Prediction method for the installation of suction foundations in sand: Accounting for the effect of hydraulic gradient on soil effective stress

When the required suction of the suction foundation exceeds the critical suction, piping will occur in sands, leading to the failure of the installation process. The reliable prediction method of installation suction and critical suction for the suction foundations is significant. This paper introduces and discusses five prediction methods of installation suction and seven prediction methods of critical suction which are used to analyze the installation suction and critical suction of two offshore prototype suction foundations with different lengths. It is found that the predicted critical suction is about 1.68–2.6 times the installation suction for the short foundation, while it is only about 1.06–1.34 times the installation suction for the long foundation. The calculated suctions by different methods are then compared with the in-situ measured suctions of the two foundations. The results show that the prediction methods based on the Cone Penetration Testing (CPT) results have the advantages of convenience and accuracy in engineering practice. Based on this method, the influence of hydraulic gradient on the effective stress of sands during the penetration process is considered. A new method for predicting installation suction considering the effect of hydraulic gradient on the effective stress (HG-ES method) is proposed. The accuracy of the new method is verified using the offshore in-situ test data. Using the HG-ES method instead of the DNV method to predict the installation suction will help reduce the relative error from 18% to 11% for the long foundation.