Performance of underground reinforced concrete utility tunnels under internal gas explosions: Field tests and numerical simulations

Understanding the blast-resistant performance of reinforced concrete (RC) underground utility tunnels under accidental internal gas explosions is critical for protective design and safety assessment of urban lifeline infrastructure. In this study, 1/3-scale field tests were conducted to investigate the performance of RC underground utility tunnels (UUTs) under gas explosion loads. Methane-air mixtures were ignited in a 30 m-long steel tube to simulate internal gas explosions in tunnels. The explosion intensity was varied by changing the gas cloud length, end conditions and obstacle arrangements. Specimens and soil-cover measures were used to model the real boundary conditions. The available pressure, displacement, acceleration and reinforcement strain responses were recorded and analyzed. It was found that the testing method produced variable-intensity loads with peak overpressures exceeding 1 MPa. No visible damage was observed in Tests 1–4, whereas through cracks were observed in the roof and side walls in Test 5, which involved four obstacles and a gas cloud length of 12 m. Finite element models of the RC UUT were developed using LS-DYNA and validated against the available test measurements and observed damage patterns. Parametric studies examined the effects of gas explosion load, burial depth, cross-sectional shape and tunnel type. Greater burial depth improved soil confinement, circular sections showed better blast resistance, and double-compartment tunnels were more vulnerable because the intermediate wall lacked direct soil confinement. The results provide experimental evidence and numerical insights for the protective assessment of buried RC infrastructure subjected to internal gas explosions.