An extended interpretation of the free-fall piezocone test in clay

Chow, Shiao Huey; O’Loughlin, Conleth; White, David; Randolph, Mark

doi:10.1680/jgeot.16.p.220

Cited by 18 publications

(19 citation statements)

References 21 publications

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“…Several studies (Medeiros, 2002;de Araujo et al, 2004;Brandão et al, 2006;Richardson et al, 2009;O'Loughlin et al, 2009O'Loughlin et al, , 2013Chow et al, 2014;Hossain et al, 2014Hossain et al, , 2015Kim et al, 2015) have adopted such an approach, with variations on the inclusion and formulation of the various forces acting on a torpedo anchor. A similar approach is adopted here…”

Section: Extended Bearing Resistance Methodsmentioning

confidence: 99%

“…For the frictional resistance, R f2 was taken as 2R f1 from the previous reports (Einav and Randolph, 2006;Chow et al, 2014;Steiner et al, 2014). The predictions made the same assumptions based on the findings from the parametric studies, adopting _ γ ref ¼ 0.1 s À 1 and ξ a ¼0.35.…”

Section: Extended Bearing Resistance Methodsmentioning

confidence: 99%

“…They reported typical values of η and β in the range of 0.1-2.0 and 0.05-0.15, respectively, using _ γ ref ¼0.06 s À 1 . O' Loughlin et al (2013) and Chow et al (2014) used _ γ ref ¼0.17 s À 1 and 0.1 s À 1 for analysing centrifuge test data form installation of torpedo anchors and a dynamic cone penetrometer, respectively, in kaolin clay. Based on these, here a value of _ γ ref ¼0.1 s À 1 was adopted, and rate parameters were varied as η¼ 0.1-1.5 and β ¼0.05-0.2.…”

Section: Incorporation Of Combined Effects Of Strain Rate and Strain mentioning

confidence: 99%

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Effect of strain rate and strain softening on embedment depth of a torpedo anchor in clay

2015

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a b s t r a c tTorpedo anchors (of diameter $ 1 m) are released from a height of 50-100 m from the seabed, achieving velocities up to 35 m/s at impacting the sediment. The strain rates induced in the surrounding soil by this dynamic installation is therefore significantly higher than those associated with installation of other offshore foundations and anchoring systems. The high strain rates enhance the mobilised undrained shear strength compared to that measured by in-situ penetrometer or laboratory tests. This paper reports the results from dynamic installation of a torpedo anchor in strain softening, rate dependent soft clays, quantifying the effects relative to results for ideal Tresca material. The three-dimensional dynamic large deformation finite element (LDFE) analyses were carried out using the coupled EulerianLagrangian approach. The simple elastic-perfectly plastic Tresca soil model was modified to allow strain softening and strain rate dependency of the shear strength. Parametric analyses were undertaken varying the strain rate parameter, the sensitivity and ductility of the soil, and the soil undrained shear strength. Overall, embedment depth for rate dependent, strain softening clays lay below that for ideal Tresca material. Increased strain rate dependency of the soil led to marked reduction in embedment depth, only partly compensated by brittleness. Key results have been presented in the form of design charts, fitted by simple expressions to estimate the embedment depth of a torpedo anchor.

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Section: Extended Bearing Resistance Methodsmentioning

confidence: 99%

Section: Extended Bearing Resistance Methodsmentioning

confidence: 99%

Section: Incorporation Of Combined Effects Of Strain Rate and Strain mentioning

confidence: 99%

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Effect of strain rate and strain softening on embedment depth of a torpedo anchor in clay

2015

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“…True, 1974;O'Loughlin et al 2013;Chow et al 2014;Hossain et al 2015;Kim et al 2015aKim et al , 2015b …”

Section: Dynamic Installation Of a Torpedo Anchor In Two-layered Claysmentioning

confidence: 99%

Dynamic installation of a torpedo anchor in two-layered clays

Kim¹,

Hossain²,

Lee

2018

Can. Geotech. J.

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The behaviour of a torpedo anchor during dynamic installation in two-layered nonhomogeneous clay sediments was investigated through large-deformation finite-element (LDFE) analyses. Parametric analyses were undertaken varying the top layer thickness and strength ratio between two layers. Results show that the location of the demarcation point between the acceleration and deceleration phases of the anchor in the soil relative to the layer interface is the key factor directing the anchor behaviour in layered soils including the final embedment depth. Broadly speaking, the anchor behaviour in soft-over-stiff clay deposits is somewhat similar to that in single layer clay with strength increasing with depth. In stiff-over-soft clay deposits, the anchor penetrates deeper where the anchor deceleration phase (or the demarcation point) falls within the soft layer. Where the demarcation point lies within the top stiff layer, the anchor penetration depth decreases with increasing strength ratio, and the anchor penetration is terminated between the two layers for strength ratios ≥15. For assessing the anchor embedment depth in two-layered fine-grained ocean sediments in the field, an extended total energy–based method, along with a design expression, is proposed.

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“…Bearing resistance method Due to the relative scarcity of investigations to assess installation depths of torpedo anchors, current practice relies on the limit equilibrium method proposed by True (1974), based on Newton's second law of motion and considering uniform clay. Several studies (Medeiros, 2002;de Araujo et al, 2004;Brandão et al, 2006;Richardson et al, 2009;O'Loughlin et al, 2009, Chow et al, 2014Hossain et al, 2014) have adopted a similar approach, with variations on the inclusion and formulation of the various forces acting on the torpedo anchor. The equations of motion may be expressed as …”

Section: Previous Workmentioning

confidence: 99%

Numerical investigation of dynamic installation of torpedo anchors in clay

Kim¹,

Hossain²,

Wang³

et al. 2015

Ocean Engineering

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a b s t r a c tThis paper reports the results from three-dimensional dynamic finite element analysis undertaken to provide insight into the behaviour of torpedo anchors during dynamic installation in non-homogeneous clay. The large deformation finite element (LDFE) analyses were carried out using the coupled EulerianLagrangian approach, modifying the simple elastic-perfectly plastic Tresca soil model to allow strain softening, and incorporate strain-rate dependency of the shear strength using the Herschel-Bulkley model. The results were validated against field data and centrifuge test data prior to undertaking a detailed parametric study, exploring the relevant range of parameters in terms of anchor shaft length and diameter; number, width and length of fins; impact velocity and soil strength. The anchor velocity profile during penetration in clay showed that the dynamic installation process consisted of two stages: (a) in Stage 1, the soil resistance was less than the submerged weight of the anchor and hence the anchor accelerated; (b) in Stage 2, at greater penetration, frictional and end bearing resistance dominated and the anchor decelerated. The corresponding soil failure patterns revealed two interesting aspects including (a) mobilization of an end bearing mechanism at the base of the anchor shaft and fins and (b) formation of a cavity above the shaft of the installing anchor and subsequent soil backflow into the cavity depending on the soil undrained shear strength. To predict the embedment depth in the field, an improved rational analytical embedment model, based on strain rate dependent shearing resistance and fluid mechanics drag resistance, was proposed, with the LDFE data used to calibrate the model.

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An extended interpretation of the free-fall piezocone test in clay

Cited by 18 publications

References 21 publications

Effect of strain rate and strain softening on embedment depth of a torpedo anchor in clay

Effect of strain rate and strain softening on embedment depth of a torpedo anchor in clay

Dynamic installation of a torpedo anchor in two-layered clays

Numerical investigation of dynamic installation of torpedo anchors in clay

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