基于孔压静力触探的杭州湾海域软黏土强度解译参数研究

Strength interpretation parameter of piezoncone penetration test for soft clay in offshore area of Hangzhou Bay

我国海域广泛分布有低强度软黏土,其工程特性评价将直接影响风机基础设计和安全运行。孔压静力触探是目前海洋勘察中使用最多的原位测试手段,其优点在于对土体扰动小,缺点在于需要通过解译获取土体参数,而不同地区的解译参数往往存在场地特异性。依托浙江杭州湾嘉兴海域某海上风电工程,开展了室内试验和原位孔压静力触探试验(piezoncone penetration test,简称CPTU),标定得到了适合我国浙江杭州湾海域的淤泥质粉质黏土的CPTU锥尖因子N_(kt)范围为14.15~30.18,总平均值为20.25。标定结果显示杭州湾海域淤泥质粉质黏土锥尖因子N_(kt)与孔压比B_(q)呈现负相关性,而与含水率w、孔隙比e、液限w_(L)、塑限w_(p)、塑性指数I_(p)呈现正相关性,并得到了N_(kt)与孔压比B_(q)和塑性指数I_(p)的多元回归分析公式。将建立的N_(kt)关系式应用于临近平湖海域的风电场工程中,结果显示采用含水率w、孔隙比e与锥尖因子N_(kt)的关系式以及孔压比B_(q)和塑性指数I_(p)的多元回归分析公式,可以较好地解译杭州湾海域软黏土的强度,不仅适用于淤泥质粉质黏土地层,还可以应用于淤泥质黏土和粉质黏土地层,具有较好的场地适用性。

The soft clay with low strength is widely distributed in the offshore area of China,the evaluation of its engineering properties will directly affect the design and safe operation of wind turbine foundation.Piezocone penetration test is the most widely used in-situ test method in offshore geotechnical investigation,which has less disturbance on soil.The disadvantage is that soil parameters can only be obtained through interpretation,which are site specific.Based on an offshore wind power project in Jiaxing offshore area of Hangzhou Bay,Zhejiang province,this paper carried out laboratory tests,in-situ piezocone penetration test.The range of calibrated CPTU cone factor N_(kt) for muddy silty clay in Hangzhou Bay offshore area is from 14.15 to 30.18,with a total average value of 20.25.The calibration results show that the cone factor N_(kt) is negatively correlated with pore pressure ratio B_(q),but positively correlated with water content w,void ratioe,liquid limit w_(L),plastic limit wp and plasticity indexI_(p).And a multiple regression formula between N_(kt) and pore pressure ratio B_(q),plasticity index I_(p) are obtained.By applying the N_(kt) correlations into the wind farm at Pinghu offshore area near this project,the results show that the correlations between water content w,void ratio e and cone factor N_(kt) and multiple regression formula between N_(kt) and pore pressure ratio B_(q),plasticity index I_(p) have better interpretion quality on the strength of soft clay in Hangzhou Bay offshore area.The established correlations are not only suitable for the muddy silty clay,but also for the muddy clay and silty clay,which have good site applicability.