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ItemPlate anchor capacity estimation through CPT tip resistance in sandRoy, A ; Chow, S ; Gottardi, G ; Tonni, L (Taylor and Francis group, 2022-06-15)Reliable estimation of plate anchor uplift capacity in sand through analytical and empirical equations is often complicated due to uncertainties in estimation of soil properties required in the equations. In order to address this uncertainty, this study proposes a correlation to estimate plate anchor vertical uplift capacity in sand based on cone tip resistance measured from cone penetrometer tests (CPT). The correlation was established using a database of reported centrifuge experiments on circular, rectangular and strip anchors in loose and dense silica sand at various embedment depths and g-levels, along with the corresponding centrifuge CPTs performed in the same testing boxes. The centrifuge cone tip resistances were also depth-corrected to remove the effect of shallow embedment. Through regression analyses, the correlation between plate anchor capacity and cone tip resistance in dimensionless form was developed, with different coefficients fitted for circular, rectangular and strip anchors respectively.
ItemMacro-element modelling of plate anchor kinematics under cyclic loading in clayda Silva, AP ; Diambra, A ; Karamitros, D ; Chow, SH (Deep Foundations Institute, 2020)With the recent shift of offshore renewable energy sector towards deeper waters, the use of floating structures anchored to the seabed through mooring lines is becoming an appealing solution. Several researchers have carried out experimental and numerical analyses to assess the behaviour of plate anchors. However, being able to quickly predict the overall anchor behaviour during keying and operational loads is important for design purposes and to assess their field performance; for this purpose, macro-element modelling is a powerful and timeefficient tool which requires minimal computational effort. In that context, this paper expands a non-associative model for plate anchors to account for the effects of cyclic loading. Whereas the effects of pore-pressure generation, consolidation and eventual material de-structuration were neglected and need to be accounted for in future studies, this study shows that the anchor’s capacity decrease occurs not only due to changes in soil conditions, but also to the particular evolution of anchor’s kinematics due to anchor re-orientation during cyclic loading.
ItemCyclic capacity of plate anchors in loose sandChow, SH ; Diambra, A ; Roy, A ; O'Loughlin, C ; Gaudin, C (Deep Foundations Institute, 2020)This paper describes a centrifuge investigation on drained monotonic and cyclic capacity of a plate anchor in dry loose sand. The model rectangular plate anchor was pre-embedded vertically at an embedment depth of 5 times the plate width, and was loaded horizontally at the mudline with monotonic or irregular cyclic loading to failure. The anchor was also instrumented with an accelerometer to investigate the plate rotation or ‘keying’ behaviour. The monotonically and cyclically loaded anchors are found to share similar plate rotation behaviour. Depending on the applied cyclic load magnitude, the anchor produces post-cyclic ultimate capacity that is up to 7% higher than the reference ultimate monotonic capacity. When compared to existing studies using similar plate anchor in dense sand, the plate anchor in loose sand exhibits a lower gain in post-cyclic ultimate capacity relative to the ultimate monotonic capacity, a softer load-displacement response and a higher plate anchor rotation at ultimate capacity.
ItemRapid penetration of spudcans in sandChow, SH ; Bienen, B ; Randolph, M (Deep Foundation Institute, 2020)The growing pressure for jack-up rigs to relocate during more challenging metocean conditions for offshore wind turbine installation and maintenance has increased the risk of dynamic leg loading during the set down of the spudcan footings into the seabed. To better understand the rapid sand-spudcan interaction, this study presents experimental results of a model spudcan jacked at a range of penetration rates into dry and saturated sand at both 1g and 50g gravitational acceleration. In order to achieve a wide range of consolidation conditions, the sand was saturated using both water and a viscous pore fluid (methocel cellulose ethers) with kinematic viscosity 680 times higher than water in the 50g centrifuge tests. The results indicated up to 120% increase in spudcan penetration resistance due to the dilatancy-induced suction when the consolidation response changes from drained to undrained. This change in spudcan penetration resistance is quantified using a proposed backbone curve framework.