为研究极端波浪荷载作用下近海桥梁下方密实海床的瞬态液化稳定性，通过求解RANS方程和Biot方程，建立了极端波浪作用下箱梁下方密实海床动力响应的有限元数值模型。将该模型与以往试验结果对比，验证了该模型的准确性，基于此模型进一步研究了极端波浪作用下箱梁周围的波浪压力场分布及波浪特性、淹没深度对桥梁下方密实海床瞬态液化稳定性的影响。研究结果表明：处于淹没状态的箱梁对周围波压场影响较大，箱梁迎浪侧密实海床的瞬态液化深度大于背浪侧，液化深度幅值距离箱梁1/10～1/8波长范围内达到最大；随着波高与波浪周期的增大，箱梁左、右两侧密实海床瞬态液化深度均增大；在迎浪侧，当箱梁刚好完全被淹没时，海床瞬态液化深度最大，而在背浪侧，随着淹没深度增加，箱梁下方海床趋于安全。其研究结果可为跨海桥梁安全性分析提供参考。

To investigate the transient liquefaction stability of dense seabed soil beneath the offshore bridge under extreme wave loads, a finite element numerical model for simulating dynamic response of seabed is developed and solved by RANS equation and Biot equation. Accuracy of the proposed model is verified by experimental data from literatures. The distribution of the wave pressure field is applied to analyze the effects of the wave characteristics and the submerged depth on the transient liquefaction stability of dense seabed. Results of numerical simulation indicate that the submerged girder can significantly affect the wave pressure field, and the amplitude of the liquefied depth in front of the girder is greater than that in rear of the girder. The largest liquefied depth is located within the range of 1/10-1/8 distant from the front of the box girder. The amplitude of the liquefied depth increases with the increment of both wave height and wave period. The seabed in front of the box girder is the easiest to be liquefied when the box girder is just submerged while the seabed gets more stable with the increment of the submerged depth in rear of the girder. The results of the study can provide a reference for the safety analysis of cross-sea bridges.