To investigate the propagation characteristics of shock waves generated by thermobaric explosives detonated at different external positions of a tunnel

experimental studies were conducted based on a constructed long straight tunnel model

examining shock wave propagation patterns at varying distances outside the tunnel entrance. A numerical model incorporating the afterburning enhancement effect of thermobaric explosives was employed to analyze the formation

propagation

and evolution characteristics of shock waves at different external positions

specifically exploring the variation patterns of peak overpressure

positive-phase duration

and impulse. The results indicate that as the detonation distance from the tunnel entrance increases

the peak overpressure

impulse

and positive-phase duration of shock waves propagating into the tunnel gradually decrease. Near-/far-entrance explosions were defined based on the ratio of Mach stem height to entrance height upon shock wave arrival at the tunnel entrance. Near-entrance explosions exhibit multi-peak pressure profiles and secondary pressure rise due to reflection-superposition interactions between incident waves and tunnel structures. A decay model for peak overpressure inside the tunnel relative to scaled distance was established

and a calculation method for equivalent sealed-entrance yield coefficients of shock wave overpressure and impulse was first proposed. Compared to sealed-entrance explosions

the average equivalent overpressure yield coefficients at 1.0 m

2.0 m

3.0 m

4.0 m

5.0 m

and 7.5 m outside the entrance are 0.423

0.252

0.166

0.151

0.075

and 0.062

respectively

while the average impulse yield coefficients are 0.574

0.325

0.169

0.148

0.088

and 0.063

This methodology provides a robust technical framework for rapid assessment of thermobaric explosive effects in external tunnel entrance detonations.