Study On Fracture Field Evolution Of Surrounding Rock And Gas Migration Law In Steeply Inclined Coal Seam With Sublevel Mining

Xinjiang is one of the 14 large-scale bases with 100Mt coal production in China,and the reservation of steep seam is more than 30%to the total reservation of similar coal in the world.As the occurrence of steep coal seam is very complex and difficult to recover,the current mining method commonly used in Xinjiang area is horizontal or oblique sublevel caving mining method.Because of the large extraction-caving ratio,the difficulty of coal and roof controling,the gas emmission from bottom coal during pressure releasing and losing large amount of coal in the goaf,it is very difficult to control and prevent gas in the workface and accidents frequently happen.The Wudong Coal Mine has respresentativeness in its seam conditions,coal mining method and gas control technology,so it will be the study object in this thesis.Totally,the rock fracture field with sublevel mining method,gas emission and migration law,prediction model of gas emission and a drainage process optimization were studied in steep coal seam.The main research the work is as follows:With similar material simulation,a model of sublevel mining in steep coal seam is built according to the coal seam occurrence and mining method in Wudong Coal Mine,which includes six mining block from top to bottom,and was caved in an extraction-caving ratio of 1:7.3.During the caving,the destruction and displacement of the floor and top in workface are real-time measured with the stress and displacement sensors installed in the model,and the law of stress change in the floor and top of the workface is analyzed..Using the numerical simulation software PFC^3D,a three-dimensional model of steep seam sublevel mining is built,and the calculation parameters of numerical simulation are selected based on the mechanics parameters of rock mass.After the model is dynamically resolved with high performance computer workstation,the dataset of the fracture field evolution and the fracture porosity distribution field in the surrounding rock of the workface are calculated out,in which the floor stress variation consistents to that in similar material simulation experiment.Importing the dataset of porosity distribution into coupling multi-physics simulation software COMSOL,the mathematical model of the gas emmision and migration is established,and the concentration distribution and migration law of gas in a certain condition of gas pressure and gas crack field in sublevel caving of steep coal seam are reached.Analysising the law of stress evolution in the coal mass,a stress evolution model of floor coal mass is established,which is in the mining direction of the workface and involved in several stages,such as original stress stage,stress concentration stage,workface mining stage and goaf stability stage after mining.The model is import into MathCAD softwar with programming,and the trend graph of the floor coal stress is drawn.Meanwhile,a prediction model of gas permeability and emmision from floor coal mass during stress concentration and self stress unloading is established.Combining the stress monitoring data from the similar simulation experiment and the gas permeability situation under defferent stress states,the areas of difficulty level about gas drainage from floor coal mass are distinguished,which are the base to predict gas emmission from the floor coal mass and select the design parameters for gas drainage.On the basis of elementary gas parameters,combining with the models about the gas migration law in fracture field of surrounding rock and gas release prediction in workface floor coal during self unloading,the shortage of the raditional mine gas emission prediction is analysised and summerized when it is used in horizontal sublevel mining of steep coal seam.The parameters that are unsuitable to apply in horizontal sublevel mining of steep coal seam are improved and optimized,and a new suitable prediction model is established.Applying the model to the gas emmision prediction of Wudong coal mine,the error between the prediction and the real data is less than 10%.According to the evolution law of the fracture field in surrounding rock and the stress field in floor coal mass,using of gas permeability coupling effection model combined with gas migration law,the key parameters for top and floor interception gas drainage art optimized.The method is applied in the production of Wudong Coal Mine,and the sets of gas drainage technology are set in the 43#west workface in+575m level.The excellent effection of gas drainage achieved,and the gas concentration is controlled below 0.3%for a long period at return corner,gas emission from the working face is effectively controlled.Using a variety of research mothods,such as similar simulation experiment,numerical simulation,thoeretical analysis,field measurement and so on,the thesis mainly reveals the distribution charateristics of surrounding rock damage and fracture in steep coal workface with sublevel mining method,anylysises the influence of gas migration in surrounding rock by fracture field,builds a theotetical model of gas permeability and emission from bottom coal mass in workface,builds a safer and accuracier prediction model of gas emission suitable for sublevel mining of steep coal workface,optimized the sublevel mining gas drainage technology system of steep coal seam..