波浪荷载作用下近海粉质土液化特性及动本构关系的试验研究与理论分析

The liquefaction characteristics of typical offshore silty soils in the area of Hangzhou Bay are investigated in details using theoretical, experimental and numerical simulation methods. In the analysis, the dynamic stress- strain relationship and the dynamic strength- cumulative pore pressure relationship of offshore silty soils are analyzed using cyclic dynamic triaxial tests and cyclic shearing tests, where the effect of the parameters, such as frequency, vibration times, consolidation ratio, confining pressure, initial orientation of principal stress, coefficient of intermediate principal stress and the clay particle content and silt particle content, etc., on the cyclic cumulative pore pressure, is studied. The normalized relation of cumulative pore pressure ratio and degraded dynamic deformation and dynamic pore water pressure rising model are established under the condition of cyclic strain. Based on the principal of plasticity and lab experimental results, the equivalent visco-elastoplastic dynamic constitutive model is established and introduced into the dynamic analysis program of saturated silt layer under wave loading. The proposed visco-elastoplastic dynamic constitutive model and dynamic excess pore water pressure rising model are calibrated using the experimental data of cyclic triaxial tests and the dynamic response of the sample used in the cyclic triaxial tests is numerically simulated in the case of non-equal stress amplitude. The distinguishing method of liquefaction possibility of offshore silty soils under wave loading is proposed. The study can further enrich and improve the existing fundamentals of soil dynamics and can provide certain theoretical basis for the evaluation of liquefaction possibility of offshore silty soil under wave loading and of the stability of seabed and offshore engineering structures.

本研究采用理论、试验与数值模拟相结合的方法，系统研究波浪荷载作用下杭州湾典型近海粉质土的液化特性。在研究中，采用循环动三轴和循环剪切试验分析近海粉质土的动应力-应变关系、动强度和累积孔压关系，分析振动频率、振次、固结比、围压、初始主应力方向、中主应力系数等参数以及细粒和粉粒含量对循环累积孔压比的影响，建立循环应变下的累积孔压比和衰化动变形归一化关系和动孔隙水压力上升模型；基于塑性力学基本原理和室内试验结果建立等效粘弹塑性动本构模型并将其引入到波浪荷载作用下饱和粉质土层的动力反应分析程序中；利用不等应力幅值的循环三轴试验结果标定粘弹塑性动本构模型和动孔隙水压力上升模式并对不等应力幅值的循环三轴试验进行动力反应数值模拟，提出一种判别近海粉质土在动荷载下液化可能性的方法。本研究可进一步丰富和完善现有土动力学基本理论，为近海粉质土在动荷载下液化可能性和海床与近海结构物地基稳定性的评判提供理论依据。

波浪荷载作用下海床地基内部会引起孔隙水压力累积和有效应力降低，导致海床土体抗剪强度的损失，可能引发流滑、剪切破坏或者液化，严重威胁到海岸和近海建筑物以及海底管线等的安全。海床的稳定性是影响近海建筑物和构筑物安全的重要因素之一。本项目拟采用理论、试验和数值模拟相结合的方法，系统研究波浪荷载作用下海床地基土的动力响应和液化机理。通过求解饱和地基的波动方程，获得波浪荷载作用下海床地基土的应力和孔隙水压力的解析表达式，探讨了周期、水深、波高等波浪参数以及渗透系数、泊松比、剪切模量、水的压缩性、土体的各向异性等海床参数对海床地基土应力和孔隙水压力的影响，分析液化深度的主要影响因素和变化规律；采用室内循环动单剪试验探讨了砂土粒径、粘粒含量、循环剪应力幅值比、循环振次等参数对海床地基土动强度和动应变等的影响规律；采用数值模拟手段研究了波浪荷载作用下海床土体的动应力-动变形特性、总应力、孔隙水压力和有效应力的变化规律，探讨了海床土体的液化情况，分析水深、周期、波高等对近海粉土抗液化能力的影响。本项目研究对进一步丰富和完善现有土动力学基本理论、为近海地基土在动荷载作用下的动力特性和液化可能性以及海床与近海结构物地基稳定性的评判提供理论依据，具有重要的学术和实用价值。

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