simplified quantitative risk assessment of rainfall induced landslides modelled by infinite slopes abstract rainfall induced landslides vary in depth and the deeper the landslide the greater the damage it causes this paper investigates quantitatively the risk of rainfall induced landslides by assessing the consequence of each failure the influence of the spatial variability of the saturated hydraulic conductivity and the nature of triggering mechanisms on the risk of rainfall induced landslides for an infinite slope are studied it is shown that a critical spatial correlation length exists at which the risk is a maximum and the risk is higher when the failure occurs due to a generation of positive pore water pressure

failure characteristics of gently inclined shallow landslides in nanjiang southwest of china abstract large number of rain induced landslides occurred on 16 september 2011 in nanjiang southwest of china the typical depth of failure surface was from 1 to 5 m at the gently inclined interface between the superficial red silty clay and bedrock in order to explain the failure characteristics of these shallow landslides we conducted a rainfall infiltration simulation test calculated rainfall infiltration depth using modified green ampt g a infiltration model as well as considered the atmospheric effects on the slope failures results show that the permeability of red clay is extremely low and the rainfall infiltration depth is limited to around 0 5 m during a rainstorm the rainfall infiltration capacity can be enhanced within the depth of atmospheric influence which is determined as 5 4 m in the study area with the increase of soil depth and the lower degree of weathering the void ratio and permeability are gradually reduced thus the rainfall infiltration continues following a decreasing trend until the bedrock is reached within the shallow landslides in the study area under the condition of rainfall the slope can keep in a stable state when the depth of wetting front is less than the thickness of soil layer when the wetting front proceeds to the interface between the silty clay and bedrock the potential slip surface can develop on such soil bedrock interface in relation to the increased pore water pressure and ground water level consequently shallow failures will occur along the soil bedrock interface in a depth of 1 5 m

a comparative study of suction stress between sand and silt under unsaturated conditions abstract the purpose of this study is to estimate and compare suction stress between sand and silt sampled from the coast of korea the water content and matric suction of sand joomunjin and silt saemangeum were first examined using an automated soil water characteristic curve swcc apparatus based on the axis translation technique swccs were then estimated from the test results using the van genuchten 1980 model at equal matric suction the corresponding water content of silt was higher than that of sand moreover the saturated water content and air entry value aev of silt were larger than those of sand using the fitting swcc parameters suction stress characteristic curves ssccs were estimated according to the method proposed by lu and likos 2006 the sscc behavior for sand and silt was different and significantly depended on the material properties particularly pore size and pore size distribution for sand the suction stress exhibited rapid variation with changes in matric suction but for silt the suction stress approached a constant value as the matric suction increased in addition when the matric suction was smaller than the aev of soil the suction stress was equal to the magnitude of the matric suction in contrast when the matric suction exceeded the aev of soil suction stress had a nonlinear shape with respect to the matric suction

strength of weakly cemented sands from drained multistage triaxial tests characterizing the strength of weakly cemented and sensitive soils in the laboratory is difficult because of the difficulty in obtaining high quality replicate samples necessary for defining the failure envelope multistage triaxial tests have long been used to reduce the variability caused by testing multiple samples however traditional criteria used for transitioning from one loading stage to another often lead to destructuring or failure in sensitive or structured soils the objective of this paper is to present a methodology for conducting multistage drained triaxial tests on weakly cemented sands and estimating the resulting shear strength parameters both multistage and single stage drained triaxial tests were performed on artificially cemented samples of a silty sand at two levels of densities and cementation the use of dev dea 0 as a termination criterion to move on to the next stage of loading and ev 0 as the failure criterion for the final stage of the shear resulted in an average error of 6

strength and dilatancy of a silt stabilized by a cement and fly ash mixture the mechanical behaviour of a weakly cemented silt was studied experimentally the cementing agent was a cement and fly ash slurry and the samples so formed were slightly cemented in triaxial tes

mechanisms of shallow landslides on soil mantled hillslopes with permeable and impermeable bedrocks in the boso peninsula japan abstract rainfall induced shallow landslides play a vital role in hillslope denudation processes in humid temperate regions this study demonstrates the contrasting mechanisms of landslides in adjoining hills with permeable sandstone and impermeable mudstone bedrock in the boso peninsula japan the characteristics of slope hydrology were inferred from pressure head monitoring and rainfall runoff observations an analysis of slope stability provided critical conditions for several previously occurring landslides the results are as follows 1 in slopes with the permeable sandstone infiltrated rainwater percolates through the bedrock as an unsaturated gravitational flow the wetting front migration results in a decrease of soil cohesion and causes landsliding at the steep lower part of the hillslopes 2 in contrast the impermeable mudstone beneath a thin soil layer causes a transient positive pressure head that generates a saturated subsurface storm flow the reduction in effective normal stress triggers shallow soil slipping at the uppermost part of a hollow

experimental validation of suction stress characteristic curve from nonfailure triaxial k0 consolidation tests abstractin recent years the suction stress characteristic curve sscc has been shown to represent a key constitutive relationship for defining effective stress in variably saturated soils the sscc can be deduced either from shear strength tests under variably saturated conditions or from soil water retention tests this paper provides an alternative way to obtain the sscc by conducting nonfailure k0 consolidation tests multiple remolded specimens from two different granitic residual soils a silty sand sm and a clayey sand sc were evaluated in suction controlled triaxial tests under k0 conditions the results from these tests show that the stress paths for remolded specimens with different initial suction values differ during k0 consolidation when plotted in terms of the net normal stress but follow a single path when plotted in terms of the effective stress defined using the sscc this observation confirms the validity of the effective stress principle before failure further the results of th

20th century sea level change along the eastern us unravelling the contributions from steric changes greenland ice sheet mass balance and late pleistocene glacial loading we have considered the influence of ocean temperature and salinity changes mass changes of the greenland ice sheet gis and the isostatic response of the solid earth to the most recent glacial cycle on 20th century sea level change along the us east coast with the intention of better understanding the observed signal as well as determining the potential of the tide gauge data for constraining the recent past 50 100 yr mass balance of the gis and earth viscosity structure our results show that the signal due to steric changes is large and displays a complex spatial variation which can account for a significant portion of the observed signal in contrast that due to changes in the gis is relatively small and insensitive to the specific geometry of the mass balance model adopted as a consequence the tide gauge data alone are not capable of providing useful constraints on either the magnitude or form of recent gis mass balance our inference of mantle viscosity structure based on the tide gauge data was affected dramatically when the steric effect was accounted for an earth model with an upper mantle viscosity of 8 1019 pa s and a lower mantle viscosity of 5 1022 pa s produced the best fit to the steric corrected data the optimal fit to the uncorrected data was obtained for upper and lower mantle viscosities of 5 1020 pa s and 1022 pa s respectively

prediction of the unconfined compressive strength of compacted granular soils by using inference systems adaptive neuro fuzzy inference system anfis and artificial neural network ann models have been extensively used to predict different soil properties in geotechnical applications in this study it was aimed to develop anfis and ann models to predict the unconfined compressive strength ucs of compacted soils for this purpose 84 soil samples with different grain size distribution compacted at optimum water content were subjected to the unconfined compressive tests to determine their ucs values many of the test results for 64 samples were used to train the anfis and the ann models and the rest of the experimental results for 20 samples were used to predict the ucs of compacted samples to train these models the clay content fine silt content coarse silt content fine sand content middle sand content coarse sand content and gravel content of the total soil mass were used as input data for these models the ucs values of compacted soils were output data in these models the anfis model results were compared with those of the ann model and it was seen that the anfis model results were very encouraging consequently the results of this study have important findings indicating reliable and simple prediction tools for the ucs of compacted soils

behavior of a compacted completely decomposed granite soil from suction controlled direct shear tests a series of single staged consolidated drained direct shear tests are carried out on recompacted completely decomposed granite cdg soil a typical residual soil in hong kong under different matric suctions and net normal stresses matric suction is controlled by applying air pressure in the pressure chamber and water pressure at the bottom of the high air entry ceramic disk the experimental results show that the contribution of suction to shear strength is significant shear strength of cdg soil increases with the increase of matric suction net normal stress has a remarkable influence on the shear strength of unsaturated cdg soil the increase in shear strength due to an increase in matric suction suction envelope is observed as nonlinear i e b value varies with matric suction no soil dilatancy is observed for zero matric suction saturated case but as the suction value is increased higher soil dilatancy is obvious in lower net normal stresses the rate of increase of soil dilatancy is greater

shear strength characteristics of statically compacted unsaturated kaolin the shear strength characteristics of statically compacted unsaturated soil specimens of commercial kaolin ip 15 were determined using conventional triaxial shear testing apparatus extending total stress analysis the testing program consists of two different types of confined compression shear strength tests on unsaturated soil specimens in the first series of tests the specimens were sheared immediately after the application of the confining pressure under undrained loading conditions in the second series of tests the specimens were first allowed to come to equilibrium with respect to volume change and suction value under the applied confining pressure and sheared at two different rates of strain a psychrometer was used for measuring suction values in addition conventional consolidated undrained tests were also conducted on specimens that were saturated using the back pressure technique before shearing comparisons with respect to the shear strength behavior are provided for both saturated a

a relationship describing the shear strength of unsaturated soils a relationship describing the shear strength profile of a desiccating soil deposit is essential for the purpose of analysis especially when a numerical method is adopted where each zone in a discretised grid is assigned an elevation dependent shear strength value the matric suction profile of a desiccating soil deposit is nonlinear up to the air entry value an increase in matric suction is associated with a linear increase in shear strength beyond air entry as the soil starts to desaturate a nonlinear increase in shear strength occurs the soil water characteristic curve is stress dependent as is the shear strength gain as matric suction increases in this paper a three dimensional nonlinear regression analysis showed that a power additive function is suitable to describe the variation of the shear strength of unsaturated soils with matric suction the proposed function incorporates the effect of normal stress on the contribution of matric suction to the shear strength

stability analyses of rainfall induced landslides the slope stability issues concerning rainfall induced slope failures are investigated and presented specifically the effect of both negative and positive pore water pressures on the stability of initially unsaturated slopes are carefully explained and coupled with infinite slope analysis methods in order to present a predictive formulation of slope failures that occur as a result of rainfall events the formulation serves as a baseline analysis method for evaluating potentially unstable soil slopes that are subject to surface infiltration and explains the various triggering mechanisms that may occur based on individual combinations of the slope geometry soil strength and infiltration parameters a procedural method is outlined for utilizing the analytical formulation to predict the change in the factor of safety for a slope subject to infiltration and a detailed analysis of a case study is presented to verify the method quantitative statements are made concerning the time and depth of failure in relationship to the soil slope and rainfall parameters

ice 3g a new global model of late pleistocene deglaciation based upon geophysical predictions of post glacial relative sea level change a new high resolution global model of late pleistocene deglaciation is inferred on the basis of geophysical predictions of postglacial relative sea level variations in which the ice ocean solid earth interaction is treated in a gravitationally self consistent fashion for the purpose of these analyses the radial viscoelastic structure of the planet is assumed known on the basis of previously published sensitivity tests on solutions of the forward problem only radiocarbon controlled relative sea level histories from sites that were actually ice covered with one or two additions are employed to constrain the model leaving relative sea level rsl data from sites that were not ice covered to be employed to confirm its consistency results for these confirmatory analyses are reported elsewhere here the new deglaciation model referred to as ice 3g is compared to previous models derived by several independent means and tested against a number of additional observations other than sea level histories including geologically controlled retreat isochrones oxygen isotope data from deep sea sedimentary cores and coral terrace elevations the latter two observations strongly constrain the net sea level rise that has occurred since the onset of deglaciation and therefore the mass of ice that melted during the last glacial interglacial transition

glacial isostatic adjustment and the anomalous tide gauge record of eastern north america sea level variations as recorded by the global network of tide gauges represent a rich data set for studying a wide range of natural and anthropogenic phenomena such as the sea level rise induced by possible global warming for this purpose long term sea level trends must be corrected for the contaminating effects of continuing glacial isostatic adjustment1 5 gia the numerical correction procedure has for sites on the east coast of north america yielded a set of highly anomalous sea level rates characterized by systematic geographical trends2 4 5 we demonstrate that these trends are a consequence of inadequacies in the previous standard numerical prediction for gia in particular we find that the well known trends in the gia corrected tide gauge rates are eliminated if the lower mantle viscosity of the earth model used in the gia prediction is increased this result obviates the need to explain the anomalous trend as a manifestation of gulf stream ocean circulation4 or neotectonic processes2

dynamic earth system and ecological controls of rainfall initiated landslides abstract rainfall initiated landslides continue to inflict damages and loss of life throughout the world processes and mechanisms revealed from hydrological geomorphic geotechnical pedological geological hydrochemical and biological investigations have advanced our understanding of these effects on slope stability however the interactions amongst these processes and attributes as they affect the initiation and propagation of landslides are not as well understood too often landslide studies are conducted from only one or at most two of these perspectives moreover while precipitation and hydrology are recognized as dynamic influences the earth system and ecological effects are often assumed to be static we assess the interplay of these processes related to landslides triggered by positive pore water accretion and loss of soil suction each of these conditions arguably requires a different view on the processes that cause slope failure and predictive approaches this review starts from the perspective of dynamic adapting earth and ecological systems and discusses how these attributes relate to landslide initiation mode location and timing specifically the role that large and small scale preferential flow plays in both contributing to and mitigating instability is elucidated including effects of bedrock exfiltration we also examine how and under what conditions these pathways manifest in different soils lithology and landforms the multiple effects of rhizosphere processes on slope stability are discussed including root reinforcement evaporation from canopies and litter layers transpiration and the role of root structure affecting preferential flow paths rainfall initiated landslides involve highly dynamic hydrologic earth surface and ecological processes that persist over a range of spatial and temporal scales however guidance for overcoming these challenges has been elusive a conceptual framework is presented to shed light on these dynamic and interactive processes that should lend insights into why and when certain slopes fail during storms while other seemingly similar slopes do not fail such advances will benefit landslide hazard assessments and disaster responsiveness protocols

a microstructure based elastoplastic model to describe the behaviour of a compacted clayey silt in isotropic and triaxial compression the paper focuses on the hydromechanical behaviour of an unsaturated compacted clayey silt accounting for fabric changes induced by drying wetting cycles occurring at low stress levels the respon

the influence of a ductile crustal zone on glacial isostatic adjustment geodetic observables along the u s east coast we consider the influence of a 15 km thick ductile crustal layer of viscosity 1018 pa s embedded in an elastic 80 km lithosphere on predictions of on going glacial isostatic adjustment henceforth gia along the u s east coast crustal velocities are perturbed by 0 5 mm yr or more by the inclusion of the ductile layer furthermore perturbations in predictions of sea level rates along the u s east coast due to the ductile layer have a geographic pattern that is similar to residual trends evident in previous gia corrections of tide gauge records along this coast

experimental evaluation of mechanical behavior of unsaturated silty sand under constant water content condition abstract there are very few experimental data on the mechanical behavior of unsaturated soils particularly in constant water content condition because of the technical difficulties and time consuming nature of measuring suction and deformation this paper presents the results of a series of constant water constant triaxial tests on the specimens of an unsaturated silty sand constant water content tests correspond to a field condition where the rate of loading is much quicker than the rate at which the pore water is able to drain out of the unsaturated soil the axis translation technique and a double walled triaxial cell have been used to measure the soil matric suction and variation of pore air volume respectively test specimens were prepared at two different compaction conditions prior to testing to achieve different initial density it is found that the mechanical behavior of the soil mainly depends on the initial density the mean net stress and the initial matric suction also the volume and pore water pressure changes are significantly different in specimens with different initial condition the results of tests indicated that the shearing strength of silty sand increases non linearly with matric suction

the shear strength of partly saturated soils a direct shear apparatus is described which could be used to study the shear strength of partly saturated soils under controlled conditions the principle of this device is described and the test results are presented and discussed with this apparatus it is also possible to determine the effect on the shear strength of a change in solute suction

determination of the shear strength of unsaturated soils using the multistage direct shear test the determination of the shear strength of unsaturated soils is generally more complicated time consuming and expensive compared to the determination of the shear strength of saturated soils although much research has been done on unsaturated soil testing methods there is still a strong need to translate these studies into practice further studies are needed on practical testing methods that can reduce both the cost of and time associated with shear strength testing of unsaturated soils this paper presents a comprehensive evaluation of the validity of using the multistage direct shear test as a rapid and practical method to determine the shear strength of unsaturated soils the laboratory tests were performed using a newly constructed modified direct shear test apparatus that allows independent control of matric suction referred to as a suction controlled multistage direct shear test unsaturated shear strength was established using multistage loading over a range of net normal stresses and matric suction values shear strength parameters obtained from the multistage tests are compared with those from conventional direct shear tests using multiple soil specimens recommendations are given on how to carry out multistage direct shear tests to ensure reliable unsaturated shear strength measurements the tests were performed on undisturbed soil samples obtained from the riverbank of the lower roanoke river in eastern north carolina usa

undrained response of clays to varying strain rate the undrained stress deformation behavior of clays is significantly affected by the loading rate based on the observed experimental response it is possible to model the strain rate response of clays as an apparent overconsolidated clay response in this work we have quantitatively determined the change in the overconsolidation ratio ocr due to a change in the strain rate our results show that the shear strength response and the excess pore water pressure response at the peak stress provide quantitatively similar magnitudes of change in the ocr with increasing strain rate this finding holds true for both normally and overconsolidated clays this suggests that the relationship between strain rate and change in the ocr can be considered as an inherent material characteristic and is quantifiable a relationship between the change in the ocr and change in the strain rate is described

global sea level rise published values for the long term global mean sea level rise determined from tide gauge records exhibit considerable scatter from about 1 mm to 3 mm yr this disparity is not attributable to instrument error long term trends computed at adjacent sites often agree to within a few tenths of a millimeter per year instead the differing estimates of global sea level rise appear to be in large part due to authors using data from gauges located at convergent tectonic plate boundaries where changes of land elevation give fictitious sea level trends in addition virtually all gauges undergo subsidence or uplift due to postglacial rebound pgr from the last deglaciation at a rate comparable to or greater than the secular rise of sea level modeling pgr by the ice 3g model of tushingham and peltier 1991 and avoiding tide gauge records in areas of converging tectonic plates produces a highly consistent set of long sea level records the value for mean sea level rise obtained from a global set of 21 such stations in nine oceanic regions with an average record length of 76 years during the period 1880 1980 is 1 8 mm yr 0 1 this result provides confidence that carefully selected long tide gauge records measure the same underlying trend of sea level and that many old tide gauge records are of very high quality

strength of moist sand controlled by surface tension for tectonic analogue modelling abstract a technique has been developed to control the strength of moistened sand in a quantifiable accurate and reproducible way while other mechanical properties were maintained strength of dry sand was increased through adding a small amount of liquid in order to control the additional cohesion of moist sand the influence of the surface tension of the liquid was investigated direct shear experiments were performed on four granular materials at confining stress levels below 1 kpa it has been found that the surface tension of the added liquid controlled the additional apparent cohesion of sand with high accuracy the mechanical properties of moist sand show dynamic similarity towards natural brittle rock which enables analogue modelling of fault formation fault reactivation and tension fracture formation in the brittle regime with a controlled strength profile furthermore experimental results fit well to shear strength models from this followed the direct proportionality of the unsaturated shear strength parameter b relative to the matrix suction measured at low stress levels moreover shear strength turned out to be also a function of grain size and the grain shape

rheological stratification of the lithosphere abstract the rheology of the lithosphere is estimated on the basis of pore pressure dependent frictional failure in the brittle regime and power law steady state creep in the ductile regime different petrological models of the continental and oceanic lithosphere combined with different geotherms and thicknesses are used to generate models covering a variety of geodynamic situations results show that the depth dependence of lithospheric rheology varies with the tectonic province and that in many instances the continental lithosphere has one at the bottom of the crust or two the previous one plus another at mid crustal levels soft ductile layers sandwiched between brittle layers the depth distribution of geophysical parameters seismicity seismic wave velocity and electrical conductivity matches the theological predictions well the lithospheric rheological profiles are used to analyze observed variations in the structural style of deformed continental margin and oceanic terranes in the southeastern canadian cordillera the large scale characteristics of the system show a satisfactory agreement with the inferred rheological structure sub horizontal decollements should be the rule rather than the exception where the lithospheric rheology is strongly stratified

numerical modelling of the effects of weak immediate roof lithology on coal mine roadway stability abstract the stability and associated design of roof reinforcement requirements of tunnels driven in united kingdom coal measures strata is directly related to the engineering characteristics of the immediate roof lithology and the effects of redistribution of the in situ stress numerical modelling carried out by the authors has been used to simulate the widely observed detrimental effects of both high horizontal stress and weak immediate roof lithology on tunnel roof stability different numerical modelling techniques such as continuum discontinuum and hybrid finite element discrete element codes have been used to model the deformational behaviour of coal measures strata and are discussed in the context of specific case examples to highlight their application and suitability for modelling of weak rock the modelled results demonstrate that the thickness of the relatively weak mudstone in the roof of the tunnel has a significant influence on the extent of failure and ultimately the need for additional reinforcement

effects of degree of saturation on shallow landslides triggered by rainfall the empirical rainfall threshold concept and the physical based model are two commonly used approaches for the assessment of shallow landslides triggered by rainfall to investigate in detail the rainfall triggered shallow landslides many physical based models coupling the infinite slope stability analysis with the rainfall infiltration modeling in variably saturated soil were developed however in those physical based shallow landslide models the unit weight and the unsaturated shear strength were assumed constant rather than depending on the degree of saturation in this study the effects of the unit weight and the unsaturated shear strength as function of degree of saturation on rainfall triggered shallow landslides are examined several designed scenarios and a real case scenario are used to conduct the examinations the results show that not only the occurrence of shallow landslides but also the failure depth and the time to failure could be misassessed if the influences of degree of saturation on the unit weight and the unsaturated shear strength are neglected

variability of residual soil properties rainfall induced slope failures are commonly observed in residual soil due to weathering the residual soil properties vary with depths especially in tropical countries such as singapore therefore it is important to characterize the properties of residual soil with depth index properties soil water characteristic curve and saturated and unsaturated shear strength tests were carried out on residual soils from sedimentary jurong formation bukit timah granite and old alluvium in singapore the variations of residual soil properties in singapore were determined from the laboratory test results and evaluated as a function of soil inherent variability typical upper and lower bounds of soil properties for the residual soils in singapore were described using confidence interval approach and coefficient of variation cov in this paper the variations in residual soil properties can be incorporated in design based on risk or reliability approach the cov of index and engineering properties of residual soils in singapore indicate that residual soils from bukit timah granite and old alluvium are coarser than residual soil from sedimentary jurong formation the particle size distribution of residual soil from old alluvium is more uniform than that from bukit timah granite on the other hand the particle size distribution of residual soil from bukit timah granite is more uniform than that from sedimentary jurong formation the shear strengths of residual soils from bukit timah granite and old alluvium are higher than that from sedimentary jurong formation

implications of a ductile crustal layer for the deformation caused by the fennoscandian ice sheet summary previous studies of glacial isostatic adjustment have usually considered earth models with a purely elastic lithosphere a possibly significant deviation from this assumption is the presence of a ductile crustal layer embedded in an otherwise elastic lithosphere such a layer has been suggested for various continental regions on the basis of seismic and tectonic evidence the present study investigates the implications of a ductile crustal layer for the interpretation of glacial isostatic adjustment using a layered incompressible maxwell viscoelastic earth model and a simplified representation of the fennoscandian glaciation the relaxation time and amplitude spectra show that besides the conventional buoyancy mode m0 also present in earth models with a purely elastic lithosphere the ductile layer supports a slowly decaying mode mc which is capable of modifying the deformation markedly thus measures of the absolute deformation such as the stress clearly reflect the presence of the ductile layer in contrast to this are measures of the relative deformation such as the vertical displacement rate and the rate of gravity change to a good approximation these rates are inversely proportional to the relaxation time of the more quickly decaying mode m0 and are therefore less affected by the ductile layer taken together the present study suggests that provided a ductile crustal layer exists its presence should be accounted for in interpretations of the glacial isostatic adjustment following the fennoscandian or smaller glaciations

a shearbox for testing unsaturated soils at medium to high degrees of saturation unsaturated shear strength is of relevance in many geotechnical applications involving either compacted or natural soils

shear strength of a compacted residual soil from consolidated drained and constant water content triaxial tests rainfall induced landslides in unsaturated residual soils can occur slowly under drained conditions or rapidly under undrained conditions consolidated drained cd and constant water content cw

the westward drift of the lithosphere a rotational drag net westward rotation of the lithosphere relative to the underlying mantle is a controversial phenomenon fi rst attributed to tidal effects and later to the dynamics of mantle convection in spite of a number of independent geological and geophysical arguments for westward tectonic drift this phenomenon has received little recent attention we suggest that this differential rotation is a combined effect of three processes 1 tidal torques act on the lithosphere generating a westerly directed torque decelerating earth s spin 2 the downwelling of the denser material toward the bottom of the mantle and in the core slightly decreases the moment of inertia and speeds up earth s rotation only partly counterbalancing the tidal drag 3 thin 3 30 km layers of very low viscosity hydrate channels occur in the asthenosphere it is suggested that shear heating and the mechanical fatigue self perpetuate one or more channels of this kind which provide the necessary decoupling zone of the lithosphere

shallow upper mantle rheology and secular ice sheet fluctuations on time scales from decades to centuries continental cryospheric forcing in response to climate change constitutes a major source of isostatic disequilibrium that may influence future regional sea level variations current vertical displacements and gravity field variations are often estimated neglecting rheological effects and thus assuming a fully elastic response of the earth in this study we adopt a more general point of view aiming at describing ongoing surface movements resulting from recent glacial instabilities also taking into account the effects associated with shallow upper mantle and crustal rheologies our computations are based on the post widder laplace inversion formula which permits the straightforward computation of load deformation coefficients for steady state and transient rheologies up to very high harmonic degrees using a surface load with a simple geometry and time history we compare the classical elastic solutions to those obtained considering the rheological response of the shallow upper mantle while at the center of the ice sheet rheology only magnifies the elastic response the pattern and time history of vertical displacement at the ice sheet margins show a greater complexity mainly due to the development of lateral forebulges whose shape and amplitude are particularly sensitive to the rheology of the shallow upper mantle in this region assuming an elastic rheology is generally appropriate on a century time scale but significant deviations from a purely elastic response both sign and amplitude are observed at longer time scales or when a low viscosity zone with maxwell rheology is taken into account

rainfall induced landslides and debris flows in this preface we introduce the special issue on rainfall induced landslides and debris flows the topic is of high interest for many practical and scientific reasons in fact rainfall is the most relevant factor for the triggering of both shallow and deep seated landslides and rainfall analysis is the most frequently adopted approach for forecasting the occurrence of such phenomena the six papers of the special issue cover most of the key issues relative to rainfall induced landslides starting from the analysis of these contributions we identify and discuss in this paper several main topics that deserve further research in the field of rainfall induced landslide such as the uncertainty of the data the quality of geotechnical analysis the validation of the models and the applicability of results in the framework of natural hazards copyright 2007 john wiley sons ltd

a new cavability assessment for longwall top coal caving from discontinuum numerical analysis abstract this paper presents a new criterion for assessing top coal cavability in longwall top coal caving mining technology top coal cavability index tci criterion was developed through a parametric study statistical analysis and validation against field monitoring data a discontinuum modelling technique with plastic rock material was used to quantify the impact of parameters on top coal cavability in a more realistic manner the study demonstrated that an increase in the value of parameters such as immediate rock strength coal strength coal elastic modulus coal vertical joint spacing coal discontinuity friction angle and top coal thickness causes a decrease in top coal cavability whereas an increase in the value of cover depth leads to an increase in the cavability coal elastic modulus was found to have a minor impact while coal vertical joint spacing has the most significant impact on the cavability the tci criterion successfully incorporates the impacts of coal strength rock strength and discontinuity friction angle into the evaluation of top coal cavability the proposed criterion can thus be utilised to explicitly assess top coal cavability taking into account coal seam characteristics surrounding rock mass properties and the nature of discontinuities which contributes to improving reliability of the criterion

nineteenth canadian geotechnical colloquium the soil water characteristic curve a historical perspective the constitutive relationship between water content or degree of saturation and suction is called the soil water characteristic curve the soil water characteristic curve provides a conceptual framework in which the behavior of unsaturated soils can be understood a historical review illustrates how the work of early researchers in soil science and geotechnical engineering laid the foundation for our current understanding of this relationship key elements of these early studies were a conceptual understanding of the soil water characteristic curve as a relationship between the mass or volume of water stored within the soil and the energy in the water phase it was on the basis of this conceptual model that current methods of measuring the soil water characteristic curve were developed interpretative models for the distribution and geometry of the water phase in an unsaturated soil based on the capillary model have provided a useful conceptual model for understanding the effects of soil texture gradatio

drawing mechanism of fractured top coal in longwall top coal caving abstract this work proposed a progressive sectional failure model psfm based on particle flow code pfc to simulate top coal drawing process in longwall top coal caving ltcc mining the progressive sectional fracturing of top coal was reproduced in simulation 4 drawing schemes are numerically performed by considering drawing sequences and strategies the results of simulations were compared in terms of top coal drawn out mass drawing body top coal recovery ratio tcrr top coal loss etc the results show that tcrr in psfm is closer to average tcrr based on 9 ltcc coal mines measured in situ the top coal loss in psfm is larger than loose granular model lgm the top coal boundary tcb in psfm shows a step subsidence and is different from that in lgm the factors to influence initial drawing body idb are comprehensively analysed a new mathematical model was proposed to specifically characterize idb in ltcc the results show that new model is well consistent with simulation results and is much more effective and accurate than former models

new structure based model for estimating undrained shear strength this paper presents an experimental study of the strength in anisotropic clays by means of centrifuge model cone penetration and vane shear tests to understand the effects of void ratio overconsolidation ratio and testing rate on the undrained shear strength su of anisotropic speswhite clay a new centrifugal testing technique is designed to obtain constant overconsolidation ratio ocr profiles with varying void ratios e called the descending gravity test the parameters controlling the generation of peak shear strength are quantified as a result of this function a new material and rate dependent surface is defined in the e ocr su space which is identified as a structural state capacity surface since it relates the anisotropic structure to structure inherent capacity and properties a new function for the estimation of excess pore pressure uex generated by cone penetration is found by combining the strength and pore pressure functions a new model is proposed called the cu mod

a discontinuum modelling approach for investigation of longwall top coal caving mechanisms abstract this paper presents a discontinuum modelling approach to investigate longwall top coal caving ltcc behaviour including stress distribution coal and rock failures top coal caving and roof strata rupture and to analyse the impact of overburden movement on top coal caving the current model ia successful in using plastic material in a discontinuum code for intact rocks the model scale is large enough to capture the critical features of ltcc including steady state caving of top coal and repeatable periodic weighting of roof strata the applicability of the numerical model was assessed by calibration with field measurements obtained from a longwall mine site the numerical study found that the stress distribution caused by ltcc mining is in general similar to that caused by conventional longwall mining top coal predominantly fails in shear whereas roof rock mostly fails in tension top coal starts to cave in stress caving while main roof strata first rupture in crushing mode and roof strata weightings periodically increase and decrease top coal cavability the findings of this study should assist engineers in better understanding fundamental rock mechanics associated with ltcc identifying key geotechnical parameters dominating caving behaviour and managing top coal productivity and mine safety involved in ltcc operation

probabilistic back analysis of rainfall induced landslide a case study of malin landslide india on 30th july 2014 a devastating landslide resulted in the burial of a village called malin in western india and led to about 160 deaths the catastrophic failure was triggered by heavy rainfall over the last 3 days site investigation was conducted to obtain representative information about the area to understand the relevant physics which initiated landslide seepage and back analysis of the unsaturated slope was performed transient seepage analysis was carried out using finite difference method to simulate the slope behavior during rainfall infiltration a coupled fluid flow analysis was employed to capture the fluid mechanical interaction in unsaturated soils accurately the results show that antecedent rainfall played a role in slope instability rainfall intensity and duration also have a big impact on slope instability this paper presents a methodology to back analyse the slope so as to identify the mechanisms responsible for landslide initiation back analysis is performed using a probabilistic method based on bayesian analysis probabilistic methods can back analyse numerous sets of uncertain slope stability parameters the uncertain parameters are imported as random variables in the analysis and are described by their probability distributions bayesian analysis updates these distributions based on the observed slope behavior the method evaluates the reduction in matric suction which initiated landslide in malin slope the results show that the decrease in matric suction of about 100 in addition to the development of positive pore pressures is the main mechanism which has triggered the landslide this amount of reduction in matric suction and the development of positive pore pressures decreases the mobilized shear strength in soil below the threshold value required to maintain equilibrium in the slope and hence the slope failed c 2016 elsevier b v all rights reserved

shear strength characteristics of an unsaturated expansive clay the shear strength characteristics of an expansive clay from china were studied by performing suction controlled direct shear tests on both natural and compacted specimens the tested soil was a silty clay with intermedi ate plasticity and medium expansion potential a modified direct shear apparatus with a newly developed water volume indicator was used for this laboratory study the experimental results clearly show that the dilatancy of the expansive clay increases with an increase in the applied suction for both the natural and compacted specimens matric suction contributes to the shear strength of the expansive clay via two different mechanisms the contribution of capillary force to interparticle normal stress and the effect of suction on soil dilatancy as a result of the second mechanism the con tribution of suction to peak shear strength for the clay is more significant than that to post failure shear strength par ticularly at a high suction range the contribution of suction to post failure shear strength for the natural specimen is basically consistent with that for the compacted specimen the higher peak shear strength and dilatancy for the natural specimen are related to the cementation effect of the iron and manganese oxides the contribution of suction to shear strength for the compacted expansive clay is more significant than that for a compacted kaolin at suctions less than 100 kpa

response of a residual soil slope to rainfall rainfall induced landslides are a common problem in residual soil slopes of the tropics it is widely known that rainfall induced slope failures are mainly caused by infiltration of rainwater howe

the effects of normal and shear stress wave phasing on coseismic landslide displacement predictive models used to assess the magnitude of coseismic landslide strain accumulation in response to earthquake ground shaking typically consider slope parallel ground accelerations only and ignore both the influence of coseismic slope normal ground accelerations and the phase relationship between dynamic slope normal and slope parallel accelerations we present results of a laboratory study designed to assess the significance of the phase offset between slope normal and slope parallel cyclic stresses on the generation of coseismic landslide displacements using a dynamic back pressured shearbox that is capable of simulating variably phased slope normal and slope parallel dynamic loads we subjected sediment samples to a range of dynamic loading scenarios indicative of earthquake induced ground shaking we detail the variations in strain accumulation observed when slope normal and slope parallel stresses occur independently and simultaneously both in and out of phase using a range of dynamic stress amplitudes our results show that the instantaneous phasing of dynamic stresses is critical in determining the amount of coseismic landslide displacement which may vary by up to an order of magnitude based solely on wave phasing effects instantaneous strain rate is an exponential function of the distance normal to the mohr coulomb failure envelope in plots of shear stress against normal effective stress this distance is strongly controlled by the phase offset between dynamic normal and shear stresses our results demonstrate that conditions considered by conventional coseismic slope stability models can either overestimate or underestimate earthquake induced landslide displacement by up to an order of magnitude this has important implications for accurate assessment of coseismic landslide hazard

geoid heights due to a crustal low viscosity zone in glacial isostatic adjustment modeling a sensitivity analysis for goce 1 seismic observations and the occurrence of post seismic deformation in several continental regions indicate the presence of one or more layers with relative low 1018 1019 pas viscosity in the earth s crust this study simulates the effect of thickness viscosity and depth of such a low viscosity zone lvz on geoid heights that are the result of glacial isostatic adjustment to pleistocene ice loads it is found that an lvz introduces variations in geoid heights up to 1 meter with spactial scales larger than a few hundred kilometers underneath and just outside former glaciated areas the response to changes in the properties of the lvz is shown to be wavelength dependent the lvz induced geoid signal is within the accuracy of the upcoming goce satellite mission which means that in principle it should be possible to detect the presence of a supposed lvz with goce data

behavior of unsaturated weathered residual granite soil with initial water contents abstract there is a significant difference between the swccs response for drying and wetting curves in unsaturated state in other words the initial water content condition can influence the behavior of unsaturated soils to find this out a series of triaxial compression tests was performed on samples of compacted granite soils in a modified triaxial cell that can separately control pore air pressure u a and pore water pressure u w unsaturated granite soil samples were prepared with different initial water contents dry wet and optimum moisture by compaction in a mould these samples were tested at different suction and confining stresses the volume change of an unsaturated soil during shearing is more sensitive to the confining pressure compared to the initial water content and the matric suction the volume expands during shearing and the volumetric strain is much larger at the smaller confining pressure and at the higher matric suction the variation of the internal frictional angle with the initial water content and the matric suction is negligible but the effective cohesion increases with matric suction

on postglacial geoid subsidence over the equatorial oceans we develop two new spectral formalisms for the gravitationally self consistent solution of the sea level equation which governs the redistribution of glacial meltwater on a visco elastic earth the first is a purely spectral technique based on an extension of theory outlined by dahlen 1976 for determining the equilibrium oceanic tide on an elastic planet using this technique with a feasible spherical harmonic truncation level l 30 we can obtain convergence in the computed sea level variations within the degree range l 10 we also develop a second pseudospectral technique however which permits the construction of gravitationally self consistent solutions to much higher degree and order l 100 the pseudospectral formalism is employed here to develop a comprehensive physical explanation for the global pattern of present day sea level variations due to ongoing glacial isostatic adjustment in particular we focus upon a mechanism which we term equatorial ocean syphoning that acts to draw water toward the oceanic portion of the collapsing peripheral bulge that encircles previously glaciated regions the collapse of the forebulge induces a flow of water which is required to maintain hydrostatic equilibrium the syphoning mechanism dominates the relative sea level rsl variation in oceans in the far field of the ice sheets that is beyond the peripheral bulge during periods such as the interglacial of the past 4000 years during which the volume of the ice sheets has not apparently changed appreciably while at the same time isostatic adjustment persists the rsl change in the near field is in contrast dominated by the local vertical displacement of the solid surface finally comparison of gravitationally self consistent predictions of rsl change in the far field with the observational data at small pacific island sites has provided an upper bound of 1 to 2 m for the eustatic sea level rise produced by any recent last 3000 years melting of the antarctic ice sheet

the relationship of the unsaturated soil shear strength to the soil water characteristic curve the measurement of soil parameters such as the permeability and shear strength functions used to describe unsaturate soil behaviour can be expensive difficult and often impractical to obtain this paper proposes a model for predicting the shear strength versus matric suction function of unsaturated soils the prediction model uses the soil water characteristic curve and the shear strength parameters of the saturated soil i e effective cohesion and effective angle of internal friction once a reasonable estimate of the soil water characteristic curve is obtained satisfactory predictions of the shear strength function can be made for the unsaturated soil closed form solutions for the shear strength function of unsaturated soils are obtained for cases where a simple soil water characteristic equation is used in the prediction model key words soil suction soil water characteristic curve shear strength function unsaturated soil

performance of an unsaturated expansive soil slope subjected to artificial rainfall infiltration a major infrastructure project the south to north water transfer project has been proposed to carry potable water from the yangtze river region in the south to many arid and semi arid areas in the northern regions of china including beijing the proposed 1200 km middle route of the project is likely to be an open channel with a trapezoidal cross section at least 180 km of the proposed excavated canal will pass through areas of unsaturated expansive soils an 11 m high cut slope in a typical expansive clay with medium plasticity in zaoyang close to the middle route in hubei was selected for a comprehensive and well instrumented field study of the effects of rainfall infiltration two artificial rainfall events were created during a month of field investigation and monitoring prior to the rainfall events high soil suction was measured within the top 1 m of soil this high initial soil suction created an upward flux of water and moisture the abundant cracks and fissures near the ground surface p

shear strength and dilative characteristics of an unsaturated compacted completely decomposed granite soil shear strength and dilative characteristics of a re compacted completely decomposed granite cdg soil are studied by performing a series of single stage consolidated drained direct shear tests under different matric suctions and net normal stresses the axis translation technique is applied to control the pore water and pore air pressures a soil water retention curve swrc is obtained for the cdg soil from the equilibrium water content corresponding to each applied matric suction value for zero net normal stress using a modified direct shear apparatus shear strength increases with matric suction and net normal stress and the failure envelope is observed to be linear the apparent angle of internal friction and cohesion intercept increase with matric suction a greater dilation angle is found at higher suctions with lower net normal stresses while lower or zero dilation angles are observed under higher net normal stresses with lower suctions also at a saturated condition experimental shear strength

model for the prediction of shear strength with respect to soil suction experimental studies on unsaturated soils are generally costly time consuming and difficult to conduct shear strength data from the research literature suggests that there is a nonlinear increas

shear strength and shear induced volume change behavior of unsaturated soils from a triaxial test program a series of unsaturated soil triaxial tests were performed on four soils including sand silt and a low plasticity clay attempts were made to correlate unsaturated soil properties from these tests and data from the literature with soil water characteristics curve swcc soil gradation and saturated soil properties the feasibility of estimating unsaturated soil property functions from saturated soil properties swccs and gradation data is demonstrated a hyperbolic model for estimation of the unsaturated soil parameter b versus matric suction is presented shear induced volume change behavior was also studied and results are included in this paper although not correlated with soil index properties these shear induced volume change data are important to complete stress deformation analyses and represent a significant addition to the existing data base of unsaturated soil properties

effects of soil structure on the shear behaviour of an unsaturated loess at different suctions and temperatures previous studies of shear behaviour at different suctions and temperatures focused mainly on recompacted soils limited attention has been paid to intact soil in this paper the shear behaviour of

influences of soil water characteristic curve on rainfall induced shallow landslides the analysis of slope instability induced by rainfall was usually performed using the main drying curve as the measurement of the main wetting curve is a more time consuming and costly task in this study the influences of the main drying and wetting curves on rainfall induced shallow landslides are examined three designed scenarios and a real case scenario are used to conduct this examination the prediction of shallow landslide occurrence is related to the main drying and wetting curves due to the strong relation between groundwater pressure head and hysteresis effect the main wetting curve may have a less minimum landslide triggering rainfall amount and a less rainfall duration threshold for landslide occurrence than the drying wetting curve for safety s sake an underestimation of shallow landslide occurrence may be produced by the commonly used main drying curve in addition besides the shallow landslide occurrence the failure depth and the time to failure are also influenced by the main drying and wetting curves the hysteresis effect should be taken into account for assessing rainfall induced shallow landslides

critical state soil constitutive model for methane hydrate soil 1 this paper presents a new constitutive model that simulates the mechanical behavior of methane hydrate bearing soil based on the concept of critical state soil mechanics referred to as the methane hydrate critical state mhcs model methane hydrate bearing soil is under certain geological conditions known to exhibit greater stiffness strength and dilatancy which are often observed in dense soils and also in bonded soils such as cemented soil and unsaturated soil those soils tend to show greater resistance to compressive deformation but the tendency disappears when the soil is excessively compressed or the bonds are destroyed due to shearing the proposed model represents these features by introducing five extra model parameters to the conventional critical state model it is found that for an accurate prediction of ground settlement volumetric yielding plays an important role when hydrate soil undergoes a significant change in effective stresses and hydrate saturation which are expected during depressurization for methane gas recovery

rainfall triggered shallow landslides at catchment scale threshold mechanics based modeling for abruptness and localization 1 rainfall induced shallow landslides may occur abruptly without distinct precursors and could span a wide range of soil mass released during a triggering event we present a rainfall induced landslide triggering model for steep catchments with surfaces represented as an assembly of hydrologically and mechanically interconnected soil columns the abruptness of failure was captured by defining local strength thresholds for mechanical bonds linking soil and bedrock and adjacent columns whereby a failure of a single bond may initiate a chain reaction of subsequent failures culminating in local mass release a landslide the catchment scale hydromechanical landslide triggering model chlt was applied to results from two event based landslide inventories triggered by two rainfall events in 2002 and 2005 in two nearby catchments located in the prealps in switzerland rainfall radar data surface elevation and vegetation maps and a soil production model for soil depth distribution were used for hydromechanical modeling of failure patterns for the two rainfall events at spatial and temporal resolutions of 2 5 m and 0 02 h respectively the chlt model enabled systematic evaluation of the effects of soil type mechanical reinforcement soil cohesion and lateral root strength and initial soil water content on landslide characteristics we compared various landslide metrics and spatial distribution of simulated landslides in subcatchments with observed inventory data model parameters were optimized for the short but intense rainfall event in 2002 and the calibrated model was then applied for the 2005 rainfall yielding reasonable predictions of landslide events and volumes and statistically reproducing localized landslide patterns similar to inventory data the model provides a means for identifying local hot spots and offers insights into the dynamics of locally resolved landslide hazards in mountainous regions

shear strength and pore water pressure characteristics during constant water content triaxial tests shear strength parameters used in geotechnical design are obtained mainly from the consolidated drained cd or consolidated undrained cu triaxial tests however in many field situations soils are compacted for construction purposes and may not follow the stress paths in cd or cu triaxial tests in these cases the excess pore air pressure during compaction will dissipate instantaneously but the excess pore water pressure will dissipate with time under this condition it can be considered that the air phase is drained and the water phase is undrained this condition can be simulated in a constant water content cw triaxial test the purpose of this paper is to present the characteristics of the shear strength volume change and pore water pressure of a compacted silt during shearing under the constant water content condition a series of cw triaxial tests was carried out on statically compacted silt specimens the experimental results showed that initial matric suction and net confining stress play an important role in affecting the characteristics of the shear strength pore water pressure and volume change of a compacted soil during shearing under the constant water content condition the failure envelope of the compacted silt exhibited nonlinearity with respect to matric suction

critical state for overconsolidated unsaturated silty soil the critical state concepts have been investigated for an overconsolidated unsaturated silty soil through a comprehensive set of controlled suction triaxial laboratory experiments the experimental

work input analysis for soils with double porosity and application to the hydromechanical modeling of unsaturated expansive clays a mechanical approach for unsaturated expansive soils considering double porosity has been developed based on the porous media theory in this approach the adsorbed and the capillary water as well as the micropores and macropores are two distinct phases an interaggregate stress considered as the work conjugate of the macrostructural strain increment has been defined both physicochemical and capillary effects of the pore water have been introduced at the macroscopic level other work conjugate variables relevant for the constitutive modeling of double porosity unsaturated media have also been identified consisting of the modified suction as conjugate of the increment of the macrostructural degree of saturation and the microstructural effective stress as conjugate of the microstructural volumetric strain increment a hydromechanical model for unsaturated expansive clays taking into account the interaction between the micro and the macrostructures in expansive clays can thus be built based on the bou

quantification of mechanical and hydric components of soil reinforcement by plant roots the use of vegetation to stabilize slopes with regard to shallow landslides is an ecological and economic alternative to traditional solutions of civil engineering this study aims at quantifying the effect of soil water content on the reinforcement of soil by plant roots and determines how soil water content influences the failure modes of roots during shear direct shear box tests were performed on three species used in hillslope reforestation programs in yunnan china reinforcement was quantified and divided into a hydric component corresponding to the effect of water removal and a mechanical component reflecting the influence of roots on apparent cohesion and friction angle it was shown that the hydric component of reinforcement can be of the same order as the mechanical component and that root system architectural traits influence the type of mechanical reinforcement cohesive or frictional we also demonstrate the potential development of matric suction effects on the shear strength of soil

a time space based approach for mapping rainfall induced shallow landslide hazard a rainfall induced shallow landslide is a major hazard in mountainous terrain but a time space based approach is still an unsettled issue for mapping rainfall induced shallow landslide hazards rain induces a rise of the groundwater level and an increase in pore water pressure that results in slope failures in this study an integrated infinite slope analysis model has been developed to evaluate the influence of infiltration on surficial stability of slopes by the limit equilibrium method based on this new integrated infinite slope analysis model a time space based approach has been implemented to map the distributed landslide hazard in a gis geographic information systems and to evaluate the shallow slope failure induced by a particular rainfall event that accounts for the rainfall intensity and duration the case study results in a comprehensive time space landslide hazard map that illustrates the change of the safety factor and the depth of the wetting front over time

application of suction stress for estimating unsaturated shear strength of soils using direct shear testing under low confining pressure the primary objective of this study is to evaluate effects of suction on shear strength of unsaturated soils under low confining pressure and to examine the relationships between suction shear strength behavior and volumetric deforma tion using newly developed direct shear testing equipment for compacted weathered granite soils the soil water retention curves swrcs of unsaturated soils were obtained under various overburden pressures to analyze test results from the direct shear test under unsaturated conditions a new method suction stress swrc method ssm is proposed to deter mine the suction value for each overburden pressure and the suction stresses as a result it has been found that the stress states at the peak shear strength point are on the same failure line for the saturated state when the suction stress is treated as a component of confining pressure the relationship between stress ratio and dilatancy for the saturated state can be ex tended to the unsaturated state it is also noted that the estimated unsaturated shear strengths using the ssm agree well with the measured values from laboratory testing

residual shear strength of unsaturated soils via suction controlled ring shear testing abstract results from a comprehensive series of suction controlled ring shear tests conducted on statically compacted specimens of silty clayey sand and silty sand are presented the experiments were accomplished in a newly developed servo suction controlled ring shear apparatus suitable for testing unsaturated soils under large deformations and suction controlled conditions via the axis translation technique the present work focuses primarily on two crucial aspects of compacted unsaturated soil behavior namely the behavior of silty clayey sand under suction controlled ring shear testing and the effects of pre shearing and suction histories on unsaturated residual shear strength of compacted silty sand test results corroborate the important role played by matric suction on residual shear strength properties of unsaturated soils for the range of net normal stresses and suction states investigated the increase in residual shear strength with increasing suction was confirmed to be a linear trend for silty sand but significantly nonlinear for silty clayey sand results from multi stage ring shear tests confirmed that the residual shear strength of unsaturated soils is virtually independent of the pre shearing and suction histories experienced by the soil

evaluation of surficial stability for homogeneous slopes considering rainfall characteristics shallow slope failures in residual soil during periods of prolonged infiltration are commonly occurring in the world this study examines an infinite slope analysis to estimate the influence of infiltration on surficial stability of slopes by the limit equilibrium method an approximate method that accommodates the boundary condition of a uniform rainfall has been proposed to evaluate the likelihood of shallow slope failure that is induced by a particular rainfall event the method based on the mein and larson model which provides an explicit solution for preponding infiltration has been applied to various types of soil having measured unsaturated hydraulic properties to compare results with those obtained from the approximate method a series of numerical analyses were carried out according to the results with the use of properly estimated input parameters the approximate method was found to give results that compare reasonably well with those of more rigorous finite element analyses

comparative analysis of contributing parameters for rainfall triggered landslides in the lesser himalaya of nepal in the himalaya people live in widely spread settlements and suffer more from landslides than from any other type of natural disaster the intense summer monsoons are the main factor in triggering landslides however the relations between landslides and slope hydrology have not been a focal topic in himalayan landslide research this paper deals with the contributing parameters for the rainfall triggered landslides which occurred during an extreme monsoon rainfall event on 23 july 2002 in the south western hills of kathmandu valley in the lesser himalaya nepal parameters such as bedrock geology geomorphology geotechnical properties of soil and clay mineralogy are described in this paper landslide modeling was performed in seep w and slope w to understand the relationship of pore water pressure variations in soil layers and to determine the spatial variation of landslide occurrence soil characteristics low angle of internal friction of fines in soil medium range of soil permeability presence of clay minerals in soil bedrock hydrogeology and human intervention were found to be the main contributing parameters for slope failures in the region

influence of stress history on the strength parameters of an unsaturated statically compacted soil unsaturated soils are generally near the ground surface and are commonly overconsolidated due to environmental effects the stress state variables for an unsaturated in situ profile consist of the

strain rate dependent stress strain behavior of overconsolidated hong kong marine clay a total number of 24 consolidated undrained triaxial shear tests on reconsolidated saturated hong kong marine clay hkmc have been performed in both compression and extension shear states the specimens were prepared in four different overconsolidation ratios ocrs and sheared at three different axial strain rates the strain rate dependency of undrained shear strength pore water pressure stress path and secant young s modulus are investigated the influence of ocr on the stress strain strength behavior of hkmc is also examined the results of all tests are presented and interpreted the interpreted results are compared with the results in the literature for the hkmc with ocr varying from 1 to 8 the average value of the strain rate parameter 0 15 is 5 5 for compression tests and 8 4 for extension tests most interpreted results are conclusive and consistent with the published results whereas some results are not conclusive a new parameter for describing the strain rate dependency of undrained

lithospheric thickness inferred from australian post glacial sea level change the influence of a ductile crustal zone 1 we investigate the influence of a crustal low viscosity zone clvz on numerical predictions of post glacial late holocene sea level variations in the australian region specifically we compare predictions from a model with a 15 km thick clvz within an otherwise elastic plate to results from a suite of models in which the thickness of a purely elastic crust lithosphere is varied we conclude that previous inferences of lithospheric thickness based on differential highstands from the region represent approximately the thickness of the elastic layer above the clvz and thus if a clvz exists these inferences may be significantly underestimating the total depth extent of the crust lithosphere system

rainfall characteristics for anisotropic conductivity of unsaturated soil slopes the purpose of this study was to investigate the effects of the anisotropic ratio on the stability of slopes using the reliability index approach a numerical analysis of the relationship between the three rainfall patterns advanced normal and delayed and the anisotropic ratios was designed this study also considered three different soil properties sand silt and clay to simulate rain infiltration in this study probability analysis was used to evaluate the stability of unsaturated soil slopes the finite element computer program geo studio was used to simulate the process of rainwater infiltrating a slope the pore water pressure results evaluated from seepage analysis seep w were imported into the slope stability program slope w results for the anisotropic ratio of hydraulic conductivity indicate that when the anisotropic ratios become higher the reduction in the reliability index is insignificant in addition the simulation results indicated that when saturated hydraulic conductivity ks was less than rainfall intensities i the percentage probability of the occurrence of a landslide was larger than when ks was greater than i finally in the cases of anisotropic ks stability of the high ratio soil slopes was not found to be sensitive to the reliability index variation during the simulation period moreover when ks was greater than i slope stability decreased earlier than was the case in the opposite situation

lower crustal flow in an extensional setting constraints from the halloran hills region eastern mojave desert california postextensional uplift and tilting of quaternary lake sediments in the halloran hills eastern mojave desert california suggest that regional scale flow within the lower crust is occurring in response to tectonic loads created during upper crustal extension in late miocene time the concept that significant flow within the lower crust may occur for millions of years after the cessation of extension indicates that topographic gradients can be modified by regional scale flow within the lower crust and that direct constraints on lower crustal flow can be obtained by quantitative analysis of rates of postextensional surface tilting an analytic solution developed in this paper combines viscous flow in the lower crust flexural bending within the midcrust and isostasy into an invertible linear differential equation that describes the topographic response to upper crustal extension assuming that there was no topographic relief across the halloran hills region prior to extension inversion of modern topographic data indicates that crustal thinning above the halloran hills detachment increases westward with a listric geometry and that little crustal thinning has occurred east of the western flank of clark mountain in good agreement with the known geometry of the fault and the location of its breakaway zone incorporation of quaternary tilting data indicates that the modern viscosity beneath the halloran hills assuming a 10 km lower crustal channel is a maximum of 1019 pa s and that the viscosity of the lower crust has decreased by at least 1 to 2 orders of magnitude since 8 ma this corresponds to a temperature increase of at least 75 to 100 c at the moho in our opinion the most likely source of this temperature increase is a regional scale thermal event within the underlying mantle and diffusion of heat upward into the lower crust if correct these results have important implications for the way in which crustal extension is linked to mantle heating within the basin and range province

influence of structure on shear characteristics of the unsaturated loess in lanzhou china abstract loess is typically a kind of soil with metastable structure which makes loess sensitive to collapse and sliding upon wetting such structure has thus profound influence on loess s mechanical behavior however there have been arguments about how the metastable structure influences on loess s mechanical behavior and what the mechanism behind is in this study the influence of structure on shear characteristics of the unsaturated loess in lanzhou city of china was investigated with comparison of variation of shear strength and its parameters between six pairs of the undisturbed and remolded samples it is found that the peak shear strength and strength parameters of the loess significantly reduced once its structure was destroyed while shear behavior of the loess showed little change strength parameter c was much more sensitive to structure of the loess than shear strength reduction of the loess due to change of structure should be largely attributed to breaking up of cementation bonds between particles evidenced by the difference in pore size distribution and microstructure of soil fabrics between the undisturbed and remolded samples the bonds provided by clays and carbonates contributed the most to structure of the loess with minor by soluble salts while matric suction played little role in structure of the loess

influence of suction on the strength and stiffness of compacted sand bentonite this paper examines the constitutive behaviour of unsaturated mixtures of compacted sand bentonite material two different techniques have been used to modify soil suction in laboratory specimens to examine the influence of suction on the behaviour of compacted materials the two methods generated inherent differences in material fabric and therefore in stress strain behaviour the difference in microstructure generated by these two preparation techniques created different properties for the two series of specimens this paper compares the behaviour of the two series of specimens and relates the observed mechanical behaviour to the initial soil fabric created by the two different preparation techniques specimens of similar compacted material were taken from two full scale in ground experiments conducted at atomic energy of canada limited s underground research laboratory at lac du bonnet manitoba and sheared using the same triaxial equipment the results are compared to the results of shearing laborator

fragility curves for rainfall induced shallow landslides on transport networks many of the earthworks assets on rail transport networks were constructed in the 1800s and have thus operated for periods far in excess of their expected service life incidences of failure parti

shear strength characteristics of a residual soil shallow landslides in natural residual soils slopes are common all over the world the slip surfaces associated with these landslides are often situated above the groundwater table therefore it i

confined groundwater zone and slope instability in weathered igneous rocks in hong kong in hong kong slope failure in weathered granite and volcanic rocks has been studied extensively but the impact of hydrogeological conditions on slope stability has received much less attention it is customary in hong kong to assume that the hydraulic conductivity k of weathered igneous rocks decreases with depth or as the rock mass becomes less weathered generally studies of groundwater for determining slope stability treat the saprolite above the rockhead as an aquifer and the rockhead as an impermeable boundary this paper examines direct and indirect aquifer hydraulic information scattered in various sources and demonstrates that such a model may be inappropriate evidence is cited to show that at least in some places a relatively high hydraulic conductivity k zone hkz may exist at depth either in the lower saprolite or at the rockhead the completely decomposed igneous rocks if significantly kaolinized may have low permeability and behave as a confining zone for the hkz the groundwater flow regime in such an hkz may be confined resulting in a higher rise in water pressure in response to rainfall than might otherwise be expected these high pressures may result in a significant reduction in slope stability an examination of the cross sections of some well known landslides in hong kong reveals a chairshaped rockhead profile numerical models coupling saturated and unsaturated subsurface flow are used to investigate the saturation process in the presence of an hkz in slopes in response to typical rainstorms the simplified bishop s method is used to calculate changes in the factor of safety for slopes during such rainstorms the saturation process and pressure distribution in a slope are complicated by the presence of an hkz an hkz that is blocked at the toe represents the worst hydraulic condition for slope stability the paper concludes that although slope stability studies in hong kong have tended to focus on perching within the regolith a critical hydraulic boundary condition may exist locally at the base of the regolith d 2005 elsevier b v all rights reserved

determination of the shear strength parameters of an unsaturated soil using the direct shear test multistage direct shear tests have been performed on saturated and unsaturated specimens of a compacted glacial till a conventional direct shear apparatus was modified in order to use the axis tra

effects of the spatial variability of permeability on rainfall induced landslides abstract the saturated hydraulic conductivity ks of soil is characterized by strong spatial variability and often decreases with depth the main objective of this paper is to investigate how the trend function of the mean of saturated hydraulic conductivity k s and its spatial variability affect the distribution of critical failure surfaces and the probability of slope failure during a period of rainfall a random field method is used to simulate the spatial variability structure in the numerical analysis of a slope and a numerical procedure for a probabilistic slope stability analysis based on monte carlo simulations is presented in which ks is modeled as a non stationary lognormal random field for a hypothetical weathered soil slope subjected to rainfall a deterministic analysis and a sequence of probabilistic analyses are conducted using an infinite unsaturated slope model the results show that these shallow failures are attributed to the reduction of matric suction and the development of positive pore pressure the probability of slope failure increases with an increase in the variation of the trend component k but the rate of increase levels off at the later stage of rainfall ignoring the trend component of k s would lead to less conservative estimates of the failure probability the coefficient of variability has a more significant influence on the distribution of the critical failure surfaces and the probability of failure than does the correlation length of ks

unsaturated soil mechanics in rainfall induced flow landslides abstract rainfall induced flow landslides in coarse grained soils pose significant threats to populations and structures due to their high velocities long travel distance and the absence of definite warning signs during the pre failure stage the triggering phase of these phenomena is frequently related to rainfall events which significantly reduce matric suction in the shallower soil layers in this paper the processes leading to the onset of such phenomena are illustrated and some observations on their modelling are briefly recalled the failure stage at different scales is then modelled with reference to a case study from southern italy which draws on high quality experimental data sets from extensive in situ and laboratory investigation

shear strength characteristics of two saprolitic soils the saturated and unsaturated shear strength behavior of an undisturbed completely decomposed fine ash tuff and an undisturbed completely decomposed granite from hong kong were studied using direct shear and triaxial tests the completely decomposed fine ash tuff is a fine to medium grained saprolite the completely decomposed granite is a coarse grained saprolite results show that matric suction increases the shear strength of both soils the extent of the increase is the shear strength with matric suction is related to the soil water characteristic curve for the soil and to the amount of dilation during shear the effect of matric suction on the shear strength was more pronounced for the fine to medium grained completely decomposed fine ash tuff than for the coarse grained completely decomposed granite these studies on the saprolitic soils provide insight into the understanding of the shear strength of unsaturated coarse grained soils key words saprolites shear strength matric suction triaxi

infiltration analysis to evaluate the surficial stability of two layered slopes considering rainfall characteristics abstract shallow slope failures in residual soil during periods of prolonged infiltration are common throughout the world using a one dimensional infiltration model and an infinite slope analysis this study examines an approximate method of determining how infiltration influences the surficial stability of two layered slopes the method extends moore s infiltration model which is based on the green ampt model to cover more general situations including those where water moves upward from a perched water table in decreasingly permeable soil the method has also been used to evaluate the likelihood of a shallow slope failure being induced by a particular rainfall event in making this evaluation the method takes into accounts the rainfall intensity and duration of various return periods in a two layered soil profile a comparison of the results of the infiltration model with the results of numerical analyses shows that with the use of properly estimated input parameters the proposed model compares reasonably well with other model that rely on more rigorous finite element method