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

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

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

nearest neighbor analysis of small features on mars applications to tumuli and rootless cones 1 fields of low relief cones domes and mounds on mars have been interpreted as tumuli rootless cones and pingos the spatial distribution of such features can be characterized by their nearest neighbor nn distances the nn distributions can provide insight into the physical processes that affected field formation and can possibly provide a future diagnostic of the feature type present on mars the conventional approach for analyzing the observed nn distribution is based on the poisson probability distribution and uses one statistic c our simulations of spatial randomness show that there is an unrecognized bias in c that often leads to erroneous conclusions three alternative extensions of the poisson distribution are proposed here the first accounts for a minimum threshold on the size of features discerned the second considers the scavenging of the resources necessary to form neighboring features e g inflation pressurization and subsurface volatiles and the third models self limiting growth of the feature population three statistical tests are proposed to improve the conventional nn analysis we provide the critical regions needed to perform these tests for common sample sizes of these geologic features our methodology is applied to tumuli at mauna ulu hawaii and conjectured tumuli and rootless cones on mars each example exhibits a different aspect of spatial randomness these applications suggest avenues for further field and theoretical studies to develop this approach as a remote sensing diagnostic

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

statistical distribution of tumuli on pahoehoe flow surfaces analysis of examples in hawaii and iceland and potential applications to lava flows on mars 1 spatial distributions of tumuli on lava flow surfaces can be quantitatively linked to subsurface inflation processes three distinct styles of flow emplacement are studied 1 lava flows undergo inflation that changes as a function of space and time resulting in random spatial distributions of tumuli 2 lava flows with preferred pathways result in systematic clustering of inflation features and 3 established tubes or narrow pahoehoe flows produce chains of tumuli statistical analyses are required to distinguish between styles one and two comparison of the spatial distribution of tumuli on a portion of a lava flow at mauna ulu with the poisson distribution indicates that tumuli are randomly distributed on the flow surface typical of style one emplacement where small scale topographic variability and low slope influence development of preferred pathways that evolve over time at thrainsskjoldur direct statistical comparisons to the poisson spatial distribution are inconclusive but nearest neighbor analysis indicates significant clustering an initially random spatial distribution is inferred that developed preferred pathways and systematic clustering of inflation features as with style two at elysium planitia on mars the flow margin is significantly deficient in inflation features while away from the margin the flow exhibits a random spatial distribution of tumuli typical of style one emplacement the flow is interpreted as multiple units or a single flow that migrated in space during emplacement at the 1843 flow on mauna loa tumuli occur on a linear trend consistent with style three emplacement

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

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

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

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

interactions between hyporheic flow produced by stream meanders bars and dunes 1 stream channel morphology from grain scale roughness to large meanders drives hyporheic exchange flow in practice it is difficult to model hyporheic flow over the wide spectrum of topographic features typically found in rivers as a result many studies only characterize isolated exchange processes at a single spatial scale in this work we simulated hyporheic flows induced by a range of geomorphic features including meanders bars and dunes in sand bed streams twenty cases were examined with 5 degrees of river meandering each meandering river model was run initially without any small topographic features models were run again after superimposing only bars and then only dunes and then run a final time after including all scales of topographic features this allowed us to investigate the relative importance and interactions between flows induced by different scales of topography we found that dunes typically contributed more to hyporheic exchange than bars and meanders furthermore our simulations show that the volume of water exchanged and the distributions of hyporheic residence times resulting from various scales of topographic features are close to but not linearly additive these findings can potentially be used to develop scaling laws for hyporheic flow that can be widely applied in streams and rivers

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

coronae of parga chasma venus 1 parga chasma is a 10 000 km long fracture and trough system in the southern hemisphere of venus in this study we analyze coronae in the parga region addressing the relationship between corona and rift formation the relationship of volcanism to rifting and coronae and the overall evolution of the rift system our observations are compared with various models with the aim of determining any causative relationships between corona formation volcanism and rifting our statistical analysis shows that coronae are randomly located within this region indicating that corona locations are not significantly controlled by rifting or by lithospheric loading caused by the earlier formation of other coronae our observations suggest that the two processes of corona and rift formation were occurring more or less synchronously with no specific control on each other but that coronae and rifting in this region are genetically related we find a wide variation in the amount of volcanism associated with coronae across the parga region and no evidence for a deep seated plume or multiple plumes beneath parga chasma we suggest that the concentration of volcanic features in the beta atla themis region may actually result from three independent but overlapping broad zones of deformation corona formation and enhanced volcanism associated with the three rifts parga hecate and devana chasmata rather than one large zone of activity covering the whole of the region simultaneously

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