摘要
从形态上看,自然界存在平坦、凸起和凹陷3种常见的地形及场地条件,而河谷场地是一种常见的凹陷地形,且在河谷场地修建了大量工程(如土石坝、桥梁等)。实际震害调查表明地形及场地条件对地震灾害影响很大。针对河谷场地地震波传播解析模型及放大效应,全面总结了笔者及其课题组长期以来的研究成果。主要包括以下4个方面:(1)提出了近源地形与场地效应的概念,用线源柱面SH波模拟入射地震波,平面波是其远场入射的特例,构造了线源柱面SH波自由场,定义了近源激励下的放大因子,实现了入射波波前弯曲及其地形放大效应,为其它地形和场地引起的近源放大效应研究开启了新的可能。(2)构建了非对称V形河谷地震波传播解析模型,包括亥姆霍兹运动方程、河谷表面自由边界条件及虚拟辅助边界应力与位移连续条件,提出了区域分解与区域匹配分两步走的策略,首先将整个区域分解成3个符合极坐标系的子区域,在子区域中对运动方程进行求解获得相应的波场(含有未知系数),然后将各个子区域的波场在边界进行匹配,利用边界条件求解未知系数,从而获得整个区域的波场解答以及柱面SH波的二维散射规律,揭示了非对称V形河谷的差异放大效应,这将对建在非对称V形河谷上的长大跨度工程有着不可忽视的影响。(3)U形河谷在地球表面是普遍存在的,由于缺少实际地震记录和理论研究,U形河谷的地形放大效应仍然未知。构建了U形河谷解析模型,本质上也就是亥姆霍兹方程的边值问题,并得到了这个问题的波函数级数解,发现了U形河谷谷底对地震波的异常放大现象,改变了学术界以往认为凹陷地形底部地震动一定会衰减的不全面认识,并被用来解释中世纪暖期美国亚利桑那州的大量山体落石与滑坡现象。(4)河谷常有沉积物(覆盖层),覆盖层将进一步加剧地震放大
Morphologically, there are three types of topographic and site conditions in nature: flat, convex and concave sites. The canyon(or valley) is a common concave site, and a large number of structures such as earth-rock dams and bridges have been built in such a site. Investigation of actual earthquake damage shows that the topographic and site conditions have great influences on earthquake disasters. Aiming at the analytical models and amplification effects of seismic wave propagation in canyon sites, the long-term research achievements of the author and his research group are summarized comprehensively. They include four aspects:(1) The concept of near-source topographic and site effects is proposed by simulating the incident seismic waves with a line source of cylindrical SH waves. The planewave is a special case of its far field incidence. The free wave field under the line source of cylindrical SH waves is constructed to realize the curvature of the incident wavefront. The amplification factor is defined to describe the topographic effects under near-source excitation, which opens new possibilities for studying the near-source amplification effects of other topographies and sites.(2) An analytical model for seismic wave propagation in non-symmetrical V-shaped canyon is constructed, including the Helmholtz equation, traction-free boundary conditions on canyon surface, and continuity conditions of traction and displacement on the auxiliary boundary. A two-step strategy for region decomposition and region matching is proposed. Firstly, the whole region is decomposed into three sub-regions in accordance with the corresponding polar coordinate systems. The corresponding wave fields(including unknown coefficients) are obtained by solving the equation of motion in the sub-regions. Then, the wave fields of each sub-region are matched at the boundary, and the unknown coefficients are solved by using the boundary conditions. The wave-field solutions of the whole region and the two-dimensional scattering patterns of cylin
作者
高玉峰
GAO Yu-feng(Geotechnical Research Institute,Hohai University,Nanjing 210024,China)
出处
《岩土工程学报》
EI
CAS
CSCD
北大核心
2019年第1期1-25,共25页
Chinese Journal of Geotechnical Engineering
基金
国家自然科学基金重点项目(41630638)
国家重点基础研究发展计划("973"计划)项目(2015CB057901)
关键词
河谷场地
地震波
波函数级数解
放大效应
边坡地震稳定性
土石坝地震反应
坝坡地震稳定性
canyon site
seismic wave
wavefunction series solution
amplification effect
seismic stability of slope
seismic response of earth and rockfill dam
seismic stability of dam slope