Abstract: 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.

Key words: critical liquefaction curve, soil layer depth, liquefaction evaluation, cone penetrate test, standard penetrate test