| Suction caissons have become the most widely used type of anchor for various types of mooring systems ranging from catenary chains to lightweight taut polyester cables.A suction caisson is a cylindrical shell,which is sealed by a top cap equipped with valves.Several researches had been carried out to study the inclined pull out capacities of suction caissons.Generally in these studies,the combined horizontal and vertical capacities,their failure mechanisms,and the influence of one on the other had also been examined.In this thesis,parametric studies were done using finite element analyses to investigate the effects of caisson geometry i.e.the changes in the aspect ratio,optimal depth,and cohesion value on both uniform soil and a soil with linearly increasing strength.Displacement loading at a reference point on the top of the caisson was applied to study the ultimate limit state of the suction caissons under inclined load and the results are presented in VH interaction diagram load space.For studying the different parameters,model validation has been carried out to establish an appropriate element type and other analysis conditions.The results of these validation analyses were in very good agreement with the selected study paper.Based on that the parametric studies of this thesis work were carried out.In the first part of the study,for uniform soil,the analyses were undertaken without allowing the separation of the caisson.It was found that the increase in the cohesion value has a big impact on the resultant capacity of the caisson.A comparison was made between the capacities of different aspect ratios,and the results were presented in graphs.Vertical and horizontal capacities for different translation angles were combined to illustrate the failure envelope of the suction caissons for the three selected aspect ratios.For the case of the variation of the interface(penalty)friction ratio,it was found that there is a slight change in the resultant capacity with α = 1 giving higher capacity.When the crack formation is allowed the optimal depth(Zcl)showed an increase in length for the L/D ratios of the caisson.In the second part of the parametric study of suction caisson in uniform soil,analyses were carried out for caissons with a crack allowed to form.To investigate the effect on the capacity the analysis was done for L/D=2 for the different cohesion values.The overall capacity of the caisson showed a significant reduction in capacity compared with the results of crack formation not allowed.The crack formation for the three aspect ratios has shown an important difference,in which for the smaller one a full gab was formed.Moreover,the VH envelopes for both the cases has been plotted in one graph for comparison.For the uniform soil selected in the study,the bounding limits of the envelopes showed a reduction in capacity when a crack formation is allowed.A study has also been done for investigating the effects of soil cohesion,aspect ratio in a soil with linearly increasing strength.The capacity of the suction caisson showed a large increase with the increase of both the cohesion value and aspect ratio.Normalized VH interaction diagram for different aspect ratios was also presented. |
