适于不同深度土层液化的剪切波速判别公式
Depth-consistent vs-based approach for soil liquefaction evaluation
-
摘要: 剪切波速测试是工程上常用的现场技术,正逐步成为液化判别方法的基本指标之一。利用早期的Andrus数据库对中国《岩土工程勘察规范》方法和Andrus方法进行检验,发现了二者存在的问题。提出了双曲线形式的剪切波速判别模型和公式。采用新的Kayen数据库对三者进行了对比检验,并讨论了提高判别精度的可能性和方式。结果表明:中国现行的《岩土工程勘察规范》中剪切波速判别液化方法,无论对浅层还是深层土,判别结果均严重保守,甚至会把十分密实的砂土判成液化,十分不合理;国际上应用广泛的Andrus方法对浅层土判别结果过于保守,对深层土判别成功率可以接受,但其临界剪切波速曲线在深处存在回弯的不合理现象;所提出的双曲线液化判别模型和公式,能够深浅兼顾,无论对浅层还是深层土都能给出较好的判别结果,克服了中国规范方法和Andrus方法的弊端,且形式简单便于工程应用;采用剪切波速进行液化判别时,应采取多次测试,以降低数据离散性,提高判别的准确性。Abstract: The shear wave velocity tests have been commonly used as an engineering field testing technique, and are gradually becoming a basic index for soil liquefaction evaluation. The shortcoming of the Andrus' method and Chinese code method has been found by using the database from Andrus, and the new hyperbolic model and formula Vs-based for estimating liquefaction potential of liquefiable layer are proposed. The reliability of the above three methods is verified through the data newly collected by Kayen, and the possibility and approach of improving the discrimination accuracy are discussed. The results indicate that the Chinese code method is significantly conservative for both shallow soil layer and deep soil layer and will predict the dense sand as liquefiable. The Andrus' method is conservative for shallow soil layer, and an irrational phenomenon of back bending occurs in the deep soil layer. The proposed hyperbolic model can provide good results for both shallow soil layer and deep soil layer and solve the deficiency of Chinese code method and Andrus' method. When the in-situ shear-wave velocity tests are used to predict soil liquefaction for a specific site, multiple tests should be taken to reduce data discreteness.