Study On Outburst Risk And Outburst Prevention Technology In Songkan Tunnel

In this paper,Songkan Tunnel of Chongzun Expressway is taken as the research object,and the relevant factors affecting tunnel safety are investigated and analyzed by using the method of field investigation,theoretical analysis and numerical simulation;Using FLAC software,a three-dimensional tunnel model of steeply inclined outburst coal seam is established,and the stress and plasticity of coal and rock at different excavation distances from the coal outcrop point are compared and analyzed.By using COMSOL Multiphysics software,the change law of stress and displacement of coal seam and surrounding rock mass under different initial gas pressures is analyzed.The reasonable construction scheme was finally designed and successfully implemented.The specific results are as follows:(1)The COMSOL Multiphysics software is used to combine the gas seepage theory,gas diffusion theory and M-C criterion,conduct multi field coupling analysis,and analyze the change law of the stress and displacement of the coal seam and surrounding rock mass under different initial gas pressures.The stress and displacement of the coal seam and surrounding rock mass will increase with the increase of the initial gas pressure;Through the coal seam crushing coefficient formula,the coal seam crushing coefficient under different initial gas pressures in the numerical simulation is calculated,and it is concluded that the coal seam crushing coefficient is greater than 1,which will cause damage,and the greater the initial gas pressure,the greater the coal seam crushing coefficient.(2)The factors influencing the critical thickness of coal uncovering in tunnel are theoretically analyzed and deduced.The greater the tunnel clearance and ground stress are,the smaller the elastic modulus is,the greater the risk of coal and gas outburst is.Therefore,the critical thickness of coal uncovering in tunnel that needs to be reserved is larger.By observing the change of the rock plastic zone,comparing the relationship between the maximum and minimum principal stresses,and combining the two,it is concluded that the critical thickness of coal uncovering for large section excavation of Songkan Tunnel is about 4.8m.Due to the more complex construction site conditions,6m is finally determined as the critical thickness of coal uncovering for this tunnel,the horizontal and axial distance from the face to the coal outcrop is 8.8m.(3)On the basis of the previous research,the design of coal uncovering and outburst prevention was carried out for the left tunnel excavation of Songkan Tunnel.The relevant measures for coal uncovering and outburst prevention were implemented in strict accordance with the design scheme at the construction site,and the effect inspection was carried out after the implementation of coal uncovering and outburst prevention measures.The inspection results showed that the outburst prevention and control effect was good,the gas concentration,flow and other parameters met the requirements,and the average gas extraction rate reached 76%,After taking safety protection measures,Songkan Tunnel successfully uncovers coal.