vertical cyclic loading response of shallow skirted foundation in soft normally consolidated clay skirted foundations are a potential foundation solution for a range of offshore structures including hydrocarbon and renewable energy platforms and subsea structures offshore foundations can be s

effects of preloading and consolidation on the uplift capacity of skirted foundations centrifuge tests investigating the effect of compressive preloading and consolidation on the subsequent uplift capacity of shallow skirted foundations that rest on lightly over consolidated kaolin clay are reported the uplift resistance total and pore pressures at the foundation invert were monitored during the installation consolidation and uplift the results show that uplift performed immediately after the preloading generates a lower capacity due to the remoulding of the clay and reduction in soil strengths that result from the application of preloading the soil strength can be recovered and eventually enhanced by the subsequent consolidation process a theoretical framework where the variation of the soil operative strength with preloading and consolidation is interpreted using the critical state concept is proposed to explain and justify the experimental observations the framework is validated through retrospective prediction of the uplift resistance of the centrifuge model tests with good ag

oceanic and atmospheric transport of multiyear el nino southern oscillation enso signatures to the polar regions 1 using monte carlo singular spectrum analysis mc ssa and wavelet transform wt we separate statistically significant components from time series and demonstrate significant co variance and consistent phase differences between ice conditions and the arctic oscillation and southern oscillation indices ao and soi at 2 2 3 5 5 7 and 13 9 year periods the 2 2 3 5 and 5 7 year signals detected in the arctic are generated about three months earlier in the tropical pacific ocean in contrast we show that the 13 9 year signal propagates eastward from the western pacificasequatorialcoupledwaves ecw 0 13 0 15ms 1 and then as fast boundary waves 1 3 ms 1 along the western margins of the americas with a phase difference of about 1 8 2 1 years by the time they reach the arctic our results provide evidence of dynamical connections between high latitude surface conditions tropical ocean sea surface temperatures mediated by tropical wave propagation the wintertime polar vortex and the ao index terms 1620 global change climate dynamics 3309 3309 meteorology and atmospheric dynamics climatology 1620 0312 atmospheric composition andstructure air seaconstituent fluxes 3339 4504 4504 oceanography physical air sea interactions 0312 4522 oceanography physical el nino citation jevrejeva s j c moore and a grinsted 2004 oceanic and atmospheric transport

direct observations of the upper layer circulation in the southern gulf of mexico abstract the upper layer circulation in the bay of campeche is analyzed with three years of data recorded by surface drifters current meter moorings and satellite altimetry the measurements show that the mean cyclonic circulation observed by previous authors extends below 1000 m and that its size and location are delimited by the particular topography of the region a deep basin to the west and a shallower and gentle sloping submarine fan to the east an empirical orthogonal function analysis and large correlations of the surface flow with the deeper currents suggest that the topographic constraint is the result of potential vorticity conservation for an equivalent barotropic flow the variability of the surface currents in the western basin is mostly due to changes in the size form position and intensity of the cyclonic gyre due to its interaction with northern gulf of mexico eddies particularly loop current eddies traveling the southern route towards the western boundary by contrast the eastern basin is characterized by a weak northward drift with the occasional generation of anticyclones in the southeastern boundary the genesis of which remains to be understood this suggests that the variability in the eastern basin is mostly driven by locally generated disturbances rather than by an influx of northern gulf of mexico eddies strong northward flows in the central and eastern basins result from the flow convergence between locally generated anticyclones and the cyclonic gyre

experimental investigation of reverse end bearing of offshore shallow foundations shallow skirted foundations can mobilize uplift resistance from end bearing in the short to medium term however uncertainty exists over the magnitude of reverse end bearing resistance compared wi

seasonal patterns of wind stress and wind stress curl over the gulf of mexico meteorological observations from an array of stations deployed along the periphery of the gulf of mexico between 1990 and 1993 are used to describe the seasonal fluctuations in patterns of atmospheric variables from a contemporary set of measurements seasonal maps of wind stress based on these measurements resemble wind stress maps based on ship observations as published by elliott 1979 rather than maps based on analyses of numerical weather forecasts as published by rhodes et al 1989 particularly near the western boundary of the gulf seasonal maps of wind stress curl are characterized by positive curls over the western and southwestern gulf the central result of this study is to document the important role of the mountain chain which extends along the southwestern section of the gulf in channeling the wind toward the isthmus of tehuantepec

a linear equivalent barotropic model of the antarctic circumpolar current with realistic coastlines and bottom topography abstract a linear equivalent barotropic eb model is applied to study the effects of the bottom topography h and baroclinicity on the total transport and the position of the antarctic circumpolar current acc the model is based on the observation of killworth that the time mean velocity field of the fram model is self similar in the vertical a realistic large scale topography h is constructed by filtering 5 minute resolution data with an appropriate smoothing kernel it is shown that the asymptotic behavior of the solution of the barotropic model a particular case of the eb model in the limit of very small bottom friction depends on subtle details of topography and basin geometry given the uncertainties of the smoothing procedure the authors conclude that the barotropic model is not robust with respect to possible variations of model topography the authors found that the eb model with a vertical profile function similar to that of killworth reproduces the major features of the time and depth ave

an equivalent barotropic mode in the fine resolution antarctic model abstract both the 6 year time mean flow and the eddy kinetic energy in the fine resolution antarctic model are found to be approximately self similar in the vertical with the velocity showing a rapid decay with depth a simple argument is given as to why this would be expected to occur in this and other numerical models and an analysis is given as to the degree of steering of the mean flow by topography

k o ocr relationships in soil the relationships between k o and ocr are investigated for primary loading unloading reloading conditions the study reviews laboratory data from over 170 different soils and presents an approach common to clays silts and sands simple empirical methods for predicting k o for normally consolidated and overconsolidated soils are evaluated the validity of the methods is supported by statistical analyses on the basis of the findings only the effective stress friction angle o and prior stress history ocr and ocrmax are needed to predict approximate values of k o

propagation of coastal trapped waves at low latitudes in a stratified ocean with continental shelf slope abstract poleward propagation of coastal trapped waves induced by a baroclinic equatorial kelvin wave incident on the eastern boundary is studied in numerical models when the thermocline is shallower than shelf depth and so intersects a vertical coastal wall a coastal trapped internal kelvin type wave keeps propagating poleward the only change in its structure is that its trapping width decreases in accordance with the decrease in the local deformation radius on the other hand when the thermocline intersects a continental slope which represents a typical situation for the eastern tropical pacific baroclinic disturbances decrease in amplitude as they propagate poleward and eventually disappear at middle latitudes transformation of the baroclinic disturbances to quasi barotropic shelf waves takes place part of the barotropic energy leaks away from the coastal region in the form of barotropic rossby waves as the period wavelength of an incident equatorial kelvin wave increases baroclinic distu

base stability of multi propped excavations in soft clay subjected to hydraulic uplift excavations in soft clay underlain with an aquifer may be destabilized by hydraulic uplift previous studies on this subject are based mainly on field observations dewatering from the aquifer is a

eddy energy and shelf interactions in the gulf of mexico sea surface height anomaly data from satellite are continuously available for the entire gulf of mexico surface current velocities derived from these remotely sensed data are compared with surface velocities from drifting buoys the comparison shows that satellite altimetry does an excellent job resolving gulf eddies over the shelf rise depths between 200 and 2000 m if the proper length scale is used correlations between altimeter and drifter derived velocities are statistically significant r 0 5 when the surface slope is computed over 125 km indicating that remotely sensed sea surface height anomaly data can be used to aid the understanding of circulation over the shelf rise velocity variance over the shelf rise from the altimetry data shows regions of pronounced eddy energy south of the mississippi outflow south of the texas louisiana shelf and in the northwest and northeast corners of the gulf these are the same locations where surface drifters are most likely to cross the shelf rise suggesting gulf eddies promote cross shore flows this is clearly exemplified with both warm and cold eddies finally the contribution of gulf eddies and wind stress to changes in the mean circulation are compared results indicate that the eddy generated vorticity flux to the mean flow is greater than the contribution from the surface wind stress curl especially in the region of the loop current and along the shelf rise base in the western gulf future modeling efforts must not neglect the role of eddies in driving gulf circulation over the shelf rise

coherent sea level fluctuations along the global continental slope signals in sea level or more properly sub surface pressure ssp sea level corrected for the inverse barometer effect are expected to propagate rapidly along the continental slope due to the effect of sloping topography on wave modes resulting in strongly correlated ssp over long distances observations of such correlations around the arctic and antarctic are briefly reviewed and then extended using satellite altimetry to the rest of the global continental slope it is shown that such long distance correlations are common especially in extra tropical regions simple correlations from altimetry cannot however establish the wave speed or whether waves are responsible for the correlations as opposed to large scale coherence in the forcing a case study around south america is used to highlight some of the complications and is found to strengthen the case for the importance of wave modes in such long distance ssp coherence although more detailed in situ data are required to resolve the cause of the correlations

centrifuge modelling of uplift response of suction caisson groups in soft clay this paper describes a program of centrifuge model tests on the uplift behaviour of suction caisson foundations the parameters considered were the loading rate caisson diameter d soil strength

baroclinic adjustment in drake passage driven by tropical pacific forcing the time series of high quality hydrographic measurements of the acc in drake passage is revisited to investigate the extent of baroclinic adjustment in the region on time scales of up to two decades we find that substantial adjustment of the upper kilometer of northern drake passage has occurred on interannual to decadal time scales driven primarily by tropical pacific forcing via the poleward propagation of boundary waves the decadal scale signal consists of a marked deepening of isopycnals by 200m between the early 1990s and the late 2000s and reflects enso forced wind driven baroclinic changes over an extensive region of the eastern south pacific 2012 american geophysical union all rights reserved

numerical experiments on stratified wind induced circulation in tokyo bay japan during summer in tokyo bay the upwelling of the anoxic water strongly affects eggs and larvae of fish and shellfish the northerly wind causes the upwelling along the eastern coast and near the bay head and downwelling along the western coast numerical experiments were carried with a three dimensional model to explain the wind induced circulation in tokyo bay when a uniform north easterly wind is imposed at the sea surface the circulation almost reaches steady state due to geostrophic adjustment after one inertial period from the beginning of the computation a forced internal kelvin wave propagating with the land on the right is found to have a great effect on the development of the steady state when the observed variable wind is given as the surface boundary condition the results of the numerical experiment agree qualitatively with data from both the sea surface temperature obtained by satellite images and field measurements at moored stations in the bay

ekman effects in a rotating flow over bottom topography this paper presents a general two dimensional model for rotating barotropic flows over topography the model incorporates in a vorticity stream function formulation both inviscid topography effects associated with stretching and squeezing of fluid columns enforced by their motion over variable topography and viscous effects due to the ekman boundary layer at the solid bottom from the present formulation conventional two dimensional models can be recovered the model is tested by means of laboratory experiments on homogeneous vortices encountering irregular topographies the experimental observations are then compared with the corresponding numerical simulations based on the general model the results suggest that such a formulation incorporates both inviscid and viscous topography effects correctly

experimental study of uplift resistance of shallow skirted foundations in clay under transient and sustained concentric loading wind wave and current forces cause significant overturning loads to be transmitted to foundation systems of fixed bottom offshore structures while buoyancy forces in conjunction with environmental loading impart direct tensile loads to foundations of floating facilities shallow skirted foundations are a potentially attractive foundation solution when overturning or tension loading is significant as suctions mobilised within the soil plug provide tensile resistance while passive suctions are maintained undrained reverse end bearing will govern failure providing enhanced uplift resistance compared with vented pull out of the foundation unit with or without the soil plug governed by skirt soil friction currently uncertainty exists over the limiting ratio of skirt depth to foundation diameter to mobilise undrained reverse end bearing and the duration over which passive suctions can be sustained this paper reports results from beam centrifuge tests investigating the response of shallow skirted fou

effect of perforations on uplift capacity of skirted foundations on clay the retrieval of deep water subsea installations resting on soft soil such as mudmat shallow foundations can be a difficult and costly operation if significant resistance to uplift is experienc

large deformation numerical modeling of short term compression and uplift capacity of offshore shallow foundations abstractlarge deformation finite element analysis has been used to model the undrained response of skirted shallow foundations in uplift and compression large deformation effects involve changes in embedment ratio and operative local soil shear strength with increasing foundation displacement either in tension or compression centrifuge model testing has shown that these changes in geometry affect the mobilized bearing capacity and the kinematic mechanisms governing failure in undrained uplift and compression small strain finite element analysis cannot by definition capture the effects of changing foundation embedment ratio and variation in local soil strength with foundation displacement in this paper load displacement relationships ultimate capacities and kinematic mechanisms governing failure from large deformation finite element analyses are compared with centrifuge model test results for circular skirted foundations with a range of embedment between 10 and 50 of the foundation diameter the re

undrained bearing capacity factors for conical footings on clay introduction the bearing capacity of circular foundations on undrained clay is of fundamental importance in many geotechnical problems in particular there are a number of designs of offshore foundations where the foundation can be treated approximately as a large circular footing for instance some gravity bases the spudcan foundations of jack up units and the more recently developed caisson foundations in most cases the footing is not placed at the ground surface and it is important to take into account the depth of embedment furthermore the base of a spudcan is generally not flat but approximates a shallow cone for foundations on soft clays the effect of the increase of strength of the soil with depth needs to be taken into account and this is particularly important for large foundations the purpose of this note is to present calculations of bearing capacity factors for shallow circular foundations accounting for embedment cone angle rate of increase of strength with depth and surface roughness of the foundation the results have widespread application particularly in the offshore industry the soil is assumed to be rigid plastic with yield determined by the tresca condition with an undrained strength su the method of characteristics is used for the bearing capacity calculation as described by shield 1955 eason shield 1960 houlsby 1982 and houlsby wroth 1982a for application to undrained axisymmetric problems some previous results have been published for this problem using similar numerical techniques e g houlsby wroth 1982b salencon matar 1982 houlsby wroth 1983 tani craig 1995 martin 2001 but the study presented here involves a much more comprehensive coverage of the parameters where comparisons can be made with the previous solutions the factors differ by up to about 0 5 which gives some indication of the level of accuracy attainable with this numerical technique exceptionally the rough footing results given by tani craig 1995 are higher by up to about 5 but this may be due to a problem with their numerical integration procedures see martin randolph 2001

science and empiricism in pile foundation design scientific approaches to pile design have advanced enormously in recent decades and yet still the most fundamental aspect of pile design that of estimating the axial capacity relies heavily upon empirical correlations improvements have been made in identifying the processes that occur within the critical zone of soil immediately surrounding the pile but quantification of the changes in stress and fabric is not straightforward this paper addresses the degree of confidence we can now place a on the conceptual and analytical frameworks for estimating pile capacity and b on the quantitative parameters required to achieve a design the discussion is restricted to driven piles in clays and siliceous sands with particular attention given to extrapolating from design approaches derived for closed ended piles of relatively small diameter to the large diameter open ended piles that are used routinely in the offshore industry from a practical viewpoint we need design approaches that minimise sensitivity

external radial stress changes and axial capacity for suction caissons in soft clay a series of centrifuge tests was performed on instrumented model caissons in normally consolidated lightly overconsolidated and sensitive clays to investigate the external radial stress changes around suction caissons during installation consolidation and pullout and axial capacity after consolidation total pressure transducers embedded at different elevations of the caisson wall showed external radial total stresses that varied almost linearly with depth during both penetration and extraction of the caisson with smaller gradients during post consolidation pullout only slight differences were found in the measured external radial total stress when pressure transducers entered the suction affected zone from the jacking affected zone comparisons are presented between measurements and two theoretical predictions for both the external radial total stress during caisson installation and the radial effective stress after consolidation a simple cavity expansion approach was found to give reasonable pr