history of upwelling in the tropical eastern pacific and the paleogeography of the isthmus of panama article i nfo today there is a tight knit relationship between the elevation of the central american isthmus and the ocean ographic conditions of the tropical eastern pacific where the elevation drops below 500 m low level wind jets pass seasonally from the atlantic to the pacific driving coastal upwelling in the tropical eastern pacific this paper determines if seasonal upwelling was present in five pliocene and pleistocene fossiliferous sites on the pacific coast of the burica region of the isthmus of panama using two independent approaches that compare bryozoan morphology and whole community composition of fossiliferous localities with material from upwelling and non upwelling modern localities no definitive evidence of seasonal upwelling exists in the pliocene implying non analogous oceanographic conditions because of continued interoceanic connection prior to the closure of the isthmus of panama conversely data from three mid pleistocene sites reveal robust evidence of strong seasonal upwelling suggesting that the elevat ion of the isthmus must have been sufficiently low to permit wind jets to form a low elevation isthmus of panama may have persisted until as recently as the mid pleistocene

palaeogene climate evolution in the paris basin from oxygen stable isotope δ18o compositions of marine molluscs the constraint of temperature evolution in coastal environments is an important factor in deciphering the earth s global climatic history in this study we reconstruct the evolution of sea surface palaeotemperatures from the oxygen stable isotope compositions in four marine molluscs families in the paris basin during the palaeogene the combination of several taxa living in different environments is used to limit uncertainties related to the influence of salinity variations on palaeotemperature estimations one family of bivalves oysters and three families of gastropods volutidae cerithiidae and turritellidae were sampled in the french part of the paris basin in belgium and in the isle of wight southern england maximum seawater temperatures were observed during the early eocene c 30 c which correspond to the early eocene climatic optimum and temperatures then decreased until the lutetian c 20 c a transient warming identified as the middle eocene climatic optimum occurred during the bartonian when temperatures reached 32 c temperatures decreased through the eocene oligocene boundary the coolest interval of the palaeogene c 12 c a final warming period occurred throughout the early oligocene with temperatures reaching 24 c the fossils analysed thus record the global climatic intervals of the palaeogene

eocene climate record of a high southern latitude continental shelf seymour island antarctica a high resolution record of eocene paleotemperature variation is preserved within the high southern latitude marine shelf succession of the la meseta formation on seymour island off the ne side of the antarctic peninsula 87 sr 86 sr ratios of bivalve shell carbonate indicate that the la meseta formation spans virtually the entire eocene and suggest the presence of an early middle eocene unconformity paleoclimatic and paleoceanographic inferences are based on the stable oxygen and carbon isotope values of two genera of bivalves collected with a high degree of stratigraphic resolution within the formation and with multiple replicate samples from each horizon 18 o data indicate roughly 10 c of cooling from the early eocene climatic optimum 15 c through the end of the eocene minimum 5 c much of which took place in two comparatively short intervals at ca 52 and ca 41 ma many features of the isotope curves generated from this eocene shelf section are apparent in 18 o and 13 c data from the southern and global oceans including warm intervals that likely correspond to the early and middle eocene climatic optima eeco and meco a rapid middle eocene shift to much more positive values is the most signifi cant in the section and refl ects a drop to universally cooler temperatures in the late middle and late eocene that might also be associated with a short lived glacial advance however even using a somewhat depleted value for 18 o of seawater in the antarctic peninsular region average seymour island shelf water paleotemperatures did not reach freezing before the end of the eocene 13 c data similarly refl ect the documented middle eocene surface ocean enrichment followed by more negative values but depletion is much more pronounced on seymour island and persists for the remainder of the eocene suggesting a combination of upwelling metabolic effects and or atypical carbon cycling on the shelf in this region isotope data capture information about changes in the paleoenvironment that also had consequences for the biota as published paleontological records document marked change in the nature of terrestrial and marine biota at this time the fact that middle eocene cooling and biotic turnover in the peninsular region correspond well in time to the proposed initial opening of drake passage suggests that the formation of gateways in addition to changes in pco 2 had signifi cant consequences for the earth s climate system during the paleogene

high calcification rates and inferred metabolic trade offs in the largest turritellid gastropod turritella abrupta neogene abstract turritella abrupta miocene pliocene is the largest species known from the diverse jurassic recent gastropod family turritellidae in addition to having achieved long length and substantial width the species produces shells of exceptional thickness even before secondary shell deposition we investigated the paleoecology of this species through analysis of drilling and peeling frequencies with comparisons to co occurring turritellid species we used oxygen isotopic sclerochronology to infer the growth rate and lifespan of t abrupta and to make comparisons with other modern and fossil tropical species including the living species turritella terebra with the first sclerochronologies for both of these species presented herein we find that t abrupta was fast growing long lived and comparatively effective at resisting predation t abrupta was notably widespread geographically and temporally but was a relatively rare component of faunas when compared with co occurring turritellids high rates of shell carbonate construction in excess of 35 g in the first year of life likely depended on habitats conducive to calcification late miocene cooling and eastern pacific carbonate limitation are implicated in the range contraction and eventual extinction of this species

drained and undrained anisotropic elastic stiffness parameters equations that map drained to undrained elastic stiffness parameters in a cross anisotropic material are presented graphs of various anisotropic stiffness ratios are used to illustrate the important trends a new 2 d graph showing the elastic bound enables measured elastic parameters to be plotted which all lie well within it the 2 d graph enables uncoupled and incompressible materials to be shown plus materials with particular initial effective stress path slopes in an undrained triaxial test bounds more restrictive than the elastic one are also discussed and the likely ranges of various anisotropic stiffness ratios are presented in general undrained anisotropy is much less than drained that is closer to isotropic in undrained plane strain conditions vertical and horizontal moduli are found to be the same in drained plane strain conditions the ratios of the moduli are almost the same as the young s moduli

subsurface settlement profiles above tunnels in clays designers assessing the possible effect of tunnelling on structures relatively close to the tunnel crown need to know how subsurface settlement profiles develop and how these relate to surface settlement profiles the effect on piled foundations or existing tunnels depends on the width of the subsurface settlement profile and on the magnitude of the settlement this note uses available field measurements and centrifuge model test data to determine how the widths of the settlement profiles and the magnitudes of settlement vary with depth above tunnels constructed in clays the results reveal a fairly consistent pattern of behaviour the width of the subsurface settlement troughs at depth is significantly greater than would be predicted by assuming a constant trough width parameter k of 0 5 smaller more realistic subsurface settlements and strains will be predicted if account is taken of the proportionally wider trough widths at depth

undrained stiffness anisotropy from hollow cylinder experiments on four eocene to jurassic uk stiff clays the paper describes the anisotropic undrained stiffness behaviour of four medium plasticity heavily overconsolidated uk stiff marine clays as revealed through hollow cylinder testing the experimen

stress strain responses of block samples of compressible chicago glacial clays this paper presents the results and analysis of a laboratory investigation of the behavior of lightly overconsolidated compressible chicago glacial clays over a wide strain range each specimen was trimmed from high quality block samples taken from an excavation in evanston illinois specimens were instrumented with three sets of bender elements and local lvdts after k0 consolidation to the in situ vertical effective stress of the block drained stress probe tests were conducted results of bender elements tests obtained prior to stress probing show that compressible chicago glacial clay initially is cross anisotropic propagation velocities measured by bender elements in axial direction after k0 reconsolidation and drained creep agrees well with the in situ shear wave velocity measured by seismic cone penetration tests results of drained stress probe tests are analyzed in terms of shear volumetric and coupled stiffness stiffness degradation and direction of loading the significant variability of s

ground movements due to shallow tunnels in soft ground i analytical solutions this paper presents simplified closed form analytical solutions that can be used to interpret and predict ground movements caused by shallow tunneling in soft ground conditions these solutions offer a more comprehensive framework for understanding the distribution of ground movements than widely used empirical functions analytical solutions for the displacement field within the ground mass are obtained for two basic modes of deformation corresponding to uniform convergence and ovalization at the wall of a circular tunnel cavity based on the assumption of linear elastic soil behavior deformation fields based on the superposition of fundamental singularity solutions are shown to differ only slightly from analyses that consider the physical dimensions of the tunnel cavity except in the case of very shallow tunnels this work demonstrates a simplified method to account for soil plasticity in the analyses and illustrate closed form solutions for a three dimensional 3d tunnel heading a companion paper describes applications of these analyses to interpret field measurements of ground response to tunneling

naticid drilling predation on gastropod assemblages across the k t boundary in rajahmundry india new evidence for escalation hypothesis abstract one of the important and well documented prey predator interactions in the fossil record is drilling predation done by naticid gastropods which diversified during the cretaceous although drilling frequencies showed fluctuating patterns most of the previous studies argued that naticid drilling predation was less intense during the cretaceous and the modern values were achieved since the paleocene we here present a new dataset of naticid drilling predations involving 31 929 gastropod specimens from the latest maastrichtian infratrappean bed in rajahmundry southern india these specimens belonged to 40 species of 20 families thus representing a spectacular gastropod diversity that was not known until recently from this region we examined 5884 complete or near complete specimens to quantify naticid drilling predation on this assemblage it appeared that drilling frequency was significantly higher from all previous cretaceous values this was true for both assemblage level and lower taxon level results along with high successful drilling and low unsuccessful drilling frequencies site and size stereotypy of drillholes suggest that naticid predators were highly efficient even in the cretaceous predators were prey selective and there was poor correlation between relative abundance and drilling frequency of prey taxa the present maastrichtian assemblage underlies the k t mass extinction level drilling frequency was zero in the straddler prey community in the intertrappean bed found immediately above the k t boundary the absence of any drillhole in surviving prey taxa may be due to sudden reduction in abundance of escalated predators although some prey taxa e g cerithiids continued this emphasizes the role of mass extinction in disrupting predator prey interaction we conclude that naticid drilling induced escalation was already established during the cretaceous and the present find extends the paleobiogeography of naticid predation which was previously reported from the western world up to india

modelling of viscous effects in natural clays a new approach to allow the modelling of the viscous behaviour of natural clay soils including creep stress relaxation and the effects of applied strain rate on soil stiffness has been developed based on the brick constitutive model published by simpson in 1992 the new model strain rate dependent srd brick was used in a series of simulations to demonstrate its capabilities in predicting realistic behaviour during one dimensional compression and undrained triaxial tests in which applied strain rates were varied triaxial stress path tests conducted by gasparre et al in 2007 to assess the influence of creep resulting from recent stress history on soil stiffness were also simulated the observed trends concerning the stiffness at small strains were successfully modelled

effects of stress path rotation angle on small strain responses abstractthe results of experimental studies on the stress strain behavior of chicago glacial clays are presented and discussed this paper describes small strain responses as a function of stress path rotation angle undrained compression and extension tests with three different preshear stress paths were conducted on high quality hand cut block samples obtained at two different depths from the excavation for the block 37 project in chicago one preshear stress path was applied to investigate the stress strain response representative of the in situ conditions via a recompression technique the other two preshear stress paths were selected to isolate the effects of recent stress history such that the only difference between the two sets of paths was the direction of loading to a common effective stress condition a period of drained creep at constant effective stress was imposed on all specimens prior to shearing to negate the possible effects of creep on the small strain responses the results are discus

shear strength anisotropy of natural london clay the paper reports the shear strength anisotropy of the natural highly overconsolidated london clay from heathrow terminal 5 as established by comprehensive hollow cylinder apparatus hca testing

role of temperature and nutrients in extinction of turritelline gastropods cenozoic of the northwestern atlantic and northeastern pacific abstract turritelline gastropods mesogastropoda turritelline are common to abundant components in many fossil cretaceous cenozoic and recent marine benthic communities but the environmental factors affecting their evolution and extinction are poorly understood this is in large part because today they occur most abundantly in cooler waters associated with upwelling or other high nutrient conditions but thermal tolerances and preferences are unclear for extinct turritelline species turritellines were diverse and abundant throughout the new world for much of the cenozoic beginning in the early neogene through both extinction and range contraction however they started to disappear from higher latitudes on both atlantic and pacific coasts of north and central america the highest rate of extinction took place in the western atlantic in the plio pleistocene when almost all turritelline species in this area became extinct preliminary comparison of the available stratigraphic record suggests that this paleobiogeographic pattern is not an artefact of the record this biogeographic shift coincides with a postulated regional mass extinction among all marine mollusks in the western atlantic at around the same time causes for turritelline extinction however appear to be more complex than the decline in temperature that is cited most often as the probable cause of the western atlantic molluskan extinction event neogene turritellines in the western atlantic appear to have been adversely affected by collapse and or major reorganization of oceanic productivity associated with the formation of the isthmus of panama nutrients thus may have been more important than temperature change in controlling extinction probability in this group

the measurement of local axial strains in triaxial tests using lvdts in this technical note the author describes an experiment in the use of linear variable differential transformer lvdt to allow accurate measurement of axial displacement over the complete range of strains of interest to geotechnical engineers

ground coupled air waves and diffracted infrasound from the arequipa earthquake of june 23 2001 1 on june 23 2001 a strong earthquake measuring mw 8 4 occurred along the coast of south central peru coherent infrasonic waves were detected over a period of one hour by the is08 infrasound station in bolivia analysis of the ground coupled air waves shows that the rupture propagated from the northwestern to the southeastern part of the fault with a rupture velocity of 3 3 km s the azimuth variation of the infrasonic waves is attributed to a distribution of secondary sources along the highest mountain ranges which excite infrasonic waves that are diffracted to the ground the predominant source of infrasound is likely distributed along the andean cordillera using the azimuth and arrival time determination the horizontal scale size of the distant source regions of infrasonic waves is reconstructed over distances greater than 400 km

ground characterisation for pisa pile testing and analysis this paper is the first of a set of linked publications on the pisa joint industry research project which was concerned with the development of improved design methods for monopile foundations in

sedimentology and high resolution sequence stratigraphy of the late middle to late miocene angostura formation western borbon basin northwestern ecuador an integrated analysis of facies and palaeontological content of the middle to late miocene c 12 4 9 1 ma angostura formation led to the identification of facies associations indicative of shoreface and inner shelf settings the angostura formation comprises eight high frequency sequences that are stacked to form a tectonically driven lowstand sequence set the most complete examples of sequences are bounded by transgressively modified unconformities and exhibit a threefold subdivision 1 a basal suite of deepening upward shoreface sediments transgressive systems tract including a base of cycle shell concentration 2 a mid cycle shell bed consisting of molluscan shells dispersed in a matrix of inner shelf muddy fine grained sandstones 3 a shallowing upward unit of inner shelf to lower shoreface sediments almost barren of mollusc fossils highstand systems tract biostratigraphic constraints allowed a reasonable correlation between sequence bounding unconformities and the late middle to late miocene high frequency glacio eustatic changes derived from recent 18 o studies this correlation has far reaching implications and leads to the following conclusions 1 glacio eustasy in tune with oxygen isotope changes at fourth order frequency 200 ka 1 ma duration may have been the principal factor regulating stratigraphic packaging in the angostura formation 2 these sequences provide an excellent shallow marine outcrop record of late middle to late miocene antarctic glaciations

characteristics of the london clay from the terminal 5 site at heathrow airport the innovative engineering approach adopted for the new terminal 5 at heathrow airport called for an advanced investigation of the london clay strata including detailed in situ profiling and stress path laboratory testing on high quality rotary cored samples although the scope of the investigations exceeded that normally specified for conventional design questions relating to the structure and anisotropy of stiffness and strength of the clay remained that could not be answered further research was required and the deep excavations at the site provided the opportunity for a team from imperial college to take multiple block samples from three depths supplemented by two additional dedicated rotary cored boreholes intensive research was performed at imperial college on these samples as described in three companion papers by gasparre et al and nishimura et al this overview paper integrates the findings from the recent research with those from the commercial investigation and with earlier studies to e

correlation of winds and geographic features with production of certain infrasonic signals in the atmosphere summary of the waves which propagate in the atmosphere at acoustic velocity in the period range from 10 to 100 s one type has been classified by triangulation as arising principally from mountainous regions these signals were first described as northwesters or 310 ers by the nbs geoacoustics group under r k cook at washington d c from the predominant direction of arrival subsequent operation of an observatory at boulder colorado by vernon goerke gave a source region by triangulation in the pacific northwest primarily in montana and alberta installations of observatories at college alaska wilson and pullman washington moscow idaho craine and thomas enlarged the data base available and triangulation showed the principal source areas to be along the coast of british columbia and in the inland rocky mountains of the british columbia alberta border this paper discusses the presently known characteristics of this class of infrasonic waves locates the triangulation areas reviews selected events and suggests that certain of these waves are produced as aerodynamic sound the paper shows a correlation between the 500 mb jet stream velocity and direction in these mountainous regions and the detection of these atmospheric pressure waves infrasonic waves 10 to 100 s periods there are a number of atmospheric wave structures travelling at acoustic velocities that appear in the 10 to 100 s period range an observatory through four pressure sensitive transducers provides basic information on the amplitude variations of pressure with time from which the waveform period and time sequence of the event at an individual microphone can be obtained by overlaying the charts and visually correlating the waveforms from several transducers a signal can be identified in the noise and arrival time differences measured the azimuth of the direction of arrival and the horizontal velocity across the transducer array can then be calculated assuming a plane wave detection of signals is often difficult since local wind noise may obscure the desired signal and changes in waveform caused by frequency dispersion of the signal or the effects of other signals arriving from different directions may make the waveform vary at each transducer we define an event as a series of signals that appear to be related

analysis of undrained soil deformation due to ground loss closed form solutions are presented for obtaining the strain field in an initially isotropic and homogeneous incompressible soil due to near surface ground loss this problem fits into a category of cases in which the imposed boundary conditions are only or mainly in terms of displacements strain controlled problems in these cases there is a possibility of eliminating the stresses and obtaining the strains by using only the incompressibility condition the presence of the top free surface is considered by means of a virtual image technique and some results for the elastic half space the results are simple especially for the movements of the soil surface the application to some typical problems such as soft ground tunnelling and pile driving or extraction shows that the calculated movements agree well with the experimental observations and compare favourably with commonly used numerical methods some hints are given for extending the method to other cases such as to compressible materials des sol

infrasound and gravity waves over the andes observed by a pressure sensor on board a stratospheric balloon the study of infrasound acoustic and gravity waves sources and propagation in the atmosphere of a planet gives us precious insight on atmosphere dynamics climate and even internal structure the implementation of modern pressure sensors with high rate sampling on stratospheric balloons is improving their study we analyzed the data from the national aeronautics and space administration ultra long duration balloon mission 16 may to 30 june 2016 here we focus on the balloon s transit of the andes mountains we detected gravity waves that are associated to troposphere convective activity and mountain waves an increase of the horizontal wavelengths from 50 to 70 km with increasing distance to the mountains is favoring the presence of mountain waves we also report on the detection of infrasounds generated by the mountains in the 0 01 0 1 hz range with a pressure amplitude increase by a factor 2 relative background signal besides we characterized the decrease of microbaroms power when the balloon was flying away from the ocean coast these observations suggest in a way similar to microseisms for seismometers that microbaroms are the main background noise sources recorded in the stratosphere even far from the ocean sources finally we observed a broadband signal above the andes between 0 45 and 2 hz probably associated with a thunderstorm the diversity of geophysical phenomena captured in less than a day of observation stresses the interest of high rate pressure sensors on board long duration balloon missions

ground motions induced by a producing hydrocarbon reservoir that is overlain by a viscoelastic rocksalt layer a numerical model hydrocarbon reservoir pressure depletion leads to stress changes inside the reservoir and ground deformation which is registered at the surface as subsidence as reservoirs are often overlain by layers of rocksalt or other evaporites which are materials that flow so as to relax stresses inside them there is the potential for time varying surface subsidence this work focuses on understanding the macroscopic mechanisms that lead to rocksalt flow induced ground displacements a finite element model is used for this purpose in which the rocksalt layer is represented by a viscoelastic maxwell material two distinct mechanisms that lead to displacement are observed these are active during different stages of the deformation and have different timescales associated with them an important observation is that the timescale for deformation that is measured at the ground surface is not equal to the timescale for deformation of a viscoelastic material element but can be many times larger than that the sensitivity of the response to the thickness and location of the rocksalt layer is also presented conclusions are drawn which allow for the relative importance of the presence of the rocksalt layer to be assessed and for a framework for understanding time dependent subsidence above producing hydrocarbon reservoirs to be developed finally the changes in stress distribution around a producing reservoir are also briefly discussed

the influence of structure on the behaviour of london clay an intensive investigation is described into the london clay units from heathrow terminal 5 intrinsic properties and composition were established and relating the behaviour of intact and reconsti

a case study on the behavior of shield tunneling in sandy cobble ground this study investigates the behavior of shield tunneling based on a complete case record of an excavation in sandy cobble ground both numerical and analytical analyses were conducted to estimate the surface displacement along the tunnel axis and the surface zone affected by the shield tunneling this paper presents the performance of the peck method in forecasting the transversal surface settlement trough caused by the shield tunneling in a sandy cobble layer in particular this study has made a comparison with the vertical surface displacement monitored during the advancing excavation to the settlements estimated by using the peck method and by conducting a three dimensional finite element analysis the effective measures to provide the necessary face support pressure and to reduce the formation of sinkholes and ground settlements in sandy cobble ground were also investigated and discussed

the undrained shear strength anisotropy of four jurassic to eocene stiff clays the shear strength of heavily overconsolidated stiff to hard plastic clays is crucial to their stability and also influential on the ground movements they develop in many geotechnical engineering applications this paper considers the shear strength anisotropy of the london gault kimmeridge and oxford clays through advanced hollow cylinder experiments on multiple high quality samples taken at similar depths from inland sites where the geotechnical profiles have been established by comprehensive laboratory and in situ testing suites of undrained tests are reported which loaded specimens from their in situ stress states to reach ultimate failure at pre defined final major principal stress axis orientations defined in the vertical plane while also controlling or monitoring the intermediate principal stress ratio b both stress path and simple shear tests were undertaken with the hollow cylinder apparatus which offers key advantages over conventional simple shear equipment the interpretation reveals

a kinematic hardening constitutive model for natural clays with loss of structure a rate independent constitutive model for natural clays is presented formulated within the framework of kinematic hardening with elements of bounding surface plasticity the modelling framework is intended to include effects of damage to structure caused by irrecoverable plastic strains caused by sampling laboratory testing or geotechnical loading the incorporation of a structure measure allows the size of the bounding surface to decay with plastic deformations this model can be seen as a logical extension from the cam clay model the steady fall of stiffness with strain towards the cam clay value is controlled by a particular interpolation function this ensures a smooth degree of approach between a kinematically hardening bubble which is the boundary of the elastic region and the bounding surface during their relative translation with stress history the model describes the essential phenomena of pre failure behaviour of natural clays stiffness variation with strain volumetric change accompanyi

analysis of tunnel excavation in london clay incorporating soil structure recent studies on london clay have identified a number of different units in the geological profile and have highlighted the role of soil structure in mechanical behaviour in fact structure is the dominant factor determining the differences in the mechanical response of different units in the paper numerical analyses simulating the undrained excavation of a tunnel in st james s park are presented london clay behaviour is characterised by a kinematic hardening structured soil model incorporating structure and stiffness degradation the parameters and initial conditions are based on a careful calibration that takes into account the presence of different units within the london clay formation and the different degrees of soil structure the analyses performed result in a very satisfactory reproduction of the magnitude and patterns of short term surface and subsurface displacements as well as pore pressures the paper concludes with a discussion of the results in the context of other analyses performed

a biostratigraphy for the london clay in london biostratigraphy enables specific layers of strata to be given a unique stratigraphic address that can be used to identify the horizons in which in situ tests are conducted and from which samples for testing are collected this is particularly valuable when working in fine grained deposits where stratigraphic position is not easily recognised by lithology alone and permits any data bank of geotechnical values and performance to be used without fear of confusing one stratigraphic layer with another construction in the london clay formation and its supporting research has necessitated an accurate and speedy method for identifying with a precision of centimetres the stratigraphic layer from which geotechnical data have been obtained the principles that enable biostratigraphy to be used for this purpose are explained and illustrated with reference to the london clay formation in london this approach can be used in most sedimentary strata an example of biostratigraphic data used in london is presented

shaft resistance and setup factors for piles jacked in clay abstractinstallation of a displacement pile often involves complex loading modes that cause substantial changes in the state of the soil surrounding the pile when a displacement pile is installed in saturated clay significant excess pore pressure develops as the excess pore pressure dissipates over time the effective stresses in the soil surrounding the pile and the pile capacity increase this paper investigates jacking of piles into clay using finite element analysis a two surface plasticity based constitutive model for clays was implemented in the finite element code solid nonlinear analysis code based on the numerical results equations are developed for quantifying the effects of undrained and residual shear strength on the shaft resistance of jacked piles in clay the gain in shaft resistance over time is assessed and setup factors are proposed that can be used to estimate the gain in shaft resistance as a function of time after installation of a jacked pile in clay good agreement was obtaine

wave velocity and stiffness measurements of the crag and lower london tertiaries at sizewell this paper describes an investigation into the body wave velocity and stiffness characteristics of the foundation soils at the site formerly considered for sizewell c nuclear power station results from both in situ and laboratory tests are presented in situ measurements comprised shear and compression wave velocities using cross hole and down hole techniques including the velocity of horizontally propagating horizontally polarized shear waves laboratory tests included torsional shear tests on hollow cylindrical samples triaxial compression and extension tests with local measurements of strain and resonant column tests sample quality and the effects of destructuring are evaluated the anisotropy of the wave velocity and of the stiffness characteristics is highlighted l article decrit des recherches sur la vitesse de propagation des ondes de volume et les caracteristiques de rigidite des sols d assise de l emplacement propose de la centrale nucleaire sizewell c il presente les resultats des essais

paleoecology and paleoenvironmental implications of turritelline gastropod dominated assemblages from the gatun formation upper miocene of panama abstract turritelline dominated assemblages tdas frequently occur in the middle late miocene gatun formation and are not uncommon features in the broader fossil record by gaining a better understanding of the paleoenvironment and taphonomic processes leading to their formation we can gain insight into the conditions in the western atlantic wa during the miocene shoaling of the central american seaway as well as the conditions which may lead to tda formation generally tda and non tda beds within the gatun were examined for shell orientation sclerobiont coverage drilling predation frequency and site stereotypy and sediment composition the most abundant species t altilira was also examined using oxygen isotopic sclerochronology to compare growth rate and environmental conditions during the formation of tda and non tda beds mean annual range of temperature mart was found to be 6 2 c with a moderate associated negative o c correlation these data confirm the influence of tropical eastern pacific tep upwelling waters in the wa at this time upwelling conditions were found to be associated with all t altilira regardless of their source indicating that gatun tdas are not the result of variation in nutrient supply orientation data from within a tda grain size and sclerobiont coverage all suggest that tdas in the gatun are the result of variation in sediment supply winnowing we used the theoretical apex system and a calculated minimum number of individuals to determine that the frequency of drilling predation and site stereotypy within and without tdas was statistically indistinguishable t altilira was found to live up to 3 years growing between 50 and 60 mm in the first year of life with a subsequent decline in growth rate

gradients and patterns of sclerobionts on experimentally deployed bivalve shells synopsis of bathymetric and temporal trends on a decadal time scale bivalve shells deployed experimentally in a variety of environments of deposition eods and over a wide range of depths from 15 to 570 m in the bahamas and gulf of mexico were assessed for encrusting and endolithic bionts sclerobionts sensu taylor and wilson 2002 that accumulated over 1 2 8 and 12 13 year intervals data include percent coverage and when possible identification to generic or species level taxonomic categories data were binned into two further categories based on guilds and whether or not sclerobionts were judged to be preservable each study site shows substantial variability in both percent coverage and species richness composition which we attribute to partial burial of different individuals or parts of arrays average values of taxonomic richness guild number and percent coverage for a given eod represent a combination of exposed and buried shells as would be typical of a time averaged fossil assemblage maximally covered shells give the potential coverage for each site in both study areas there are characteristic patterns in terms of overall percentage of shells covered by sclerobionts numbers and extent of coverage by different guilds as well as by different taxa for most eods there is a progressive though non linear increase in both species richness and areal coverage through the twelve years exceptions are in the 30 m site in the bahamas and parker bank and flower garden sites in the gulf of mexico which show a significant decline in areal coverage though not in richness this effect may result from differences in sediment cover over time these sites showed a tendency to have many or all experimental bags completely sediment covered in the later sampling cluster analysis and non metric multidimensional scaling nmds of various shell substrate species at all eods from the bahamas and gulf of mexico reveal discrete groupings that are related to both depth light gradient and other factors such as variations in sedimentation and salinity similar numbers of guilds are found at various eods although the specific guild types represented differ in general highest average richness values are recorded for carbonate 70 90 m wall and deep reef sites 69 to 70 taxa and lowest are for the efg brine pool no sclerobionts other than bacterial films after 12 13 years and deeper dysphotic to subphotic sites max values 25 taxa surprisingly shallow water sites 30 m yield only moderate diversities of 40 50 taxa this results in part from the fact that certain encrusters especially the foraminifer gypsina and coralline algae tend to overgrow others and dominate space in addition to burial effects certain taxa notably the serpulid pseudovermilia are ubiquitous while other taxa e g larger foraminifera vermetid gastropods and many bryozoans are largely restricted to shallower depths a combination of species richness average coverage and key taxa permits discrimination of groups of eods and potentially in tandem with other evidence of depth gradients

the seawater neodymium and lead isotope record of the final stages of central american seaway closure the shoaling and final closure of the central american seaway cas resulted in a major change of the global ocean circulation and has been suggested as an essential driver for strengthening of atlantic meridional overturning circulation amoc the exact timing of cas closure is key to interpreting its importance here we present a reconstruction of deep and intermediate water nd and pb isotope compositions obtained from fossil fish teeth and the authigenic coatings of planktonic foraminifera in the eastern equatorial pacific ocean drilling program odp site 1241 and the caribbean odp sites 998 999 and 1000 covering the final stages of cas closure between 5 6 and 2 2 ma the data for the pacific site indicate no significant atlantic caribbean influence over this entire period the caribbean sites show a continuous trend to less radiogenic nd isotope compositions during the pliocene consistent with an enhancement of upper north atlantic deep water unadw inflow and a strengthening of the amoc superimposed onto this long term trend shorter term changes of intermediate caribbean nd isotope signatures approached more unadw like values during intervals when published reconstructions of seawater salinity suggested complete closure of the cas the data imply that significant deep water exchange with the pacific essentially stopped by 7 ma and that shallow exchange which still occurred at least periodically until approximately 2 5 ma may have been linked to the strength of the amoc but did not have any direct effect on the intermediate and deep caribbean nd isotope signatures through mixing with pacific waters

anisotropy of small strain stiffness in ticino sand comprehensive tests performed in a large calibration chamber and consisting of the propagation of seismic body waves in dry ticino silica sand are presented by virtue of the fact that both shear and constrained compression waves have been propagated in vertical horizontal and oblique directions five independent constants of the cross anisotropic elasticity model of the test have been established the tests have also made it possible to evaluate the influence of the structural inherent and stress induced anisotropy on the velocity of the propagated seismic body waves the influence of the principal effective stresses on the velocity of these waves is also described de nombreux essais realises dans une grande chambre d etalonnage et consistant en la propagation d ondes sismiques dans des sables siliceux et sec de ticino sont presentes les ondes de cisaillement et de compression ayant w emises dans des directions verticales horizontales et obliques les 5 constantes independantes du modele eastique

bayesian identification of soil strata in london clay identification of soil strata in the london clay formation lcf is of practical significance as it allows geotechnical property data within the same soil strata to be compared or used effectively the soil strata in lcf are generally determined based on their lithological characters and fossil contents with which geotechnical engineers are less familiar to assist geotechnical engineers in identifying the soil strata in lcf this paper aims to develop bayesian approaches to identification of soil strata in lcf using water content data equations are derived for the proposed bayesian approaches and the approaches are illustrated using a water content profile at st james s park london the proposed bayesian approaches are shown to correctly identify the soil strata in lcf in addition a sensitivity study is performed to explore the effect of data quantity i e both the measurement interval and number of measurements at the same depth in a water content profile and provide guidance on the water conten

cross anisotropic deformation characteristics of natural sedimentary clays the cross anisotropic elasticity parameters were experimentally determined for six sedimentary clays of different ages and origins at both natural and reconstituted states by using high precision triaxial apparatus all the parameters and their dependency on the effective stress are satisfactorily described by a simple conventional power law model the patterns of the inherent anisotropy exhibited close agreement between the natural and reconstituted states suggesting that the development of natural microstructures due to ageing and diagenesis does not play a primary role in determining the anisotropy patterns in clays despite different degrees of stiffness anisotropy observed in the six clays relatively well defined correlations encompassing all the tested clays were found between certain stiffness parameters while fully characterising the drained elasticity moduli is still a challenging laboratory task these correlations will help estimate some of them based on more readily measurable undrained mo

a method of estimating surface settlement above tunnels constructed in soft ground a technique suitable for the analysis of lined tunnels constructed in soft soil is described this technique permits consideration of the soil lining interaction lining weight and plastic failure within the soil particular attention is given to the simulation of loss of ground including the annular void created by the difference between the tunnelling machine and lining diameters the analysis is used in a parametric study to identify potentially significant factors affecting the prediction of surface settlement due to tunnel construction consideration is given to the effects of elastic modulus the distance between the tunnel and the underlying rigid base stratum plastic failure initial stresses ground loss including the annular void and the injection of clay grout into the tailpiece void the results of this analysis indicate that elastic anisotropy ground loss and clay grout injection are all important factors that are not usually considered in analyses in particular a parameter called th

measurements and numerical simulations of inherent stiffness anisotropy in soft taipei clay abstractsoils are generally known not to be isotropic materials the inherent anisotropy of clays results from the deposition process which tends to induce a horizontal bedding plane in the soil layer in this paper the anisotropy of clays was studied to obtain more accurate analytical results for geotechnical problems especially for deep excavations in soft clay with nearby structures a series of k0 consolidated undrained triaxial compression ck0uc tests thus was conducted on tube samples of natural taipei silty clay with multidirectional bender elements a newly designed triaxial testing system equipped with a high precision servo motor and local strain sensors was developed a new soil suction control system was also developed to perform soil saturation for triaxial tests the suction control system was used to reduce the change in the void ratio during saturation in the triaxial tests soil samples were retrieved from a site near a well documented excavation case in taipei the anisotropy ratios

oxygen isotopes upper ocean salinity and precipitation sources in the eastern tropical pacific westward transport of freshwater across the panama isthmus helps to maintain the salinity s contrast between the atlantic and pacific oceans important in global thermohaline circulation and climate relatively low sea surface salinities in the panama bight reflect high net precipitation we infer sources of this freshwater input to the region based on oxygen isotopes 18o of precipitation p and seawater sw the primary trend of the surface water sw s relationship implies a freshwater endmember 18o of 8 5 0 3 significantly lower than the mean p of rainwater we measured in the region 4 8 1 8 mixing with waters upwelled from the subsurface s 34 9 35 1 psu sw 0 3 0 4 based on limited isotope and salinity data these upwelling waters are a mixture of 60 tropical waters and 40 subtropical mode waters three secondary trends in the surface water sw s distribution point to similar freshwater sources with 18o of 2 5 1 2 4 7 0 5 and 4 8 0 6 consistent with local precipitation sources accounting for the primary surface water trend intermittent cross isthmus transport of moist air masses from the caribbean may introduce relatively 18o depleted rainfall due to a combination of recycling and orographic distillation in addition relatively infrequent but large tropical storms which may contain freshwater of both pacific and caribbean origin deliver rainfall with p of 10 to 14 the primary trend of regional surface seawater data which integrates the different sources over time suggests that about half of the total precipitation reflects local sources and half reflects a combination of cross isthmus transport and large storms the regional sw s distribution is sensitive to the relative contributions of these freshwater sources which may change under different climate regimes

the stiffness of natural london clay an investigation of natural london clay is reported involving advanced triaxial hollow cylinder apparatus hca and dynamic testing techniques significant anisotropy was revealed at all scales of deformation and the framework of cross anisotropic elasticity was found to apply broadly to the initial elastic behaviour the stiffness parameters obtained by independent techniques generally exhibited good agreement with the greatest deviation being seen in the poisson s ratios which fell far from the values usually assumed in conventional foundation analysis probing tests established the limits to the elastic domain over a range of depths showing that these scaled in proportion to the mean effective stress level as did those of a second kinematic surface that surrounded the elastic domain once engaged this second surface signified a new pattern of strain increment directions faster elastic plastic stiffness decay with strain and also a greater dependence of behaviour on recent stress history howev

shifts in oxygen and carbon isotope signals in marine molluscs from the central paratethys europe around the lower middle miocene transition abstract stable isotope data of mollusc shells from two adjacent time slices karpatian badenian from the central paratethys were investigated to detect differences in environmental parameters and to depict shifts in the isotope signature of the paratethyan seawater around the early middle miocene transition altogether seventeen different gastropod species and one bivalve species from the karpatian korneuburg basin and the badenian northern alpine foreland basin were selected representatives of various ecological guilds yielded different isotope patterns especially in 13c reflecting different original habitats or nutrition although molluscs precipitate their shells in oxygen isotopic equilibrium we preferred to compare isotope data of shells of the same genus of the family turritellidae from the karpatian and badenian the badenian turritella shells from the northern alpine foreland basin yielded distinctly higher 18o and 13c values than the respective karpatian shells from the korneuburg basin as the main factors controlling 18o values in gastropod shells are temperature and 18o of the water during precipitation the differences between the oxygen isotope data of the two time slices can only be explained by these factors good independent palaeotemperature proxies exist for the early to middle miocene of central europe they do not indicate a significant temperature variation therefore different 18o values of the seawater in the different basins of the central paratethys must be responsible for the contrasting 18o values when calculated with commonly assumed 18o seawater values for the miocene badenian turritella shells indicate too cold temperatures these data clearly document the danger of palaeotemperature interpretations based solely on stable isotopes as smaller and marginal marine settings such as the paratethys sea can be seriously influenced by regional differences in the isotope composition of the seawater only a thorough consistent control by other climate proxies e g palaeoecology of molluscs as in this study allows a sensible interpretation

palaeoecology and evolution of marine hard substrate communities abstract marine organisms have occupied hard substrates since the archaean shells rocks wood and sedimentary hardgrounds offer relatively stable habitats compared to unconsolidated sediments but the plants and animals which inhabit them must develop means to gain and defend this premium attachment space hard substrate communities are formed by organisms with a variety of strategies for adhering to and or excavating the substrates they inhabit while mobile grazers organically attached and even soft bodied organisms may leave evidence of their former presence in ancient hard substrate communities a superior fossil record is left by sessile encrusters with mineralised skeletons and by borers which leave trace fossils furthermore encrusters and borers are preserved in situ retaining their spatial relationships to one another and to the substrate spatial competition ecological succession oriented growth and differential utilisation of exposed vs hidden substrate surfaces can all be observed or inferred hard substrate communities are thus excellent systems with which to study community evolution over hundreds of millions of years here we review the research on modern and ancient hard substrate communities and point to some changes that have affected them over geological time scales such changes include a general increase in bioerosion of hard substrates particularly carbonate surfaces through the phanerozoic this is at least in part analogous to the infaunalisation trends seen in soft substrate communities encrusting forms show an increase in skeletalisation from the palaeozoic into the mesozoic and cenozoic which may be a response to increasing levels of predation hard substrate communities considering borers and encrusters together show a rough increase in tiering through the phanerozoic which again parallels trends seen in soft substrate communities this extensive review of the literature on living and fossil hard substrate organisms shows that many opportunities remain for large scale studies of trends through time at the community and clade levels palaeontologists will especially benefit by closer integration of their work with that of neontologists particularly in aspects of ecology such as larval recruitment competition and succession

the late miocene panama isthmian strait miocene sediments of the caribbean gatun and chagres formations panama canal basin were deposited within an archipelagic strait that connected caribbean and pacific waters shallow water 25 m benthic foraminifera of the gatun formation have a strong caribbean affinity indicating that a significant interoceanic biogeographic barrier had formed at 8 ma however benthic foraminifera of the overlying chagres formation are bathyal and markedly pacific in affinity indicating that at 6 ma waters of the panama isthmian strait deepened to 200 500 m and pacific bathyal waters flowed into the caribbean the chagres formation crops out at the caribbean entrance to the panama canal in a large wedge of cross laminated sandstone and coquina the cross laminations and coarse grain size indicate high energy currents atypical of bathyal settings we infer that a jet of the pacific north equatorial countercurrent equatorial undercurrent passed through the panama isthmian strait to deposit these sediments on the caribbean side this later entry of pacific taxa into the caribbean had no apparent effect on the subsequent composition of caribbean faunas

the shear stiffness characteristics of four eocene to jurassic uk stiff clays a large proportion of the southern uk is underlain by stiff clays improving their geotechnical characterisation is important for many current and future infrastructure projects this paper presents an integrated study of the complex stiffness behaviour of four key medium plasticity highly overconsolidated strata the gault kimmeridge oxford and london clays the latter were deposited between the jurassic and the eocene under broadly similar marine conditions coordinated programmes of advanced static and dynamic laboratory measurements have been undertaken on high quality samples concentrating on samples taken from similar depths at inland sites and including triaxial and hollow cylinder stress path experiments employing high resolution local strain multi axial bender element and resonant column techniques a new approach was employed to interpret the hollow cylinder experiments and the laboratory measurements are examined in combination with independent field shear wave data the clays stiffness c

effects of undrained strength anisotropy on surface subsidences induced by the construction of shallow tunnels the implementation of an anisotropic soil model that allows consideration of the variation of undrained strength due to anisotropy is described this analysis is then used to identify the significance of strength anisotropy on the prediction of deformation behaviour of a shallow tunnel it is found that for the case of an unlined tunnel attention should be given to the effect of strength anisotropy particularly for a soil possessing type k anisotropy i e where the smallest undrained strength occurs at an angle other than the vertical or the horizontal and the smallest value usually occurs at an angle of 45 deg on the other hand for a lined tunnel the effect of strength anisotyopy upon the surface settlement profile will depend upon the size of a so called gap parameter the gap represents the net effect of loss of ground and some workmanship factors in a plane strain finite element analysis increasing the gap eases the restrictions imposed by the tunnel lining upon possible soil deformations thereby increasing the effect of strength anisotropy however it is shown that for a lined tunnel with a moderate value of gap detailed consideration of strength anisotropy may not be necessary

three dimensional modelling of natm tunnelling in decomposed granite soil three dimensional analyses of tunnel excavation and lining construction are rarely performed in practice because it is difficult to reproduce the exact boundary conditions involved in this process and because such analyses require considerable computing resources if realistic non linear soil behaviour is to be reproduced this paper presents a pseudo three dimensional analysis of tunnel construction by utilising the fourier series aided finite element method fsafem the theory behind this approach and its validation when applied to a tunnelling problem are described the method is then used to predict the behaviour of tunnels forming part of the seoul subway system in korea the results are compared with field measurements

interpretation of free field ground movements caused by mechanized tunnel construction abstractthis paper summarizes greenfield ground movements caused by the construction of twin 7 1 m diameter tunnels for london s crossrail project using earth pressure balance epb tunnel boring machines tbm the data include surface deformations from a series of transects in hyde park together with subsurface data from one well instrumented test section although far field ground movements can be well fitted using established empirical methods or simplified analytical solutions elastic half space nonlinear inelastic soil behavior is expected to affect measurements close to the tunnel this paper considers the effects of constitutive behavior on the observed ground movements simple mohr coulomb m c and more complex mit s1 soil models are calibrated using results of high quality laboratory element tests on intact london clay the models are then used in two dimensional 2d numerical simulations in order to optimize three independent cavity deformation parameters that control the spatial dist

storm and fair weather wave base a relevant distinction surface waves are an important mechanism for the redistribution of sediment on shallow marine shelves and are commonly interpreted as comprising two distinct populations fairweather waves and storm waves the latter of which are generally thought to penetrate to greater water depths here we used 2 3 10 6 spectral density estimates for the surface ocean collected between 1996 and 2008 from 32 buoys in the caribbean the gulf of mexico and the western atlantic to test the hypothesis that surface waves in the modern ocean comprise two size modes although distinct wave size classes occur in some individual measurements and over the time scales of some individual storms time averaged frequency distributions of wave size are unimodal thus there is no empirical basis for presupposing a distinct bimodal separation in the size of fair weather and storm waves or in the manifestation of such differences in stratigraphic successions instead there is a continuously increasing probability that a wave will reach the bottom with decreasing water depth and a separate probability that describes the hydrodynamic state of the sediment water interface wave size does however exhibit signifi cant geographic bimodality locations in the relatively protected gulf of mexico and caribbean regions have modal wavelengths that are 50 m less than waves at locations along the western atlantic time integrated estimates of the depth of wave penetration provide empirical constraints on the paleo water depths of ancient sedimentary deposits and highlight differences between sheltered shelf environments such as those that characterized many ancient epeiric seas and open ocean facing narrow continental shelves

consequences of shoaling of the central american seaway determined from modeling nd isotopes the central american seaway played a pivotal role in shaping global climate throughout the late cenozoic recent geological surveys have provided new constraints on timing of the seaway shoaling while neodymium isotopic e nd data measured on fossil teeth debris and ferromanganese crusts have helped define the history of water masses in the region here we provide the first 3 d simulations of e nd responses to the shoaling seaway our model suggests that a narrow and shallow seaway is sufficient to affect interoceanic circulation that inflow outflow balance between the caribbean and the antilles responds nonlinearly to sill depth and that a seaway narrower than 400 km is consistent with an active atlantic meridional overturning circulation during the late miocene simulated e nd values in the caribbean confirm that inputs from radiogenic pacific waters in the caribbean decrease as the seaway shoals despite model limitations a comparison between our results and e nd values recorded in the caribbean helps constrain the depth of the central american seaway through time and we infer that a depth between 50 and 200 m could have been reached 10 ma ago

surface settlements due to deformation of a tunnel in an elastic half plane deformations of a tunnel may result in settlementsof the ground surface in engineering practice thesesurface settlements are often described by empiri cal formulae based upon eld observations forinstance a normal gaussian distribution curve peck 1969 attewell woodman 1982 in thisnote an approximate analytical solution is presented considering the soil as a linear elastic material although it is realized that this is a very poorschematization of the real behaviour of soils anelastic solution may well serve to investigate someof the characteristics of the resulting elds of stressand strain and it may also serve as a reference formore re ned numerical computations two basic deformation mechanisms of thetunnel are considered a uniform radial displace ment representing in rst approximation theground loss that may occur during constructionof the tunnel and an ovalization of the tunnel see fig 1 even though in practice the tunnellingprocess may be executed very carefully andappropriate engineering techniques may be appliedto minimize the deformations for instance theinjection of grout into the soil surrounding thetunnel it remains of interest to study the defor mations and stresses caused by both ground lossand ovalization the method used is an extension of a methodsuggested by sagaseta 1987 for the case ofground loss in an incompressible soil the startingpoint is the solution for a singularity at a point ofan elastic half plane at the axis of the tunnel byadding the image solution for a singularity at apoint located symmetrically above the soil surface the shear stresses at the surface are made equal tozero in order to balance the normal stresses at thesurface a third solution is added by solving aboussinesq type problem the approximation inestablishing the solution is that in balancing thenormal and tangential stresses on the surface thepresence of the tunnel with its prescribed dis placements is disregarded although an exactsolution might well be obtainable by the methodsoutlined by mindlin 1939 using bipolar coordi nates such a solution is very complicated thepresent approximate solution will be seen to bevery simple and easy to apply the solution given in this technical note is ageneralization of sagaseta s solution in that it givesthe solution for the case of ground loss not onlyfor the incompressible case with poisson s ratioequal to 0 5 but for arbitrary values of poisson sratio and that it includes the effect of ovalization the process of ovalization has been studied beforefor a tunnel in an in nite elastic medium muirwood 1975 here the surface displacements for atunnel in a semi in nite medium are considered aswell as the displacements and stresses throughoutthe half space

ecological and paleoenvironmental information using stable isotope profiles from living and fossil molluscs stable oxygen and carbon isotopic profiles from recent specimens of spisula solidissima and placopecten magellanicus collected off the virginia coast are used to calibrate annual temperature controlled cycles in the 18o profile and shell growth characteristics the amplitude of the annual 18o cycles decreases with increasing water depth and may be used as a relative depth indicator the isotopic of profiles of two fossil specimens of pleistocene spisula are very similar in amplitude and character to modern analogues and verify the formation of annual growth increments in these fossil specimens offsets between the 18o profiles of the fossil and modern specimens are related to known temperature and ice volume effects during the late pleistocene and support the utility of mollusc isotope records as a stratigraphic tool carbon isotopic profiles from all specimens show light values in the spring and or fall associated with seasonal phytoplankton productivity offsets in the carbon isotopic composition between infaunal and epifaunal species may be related to sediment porewater geochemistry and oxidation of organic matter trends toward lighter 13c values through ontogeny suggest the effects of metabolic changes from a fast growing juvenile into a slower growing sexually mature adult anomalies in both the oxygen and carbon isotopic profiles identify the formation of minor shell growth increments as corresponding to hydrographic perturbations and to winter cold temperatures

simple approach to predicting ground displacements caused by tunnelling in undrained anisotropic elastic soil an attempt to develop a kinematically based approach to predicting ground settlements due to tunnelling is represented by using the more reliable data of the commonly observed settlement troughs rather than imposing the boundary conditions on the tunnel surface which have a high level of uncertainty the anisotropic elastic model used in this work is highly simplified and the resulting analytical solution is of an approximate nature nevertheless it seems to provide good agreement with both the shape and the magnitude of the observed settlement trough based on this solution a modification is proposed for the widely used empirical gaussian curve by correlating the trough width parameter k with the ratio between the two anisotropic shear moduli ghh gvh

isotopic paleoceanography of the caribbean and east pacific role of panama uplift in late neogene time comparisons of carbon isotopic data on benthic foraminifera from deep sea drilling project sites 502 western caribbean and 503 eastern pacific indicate that the difference between the atlantic and the pacific in the per mil enrichment in carbon 13 of total dissolved carbon dioxide increased about 6 million years ago and again 3 million years ago when the difference reached the modern level 1 per mil comparisons of planktonic foraminiferal oxygen isotopic data for the caribbean and the pacific suggest that the salinity of caribbean surface waters began increasing 4 million years ago possibly in response to shoaling of the panama isthmus these results suggest that modern circulation patterns in the caribbean and eastern pacific developed by 3 million years ago in concert with changing tectonic climatic and biogeographic patterns

tunnelling induced deformation and damage on historical masonry structures the analysis of deformation and damage mechanisms induced by shallow tunnelling on masonry structures is carried out using an integrated geotechnical and structural numerical approach based on two dimensional finite element analyses the masonry construction schematised as a block structure with periodic texture is regarded at a macroscopic scale as a homogenised anisotropic medium the overall mechanical properties display anisotropy and singularities in the yield surface arising from the discrete nature of the block structure and the geometrical arrangement of the blocks the soil is modelled by means of a linear elastic perfectly plastic model the numerical analyses are performed assuming plane strain and plane stress conditions for the soil and the masonry structure respectively a displacement controlled technique is adopted to simulate the tunnel construction which produces settlement troughs in agreement with the empirical gaussian predictions at different volume losses under free field con

rock mass collapse mechanism of concealed karst cave beneath deep tunnel abstract local collapse of the surrounding rock often occurs during tunnel construction in a karst area particularly when the rock pillar between the tunnel and the karst cave is very thin the collapse of the surrounding rock in tunnel construction is sudden and may lead to great economic loss or even loss of life to predict the collapse of rock mass where a tunnel is excavated above a karst cave an analytical expression of the collapse surface is derived from variational calculation in the framework of the upper bound theorem based on the analytical solution the shape of the collapse surface is plotted to investigate the effects of rock parameters on the collapse surface of the rock mass where a karst cave exists beneath a tunnel according to the changing law of the collapse surface varying with the distance between tunnel and cave the computational formula of the minimum safety thickness for preventing the collapse of rock pillar is derived to evaluate the validity of the proposed method in this paper we compared the analytical solution with numerical solution the comparison result indicates the analytical solution matches up with the numerical solution very well which suggests that the analytical approach proposed in this paper is valid

evolution of early cenozoic marine temperatures the equator to high southern latitude sea surface and vertical temperature gradients are reconstructed from oxygen isotope values of planktonic and benthic foraminifers for the following five time intervals late paleocene early eocene early middle eocene late eocene and early oligocene paleotemperatures are calculated using standard oxygen isotope temperature equations with adjustments to account for 1 variations in sea water 18o related to changes in global ice volume over time and 2 latitudinal gradients in surface water 18o these reconstructions indicate that sea surface temperatures sst of the southern oceans in the early eocene were as high as 15 c whereas temperatures during the late paleocene and early middle eocene reached maximum levels of 10 12 c by the late eocene and early oligocene high latitude sst had declined to 6 and 4 c respectively for most of the early paleogene low latitude sub tropical temperatures remained constant and well within the range of holocene temperatures 24 ndash 25 c but by the late eocene and early oligocene declined to values in the range of 18 to 22 c the late paleogene apparent decline in tropical temperatures however might be artificial because of dissolution of near surface foraminifera tests which biased sediment assemblages toward deeper dwelling foraminifera moreover according to recent plate reconstructions it appears that the majority of sites upon which the late eocene and early oligocene tropical temperatures were previously established were located either in or near regions likely to have been influenced by upwelling global deepwater temperature on average paralleled southern ocean sst for most of the paleogene we speculate based on the overall timing and character of marine sea surface temperature variation during the paleogene that some combination of both higher levels of greenhouse gases and increased heat transport was responsible for the exceptional high latitude warmth of the early eocene

deformation characteristics of a clayey interbed during fluid injection surface deformation due to fluid withdrawal has long been observed at the surface above aquifers and oil reservoirs uplift associated with fluid injection has also been observed although the processes of subsidence and uplift are reversible in a poroelastic setting the presence of clayey interbeds can result in ground deformation behavior non reversible because of their low permeability and nonlinear behavior in this investigation a cam clay model is used in conjunction with a poroelastic model to simulate the presence of a laterally extensive lens shaped clayey interbed in a sandstone aquifer during fluid injection spatial and temporal changes associated with this interbed during aquifer pressurization are captured and can be clearly differentiated from the deformation of the surrounding poroelastic aquifer formation results for pore pressures and ground surface deformation patterns can be categorized into three distinct time intervals an early time interval where the aquifer is pressurized but not the interbed leading to a lower region above the interbed an intermediate time interval in which the interbed pressures slowly increase approaching the pressure of the adjacent aquifer leading to a potentially large surface uplift above the interbed and a late time interval in which pressure equilibration is achieved between the interbed and aquifer and a highly non symmetrical irregular surface deformation pattern results which may be higher or lower than the background depending on the interbed characteristics reservoir configuration is found to be an important factor influencing ground deformation behavior with more obvious deformation always occurring in a laterally confined aquifer as opposed to a laterally infinite aquifer

cretaceous marine nutrients greenhouse carbonates and the abundance of turritelline gastropods abstract modern marine carbonate sediments accumulate where carbonate producing organisms are abundant and siliciclastic input is low such accumulations occur today in two main environments and may be characterized as warm low nutrient wln also known as tropical or chlorozoan carbonates or cool high nutrient chn also known as cool water temperate nontropical foramol or heterozoan carbonates few carbonates form today in warm high nutrient whn conditions because such environments are very rare modern wln environments occur mainly in low latitudes where nutrients from upwelling or terrestrial runoff are low modern chn environments occur mainly in middle to high latitudes where nutrients mostly from upwelling are abundant however whn depositional environments may have been widespread during the cretaceous and paleogene during these times upwelled nutrient rich waters would in general have been warmer than they are today nutrients in these waters supported diverse carbonate produc

analytical prediction for tunneling induced ground movements in clays current design practice to predict tunneling induced ground movements is generally based on empirical methods that are subjected to some important limitations for a ground deformation prediction d

the use of kinematic hardening models for predicting tunnelling induced ground movements in london clay the use of a kinematic hardening soil model for predicting short and long term ground movements due to tunnelling in london clay is investigated the model is calibrated against oedometer and triaxial tests on intact samples from different units of the london clay the calibrated model is then used in finite element analysis to simulate the field response at st james s park during excavation of the jubilee line extension tunnels the finite element predictions compare well with the available field monitoring data the importance of using consistent initial conditions for this complex boundary value problem in conjunction with the model parameters selected is highlighted the stiffness response of different regions of the finite element mesh indicates that the rate at which the stiffness degrades and the stiffness response further away from the tunnel boundary affect the short term predictions significantly the long term predictions confirm that the compression characteristics of the soil control the mag

effect of recent stress history on the stiffness of overconsolidated soil the stress strain behaviour of overconsolidated soil is non linear and the stiffiiess depends on the current state and stress history in addition to the overall stress history which is best described by the overconsolidation ratio the recent stress history either a sudden change in the direction of the stress path or a period of time at a constant stress state has a major effect on subsequent stiffiiess the effects of a change in the direction of the loading path on the stiffness of overconsolidated soil were examined in laboratory stress path tests on reconstituted samples of london clay further tests were carried out on reconstituted samples of other soils with a range of plasticities the test results showed that the behaviour of over consolidated soil is largely inelastic and highly nonlinear and that the recent history has a major effect on the subsequent stiffiiess particularly for relatively small changes of stress or strain for reconstituted samples of london clay the stiffiiess near the s

recent stress history effects on compressible chicago glacial clays this paper presents the results of an experimental program to investigate recent stress history effects on small strain stiffness of lightly overconsolidated compressible chicago glacial clays stress probe tests with different recent stress histories were conducted on high quality block samples taken from an excavation in evanston illinois the stress histories applied prior to probing represent in situ greenfield conditions and an unloading path associated with a common situation encountered when building in congested urban areas results of the stress probe tests are compared in terms of shear volumetric and coupled components and their stiffness degradation strain response envelopes were constructed in shear and volumetric strain space to graphically show the significant difference in these responses between the two sets of stress probe tests the results clearly indicate that the recent stress history affects shear bulk and the two cross coupled moduli of the chicago clays as a function of the

an analysis of three dimensional ground movements the thunder bay tunnel a three dimensional 3d elastoplastic finite element analysis which is capable of simulating the advance of a tunnelling shield and the associated ground losses resulting from the tunnelling process is used to calculate the deformations caused by the excavation of the thunder bay sewer tunnel the soil parameters adopted in the analysis were based on the results determined from stress dependent triaxial tests the results of this analysis are compared with the measured soil displacements reasonable agreement between the calculated and observed 3d settlement distribution and horizontal displacements at different distances from the tunnel face is reported this overall agreement for displacements under 3d conditions suggests that the method of analysis may be applicable to design problems involving tunnelling in soft clays similar to that at the thunder bay sewer tunnel provided that the soil parameters are reliably determined key words tunnelling three dimensional analysis finite element elastopla

quaternary glaciation and the great american biotic interchange recent geological studies demonstrate that the isthmus of panama emerged some 10 m y earlier than previously assumed although absent today in panama central american savanna environments likely developed in connection with the onset of northern hemisphere glaciations as is widely recognized most of the mammals crossing the isthmus since 2 5 ma lived in savannas could climate induced vegetational changes across panama explain the delayed migration of mammals rather than terrestrial connectivity we investigate the congruence between cross continental mammal migration and climate change through analysis of fossil data and molecular phylogenies evidence from fossil findings shows that the vast majority of mammals crossed between south and north america after ca 3 ma by contrast dated mammal phylogenies suggest that migration events started somewhat earlier ca 4 3 ma but allowing for biases toward greater ages of molecular than geologic dating and uncertainties in the former we consider this age range not to be significantly earlier than 3 ma we conclude that savanna like environments developed in response to the vast laurentide ice sheet at the first quaternary glaciation triggered the initiation of the great american biotic interchange in mammals

flow reorganizations in the panama seaway a cause for the demise of miocene corals 1 a large number of coral species in the caribbean sea disappeared in the early miocene based on climate model simulations we propose that this regional extinction is related to a flow reorganization in the panama seaway it is shown that large scale tectonic events such as the opening of drake passage and the closing of the tethys seaway reorganized the global ocean currents to induce a reversal of the volume transport between atlantic and pacific this flow reversal which is timed near the oligocene miocene boundary allowed cool pacific waters to enter the caribbean sea possibly affecting the habitat of warm water tolerant coral species

effect of the formation of the isthmus of panama on atlantic ocean thermohaline circulation the late cenozoic closure of the seaway between the north andsouth american continents is thought to have caused extensive changes in ocean circulation and northern hemisphere climate1 2 but the timing and consequences of the emergence of the isthmus of panama which closed the seaway remain controversial1 2 3 4 5 here we present stable isotope and carbonate sand fraction records from caribbean sediments which when compared to atlantic and pacific palaeoceanographic records indicate that the closure caused a marked reorganization of ocean circulation starting 4 6 million years ago shallowing of the seaway intensified the gulf stream and introduced warm and saline water masses to high northern latitudes these changes strengthened deep water formation in the labrador sea over the next million years as indicated by an increased deep water ventilation and carbonate preservation in the caribbean sea and favoured early pliocene warming of the northern hemisphere the evaporative cooling of surface waters during north atlantic deep water formation would have introduced moisture to the northern hemisphere although the pronounced intensification of northern hemisphere glaciation between 3 1 and 2 5 million years ago substantially lagged the full development of north atlantic deep water formation we propose that the increased atmospheric moisture content was a necessary precondition for ice sheet growth which was then triggered by the incremental changes in the earth s orbital obliquity

tracking changes in the specific storage of overburden rock during longwall coal mining the hydraulic properties of geologic formations such as specific storage and hydraulic conductivity are known to vary spatially due to formation heterogeneity however they may also change temporally if the formation undergoes mechanical disturbance such as occurs during mining characterising changes in hydraulic properties is important for groundwater systems that are disturbed by mining conventional hydrogeological investigations rely on literature derived values or limited programs of field testing e g pumping test to define specific storage but these approaches do not consider the change in compressibility that may occur due to mechanical disturbance this paper presents for the first time direct in situ measurements of the changes in compressibility and consequently specific storage as a result of mechanical disturbance within geologic formations overlying underground mining operations the in situ measurements of compressibility are derived in this study from the pore pressure response to barometric loading or strains induced by earth tides even prior to disturbance the compressibility obtained from in situ measurements was found to be an order of magnitude lower than that measured on core samples by unconfined strength test in the laboratory the differences in compressibility for the intact formation are likely due to sample disturbance and the differences in strain level imposed by the field and laboratory methods the increase in compressibility of the overburden rock varied with the location of the monitoring site relative to longwall extraction and the level of strain the formation sustained the study found that quantifying the changes in compressibility and consequently specific storage as a result of mine induced disturbance is critical to our understanding of subsidence the extent of depressurization and the impact that mining may have on regional groundwater flow systems

cenozoic deep sea temperatures and global ice volumes from mg ca in benthic foraminiferal calcite a deep sea temperature record for the past 50 million years has been produced from the magnesium calcium ratio mg ca in benthic foraminiferal calcite the record is strikingly similar in form to the corresponding benthic oxygen isotope 18o record and defines an overall cooling of about 12 c in the deep oceans with four main cooling periods used in conjunction with the benthic 18o record the magnesium temperature record indicates that the first major accumulation of antarctic ice occurred rapidly in the earliest oligocene 34 million years ago and was not accompanied by a decrease in deep sea temperatures

role of panama uplift on oceanic freshwater balance comparison between planktic foraminiferal oxygen isotope records from the caribbean sea ocean drilling program odp site 999 and the equatorial east pacific odp site 851 suggests an increase in caribbean surface water salinity between 4 7 and 4 2 ma the modern atlantic pacific salinity contrast of about 1 became fully established at 4 2 ma as reflected by a 0 5 planktic foraminifera 18o enrichment in the caribbean sea this is interpreted as the result of restricted surface water exchange between the tropical atlantic and pacific in response to the shoaling of the central american seaway as a consequence the atlantic and pacific surface ocean circulation regime changed as did the freshwater balance between the major ocean basins simultaneous shifts in benthic carbon isotope records in the caribbean sea suggest an intensification in north atlantic thermohaline circulation these results indicate that the panamanian isthmus formation caused several new ocean atmosphere feedback mechanisms that have affected climate since the early pliocene

changes in caribbean surface hydrography during the pliocene shoaling of the central american seaway pliocene d18o records of shallow and deep dwelling planktonic foraminifers from the caribbean ocean drilling program sites 999 and 1000 the tropical east pacific sites 1241 and 851 and the atlantic site 925 ceara rise and site 1006 western great bahama bank were used to examine atlantic caribbean pacific atmospheric and oceanic linkages associated with the progressive closure of the central american seaway 5 5 3 ma comparisons indicate the development of an inner caribbean salinity gradient in the mixed layer and salinity changes on precessional periodicities after 4 4 ma site 1000 when the pacific caribbean throughflow became significantly restricted the high amplitude variability in salinity is also observed at site 1006 monitoring the caribbean outflow into the atlantic comparisons of caribbean and atlantic planktonic d18o records suggest the north atlantic subtropical gyre as a major source for high salinity surface waters precession induced variations in the volume transport of pacific surface water masses through the panamanian seaway are considered a main factor to explain the caribbean salinity minima results from a coupled climate model point to changes in the el nin o southern oscillation state as a potential trigger for changes in the amount of pacific inflow into the caribbean

winter and summer temperatures of the early middle eocene of france from turritella δ18o profiles the mean annual range of temperature is from a climatological point of view at least as important as the mean annual temperature in order to examine intra annual temperature variations in the warm early cenozoic we have analyzed stable oxygen and carbon isotopes along the transect of growth on excellently preserved specimens of the gastropod turritella imbricataria and the bivalve venericardia imbricata from sedimentary rocks of early middle eocene age ca 46 ma in the paris basin turritella shell growth is fast throughout the year and the isotopic records give the first detailed information about early middle eocene seasonal variations the oxygen isotope profiles indicate winter temperatures of about 14 c and summer temperatures of up to 28 c i e a seasonality indistinguishable from the present situation but an annual temperature some 10 c higher our results contradict the opinion that the climate during this period was more equable than that of today