instability conditions of loose sand in plane strain when a loose sand specimen is loaded under an undrained condition it may become unstable the instability conditions may be specified by an instability line determined using undrained tests however the instability behavior of sand has seldom been studied under plane strain conditions experimental data obtained under both triaxial and plane strain conditions are presented in this paper to define the instability conditions of loose sand under plane strain conditions using the state parameter a unified relationship can be established between the normalized slope of instability line and the state parameters for both axisymmetric and plane strain conditions using this relationship the instability conditions established under axisymmetric conditions can also be used for plane strain conditions

scaling law of static liquefaction mechanism in geocentrifuge and corresponding hydromechanical characterization of an unsaturated silty sand having a viscous pore fluid fast landslides induced by rainfall impose considerable damage on infrastructure and cause major casualties worldwide static liquefaction is one of the triggering mechanisms mentioned frequently in the literature as a cause of this type of landslide the scaling laws required to model this mechanism in the geotechnical centrifuge are developed and it is shown that either a reduction in the soil pore size or use of a viscous pore fluid is needed to unify the time scaling factors of contractive volume change of the saturated voids and dissipation of the excess pore pressure generated the latter option was used in this research therefore the influences of the viscous pore fluid on the hydromechanical characteristics of a silty sand were investigated subsequently geocentrifuge tests were conducted to compare the behaviour of a slope having a viscous solution as the pore fluid with that of a model with water as the pore fluid both slopes were subjected to rainfall and the evolution of the pore pressur

influence of state and compressibility on liquefied strength of sands critical state soil mechanics is a useful framework to understand sand behavior in this paper a relationship is developed for estimating undrained critical shear strength of sands based on the critical state framework the application of this relationship is demonstrated by comparison with laboratory test results and sand liquefied strength from field liquefaction flow failure case histories using this relationship the effects of effective stress variation and density on undrained critical shear strength are studied for different combinations of critical state line parameters corresponding to several reference sands the parametric study indicates that depending on sand void ratio undrained critical shear strength may increase remain the same or decrease as sand shearing compressibility represented by the slope of the critical state line increases the underlying mechanisms of field failures in dense sands and reverse behavior of compressible sands are explained through this relationship it is su

instability of loose sand under drained conditions a type of prefailure instability which occurs under fully drained conditions is studied in this paper it is observed experimentally that when a specimen is sheared along a drained stress path involving a decrease in effective mean stress it becomes unstable after the stress path crosses an instability line the instability occurring under drained conditions is different from the type observed under undrained conditions the differences and similarities between the two types of instability are elaborated the practical implication of the study in analyzing the failure mechanisms of granular soil slope is also discussed

forewarning of static liquefaction landslides abstractstatic liquefaction failure and the ensuing flow slide of slopes have produced significant damages to structures and even loss of lives based on a very large number 1 632 of laboratory s

unstable behaviour of sand and its implication for slope instability results of some constant shear drained csd tests conducted on both loose and dense sand are presented using the critical state line and a modified state parameter a new framework for analysing the instability of granular soil slopes is proposed the test data were examined and interpreted using the new framework instability lines for sand with different void ratios were established within this framework the conditions for the occurrence of instability in both contractive and dilative granular soil slopes under various shear stress levels were examined using the proposed framework key words deformation laboratory tests liquefaction sands shear strength slope stability

yield strength ratio and liquefaction analysis of slopes and embankments a procedure is proposed to evaluate the triggering of liquefaction in ground subjected to a static shear stress i e sloping ground using the yield strength ratio su yield v0 thirty liquefaction flow failures were back analyzed to evaluate shear strengths and strength ratios mobilized at the triggering of liquefaction strength ratios mobilized during the static liquefaction flow failures ranged from approximately 0 24 to 0 30 and are correlated to corrected cone and standard penetration resistances these yield strength ratios and previously published liquefied strength ratios are used to develop a comprehensive liquefaction analysis for ground subjected to a static shear stress this analysis addresses 1 liquefaction susceptibility 2 liquefaction triggering and 3 post triggering flow failure stability in particular step 2 uses the yield strength ratio back calculated from flow failure case histories and the cyclic stress method to incorporate seismic loading

1907 static liquefaction flow failure of the north dike of wachusett dam a static liquefaction flow failure occurred in the upstream slope of the north dike of wachusett dam near clinton massachusetts on april 11 1907 during the first reservoir filling the fine sands of the upstream dike shell liquefied and flowed approximately 100 m horizontally into the reservoir this paper presents a description of the construction of the north dike failure of the upstream slope and the results of stability analyses that were conducted to estimate the shear strength mobilized in the liquefied soils during failure analyses of the postfailure geometry the prefailure geometry and an analysis incorporating the kinetics of failure were conducted the back calculated shear strength considering the kinetics of failure is in agreement with other liquefaction flow failure case histories published in the literature as a result it is recommended that the kinetics of failure be considered to determine the shear strength mobilized during a liquefaction flow failure

evaluation of static liquefaction potential of silty sand slopes the mechanism of instability in granular soils is explained and its requirement as a forerunner to the liquefaction of level or sloping ground is described case histories support the observation t

modelling diffuse instabilities in sands under drained conditions this paper presents a criterion for detecting diffuse homogeneous instabilities in granular soils sheared under fully drained conditions the criterion is based on bifurcation theory and applied to elasto plasticity by allowing multiple incremental solutions in elasto plastic soils physically losing controllability of stress boundary conditions drained diffuse instabilities are poorly understood and are induced by kinematic modes different from those observed in shear bands and liquefaction instabilities unlike shear bands diffuse instabilities occur under fairly homogenous deformation modes and unlike liquefaction drained instabilities are not generated by the excess pore pressures recent experiments under drained constant shear report sudden homogeneous instabilities in samples of relatively dense and loose sands the criterion presented in this paper is used in conjunction with an elasto plasticity model for sands to predict and explain these reported drained instabilities from a practical s

the liquefaction of sands a collapse surface approach recent large scale slides occurring during the hydraulic placement of an artificial island berm in the beaufort sea resulted from the liquefaction of the berm sand subsequent laboratory tests and

residual strength of clays in landslides folded strata and the laboratory the post peak drop in drained shear strength of an overconsolidated clay may be considered as taking place in two stages first at relatively small displacements the strength decreases to the fully softened or critical state value owing to an increase in water content dilatancy second after much larger displacements the strength falls to the residual value owing to reorientation of platy clay minerals parallel to the direction of shearing if the clay fraction is less than about 25 the second stage scarcely comes into operation the clay behaves much like a sand or silt with angles of residual shearing resistance typically greater than 20 degrees conversely when the clay fraction is about 50 residual strength is controlled almost entirely by sliding friction of the clay minerals and further increase in clay fraction has little effect the angles of residual shearing resistance of the three most commonly occurring clay minerals are approximately 15 degrees for kaolinite 10 degrees for illite or clay mica and 5 degrees for montmorillonite when the clay fraction lies between 25 and 50 there is a transitional type of behaviour residual strength being dependent on the percentage of clay particles as well as on their nature the post peak drop in strength of a normally consolidated clay is due only to particle reorientation measurements of strength on natural shear surfaces agree within practical limits of variation with values derived from back analysis of reactivated landslides this field residual strength can be recovered by multiple reversal shear box tests on cut plane samples but in high clay fraction materials it is typically somewhat higher than the strength measured in ring shear tests residual strength is little affected by variation in the slow rates of displacement encountered in reactivated landslides and in the usual laboratory tests but at rates faster than about 100 mm min qualitative changes take place in the pattern of behaviour a substantial gain in strength is followed with increasing displacement by a fall to a minimum value in clays and low clay fraction silts this minimum is not less than the slow or static residual but in clayey silts with clay fractions around 15 25 according to tests currently in progress the minimum can be as low as one half of the static value author trrl

influence of silt size and content on liquefaction behavior of sands this study investigates the fines content influence on liquefaction potential of a single base sand mixed with three different essentially nonplastic silts through strain controlled monotonic undra

alteration of the callovo oxfordian clay from meuse haute marne underground laboratory france by alkaline solution i a xrd and cec study the reaction of the clay fraction of the callovo oxfordian hard shale formation hosting the french underground laboratory site with high ph naoh koh and ca oh 2 solutions has been investigated through closed system experiments at 60 90 and 120 c over 6 24 and 168 h the mineralogical composition of the run samples has been determined using x ray diffraction xrd of randomly oriented powders showing the formation of different species of zeolites analcime chabazite phillipsite and ca silicates tobermorite katoite the phyllosilicates were studied using xrd of oriented preparations and cation exchange capacity measurements detrital or diagenetic mica and chlorite in the 2 m fraction remain unchanged on the contrary the smectite and random illite smectite mixed layer minerals are strongly reactive the expandable layers of montmorillonite type are selectively dissolved while beidellitic ones survive or are transitionally formed

influence of landslide geometry and kinematic deformation to describe the liquefaction of landslides some theoretical considerations abstract the generation of excess pore pressure and possible liquefaction can be explained by different mechanisms in literature less attention is given to the effects of landslide geometry and kinematic deformation on the generation of excess pore pressure and possible liquefaction of sliding blocks the objective of this paper is to discuss these factors by proposing a simple analytical model of landslide liquefaction using classic soil mechanics theory the model describes the initial state of failure and solves forces for each slice with the bishop s limit equilibrium method immediately after failure the difference in movement for each slice is calculated assuming a viscous shear band and using the coulomb viscous model the differential movements conduct to differential strains which are transferred to excess pore pressures in slides characterized by curved slip surfaces the lower parts showed compaction and increase in pore pressures during displacement while the upper parts showed dilatation and a decrease in pore pressures the potential liquefaction is then evaluated for each slice in relation to the displacement the model is applied to a slump type failure that occurred on the super sauze mudslide southeast france in compact clay rich material it was observed that the slump completely liquefied into a flow however the model simulations were not able to completely liquefy all the slices of the slump in case a decrease in pore pressures through dilatation was assumed in the upper part of the slump the decrease in pore pressures caused a rapid stabilisation of the remaining sliding body in case a neutral pore pressure was assumed in the upper part with dilatation movement and deformation of the remaining slices could continue leading to a nearly complete liquefaction of the slump model simulations for many geometries of curved slip surfaces reveal that the liquefied volume increases with steeper slopes and more curved slip surfaces it is discussed also how planar slides which in theory show small differential movement of the individual slices and hence no large compaction can completely liquefy through deformation at the toe

exploring the micro mechanics of triaxial instability in granular materials the instability of granular materials due to water infiltration under fully drained conditions has been previously considered in experimental studies while laboratory experiments can provide macro scale insight into drained instability the micro mechanics under such conditions are yet to be explored this study has employed the discrete element method dem to simulate constant shear drained csd tests for an ideal soil csd tests were initiated from a range of packing densities and stress conditions the dem simulations were able to qualitatively replicate laboratory csd tests the choice of the loading control parameter was seen to play a central role in the macro scale second order work to identify an effective failure all samples considered attained an onset of instability that coincided with fluctuations in the second order work from a particle scale the time of occurrence of the onset of instability was seen to depend on initial packing density and stress state a change in the evolution of mac

the temporal variability of centimeter scale surface roughness in a playa dust source synthetic aperture radar investigation of playa surface dynamics abstract emission of mineral dust aerosols is highly dynamic in part due to variability in surface erodibility investigation of the variations of surfaces within dust source regions has the potential to elucidate the processes that control erodibility and to improve model representations of dust emission in this study we investigate surface temporal variability in the black rock playa nevada usa using synthetic aperture radar sar satellite data from between 2004 and 2010 the sar backscatter 0 observations of the playa surface are compared to weather station observations and temporally resolved measurements of water inundation derived from multi spectral modis satellite data the data illustrate that centimeter scale surface roughness on the playa is surprisingly heterogeneous over multi meter length scales and evolves dynamically on annual time scales interannual changes in surface roughness on the playa are quite large compared to the variability of surface roughness during the summer months july september suggesting that summer anthropogenic and aeolian processes are substantially less important than water related processes for controlling the evolution of the playa surface playa median 0 is relatively low in years with high annual precipitation 140 mm suggesting that surface water controls centimeter scale surface roughness and potentially erodibility spatially there is a relationship between 0 and the time of year at which a surface dries areas drying in july have significantly higher 0 than surfaces that dry earlier in the year suggesting that spatial heterogeneity in 0 is controlled by cycles of wetting and drying at the edge of the playa lake the implications in the black rock playa and potentially more broadly are that water is a critical factor controlling playa surface evolution and the annual time scale is crucial for investigations of playa erodibility

drained instability of sand in plane strain flowslide or failure of loose granular soil slopes is often explained using liquefaction or instability data obtained from undrained triaxial tests however under static loading conditions the assumption of an undrained condition is not realistic for sand particularly clean sand case studies have indicated that instability of granular soil can occur under essentially drained conditions e g the wachusett dam failure in 1907 laboratory studies on changi sand by chu et al in 2003 have shown that sand can become unstable under completely drained conditions however these studies were carried out under axisymmetric conditions and thus cannot be applied directly to the analysis of slope failures in this paper experimental data obtained from plane strain tests are presented to study the instability behaviour of loose and dense sand under plane strain conditions based on these test data the conditions for the occurrence of drained instability in plane strain are established using the modified sta

modelling the static liquefaction of sand with low plasticity fines there have been significant advances in understanding of the effect of fines content fc on the mechanical response of sand with fines the concepts of equivalent granular void ratio e and equivalent granular state parameter which were developed for sands with fines can be used in lieu of e and to provide a unifying framework for characterising the undrained response of sands with low plasticity fines irrespective of fc in addition a recently developed constitutive model was able to capture the influence of both density using e and stress states on the stress strain responses of clean sand under drained or undrained shearing with one set of parameters this was achieved by rendering dilatancy and peak failure stress ratio functions of the present work combines these two powerful unifying propositions and by merely substituting e and for e and into the equations of the aforementioned model for clean sands obtains a constitutive model for sand with fines that can capture the infl

correction for geometry changes during motion of sliding block seismic displacement the sliding block model is often used for the prediction of permanent coseismic displacements of natural slopes and earth structures this model assumes motion in an inclined plane but does not consider the decrease in inclination of the sliding soil mass as a result of its downward motion which is the usual condition in the field the paper studies the above effect and proposes an empirical equation correcting the predictions of the sliding block model the investigation is performed by using a recently developed multiblock model the equation correcting the predictions of the sliding block model depends on the slip length the difference in inclinations of the upper and lower part of the slip surface the seismic displacement predicted by the sliding block model and the maximum value of the applied horizontal acceleration

alteration of the callovo oxfordian clay from meuse haute marne underground laboratory france by alkaline solution ii modelling of mineral reactions abstract one of the french options for the final disposal of high level radioactive waste is a deep geological repository the callovo oxfordian formation in the meuse and haute marne france was proposed by the french agency for the management of radioactive wastes andra to be the site of a research laboratory in order to evaluate in situ the interaction between the host formation and the engineered barriers in the previous experimental part secondary minerals such as zeolites tobermorite and katoite have been observed after the alteration of the callovo oxfordian clay under alkaline conditions three different reactions of phyllosilicates alteration have been proposed as a function of both ph and chemical composition of the reacting solutions the aim of this work was to simulate the reaction between the callovo oxfordian clay and high ph solutions in order to validate the proposed alteration reactions from experimental data the thermodynamic modelling of stability relationships among minerals in the callovo oxfordian clay was performed using the solution speciation solubility modelling code kindis at 120 c for different chemical media naoh koh and ca oh 2 input data were the mineralogical composition of the

undrained behavior of silty sand and the role of isotropic and k0 consolidation abstractthe characteristic features of undrained behavior of a silty sand are investigated for a range of initial conditions e p for both isotropic consolidation ciu and k0 consolidation k0u