Penetration of dynamically installed anchors in clay

Abstract

This paper utilises centrifuge data to explore the penetration response of dynamically installed anchors in normally consolidated clay. The data indicate that for anchors with no flukes, expected anchor tip embedment depths are two to three times the anchor length for impact velocities approaching 30 m/s, with a strong dependence on the net density of the anchor and smaller dependence on the impact velocity. Total energy, defined as the sum of the kinetic energy of the anchor at the mudline and the potential energy released as it penetrates the seabed, is shown to be a useful quantity for comparing the embedment depth of anchors with markedly different geometries and mass, impacting the soil at different velocities. The centrifuge data were used to calibrate an analytical embedment model, based on strain-rate-dependent shearing resistance and fluid mechanics drag resistance. The merit of the anchor embedment model has been demonstrated by predicting the final embedment depths for a series of offshore field trials to within 4% of the measurements.

Experience with a dual pore pressure element piezoball

“…After ten cycles, the net penetration resistance is 0·4 times the initial resistance, indicating a sensitivity (in terms of penetration resistance) of 2·5 which is typical of that reported in previous studies on UWA kaolin (Chen and Randolph, 2008;O'Loughlin et al, 2013;Sahdi et al, 2014;Watson et al, 2000).…”

Damage Assessment of Free-fall Dropped Object on Sub-seabed in Offshore Operation

“…As shown in Figs. 9 and 11, a low estimation of the decrement slope of the velocity in the soil and the final embedment depth in the analytical results guarantee a conservative estimation and time consumption if the CEL method-based numerical analysis works well and reports precise values, as in several previous studies O'Loughlin, , 2013Hossain, 2014). In Fig.…”

“…It is chiefly based on Newtonian mechanics and assumes uniform clay. Several investigations have used similar approaches based on True's model for freefall anchor installation (de Araujo, 2004;Brandão, 2006;O'Loughlin, , 2013Hossain, 2014). A modified equation of motion is shown in Eq.…”

“…1. The bearing and frictional resistance forces, and the shear strain function (O'Loughlin et al, 2013) are expressed in Eqs. 4-6, respectively.…”

On the instability of offshore foundations: theory and mechanism

“…The cost of installing anchors increases exponentially as water depths increase, which has inspired the development of dynamically penetrating anchors that embed themselves into the seabed under free-fall and thus are less sensitive to increasing water depth compared to conventional concepts [112,113]. Dynamically penetrating anchors or termed as Gravity-installed anchors are usually released from a height of 50-100 m above the seabed and reach velocities of 20-30 m/s at the seabed, eventually installed to the tip penetration of 1.5-3 times their length.…”