Comparative study on the liquefaction properties of seabed silt under wave loading in the Huanghe River Delta
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摘要: 作为一种常见的近海海底灾害地质现象，波致海床液化严重威胁着黄河三角洲地区海底工程设施的安全。粉质海床液化后，海底粉土的结构、物理和力学性质均发生了改变，研究该变化规律尤其是评估液化后海底粉土再次发生液化的可能性具有重要的理论意义和应用价值。本文利用室内动三轴仪对取自黄河三角洲已液化和未液化海底粉土开展了液化试验对比研究，讨论了已液化和未液化海底粉土在孔压增长模式和轴向动应变发展趋势方面的异同，对比分析了二者的液化势。研究结果表明：应变标准比孔压标准更适用于评估黄河三角洲地区海底粉土的液化势；孔压和动应变发展模式均表明与未液化粉土相比，已液化海底粉土再次发生液化的抗力有所提高；已液化和未液化海底粉土归一化孔压比ud/σ3与循环加载次数比N/Nf间相关关系可采用双曲线或指数函数模型进行定量化描述；未液化海底粉土的波致液化临界循环应力比约为0.20，已液化海底粉土的临界循环应力比约为0.35。研究成果有助于加深对海底粉土波致液化特性的认识，亦可为循环应力历史影响下的土体力学性质研究提供参考。Abstract: As a common submarine geological disaster, wave-induced seabed liquefaction seriously threatens the safety of subsea engineering facilities in the Huanghe River Delta. The structure, physical and mechanical properties of seabed soil after wave-induced liquefaction all have changed, so it has important theoretical significance and practical value to study on the evaluation of potential possibility of re-liquefaction of seabed soil after previous liquefaction. In this paper, a series of cyclic triaxial liquefaction tests were conducted on core samples collected from submarine non-liquefied and liquefied zone in the Huanghe River Delta, respectively. The differences between non-liquefied and liquefied seabed soil in the developing trends of pore pressure and axial dynamic strain with cycles were analyzed and discussed, and the corresponding liquefaction potentials were also comparatively evaluated. The test results show that compared to pore pressure, the strain standard is more suitable to evaluate the liquefaction potential of the seabed silt in the Huanghe River Delta. The pore pressure and dynamic axial strain development characteristics indicate that the re-liquefaction resistance of the liquefied seabed silt is improved to some extent compared with the non-liquefied silt. Furthermore, the correlations between the normalized pore pressure ratio ud/σ3 and the normalized cycle ratio N/Nf could be described quantitatively by the hyperbolic or exponential functions for liquefied and non-liquefied seabed silts. Finally, the critical cyclic stress ratio for the non-liquefied seabed silt is around 0.20 compared to 0.35 for the liquefied one in the Huanghe River Delta. The research findings will contribute to deepening the understanding of the wave-induced liquefaction mechanism of seabed silt, and also provide an example reference for the study of the mechanical properties of soil subjected to previous cyclic stress history.
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Key words:
- Huanghe River Delta /
- seabed silt /
- re-liquefaction /
- cyclic triaxial test
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图 6 液化前后海底粉土归一化孔压增长曲线对比
Fig. 6 Comparison in the normalized pore pressure development between liquefied and non-liquefied seabed silt
图 7 孔压发展双曲线模型和指数模型拟合结果
Fig. 7 Fitting results of hyperbolic and exponential models for pore pressure development
图 9 液化前后海底粉土轴向动应变发展模式对比
Fig. 9 Comparison in the axial strain developing patterns between liquefied and non-liquefied seabed silt
图 10 循环应力比CSR与循环加载破坏次数Nf之间相关关系
Fig. 10 Correlations between cyclic stress ratio and cycles at failure for seabed silt
表 1 海底粉土基本物理性质指标
Tab. 1 Physical properties of seabed silt
分类 海床以下深度/m 含水量/% 干密度/（g·cm−3） 比重 孔隙比 塑限/% 液限/% 塑性指数 未液化粉土 0.5 23.3 1.62 2.71 0.70 18.7 26.8 8.1 1.0 23.4 1.62 2.70 0.69 19.1 27.0 7.9 1.5 23.0 1.63 2.71 0.69 17.6 26.8 9.2 2.5 26.7 1.58 2.70 0.71 21.3 28.5 7.2 3.0 25.9 1.59 2.71 0.71 21.9 30.5 8.6 3.5 25.3 1.60 2.70 0.69 21.7 29.9 8.2 4.3 27.9 1.57 2.70 0.72 22.6 31.6 9.0 4.7 25.6 1.59 2.70 0.69 21.6 29.7 8.1 已液化粉土 0.5 24.5 1.61 2.70 0.70 20.6 27.6 7.0 1.0 24.2 1.61 2.70 0.70 20.6 26.3 5.7 1.5 24.9 1.61 2.70 0.69 18.6 26.1 7.5 2.5 23.4 1.62 2.70 0.66 20.6 28.1 7.5 3.0 23.9 1.62 2.70 0.67 20.6 27.9 7.3 3.5 23.6 1.62 2.71 0.67 19.7 27.7 8.0 4.3 21.9 1.64 2.70 0.64 15.9 25.2 9.3 4.7 22.1 1.64 2.71 0.65 16.7 24.5 7.8 
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表 2 循环应力加载方案
Tab. 2 Cyclic dynamic stress loading program
分类 钻孔编号 海床以下深度/m 固结围压/kPa 循环应力比 初始模拟波浪状态 波高/m 波长/m 水深/m 未液化粉土 ZK1 0.75～1.60 20 0.35, 0.40, 0.50 6.0 60.0 10.0 2.55～3.60 30 0.23, 0.33, 0.37, 0.42, 0.47 4.7 60.0 10.0 3.75～4.70 40 0.23, 0.25, 0.30, 0.44, 0.48 5.2 60.0 10.0 已液化粉土 ZK3 0.95～1.85 20 0.37, 0.45, 0.50 6.4 60.0 10.0 2.48～3.50 30 0.37, 0.42, 0.50 7.5 60.0 10.0 3.70～4.70 40 0.43, 0.45, 0.50 9.0 60.0 10.0
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表 3 孔压发展双曲线模型拟合参数
Tab. 3 Coefficients of hyperbolic model for pore pressure development
分类 围压/kPa 模型 CSR 参数a 参数b 相关系数R2 未液化粉土 20 双曲线 0.35 0.512 0.918 0.99 0.40 0.818 0.761 0.99 0.50 0.375 1.494 0.98 30 双曲线 0.23 0.041 1.025 0.99 0.33 0.042 0.971 0.99 0.37 0.297 0.890 0.99 0.42 0.951 0.845 0.99 0.47 0.662 0.567 0.99 40 双曲线 0.23 0.133 0.973 0.99 0.25 0.154 0.955 0.99 0.30 0.394 1.149 0.99 0.44 0.275 0.890 0.99 0.48 0.365 1.090 0.99 已液化粉土 20 双曲线 0.37 0.146 0.906 0.99 0.45 0.128 1.072 0.99 0.50 0.022 0.969 0.99 30 双曲线 0.37 0.410 1.072 0.98 0.42 0.277 1.148 0.99 0.50 0.519 0.712 0.99 40 双曲线 0.43 0.577 0.427 0.99 0.45 0.292 0.913 0.99 0.50 0.410 0.952 0.98
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