ORCID Profile
0000-0002-7798-3266
Current Organisation
University of Western Australia
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Publisher: American Society of Civil Engineers (ASCE)
Date: 12-2011
Publisher: Elsevier BV
Date: 05-2008
Publisher: Thomas Telford Ltd.
Date: 11-2005
DOI: 10.1680/GEOT.2005.55.9.679
Abstract: Centrifuge model tests and finite element (FE) analysis have been conducted to study the penetration of spudcan foundations in uniform clay with nominally constant strength with depth. In particular, the transition between shallow penetration, with soil heaving to the ground surface, and deep penetration, with a localised flow-round mechanism, has been investigated. This transition governs the onset of back-flow and hence the depth of soil lying on the installed spudcan, which in turn influences the bearing capacity and also the potential for suction to develop and hence the uplift capacity and moment resistance of the foundation. The maximum cavity depth above the spudcan prior to any back-flow is therefore a critical issue for spudcan assessment in clay. In the centrifuge model tests, a half-spudcan model penetrating against a transparent window has been used to visualise the soil flow mechanisms around the spudcan during penetration. The formation of a cavity above the spudcan is revealed by both centrifuge modelling and FE analysis. It is found that there are three distinct penetration mechanisms during spudcan installation: during initial penetration, an open cavity is formed with vertical walls with further penetration, soil flows partially around the spudcan into the cavity during deep penetration, the spudcan is fully embedded and the soil flow mechanism is entirely localised. Over the wide range of normalised soil strengths explored, the soil back-flow in the second stage was shown to be due to a flow failure that was triggered by the spudcan penetration and not by wall failure, that is, the collapse of the vertical sides of the soil cavity. This observation is supported by FE analysis. The cavity depth due to flow failure is much shallower than the criterion for wall failure that is incorporated in current design guidelines. Instead, a new design chart and expression is suggested with the normalised cavity depth expressed as a function of the soil shear strength, normalised by the effective unit weight of the soil and the spudcan diameter.
Publisher: American Society of Civil Engineers (ASCE)
Date: 07-2016
Publisher: American Society of Civil Engineers (ASCE)
Date: 05-2016
Publisher: Thomas Telford Ltd.
Date: 28-06-2023
Abstract: The T-bar penetrometer is currently used to characterise seabed sediments, mostly based on the full-flow mechanism around the probe in soft clays. However, open and trapped cavities may form above the T-bar during its penetration in stiffer clays, which can make the traditional interpretation method inaccurate and requires complex corrections. This paper proposes a novel T-bar test method by adding sufficient surface pressure on the soil surface to ensure the full-flow mechanism and no cavity. In this way, the current formulas based on the full-flow soil mechanism can be directly used to interpret soil strength. To verify the effectiveness of the proposed method, both laboratory tests on kaolin clay and Guangzhou offshore clay and large-deformation finite-element analyses with various surface pressures and soil strengths were conducted. The results show that, if the surface pressure is sufficient, no open cavity or trapped cavity was formed during a monotonic T-bar penetration and the first cycle of cyclic T-bar penetration tests. Without surface pressure, however, an open cavity or trapped cavity was always formed. The cavity formation contributed to a T-bar resistance 7·9–18·6% lower relative to that of a T-bar with sufficient surface pressure to maintain a full-flow mechanism. In the cyclic tests, with an additional number of T-bar loading cycles, the cavity effect diminished and the surface pressure showed minimal effect on the T-bar resistance. A critical surface pressure that ensures the full-flow mechanism was suggested for T-bar monotonic and cyclic tests in the box core s le.
Publisher: Thomas Telford Ltd.
Date: 20-06-2023
Publisher: Thomas Telford Ltd.
Date: 03-2011
DOI: 10.1680/GEOT.8.P.071
Abstract: Although the pullout capacity of plate anchors in clay has been studied extensively, the results considering the coupling effects of anchor inclination, clay non-homogeneity and self-weight are relatively rare. In the present paper, finite-element analyses are carried out to investigate the coupling effects of these factors on the pullout capacity of strip plate anchors in clay. The numerical solutions are presented in the familiar form of pullout capacity factors based on various anchor embedment depth, clay strength profile and clay self weight, and are also compared with existing numerical and empirical solutions. A design procedure based on the data-fitting equations of the present finite-element solutions is also presented for the convenience of design engineers.
Publisher: Elsevier BV
Date: 11-2012
Publisher: Trans Tech Publications, Ltd.
Date: 05-2014
DOI: 10.4028/WWW.SCIENTIFIC.NET/AMM.553.458
Abstract: The effect of the centrifuge strongbox boundary on the penetration resistance of a spudcan foundation in uniform clay has been studied using Large Deformation FE analysis. Both smooth and rough strongbox boundaries were considered with various strongbox sizes. The spudcan penetration resistance and soil flow mechanisms were analysed. It was observed that, when the strongbox size was reduced, the spudcan penetration resistance was decreased for a smooth boundary and increased for a rough boundary. The depth of cavity formed above the spudcan during its penetration, in most cases, was determined by the soil flow around mechanism without cavity wall failure. However, cavity wall failure could be initiated when a smooth strongbox boundary was very close to the spudcan. The strongbox boundary effect on the spudcan penetration resistance can be avoided when the distance of the strongbox boundary to the spudcan centre is larger than 1.5 times of spudcan diameter for a rough boundary or 2 times of spudcan diameter for a smooth boundary.
Publisher: American Society of Civil Engineers (ASCE)
Date: 09-2018
Publisher: Canadian Science Publishing
Date: 08-2017
Abstract: The presence of a thin soft clay layer inside a bed of sand may significantly reduce the bearing capacity of the sand layer, imposing a risk of punch-through failure. In this paper, finite element (FE) simulations are reported using a hardening soil (HS) model for sand. The FE model has been verified against centrifuge tests involving loose and dense sand layers overlying clay soil. The effects of sand stiffness, foundation roughness, sand friction angle, undrained clay strength, clay strength nonhomogeneity, and sand and clay layer geometries on the foundation peak capacities have been studied. Punch-through failure is initiated with an inclined sand plug being sheared and pushed into the underlying soft clay. During punch-through, the clay layer fails due to significant radial squeezing. Existing analytical models do not capture the combined failure mechanism of sand shearing and clay radial squeezing. A new analytical model is developed to estimate the peak punch-through capacity of a spudcan in sand with an interbedded clay layer, showing improved performance over the current industry guidelines.
Publisher: Thomas Telford Ltd.
Date: 06-2013
Abstract: The spherical ball penetrometer is increasingly being used for profiling the undrained shear strength of soils in centrifuge and offshore site investigations. This paper reports the results from large-deformation finite-element (LDFE) analysis undertaken to provide insight into ball penetrometer behaviour during undrained vertical penetration through uniform and stratified clay deposits. The LDFE analyses simulated continuous penetration of ball penetrometers from the seabed surface. The results were validated against centrifuge test data and plasticity solutions prior to undertaking a detailed parametric study, exploring a range of normalised soil properties and layer thicknesses and roughnesses of the soil/ball interface. The influence of the shaft (or area ratio) was also identified. The evolving soil failure patterns in single- and double-layer soils revealed two interesting aspects: soil backflow above the penetrometer, and trapping of the stronger material beneath the penetrometer. A framework has been proposed to account for these effects, which will allow accurate interpretation of soil undrained shear strength from the ball penetration resistance.
Publisher: Elsevier BV
Date: 12-2022
Publisher: Thomas Telford Ltd.
Date: 10-2000
DOI: 10.1680/GEOT.2000.50.5.573
Abstract: The shear strength of soft sediments may be assessed by field tests, principally either vane tests or cone penetrometer tests. The continuous profile of strength obtained from the cone penetrometer is an advantage over the vane test, although the significant corrections for overburden stress, and pore pressure acting on the back face of the cone, limit its accuracy in soft soils. Alternative shapes for penetrometers have been suggested, for ex le a cylindrical T-bar and a spherical ball, both of which allow full flow of soil around the probe, thereby obviating the need for corrections due to the ambient stress level. Plasticity solutions have been available for some while relating the (average) shear strength of the soil to the net bearing pressure for plane strain flow around the cylindrical T-bar. This paper documents a corresponding solution for a spherical penetrometer, using upper and lower bound approaches supported by finite element analysis. Effects of strength anisotropy are discussed in the light of ex le results comparing the measured resistance of cone, T-bar and ball penetrometers.
Publisher: Elsevier BV
Date: 06-2012
Publisher: American Society of Civil Engineers (ASCE)
Date: 2016
Publisher: Elsevier BV
Date: 10-2018
Publisher: Elsevier BV
Date: 07-2020
Publisher: Elsevier BV
Date: 09-2017
Publisher: Informa UK Limited
Date: 16-07-2020
Publisher: Canadian Science Publishing
Date: 04-2016
Abstract: Cast-in-place concrete large-diameter pipe (PCC) piles have been widely used in highway construction for foundation reinforcement, where soft ground was encountered, due to their fast on-site construction and high capacity, hence economics. This paper reports the performance of their first application in high-speed railway foundation reinforcement on soft soil ground. To satisfy the strict settlement requirement for railway design, PCC piles with large diameters (D = 1 m), thick pile wall thicknesses (t = 0.15 m), and close spacing (s = 2.5 m) were constructed. The foundation performance has been monitored by measuring in situ foundation settlement, excess pore pressure in soil, lateral displacement of soil, and tension in the geogrid during and after embankment construction. The measurements of this project have been compared with that of a previous project when PCC piles were used. It is found that the PCC pile arrangement in this project has performed as predicted and fulfilled the strict settlement requirement set by the Chinese design guidelines.
Publisher: American Society of Civil Engineers (ASCE)
Date: 08-2020
Publisher: American Society of Mechanical Engineers
Date: 19-06-2016
Abstract: The interaction between a spudcan and an existing footprint is one of the major concerns during jack-up rig installation, especially in the surface clay layer. No guidance was provided in the recently finalised version of ISO guidelines 19905-1 [1] in regards to mitigating spudcan-footprint interaction issues except some proposed considerations due to the lack of detailed investigations. This paper reports a measure for easing spudcan-footprint interaction issues, with the efficiency of a novel spudan shape tested through 3D large deformation finite element (LDFE) analyses. The LDFE analyses using the Coupled Eulerian-Lagrangian (CEL) approach in the commercial finite element package ABAQUS. The soil conditions tested simulate soft seabed strength profiles close to the mudline. A critical reinstallation locations of 0.55D (D = spudcan diameter) and existing footprint depth (of 0.33D) were investigated. The main aim was to investigate if the spudcan shape itself can be used to mitigate potential footprint interaction when compared to a conventional spudcan. The results from this study indicated that the novel spudcan had the potential to ease spudcan-footprint interaction issues.
Publisher: Elsevier BV
Date: 07-1998
Publisher: Elsevier BV
Date: 04-2020
Publisher: Thomas Telford Ltd.
Date: 05-2017
Abstract: This paper presents a comparison of extraction resistance between spudcan and skirted foundations in sand-over-clay deposits. A series of centrifuge model tests was undertaken on a spudcan and two skirted foundations, varying the length of the skirt relative to the foundation diameter. The thickness of the sand layer was also varied to cover a range of practical interest. It was found that the ultimate breakout forces of the spudcan and ‘sealed’ skirted foundations in the sand-over-clay deposits are lower than that of a spudcan in a single-layer clay deposit. On the sand-over-clay deposits, when the skirted foundations are sealed, the breakout forces are 60∼61% higher than that of the spudcan. However, when the skirted foundations are vented, this difference becomes minimal, regardless of the skirt length and the effective sand layer thickness beneath the foundation, with the height of the sand plug left in the clay layer being similar to the thickness of the sand layer.
Publisher: Informa UK Limited
Date: 04-2012
Publisher: Canadian Science Publishing
Date: 04-2012
DOI: 10.1139/T2012-008
Abstract: Structural stiffeners placed inside caissons have created significant uncertainty regarding soil flow mechanisms, side friction, and end bearing, and consequently in the prediction of the underpressure required for installation. This paper describes centrifuge modelling of the penetration of stiffened skirts in overconsolidated clay, identifying the soil flow mechanisms around and between stiffeners and the penetration resistance. The effects of stiffener width and spacing as well as soil strength ratio are discussed. The present guidelines for predicting the point of soil backflow in the gap that forms between the stiffeners are shown to be invalid and a new expression, based on a stability factor (s u /γ′B, where s u and γ′ are the undrained shear strength and effective unit weight of the soil, respectively, and B is the combined width of the skirt and stiffener close to the caisson tip) is proposed. End bearing at the skirt tip and base stiffener are seen to dominate installation resistance. The normalized installation resistance stabilizes at a value of ∼17.5 at deep penetrations and is shown to be independent of whether the cavity between the stiffeners remains open or is backfilled with a soil–water mixture. This factor of 17.5 is shown to be in good agreement with reported field data and centrifuge test data and hence may be used to obtain a first-order estimate of the installation resistance of a caisson with stiffeners.
Publisher: CRC Press
Date: 14-05-2015
DOI: 10.1201/B18442-187
Publisher: Elsevier BV
Date: 06-2018
Publisher: American Society of Mechanical Engineers
Date: 08-06-2014
Abstract: Continuous profiles from in-situ penetrometer tests are now identified as essential for site specific soil investigation as part of designing offshore structures in deep and ultradeep waters and in highly layered seabed conditions. This paper describes the results from large deformation FE (LDFE) analysis undertaken to provide insight into the behavior of cone penetrometer penetrating through single layer non-homogeneous clays and three-layer uniform soft-stiff-soft clays. For the smooth cone penetration in non-homogeneous clays, the soil strength non-homogeneity factor was shown to have insignificant effect on the cone bearing capacity factor. However, for the rough cone, the bearing capacity factor in non-homogeneous clay was about 10∼12% lower than that in uniform clay. Bearing capacity factors for smooth and rough cones were also similar for non-homogeneous clay. For cone penetration in stratified soft-stiff-soft clays, a minimum layer thickness of 20 diameters was required to mobilise the full resistance of the stiff layer. The corresponding soil flow mechanisms are also discussed linking directly to the profile of penetration resistance.
Publisher: American Society of Civil Engineers (ASCE)
Date: 09-2017
Publisher: Springer Science and Business Media LLC
Date: 27-04-2021
Publisher: CRC Press
Date: 23-06-2022
Publisher: Elsevier BV
Date: 2009
Publisher: CRC Press
Date: 18-12-2014
DOI: 10.1201/B16200-51
Publisher: American Society of Civil Engineers (ASCE)
Date: 09-2020
Publisher: Thomas Telford Ltd.
Date: 09-2017
Abstract: Large deformation finite-element analyses were conducted to explore the effect of the container lateral boundary in centrifuge tests where a large offshore foundation is tested. A spudcan foundation, typically used to support jack-up drilling rigs, was penetrated into uniform clay, uniform sand and sand overlying clay stratigraphies under rough and smooth lateral boundary conditions. The effect that the proximity of the container lateral boundary has on the measured load–penetration response is quantified. The boundary impact varies with the soil profile and boundary roughness, and for sand-only or sand-over-clay conditions the required separation between the foundation and the container boundary is far greater than in clay-only conditions. In most cases, during large penetration of the spudcan foundation, the largest influence from the lateral boundary was on peak resistance, and diminished during the subsequent deeper penetration. For practical use, a centrifuge container design chart is proposed to check whether the dimensions are adequate for the foundation and model size to be used in an experiment. It is shown that the results from many earlier studies could have been potentially influenced by container boundary effects.
Publisher: Springer Singapore
Date: 04-09-2019
Publisher: American Society of Mechanical Engineers
Date: 09-06-2019
Abstract: This paper describes a numerical study on soil characterization of stiff over soft clays in centrifuge test using cone penetration test (CPT), especially when the top stiff layer is thin relative to the centrifuge cone size. An extensive parametric study was conducted using large deformation finite element (LDFE) analysis, with the cone penetrating continuously from the soil surface. The LDFE model has been validated against existing physical test data with very good agreement. Since the bottom soft clay was normally thick enough to fully mobilise the ultimate cone resistance, its undrained shear strength can be interpreted by the existing approach for cone deep penetration in a uniform clay layer. Thus, the challenge was to interpret the strength of the top stiff layer, where the layer thickness was not thick enough to fully mobilise its ultimate resistance. Both top layer thickness ratios (to the cone diameter) and layer strength ratios were considered in the parametric study. Based on the results from LDFE analyses, the interpretation formula of the undrained shear strength in the top stiff layer was proposed as a set of new bearing factors. The proposed cone bearing factor was a function of the ratio of the measured peak cone resistance in the top layer to the stable/ultimate cone resistance in the bottom layer and the ratio between the top layer thickness to the cone diameter. The formula can be used directly when the top layer thickness was known based on the s le preparation. However, the layer interface can be identified based on the study here, if the top layer thickness was not certain. A design flow chart was provided for interpretations of top clay layer strength and top layer thickness based on the cone resistance profile obtained from CPT test.
Publisher: American Society of Civil Engineers (ASCE)
Date: 02-2010
Publisher: Thomas Telford Ltd.
Date: 09-2014
Abstract: Centrifuge model tests of deeply penetrating foundations have been widely used to assess the vertical bearing response, particularly in relation to the installation of spudcan foundations that support offshore drilling rigs. The potential influence of boundary effects owing to the proximity of these large foundations to the rigid base of the model container has not been previously addressed. In this study, large deformation finite-element (LDFE) analyses were conducted to assess the extent of the bottom boundary influence zone. Various foundation diameters were considered, with soil s les of sand overlying clay and uniform clay. The sand plug developed beneath the foundation is a major contributary factor to the boundary effect problem. The boundary effect is increased for sand over clay conditions, where a sand plug is entrapped beneath the foundation. The LDFE results were utilised to predict the thickness of the entrapped sand plug for different geometry and soil strength conditions. The results are distilled into a simple relationship that can be used to ascertain the bottom boundary influence zone when planning physical model tests and reinterpreting previous studies. The boundary influence zone predicted by the LDFE analysis agreed well with a corresponding centrifuge test.
Publisher: American Society of Civil Engineers (ASCE)
Date: 10-2009
Publisher: Elsevier BV
Date: 06-2017
Publisher: Elsevier BV
Date: 03-2019
Publisher: Thomas Telford Ltd.
Date: 05-2020
Abstract: Spudcan punch-through in layered seabed sediments is one of the major concerns for the jack-up industry. This paper reports the results from a series of centrifuge model tests undertaken to assess the effect of various shapes of spudcan base at mitigating punch-through in sand-over-clay deposits. The experimental programme was carried out in a drum centrifuge by varying the spudcan base profile, skirt length on the periphery and number of holes through the spudcan. The large testing area of one soil s le prepared along the full drum channel enabled an extensive number of 13 spudcan penetration tests under consistent soil conditions. Additional large-deformation finite-element analyses were carried out to explore the soil failure mechanisms around each spudcan with different shapes. The spudcan base profile and number of holes through the spudcan showed no apparent influence on the spudcan penetration behaviours, as the sand blocked the spudcan holes during penetration. Only the skirt showed a positive influence at mitigating punch-through. The positive influence was greater with a longer skirt.
Publisher: Thomas Telford Ltd.
Date: 03-2014
Abstract: Mitigation of spudcan punch-through is one of the principal aspects for inclusion in the ISO standard 19905-1. This paper investigates the potential for using skirted foundations as an alternative to spudcans in an attempt to mitigate punch-through failure of jack-up rigs during installation and preloading in sand-over-clay deposits. A series of centrifuge model tests is undertaken on a spudcan and two skirted foundations, varying the length of the skirt relative to the foundation diameter. The thickness of the sand layer is also varied to cover a range of practical interest. The results from this study confirm that the use of skirted foundations as an alternative to spudcans can eliminate the potential of punch-through failure on sand-over-clay deposits. The degree of post-peak bearing reduction, one of the key measures of the severity of punch-through failure, is shown to be linked directly to the effective sand layer thickness beneath the foundations. Skirted foundations assist in mitigating the severity of punch-through failure by reducing the effective sand layer thickness.
Publisher: American Society of Civil Engineers (ASCE)
Date: 11-1999
Publisher: Elsevier BV
Date: 12-2022
Publisher: Canadian Science Publishing
Date: 07-2016
Abstract: There is a historic lack of research examining inner soil plugging and outer lateral soil deformation during installation of pipe piles in clay. Furthermore, the influence of the pile tip geometry on soil deformation has not been investigated. Cast-in-place concrete pipe (PCC) piles are a recent generation of pipe piles for soft ground improvement applications, and are cast in place using an innovative double-walled steel casing with a tapered tip. This paper investigates the effect of tip geometry on soil flow mechanisms inside and outside the PCC pile casing during installation in clay. Large-deformation finite element (LDFE) analysis was conducted simulating the continuous penetration process of the casing installation. The LDFE results were validated against (i) field monitoring data in terms of soil lateral displacement and heave outside the casing and (ii) centrifuge test data in terms of penetration resistance, with excellent agreement obtained. An extensive parametric study was then performed encompassing a practical range of parameters. The geometry of the casing tip was shown to have significant influence on the soil movements inside and outside the casing, but minimal effect on the casing penetration resistance. The optimal tapered tip with a tip angle of 45° and minimal extended tip length beneath the tip angle allowed more soil to be pushed inside the casing and less lateral displacement outside the casing, which dictates the amount of concrete required to fill the cavity inside the pile and the pile construction sequence, respectively. Design expressions are proposed for estimating soil movements inside and outside the casing with optimal tip geometry being installed.
Publisher: Elsevier BV
Date: 06-2018
Publisher: American Society of Civil Engineers (ASCE)
Date: 09-2022
Publisher: Elsevier BV
Date: 10-2021
Publisher: American Society of Civil Engineers
Date: 05-05-2014
Publisher: CRC Press
Date: 11-07-2018
Publisher: Thomas Telford Ltd.
Date: 08-2017
Abstract: Severe punch-through of jack-up rig foundations can occur due to the presence of a stronger sand layer in a bed of relatively soft clay. Analytical estimation of the bearing capacity and leg load–penetration response on such multi-layer stratigraphies is challenging. Accurate mechanism-based models need to be established in each of the layers involved and the effects of the mechanisms in each of the layers on the response in the other layers must be captured. Based on the recently developed failure stress-dependent punch-through models for sand–clay stratigraphies, an extended model is proposed for clay–sand–clay stratigraphies. Half-spudcan particle image velocimetry centrifuge tests and full-spudcan centrifuge tests are used in developing and validating the extended model. The centrifuge test results were discussed in a companion paper and this paper focuses on the analytical developments and prediction assessment. Both spudcan peak resistance (q peak ) and spudcan punch-through depth (d punch ) can be estimated using the model. The predictions by the extended model and by the current industry guidelines are compared against the centrifuge test data. The extended model proposed in this paper outperforms the approaches suggested in the guidelines. An advantage of the proposed approach is that it can be used for either sand–clay or clay–sand–clay scenarios and exhibits excellent performance compared to the model testing dataset considered in this work for both cases. The resulting penetration resistance model is a useful design tool for routine punch-through risk assessment.
Publisher: Thomas Telford Ltd.
Date: 10-2017
Abstract: This paper is concerned with the vertical penetration resistance of conical spudcan and flat footings in layered soils. Centrifuge tests are reported for a clay bed with strength increasing with depth interbedded with dense and medium dense sand. Both non-visualising (full-model) and visualising (half-model) tests were conducted with high-quality digital images captured and analysed using the particle image velocimetry technique for the latter. The load–displacement curves often show a reduction in resistance on passing through the sand layers, which creates a risk of punch-through failure for the foundations when supporting a jack-up drilling unit. For a given foundation, the peak punch-through capacity (q peak ) is dependent on the thickness of both the overlying clay and the sand layer. The failure mechanism associated with the peak resistance in the sand layer involves entrapment of a thin band of top clay above the sand layer that subsequently shears along an inclined failure surface before being pushed into the underlying clay. The top clay height when normalised by the foundation diameter affects the soil failure pattern in this layer and along with the sand layer thickness controls the severity of the punch-through failure (i.e. the additional penetration before the resistance returns to the peak value). Comparisons are made with current industry guidelines for predicting q peak and the risk of punch-through failure for sand overlying clay. These methods are shown to be conservative in their prediction of q peak but inconsistent in predicting punch-through.
Publisher: ASTM International
Date: 12-05-2017
DOI: 10.1520/GTJ20160163
Publisher: Elsevier BV
Date: 10-2021
Publisher: Springer Science and Business Media LLC
Date: 17-06-2018
Publisher: Elsevier BV
Date: 06-2019
Publisher: American Society of Civil Engineers (ASCE)
Date: 2011
Publisher: American Society of Civil Engineers (ASCE)
Date: 06-2008
Publisher: American Society of Mechanical Engineers
Date: 08-06-2014
Abstract: The rapid penetration of one or more of the foundations of a mobile jack-up rig into the seabed is an ongoing major problem in the offshore industry, with the potential to cause major damage to the structure and endangering any personnel on board. A recent ex le is the jack-up drilling rig Perro Negro 6 incident happened near the mouth of the Congo river in July 2013 with one of the rig’s crew of 103 reported missing and six others injured. This uncontrollable displacement is due to a form of failure known as punch through failure and commonly occurs on stratified seabed profiles. It has been reported that unexpected punch-through accidents have resulted in both rig damage and lost drilling time at a rate of 1 incident per annum with consequential costs estimated at between US$1 and US$10 million [1]. This paper presents the bearing capacity profiles and associated soil flow mechanisms of a common spudcan foundation penetrating into a three layer soft-stiff-soft clay soil through the use of large deformation finite element (LDFE) analysis. The Remeshing and Interpolation with Small Strain (RITSS) [2, 3] technique was implemented in the software package AFENA [4] to conduct the LDFE analysis. Both soil layer thickness and soil layer strength ratios were varied to study their effect on the spudcan penetration responses. The LDFE results of spudcan penetration into the soft-stiff-soft clay soils were calibrated by existing centrifuge test data. A parametric study was then conducted to study the bearing capacity responses and soil flow mechanisms during spudcan large penetrations by varying the soil layer strength ratio and relative layer thickness to the diameter of spudcan. It was found that there were three types of bearing responses during continuous penetration of spudcan: (a) when the top soft layer is relatively thin, the spudcan bearing response was similar to that of two layer soils with stiff over soft clays (b) when the top soil layer thickness is medium, a peak resistance is observed when spudcan penetrates into the middle stiff layer followed by reduction (c) when the soil layer is thick, the peak resistance occurs when spudcan gets into the bottom soft soil layer. The critical thickness of top soil layer is a function of soil strength ratio and middle stiff soil layer thickness. The bearing response types were also corresponding to the soil cavity formations during spudcan initial penetration.
Publisher: Canadian Science Publishing
Date: 11-2020
Abstract: This paper reports the soil flow mechanisms observed in centrifuge tests around full-flow (T-bar and ball) penetrometers in layered clays. The layered clay s les consisted of soft–stiff, stiff–soft, soft–stiff–soft, and stiff–soft–stiff soil profiles. Particle image velocimetry (PIV), also known as digital image correlation (DIC), allowed accurate resolution of the flow mechanism around the faces of the T-bar and half-ball penetrated adjacent to a transparent window. For the T-bar, overall, a full symmetrical rotational flow around the T-bar dominated the behavior. A novel “trapped cavity mechanism” was revealed in stiff clay layers, with the evolution of the trapped cavity being tracked. No soil plug was trapped at the base of the advancing T-bar regardless of penetration from stiff to soft layer or the reverse. For the ball, two key features of the soil flow mechanism were identified, including (i) a combination of vertical flow, cavity expansion type flow, and rotational flow for a fully embedded ball and (ii) a stiff soil plug trapped at the base of the ball advancing in a stiff–soft clay deposit. For both penetrometers, a squeezing mechanism mobilized as they approached a soft–stiff layer interface.
Publisher: Elsevier BV
Date: 03-2016
Publisher: Thomas Telford Ltd.
Date: 05-2004
Publisher: Canadian Science Publishing
Date: 05-2018
Abstract: The length of suction caisson anchors has been increasing to support increasing dimensions and weight of floating facilities, which necessitates employing horizontal ring stiffeners at intervals along the inner wall of the thin skirt of caissons to ensure structural integrity. The addition of these stiffeners has created significant uncertainties regarding soil flow mechanisms, in particular soil heave inside the caisson, which may reduce the caisson final penetration depth and influence the process of installation due to the need to avoid inside soil suction in the pumping equipment. This paper reports results of large-deformation finite element (LDFE) analyses investigating soil heave inside stiffened caissons during installation in nonhomogeneous clay deposits, with the corresponding evolution of soil flow mechanisms and penetration resistance profiles reported by Zhou et al. in 2016. The LDFE analyses have simulated continuous penetration of stiffened caissons from the seabed surface. A detailed parametric study has been undertaken, exploring the relevant range of soil strength nonhomogeneity and normalized strength, stiffened caisson geometry, soil effective unit weight, and caisson roughness. Of particular interest is the influence of stiffeners on soil heave and potential penetration refusal. The results have been validated against previously published centrifuge test data in terms of soil heave and penetration resistance profile, with good agreement obtained. It is shown that the soil normalized strength at the mudline and its nonhomogeneity, caisson diameter relative to the sum of skirt thickness and stiffener width, and caisson penetration depth have significant influence on the inner soil heave and its profile across the caisson radius. An expression, based on the LDFE results is proposed to predict the maximum inner soil heave during installation of stiffened caissons in the field.
Publisher: Elsevier BV
Date: 07-2018
Publisher: Informa UK Limited
Date: 31-05-2023
Publisher: Thomas Telford Ltd.
Date: 05-2022
Abstract: The cone penetrometer test is widely used for in situ site investigations and for establishing direct penetrometer-to-foundation or -anchor design correlations. This paper focuses on soil flow mechanisms during the continuous penetration of a cone penetrometer in layered clays. A series of centrifuge tests was conducted with the cone penetrating through soft–stiff, stiff–soft, soft–stiff–soft and stiff–soft–stiff clay profiles. Particle image velocimetry allowed accurate resolution of the soil flow mechanism around the cone where a half-cone model was penetrated into layered clays against a transparent window. The observed soil movement was compared both with previous observations for piles/cones and with movement from the shallow strain path method (SSPM). A comparison with SSPM results showed that the SSPM can provide reasonable evaluations on maximum lateral and vertical displacements even though the upheave movement can be overestimated. The effect of soil layering on the failure mechanisms was studied extensively by exploring soil flow mechanisms and soil displacement paths at various distances from the advancing cone centreline and soil layer interface. The reported characteristics of cone penetration in layered soils provided in-depth understanding of cone penetration responses that will lead to the development of mechanism-based theoretical models for cone penetration in layered fine-grained soils.
Publisher: International Society of Offshore and Polar Engineers
Date: 12-2017
Publisher: American Society of Civil Engineers (ASCE)
Date: 11-2023
Publisher: Elsevier BV
Date: 05-2009
Publisher: American Society of Civil Engineers (ASCE)
Date: 02-2016
Publisher: CRC Press
Date: 11-07-2018
Publisher: Elsevier BV
Date: 07-2018
No related grants have been discovered for Yuxia Hu.