循环荷载作用下海上风机单桩基础周围砂土沉降与对流特性

将实际海况中的风、浪、流及叶片转动产生的动力荷载简化为作用在模型桩顶部的水平循环荷载，设计了室内概化二维模型试验，研究海上风机单桩基础周围土体的运动特性。采用PIV和PTV技术对振动单桩及其周围土体运动过程进行测量，获得了不同工况下单桩及其周围土体的沉降与对流运动规律。结果表明:桩顶加载频率和位移幅值与土体变形各特征尺度均基本呈线性关系，加载频率和桩顶位移幅值越大，土体变形特征尺度也越大；准平衡时刻沉降坑深度与对流区深度比值范围为0.24~0.34，沉降坑宽度与对流区宽度比值范围为1.47~2.34；桩周砂土颗粒对流运动由桩土相互作用产生的摩擦剪切应力驱动并持续存在，其运动速度量级为10^-4 cm/s，一般比桩体振动速度低3个量级。

Characteristics of soil subsidence and convective motion around offshore windfarm monopile foundations subjected to long-term cyclic loading

Two-dimensional physical model tests are designed to study the soil motion characteristics around offshore windfarm monopile foundations. Periodical loading induced by wind, wave, current, and rotor motion in the field is simplified to lateral cyclic loading exerted on the top of monopile models in the tests. PIV and PTV technology were used to measure the motion process of vibrating monopile and its surrounding soil. The properties of the soil subsidence and convective motion around the monopiles under different test conditions were obtained. The results show that each characteristic scale of soil deformation approximately has a linear relation with the loading frequency and displacement amplitude of pile-top. The characteristic scale of soil deformation increases with the increase of the loading frequency and the displacement amplitude. At the quasi-equilibrium stage, the depth and width ratios of the subsided hole and convection area are 0. 24-0. 34 and 1. 47-2. 34, respectively. The convective motion of soil is driven by the frictional shear stress generated by the monopile-soil interaction. The velocity of the sand convection motions is around 10^-4 cm/s, which is generally three orders of magnitude smaller than the vibration velocity of monopile.