Research on the escape mechanism and influencing factors of harmful gas induced by blasting excavation in deep rock tunnel

Abstract

Based on real-time monitoring data of harmful gasses during blasting and excavation of Yuelongmen Tunnel on Chengdu–Lanzhou Railway, this study summarized laws and distribution characteristics of harmful gas escape intensified by the blasting excavation, and the effectiveness of shotcreting and grouting for water blocking to inhibit gas escape is verified. Then, taking water-containing and gas-containing voids as carriers, considering the influence of different in-situ stress, explosion load and void parameters (including void pressure, void diameter and distance between void and tunnel), to carry out research on the escape mechanism of water-soluble (H2S) and insoluble (CH4) toxic and harmful gasses under the coupling effect of stress-seepage-damage. The relationship between the amount of harmful gas escaped and the damage degree of the surrounding rock of the tunnel is analyzed, and the functional relationship between it and the in-situ stress, explosion load and cave parameters is established. The results further demonstrate that the amount of escaped harmful gasses, such as methane and H2S is closely related to lithology of surrounding rock, occurrence conditions of the deep rock mass, development degree of structural fractures and void parameters. The damage of surrounding rock caused by dynamic disturbance during blasting excavation is the main reason of aggravating harmful gas escape. The water inflow and gas inflow into the tunnel both exponentially increase with the blasting load, the gas inflow into the tunnel from the gas-containing void constantly, after the blasting load exceeds 25 MPa, the water inflow in the tunnel with the water-containing void in the surrounding rock is basically not affected by the increase in the blasting load. When the diameters of the water-containing void and gas-containing void increase, the gas inflow and water inflow into the tunnel both exponentially rise, the net distance of 15 m from the water-containing void and gas-containing void to the tunnel is considered as the critical distance of influence.