挡土墙墙趾地震作用的波动分析

目前国内外规范中对挡土墙墙趾处地震作用的规定很不一致,给工程设计及工程评价带来诸多困难,如何合理考虑其作用已成为岩土工程中的重要课题之一。针对强震地区的重要挡土工程,以墙前2 m覆盖土层的挡土墙为例进行了设计和讨论;基于近场波动数值模拟技术,输入El Centro波、Taft波、河北迁安滦河桥波和天津医院宁河波这四种不同场地条件的地震动进行动力分析,对比墙趾及墙背处的土动剪力时程发现,墙趾土动剪力对挡土墙的动态稳定性起着重要作用;墙趾覆盖土层所产生的动土压力,较有益于挡土墙的抗倾覆、抗滑稳定性。用简化估计的方法,对动土压力及剪力的合力作用点进行分析,发现相同位置的动土压力和剪力的合力作用点比较接近,其值分别是,墙趾处约距墙底0.62H2(H2为墙前覆土厚度),而墙背处约为H1/3,这与以往研究并不相同。最后对地震作用效应折减系数进行讨论,并建议了墙趾地震作用的合理设计取值。这些结果为改进挡土墙的抗震设计、指导工程实践提供了有益的基础。

Wave motion analysis of earthquake action on the toe of retaining walls

It is difficult to design and evaluate retaining walls,due to the disagreement regarding the treatment of earthquake action on the toe of retaining walls in design codes in China and other countries.For example,a 2m-soil layer covered at the front of a retaining wall is considered and,the effective design and analysis of the associated retaining walls under strong earthquake motions are explored.Based on the numerical simulation of near-field wave motion,the dynamic response of the retaining wall is analyzed with four records-El Centro,Taft,Qi'an(Luan he),Tianjin Hospital(Ning he)waves under different site conditions.By comparing the shear force history of the back with that of the toe,it is found that the shear forces of the toe of wall are significant to the dynamic stability of the retaining wall,and they provide resistances to the overturning and sliding actions resulting from the dynamic earth pressure.Using a simplified method,the resultant force action points of pressure and shear on both the toe of wall and the back are obtained.At a given location,the resultant force action points of both pressure and shear are close to each other,about 0.62H2(H2 denoting the buried thickness at the front of retaining wall) and 1/3H on the toe and the back,respectively.A reliable value of earthquake action on the toe of wall is proposed in design and the reduced coefficient of seismic action effect is discussed.