Study On Collapse Mechanism And Treatment Of Large Cross-Section Tunnel Induced By Gas Dynamic Phenomenon In Steep Seam

Taking Songkan tunnel of Chongzun expressway as the engineering background,this paper investigates and analyzes the causes and factors of gas tunnel collapse by means of theoretical analysis,numerical simulation and field investigation;The mechanism of gas tunnel collapse induced by steep coal seam is studied;The support effects of different advance pipe shed support parameters on the collapse section are compared and analyzed,the reasonable support parameters are selected,and the corresponding treatment scheme is formulated.The specific results are as follows:(1)By investigating the collapse site of gas tunnel and analyzing the accumulation of coal and rock in the collapse site,it is concluded that the collapse is caused by the dumping of coal and gas,and the position and size of the cavity after the collapse are inferred;Various factors causing the tunnel collapse were analyzed.(2)Using COMSOL multiphysics multi field coupling simulation software,the gas seepage theory,gas diffusion theory and M-C quasi measurement are combined to carry out multi field coupling analysis,calculate the coupling law between each field,and analyze the change law of stress and displacement of coal seam and surrounding rock mass under different high initial gas pressure.The experience of coal seam and surrounding rock will increase with the increase of initial gas pressure;Through the formula of coal seam fracture coefficient,the coal seam fracture coefficient under different high initial gas pressure in numerical simulation is calculated.It is concluded that if the coal seam fracture coefficient is greater than 1,it will produce destructive production,and the greater the initial gas pressure is,the greater the coal seam fracture coefficient is;Finally,it analyzes how the gas dynamic phenomenon under the action of gas pressure induces tunnel collapse after coal seam breakage.(3)The FLAC3 D finite element numerical simulation software is used to simulate the support treatment scheme after gas tunnel collapse,and the support simulation comparison is carried out for different advance pipe shed support parameters.Through the analysis of the simulation results,the more reasonable advance shed support parameters are obtained,and the gas tunnel collapse treatment scheme is specified and applied to practice.After the implementation of the treatment scheme,the tunnel excavation is carried out smoothly without secondary collapse,The vault settlement and arch waist convergence data of the collapse section during excavation are within the specified range,and the collapse section has been excavated at the scheduled time and the coal seam has been completed,indicating that the collapse treatment scheme is feasible.This paper preliminarily explains the characteristics and mechanism of large section tunnel collapse induced by gas dynamic phenomenon in steeply inclined coal seam.The proposed treatment measures for gas tunnel collapse have been applied to practice and achieved good results,which has practical significance.