This paper describes the results from a centrifuge investigation into the rate dependence of T-bar and ball penetrometer resistance in kaolin. Four T-bar diameters and two ball diameters were installed in kaolin with overconsolidation ratios of 1, 2 and 5 at penetration velocities varying over five orders of magnitude. The penetration resistances are compared with the properties of kaolin as measured in element tests to assist in the development of a framework that describes this resistance over the full velocity range. Consistent trends emerge when the soil viscosity is assumed to affect the penetration resistance in both the partially drained and undrained conditions, enabling the dependence of the T-bar and ball resistances on diameter, velocity and soil characteristics to be quantified.

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.

Vertically installed plate anchors have been investigated in this paper by numerical analysis and centrifuge modeling. In the numerical analysis, the large deformation finite-element method (remeshing and interpolation technique with small strain) was used to simulate strip plate anchor rotation. In the centrifuge model tests, transparent soils were used to observe square anchor rotation. The loss in anchor embedment during anchor keying was assessed for anchors in uniform and normally consolidated soils with anchor pullout angle varying from 30° to 90° to the horizontal. It was found that the loss in anchor embedment during anchor keying may be expressed in terms of a nondimensional anchor geometry factor, which is a function of the eccentricity of the padeye, angle of loading, and the net moment applied to the anchor at the stage where the applied load balances the anchor weight. However, once the anchor geometry factor reaches a certain value, the loss in anchor embedment stabilizes at 0.25–0.5 times t...

This paper describes a series of centrifuge tests performed in order to investigate the influence of the installation process on the capacity of a suction embedded plate anchor. A 1/145th reduced scale model suction caisson and plate anchor were used for this purpose, embedded in a normally consolidated clay sample. The full installation and retrieval process was simulated as well as loading of the anchor to failure. Results are compared with similar pullout tests where the anchor was pre-embedded manually in the sample. The keying process and the anchor capacity were also investigated. Results show a loss of performance of the suction embedded anchor immediately following the retrieval of the caisson due to weakening of the clay in the vicinity of the anchor. As the clay regains strength with time, the anchor capacity increases to match those of the jacked anchors. The normalised anchor capacity following consolidation agreed well with theoretical solutions. The loss of anchor embedment during the keying process was observed to be lower for the suction embedded anchors than for the jacked anchors, but both sets of data correlated closely with the load inclination at the anchor padeye.

This paper considers centrifuge modelling of free-fall piezocones in soft clay, and interprets the test data to estimate the undrained shear strength and coefficient of consolidation. Data from the free-fall piezocones, which involved dynamic embedment in a normally consolidated kaolin clay sample from various drop heights, were compared with equivalent data from piezocone tests. The undrained shear strength, as interpreted from the acceleration trace of the free-fall piezocone, was found to be in good agreement with that derived from the piezocone penetration tests. The free-fall piezocone is also found to produce identical pore pressure dissipation behaviour as for a statically penetrated piezocone, despite a significant rise in the pore pressure at the start of the dissipation phase.

Challenges associated with dynamically installed anchors include prediction of the anchor embedment depth, which dictates the anchor's holding capacity. This is particularly true for calcareous sediments, as very little performance data exist for this anchor type in these soils. This paper reports results from a series of model tests undertaken to provide insight into the behaviour of a torpedo anchor during dynamic installation and monotonic pullout in lightly overconsolidated calcareous silt. The tests were carried out in a beam centrifuge, varying the drop height and consequently the impact velocity, and the consolidation period prior to anchor pullout. The mudline load inclination was also varied to encompass various mooring configurations. The centrifuge model test data were used to calibrate: (a) an analytical dynamic embedment model, based on conventional bearing and frictional resistance factors but with strain-rate-dependent undrained shear strength for the soil; and (b) an analytical quasi-static vertical pullout capacity model, accounting for reverse end bearing and frictional resistance. A total energy based expression, appropriate for calcareous silts, was proposed for predicting anchor embedment depth for a given anchor geometry, mass and impact velocity. For assessing anchor vertical holding capacity, a piezocone based direct design approach was also proposed, deriving anchor end bearing and frictional resistance from cone tip resistance and sleeve friction, respectively. Anchor capacity under inclined loading was presented as failure envelopes expressed in terms of dimensionless vertical and horizontal components of anchor net resistance, which agreed well with a finite-element based envelope developed for embedded foundations. The regain of anchor capacity was found to be in good agreement with predictions based on the cavity expansion framework. Challenges associated with dynamically installed anchors include prediction of the anchor embedment depth, which dictates the anchor's holding capacity. This is particularly true for calcareous sediments, as very little performance data exist for this anchor type in these soils. This paper reports results from a series of model tests undertaken to provide insight into the behaviour of a torpedo anchor during dynamic installation and monotonic pullout in lightly overconsolidated calcareous silt. The tests were carried out in a beam centrifuge, varying the drop height and consequently the impact velocity, and the consolidation period prior to anchor pullout. The mudline load inclination was also varied to encompass various mooring configurations. The centrifuge model test data were used to calibrate: (a) an analytical dynamic embedment model, based on conventional bearing and frictional resistance factors but with strain-rate-dependent undrained shear strength for the soil; and (b) an analytical quasi-static vertical pullout capacity model, accounting for reverse end bearing and frictional resistance. A total energy based expression, appropriate for calcareous silts, was proposed for predicting anchor embedment depth for a given anchor geometry, mass and impact velocity. For assessing anchor vertical holding capacity, a piezocone based direct design approach was also proposed, deriving anchor end bearing and frictional resistance from cone tip resistance and sleeve friction, respectively. Anchor capacity under inclined loading was presented as failure envelopes expressed in terms of dimensionless vertical and horizontal components of anchor net resistance, which agreed well with a finite-element based envelope developed for embedded foundations. The regain of anchor capacity was found to be in good agreement with predictions based on the cavity expansion framework.