The Suction Force Study In Silty Sediments For Spudcan

The pickup is a must in the construction of wind driven generators. The march of pickup is a procedure of pullout and push down for spudcans. It usually generates suction force which hinders the pullout of spudcans, even damages stability of pickup and endangers the workers.The thesis concentrates on the suction force occurring in the pullout of spudcans, researches on the decisive factors in the suction force creation and its influential factors play important role in number of suction force. The main content of thesis consists of three parts as followed.(1) There are two series of experiment in thesis, ones are the soil tests to acquire mechanics parameters of soils and the others are spudcan models tests to research suction force. The tests results will be compared with numerical simulation for finite element software ABAQUS. There are two similar models in the suction force tests to eliminate the dimensional effect. It is shown in tests results that mechanical properties of silty sand are decisive factors to generate the suction force in the tests results, especially the cohesive force and permeability. Because the cohesive force is much less than the permeability coefficient, the permeability plays a much more important role in suction force tests. It is also shown that the unit suction force is more scientific than relative burial depth to evaluate the suction force. On condition of burial depth is low, the unit suction force is linear correlation with burial depth. With the growth of loading rate, suction force increases correspondingly. While the loading rate grows to some extent, the suction force will not continue to increase, but remain stable. Venting in the underside surface can effectively decrease the unit suction force, but reduction relates to position and pressure of venting.(2) Take advantage of theoretical calculation to compute suction force, then compared with tests results. It is shown in calculation that classic Skempton’s Model is not adaptive to compute suction force on condition of low burial depth. On that condition, mainly occurs elastic displacement in soils, not plastic displacement. Based on ultimate bearing capacity, Skempton’s Model calculation differ huge with tests results, as large as ten times. Lee have summarize the calculation of suction force on the foundation of NCEL lab tests and in situ tests results, its calculation results is larger50%than model tests. There is time factor in empirical formula, but no burial depth factor.(3) ABAQUS is one of huge finite element softwares and is used to simulate suction force in the engineering construction. It is applied in ABAQUS simulation to compute suction force for soils that modified Cam-Clay Model and porous elastic model. It is found that the computation results of ABAQUS simulation is in high accordance with models tests results which are well distributed in the range of ABAQUS simulation. It is shown as models tests results that only the negative pore pressure is the decisive factor, yet the influence of adhesive force can be ignored because the stress of soils remains pressure in the process of numerical computation. In comparision of vertical stress and pore pressure of soils at interface, the vertical stress reduces but still remain pressure, but the pore pressure immediately reduces to a negative limit value from zero. It is the negative pore pressure come into suction force which is like a pull of vacuum and gradually dissipates until less than the exterior pull as a result of pullout of spudcan. Loading time is one of the most importantly influential factors, suction force gradually reduces as loading time lasting, nearly inverse ratio. It is also simulated that stress field and displacement field of soils at interface in the process of spudcan’s pullout. It is found in calculation results that horizontal stress is in negative correlation with horizontal displacement, because with the spudcan’s pullout, the soils moves centrally, as like a relief of soils interior stress. While vertical stress is in accordance with vertical displacement, the vertical stress reduces gradually to a minimum value, meanwhile vertical displacement grows up to a maximum value.In the thesis, the ABAQUS simulation results can match well with models tests results, but the theoretical calculation results is higher50%. It is not matured as well.