Abstract: 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 Nkt 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 Bq, 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.

Key words: offshore wind farms, muddy silty clay, piezocone penetration test (CPTU), cone factor