核岛结构设计地基场地及计算基底效应研究

针对新型核电工程结构AP1000核岛结构设计地基中的5类非坚硬岩场地，即硬岩场地、软岩场地、上限软-中等土场地、软-中等土场地和软土场地，采用一维土层场地模型开展场地土和计算基底条件对设计地震动影响计算分析。分析中，场地模型的计算基底剪切波速分别取为700、1 100、2 438 m/s，计算基底输入地震动分别选择基于核电建设相关技术文件和规范规定的反应谱RG1.60谱、AP1000谱和HAD101/01谱（5个阻尼比）合成的人工地震动时程。计算分析表明：非坚硬岩场地会导致场地地震动峰值加速度及频谱特性显著变化，场地越软影响程度越显著；除软土场地外，场地对地震动峰值加速度和反应谱的影响均为放大作用，软土场地对地震动较低频段反应谱有放大作用，但对峰值加速度和较高频段反应谱具有强烈的减小作用；对于各类场地，计算基底及其剪切波速的变化均会导致地表地震动峰值及频谱特性明显甚至显著变化，其影响程度与计算基底剪切波速成正比；随着场地由硬变软，计算基底剪切波速的变化对场地地震动的影响程度大为减小，至软土场地几乎不产生影响。考虑到场地类型及计算基底选取对场地地震动的显著影响，我国核电厂建设引用AP1000标准设计时应合理分析场地的适宜性。

Research on site effects of soil layers and bedrock on designing the foundation of nuclear island structure

An one-dimensional soil layer model is employed to analyze the site effects of the designing ground motion in five kinds of non-hard rock sites, including firm rock site, soft rock site, upper bound soft-to-medium soil site, soft-to-medium soil site and soft soil site, for designing the foundation of AP1000 nuclear island (NI) structure. In this study, the shear wave velocity in the bedrock of the computational model is selected as 700, 1 100 or 2 438 m/s. The input motion of the bedrock is taken as RG1.60, AP1000 and HAD101 spectra (with 5 damping ratios) matching with the synthetic acceleration time histories of ground motion provided in the relative technical documents and standards, respectively. Analytical results indicate that non-hard rock sites induce the significant changes of the peak ground acceleration and response spectrum of the ground motion, which is enhanced further by a softer site. The effects of non-hard rock sites, except the soft sites, amplify the peak ground acceleration and response spectrum. However, the effect of the soft site increases the peak ground acceleration and response spectrum in a lower frequency range, and it is opposite in a higher frequency range. The peak ground acceleration and response spectrum of the site ground motion are significantly influenced by the changes of the bedrock and its shear wave velocity of all non-hard rock sites. Moreover, the effect is proportional to the shear wave velocity of the bedrock, and the ground motion decreases obviously with the increase of shear wave velocity. The ground motion is unaffected by the shear wave velocity as the site changes from hard to soft. Considering the great effects of the site type and the bedrock selection on ground motion, it is thus necessary to analyze the applicability of the sites by using the AP1000 standard design in the nuclear power plant construction in China.