yield strength and critical state behavior of a tropical saturated soil the paper reports laboratory investigations carried out on a tropical soil profile to study its compressibility strength critical state and limit state conditions and their variation with depth the soil profile comprises a reddish lateritic layer horizon b underlain by a saprolitic soil horizon c from which a number of block samples were taken a series of isotropic and anisotropic compression tests and drained and undrained triaxial tests were conducted on specimens sampled at depths between 1 0 and 7 0 m and also in the exposed saprolitic soil special triaxial tests with the pore pressure increased to induce failure were performed to investigate the failure at low stress levels on this basis a tensile cutoff on the failure envelope was defined in order to assess the influence of the natural soil structure drained and undrained triaxial tests were carried out on compacted samples obtained from depths of 1 0 and 5 0 m higher strength parameters were measured for the horizon c soil which

structural control and tectonic setting of mesozoic volcanism in hong kong middle jurassic to lower cretaceous silicic volcanic rocks and granitoid plutons in hong kong form part of the broad ne trending yanshanian tectonomagmatic belt that extends through se china pyroclastic deposits in hong kong are typically proximal and infill linear flared vents and ellipsoidal calderas these pass down through elongate rift like conduits into extensive multiple fault and shear zone hosted 9sheeted9 dyke complexes and granitoid plutons dykes also emphasize the limits of calderas the spatial distribution and geometry of the vents calderas dykes and plutons are structurally controlled during each of four temporally well constrained periods of petrogenetically related volcanism and plutonism e and ene trending axes of extension and transtension were dominant nw trending faults increased in importance with time and their intersections with ene trending faults influenced the loci of volcanic centres nesting of the calderas confirms persistent reactivation of some faults the loci of magmatism migrated over 25 ma from nw to se zones of silicic crust created during these magmatic episodes have a broadly tripartite crustal 9stratigraphy9 pluton dyke volcanic reminiscent in very general terms of ophiolites the zones were created during periods of unusually rapid extension as the continental margin of se china changed from an active margin dominated by subduction to a back arc regime and dextral strike slip along ene trending faults gave way to sinistral strike slip

independence of geostatic stress from overconsolidation in some beaufort sea clays reply since 1982 extensive use has been made of the self bored pressuremeter in arctic offshore site investigations one finding of this work is that the in situ geostatic stress ratio k0 of beaufort sea clays is apparently unrelated to the overconsolidation ratio ocr the procedures and data to support this finding are documented and the finding is discussed in light of the present geological understanding for the area it is concluded that the independence of k0 from ocr may be quite widespread a finding that contradicts the widely held tenet regarding the existence of a single valued function relating k0 and ocr if k0 is regarded as important then it should be measured in situ key words self bored pressuremeter geostatic stress ratio k0 beaufort shelf geologic history overconsolidation ratio

influence of compaction procedure on the mechanical behaviour of an unsaturated compacted clay part 2 shearing and constitutive modelling the influence of compaction pressure compaction water content and type of compaction static or dynamic on subsequent soil behaviour was investigated by conducting controlled suction triaxial tests on samples of unsaturated compacted speswhite kaolin compaction pressure influences initial state by determining the initial position of the yield surface thus affecting among other things the shape of stress strain curves during shearing compaction pressure also influences to a limited degree the positions of the normal compression lines for different values of suction but it has no effect on critical state relationships the effect of compaction pressure can probably be modelled solely in terms of initial state if an anisotropic elastoplastic model incorporating rotational hardening is employed whereas the parameters defining the slopes and intercepts of the normal compression lines for different values of suction require adjustment with variation of compaction pressure if a conventional isotropic

facies and climate environmental changes recorded on a carbonate ramp a sedimentological and geochemical approach on middle jurassic carbonates paris basin france a detailed sedimentological geochemical and mineralogical study is carried out on the early bajocian to early callovian middle jurassic limestones of the paris basin objectives are to document and explain the facies changes in the context of the climate environmental evolution at the nw european scale deposits include 18 lithofacies which are stacked into 10 third order depositional sequences at a greater time scale 4 biosedimentary packages are distinguished by their allochems associations 1 an intracratonic carbonate environment with coral reefs and crinoid rich facies is typical of the early bajocian 2 a major facies change occurred at the early late bajocian transition with a shift from crinoid and coral rich facies to ooid rich facies during the late bajocian a southward dipping ooid ramp with successive progradational trends was emplaced 3 a large lagoon protected by ooid shoals developed during the bathonian in a muddy ramp setting 4 at the bathonian callovian boundary a second major change occurred with the lagoonal facies being superseded by an ooid bioclastic crinoids corals ramp associated with a waning of carbonate productivity retrogradational trend our geochemical study including a compilation of bibliographic data allows us to refine the existing sea surface palaeotemperature pattern a cooling from the latest early bajocian to the late bajocian and a subsequent warming from the earliest callovian to the early middle callovian transition are described using a proxy of sea surface temperatures together with 13c and mineralogical data our new 18o values suggest a palaeo climatic palaeo environmental control of facies in this shallow carbonate ramp environment

geochemistry of coeval mesozoic plutonic and volcanic suites in hong kong middle jurassic to lower cretaceous intermediate to silicic plutonic and volcanic rocks of hong kong record a transition from calc alkaline through high k calc alkaline to transitional shoshonitic compositions with time close spatial and temporal associations among comagmatic volcanic plutonic pairs indicate that magmatism occurred in discrete episodes mostly of less than one million years duration synchronous high k calc alkaline and transitional shoshonitic magmatic activity during at least one pulse suggests a relatively rapid transition from a subduction related to an extension related tectonic setting geochemical signatures indicate that the magmatic suites have a mantle origin with a decreasing crustal contribution from two distinct sources the earliest mantle derived magmas interacted strongly with a dominantly archaean crustal protolith younger magmas show evidence for interaction with a dominantly proterozoic crustal protolith the strongest mantle influence is shown by magmas which were intruded along the boundary between the two dominant crustal sources this interface marks a deep crustal discontinuity which promoted the passage of magmas to the surface

yield states and stress strain relationships in a natural plastic clay reply natural clays are commonly anisotropic due to their mode of deposition and lightly overconsolidated because of a variety of subsequent geological processes they exhibit marked changes in stiffness when they yield yield stresses from individual tests can be generalized into a yield surface for the clay if displacements during loading are taken into account by calculating specific volumes v 1 e throughout the tests this paper describes tests on 76 mm diameter triaxial samples of natural plastic lake agassiz clay from winnipeg the samples were carefully trimmed reconsolidated to approximately their in situ stresses and loaded in stress controlled tests along various stress paths in p q stress space the tests produced well defined yield envelopes in p q p v and q v plots and in corresponding plots where the stresses were normalized with respect to the vertical preconsolidation pressure vc comparison of one dimensional yielding states with results from k0 triaxial tests that were continu

modified cam clay modelling of temperature effects in clays the cam clay model for isothermal mechanical behaviour of clays has been extended to take account of the effects of temperature on stress strain behaviour the assumptions used in constructing the new model are based on published results and on new data presented in the paper the model allows prediction of how heating and cooling af fect volume changes pore water pressures and strengths for both normally consolidated and overconsolidated saturated clays it permits modelling of observed reductions in the overconsolidation ratio with increasing temperature the model provides accessible qualitative explanations for temperature effects that were previously difficult to understand it will also allow easy implementation for quantitative modelling in triaxial stress fields results predicted by the model are compared with data collected by the authors at temperatures up to 100 c the model does not account for changes that occur in clay minerals at higher temperatures for example in bentonites at temperatures higher than about 150 c

seepage leaching and embankment instability water retention dykes at a hydroelectric generating station in southeastern manitoba experienced irregular instabilities over many years after they were heightened in the late 1940s samples from an unstable section of dyke showed considerable reductions in gypsum content and increased brittleness compared with those of neighbouring unloaded clay the samples also showed that lowering the content of gypsum reduced the sizes of yield loci and the strains required for strain softening to occur these observations and the time dependent nature of the problem suggested that seepage from the forebay had leached naturally occurring cementation from the foundation clay and subsequently changed its behaviour stress deformation modeling indicated the foundation clay had yielded during initial construction and again when the dykes were heightened seepage from the forebay occurred at different rates in different locations through the irregular sand silt partings that are generally present in proglacial clays leac

new u pb age and geochemical constraints on the stratigraphy and distribution of the lantau volcanic group hong kong abstract seven new high precision u pb single crystal zircon ages are reported from jurassic and early cretaceous volcanic rocks in the hong kong special administrative region sar these ages are used in combination with zr vs tio2 ratios to refine the stratigraphy of the lantau volcanic group on lantau island and in adjoining districts in hong kong as a result three major unconformities are proposed and the rift controlled paleogeography of the region which influenced the development of the lantau caldera and lacustrine basins during the latest jurassic to earliest cretaceous is clarified the data also suggest the possibility that the base of the cretaceous system may be preserved within the sequence

an assessment of the earth pressure coefficient in overconsolidated clays the determination of the earth pressure coefficient k0 in a natural clay deposit is a problem of considerable significance in geotechnical engineering while the methods for evaluation of k0 are reliable for normally consolidated soils significant difficulties still exist in evaluating k0 in overconsolidated clays given that it is influenced by the stress history of the material together with the age structure mineralogical composition and depositional environment indeed some of these factors are responsible for the soil becoming anisotropic the existing framework for prediction of k0 in overconsolidated soils does not account for any influences caused by anisotropy the work reported in this paper evaluates the validity of a revised relationship between k0oc and ocr overconsolidation ratio using data obtained from laboratory investigations the tests were performed on reconstituted and undisturbed samples of belfast upper boulder clay london clay and gault clay tests were also performed on re

yielding and plastic behaviour of boom clay an underground research laboratory url has been excavated in a deposit of boom clay at a depth of 223 m by the sck cen belgian organisation near the city of mol this url is devoted to research into nuclear waste disposal this paper presents the results of an investigation carried out in the triaxial apparatus on specimens that were trimmed from blocks extracted during excavation sequences in the url in order to characterise the mechanical behaviour of the natural boom clay and to examine the effect of initial and induced anisotropy on its constitutive behaviour two series of triaxial tests were carried out special attention was devoted to the yield behaviour and the effects of stress history experimental results showed a clear relation between the shape of yield curves and stress history the yield curve of the clay in its initial state was oriented along the k0 line illustrating the anisotropy of fabric that was generated during the soil deposition subsequent isotropic compression up to 9 mpa

evaluation of the predictive ability of two elastic viscoplastic constitutive models two elastic viscoplastic constitutive formulations are evaluated using laboratory and field data from sackville new brunswick and gloucester ontario both constitutive models have been implemented in a finite element program and formulated for undrained analysis and fully coupled analysis based on biot consolidation theory a laboratory study of the rate sensitive behaviour of sackville clay is described the response of sackville clay during consolidated anisotropic undrained cau triaxial creep cau triaxial compression and incremental oedometer consolidation is compared with the calculated behaviour the comparisons demonstrate the general ability of three parameter elastic viscoplastic constitutive models to satisfactorily describe the rate dependent behaviour of sackville clay the measured response of gloucester clay during long term rowe cell consolidation tests is compared with the calculated behaviour and the predictive ability of both constitutive formulations is evaluated using the field p

stress release undrained storage and reconsolidation in simulated underwater clay triaxial testing has examined the influence of storage time and reconsolidation procedures on normally consolidated and overconsolidated samples of reconstituted clay prepared with high pore water pressures to simulate underwater deposits samples of illite were consolidated one dimensionally off loaded without drainage stored undrained reconsolidated and sheared undrained the storage times were 15 min 1 day and 7 days reconsolidation pressures were 1 isotropic to 2 isotropic to and 3 anisotropic to the results were compared with specimens that had not been off loaded different undrained storage times had no effect on the strengths after reconsolidation but the strengths were affected by the reconsolidation pressures anisotropic reconsolidation produced the best agreement between the control specimens and samples in terms of their strengths and af values the duration of storage time did affect stress strain parameters such as the undrained compression modulus e50 and the pore

volcanic plutonic connections in a tilted nested caldera complex in hong kong 1 exceptional exposures of four precisely dated middle jurassic to early cretaceous silicic volcanic centers and their plutonic equivalents in hong kong have provided an excellent opportunity to examine close connections in time and space between magma chambers and their overlying calderas here we describe a 14 km crustal section through a collapsed caldera in southeastern hong kong where the intracaldera fill suggests that the magmatic discharge was of supereruption scale the main subvolcanic components that link a magma chamber with surface are revealed by well established field relationships supplemented by high precision geochronology whole rock geochemistry and geophysical data exposures and outcrop patterns reveal kilometer scale caldera subsidence and evidence of the simultaneous evacuation of hundreds of cubic kilometers of high silica rhyolite magma through dike like conduits from a shallow subcrustal reservoir the resultant volcanotectonic depression within which is preserved a single cooling unit of massively columnar jointed densely welded tuff high island tuff is interpreted to form part of a larger tilted early cretaceous nested caldera complex the high island eruption signaled the end of a 24 myr period of voluminous pulsed middle jurassic to early cretaceous silicic magmatism in the hong kong region characterized by four discrete ignimbrite flare ups

an experimental investigation of the mechanical behaviour of an unsaturated gneiss residual soil the paper presents compression and triaxial tests conducted under controlled suction in horizons b and c of a residual soil gneissic rock profile from south east brazil horizon b found at the surface consists of a 2 m thick reddish lateritic clayey soil layer whereas horizon c is a saprolitic soil layer that reaches great depths the block samples representing horizons b and c were manually taken from depths of 1 m and 5 m respectively the test programme carried out consisted of isotropic and anisotropic compression tests as well as drained and constant water content triaxial tests tests were performed under saturated and unsaturated conditions at controlled suction strength parameters c and were shown to increase with matric suction the critical state parameters were shown to vary with suction which also expanded the yield curve data obtained may be useful for the development of soil constitutive models for unsaturated soils

considerations of the dilatancy angle in rocks and rock masses the present study responds to the poor treatment given to dilatancy in classical rock mechanics post failure problems such as tunnel or mine pillar design a comprehensive review of the literature and observations in regard to published test results would indicate that dilatancy is highly dependent both on the plasticity already experienced by the material and confining stress moreover it also appears that scale may play a non negligible role in our article we provide a detailed analysis of published test data with a view to proposing a sufficiently significant but conveniently simple formulation of the dilatancy angle that reflects these dependencies and that can be readily implemented in numerical codes the model is then tested demonstrating that it is capable of representing rock sample strain behaviour in compressive tests finally the model is applied to the resolution of ground reaction curves for tunnels in poor to average quality rock masses showing a good correlation with results obtained using practical rock engineering techniques r 2005 elsevier ltd all rights reserved

instability of dykes at seven sisters generating station water retention dykes at seven sisters generating station in manitoba have experienced irregular instabilities since they were heightened in the late 1940s an investigation was undertaken to compa

the general and congruent effects of structure in natural soils and weak rocks the engineering properties of naturally occurring sedimentary and residual deposits which are usually treated in geotechnical engineering as soils are reviewed and it is shown that usually they have characteristics due to bonded structure which are similar to those of porous weak rock while this structure can arise from many causes its effects follow a simple general pattern that involves stiff behaviour followed by yield this yield can be described in a similar way to that occurring due to overconsolidation although it is a separate phenomenon the effects of structure are as important in determining engineering behaviour as are the effects of initial porosity and stress history which are the basic concepts of soil mechanics as it can be described in a general way it is concluded that structure and its effects should be treated as a further basic concept of equal importance l article passe en revue les proprietes des depots sedimentaires et residuels naturels qui sont nor malement traites comm

the 2003 r m hardy lecture soil parameters for numerical analysis in clay engineers in geotechnical practice work on increasingly complex problems with increasingly powerful numerical tools effective solutions to design problems need good information about the site and parameters or functions that describe how the soil will behave under the proposed loadings these loadings can include heating drying or wetting time effects and chemical changes as well as the more common structural loads this paper outlines issues that need to be considered when laboratory tests are used to produce soil properties for use in numerical analyses the focus is on soft to moderately stiff saturated clays similar considerations for in situ tests stiff clays and sands are not considered key words clay testing characterization properties constitutive modeling

anisotropic three dimensional behavior of a normally consolidated clay an experimental study is presented of the influence of the intermediate principal stress on the stress strain pore pressure and strength characteristics of a normally consolidated natural anisotropic clay san francisco bay mud under undrained conditions consolidated undrained triaxial compression tests and triaxial tests with independent control of all three principal stresses on cubical specimens were performed the stress strain behavior and the pore pressure characteristics as well as the effective stress failure surface can be described as being cross anisotropic key words anisotropic soils clays deformation shear strength triaxial tests

carbon cycle and sea water palaeotemperature evolution at the middle late jurassic transition eastern paris basin france abstract a very high resolution carbon and oxygen stable isotope analysis bulk carbonate of a biostratigraphically well constrained callovian oxfordian series is provided here for the first time the homogeneity of the clayey series and the weak diagenetic alteration allow the isotopic signal variations to be considered as primary in origin a prominent and brief negative excursion in the 13c curve 2 occurring at the start of the middle callovian jason zone obductum subzone and correlated regionally suggests a possible methane release the increasing 13c values thereafter up to the early oxfordian concomitant with a warming episode highlight the burial of carbon in organic rich layers which in return may have triggered a decrease in atmospheric pco2 at higher frequencies observed fluctuations of the 13c and 18o values are orbitally driven 405 kyr and 100 kyr eccentricity cycles and may correspond to the salinity and temperature variability recorded in sea water the 18o isotopic measurements from well preserved diagenetically screened belemnites and bivalves along the series compared to available data from tethyan domains agree with the scenario of a global cooling at the middle late jurassic transition the well dated 18o isotopic curve suggests that the onset of this cooling event occurred at the end of the coronatum zone middle callovian

influence of geology and geological processes on the geotechnical properties of a plastic clay abstract the complex properties of postglacial clay at winnipeg canada have major impact on civil engineering construction in the city problems include house foundation movements low stability of riverbanks poor highway pavement performance difficult excavation and a high incidence of watermain breaks the research in this paper presents an understanding of the geologic factors that cause these problems and how to ameliorate their effects in engineering design the geotechnical properties of the clay were measured from carefully sampled 76 mm diameter triaxial specimens the clay is nonhomogeneous anisotropic active overconsolidated and fissured these properties are related to the depositional and post depositional geology of the area the depositional geology of the extensive lake agassiz clays is straightforward and well known however it does not fully explain the measured geotechnical properties attention is then directed towards post depositional geological processes such as regional groundwater hydrology cementation aging freeze thaw and desiccation consideration of effective stress strengths quasi elastic anisotropy the variation of overconsolidation ratio with depth yielding and porewater pressure generation suggests strongly that the clay is cemented by carbonates and sulphates from upwards movement of salt rich groundwater freeze thaw disturbance causes marked changes in behaviour especially at low stresses

dating of debris flow fan complexes from lantau island hong kong china the potential relationship between landslide activity and climate change five debris flow fan complexes bordering the coastal foothills of western lantau island hong kong have been the subject of a stratigraphic and dating study to explore the potential relationship between past periods of climate change and landslide activity luminescence osl ages from the fan complexes supported by a few calibrated radiocarbon 14c ages on duplicate samples suggest six main periods of accumulation 28 000 20 000 ka 14 500 10 500 ka 5800 5000 ka 4370 4230 ka 3560 3320 ka and 1350 1050 ka the younger periods 10 000 ka appear to be dominated by relatively thin 0 5 1 5 m units deposited mainly by debris flood events whereas the older periods are dominated by thicker 1 0 3 5 m units deposited by debris flow events we hypothesise that immediately prior to the last glacial maximum lgm i e 21 000 ka the climate was cool and dry upland areas were probably devoid of vegetation providing favourable conditions for sediment production in source areas these debris laden source areas are likely to have been mobilised during periodic rainstorm activity rapidly channelised over relatively short drainage courses and then deposited as thick sediment rich debris flow deposits along the coastal foothills during the early to middle holocene the climate was warmer and more humid pluvial conditions dominated forests occupied the upland source areas leading to possibly reduced sediment yields more frequent flash floods and deposition dominated by debris floods compared with recent studies on the weathering and erosion history of the pearl river delta our landslide age data are indicative of a potential link between increased landslide activity and intensification of the east asian monsoon during the early to middle holocene

u pb dating of mesozoic igneous rocks from hong kong twenty two new zircon and monazite u pb ages have been obtained for mesozoic plutonic and volcanic rocks of hong kong these have revealed the existence of four distinct periods of mid jurassic to lower cretaceous volcano plutonism 164 6 0 2 to 159 3 0 3 ma 146 6 0 2 to 146 2 0 2 ma 143 7 0 3 to 142 5 0 3 ma and 140 9 0 2 to 140 4 0 2 ma a concordant monazite age of 236 3 0 8 ma has also been obtained from one intrusive body representing the first known occurrence of a mid triassic granitoid in the territory among these rocks discordant u pb data projected to the concordia curve have given a broad range of inheritance ages from early phanerozoic to late archaean a xenocrystic zircon from one sample has yielded a concordant age of 1872 3 ma the new u pb ages have refined the results of recent rb sr whole rock age dating of the granitoid rocks and have considerably improved correlation between intrusive and extrusive units the occurrence of inherited components in many of the analysed rocks indicates that they were derived from or erupted through older crust containing a wide variety of age components either as primary igneous or detrital material

effects of freeze thaw and softening on a natural clay at low stresses weathering processes such as softening and freeze thaw cycling affect the properties of clays care must therefore be taken when selecting strength and compressibility parameters for analysis of natural slopes compacted clay embankments and trench excavations in which significant proportions of the cross section can be affected by climatic weathering samples of plastic lake agassiz clay from winnipeg were consolidated anisotropically in the laboratory to axial stresses less than or equal to the in situ effective overburden pressure they were therefore all overconsolidated with respect to the field preconsolidation pressure the samples were then loaded under drained or undrained conditions along steeply rising stress paths in p q stress space one group of samples was tested immediately to identify the undisturbed behavior a second group was subjected to freeze thaw cycles and a third group allowed to swell freely before testing the freeze thaw cycling produced increased compressibility and pore

observations and numerical simulations of large eddy circulation in the ocean surface mixed layer two near surface dye releases were mapped on scales of minutes to hours temporally meters to order 1 km horizontally and 1 20 m vertically using a scanning depth resolving airborne lidar in both cases dye evolved into a series of rolls with their major axes approximately aligned with the wind and or near surface current in both cases roll spacing was also of order 5 10 times the mixed layer depth considerably larger than the 1 2 aspect ratio expected for langmuir cells numerical large eddy simulations under similar forcing showed similar features even without stokes drift forcing in one case inertial shear driven by light winds induced large aspect ratio large eddy circulation in the second a preexisting lateral mixed layer density gradient provided the dominant forcing in both cases the growth of the large eddy structures and the strength of the resulting dispersion were highly dependent on the type of forcing

soil behaviour through field instrumentation an improved version of the observational method is developed and proposed the method uses field measurements as the direct inputs to the framework of the constitutive behaviour and analyses the be

a triaxial investigation of kinematic yielding in sand the elastic plastic behaviour of a reconstituted sand is considered under triaxial conditions covering a wide range of strains monotonic probing tests are used to identify two types of kinematic yield surface for samples with loose and dense initial states under drained and undrained conditions and after different patterns of consolidation plastic strain development and global stiffness degradation are found to be closely interrelated and the interpretation involves decoupling the elastic and plastic strain components the sizes and the shapes of the loci are strongly affected by effective stress states and histories including any periods allowed for creep and ageing a tentative qualitative micromechanical explanation is offered for the phenomena observed