On Application of a Caisson with Suction to Breakwater Structure

将一种将吸力作用纳入稳定性的带裙边钢沉箱应用于软海底海岸结构，采用先进的沉箱结构-海底相互作用分析方法，模拟了具有吸力的沉箱结构及其软基础在波浪冲击下的动力响应。为了探讨扩端桩支撑海上沉箱型结构基础的可行性，采用有限元方法对波浪荷载作用下沉箱型桩基础的动力响应进行了数值计算。研究结果表明：1)随着估计位置无因次频率wa/Vs和深度z/a的增加，沉箱结构下估计位置的位移响应变小，相位角增大。因此，沉箱结构下海床的位移响应在很大程度上取决于沉箱结构裙边长度，这可以从沉箱本身的位移响应中看出。2)在刚度和横波速度较小的海床上安装吸力沉箱结构时，有必要仔细考虑其位移和相位响应的行为。3)沉箱下孔隙水压力的动力响应在隔室附近达到最大值，并随着离沉箱底部距离的增加而逐渐减小。4)当沉箱安装在桩基础上时，无论沉箱与桩的连接情况如何，沉箱在桩基周围海底的位移响应与沉箱本身的位移响应几乎相似。5)桩基础防止沉箱下海床的差速沉降，因为沉箱下的波浪引起的孔隙水压力分布到扩展基础周围的深基础上。

To apply a steel caisson with skirt, which takes suction effect into the stability, to the coastal structure on soft seabed, dynamic responses of the caisson structure with suction and its soft foundation under wave attack were simulated by an advanced caisson structure-seabed interaction analysis. Also, the dynamic response of a caisson-type structure resting on pile foundation loaded by waves was numerically evaluated by FEM analysis in order to investigate the feasibility of a pile with an expanding end to support such offshore structure foundations.The results obtained in this research is summarized as follows :1) The displacement response at an estimating location under a caisson structure becomes small and the phase angle is large as the non-dimensional frequency wa/Vs and the depth z/a of an estimating location increases. Consequently, the displacement response of seabed under a caisson structure greatly depends on the skirt length of a caisson structure as seen in the displacement response of a caisson itself.2) It is necessary to give careful consideration to the behavior of both the displacement and phase responses in case of installing a caisson structure with suction on the seabed, whose stiffness and shear wave velocity are small.3) The dynamic response of pore water pressure under caisson has a maximum value in the vicinity of compartments, and also gradually decreases with the distance from the bottom of caisson increasing.4) When a caisson is installed on a pile foundation, the displacement response in the seabed around the pile foundation, as well as that of the caisson, are almost similar regardless of the connecting condition between caisson and piles.5) The pile foundation prevents the differential settlement in the seabed under a caisson, because the wave-induced pore water pressure beneath the caisson is distributed to the deep foundation around the expanding base.