驻波作用下有限厚度海床动应力路径特性研究

Study on characteristics of dynamic stress path of finite-thickness seabed under standing waves

基于驻波作用下有限厚度海床动力响应的解析解,推导了海床内土体单元在以轴向偏差应力的一半为横坐标,剪应力为纵坐标的应力平面上的动应力路径,得出土体单元位于波节处的动应力路径为纵轴上的一条线段;位于波腹处为横轴上的一条线段;位于波节与波腹之间为非标准椭圆形。以北海区域为例对确定动应力路径的初始相位差θ、轴向偏差应力幅值的一半a、剪应力幅值b 3个参数进行分析,得出在0-0.35倍海床深度范围内时,波节与波腹之间土体单元的动应力路径趋近于线段,而在0.35-1倍海床深度范围内时,动应力路径为非标准椭圆形,且初始相位差？沿相对深度的增加在-180°--150°范围内变化。通过海床渗透系数、波浪周期、海床厚度对海床内土体单元动应力路径的影响分析可得：海床渗透系数、波浪周期的变化不会改变海床内相同位置土体单元a,b的取值,而对？的取值会有影响。当海床渗透系数不小于10-2 m/s时,海床内土体单元的动应力路径均为线段;而在不同波浪周期下,？在海床下部区域的变化范围均为-180°--150°。当海床厚度较薄时,动应力路径在表层0-0.03倍波长范围内趋近于线段;当海床厚度在0.3-2倍波长范围内时,随着海床厚度的增加,海床表层动应力路径趋近于线段的深度范围逐渐增大。

Based on the analytical solutions for standing wave-induced soil response in the finite-thickness seabed, the dynamic stress path of soil element is deduced in the stress plane with half of the axial deviation stress on the horizontal axis and shear stress on the vertical one. The results of the analysis show that the dynamic stress path of the soil element located at the nodes is a line segment on the vertical axis, that located at the antinodes is a line segment on the horizontal axis, and that at other locations is non-standard ellipse. Taking the North Sea as an example, the initial phase difference（θ）, half of the amplitude of the axial deviation stress（a） and the amplitude of the shear stress（b） are analyzed. It is shown that when the soil element is located between the node and the antinode, the dynamic stress path approaches a line segment with the depth of 0-0.35 times the thickness of seabed, while with the depth of 0.35-1 times the thickness of seabed, it is a non-standard ellipse, and the value of ？ varies along the relative depth in the range of-180 ° to-150°. Additionally, the influences of permeability of seabed, wave period and thickness of seabed on dynamic stress path are analyzed. The results indicate that the change of the coefficient of permeability and wave period do not alter the values of a and b, but the value of θ is affected. When the coefficient of permeability of seabed is larger than 10-2 m/s, the dynamic stress path of the soil elements is a line segment in the whole of seabed. And the value of θ changes in the range of-180 ° to-150 ° when the seabed is under different wave periods. Moreover, the dynamic stress path approaches a line segmentwith the depth of 0-0.03 times the wavelength when the thickness of the seabed is thinner. When the thickness of the seabed is in the range of 0.3-2 times the wavelength, thesurface area where the stress path is a line segment increases with the increase of the thickness of the seabed.