| As a kind of offshore platform foundations, the bucket foundation has beengradually used as the foundation of offshore wind turbines recently with theadvantanges of economic feasibility and environment-friendly work principles. Thesuction penetration is a vital installation procedure and the premise of the engineeringapplication. Howerer, there are still some problems which are exigent to be solved.Focusing on the installation of bucket foundation, this thesis studies the soil-skirtinteraction through laboratory tests and numerical simulation, and reveals the soilcompaction effect during jacked penetration, resistance reduction effect duringsuction penetration, characteristics of the penetration resistance and seepage andcharacteristics of the suction penetration and leveling. Based on the study, the existingcalculation methods for the penetration resistance and required suction are revised.The main content of the innovation and contribution in this thesis are listed as follow.(1) Several jacked installation tests are carried out with two models of L/D=1.0and0.33respectively. The test results show that the soil around the skirt is compactedstrongly and the stress level of the soil is increased greatly during installation. Theinner soil plug emerges during the penetration of the model of L/D=1.0and the innersoil pressures acting on the skirt are much higher than the outer. The test results alsoshow that the tip resistance plays a main role in the total resistance and the resistancecannot be calculated with the existing calculation methods. Based on the test data, theexisting calculated methods are revised.(2) Aiming at the problems in the suction installation of bucket foundations, severalsuction penetration tests are carried out with the above two bucket foundations and thevariations of the inner and outer frictions and the tip resistance are revealedrespectively. The test results show that the inner friction and tip resistance are reducedconsiderably but the outer friction barely changed nevertheless. The results also showthat the existing nominal critical suction is too consertive. Based on the rsults theresistance reduction effect is quantized and the previous calculated method for therequired suction of bucket foundations is revised and evaluated.(3) As for the composite bucket foundation for offshore wind turbine, suctionpenetration and leveling tests are carried out through numerical simulation andlaboratory tests. The study reveals the characteristics of the suction and seepage fieldduring suction penetration and leveling and establishes the calculation methods for the critical suction of penetration and leveling respectively. The study shows that therequired suction for the installation of composite bucket foundation is slightly smallerthan that of the traditional bucket foundation. The study also shows that suction in theraised compartment is able to adjust the foundation when it tilts during installationand the applied adjusting suction is smaller than the critical adjusting suction. |
