https://research-information.bris.ac.uk/files/89440297/OA_Arany_10_STEP_design_Monopile.pdf

Design of monopiles for offshore wind turbines in 10 steps

https://api.research-repository.uwa.edu.au/ws/files/119880944/Full_text.pdf

Large deformation finite element analyses in geotechnical engineering

Recent advances in offshore geotechnics for deep water oil and gas developments

Three-dimensional large deformation finite-element (FE) analyses were performed to investigate plate anchor capacity during vertical pullout. The remeshing and interpolation technique with small strain approach was expanded from two-dimensional to three-dimensional conditions and coupled with the FE software, ABAQUS. A modified recovery of equilibrium in patches technique was developed to map stresses after each remeshing. Continuous pullout of rectangular plate anchors was simulated and the large deformation results for strip, circular, and rectangular anchors were compared with model test data, small strain FE results, and plastic limit solutions. Interface conditions of no breakaway (bonded) and immediate breakaway (no tension) were considered at the anchor base. The effects of anchor roughness, aspect ratio, soil properties, and soil overburden pressure were investigated. It was found that the anchor roughness had minimal effect on anchor performance. For square and circular deep anchors under immediate breakaway conditions, the maximum uplift capacity increased with soil elastic modulus, which suggests that lower bound limit analysis and small strain FE analysis may overestimate the capacity. The soil beneath the anchor base separates from the anchor at a certain embedment depth near the mudline, once tensile stresses were generated. The ratio of separation depth to anchor width was found to increase linearly with the ratio of soil undrained shear strength to the product of soil effective unit weight and anchor width and was independent of the initial anchor embedment depth.

Three-dimensional large deformation finite-element analysis of plate anchors in uniform clay

This paper discusses the development of a framework for classifying soil using normalized piezocone test (CPTU) data from the corrected tip resistance ( qt ) and penetration pore-water pressure at the shoulder ( u2 ) . Parametric studies for normalized cone tip resistance (Q= qcnet ∕ σ v0 ′ ) and normalized excess pressures (Δ u2 ∕ σ v0 ′ ) as a function of overconsolidation ratio (OCR= σ vy ′ ∕ σ v0 ′ ) during undrained penetration are combined with piezocone data from clay sites, as well as results from relatively uniform thick deposits of sands, silts, and varietal clays from around the globe. The study focuses on separating the influence of yield stress ratio from that of partial consolidation on normalized CPTU parameters, which both tend to increase Q and decrease the pore pressure parameter ( Bq =Δ u2 ∕ qcnet ) . The resulting recommended classification chart is significantly different from existing charts, and implies that assessment of data in Q–Δ u2 ∕ σ v0 ′ space is superior to Q– Bq space when...

Analysis of Factors Influencing Soil Classification Using Normalized Piezocone Tip Resistance and Pore Pressure Parameters

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.

Rate effects on penetrometer resistance in kaolin

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 fiel...

Penetration of dynamically installed anchors in clay

This paper describes a series of centrifuge model tests designed to assess the increase in capacity of dynamic anchors due to setup in normally consolidated clay. The tests involved measurement of the vertical capacity of 1:200 reduced scale model anchors following various periods of postinstallation consolidation. The short-term capacity was shown to be dependent on the anchor impact velocity. Cavity expansion solutions for consolidation around a solid driven pile were found to provide agreement with the experimental results. A simplified capacity calculation technique predicted higher friction ratio values than is typically observed for driven piles; however, these calculations were complicated by the unusual dynamic anchor load — displacement response and uncertainty regarding the true sample shear strength. Dynamic anchor consolidation proceeds at a slower rate than for suction caissons and open-ended piles of similar equivalent diameter. However, the results indicate that depending on the site conditions, dynamically installed anchors remain a viable alternative to conventional deep-water mooring techniques.

Setup Following Installation of Dynamic Anchors in Normally Consolidated Clay

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 (remesh...

Loss in Anchor Embedment during Plate Anchor Keying in Clay

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...

Conleth O'Loughlin

Papers

Rate effects on penetrometer resistance in kaolin

Penetration of dynamically installed anchors in clay

Setup Following Installation of Dynamic Anchors in Normally Consolidated Clay

Loss in Anchor Embedment during Plate Anchor Keying in Clay

Influence of the installation process on the performance of suction embedded plate anchors