波浪作用下单桩周围海床孔压和液化响应数值研究

Numerical study on pore pressure and liquefaction responseof seabed around monopile under wave load

基于RANS方程和u-p形式的比奥固结方程建立波浪—单桩—海床的耦合模型,讨论了桩周海床两类孔压响应分布及相应液化发展特点.通过与物理模型试验数据、解析值和数值结果对比,验证模型的准确性.在此基础上,研究了单桩周围海床中瞬态孔压和累积孔压的分布以及相应的液化发展特征.结果表明:桩前土体的累积孔压可达到瞬态孔压幅值的144倍,累积孔压占主导的区域处于桩周距土表0~4 m,并随波浪作用时间增加而向下扩大;瞬态孔压占主导的区域处于桩周距土表4~20 m,并随土体剪切模量的减小而缩小;随着土体饱和度、渗透系数和剪切模量减小,累积孔压相对瞬态孔压幅值的比值增大,桩周土体最大瞬态液化深度增加;桩周土体最大综合液化深度受土体剪切模量和渗透系数影响显著,并表现出振荡特性;水平向渗透系数对土体液化深度影响微弱.研究结果有助于进一步评估单桩周围海床的液化灾害.

Based on RANS equation and Biot consolidation equation of u-p form,a coupled wave-monopile-seabed model is proposed to discuss the distribution of two types of pore pressure response and corresponding liquefaction development.The accuracy of this model is verified by comparing results with physical model test,analytical and numerical solutions.On this basis,the distribution of transient and cumulative pore pressure in the seabed around a single pile and the corresponding characteristics of liquefaction development are discussed.The results show that the cumulative pore pressure of soil in front of the monopile could reach 144 times the amplitude of transient pore pressure.The region dominated by the cumulative pore pressure is located in the range of 0~4 m from seabed surface around monopile and continuously develops downwards with the time of wave load increasing.The region dominated by transient pore pressure is located in the range of 4~16 m from seabed surface around monopile and shrinks with the decrease of soil shear modulus.With the decrease of soil saturation,permeability coefficient and shear modulus,the ratio of cumulative pore pressure to transient pore pressure amplitude increases,and the maximum transient liquefaction depth around monopile increases.The maximum integrated liquefaction depth around monopile is significantly influenced by shear modulus and permeability coefficient of soil and shows oscillatory characteristics.Horizontal permeability has limited effect on liquefaction depth.This study helps to further assess liquefaction hazards of seabed around monopile.