利用剪切波速对饱和砂土地震液化的判别

现行有关抗震规范的液化判别方法大多使用标贯试验方法,最大判别深度不超过20 m,而近些年来的地震灾害调查显示超过20 m的饱和砂土深层液化现象是客观存在的。为此,基于Kayne场地液化数据库和修正的双曲线模型,建立了临界剪切波速液化判别公式,其判别成功率可达到80%以上。以西藏某水利枢纽为例,结合现行规范中的判别方法,对比分析并评价了本文剪切波速液化判别方法的适用性。结果表明:(1)对于埋深20 m以内的饱和砂层,《水力发电工程地质勘察规范》(GB 50287—2016)中规定的标贯判别方法得到的液化判别结果最为安全;(2)《岩土工程勘察规范》(GB 50021—2001)中规定的剪切波速液化临界曲线,对埋深超过20 m的饱和砂层液化判别过于保守,在高地震烈度时可导致极其密实的砂土被判别为液化,但在Ⅶ度时,该法对埋深10 m以内的浅层砂土的液化判别结果偏不安全;(3)对于高地震烈度区或者埋深超过20 m的深层液化判别来说,本文剪切波速方法既能克服《岩土工程勘察规范》(GB 50021—2001)判别方法过于保守的弊端,又能得到相对合理的液化判别结果。当场地缺少标贯数据或者需要对埋深超过20 m的砂土进行液化判别时,本剪切波速判别液化方法具有较强的实用性。

Seismic liquefaction discrimination on saturated sand by shear-wave velocity

The current liquefaction discriminating methods for seismic codes mostly utilize standard penetration test，and the maximum discriminate depth is 20 m． But the earthquake disaster surveys in recent years show that deep liquefaction of saturated sand with the depth over 20 m is possible． According to the liquefaction database provided by Kayne and the modified hyperbolic model，a critical formula for liquefaction discrimination using shear-wave velocity is established，the discriminant success rate of which can reach more than 80%． Taking a water conservancy hub in Tibet as an example，the method for liquefaction discrimination in the current Chinese norms are compared and analyzed to study the applicability of the shear-wave velocity method． The results show that: ( 1) For saturated sand layers with a depth less than 20 m，the results for liquefaction discrimination obtained by the standard penetration test method specified in the“Code for Hydropower Engineering Geological Survey”are the safest． ( 2) The critical liquefaction curve based on shear wave velocity specified in the“Geotechnical Investigation Specification”is too conservative for saturated sand layers with a depth of more than 20 m，according to which extremely dense sand layers may be evaluated as liquefied in high seismic intensity sites． But when the seismic intensity is Ⅶ，the result for liquefaction discrimination of shallow sand with a buried depth less than 10 m is unsafe． ( 3) For soil in the high seismic intensity or the buried depth more than 20 m，the shear-wave velocity method can obtain relatively reasonable and solve the deficiency of“Geotechnical Investigation Specifications”． When the sites lack the standard penetration test data or the discriminant depths exceed 20 m，the shearwave velocity method for liquefaction discrimination in this paper has good practicability．