Model tests and analysis method on the bearing capacity for suction anchors subjected to average and cyclic loads

Abstract

The bearing capacity of suction anchors subjected to inclined average and cyclic loads at the optimal loading point was researched using 35 model tests under 1g condition. Results show that the cyclic bearing capacity of suction anchors depends on the average load and the number of load cycles to failure. The cyclic bearing capacity decreases with an increase of the number of load cycles to failure for a given average load. The cyclic bearing capacity decreased from 91% to 75% the static bearing capacity when the number of load cycles to failure increased from 100 to 1000 for the average load which was 0.5 times the static bearing capacity based on model test results. The cyclic bearing capacity increases with an increase of the average load for a given number of load cycles to failure when the average load varies from 0.5 to 0.7 times the static bearing capacity. The cyclic bearing capacity increased from 75% to 84% the static bearing capacity when the number of load cycles to failure was 1000 for vertical failure anchors based on model test results. The paper also presents a limiting equilibrium analysis method to calculate the cyclic bearing capacity of suction anchors using the cyclic shear strengths of soft clays determined by unconsolidated and undrained cyclic triaxial tests. Two procedures to determine the cyclic shear strength of the stratum around suction anchors were suggested for the method. For the first procedure, the normalized cyclic shear strength of each failure zone around anchors is determined based on the normalized average shear stress of the zone. The average shear stress of each failure zone is considered as constant and determined using static equilibrium conditions between the average load and resistances which are expressed by the average shear stress. For the second procedure, the normalized cyclic shear strength of the stratum is determined based on the normalized average shear stress of the stratum around anchors. The normalized average shear stress is determined based on the assumption which is that the ratio of the average shear stress and the cyclic shear strength is equal to the ratio of the average load and the sum of the average and cyclic loads. The relationship between the normalized cyclic shear strength of soft clays and the normalized average shear stress is determined by unconsolidated and undrained cyclic triaxial tests. The cyclic bearing capacity is determined using limiting equilibrium analyses. To check the validity of the calculation method, model test results were predicted using the method. Predicted results are generally less than model test results and most of relative errors between predicted and test results are less than 10%, which show that the method can be used to determine the cyclic bearing capacity of suction anchors in soft clays.