地震作用下南黄海海上风电场水平场地液化特性分析

Analysis of liquefaction characteristics of horizontal site of offshore wind farm under earthquake in the South Yellow Sea

江苏近海属南黄海海域,是我国海上风电场最集中的地区,目前约占全国总装机容量的70%~75%,该区覆盖层厚度大,桩长深度范围(一般40~60 m)多为粉砂、粉土、粉质黏土地层,尤其是泥面以下20 m深度为易液化粉砂-粉土地层。而南黄海地区亦是我国的地震多发区,因此,研究了该区海上风电场水平场地的地震液化特性。首先基于南黄海某海上风电场50个机位的钻探资料统计特征建立了地层概化模型;随后通过动三轴试验和共振柱试验标定了土体动力分析参数;然后反演了3条地震波(EL-Centro波、Northridge波、Kobe波),将地表附近地震动峰值加速度PGA分别调整为0.05g、0.10g、0.20g、0.40g并进行场地液化分析,重点分析了地震作用下地层的超孔压比、总沉降、分层沉降等特性。研究发现,该区地层为可液化地层。当PGA=0.05g时,各层监测点的超孔压比均小于1.0,地层总沉降为1 cm左右;当PGA为0.10g和0.20g时,仅表层(12 m内)地层完全液化,地层总沉降分别为10 cm和17 cm;PGA=0.40g输入时,泥面下20 m地层均完全液化,地层总沉降为30 cm左右。不同地震作用下,表层土体沉降占比最大,当PGA为0.10g及0.20g时,表层土体沉降约占总沉降的95%以上。因此,该区海上风机桩基础设计应考虑地震作用下场地的上述液化特性。

Jiangsu offshore belongs to the South Yellow Sea,which is the most concentrated area of offshore wind farms in China.At present,it accounts for about 70%-75%of the total installed capacity of China.The overburden layer thickness in this area is very large,soils along the pile length depth(generally 40-60 m)are mainly silty sand,silt and silty clay,especially the easily liquefied silty sand silt layer at the depth of 20 m below the mud surface.The South Yellow Sea is also an earthquake activity area in China.Therefore,the seismic liquefaction characteristics of the horizontal site of offshore wind farm in this area are studied.Firstly,based on the statistical characteristics of drilling data of 50 sites in an offshore wind farm in the South Yellow Sea,the generalized formation model is established.The soil dynamic parameters are calibrated based on dynamic triaxial test and resonance column test,and three ground motions are inversed(EL-Centro,Northridge and Kobe),and the peak ground acceleration(PGA)near the surface is adjusted to 0.05g,0.10g,0.20g and 0.40g respectively,and the site liquefaction is researched.The characteristics of excess pore pressure ratio,total settlement and layered settlement under earthquakes are analyzed.It is found that the strata in this area are liquefiable soils,the excess pore pressure ratio of each layer is less than 1.0 when input PGA is 0.05g,and the total settlement is about 1 cm.When input PGA is 0.10g and 0.20g,only the surface layer(within 12 m)is completely liquefied,and the total settlement is 10 and 17 cm respectively.When input PGA is 0.40g,the 20 m strata below the mud surface are completely liquefied,and the total settlement is about 30 cm.Under different earthquakes,the settlement of surface soil(12 m)accounts for the largest proportion(more than 95%when PGA is 0.10g and 0.20g).Therefore,the liquefaction characteristics of offshore wind farm under earthquakes should be considered for turbine pile foundation.