Large-scale experimental study on influence of gas explosions in urban utility tunnels

Gas explosion in an urban utility tunnel is a crucial safety issue which may cause heavy casualties and economic losses. In this study, a series of gas explosion experiments were conducted on a large-scale concrete utility tunnel structure (10 m in length) to evaluate overpressure, structural responses, and impact on the surrounding environment under varying methane volume concentrations and venting conditions. Time history characteristics of explosion overpressure, structural displacement, acceleration of structure, and adjacent ground motion were recorded. Results indicated that the maximum overpressure was observed at stoichiometric volume concentration (9.5%), which similarly corresponded to structural responses and ground motions intensity. Comparative experiment between unconfined and confined gas explosions revealed that while the latter exhibited longer duration, the maximum overpressure magnitudes remained identical between both scenarios. Furthermore, a significant pressure increase was observed near boundary regions, attributed to the accumulation of ignited gas mixture and energy, which can be mitigated through the implementation of a top vent. Additionally, the presence of soil and vibration isolation walls adjacent to the utility tunnel demonstrated a significant reduction in acceleration magnitudes resulting from gas explosion events.