液化判别方法中应力折减系数研究发展述评

Review of development of research on stress reduction coefficient in liquefaction evaluated method

1964年阿拉斯加大地震和新瀉地震中出现了大量土壤液化产生的震害,受到工程界的广泛关注。1971年Seed和Idriss提出了基于标准贯入试验的液化判别CSR方法,其中应力折减系数对该类液化判别方法的准确性有很大影响。本文对r_d关系的关键性研究进行了综述,指出了这些研究在r_d关系发展历程中的贡献及局限性;通过比较理想场地下各个液化判别方法的临界标贯锤击数,说明目前应用的r_d关系曲线普遍存在问题,导致临界锤击数曲线出现回弯或其他不合理现象;通过对典型场地SHAKE软件计算结果的分析以及与KiK-net实测记录的比较,说明目前r_d关系研究在软、厚场地条件下应用时可靠性普遍不高。基于以上分析,建议对r_d关系今后的研究重点应集中在Ⅲ、Ⅳ类场地,并按场地类别分别给出工程可用的关系曲线。

Following disastrous earthquakes in Alaska and in Niigata, much attention was widely paid to damage of soil liquefaction. Professors H. B. Seed and I. M. Idriss developed and published a simplified procedure based on standard penetration test for evaluating liquefaction potential, and the analytical framework has been still widely adopted so far, in which the reduction coefficient rd plays an important role in accuracy. This paper summarizes the pivotal studies regarding to the rd relationship, and indicates the achievement and limitation of these studies. By comparing the critical blow count curves of standard penetration test of each evaluating liquefaction potential method for an idealized site, this paper illustrates that the present applied ra relationship is still imperfect, which causes some irrational phenomena in critical blow count curves. Based on the seismic response analysis of typical sites by software SHAKE and comparing the calculating results with the actual records of KiK - net, the paper points out that the existing curves of rd are commonly unreliable for deep soft sites. According to the analysis above, we suggested that the key point of studies on rd relationship shouid focus on Sites Class III and Class IV and the rd correlation curves applicable to engineering should be given according to site type.