软基中多向受荷大直径单桩桩土相互作用试验研究

Experimental investigation on pile-soil interaction of monopile under multidirectional load in soft foundation

为了研究多向循环受荷大直径单桩的水平变形响应及桩土相互作用机理,开展多向受荷大直径单桩的1g大比尺模型试验,探讨不同竖向和水平循环荷载比下的桩侧受力及变形响应.试验结果表明,施加竖向循环荷载会增大桩身水平位移的发展速率;最大弯矩出现在2.0倍桩径深度处,随着循环次数的增大,桩身弯矩表现出减小的趋势;在循环荷载作用下,最大土抗力所在的位置随着循环次数的增大逐渐从1.5倍桩径深度处向2.0倍桩径深度处移动,循环土体抗力-桩身水平变形(p-y)曲线的退化主要发生在表层土体;施加竖向循环荷载会增大桩土界面的初始刚度,但同时也会加速桩土体系的刚度退化.建议在海上风电大直径单桩的设计中,特别注意竖向循环荷载对长期循环荷载作用下桩身位移及桩土相互作用的不利影响.

A 1g large-scale model test was carried out,in order to further study the lateral deformation response and pile-soil interaction mechanism of large-diameter monopile under multidirectional cyclic load.The lateral stress and the deformation response of the pile under different vertical and lateral cyclic load ratios were discussed.Test results showed that applying vertical cyclic loads would increase the development rate of lateral displacement of the monopile.The maximum bending moment appeared at the depth of 2.0 times the pile diameter,and the bending moment of the pile body showed a decreasing trend with the increase of the number of cycles.The position of the maximum soil resistance gradually moved from 1.5 times the pile diameter depth to 2.0 times the pile diameter depth under cyclic load,and the degradation of cyclic soil resistance-pile lateral deformation(p-y)curve mainly occured in the surface soil.Applying vertical cyclic load would increase the initial stiffness of the pile-soil interface,but it would also accelerate the stiffness degradation of the pile-soil system.Special attention should be paid to the adverse effects of vertical cyclic load on pile displacement and pile-soil interaction under long-term cyclic load in the design of large-diameter monopile for offshore wind turbines.