Study Of Analysis Methods Of Deformation And Bearing Capacity For Suction Anchor With Taut Mooring Systems Under Cyclic Loads

Suction anchor with taut mooring system is an important floating platform foundation. The deformation instability process and cyclic bearing capacity of suction anchors with taut mooring system are researched under static and cyclic loads in soft clays in the paper. The research includes the following aspect.The paper establishes a pseudo-dynamic visco-elastic plastic constitutive model which can describe cyclic deformation and cyclic accumulative deformation of saturated soft clays under unconsolidated undrained conditions based on the equivalent visco-elastic theory and creep theory. The constitutive model includes three parameters: the cyclic shear modulus, damping ratio and the incremental of octahedral cyclic accumulative strain. The equivalent visco-elastic model represents cyclic deformation response and the creep model describes cyclic accumulative strain response of soil elements.The relationships of parameters in the pseudo-dynamic visco-elastic plastic constitutive model are researched by the static and cyclic triaxial compression tests. The conclusion is that the change of the cyclic shear modulus and damping ratio with the octahedral shear strain is basically the same relationship under the different initial stress state. The relationships of the cyclic shear modulus and damping ratio with the octahedral shear strain can be determined by the triaxial tests under non-static deviatoric stress status. The cyclic triaxial extension tests and cyclic torsion tests results are predicted on based of the relationship of model parameters determined by cyclic triaxial compression tests. The comparison of the predicted and tests results shows that the predicted results of cyclic shear modulus and damping ratio are basically consistent with the model tests results, the predicted relationship of the octahedral accumulative shear strain with the number of cycles is basically in agreement with the tests results determined by cyclic triaxial extension tests, and the predicted relationship of the octahedral accumulative shear strain with the number of cycles is basically consistent with the tests results determined by cyclic torsion tests. These results show that the pseudo-dynamic visco-elastic plastic constitutive model established in this paper is applicability for the different stress status.The variation of the undrained cyclic strength with the average stress of the soft clays is established in this paper based on the cyclic triaxial compression tests. On based of the variations, the cyclic strength determined by the cyclic extension tests is predicted. The predicted resluts are in agreement with the tests results.Further, the pseudo-dynamic visco-elastic plastic finite element method by using of the pseudo-dynamic viscoelastic plastic constitutive model is researched in order to evaluate the deformation instability process of suction anchors subjected to the static and cyclic loads. The research includes that the pseudo-dynamic viscoelastic plastic constitutive model is combined with the finite element model through the interface program of the finite element program ABAQUS, the script procedure by which the dynamic iterative calculation is combined with the cyclic accumulative deformation calculation is compiled by the Python language, and the procedure for calculating the cyclic accumulative deformation is compiled by the Matlab language, finally the cyclic deformation and cyclic accumulative deformation are calculated for tracking the cyclic loads in the ABAQUS environment.The model tests results for suction anchors subjected to the static and cyclic loads are predicted by the pseudo-dynamic viscoelastic plastic finite element method. The comparison of the predicted and tests resluts show that the predicted cyclic deformation is smaller than that determined from model tests for suction anchors with the vertical failure mode. The variation of the cyclic accumulative deformation with the number of cycles is in agreement with that obtained from model tests. When the model tests with the lateral failure mode are predicted, the dynamic interation calculation is conducted by using of reduced 30% shear modulus of the soil elements. The cyclic deformation calculated of suction anchors is mostly smaller than that determined from model tests. The variation of the cyclic accumulative deformation calculated with the number of cycles is different from that obtained from the model tests. The cyclic accumulative deformation calculated is clearly larger than that determined from the model tests when the time of the cyclic loads is short. The incremental cyclic accumulative deformation calculated is smaller than that obtained from the model tests with the increasing number of cycles.The limiting equilibrium analysis method to determine the undrained bearing capacity of suction anchors with the mooring systems subjected to the static and cyclic loads by using of the undrained cyclic strength of soft clays is researched based on the failure mode of suction anchor in the optimal attachment point. The two methods determined the average shear stress, further the undrained cyclic strength for different failure zones are proposed in this paper. Finally, the cyclic bearing capacity of suction anchors is determined by the limiting equilibrium analysis. In order to verify the feasibility of the both methods, the model tests results are predicted. The results show that the average relative error between the predicted and tests results is lower than 10%, which shows that the both are in agreement.Finally, the bearing capacity of suction anchors subjected to static and cyclic loads are researched by the pseudo-static finite element analysis method based on the undrained cyclic strength of soft clays. The comparison of calculated and model tests results showes that the calculated results is smaller than that obtained from tests, and the average error of both is lower than 10%. The cyclic bearing capacity of suction anchors may be determined by the pseudo-static finite element analysis method.