A Study of the Effect of Permeability Difference of Depositional Architecture on Sand Liquefaction
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摘要: 目前国内外的砂土液化判别方法主要是基于易液化土层的原位测试资料建立，未考虑其周围相邻土层的渗透性差异。理论上讲，在地震荷载作用下，相邻土层渗透性差异对液化土层超孔隙水压累积具有影响。基于原位静力触探和钻孔资料，建立了新西兰地震中砂土液化场地剖面，分析表明地表液化分布区域与场地土层结构特征显著相关。物理模型试验和数值模拟计算结果表明，高渗透性的砾石土层对相邻液化土层超孔隙水压累积影响显著，其影响程度可以采用土层竖向等效渗透系数表征，等效渗透系数增大时，易液化土层超孔隙水压力累积明显变小，降低了液化势。因此，需要在砂土液化判据中考虑相邻土层渗透性差异因素，进而提高液化判别结果的准确性。Abstract: Current methods for identifying sand liquefaction, both in domestic and international contexts, are primarily based on in-situ testing data from easily liquefiable soils, without adequately considering the permeability differences between adjacent soil layers. However, under seismic loads, these permeability differences can significantly influence the accumulation of excess pore water pressure in liquefied soils. A study based on static cone penetration and drilling data from liquefaction sites in New Zealand established a detailed profile of sand liquefaction during earthquakes. The analysis revealed that the distribution of surface liquefaction was closely linked to the structural characteristics of the site's soil layers. Further investigation through physical model experiments and numerical simulations demonstrated that high-permeability gravel layers have a pronounced effect on reducing the accumulation of excess pore water pressure in neighboring liquefiable soils. This influence can be quantitatively characterized by the vertical equivalent permeability coefficient of the soil layer. As the equivalent permeability coefficient increases, the accumulation of excess pore water pressure in liquefiable soils significantly decreases, thereby reducing the potential for liquefaction. Therefore, to enhance the accuracy of liquefaction assessments, it is crucial to account for permeability differences between adjacent soil layers in the sand liquefaction criteria. This would lead to more reliable predictions, especially in areas where soil permeability varies.1)
1 2https://www.nzgd.org.nz/ -
图 1 CMHS场地地表可见液化砂土喷出区域与工程地质剖面分布示意
Figure 1. The liquefaction manifestation area and the distribution of engineering geological profiles on the CMHS site
图 4 土层结构物理模型（单位：厘米）
Figure 4. Schematic diagram of physical model of soil layer structure (Unit: cm)
图 8 物理模型与数值模拟孔压曲线对比
Figure 8. Comparison of pore pressure curves between physical models and numerical simulation
表 1 CMHS场地11处位置竖向等效渗透系数
Table 1. Vertical equivalent permeability coefficient at 11 locations of CMHS site
位置 液化情况 竖向等效渗透系数kz/(cm·s−1) A1 非液化 1.66×10−2 A2 准液化 7.46×10−5 A3 液化 5.5×10−5 A4 液化 1.14×10−4 B1 非液化 8.84×10−3 B2 液化 3.84×10−3 B3 液化 1.23×10−4 C1 液化 3.3×10−4 C2 非液化 1.31×10−2 C3 非液化 8.76×10−3 C4 非液化 1.81×10−2 
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表 2 砂土液化判别结果
Table 2. Discrimination results of sand liquefaction
位置 实测击数N 临界击数Ncr N/Ncr 判别结果 A1 6.0 9.4 0.64 液化 A2 6.0 7.4 0.81 液化 A3 6.0 6.2 0.97 液化 A4 6.0 9.4 0.64 液化 B1 7.0 9.4 0.75 液化 B2 6.0 9.4 0.64 液化 B3 8.0 10.3 0.78 液化 C1 6.0 8.5 0.71 液化 C2 6.0 8.5 0.71 液化 C3 6.0 9.6 0.63 液化 C4 6.0 8.6 0.70 液化
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表 3 计算模型土体材料物理力学参数
Table 3. Physical and mechanical parameters of soil materials
参数 砾石 细砂 中砂 饱和密度/(kg·m−3) 2 000 1 920 1 920 剪切模量/MPa 11.7 10.2 10.5 体积模量/MPa 27.3 22.5 22.8 内聚力/kPa 0 0 0 内摩擦角/(°) 38 33 40 孔隙率 0.28 0.42 0.4 渗透系数/(cm·s−1) 9.5×10−1 3.3×10−3 5.3×10−3
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表 4 竖向等效渗透系数与液化情况
Table 4. Vertical equivalent permeability coefficient and liquefaction situation
组别 竖向等效渗透系数kz/(cm·s−1) 土体峰值动孔压比 浅部孔压增量/kPa 深部孔压增量/kPa 液化情况 1A 3.3×10−3 1.1（浅部） 2.5 3.3 液化 1B 3.9×10−3 1.1（浅部） 0.5 1.5 液化 2A 4.3×10−3 1.3（浅部） 1.7 2.6 液化 2B 5.1×10−3 0.9（深部） 0.9 2.3 准液化 3A 4.7×10−3 0.9（浅部） 1.3 2.1 准液化 3B 6.8×10−3 0.7（深部） 0.5 1.8 非液化
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