Study On Physical Simulation Of Coal And Gas Outbursts Based On Centrifugal Model Testing System

The physical simulation test of coal and gas outburst is an important means to study the outburst mechanism.Crustal stress is one of the main factors affecting coal and gas outburst.The field of gravity is the most basic crustal stress field.In order to simulate more scientifically the influence of gravity action of coal seam itself and overlying rock and soil layers on outburst,and to overcome those shortcomings of the traditional testing ways,a centrifugal model test of coal and gas outburst was carried out and the test results were analyzed.The main works include:(1)The similarity criteria of centrifugal model tests of coal and gas outburst were determined.Through the analysis and comparison of the three similarity criteria of coal and gas outburst based on the energy model,gas-solid coupling model and seepage failure model,the energy model of coal and gas outburst is adopted as the similarity criterion of this test.(2)Acentrifugal model test device for coal and gas outburst was developed.The device includes stratigraphic model box,uncovering coal device,gas charging device and data acquisition device.The stratigraphic model box is a cylindrical container and its size isfmm900mm300 ′.The uncovering coal device was transformed from a pneumatic solenoid valve.A nitrogen cylinder was used to inject similar gas into coal seam.Some sensors were installed to measure the gas pressure inside coal and the stress of coal seam roof.(3)Coal seam similar materials were prepared in advance.The aggregate is from the raw coal of the prototype coal mine,after crushed into pulverized coal less than 1mm.Sodium humate aqueous solution was used as the cementing agent with eight percent water content.Shaped coal samples were made under different pressure and the relationships of the physical and mechanical parameters with different pressures were tested.It provides the basis for making the coal seam model.(4)According to the coal mine prototype parameters and centrifuge capacity,the similarity scales were determined for a centrifugal model test and a lever pressurization test.The size of the coal seam model isfmm40mm300 ′ and its elastic modulus is 35 MPa.The coal roof pressure is0.875 MPa.The centrifugal acceleration of the test is 20 g.The gas pressure inside the coal is 0.75 MPa.The experimental results show that:When the coal and gas outburst occurs,the gas pressure drops rapidly and the roof stress near the outburst mouth rises first and then decreases.Both the holes formed by outbursts appeared the shape of small mouth and big abdomen.The coal seams appeared layer fracture phenomena after outbursts.A method was put forward to predict the outburst strength in coal mine site,by which the outburst strength of centrifugal model test is 336 t,while the lever pressurization test is 520 t.(5)A mathematical model of coal seam seepage failure for uncovering coal in crosscut was developed,that is used to simulate the coal layer fracture phenomena when an outburst occurs.The numerical simulation results are in agreement with the experimental phenomena.Analysis suggests that the reason why the outburst strength by the lever compression test is different from the centrifugal model test is that the gravity is body force,while the force applied by lever is surface force.In addition,lever compression test ignores the influence of coal seam self gravity.The centrifugal model test overcomes these two disadvantages.The test results show the reliability of this device and the rationality of centrifugal model test of coal and gas outburst.The centrifugal model test of coal and gas outburst provides a new method for study of outburst mechanism and prevention and controlling technology of coal and gas outburst.Figure [40] Table [5] reference [97]...