of CUPB. Uniaxial compression test, point loading test and triaxial compression test were carried out in state key laboratory for geomechanics and deep underground engineering of CUMTB. The tests results can be used for support design, later experimentation of physical model and numerical simulation. The conclusions are shown as follows.(1) Through SEM test, we find that the rock samples are compact, micro fractures are few, but politic and carbonaceous composition are of a big proportion, pore-filling minerals are most clay mineral, which is widely scattered. (2) The sandy mudstone is composed of quartz, potassium feldspar, siderite and clay mineral, and so on. Clay mineral is 19% of its weight, quartz is more than 63%, and potassium feldspar and siderite is more than 9%. (3) The main component of clay mineral is I/S mixed layer and kaoline, their content is 85% to 93% of clay mineral weight. (4) The average compressive strength of roof sandy mudstone is 58.74MPa and 55.5MPa from uniaxial compression test and point loading test results, the test data is discrete. So support design is difficult for inhomogeneous roof rock. The average elastic modulus is 26.5GPa, and its poisson ratio is 0.16. (5) Floor of roadway is post stone, whose average compressive strength is 89.3MPa if force direction is perpendicular to joint. Floor rock will not be broken for compression of continous miner, but ite shearing strength is lower. (6) Through triaxial compression test, the cohesion of sandy mudstone is 16.2MPa, and the internal friction angle is 42.6°. The breaking stress is linear growth with confining pressure, and the coefficient of association r is 0.97.2. Rock beams and bending creep tests of physical modelPhysical models of roof rock are established to carry out for regularity of bending creep, because we didn’t get the original rock beams. Physical models are convenient to implement, it’s repeatable and it can be used for back analysis. It also can guide the support design of coal roadway. According to specification for mix proportion of masonry mortar and ratio of similitude, many groups of mortar with different mix proportion were test to establish the most reasonable mix proportion. Physical model of support materials are prefabricated. A platform of creep test and monitoring system were founded. There are three types of rock beams, including beams without support, multihore beams and imbedded anchor beams. The bending creep tests were under single-stage loading and multi-stage loading. The regularities of bending creep are as follows.(1) Different mix proportion of mortar were tested and the appropriate mix proportion is 1:8:1.5. Artificially graded aggregate is better to model material. (2) There is a threshold value for bending creep, each condition of bending beams is 0.745,0.813, 0.791, the average is 0.783. When the loading is lower than the level, rock beams are elastic; while it’s bigger than 0.767, rock beams show creep characteristics. (3) The threshold value of accelerated creep is 0.878,0.875,0.948, the average value is 0.900, fractures appear in this stage. (4) Deformation creep exist both in upper surface and lower surface of rock beams, creep characteristics are typical three stages. The creep age of compressive zone is longer than tensile region, its creep characteristics is more disciplinary. (5) The stability age of beam deformation is longer because loading level is increscent, the creep curves change from decay type to non-decay type. (6) The average failure load of multi-stage creep test without support is 1.39kN, it’s lower than 1.65kN, which is the failure load of transient load. The ratio between them is 84.2%. (7) The tensile stress of beams transfers to deep rock of roof when fractures appear. The original compressive zone changes to tensile region. It will last a long time for bolt support system until the loading level become bigger. (8) The accelerated creep age of brittle materials, like rock beams, is very short, fractures transfix beams promptly if there’s no support. (9) Integrality of rock beams has big effect of its bearing capacity, it will really hard to provid reaction force for rock support with large void content. Maybe it will cost more and more support materials. (10) It can drastically improves bearing capacity of rock beam by aggrandizzing restraint, but its hard to carry out for site operation.3. Creep characteristic of rock beamsAs is well-known, indoor creep test data is indispensable to describe rock creep characteristics, the results is preconditions for deep research of rheology, it also can reveal rheological properties under different loading levels. The results of different level and conditions should be further contrasted in order to get rheology regularities, and corresponding control mechanism can be figured out.Fuctions that acquired by fitted curves can guide site construction well, they are of practicability. Through Origin we get different functions that meet lower stress, stable creep age and accelerated creep age. When the stress is lower, the strain can be described by Boltzmann. And for stable creep age, BiDoseResp function meets the rule. Logistic function comforts to accelerated creep age. All functions are of high determination coefficient, they are dependable. Comparing test results and classical creep models, we try to found a new creep model to meet bending creep, but it’s really difficult for the lack of section stress and elastic modulus.4. Theoretical analysis of support designs for coal roadwayLoading of roof beam was established based on some postulated conditions. Three mechanical model, roadway without support, roadway with side support and roadway with side and roof support, were analysed using beam theory, shearing force and moment of roof were solved. We come to a conclusion that the roof thickness and roadway parameters meet hyperbolic connection. Theory of truss-bolt system was used for theoretical analysis to design support parameters of main and branch roadways. The analysis results are as follows.(1) The max section stress of roof beam is 3.0MPa on condition that there’s no support in surrounding rock. The value is bigger than 2.45MPa, which is the average value of tensile strength of roof rock. The probability of tensile failure is fairly high. (2) The max section stress of roof beam declines to 1.1MPa when constructing sides bolts in surrounding rock. The value is lower than 2.45MPa, which is the average value of tensile strength of roof rock. The roof beam is safety theoretically.(3) On condition that sides of roadway are not stable, the roof thickness and roadway parameters meet hyperbolic connection. The function follows.The length of roof bolts is 2.3m for Ganhe Colliery in NO.1 mining area.(4) On condition that sides of roadway are stable enough, the roof thickness and roadway parameters also meet hyperbolic connection. The function follows. The length of roof bolts is 1.5m to 1.9m for Ganhe Colliery in NO.1 mining area.5. Numerical analysis of support designs by FLACNumerical method has been widely used in all fields of scientific research, it can simulate prototype of roadway and its geological conditions, also the boundary conditons can be conveniently changed for different support roadways. In this way, the cost of site support design can be largely cut down. The numerical method is of great precision. This part introduces the principles of FLAC, and numerical models are founded based on rock colomn. Four types of support designs, including roadway without support, roadway with side support, roadway with roof support and roadway with roof and side support, were analysed by FLAC, also different timings of support design were contrasted. Support parameters were optimized by contrast lengths, numbers, row spaces of bolt and anchor cables effect. Finally reasonable support designs for main and branch roadway were proposed.(1) The crustal stress first concentrates on corner of roadway of after excavation, the stress of corner rock bearing is the biggest, the bolts in corner must be well constructed. Deformation of roadway sides is largest for the coal rocks are very weak, it’s the most important part for roadway support. (2) Doing sides support only can do better to control roadway deformation than doing roof support only. (3) FRP Bolts can take the place of whorl-steel bolts in sides support, they can meet the qulity requires although their properties is little lower than steel ones. (4) The numbers and length of sides bolts have obvious effect to rock deformation, there’s a optimum value for its length, the effect will be declining if bolt is longer than this value. (5) Prestressed anchor cables can do good to control rock deformation, they have more effect to sides convergence. But the number can’t be too many for it will reduce efficiency of excavation. |
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