Full-scale experimental study on the natural gas explosion mechanism in utility tunnels

Abstract

Utility tunnels are important underground spaces for the centralised storage of municipal pipelines, and their safe and efficient operation is related to city stability. As important and dangerous municipal pipelines, natural gas pipelines pose great risks to the safe operation of utility tunnels. To reveal the mechanism and damage of natural gas explosions in utility tunnels and reduce the harm of natural gas pipeline accidents to the overall structure of utility tunnels, a field test was performed for the first time in a full-scale double-cabin utility tunnel with a cross-section of 6.75 × 3.8 m and a total length of 42 m. The internal net size of the gas cabin where the test was conducted was 2.1 × 3 m. The experiment uses a methane-free diffusion gas cloud as the basic test object and considers the influence of the gas cloud volume, gas composition and other factors. The experiment revealed that a gas explosion in a utility tunnel can be divided into two stages: laminar combustion and turbulent combustion. The peak load in laminar combustion is small and unaffected by the gas cloud volume, whereas the peak load in turbulent combustion increases with increasing gas cloud volume. When the volume of the leaked gas cloud exceeds a certain proportion, the gas explosion load surges at the mouth of the structure, which aggravates the damage consequences. In practical engineering, owing to the insufficient combination of gas and oxygen in the air in the state of free diffusion, the maximum explosion load occurs when the proportion of gas is greater than 9.5 %. The test results effectively verify the results of extended numerical simulations and guide the protection against gas explosion accidents in utility tunnels and other tunnel spaces.