人工岛余震再液化数值模拟研究

Numerical Simulation Study of Re-liquefaction of Artificial Island Induced by Aftershocks

摘要:

主震结束后,余震引起的再液化会对土工结构物带来进一步的严重灾害。以人工岛为研究对象,基于FE-FD耦合有限元方法,考虑有无余震、不同余震大小和主余震不同时间间隔因素,探讨对人工岛再液化灾害的影响规律。研究结果表明:主震结束后,随着超孔隙水压力的消散,人工岛砂土层液化区域逐渐减小,余震发生时液化区域又开始扩展,甚至可能大于主震结束时的液化区域面积,且其灾害程度比无余震发生时的要大得多;随着主、余震的时间间隔增加,间隔期的土层固结排水很大程度地提高人工岛的抗再液化能力,当超孔隙水压力消散完后,在相同余震等级情况下很难再次达到完全液化;随着余震峰值加速度的增加,人工岛的沉降量和水平侧移量都随之增加,再次液化时间点会向前提前数秒,主震结束后,随着土层的固结排水,人工岛的沉降会继续增加,甚至超过主震引起的沉降量,而水平侧移的产生主要发生在地震液化过程中,在后续的固结排水中几乎不变;余震发生前,如果人工岛的砂土土层仍处于液化状态,则液化层可能会起到隔震作用,减轻余震对岛体造成的灾害。

Abstract:

Re-liquefaction induced by aftershocks causes serious hazards on soil structures after the end of the main shock. In this study,the influences of aftershocks on an artificial island are discussed based on the FE-FD coupling finite element analysis method at different scales of aftershocks and interval time between the main shock and aftershock.The results indicate that with dissipation of excess pore-water pressure after the main shock,liquefied areas in the sand layer of the artificial island gradually decrease;however,the liquefied areas expand rapidly when an aftershock occurs,and can possibly be larger than the liquefied areas induced by the main shock;the extent of damage to the artificial island is much worse when an aftershock occurs than when it does not.The increasing of the interval time between the main shock and aftershock results in the drainage consolidation during this time significantly improving the ability of the artificial island to re-liquefy;thus,full-scale re-liquefaction in the artificial island is difficult when the excess pore-water pressure entirely dissipates.Settlement and horizontal displacement of the artificial island increases with increase of the peak acceleration of the aftershock and the liquefaction point-in-time of the sand layer occurs a few seconds early.After the main shock,with drainage by consolidation in the soil,settlement of the artificial island continues to increase,and is even larger than the settlement induced by the main shock,but the horizontal displacement barely changes.Before the aftershock,if the sand layer of the artificial island is still liquefiable,the sand layer may play a role in seismic insulation and reduce the hazards caused by the aftershock to the artificial island.Therefore,it is necessary to consider multiple seismic fortifications during a period of time for offshore structures,especially for artificial islands.