含细粒砂性土标贯液化判别方法改进研究

Improvement of SPT-based liquefaction discrimination methods for fines-containing sandy soils

含细粒砂性土相对于纯净砂在自然界中分布更为广泛,但是对于其液化判别,一直都是作为纯净砂液化判别的附属成果,没有得到足够的重视。回顾了中国规范方法与NCEER推荐方法,结合1999年台湾集集地震液化土与非液化土数据,发现两个方法定义纯净砂的矛盾,通过进一步对比判别结果,建议对两个方法做如下改进:1对中国规范方法,首先取消粉砂黏粒含量取3%的规定,并且对黏粒含量不大于3%且细粒含量大于15%的粉砂及粉土,取ρc=Fc/4,否则取3%;2对NCEER方法,当黏粒含量不大于3%时,只针对细粒含量大于20%的土,才考虑调整(N1)60。改进之后,中国规范方法过于保守的问题得到解决,NCEER方法对于黏粒含量不大于3%且细粒含量大于5%的土判别结果也不再偏于危险。

Most of natural sands contain significant amounts of fines. However, the liquefaction discrimination methods for fines-containing sandy soils are always as a subsidiary to those for clean sands, and enough attention hasn＇t been paid to. The Chinese method and NCEER method are reviewed, and the discrepancy that two methods define clean sand for Chi-Chi earthquake data is found. By comparing the identification results of soils in Chi-Chi earthquake, the following improvements are suggested for the two methods：（1） for the Chinese method, firstly we should abandon the view that the clay content for silty sands is always 3%. Secondly, for the silty sands and silts with clay content not greater than 3% and fine content more than 15%, take ρc=Fc/4, if not, take 3%;（2） for the NCEER method, if the clay content is not greater than 3%, we should adjust（N1）60 to（N1）60cs only for the soils with fine content more than 20%. In doing so, the Chinese method is not any more too conservative, and the NCEER method are no longer tending to be dangerous for the soils with clay content not greater than 3% and fine content more than 5%.