波浪诱导的超静孔压及液化将导致海床土体强度降低，进而危及海洋工程基础的稳定性。因此，定量表征波浪荷载下的海床土体响应在海洋工程实践中至关重要。实际海洋环境中存在多种波浪荷载(如规则波、随机波、破碎波)和海床土体类型(如砂土、粉土、黏土)，致使波浪-海床相互作用特征复杂多变。本文借助于物理模型试验与理论分析，研究了典型波浪荷载诱导的非粘性海床土体响应规律，旨在探索海床孔压响应与液化的主要控制参量及表征方法。

        基于水槽试验模拟和Biot多孔弹性理论，研究了波浪诱导的砂质海床瞬态孔压时空分布，即幅值衰减与相位滞后。试验结果表明，瞬态孔压的幅值衰减与相位滞后受到波浪参数以及土体性质的影响。根据Yamamoto et al. (1978)提出的瞬态孔压解析解，引入了孔隙流体与土骨架的刚度比以表征海床土体的可压缩性，推导了幅值衰减与相位滞后的显式表达，并对其进行了试验验证。参量分析表明，当刚度比远大于1.0时，波浪周期越大，海床体变模量以及渗透系数越小，沿无量纲海床深度的幅值衰减与相位滞后越显著。为同时反映波浪参数和土体性质对瞬态孔压的影响，提出了无量纲数(I_c)；继而建立了瞬态孔压时空分布之间的关联，结果表明幅值衰减与相位滞后呈现正相关关系。基于海床瞬态液化的判别准则，采用海床表面的孔压垂向梯度来表征瞬态液化势，推导了考虑相位滞后效应的瞬态液化势和液化深度解析解。相位滞后的存在将导致最大瞬态液化势和液化深度并非出现于波谷正下方。瞬态液化势和无量纲瞬态液化深度均随无量纲数I_c增大而增大。

        鉴于波浪可能发生破碎，通过水槽试验模拟了破碎波诱导的砂质海床孔压响应。在平床条件下，使一系列波长连续增大的行进波浪在指定位置发生叠加，可以生成破碎波浪。频谱分析表明，表面水波的峰值频率要大于其诱导超静孔压的峰值频率。根据上跨零点法提出了描述破碎波以及瞬态孔压不规则响应的特征参数，破碎波诱导超静孔压的时间参数大于破碎波本身的时间参数。与现有理论解的对比分析表明，初始破碎波浪和已破碎波浪诱导的瞬态孔压幅值小于由具有相同特征波高和特征周期的规则波诱导的瞬态孔压幅值，二者之间的偏差随着破碎过程的发展而逐渐增大。

        粉土的物理性质相较砂土更为复杂，开展了物理模型试验以揭示波浪作用下粉土海床液化的多力学过程耦合机理。当粉土海床累积孔压较小且未发生液化时，其内部的瞬态孔压响应可以由经典的多孔弹性理论进行预测；然而一旦海床发生累积液化，多孔弹性理论失效。液化区内的瞬态孔压响应较为紊乱并产生高幅值放大，其频谱呈现双峰结构，提出了瞬态孔压幅值比的概念以表征瞬态孔压的幅值放大效应。液化过程伴随着表面水波的衰减和界面波的生成，波高衰减幅度可达30%，界面波振幅随液化深度增大而增大。波浪停止加载后，累积孔压逐渐消散，海床发生固结沉降，相对密度显著提高。海床相对密度的增大将会导致液化深度、界面波幅值以及液化区内瞬态孔压幅值的减小。液化后的海床形貌特征可以作为衡量先期液化的依据：随着海床液化深度的减小，床面形貌逐渐由火山锥状隆起向沙纹进行转变。

    The wave-induced excess pore-pressure or liquefaction in the seabed would cause the reduction of soil strength, posing threat to the stability of offshore foundations. Therefore, a quantitative characterization of the soil response under wave loadings is crucial in the marine engineering practice. The various kinds of wave loadings (e.g., regular waves, random waves and breaking waves) and seabed soils (e.g., sand, silt and clay) would bring complicated wave-seabed interactions. In this study, the typical wave-induced soil responses in the non-cohesive seabed are physically modeled and theoretically examined, aiming to investigate the main controlling parameters and characterization methods for the excess pore-pressure and liquefaction.

    The spatial and temporal distributions of wave-induced pore pressure in the sandy seabed, i.e., the amplitude-attenuation and phase-lag, are investigated on the basis of flume observations and Biot’s poro-elastic theory. It is indicated that the amplitude-attenuation and phase-lag are related to wave parameters and soil properties. Following the analytical solutions for transient pore-pressure proposed by Yamamoto et al. (1978), a relative rigidity of pore-fluid to soil-skeleton is introduced to characterize the seabed compressibility; the explicit expressions of amplitude-attenuation and phase-lag are derived and further validated with experimental results. Parametric studies demonstrate that as the relative rigidity is much larger than 1.0, the amplitude-attenuation and phase-lag along the non-dimensional soil depth become more significant for larger wave period, but for lower bulk modulus and permeability of the seabed. For better reflecting the effects of wave parameters and soil properties on wave-induced transient pore-pressure, a non-dimensional parameter (I_c) is then proposed. The spatio-temporal correlations of transient pore-pressure is established, indicating a positive relationship between the amplitude-attenuation and phase-lag. Based on the criterion for wave-induced momentary liquefaction of seabed, the vertical gradient of excess pore-pressure on the mudline is employed to characterize the liquefaction potential. The liquefaction potential and liquefaction depth considering the effects of phase-lag are derived. Due to the existence of phase-lag, the maximum liquefaction potential and liquefaction depth would not appear just under the wave trough. Both the liquefaction potential and non-dimensional liquefaction depth increase with increasing I_c.

    Since the progressive waves may break, the breaking-wave induced pore-pressure in a sandy seabed was physically simulated with a series of flume tests. Under the flat-seabed condition, the breaking-wave was reproduced by generating waves with continuously increasing wave length; the superimposed wave would break at a specified location. The Fourier spectra in the frequency-domain reveal that the peak frequencies of the surface waves are generally larger than those of the pore-pressures. Characterization parameters are proposed for the irregular wave surface elevations and the corresponding pore-pressures by employing the upward zero-crossing method. The measured values of the characteristic time parameters for the breaking-wave induced pore-pressure are larger than those for the free surface elevation of breaking-waves. Comparisons with the existing analytical solutions indicate that under the action of incipient-breaking or broken waves, the measured values of the amplitude of transient pore-pressures are generally smaller than that for non-breaking regular waves with equivalent values of characteristic wave height and wave period. Such deviations between the experimental results and analytical predictions tend to increase with the time development of wave breaking.

    The properties of the silt are more complicated compared with those of the sand. The physical modeling was conducted to reveal the coupling mechanism of the multi-mechanics processes for wave-induced liquefaction in a silty seabed. As the residual pore-pressure is relatively low and no liquefaction occurs, the transient pore-pressure can be well predicted with the classical poro-elastic theory; nevertheless, the poro-elastic theory fails to describe the soil response once the residual liquefaction occurs. The transient pore-pressure response within the liquefied zone is disordered and amplified. Double-peak spectra were observed in the frequency-domain of the amplified transient pore-pressures. Amplitude ratios are then proposed to characterize such amplification effects. The liquefaction processes are accompanied by the surface wave damping and development of interfacial waves; the attenuation of wave height can be up to 30% and the amplitude of interfacial waves tend to increase with increasing liquefaction depth. With the cessation of wave loadings, the residual pore-pressure begins to dissipate and the silty seabed undergoes consolidation and settlement, leading to an increase of the relative density. The liquefaction depth, amplitude of interfacial waves and amplitude of transient pore-pressures within the liquefied soil tend to decrease with increasing relative density. The post-liquefaction morphology of the silty seabed is a proof of the previous liquefaction. With the decrease of liquefaction depth, the seabed morphology becomes ripples from silt volcanos.