桶形基础二次加载的大变形有限元模拟

Large deformation finite element analysis of caisson installation with secondary loading phase

桶形基础用于支撑海上风电升压站平台时,平台与电气设备分两阶段安装,中间存在数周到数月的间隔期。为探究桶形基础在二次加载阶段的峰值贯入阻力,发展了基于网格周期更新的有效应力大变形有限元方法,避免基础贯入引起周围土体单元扭曲,再现了黏土中基础“贯入固结二次加载”的全过程。对比已有的离心模型试验,验证了发展的大变形数值方法的可靠性。通过比较初始贯入阻力与固结后的贯入阻力,发现桶基与平台的安装间隔期能够有效增加桶基承载力,固结后的贯入阻力峰值仅需要很小的基础位移即可达到。开展变动参数分析,考察影响峰值贯入阻力比的主要因素,提出考虑基础尺寸、土体渗透性与固结时间的归一化时间参数,并给出峰值贯入阻力比随归一化时间增长的趋势线。

When caissons are used to support offshore wind substation platforms,the platform and electrical equipment are installed in two phases,with a waiting period of several weeks to months between the two events.To evaluate the peak resistance during secondary loading phase,this'penetration-consolidation-penetration'process in clay is reproduced by the coupled effective stress large deformation finite element analysis to avoid the severe distortion of elements during installation.The numerical model is first verified by simulating a centrifuge test.A comparison of the initial penetration resistance with the penetration resistance after consolidation shows that the waiting period can cause a dramatically increase in soil strength.And the depth of peak penetration resistance during secondary loading phase is almost equal to the initial installation,implying that only a small displacement is required to achieve the compressive ultimate limit state of the caisson after the waiting period.Parametric study is subsequently carried out to investigate the effect of consolidation.A normalized time parameter considering foundation size,soil permeability and consolidation duration is proposed,and a trend line describing the increase of peak caisson resistance with normalized time is provided.