yield stress evaluation of finnish clays based on analytical piezocone penetration test cptu models a well established analytical model based on spherical cavity expansion and critical state soil mechanics theories is applied to piezocone soundings for profiling the yield stress and overconsolida

rapid consolidation characteristics of yellow river derived sediment geotechnical characterization and its implications for the deltaic geomorphic evolution abstract the yellow river which presently discharges into the western bohai sea has been widely recognized as having one of the highest sediment loads on earth understanding the consolidation characteristics of yellow river derived sediments is critical for improving our knowledge of the riverine sediment transport depositional processes and evolution of the yellow river delta morphology in this study we conducted in situ experiments from 2004 to 2008 at an abandoned subaqueous delta lobe diaokou lobe in order to investigate the consolidation process of the sediments our results show that the initial consolidation of yellow river derived sediment is a rapid process when the excess pore water pressure caused by sediment aggradation can completely dissipate in 1500 min the change in the physical and geotechnical properties during the consolidation endows the sediments with a certain shear strength however due to the hydrodynamic conditions the distribution of the sediment strength is both temporally and spatially inhomogeneous furthermore a hard layer can develop at the depths of 10 30 cm and the adjacent layer can become a potential sliding surface this study offers some insight into the formation and evolution processes of the yellow river delta s sedimentary and geomorphic forms

undrained cyclic shear behaviour of weathered tephra weathered tephra is prevalent across volcanic islands like the north island of new zealand and is composed of volcanic airfall materials that have been subjected to various soil processes understa

characterisation and engineering properties of tiller clay abstract a detailed characterisation of the quick clay underlying the ntnu research site at tiller trondheim is presented the objective of the work is to provide guidance on quick clay parameters to engineers and researchers working with similar clays in scandinavia and north america especially on landslide hazard assessment the material is lightly overconsolidated and is characterised by its high degree of structure and very high sensitivity quick clay clay and water contents are both about 40 the plasticity index is low 5 this relates to the low active minerals of the clay and silt fractions illite chlorite and quartz feldspars respectively undrained shear strength is of the order of 30 kpa to 50 kpa medium stiff and increases with depth the deposit is consistent across the site and its properties are similar to other norwegian quick clays significant efforts have been made into examining sample disturbance effects on the material it was found that thin walled steel fixed piston samples can yield results similar to those of block samples provided the work is carried out with extreme care and storage time is minimised the piezocone cptu test proved very useful in characterising the material

sample disturbance effects in silt abstractthis paper presents results of testing good quality piston tube samples and parallel block samples from three silt sites in ireland and norway theoretical work and laboratory strain damage

introduction to special section on the northern chugach mountains southern copper river basin segment of the alaskan transect this special section of the journal of geophysical research is the second part of a collection of papers on the nature and evolution of the lithosphere in southern alaska specifically beneath the chugach mountains and copper river basin the studies in this collection were conducted under the trans alaska lithosphere investigation stone et al 1986 a coordinated geological and geophysical transect of the alaskan lithosphere along the north south trans alaska oil pipeline corridor between valdez and prudhoe bay and across the pacific and arctic continental margins the trans alaska crustal transect tact project of the u s geological survey was the primary source of support for these studies including all the seismic refraction and reflection profiling and most of the geologic field investigations the first part of the collection appeared in the april 1989 issue and focused on the geology and tectonics of the northern chugach mountains and southern copper river basin and on the interpretation of a 107 km long seismic reflection profile along the transect appended to those papers but not included in the introduction page 1989 was an interpretation of the upper crustal structure of the chugach terrane derived from a transverse east west seismic refraction profile along the axis of the chugach mountains wolf and levander 1989

the gravettian solutrean transition in westernmost iberia new data from the sites of vale boi and lapa do picareiro abstract this study presents the analysis of the lithic assemblages from layers 5 and 4e terrace of the site of vale boi southern portugal and levels u and t from lapa do picareiro central portugal we aimed to understand the technological patterns and raw material exploitation during the gravettian solutrean transition in westernmost iberia and test the traditional models with assemblages from recently excavated sites while expanding the geographic range results show the existence of two discrete phases in each site the first with high frequency of quartz use for bladelet production seems to reflect the presence of a terminal gravettian horizon as defined by almeida 2000 the second with some significant differences between sites attests the presence of vale comprido technology and lower quartz frequencies at vale boi representing a proto solutrean occupation and the presence of a blade component in lapa do picareiro that together with the respective absolute chronology may be attributed to a proto solutrean or an early solutrean horizon in general terms this study allowed to confirm that the terminal gravettian and the proto solutrean are discrete phases across the transition in agreement with the three phase model presented by zilhao 1997 it further consolidates the expansion of similar techno cultural patterns to southern portugal which may be explained by the significant changes in the dynamic of social networks cascalheira and bicho 2013

earthquake response and sliding displacement of submarine sensitive clay slopes abstract many submarine landslides occur through marine sensitive clay layers and the strain softening behavior plays a key role the changing soil properties induced by various disturbances will have marked impact on earthquake performance of submarine clay slopes in the present study undrained triaxial compression tests on reconsolidated samples of a soft sensitive marine clay were conducted and a soil disturbance dependent simple constitutive model is proposed for describing post peak nonlinear strain softening behavior of sensitive clays based on experimental results and then is implemented in quiver code to perform one dimensional seismic response analysis of mild infinite slopes to address the relative importance of soil disturbance effect on the site response and sliding displacement of submerged slopes during seismic loading detailed laboratory test descriptions and results of a soft sensitive marine clay model formulations and comprehensive computational efforts are presented parametric study of site response analysis focusing on the effects of soil disturbance degree and depth on generic clay grounds with varying sloping angles subjected to harmonic and earthquake loadings are performed the predicted acceleration amplification maximum shear strains and permanent displacements provide insight of earthquake performance of submarine sensitive clay slopes the main findings are drawn based on several key concepts first undisturbed sensitive clay is typically stiffer and stronger than disturbed clay consolidated at the same stress level and hence unless strain softening is triggered structured sensitive clay will perform better than insensitive clay of the same residual strength second post peak softening at shallow depth will lead to strain localization on a thin layer which is the main cause of sudden change of upward wave propagation characteristics and large permanent displacement at seabed surface of mild submarine clay slope thirdly soil disturbance degrees and depths have very marked effects on seismic response and displacement performance of sensitive clay slopes and such effect will be further enhanced by slope angle or earthquake intensity which should be cautiously treated in engineering design

evaluation of disturbance induced on soft offshore sediments by two types of gravity piston coring techniques abstract sample disturbance is still a key issue in offshore investigations especially when logistic and financial limitations do not allow the use of drilling equipment this paper focuses on the comparison between the disturbance induced by a conventional free fall piston corer ff and a modified piston corer ad equipped with a velocity control angel descent method twin core samples were retrieved in two successions of pelitic sediments with a prevailing non clayey fraction and a non negligible sandy fraction comparison was based on different acquisition physical and mechanical parameters ranging from accelerometer data to magnetic susceptibility logs and geotechnical parameters from laboratory investigations including oedometer compression tests and cyclic simple shear tests accelerometer data highlighted the sharp reduction in velocity obtained for ad samples magnetic susceptibility logs characterized by a pattern of peaks induced by several volcaniclastic levels present in the succession indicated that the ad method significantly reduces core shortening among geotechnical investigations cyclic shear tests provided small strain shear moduli always higher in ad samples whilst the response of oedometer compression tests was equivocal in fact methods for assessing sample disturbance have demonstrated to bear limited effectiveness when applied to soils with relatively low clay content and significant overconsolidation as it is the case of the studied sediments

a comprehensive review on the geomechanical properties of gas hydrate bearing sediments abstract natural gas hydrates ngh that form in sediments beneath the ocean beds are a potential source to meet growing global energy demand gas hydrate bearing sediments ghbs exhibit improved geomechanical properties viz shear strength stiffness compressibility and poisson s ratio that are responsible for their greater stability as compared to the native sediments however dissociation of gas hydrates during extraction of gas instability in the ghbs could trigger submarine slope failures seabed subsidence and failure of the foundations of seafloor installations in order to reduce the risk of occurrence of such geohazards it is imperative to ascertain the stability of ghbs by understanding the variations in their geomechanical properties through field and laboratory investigations which are time consuming and prohibitively expensive for many researchers with this in view the present study attempts to decipher the variation of geomechanical properties with respect to various parameters that affect them viz hydrate saturation sh hydrate morphology and confining pressure temperature conditions by critically synthesizing the existing data in the literature it has been noticed that the shear strength and stiffness are the major parameters influencing the stability of ghbs and both share power law relationship with sh further it is noticed that the cohesion is the predominant component of the shear strength of ghbs and shows significant improvement for sh values greater than 15 50 the variability of cohesion and stiffness with respect to sh have been analysed in tandem with the volumetric deformation during the shearing process to propose particle level mechanism hypothesis that provides an insight in to the stress strain behavior of ghbs the proposed relationships and mechanisms would aid in understanding the behavior and development of improved modeling of geomechanical properties of ghbs

postcyclic reconsolidation strains in low plastic fraser river silt due to dissipation of excess pore water pressures the postcyclic reconsolidation response of low plastic fraser river silt was examined using laboratory direct simple shear testing specimens of undisturbed and reconstituted natural low plastic fraser river silt and reconstituted quartz powder initially subjected to constant volume cyclic loading under different cyclic stress ratios csrs and then reconsolidated to their initial effective stresses vo were specifically investigated the volumetric strains during postcyclic reconsolidation ev ps were noted to generally increase with the maximum cyclic excess pore water pressure umax and maximum cyclic shear strain experienced by the specimens during cyclic loading the values of ev ps and maximum cyclic excess pore water pressure ratio ru max were observed to form a coherent relationship regardless of overconsolidation effects particle fabric and initial precyclic void ratio of the soil the specimens with high ru max suffered significantly higher postcyclic reconsolidation st

sampling disturbance in hydrate bearing sediment pressure cores nghp 01 expedition krishna godavari basin example sampling natural sediments causes unavoidable disturbance as recovered sediments experience changes in stress and strain during drilling core recovery transportation handling and early stages of testing in hydrate bearing sediments the potential for sampling disturbance may be aggravated since pressure and temperature changes can lead to hydrate dissociation and gas exsolution pressure core technology attempts to recover and characterize hydrate bearing sediments while preserving them under in situ pressure and temperature conditions which is an essential requirement to assess the mechanical physical chemical and biological properties of natural hydrate bearing sediments previous studies on near surface sampling effects are extended in this study to evaluate additional sampling disturbances relevant to hydrate bearing sediments 1 hydrate dissociation due to mechanical extension 2 negative pore pressure generation during unloading mandelecryer effect 3 secondary hydrate formation 4 changes in hydrate mass as a function of changes in pressure and temperature within the stability field 5 hydrate anomalous preservation and its benefits for pressure core handling and testing and 6 relaxation aging following sampling results provide valuable insight to sampler design coring and operation procedures high pressure chamber design and pressure core testing techniques

field evaluation of deformation characteristics of a lacustrine clay deposit using seismic piezocone tests abstract the use of the seismic piezocone test scptu in geotechnical site investigation offers direct field measurement on stratigraphy and soil behaviour compared with some traditional investigation methods such as drilling sampling and field inspecting method or laboratory test procedures scptu can greatly accelerate the field work and hereby reduce corresponding operation cost this paper presents the methods review to predict the constrained modulus m and to measure small strain shear modulus gmax from scptu data the capacity of current interpretation methods to predict the constrained modulus m was evaluated for lixia river lagoonal soils several sites in lixia river area were selected for this study in each site scptu tests were performed and the soundings of cone tip resistance qc sleeve friction fs pore pressure u2 and shear wave velocity vs were recorded the predicted m values obtained from the scptu interpretation methods were compared with the reference values determined from the laboratory consolidation tests results of this study showed that the sanglerat method was able to predict m better than the other methods two new correlations were also developed to predict m from the corrected cone tip resistance qt and the net cone tip resistance qn small strain shear stiffness can be tentatively estimated in the absence of direct measurement of shear wave velocity the reliable result was obtained using an association between gmax qt and pore pressure parameter bq compared to field downhole wave velocity measurements scptu can lead to a more reliable measurement of maximum stiffness profile with depth the stress strain strength response of the clays was evaluated by the maximum shear stiffness and undrained shear strength

failure mechanisms of ana slide from geotechnical evidence eivissa channel western mediterranean sea this work deals with the failure mechanisms of ana slide in the eivissa channel in between the iberian peninsula and the balearic islands under the effects of gas charging and seismic loading in situ geotechnical tests and sediment cores obtained at the eastern balearic slope of the eivissa channel suggest that the basal failure surface bfs developed as a result of subtle contrasting hydro mechanical properties at the boundary between a fine grained unit u6 overlying a methane charged relatively coarser unit u7 past methane seepage is inferred from seismic reflection profiles and high magnetic susceptibility values in sediments from the slide headwall area past methane charging is also supported by further seismic reflection data and isotopic analyses of benthic foraminifera published separately the possibility of failure for different critical failure surfaces has been investigated by using the samu 3d slope stability model software taking into account the role of free methane in the development of the landslide failure would occur after samu 3d if the undrained shear strength of units u6 and u7 is strongly degraded i e 95 wheeler s theory suggests that a 9 free gas saturation would be required to reduce the undrained shear strength by 95 however the theory of the undrained equilibrium behaviour of gassy sediments for this methane concentration shows that the excess fluid pressure generated by gas exsolution estimated at 12 of the effective stress is not high enough to bring the slope to fail this led us to consider seismic loading as an additional potential failure mechanism despite the lack of historical data including instrumental records on seismicity in the balearic islands therefore assuming that the historical period is not necessarily representative of seismic activity further back in time i e when ana slide occurred similar to 61 5 ka ago considering current slope conditions the most critical failure surface obtained by samu 3d relates to peak ground accelerations pga of 0 24g which relates to magnitude moment mw 5 at epicentral distances of 1 km and 7 mw 5 at epicentral distances 15 km to ana slide however no active faults have been identified at so short distance from ana slide only when shear strength is degraded due to the presence of free methane in units u6 and u7 is considered the most critical failure surface obtained by samu 3d fits with lower magnitude and larger epicentral distances consequently the most plausible hypothesis to explain the occurrence of ana slide is the combination of free gas and seismic loading

effects of sample disturbance and consolidation procedures on measured shear strength of soft marine norwegian clays after many decades of research the issue of sample disturbance is still important as regards to determining reliable and representative soil parameters for foundation design in soft clays parallel laboratory tests have been carried out on high quality block samples and ordinary piston tube samples from 12 deposits of soft norwegian marine clays undrained triaxial and direct simple shear dss tests on samples reconsolidated to the in situ effective stresses show that sample disturbance has a significant effect on the measured stress strain strength behaviour the more disturbed the sample the lower the shear stress at small strains and the higher the shear stress at large strains breakdown of the clay structure including cementation bonds is the assumed cause of lower shear resistance at small strains whereas at large strains the shear resistance is governed mainly by the water content which for soft clay samples reconsolidated to the in situ effective stresses will be lower and the strength t

spudcan penetration analysis for case histories in clay this paper reports advances in the prediction of spudcan resistance profiles during installation and preloading based on the soil flow mechanisms observed in model tests and numerical analysis and taking into account strain softening and rate dependency on the soil strength deep penetration of spudcan foundations was simulated for 14 case histories reported from different locations in the gulf of mexico where the soils were single layer predominantly normally to lightly overconsolidated clay axisymmetric and three dimensional analyses were carried out using two large deformation finite element ldfe approaches modifying the simple elastic perfectly plastic tresca soil model to allow strain softening and strain rate dependency of the shear strength the field data were compared with the results of the finite element analyses and with predictions using various design approaches excellent agreement was found particularly when a mechanism based design approach was used that differentiated between conditions before and after backflow of soil above the penetrating spudcan

multivariate correlation analysis of seismic piezocone penetration scptu parameters and design properties of jiangsu quaternary cohesive soils abstract a recent trend of geotechnical correlation analysis is to construct a multivariate distribution model to describe the multiple dependency characteristics of different soil parameters in this study the feasibility of this multivariate method to model the multivariate dependency of seven soil parameters including the undrained shear strength ratio overconsolidation ratio sensitivity normalized cone tip resistance normalized sleeve frictional resistance pore pressure parameter and normalized shear wave velocity is studied a database containing 372 sets of observations of these seven parameters is collected from 25 sites in the jiangsu province china two data transformations including the johnson system of distribution and box cox method were used in the construction of the multivariate model for the jiangsu cohesive soils the correlations derived from these two local models were compared with the compiled jiangsu database data points at other testing sites in china and database and correlations published in the literature for validation it was shown that the local models developed in this study were capable of the multivariate dependency of the soil parameters for the jiangsu cohesive soils whereas the global model developed in the literature tends to overestimate the uncertainties associated with the design parameters for the jiangsu soils a potential explanation is that the soil parameters in a local region were less variable with stronger correlations than those over the global sites due to the site specific effect however caution shall be taken if the local models for the jiangsu soils are used at other sites besides the johnson system of distribution is superior to the box cox transformation in the construction of the multivariate distribution model in the sense that the former is more effective to achieve the standard normal distribution especially for the soil parameters with a bounded distribution

potential improvements of design parameters by taking block samples of soft marine norwegian clays undrained triaxial and direct simple shear tests on samples reconsolidated to the in situ effective stresses and oedometer tests have been carried out on standard piston tube and on high quality bl

cyclic tests on high quality undisturbed block samples of soft marine norwegian clay the results of a study with undrained cyclic triaxial and direct simple shear dss tests on high quality undisturbed samples obtained from large blocks of a soft marine norwegian clay are presented several tests with different average shear stresses shear stress amplitudes loading frequencies and sample geometries have been performed on block samples taken from different depths in tests with small average shear stresses failure occurred due to large shear strain amplitudes while large permanent shear strains were observed in tests with higher average shear stresses diagrams quantifying the undrained cyclic strength permanent shear strain shear strain amplitude and permanent pore water pressure dependent on average shear stress shear stress amplitude and number of cycles have been developed based on the test results the undrained cyclic strength was found strongly dependent on loading frequency block samples from shallower depth showed a somewhat higher undrained cyclic strength no influen

overpressure within upper continental slope sediments from cptu data gulf of lion nw mediterranean sea data from in situ piezocone tests cptu and laboratory analyses are utilized for the interpretation of the stress history of quaternary sedimentary sequences in the upper continental slope of the gulf of lion northwestern mediterranean sea a cptu based preconsolidation pressure profile referenced to the current effective stress indicates that the deposit is underconsolidated from 12 meters below the seafloor mbsf down to at least 150 mbsf excess pore pressure below 12 mbsf is further supported by results from oedometer and dissipation tests subseafloor pockmarks and indications of free gas in seismic reflection profiles reveal four main overpressure sources si siv with overpressure ratios 0 3 at subseafloor depths coinciding with levels where the dominantly silty clayey sediment contains increased proportions of sand we relate the excess pore pressure related to free gas due to gas exsolution processes and sea level variations driven by pleistocene sea level changes