Conleth O'Loughlin

Centrifuge tests on dynamically installed anchors

Dynamically installed anchors are torpedo shaped and are designed so that after release from a designated height above the seafloor will penetrate to a target depth in the seabed by the kinetic energy obtained through free-fall and through the self-weight of the anchor. This paper presents results from an extensive series of centrifuge tests undertaken to both inform expected anchor penetrations in normally consolidated clay and form the basis for calibrating an analytical anchor embedment model. The database indicates that for anchors with no flukes, expected anchor tip embedment depths are 2 to 3 times the anchor length for impact velocities approaching 30 m/s, with a dependence on both impact velocity and to a greater extent anchor mass. The centrifuge data were used to calibrate an analytical embedment model, based on strain rate dependent shearing resistance and fluid mechanics drag resistance. Back-figured strain rate parameters increase with increasing impact velocity and are in the range 0.2–0.5 (logarithmic function) and 0.06–0.12 (power function). As the strain rates in the centrifuge tests are approximately 200 times equivalent strain rates in the field, the lower bound strain rate parameters are considered more appropriate for field conditions.Copyright