Abstract: The construction of the Hongmianlu Tunnel in soft rock is difficult and high risk due to its shallow bur? ied depth (about 6 m), large span(about 16 m) and long distance under the Jihe Expressway, which has a large traffic volume and strong dynamic load. To study mechanical behaviors during tunnel excavation, the dynamic variation laws of ground settlement, crown settlement, extrusion displacement of the tunnel face, steel arch stress in the primary support and the stress in the secondary lining were obtained by numerical calculations and field tests. The results show that the influential scope of the antecedent deformation is 1~1.5 times the tunnel span. By anchoring and shotcreting at the tunnel face, the extrusion displacement of the tunnel face decreases significantly. To guarantee successful construction under the Jihe expressway, it is necessary to determine a reasonable support time, optimize the construction procedure, decrease the closure time of the tunnel section and improve site monitoring.