关键词: 裙式吸力基础;注水拔出;渗流;数值模拟;

Abstract: The modified suction caisson （MSC） is a novel type of offshore wind turbine foundation.Compared with the regular suction caisson （RSC），the MSC can effectively increase the bearing capacity and limit deflection capacity.When the service of an offshore wind turbine is terminated，or the installation of suction caisson is failed，the suction caisson should be extracted by reversing pumping water into the caisson.Numerical simulations are carried out to investigate the seepage field distribution around the MSC and RSC during the extraction by reverse pumping water into the caisson.It is found that during extraction，seepage occurs in sand both in and around the suction caisson.Water flows from inside of the caisson to the outside soil，thus leading to the downward movement of soil and increases of effective stress and shaft frictional forces in the suction caisson and the decreases of effective stress and shaft frictional forces at outer wall of suction caisson.During the extraction，the difference between the influenced areas of seepage around the MSC and RSC is relatively small.The trends of distributions of the hydraulic head equi-potential lines，excess pore pressure and effective stress of the MSC are the same as those of RSC.However，the values of the above parameters for the MSC are higher than those for the RSC.During extraction，negative pressure is generated in the internal compartment，which is reverse to the pressure in major caisson.

Key words: modified suction caisson （MSC）；extraction by reverse pumping water；seepage；numerical simulation