Centrifuge modelling and the modified limit equilibrium prediction for drag embedment anchor installation in sand
Ying Lai, Chuan Chen, Anhao Pan, Bin Zhu
Abstract
• Utilizing a six-degree-of-freedom magnetic positioning system, the trajectory and orientation of a drag anchor were precisely assessed in centrifugal drag embedment tests. • The test results verified two kinematic rules: the drag anchor penetration aligns with the fluke orientation, and its rotation corresponds to variations in anchor line tension angle at the padeye. • Experimental results disclosed that the slip surface of failure soil wedge during installation approximated 60°∼70°, in line with field test results. • Employing piezoelectric bending elements, measurements of shear wave velocity before and after anchor installation demonstrated a slight increase behind the fluke, confirming the presence of the force behind the fluke. This study presents the measured trajectory, orientation, and capacity of drag embedment anchors (DEAs) in centrifugal installation tests conducted in sand. The 6-degree-of-freedom data obtained from the magnetometer directly verified two kinematic behaviors during the installation of DEAs: (1) the penetration of the drag anchor aligns with the orientation of its fluke; (2) its rotation corresponds to variations in the tension angle of the anchor line at the padeye. The slight increase in shear wave velocity of the soil beneath the fluke, as measured by the bender elements, directly confirmed the presence of the force behind the fluke. Based on these experimental observation, a modified DEA installation prediction model was developed using the limit equilibrium method. The predicted trajectory, pitch, and capacity of the model align well with the experimental results. The model also revealed the mechanism behind the limited capacity of DEA to resist vertical loads: an increase in the loading angle at the padeye decreases the failure angle, which reduces the volume of the three-dimensional failure soil wedge and, consequently, the anchor capacity. Finally, a series of parametric studies were conducted to analyze the influence of sand properties, the initial state of anchor, and other anchor parameters on the kinematic behavior and capacity performance of DEAs.