液化判别临界曲线的变化模式与一般规律

Variation tendencies and general rules for critical curve of liquefaction evaluation

液化临界值与砂层深度的关系是液化判别方法的基本表征,但对比分析表明,现有液化判别方法的临界曲线有不同的表现模式,甚至定性相反。以Seed-Idriss模型为基础,推导出了砂层埋深对液化势影响的理论解答,提出了砂层埋深与液化临界值的普遍关系,得到了液化判别临界曲线的变化模式和一般规律。结果表明:一般而言,随砂层深度增加,水平地震剪应力和土体抗液化强度同时增大,但前者增大速率大于后者,液化势及液化临界值与砂层深度呈正相关关系;液化临界值与砂层深度呈非线性递增关系,浅埋处饱和砂层液化势递增较为剧烈,深埋处趋于平缓;我国规范CPT液化判别公式的液化临界值与砂层深度呈递减关系,存在定性错误,需要纠正;现有一些液化判别公式中,液化临界值与砂层深度呈线性递增关系,定性正确但模型需要改进。所得结果可为液化判别方法正确发展提供理论基础和借鉴。

The liquefaction evaluation methods are basically characterized by the relationship between the critical liquefaction curve and the depth of the soil layer. However, the comparative analysis shows that the critical curves of the existing liquefaction evaluation methods have different performance modes and even qualitative opposite. In this paper, based on the Seed-Idriss model, the theoretical solution of the effect of soil depth on the liquefaction potential was derived, and the general relationship between the depth of the soil layer and the critical liquefaction value was put forward. Meanwhile, the variation trend and general rules for liquefaction critical curves were obtained. The results show that with the increase of soil depth, the increasing rate of horizontal shear stress is faster than that of liquefaction resistance of soil layer. Moreover, the liquefaction potential and critical liquefaction value have positive correlations with the depth of the soil layer. The critical value increases nonlinearly with the soil depth, which means that the liquefaction potential increases drastically in the shallow layer, but gently in the deep layer. In the CPT liquefaction evaluation of the national standards in China, it is reported that the critical liquefaction value has a decreasing relationship with the soil depth, which is qualitative error and needs to be corrected. In some existing liquefaction discriminant formulas, the critical value increases linearly with the depth of sand layer, which is qualitatively correct, but the model needs to be improved. The results of this paper can provide a theoretical basis and reference for the development of liquefaction evaluation methods and the future revision of national and professional standards.