Research Of Fracture Law And Deep Hole Advance Blasting Technology In Hard And Thick Sandstone Roof

Fully mechanized working face roof often be difficult to caving naturally, during longwall mining under the hard rock roof; with working face propelling, goaf roof hanging area increases gradually, cause gas accumulation in goaf. Large aceage goaf roof does not collapse during a long time also will make stress concentration in working face roof area, causes supporting structure damage, bring huge threat to production. At the same time, if the large overhang roof suddenly caving, strong dynamic load caused by rock broken can make a large number of supporting damage or knocking down, cause catastrophic collapse accidents of mining face; it also can easy to form damaging hurricanes and huge impact ground pressure, the hurricane wave often destroy facilities of working face and its adjacent roadway, such as supporting, air door and brick wall, even make the car overturned, orbital bending, caused serious damage and heavy casualties of personnel, and easy to make the gas accumulated in goaf instantaneous emission, cause serious accident.On the basis of a large number of domestic and foreign related research literatures, this article through theoretical analysis, model testing, numerical simulation and field testing, roof rupture law and deep hole advance blasting for thick and hard sandrock of full mechanized working face was researched. Through establishment of rock plate calculation model for roof weighting interval, mining roof caving process was researched, analyse roof breaking laws and stress and displacement distribution characteristics of rock. On basis of hole wall pressure calculation of decouple charge, with two aspects of column charge blasting mechanism and rock fracture blasting mechanism, stress propagation and law of crack propagation in rock mass was analyzed. Based on finite element software ABAQUS, rock mass mechanics model of deep hole blasting in sandstone roof is established, study blasting stress field distribution and crack propagation characteristics of different initial ground stress, influence of initial ground stress to crack propagation is analyzed, According to the field geological characteristics and site conditions, great thickness sandstone roof deep hole blasting advanced weakening field testing carried out, formaed a set of feasible roof advanced weaken blasting construction techniques. Main research work and achievements of paper are as follows: Through analysis lower and upper parts of cut drilling geological data and theoretical calculation, four edges clamped thin plate mechanics model is established, first caving space formula of roof is derived, Get first caving space of roof; after hard roof first caving, rock beam mechanics model of roof is established. First caving space and periodic caving space of roof calculated by three methods are equivalence. Model test and numerical simulation also shows that stress concentration in all parts of working face, and formed a certain degree of pressure relief in the working face overburden rockmass.Stress concentration maximum value occurrs in central part of working face, followed by upper part of working face, lower part is least. Maximum displacement of roof occurs in the middle part of working face, displacement of two-terminal is less than the central; there is an obvious caving lag,, thus causes support pressure of central part is greater than in top and bottom.According to the results of rock physical and mechanical performance test, stress distribution around the hole and crack propagation of single and double hole blasting under different initial geostress conditions are analyzed by finite element software ABAQUS, the results show that: with the increase of initial ground stress, fracture zone radius reducing, rock blasting is relatively difficult; direction of main crack extension is related to the size of the lateral pressure coefficient; the smaller the initial stress on the direction, crack length is relatively short; during double shot blasting, due to weaken the effect of initial ground stress, crack length with ground stress between two hole is shorter than length without ground stress.Therefore, in deep rock mass blasting parameters design, hole spacing should be reduce.Combination working face of210108in Xinji Coalmine, according to the current working and geological conditions, reasonable space for roof advanced caving deep hole blasting is30.0m; roof advanced caving deep hole blasting scheme and parameters are determined, put forward roof advanced caving deep hole blasting process. For evaluation of deep hole blasting effect, provides basis for support working resistance determination, blasting parameters optimization, mining pressure field testing and analysis is did according to the site conditions. The testing results show that the original roof caving average space is19.08m, which is about24.6m without loose blasting. During mineral pressure observation, working face support working resistance was basically normal range. Support intensity is relatively uniform, no large stress to compressive phenomenon. Working face of coal wall is integrity, no bond andcaving, and pressure of periodic weighting lower than average value, almost no obvious weighting phenomenon, verifies effectiveness of proposed technique.