a water retention model for deformable soils the paper presents an experimental study on water retention behaviour of two reconstituted soils a silty clay speswhite kaolin and a sandy clayey silt barcelona silt and two compacted soils a silty clay speswhite kaolin and a silty sandy gravel adige river embankment these soils were used with the aim of encompassing a wide range of soil types and soil fabrics specimens were subjected to drying and wetting hydraulic paths by removing or adding water under zero total stress and to mechanical wetting paths by compressing specimens at constant water content to investigate a broad range of void ratios the reconstituted sandy clayey silt was initially reconstituted from slurry by applying different consolidation vertical stresses whereas the compacted speswhite kaolin and adige river embankment were compacted to a broad range of water contents and compaction energy on the basis of the experimental data a modification to the van genuchten s model is proposed to account for the effect of voi

compaction behaviour of clay this paper presents an experimental study of the compaction behaviour of non active clay one dimensional static compaction tests were carried out at high and medium water content with matric suction monitoring using trento high capacity tensiometers at lower water contents a transistor psychrometer was used to measure post compaction suction samples were compacted on the dry side of optimum to cover a wide range of compaction water contents and vertical stresses three water content regions were identified in the compaction plane depending on whether post compaction suction increased decreased or remained constant as the degree of saturation was increased at constant water content hydraulic paths of specimens subjected to loading unloading cycles at constant water content have clearly shown that post compaction suction may increase as the degree of saturation increases this non intuitive behaviour was demonstrated to be associated with the coupling between mechanical and water retention behaviour to this end a coupled mechanical water retention model was formulated irreversible one dimensional mechanical paths were modelled by a boundary surface in the space average skeleton vertical stress modified suction and void ratio irreversible hydraulic wetting paths were modelled by a boundary surface in the space suction degree of saturation and void ratio this study was completed by investigating the pore size distribution of compacted samples through mip tests

influence of compaction procedure on the mechanical behaviour of an unsaturated compacted clay part 1 wetting and isotropic compression the influence of compaction pressure compaction water content and type of compaction static or dynamic on subsequent soil behaviour during wetting and isotropic loading has been investigated by conducting controlled suction tests on samples of unsaturated compacted speswhite kaolin the results are interpreted within the context of an elastoplastic framework for unsaturated soils to examine which compaction induced effects can be explained simply by variation in the initial state of the soil and which require that soils produced by different compaction procedures are modelled as fundamentally different materials the compaction pressure influences initial state by affecting the initial position of the yield surface but it also influences to a limited degree the positions of the normal compression lines for different values of suction the compaction water content influences the initial suction but also has a significant influence greater than does compaction pressure on the positions of the nor

shear strength of rock joints influenced by compacted infill abstract discontinuities such as fault planes joints and bedding planes in a rock mass may be filled with different types of fine grained material that are either transported or accumulated as gouge due to weathering or joint shearing previous laboratory studies have mainly examined the role of saturated infill that exhibits the minimum shear strength however in practice the infill materials are often partially saturated generating matric suction within the joint that can contribute to increased shear strength to the authors knowledge this is the first study to examine the influence of compacted unsaturated infill on the joint shear strength a series of laboratory triaxial tests on idealised model joints and imprinted natural joint profiles was carried out with constant water contents of the infill being maintained from the laboratory results it is observed that the peak shear strength of infilled joints increased with the decrease of degree of saturation from 85 to 35 for both idealised joints and replicated natural joints based on the laboratory observations an empirical model for describing the infilled joint shear strength was developed

the effects of historic abstraction of groundwater from the london basin aquifers on groundwater quality abstract the basal sands and chalk aquifers in the lee valley and enfield haringey areaas of north london have considerable potential for artificial recharge having been dewatered by groundwater abstraction since the late 1800s trials have been undertaken periodically since the mid 1950s however one of the drawbacks is the potential for developing poor quality groundwater as a result of pyrite oxidation in the basal sands analysis of pumped groundwaters from the basal sands has confirmed the presence of relatively high concentrations of dissolved so4 along with k ca total fe and li porewater chemistry profiles have been obtained from fresh cores through the basal sands and underlying chalk at four sites the site with the highest so4 concentration up to 33 000 mg 1 1 had a porewater ph of 3 45 and has remained dewatered owing to overpumping for more than 70 a water pumped from the chalk showed little evidence of these extreme conditions there was no overall correlation between the bulk pyrite or gypsum content of the sediment and the porewater so4 concentration within the sediment the principal mechanism governing the generation of so4 is the oxidation of pyrite which is present in small amounts the extremely high concentrations of so4 in the porewaters indicate that the extent of oxidation is controlled by the entry of air rather than the input of dissolved oxygen or nitrate in the groundwater or recharge water abstraction from the chalk aquifer over many decades has resulted in the dewatering of the overlying basal sands aquifer allowing air entry and has led to the localized oxidation of pyrite and the accumulation of poor quality porewater in the basal sands the rate of oxidation is probably greatest near to wells and boreholes which allow ready access of air the solutes produced are only available for abstraction after the water table has risen dilution with native chalk groundwater will tend to minimize potential water quality problems future oxidation will be minimized by maintaining a high water table

triggering and predisposing factors for flow like landslides in pyroclastic soils the case study of the lattari mts southern italy abstract shallow flowslides debris flows and debris avalanches are rainfall induced landslides consisting in the shear failure of few metres of soils or in some cases even less than a metre which greatly increase downslope in volume and flow velocity the southern italian region of campania has been historically affected by such events involving pyroclastic soils mainly resting on steep carbonate slopes this paper deals with the analysis of factors influencing the occurrence of flow like landslides adopting the lattari mts in campania as a case study the results of two investigation campaigns carried out in the area allowed effective large scale geological and geotechnical characterization to be set up stratigraphic profiles mean physical properties and typical friction angles at the critical state for each soil layer were investigated the effect of suction on peak and critical shear strength whose drop is responsible for soil failure was analysed using detailed information on both the stratigraphic and geotechnical features of the soils involved in past flow like landslides typical triggering models were selected representing locally recurrent geomorphologic conditions at the basin scale the identified models were adopted for slope stability analyses carried out on four cross sections of flowslides occurring prior to the event to back analyse the triggering conditions from the evidence on the triggering mechanisms and the results of analyses the infinite slope approach is not always suitable to model slope stability conditions properly because the onset of landslides is also affected by local topographic and stratigraphic factors

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

an insight into the role of hydraulic history on the volume changes of anisotropic clayey soils 1 volume changes of natural and compacted soils induced by changes in their water content have many practical implications in the service life of earth dams river and canal embankments and waste disposal facilities an insight into the overall strain response of a clayey soil upon gradual wetting and drying is provided here experimental data coming from oedometer and isotropic tests under suction and net stress control are presented for a compacted clay with an initial anisotropic fabric highlighting the relevant role played by the hydraulic path on collapse swelling and shrinkage strains irreversible strains could be observed after wetting drying paths and the subsequent drying wetting cycle both stress and hydraulic histories play a role in the evolution of the directional fabric of clayey soils the experimental data could be reproduced with a rather simple elastic plastic constitutive model with a mixed isotropic rotational hardening previously conceived for saturated soils the model is extended to unsaturated conditions by substituting the saturated effective stress with a measure of the average stress acting on the soil skeleton and by introducing generalized hardening rules governed by both plastic strains and degree of saturation coupling between the mechanical and the hydraulic behavior is provided by the water retention curve in which degree of saturation is adopted as a useful measure of the soil water content

spatial heterogeneity of high resolution chalk groundwater geochemistry underground quarry at saint martin le noeud france chalk groundwater is an important aquifer resource in france because it accounts for a production of 12 million m3 y 1 with a large proportion reserved for drinking water processes occurring in the unsaturated zone uz and the overlying superficial formations have a high impact on chalk groundwater geochemistry and require better understanding the study site is a former underground chalk quarry located near beauvais france that extends over 1200 m in length at a depth ranging from 20 to 30 m the water table intersects the cavity creating 15 underground lake that give access to the chalk groundwater lakes geochemistry has been studied water samples were collected in july 2013 and major ion concentrations were analyzed uz and clay with flints thickness above each lake were estimated qualitatively using an electromagnetic sensor em31 and underground gps the results unexpectedly showed that groundwater quality varied widely in spatial terms for both allochthonous and autochthonous ions e g hco3 ranged from 2 03 to 4 43 meq l 1 no3 ranged from 0 21 to 1 33 meq l 1 principal component analysis indicated the impact of agricultural land use on water quality with the intake of no3 as well as so42 cl and ca2 chalk groundwater geochemistry is compared with the nature and structure of the uz we highlight correlations 1 between thick clay with flints layers and the ions mg2 and k and 2 between uz thickness and na in conclusion this paper identifies various ion sources agriculture clay with flints and chalk and demonstrates different processes in the uz dissolution ionic exchange and solute storage

spatial resolution and the geologic interpretation of martian morphology implications for subsurface volatiles abstract viking orbiter images of mars provide global coverage of the major geologic and tectonic provinces on the planet however only a fraction of the orbiter images are useful for assessing the processes responsible for the generation or modification of surface landforms an example from acheron fossae illustrates that aeolian dunes visible at 9 m pixel resolution are indistinguishable at 57 m pixel resolution dunes in acheron fossae valleys lend support to an aeolian interpretation for lineated valley fill at this location this result provides an alternative hypothesis for the proposed ice rich interpretation of this terrain consequently it seems unlikely that images with a spatial resolution 50 m pixel can provide strong constraints on the relative importance of various geologic processes that have acted upon the surface a survey of the best viking orbiter images with

the influence of soil structure and stress history on the soil water characteristics of a compacted till the soil water characteristic defines the relationship between the soil suction and gravimetric water content w or the volumetric water content or the degree of saturation s theoretical and

the hydro mechanical behaviour of unsaturated pyroclastic soils an experimental investigation abstract an experimental investigation into the hydro mechanical behaviour of a pyroclastic silty sand was carried out in the framework of a research project on flowslides in pyroclastic soils in the campania region italy undisturbed soil samples were taken from the subsoil layers of a test site on a limestone relief mantled by a pyroclastic unsaturated soil cover the lab investigation was focused on the hydro mechanical behaviour of a pyroclastic silty sand originated from the ottaviano eruption of the somma vesuvius volcano some 8000 years ago the main features of the hydraulic hysteresis domain were evaluated and the matric suction range showing the peak saturation rate with respect to suction was identified using water retention data obtained by means of evaporation and soaking tests the mechanical behaviour of ottaviano pozzolana emerged from stress path controlled triaxial tests on saturated specimens and stress path and suction controlled triaxial tests on unsaturated specimens average soil skeleton stress and matric suction were adopted as stress variables to present and interpret the experimental results the effects of the unsaturated state on isotropic compressibility and on critical state shear strength are presented and discussed

water or ice in the martian regolith clues from rampart craters seen at very high resolution abstract very high resolution viking orbiter images 8 17 m per pixel have been used to investigate the morphology of martian rampart crater ejecta blankets and the crater interiors with the objective of identifying the fluidizing medium for the ejecta and the physical properties of the target rock the occurrence of well preserved small scale pressure ridges and scour marks evidence for subsidence around isolated buried blocks in partially eroded ejecta lobes and the stability of crater walls and distal ramparts argue for ground ice being the dominant state for volatiles within the target rocks at the time of impact rare examples of channels 190 650 m wide on the surfaces of ejecta blankets and on the inner walls of the crater cerulli indicate that in some instances liquid water was incorporated into the ejecta during its emplacement no morphological evidence has been found to discount the idea that atmospheric effects were partially responsible for ejecta fluidization but it is clear that these effects were not the sole reason for the characteristic lobate deposits surrounding at least some rampart craters on mars

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

experimental behaviour and modelling of an unsaturated compacted soil this paper reports the experimental study and modelling of the mechanical response of a silty sand used in the core of the metramo dam italy specimens were prepared by compacting the soil at optimum water content conditions using the modified proctor technique tests were performed under suction controlled conditions by a stress path triaxial cell and an oedometer the experimental program consists of 23 tests carried out in the suction range of 0 400 kpa the findings indicate the strong influence of suction on compressibility stiffness and shear strength the mechanical properties of the soil improve with suction following an exponential law with decreasing gradient furthermore the soil exhibited collapsible behaviour upon wetting even at low stress levels interesting results were also achieved in elastoplastic modelling as well the results led to characterization of soil behaviour with reference to widely accepted modelling criteria for unsaturated soils providing noteworthy suggestions about

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

experimental study of a naturally weathered stiff clay studying the shear strength of a naturally weathered clay is important to understand rain induced slope failures in weathered soils however experimental studies on naturally weathered soils are limited the paper focuses on the laboratory experimental investigation carried out to analyse the shear strength of a naturally weathered stiff clay that can be found in unsaturated conditions in situ this has an important practical relevance in the evaluation of the stability conditions of natural slopes at clay outcrops different experimental techniques of suction measurement were used to obtain the soil water retention curve of the clay over a wide range of suctions scanning electronic microscope sem observations and results of mercury intrusion porosimetry mip tests are also presented to highlight the considerable fabric arrangement modifications at the microstructural level induced by wetting drying processes moreover isotropic consolidated drained triaxial compression tests on undisturbed and reco

the mechanical behaviour of an unsaturated compacted silty clay a comprehensive experimental study has been carried out to investigate the volumetric and shear strength behaviour of a compacted silty clay which exhibited collapse on wetting behaviour the experiments consisted mainly of suction monitored triaxial tests carried out in a new apparatus the test results are interpreted on the basis of an elasto plastic framework using the conventional stress variable approach net stress and suction as well as an approach that takes into account the degree of saturation within two modified stress variables the evidence for critical states was examined based on the stress dilatancy relationships it was found that a critical state was observed experimentally in cases where the samples contracted over much of their stress paths but was not truly established in other cases relationships between the shear strength and specific volume at the ultimate state were established for samples over a wide range of degrees of saturation from fully saturated to the air dried state

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

ice sculpture in the martian outflow channels many landforms in martian outflow channels have characteristics that suggest sculpture by glaciers ice streams or ice sheets viking orbiter and terrestrial satellite images were examined at similar resolution to compare features of the martian outflow channels to features produced by the movement of ice on earth many resemblances were found they include the anastomoses sinuosities and u shaped cross profiles of valleys hanging valleys and linear scour marks on valley walls grooves and ridges on valley floors and streamlining of bedrock highs the question of whether ice could have moved in the martian environment is investigated since gradients on martian channel floors are extremely low or even reversed a certain thickness of ice is required to initiate glacial motion if ice filled the martian channels to the level of interior plateaus flow could have occurred even under present climatic conditions although warmer climates in the past would have been more favorable additionally if the channel fluids were brines ice might have been wet based and would have moved readily by slipping over the ground it is envisioned that springs or small catastrophic outbursts discharged fluids from structural outlets or chaotic terrains the fluids built icings that may have grown into substantial masses and eventually flowed like glaciers down preexisting valleys alternatively the fluids may have formed rivers or floods that formed ice jams and consolidated into icy masses in places where obstacles blocked their flow these masses of ice or slush were probably episodic and temporary but where they occurred within the channels they may have produced landforms that are characteristic of glacial sculpture on earth

coupling of hydraulic and mechanical behaviour in unsaturated compacted clay an experimental study was carried out to investigate the shear strength of a compacted non active clay speswhite kaolin a total of 33 statically compacted specimens were prepared at vertical stresses of 300 600 and 1200 kpa and water contents ranging from 0 24 to 0 34 this made it possible to explore a broad range of initial compaction induced conditions and hence to examine whether differences in water retention characteristics and shear strength are due to differences in initial compaction induced state or are to be attributed to fundamentally different microfabrics a shearbox was modified to allow the direct measurement of negative pore water pressure using trento high suction tensiometers tests were carried out at constant water content by monitoring suction changes in these tests it was possible to investigate the transition from unsaturated to saturated states in the first stage of the test the specimen was compressed at constant water content the specimen was therefore wetted in the s

making unsaturated soil mechanics accessible for engineers preliminary hydraulic mechanical characterisation and stability assessment the paper presents an accessible approach for preliminary hydraulic and mechanical characterisation of unsaturated soils and stability analysis of geo structures under unsaturated conditions the approach is accessible in the sense that the laboratory investigation and geotechnical analyses can be completed in a relatively short time and at a reasonable cost the overall philosophy behind this approach is that laboratory testing should not be eliminated but kept to a minimum and that any simplification introduced should be conservative the paper illustrates that shear strength can be characterised conservatively by performing constant water content tests with no facilities to control monitor suction and that water retention behaviour can be predicted successfully by performing a single water retention measurement the paper also demonstrates that stability analyses can be carried out within the classical framework of limit analysis we show that a preliminary analysis of the influence of infiltrating rainwater on suction can be carried out using a simple and conservative method that makes use of solutions available in saturated geotechnical textbooks such an approach may be used to assess when it is worthwhile or necessary to conduct further time consuming and costly unsaturated experimental testing field monitoring and numerical analyses when considering the stability of geostructures

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

relationship between soil structure and mechanical behavior for an expansive unsaturated clay to investigate the soil structure and mechanical behavior of an unsaturated expansive clay soil triaxial and mercury intrusion tests have been performed and are presented in this paper also an optical test system was developed for studying the internal structure evolution of the unsaturated expansive soil during shear loading tests the research results show a linear relationship between the cohesion intercept and the degree of saturation of the unsaturated clay for the test data for the tested soil the pore size distribution curves were found to be bimodal the measurement results from mercury intrusion tests confirm that the micropores of guangxi expansive soils of this study remain constant and that the macropores vary with the dry density of soil samples comparing the volumetric strain curves with the soil particle area curves some correlation and dependence on the macropore variation of soil samples during shear loading tests can be shown to exist key words soil structure mechanical behavior

instability of flood embankments due to pore water pressure build up at the toe lesson learned from the adige river case study a case study is presented of the adige river embankment a segment of which experienced instability of the landside slope due to the development of uplift pressures soil profile and hydromechanica

benchmark of experimental techniques for measuring and controlling suction the paper presents a benchmarking study carried out within the mechanics of unsaturated soils for engineering muse network aimed at comparing different techniques for measurement and control of suction techniques tested by the eight mechanics of unsaturated soils for engineering research teams include axis translation pressure plate and suction controlled oedometer high capacity tensiometer and osmotic technique the soil used in the exercise was a mixture of uniform sand sodium bentonite active clay and kaolinite non active clay which were all commercially available samples were prepared by one team and distributed to all other teams they were normally consolidated from slurry under one dimensional conditions consolidometer to a given vertical stress the water retention characteristics of the initially saturated specimens were investigated along the main drying path specimens were de saturated by applying suction through the liquid phase when using an axis translation technique or o

baseline geochemical conditions in the chalk aquifer berkshire u k a basis for groundwater quality management the chalk aquifer is the most important british aquifer and is also important over much of northern europe aquifer protection requires a sound knowledge of the baseline conditions and how these might vary or have varied with time this detailed geochemical study of a representative area of chalk in berkshire u k includes a consideration of several components 1 the inputs from the atmosphere 2 the interstitial water of the soil and the unsaturated zone 3 the interstitial water in the confined and unconfined sections of the aquifer and 4 the saturated mainly fissure flow along the hydraulic gradient which forms an important water supply of the thames valley region atmospheric inputs form an important source of some elements but the dominant chemical characteristics of the chalk groundwater are acquired during percolation through the soil and the upper unsaturated zone during saturated flow downgradient the chemistry is modified mainly by incongruent reactions of the carbonate matrix and by redox reactions and only to a minor extent by exchange reactions and mixing with residual saline connate water the incongruent reaction of carbonate results in a marked increase in the mg ca ratio and the sr and 13c contents of the groundwater with increased residence time oxygen concentrations are reduced mainly by oxidation of fe2 and the onset of reducing conditions allows dissolved fe2 to increase and rapid denitrification to occur the salinity profile through the confined chalk confirms that residual connate water up to one fifth sea water concentration still remains at depth and this accounts for some salinity increase in the confined groundwater resulting from fissure water pore water diffusional exchange timescales for groundwater movement have been established using tritium radiocarbon and indirectly using inert gas ratios and stable isotope ratios on balance it is concluded that all abstracted water is of holocene age although inert gas temperatures indicate cooler climatic conditions for recharge for some of the confined groundwater the implications for development and aquifer protection are discussed especially the prospect of natural in situ denitrification problems of fe solubility and the recognition of groundwater of different maturities