| At present,in the existing traffic tunnels that cross the gas seam in China,one of the preventive measures for gas protrusion in the process of coal removal is to reserve a certain thickness of safety rock columns before unearthing,and the coal seam with the risk of gas outburst can only be uncovered after the explosion treatment.Therefore,studying the destructive behavior of reserved rock pillars and proposing the thickness of safe rock pillars have important theoretical and practical engineering significance for preventing the occurrence of coal and gas outbursts.Based on the engineering background of uncovering coal during the construction of the Tianchengba highway tunnel,this thesis uses various methods such as theoretical analysis,numerical simulation,and model test to analyze various influencing factors such as gas pressure before uncovering coal,tunnel span,and surrounding rock grade,as well as the influence rules on the thickness of the reserved rock pillar and the gas seepage laws,so as to determine the minimum thickness of the reserved rock pillar.The main work and achievements are as follows:1)Through similar model tests on the failure mechanical behavior of tunnel reserved diapher,the failure characteristics of the reserved diapher are studied,and the variation of the stress of the reserved diapher with the process of excavation,the deformation and displacement rule of two different spans of reserved diapher under the action of stress,and the relationship between the surrounding rock pressure and the process of excavation are obtained.2)Taking the Tianchengba Tunnel as the background,a numerical calculation model is established for tunnels crossing gas coal seams under different gas pressures,different surrounding rock grades,and different tunnel spans.Through the calculation and solution of comsol software,the stress law of safety rock pillar,the change law of plastic failure zone,and the change law of gas pressure,porosity,and pressure gradient are obtained considering the coupling of gas and gas during the process of coal mining in the tunnel;Through orthogonal test method,eight different working conditions were designed for the above factors,and the variation rules of the thickness of the reserved rock pillar under different combinations of factors were obtained;Finally,the calculation formula for the minimum reserved rock pillar thickness is obtained through multiple factor regression analysis,providing a reference for the minimum reserved rock pillar for tunnels crossing gas coal seams3)Compared with Shimen uncovering coal in coal mine,the span of highway tunnel is larger.According to numerical simulation,the minimum reserved wall thickness of tunnel uncovering coal in the process of excavation is greater than 5m.Therefore,the minimum thickness required to be checked by anti-outburst measures in Technical Specifications for Design and Construction of Highway Gas Tunnel is 5m and2 m.The risk of coal and gas outburst is high,so it is necessary to increase the thickness of reserved safety dike to reduce the possibility of coal and gas outburst. |
