单体土遗址地震动力响应分析——以山丹县刘富寨敌台为例

Dynamic Responses of Single Earthen Sites Under Seismic Loads:A Case Study of the Liufuzhai Watchtower in Shandan,China

我国西北地区遗存有大量的单体土遗址,时刻遭受地震等各种灾害的威胁。因其种类繁多,形式各异,很难以一个确定性的模型或计算方式来获取较为准确的结论。为更好地研究及保护单体土遗址,以山丹县刘富寨敌台为例,采用FLAC3D软件对其进行地震动力响应分析,包括位移、应力以及地震波的加速度放大效应。研究结果表明:在实测双向地震荷载作用下,敌台产生了一定的永久位移,且以竖向位移为主(主要由水平地震荷载引起);敌台内部裂隙处产生了拉应力集中,且其接近抗拉强度;地震加速度放大效应随高度增加而强烈,以竖向加速度更为明显;裂隙对竖向位移的产生具有强烈的不利影响,同时裂隙处加速度放大系数最大,但会弱化相邻测点的放大效应。

Earthen architecture is one of the oldest forms of construction.It is composed of construction materials made from unfired earthen materials,including adobe,rammed earth,and a host of other earthen components and construction techniques that vary with varying cultures and regions.Numerous single earthen sites remained in the northwest region of China.However,these cultural relics have not been preserved well.The physical and chemical properties,as well as the mineral compositions and textural characteristics of the soils,are the intrinsic factors that determine the form of weathering,whereas the natural environment is the driving force promoting the damage process.Among them,the structural failures induced by earthquakes are a form of the most serious problems which affect the preservation of the sites.It is worthwhile to provide any effort to achieve a convincing explanation of the distress causes and to propose interventions that are safe and respectful of the history of the sites.To better protect the single earthen sites,FLAC3 Dsoftware was applied to analyze the dynamic response of the Liufuzhai Watchtower under seismic loads and the seismic-induced displacement,stress and the acceleration amplification effect of seismic wave was investigated.The results indicate that the Watchtower produces a certain permanent displacement,which is mainly vertical displacement under seismic loads.Meanwhile,there is a tensile stress concentration which is close to the tensile strength in the fissure of the Watchtower.The amplification effect of seismic acceleration strengthens with the increase of height,especially for the vertical acceleration.The fissure has a strong adverse effect on the vertical displacement.Meanwhile,the acceleration amplification factor on the fissure is the largest.However,the fissure can weaken the amplification effect of adjacent points.This case study provides an innovative approach to predict the stability of cultural sites when an earthquake occurs;in particular,it is suitable for earthen sites in Northwest China.