Analysis On Penetrating-levelling Mechanism And Penetration Resistance Of Bucket Foundation With Inner Compartments For Offshore Wind Turbines

With the adjustment of energy structure,wind power is more and more important in the energy structure of China.The bucket foundation has been developed as an environment-friendly foundation.Sinking and leveling,involving geotechnical mechanics,fluid mechanics and many other disciplines,are the key part in the installation of the bucket foundation with inner compartments.In this dissertation,the method of model test,numerical simulation and theoretical derivation are used.Sinking-leveling mechanism and penetration resistance of bucket foundation with inner compartments are studied.The research contents and achievements are as follows.Tests of sinking and leveling process for the models of bucket foundation with inner compartments were carried out in sand.The sinking-leveling mechanism,strategy to avoid soil infiltration and damage and the relationship between adjustable angle and adjustable depth are analyzed.The test results show that internal skirt and bulkheads significantly exacerbates the soil plug in the bucket.When the bucket is tilted,negative pressure should be applied to multiple side compartments to reduce the risk of infiltration damage.The negative pressure leveling method has some limitations on the adjustable angle and depth.Adjustable tilt angle and sinking depth are inverse relationship.Tests of sinking and leveling process for the model of bucket foundation with inner compartments were carried out in silty clay.The pressure in the compartments,earth pressure and pore water pressure of the surrounding soil were monitored in the sinking and leveling process.The experiment results show that the absolute value of the pore water pressure on the inner side of the bucket wall decreases gradually from the top to the bottom,while the absolute value of the pore water pressure on the outer side of the bucket wall changes in the opposite direction.The pore water flow and the distribution of excess pore water pressure in the sand,clay and layered soil during sinking and leveling process of the bucket foundation with inner compartments were studied by numerical simulation.The results show that during the suction installation of the bucket foundation with inner compartments in sand,the excess pore pressure varies nearly linearly along the depth of the bucket wall,internal skirt,and bulkheads.During tilt adjusting process,the soil in the location of the hydraulic outlet at the bucket wall is firstly infiltration damaged.The inclination of the foundation causes cracks between the bucket wall and the outer soil,which accelerates the formation of the seepage channel and the process of soil piping at the hydraulic outlet.Based on numerical analysis results of seepage field during penetration process of traditional bucket foundation and the bucket foundation with inner compartments,the penetration resistance and critical suction of the bucket foundation with inner compartments during penetration process were calculated.Moreover the calculated penetration resistance considering seepage effect was contrasted with the model test results in Chapter 3.The results show that the calculation method is proposed to determine the penetration resistance of a bucket foundation under seepage conditions.The ratio of the total reduction to the total resistance of the bucket foundation with inner compartments under no seepage flow is in the range of 0.35–0.55 and reaches a maximum value of 0.55 at the final penetration stage.