Introduction  Large diameter monopile is the most common used foundation in offshore wind projects. The Self Weight Penetration (SWP) usually takes up a large component of total penetration. To better predict the SWP of monopiles, three methods employing design parameters as well as CPT data have been studied in this paper and the preliminary back analysis have been carried out on the basis of the monitoring data on site.

  Method  In detail, the method calculating the soil resistance during driving from design parameters, the SWP prediction method recommended in DNV manual and a directly derived CPT method were adopted to predict the SWP of monopiles and the interpretation to the difference between predicted and real penetration depth were made after the analyses.

  Result  The results indicate that the SWP prediction with design parameters have better theoretic background but the result are strongly influenced by human factor, the latter CPT methods are based on CPT test data that are more objective but the key coefficients are heavily depend on local experience.

  Conclusion  The real SWP depth are also significantly affected by fluctuation of subsoil layers, penetration rates and pile installation procedures; Not a single method can accurately predict the SWP under all conditions; Comprehensive interpretation of analysis results from different methods can improve the reliability of prediction.