profiles of steady state suction stress in unsaturated soils application of the effective stress principle in unsaturated geotechnical engineering problems often requires explicit knowledge of the stress acting on the soil skeleton due to suction pore water pressure this stress is defined herein as the suction stress a theoretical formulation of suction stress profiles based on the soil water characteristics curve the soil permeability characteristic curve and previous shear strength experimental verification is developed the theory provides a general quantitative way to calculate vertical suction stress profiles in various unsaturated soils under steady flow rate in the form of infiltration or evaporation

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

monitoring soil water and displacement conditions leading to landslide occurrence in partially saturated clays abstract shallow landslides frequently occur during transient rainfall infiltration and under partially saturated conditions however a detailed analysis of what triggers them particularly in clayey soils is often hindered by the lack of field measurements it is uncommon in fact to capture their occurrence in an instrumented natural slope this paper presents results from an integrated field experiment monitoring the soil water and displacement conditions that lead to the occurrence of a shallow landslide in partially saturated clays the integration of a variety of experimental techniques allowed for the examination of interplay between soil hydrological and mechanical properties this research also evaluates a slope stability model based on the suction stress concept since the model was applied after the occurrence of the landslide the results are interpreted as a hind casting technique for model evaluation nevertheless the detailed field measurements acquired during the monitoring activity and the occurrence of a landslide during the experiment provided significant information on model parameters and data interpretation the station provides remote satellite monitoring of data on weather variables soil water content and soil suction a time domain reflectometry cable was installed vertically to detect potential soil failure the experimental area had a high probability of landslide occurrence indeed slope failure occurred during the observation period showing the effectiveness of the station in detecting the occurrence time and depth of landslides the landslide was triggered in consequence of changes in suction stress the failure plane occurred at a depth of 1 4 m corresponding to the interface between a superficial layer of higher permeability of 1 to 1 45 m thickness slipping over a compacted substrate having lower permeability the analysis allowed for testing of the validity of the model and the description of the triggering mechanisms of the observed shallow landslide in unsaturated conditions indicating that oscillations in soil matric suction were the dominant variables determining soil failure

effective stress behavior of quasi saturated compacted cohesive soils important geotechnical structures constructed on compacted cohesive soils often involve compaction either around or on the wet side of optimum water content in general at these water content values water voids are continuous and air voids are occluded and the soil may be assumed to be in a state termed as quasi saturated this paper evaluates the effective stress behavior of such quasi saturated compacted specimens of gangetic silt and canyon dam clay in the broad framework of the conventional modified cam clay model the initial state of quasi saturated compacted specimens is shown to lie on the recompression line in w versus ln ip space the actual recompression line on which the specimen state would lie and the corresponding equivalent past maximum pressure are found to depend only on the amount of compaction energy and the soil structure and are independent of the molding water content or initial dry density it is observed that at low effective confining stresses quasi saturated compacted soils behave like overconsolidated soils and the effective stress paths during undrained shear lie on the hvorslev surface however at confining stresses greater than the past maximum pressure these soils behave like normally consolidated soils and the effective stress paths move practically along the roscoe surface toward the critical state line

experimental and analytical framework for modelling soil compaction abstract compacted materials are fundamentally unsaturated soils whose behaviour can be expansive or collapsible depending upon changes in water content or stresses their behaviour is strongly dependent upon matric suction water content and stress history this paper presents a methodology for investigating the stress strain and suction water content paths during one dimensional compaction of unsaturated soils it focuses on anisotropic behaviour the testing programme was carried out in a new automated oedometer apparatus that allows measurement of axial strain radial and axial stresses suction and water content during tests the laboratory component used in this study involves kaolin compacted with different water contents after compaction the soil was subjected to wetting while the volumetric changes and stress paths were being examined the results were interpreted within an anisotropic elasto plastic framework the proposed methodology provides new insights into the behaviour of unsaturated soils during compaction and wetting

maturation and bulk chemical properties of a suite of solid hydrocarbons abstract in this paper we present strong correlations of solid hydrocarbon reflectance shro to vitrinite reflectance vro and bulk chemical properties aromaticity tmax h c etc these correlations suggest that like kerogen in coals and sedimentary rocks solid hydrocarbons vary systematically during maturation as a consequence shro is especially useful as a maturity indicator in rocks lacking vitrinite such as pre devonian rocks and many organic rich marine rocks unlike other organic maturationv indicators the utility of solid hydrocarbons is not limited by botanical evolution but rather the generative potential of the petroleum system solid hydrocarbons also known as solid bitumen asphalt dead oil migrabitumen and pyrobitumen are genetically defined as solid phase accumulations of predominantly hydrocarbons produced by petroleum generation in source rocks they may occur over a range of concentrations in outcrop and well samples in all components of petroleum systems although accumulations of solid hydrocarbons from exhumed reservoirs are well reported the extent and utility of disseminated solid hydrocarbons in shales is less understood solid hydrocarbons are found in organic rich to very lean mature rocks as a residual product of generation disseminated solid hydrocarbons exhibit three optical forms anisotropic coked granular and relatively uniform homogenous only the homogenous solid hydrocarbons are recommended for correlation purposes with other thermal indicators

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

near surface soils self supported unconfined drained sand specimens knowledge about soil behaviour in the near surface is fundamental to a broad range of military strategic research efforts the prevailing mathematical representations of near surface shear strength

simulated effect of soil depth and bedrock topography on near surface hydrologic response and slope stability this paper explores the effect of hillslope hydrological behavior on slope stability in the context of transient subsurface saturation development and landslide triggering we perform a series of virtual experiments to address how subsurface topography affects the location and spatial pattern of slip surface development and pore pressure dynamics we use a 3d darcy richards equation solver hydrus 3 d combined with a cellular automata slope stability model to simulate the spatial propagation of the destabilized area our results showed that the soil bedrock interface and in particular bedrock depressions played a key role in pore pressure dynamics acting as an impedance for the downslope drainage of perched water filling and spilling of depressions in the bedrock surface microtopography induced localized zones of increased pressure head such that the development of pore pressure fields not predictable by surface topography lead to rapid landslide propagation our work suggests that landslide models should consider the subsurface topography in order to include a connectivity component in the mathematical description of hydrological processes operating at the hillslope scale copyright 2012 john wiley sons ltd

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

hydromechanical triggering of landslides from progressive local failures to mass release 1 water infiltrating during intense rainfall on steep slopes gradually weakens the wet soil mass inducing localized failures that may initiate a cascade of load redistributions and successive failures propagating across a hillslope the challenge of linking the progressive nature of local events culminating in an abrupt landslide is addressed by a new hydromechanical triggering model that links key hydrologic processes with threshold based mechanical interactions a hillslope is represented as assembly of soil columns interconnected by frictional and tensile mechanical bonds represented as virtual bundles of fibers increasing water load exerted on mechanical bonds causes gradual failure of fibers until restraining forces are exceeded following failure at the soil bedrock interface the load on a column is redistributed to its neighbors via intact mechanical primarily tensile bonds which in turn may also fail and transmit the load downslope as compressive stresses when soil internal compressive strength is exceeded a load bearing column may liquefy and initiate a landslide release that could propagate downslope or retrogressively upslope the model reproduces observed power law frequency magnitude relationships of landslides with exponents ranging between 1 0 and 2 2 in agreement with landslide inventory data we applied a criticality measure defined by ramos 2011 to evaluate the specific influences of slope angle soil texture and root reinforcement on attainment of hillslope criticality in which a small local failure may trigger release of a large soil mass the model provides new insights on the conditions giving rise to an abrupt transition from a seemingly stable hillslope to a catastrophic landslide

the diagenetic and economic significance of composite grains of monazite and hydrocarbon in western australian arenites composite grains consisting of detrital monazite and solid hydrocarbon ranging up to 0 5 mm in diameter have been found in phanerozoic sedimentary rocks in three western australian basins the most common form is a monazite core surrounded by a hydrocarbon envelope the envelopes which have conchoidal fracture and radial cracks apparently congealed when hydrocarbons were polymerized and crosslinked by irradiation from the monazite some composite bodies contain fractured monazite grains within solid hydrocarbon and a few consist of a microbreccia of hydrocarbon and disseminated monazite fragments the breakup of the monazite was probably a diagenetic chemical process that began when crosslinked hydrocarbons within cracks and open cleavages swelled as they were infiltrated by fluid hydrocarbons of low molecular weight five microprobe analyses of the monazite reveal the following ranges in percent composition la 2 o 3 10 88 13 66 ce 2 o 3 25 58 28 78 pr 2 o 3 3 03 5 38 nd 2 o 3 9 15 12 11 tho 2 7 0 11 49 u 3 o 8 0 1 44 2v extends from 12 5 15 5 in the northern perth basin the composite bodies which contain cores of monazite derived from local gneissic basement rocks formed after the growth of siderite cement but before extensive silicification in the central perth basin the composite bodies seem to have formed after the growth of kaolinite and before silicification textures associated with the bodies allow them to be slotted into the diagenetic sequence and they therefore show when the oil was present analysis of the bodies has indicated a contribution of oil from the lower triassic kockatea shale but some may have grown from more than one generation of petroleum given the ubiquity of detrital monazite similar bodies are likely to be useful diagenetic and economic indicators elsewhere

unified method for estimating the ultimate bearing capacity of shallow foundations in variably saturated soils under steady flow abstractthis study presents a unified method for estimating the ultimate bearing capacity of shallow foundations resting on variably saturated soils under a steady flow the effective stress approach originally employed for predicting the bearing capacity of saturated soils is extended by incorporating a suction stress based representation a closed form equation is used to define the suction stress characteristic curve capturing changes in the effective stress because of varying soil saturation and matric suction the proposed method uses the classic effective shear strength parameters and two fitting parameters to represent the soil water characteristic curve the method can be used for different soil types various degrees of saturation and different surface flux boundary conditions the results from the proposed formulation were compared and good agreement was observed against three sets of experimental results from model footing and plate load tests a parametric study was performed and the ultim

analysis of rainfall induced slope instability using a field of local factor of safety 1 slope stability analyses are mostly conducted by identifying or assuming a potential failure surface and assessing the factor of safety fs of that surface this approach of assigning a single fs to a potentially unstable slope provides little insight on where the failure initiates or the ultimate geometry and location of a landslide rupture surface we describe a method to quantify a scalar field of fs based on the concept of the coulomb stress and the shift in the state of stress toward failure that results from rainfall infiltration the fs at each point within a hillslope is called the local factor of safety lfs and is defined as the ratio of the coulomb stress at the current state of stress to the coulomb stress of the potential failure state under the mohr coulomb criterion comparative assessment with limit equilibrium and hybrid finite element limit equilibrium methods show that the proposed lfs is consistent with these approaches and yields additional insight into the geometry and location of the potential failure surface and how instability may initiate and evolve with changes in pore water conditions quantitative assessments applying the new lfs field method to slopes under infiltration conditions demonstrate that the lfs has the potential to overcome several major limitations in the classical fs methodologies such as the shape of the failure surface and the inherent underestimation of slope instability comparison with infinite slope methods including a recent extension to variably saturated conditions shows further enhancement in assessing shallow landslide occurrence using the lfs methodology although we use only a linear elastic solution for the state of stress with no post failure analysis that require more sophisticated elastoplastic or other theories the lfs provides a new means to quantify the potential instability zones in hillslopes under variably saturated conditions using stress field based methods

osl dating of brazilian fluvial carbonates tufas using detrital quartz grains abstract robust chronologies for quaternary fluvial carbonate sediments tufas from brazil are still challenging we obtain optically stimulated luminescence osl ages of brazilian tufa deposits using the single aliquot regeneration sar dose protocol applied to single grains and multigrain aliquots of quartz extracted from tufa matrix additionally radiocarbon 14 c ages were obtained for the carbonate matrix and organic matter from tufas the methodology was applied in samples from tufa deposits in southwestern and southeastern regions with quaternary carbonate deposition equivalent doses distributions have overdispersion between 19 and 81 indicating that the studied samples comprise well bleached as well as poorly bleached sediments the quartz grains extracted from the studied tufas show an osl signal dominated by the fast component and reliable dose response curves with saturation doses 2 d 0 ranging from 35 to 210 gy most of the samples has low radiation dose rates 0 40 0 02 to 0 78 0 05 gy ka with variation in the water content due to compaction and matrix recrystallization being the major factors that could induce dose rate changes through time hard tufa samples with intense carbonate cementation show quartz osl ages from 51 9 4 8 to 150 3 35 9 years these ages are much older than the radiocarbon ages of the carbonate matrix and organic matter the osl ages of soft tufa samples related with the active fluvial system ranged from 0 8 0 1 to 5 5 0 4 years and are in the same interval of radiocarbon ages presented in the previous works we interpret that carbonate recrystallization or uptake of organic matter after tufa formation are responsible for the younger radiocarbon ages compared to quartz osl ages in the older tufa samples for these samples age differences vary up to tens of thousands years between deposition of quartz grains and the last episode of carbonate recrystallization or organic matter uptake consequently we believe that the obtained osl ages are the best estimates for the starting deposition time of the studied tufa samples

palaeoenvironmental interpretations based on molluscs from mid holocene lacustrine limestones mato grosso do sul brazil in central brazil there are continental carbonate rocks in three different geological contexts the pleistocene wackestones in the corumba city xaraies formation the mid holocene limestones lenses in the pantanal plain pantanal do miranda and old and modern tufas in the serra da bodoquena serra da bodoquena formation we present here a systematic and taphonomic study of the molluscs found in the carbonate deposits in the serra da bodoquena and the limestones lenses of the pantanal do miranda which provide information concerning the carbonate palaeoenvironments of these two distinct areas seven molluscan species were found the gastropods marisa sp pomacea canaliculata an unidentified hydrobiid idiopyrgus sp biomphalaria sp and megalobulimus sp and the bivalve pisidium sp the gastropods include species still living in the area today which supports a holocene age for the limestones as indicated by published 14c dates overall the data obtained from the serra da bodoquena carbonates suggest a freshwater environment with minimal current wave action in an area probably fed by springs close to a terrestrial environment in view of the assemblage composed of pomacea canaliculata the unidentified hydrobiid idiopyrgus sp biomphalaria sp and megalobulimus sp the lacustrine palaeoenvironment in the pantanal do miranda area was different as indicated by the presence of marisa sp and absence of shallow water species such as biomphalaria sp the gastropods from serra da bodoquena and pantanal do miranda are predominantly aquatic and amphibious they are probably younger than the terrestrial gastropods reported from fine grained limestones in the corumba area

diagenesis of low mobility elements ti rees th and solid bitumen envelopes in permian kennedy group sandstone western australia the permian kennedy group carnarvon basin western australia is a shallow marine shelf deposit of sandstone and interlaminated siltstone the original sand was apparently arkosic but was altered by dissolution of feldspar and by other diagenetic processes into a kaolinitic sideritic silicified quartz arenite after lithification hydrocarbons moved through the sandstone leaving microscopic solid bitumen envelopes that had formed around radioactive detrital minerals when irradiation polymerized crosslinked and locally solidified the oil most radioactive cores are monazite a few are zircon and xenotime some monazite grains contain minute elongate randomly oriented perforations that almost certainly represent fission tracks and are filled with bitumen the diagenetic sequence can be divided into three phases phase 1 the earliest is an episode of complex diagenesis phase 2 covers the time when pores were filled with hydrocarbons and the solid bitumen envelopes formed but other diagenetic reactions were inhibited phase 3 begins with the entry of formation waters phase 1 authigenic minerals comprise anatase anhydrite brookite florencite thorite halite muscovite pyrite quartz possible rutile siderite cryptocrystalline silica sphalerite and xenotime rare thorite thsio 4 locally replaces monazite siderite crystals contain nine zones the main variations being in fe and mg and contain solution cavities that may have formed in phase 1 two minerals not commonly reported as authigenic are florencite ce la al phosphate mainly as minute pseudocubic euhedra replacing feldspar and mica and xenotime ypo 4 as outgrowths on detrital zircon grains phase 2 diagenesis includes formation of the solid bitumen envelopes and phase 3 includes authigenesis of quartz kaolinite and zoned calcite and perhaps solution of some florencite the solid bitumen envelopes surrounding the radioactive accessory minerals enclose rare minute authigenic halite and anhydrite crystals whose absence elsewhere suggests that the envelopes preserved them from solution during phase 3 titanium dioxide probably from ilmenite or titano magnetite or both partly replaces feldspar and mica some aspects of the diagenesis are particularly significant 1 solid bitumen envelopes not only indicate the former presence of hydrocarbons but also enable the complex diagenetic sequence to be divided into three well defined phases 2 the envelopes can trap and preserve minerals apparently unable to resist solution outside the envelopes i e minerals that would otherwise have disappeared 3 the zoned siderite calcite and florencite indicate changes in pore water composition in the first and third diagenetic phases 4 ti and some ree were mobile at least on the scale of a thin section during early diagenesis

transient modeling of regional rainfall triggered shallow landslides this study investigates the transient modeling of regional rainfall triggered shallow landslides in unsaturated soil using the richards equation to model shallow landslides within a distributed regional scale framework infinite slope stability analysis coupled with the hydrological model with consideration of the fluctuation of time dependent pore water pressure and the soil water characteristic curve proposed by van genuchten was developed the validity of the proposed model is established through several test problems by comparing the numerical results with the analytical solutions a new procedure to set up wide range shallow landslide analysis and to integrate regional distribution variations for input data such as geology groundwater level hydrogeological characteristics and rainfall intensity and duration was presented the results obtained demonstrate that the computed distribution of the safety factor is consistent with the distribution of actual landslides in addition the fluctuation of pore water pressure in unsaturated soil dominates the stability of landslides during typhoons accompanied by heavy rainfall the findings observed in this study are a fundamental contribution to environmental effects for landslides in areas with higher occurrence and vulnerability to extreme precipitation

hydrological responses and stability analysis of shallow slopes with cohesionless soil subjected to continuous rainfall understanding the hydrological and physical responses of shallow slopes subject to rainfall events is vital for the efficiency of a warning system setup in this research a series of experiments were undertaken to evaluate the hydrological responses of shallow slopes of varying steepness and when subjected to varying intensities periods and inter storm periods of rainfall an analysis of infinite slopes was also undertaken to develop a fundamental understanding of rainfall induced shallow slope failure characteristics the hydrological and physical responses were characterized in the infiltration and saturation phases during the infiltration phase the maximum magnitude of water content was found behind the wetting front termed as the water content behind the wetting front wb for a certain soil type the magnitude of wb was found to be dependent on the magnitude of rainfall intensity regardless of the slope gradient and initial water content based on the relative depth of the failure plane th

quaternary of the pantanal west central brazil abstract the pantanal is a tectonic depression located at the left margin of the upper paraguay river the paraguay is the trunk river of an alluvial depositional tract composed by several large marginal alluvial fans the taquari fan being the largest one the present landscape is a complex tropical wetland characterized by month long floods every year with geomorphic features derived from the present conditions and others inherited from successive pleistocene and holocene climates some areas containing ponds are landscape relicts generated by eolian deflation during the last glacial maximum many ponds closed depressions isolated from the superficial waters by vegetated crescent ridges of fine sands were interpreted as salt pans bordered by lunette sand dunes initiation of the modern wetland has occurred during the pleistocene holocene transition with the change to a more humid climate and the individualization of lacustrine systems active tectonics has been playing an important role in the development of the pantanal landscape nowadays the paraguay river meanders in a large flood plain with extensive swamp surfaces being structurally constrained by faults in the west border of the basin sedimentation within the pantanal wetland is also affected by tectonic activity especially along faults associated with the transbrasiliano lineament

laboratory experiments on local scour around cylinder for clay and clay sand mixed beds abstract new data on scouring around cylinders embedded in clay sand mixed beds are reported and the mechanism of the scouring process is described the effects of clay content water content bed shear strength and pier froude number on maximum equilibrium scour depth equilibrium scour hole geometry scouring process and time variation of scour were investigated existing literature on scouring around cylinders in cohesive sediment beds suggested that the maximum equilibrium scour depth in clay beds was similar to that of sand while increase in the clay fraction for clay sand mixed beds reduced maximum equilibrium scour depth the present study attempted to fill this gap between observations made by different investigators in cylindrical pier scour in clay sand mixed sediment beds further equations for estimation of non dimensional maximum scour depth for cylinders embedded in clay sand mixtures were proposed as functions of pier froude number clay content water content and bed shear strength while the clay sand mixtures had clay content in the range of 20 100 and water content in the range of 20 45 92

late pleistocene mollusc assemblages and inferred paleoenvironments from the andean piedmont of mendoza argentina abstract this paper is focused on the paleoecological analysis of a mollusc succession cropping out on the right margin of la estacada stream in the andean piedmont of mendoza argentina 33 28 s 69 03 w the stratigraphic section mainly composed of fine sands interbedded with levels of silty clays and organic matter records the interval between 35 2 35 5 14c ka b p and 31 5 31 6 14c ka b p the mollusc succession is represented by freshwater and land snails biomphalaria peregrina planorbidae lymnaea viator lymnaeidae succinea meridionalis succineidae rotadiscus amancaezensis charopidae and radiodiscus sp aff radiodiscus quillajicola charopidae the dominance of semi aquatic and hygrophilous land snails suggests the development of a vegetated shallow water body probably a damp habitat occasionally submerged with four main stages of evolution related to fluctuating water levels the abundance of shells together with the stable isotope composition of carbonate shells of l viator 13c and 18o and the presence of radiodiscus sp aff radiodiscus quillajicola and r amancaezensis suggest relatively warm and wet conditions based on its radiocarbon chronology and the paleoecological reconstruction the studied section is recording a mild interval corresponding to an interstadial marine isotope stage 3 of the last glacial cycle

assessing internal stress evolution in unsaturated soils 1 internal stresses in soils evolve as a result of the various interactions among soil particles and the pore fluids in response to natural or human induced activities whether attributed to suction structure or the various physicochemical forces that may develop assessing the internal stresses in soils has been an active area of research in soil science and engineering this paper presents the restrained ring method as an experimental tool for measuring the stresses that develop in a drying soil when it is restrained from shrinking freely the internal stress that develops can be related to the water content of the soil this method is validated using results for both silty clay loam and clay loam soils tensile stress at failure estimated from the restrained ring method was compared to tensile strength ranges of similar soils and a good correlation was observed moreover internal stresses measured by the restrained ring method were compared with existing empirical relationships using suction and degree of saturation this comparison concluded that suction is not the sole contributor to the soil s internal stress

axial force displacement behaviour of a buried pipeline in saturated and unsaturated sand several pipeline projects have been proposed in the world in recent years owing to the rapid growth of the petroleum industry onshore pipeline systems are usually buried above the natural groundwa

fluorescent growth bands in irradiated bitumen nodules evidence of episodic hydrocarbon migration minute rims of solid bitumen 40 50 m thick surround detrital radioactive grains in the permian triassic sandstones and arranoo member of the kockatea shale from the northern perth basin australia the bitumen formed as th and u bearing minerals monazite xenotime zircon thorite irradiated and immobilized fluid hydrocarbons coming within range of alpha particle emissions using transmitted light and scanning electron microscopy the rims appear compositionally homogeneous but under blue violet epifluorescent illumination the bitumen displays complex concentric and contorted banding these fluorescent textures indicate that multiple influxes of hydrocarbons passed through the reservoir sandstones following radiation induced immobilization of hydrocarbons from the first oil influx the bitumen nodules grew through a process of swelling and expansion outward from the mineral core during subsequent oil

intra event scale bar bank interactions and their role in channel widening channel bars and banks strongly affect the morphology of both braided and meandering rivers accordingly bar formation and bank erosion processes have been greatly explored there is however a lack of investigations addressing the interactions between bed and bank morphodynamics especially over short timescales one major implication of this gap is that the processes leading to the repeated accretion of mid channel bars and associated widenings remain unsolved in a restored section of the drau river a gravel bed river in austria mid channel bars have developed in a widening channel during mean flow conditions the bars divert the flow towards the banks one channel section exhibited both an actively retreating bank and an expanding mid channel bar and was selected to investigate the morphodynamic processes involved in bar accretion and channel widening at the intra event timescale we repeatedly surveyed riverbed and riverbank topography monitored riverbank hydrology and mounted a time lapse camera for continuous observation of riverbank erosion processes during four flow events the mid channel bar was shown to accrete when it was submerged during flood events which at the subsequent flow diversion during lower discharges narrowed the branch along the bank and increased the water surface elevation upstream from the riffle which constituted the inlet into the branch these changes of bed topography accelerated the flow along the bank and triggered bank failures up to 20 days after the flood events four analysed flow events exhibited a total bar expansion from initially 126 m2 to 295 m2 while bank retreat was 6 m at the apex of the branch the results revealed the forcing role of bar accretion in channel widening and highlighted the importance of intra event scale bed morphodynamics for bank erosion which were summarized in a conceptual model of the observed bar bank interactions copyright 2015 john wiley sons ltd

laboratory properties of mine tailings a vast amount and variety of mine tailings are produced around the world each day these mining wastes must be properly managed to evaluate mine tailings disposal technology the appropriate engin

nature and origin of carbon in the archaean witwatersrand basin south africa the nature and origin of the carbonaceous matter carbon in the gold bearing reefs of the archaean witwatersrand basin of south africa has long been a subject of controversy and debate the importance of the carbon results from its direct association with the gold grade the studies reported here were directed at resolving the nature and origin of carbon techniques used include stope scale macroscopic mapping mesoscopic hand specimen examination and microscopic studies incorporating the use of optical reflectance measurement macroscopic mapping has demonstrated the braided habit of carbon bodies over tens of square metres with a close parallel to sedimentology mesoscopic observations however show the vein like carbon seams are often cross cutting sedimentary features with the carbon occupying an anastomosing set of bed parallel fractures microscopic observations show a globular form for the carbon and inclusions of uraninite particles in seam carbon the globules are generally modified into elongated spindles oriented perpendicular to bedding optical properties are dominated by generally high reflectance and anisotropy with a swirling liquid crystal structure classifying seam carbon as carbonaceous mesophase it is this fine mesophase texture that has previously been wrongly attributed to plant algal morphology highly significantly the optical anisotropy is bed perpendicular rather than bed parallel as in normal sedimentary burial indicating mesophase formation during fracture opening both reflectance and bireflectance of the seam mesophase show a range of values at all scales no stratigraphic or depth trends were apparent though geographic variation points to localization of the maximum temperature event s given high anisotropies maximum reflectance values in the 4 8 r o range and minima in the 1 2 r o range give arithmetic mean reflectance values of about 4 0 r o kinetic modelling equates these values with short term 50 000 years temperature events of c 400 c or burial temperatures of c 280 c lower reflectance values of c 2 0 r o obtained from the shales suggests thermal detachment of permeable and impermeable beds a characteristic of pulsed hydrothermal flux the included uraninite grains influence the orientation of the surrounding anisotropic mesophase demonstrating that uraninite predated the mesophase formation event regional palaeo stress frozen into the mesophase anisotropy indicates a nw se deviatoric stress the combination of hydrocarbon radiation and hydrothermal fluid flow marks witwatersrand basin pyrobitumens out as being different from conventional oil putative source rocks for the oil are identified in the intra basinal witwatersrand shale units lithological control in carbon seams is explained by the poro perm and mechanical properties of the unconformity sequence of footwall reef conglomerates and hanging wall quartzites favouring fracture along the unconformity surfaces an overpressured oxidizing fluid created the fracture network that hosted the oil and also introduced uranium as uranyl ion on meeting a reducing agent oil uraninite precipitated stabilizing the oil by polymerization further hotter hydrothermal flux then coked the bitumen to often fibrous spindle shaped mesophase continued flow deposited gold in the available pore spaces most notably those formed by lateral contraction between mesophase spindles the speculative role of methane in the reductive precipitation of gold is indicated by the presence of gold in any co eval porosity largely independent of the mineral matrix

influence of lateral swelling pressure on the geotechnical infrastructure in expansive soils abstractlateral swelling pressure lsp can pose significant threats to the safety and stability of the geo infrastructure for this reason it is necessary to take into account the influence of ls

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

experimental study of hydromechanical behaviour of a compacted lateritic sandy lean clay lateritic clay is widely distributed in tropical areas and used extensively for foundation materials compared to other soils it is rich in iron and aluminum oxides sesquioxides which enhance t

physical modeling investigation of rainfall infiltration in steep layered volcanoclastic slopes abstract infiltration processes in layered slopes can be strongly affected by the different hydraulic properties of the soils constituting the layers with potential downslope flow diversion that can have effects on slope stability as well as on runoff generation and groundwater recharge in this respect volcanoclastic soil covers represent a typical example as layers with strongly contrasting textures are deposited during the various eruptive phases in this paper the results of a transient infiltration test carried out in a densely instrumented physical model of a layered volcanoclastic sloping cover are presented the soil cover was constituted by a layer of gravelly pumices interbedded between two layers of finer ashes sandy loams even with such an extreme contrast in texture capable of significantly delaying the advancement of infiltration through the layer of pumices flow diversion occurred only temporarily at the interface between the upper layer of ashes and the pumices in fact although a long lasting intense rainfall was applied into an initially dry soil profile the downslope diverted water volume in form of a subsurface runoff was just a small fraction of the total applied rainfall in fact the accumulation of water above the upper edge of the pumices responsible of the subsurface runoff soon led to the establishment of a large water potential gradient which redirected the infiltrating flow through the pumices and stopped the downslope flow diversion

microstructure and soil water retention behavior of compacted and intact silt loess abstract there are an increasing number of mega engineering projects of removing the top of hills to fill in the valley for new land creation in the loess plateau of china which significantly changes the hydrological and geological equilibrium state of the site the formation of a new hydrological equilibrium state is associated with the water movement in the compacted and intact loess layers most disasters occurring in the loess area are related to water the soil water retention curve swrc is the key to the implementation of unsaturated soil mechanics in engineering practice and is required to numerically model the movement of water in the soil in this study the swrcs and microstructure of intact and compacted specimens from lanzhou and yan an two typical cities that have new land creation projects are investigated the swrc is obtained using the filter paper method the mercury intrusion porosimetry mip and scanning electron microscope sem techniques are used to explore the microstructure the results highlight that the intact loess has a higher air occlusion value aov and a similar slope of swrc in the transition zone compared with the remolded specimens that compacted at the natural water content the normalized swrc i e degree of saturation versus suction avo of the intact specimen is approximately the same as the remolded specimens compacted as the natural water content the difference in the microstructure between intact and compacted specimens originates from different existing states of the clay particles and further contributes to the variation of the swrc

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

a numerical framework for infinite slope stability analysis under transient unsaturated seepage conditions abstract this paper presents a simple numerical framework for infinite slope stability analysis under transient unsaturated seepage conditions the advantage of the proposed framework from the practical point of view is to predict the variability in stability of partially saturated slope along with rainfall data moreover the presented framework is adaptable to different types of soil water characteristic curve swcc models hydraulic boundary conditions and heterogeneity in soil properties a series of stability analyses for hypothetical hillslopes under various conditions was performed to scrutinize the potential failure mechanisms induced by rainfall the examined factors include the soil texture rainfall intensity heterogeneity in soil properties and hydraulic boundary conditions also four widely used swcc models were applied to assess the influence of this component the swcc model was demonstrated to strongly dominate the results of the infinite slope stability analysis under transient unsaturated seepage conditions for homogeneous hillslopes with a fixed water table when the rainfall intensity q equals the saturated hydraulic conductivity ks slope failure was expected to occur after a short time of rainfall with a relatively shallow slip depth in contrast for heterogeneous hillslopes or hillslopes with impermeable bedrock the failure could take place when q is less than ks and the potential failure surface was close to the discontinuity interface or at the bottom of the hillslope finally three case studies of landslides documented in literature were utilized to demonstrate the predictability of the proposed framework in practical applications

lacustrine records of holocene flood pulse dynamics in the upper paraguay river watershed pantanal wetlands brazil abstract the pantanal is the world s largest tropical wetland and a biodiversity hotspot yet its response to quaternary environmental change is unclear to address this problem sediment cores from shallow lakes connected to the upper paraguay river pr were analyzed and radiocarbon dated to track changes in sedimentary environments stratal relations detrital particle size multiple biogeochemical indicators and sponge spicules suggest fluctuating lake level lowstand conditions between 11 000 and 5300 cal yr bp punctuated by sporadic and in some cases erosive flood flows a hiatus has been recorded from 5300 to 2600 cal yr bp spurred by confinement of the pr within its channel during an episode of profound regional drought sustained pr flooding caused a transgression after 2600 cal yr bp with lake level highstand conditions appearing during the little ice age holocene pr flood pulse dynamics are best explained by variability in effective precipitation likely driven by insolation and tropical sea surface temperature gradients our results provide novel support for hypotheses on 1 stratigraphic discontinuity of floodplain sedimentary archives 2 late holocene methane flux from southern hemisphere wetlands and 3 pre colonial indigenous ceramics traditions in western brazil

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

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

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

use of vacuum for the stabilization of dry sand slopes abstractvacuum is proposed as a means for rescuing soil slopes showing signs of impending failure two aspects associated with the proposed method were studied namely the theory of airflow through dry soils and the effectiveness of vacuum for enhancing the stability of soil slopes a model test device was developed and two series of tests were carried out using this device one was a series of tests on pore air pressure distributions in dry sand slopes and the second series involved dry sand slope stability tests the results revealed that a vacuum negative pore air pressure even as small as 0 4 kpa significantly increased the stability of the model slopes with dimensions of 0 9 0 5 0 28 m length width height the pore air pressure distributions in the model slopes were simulated using a finite element partial differential equation solver flexpde fick s law and mass conservation were used to formulate the airflow through dry soils good agreement was achieved between the experiment results and

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

petrography of thoriferous hydrocarbon nodules in sandstones and their significance for petroleum exploration nodules of thorium rich hydrocarbon are recorded in sandstone sequences from several basins the hydrocarbon nodules contain mineral inclusions particularly of thorite or monazite there is evidence both for accretion of hydrocarbons around detrital heavy mineral grains and for epigenetic growth by interaction of hydrocarbons with thorium bearing fluids both mechanisms depend upon the precipitation of solid hydrocarbons induced by irradiation from thorium the nodules exhibit aggressive replacement of other grains a characteristic of radioanomalous hydrocarbons the occurrence of the nodules is dependent upon an appropriate plutonic source for the thorium but given this constraint they are important evidence for hydrocarbon migration pathways

hydro mechanical properties of unsaturated residual soil from a flysch rock mass abstract rainfall is a major triggering factor of landslides in flysch deposits along europe physical and mechanical changes of flysch rock masses caused by the weathering process result in a complex soil profile with residual soil typically present at the slope surface the research encompasses residual soils from the rjecina river valley in croatia built in flysch deposits the valley is known for several deep seated and shallow historical landslides this manuscript presents the hydro mechanical properties of the soil existing in unsaturated zone of the slope that could play an important role in landslide activation on flysch slopes presented unsaturated soil property functions are essential for modelling of the transient rainfall infiltration process and how it affects the stability of flysch slopes in time for the first time shear strength and hydraulic conductivity determination were performed in saturated and unsaturated soil conditions using both the intact as well as remolded samples of the residual soil form flysch rock mass the results indicate that in order to correctly define hydraulic and mechanical properties of the in situ soil measurements have to be performed on intact samples also the presented results highlight the importance of hysteresis effects and hydraulic paths that fine grained residual soil has been subjected to in the past

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

infinite slope stability under steady unsaturated seepage conditions 1 we present a generalized framework for the stability of infinite slopes under steady unsaturated seepage conditions the analytical framework allows the water table to be located at any depth below the ground surface and variation of soil suction and moisture content above the water table under steady infiltration conditions the framework also explicitly considers the effect of weathering and porosity increase near the ground surface on changes in the friction angle of the soil the factor of safety is conceptualized as a function of the depth within the vadose zone and can be reduced to the classical analytical solution for subaerial infinite slopes in the saturated zone slope stability analyses with hypothetical sandy and silty soils are conducted to illustrate the effectiveness of the framework these analyses indicate that for hillslopes of both sandy and silty soils failure can occur above the water table under steady infiltration conditions which is consistent with some field observations that cannot be predicted by the classical infinite slope theory a case study of shallow slope failures of sandy colluvium on steep coastal hillslopes near seattle washington is presented to examine the predictive utility of the proposed framework

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

modelling the applied vertical stress and settlement relationship of shallow foundations in saturated and unsaturated sands the bearing capacity and settlement of foundations are determined experimentally or modelled numerically based on conventional soil mechanics for saturated soils in both methods bearing capacity

effect of soil suction on slope stability at notch hill the side slopes of a railway embankment in central british columbia constructed with local lacustrine silt on relatively flat ground began to fail several years after construction shallow instability ultimately developed on both sides of the embankment over a distance of several kilometres initially the soil had a significant apparent cohesive strength with time the strength appeared to diminish owing to the dissipation of negative pore water pressures the remaining frictional strength was not sufficient to maintain stability since the slopes were constructed at angles close to the peak effective friction angle of the soil this case history together with the laboratory saturated and unsaturated strength test results and field suction measurements demonstrates the dramatic effect of negative pore water pressures on near surface slope stability key words soil suction slope stability nonsaturated soils shear resistance tensiometers

rainfall induced landslides by deficit field matric suction in unsaturated soil slopes landslides are mainly triggered by decrease in the matric suction with deepening the wetting band by rainfall infiltrations this paper reports rainfall induced landslides in partially saturated soil slopes through a field study a comprehensive analysis on umyeonsan mt landslides in 2011 was highlighted the incident involves the collapse of unsaturated soil slopes under extreme rainfall event fundamental studies on the mechanism and the cause of landslides were carried out a number of technical findings are of interest including the failure mechanism of a depth of soil and effect of groundwater flow the downward movement of wetting band and the increase of groundwater level based on this an integrated analysis methodology for a rainfall induced landslide is proposed in this paper that incorporates the field matric suction for obtaining hydraulic parameters of unsaturated soil the field matric suction is shown to govern the rate of change in the water infiltration for the landslide analysis with respect to an antecedent rainfall special attention was given to a one dimensional infiltration model to determine the wetting band depth in the absence of the field matric suction the results indicate that landslide activities were primarily dependent on rainfall infiltration soil properties slope geometries vegetation and groundwater table positions the proposed methodology has clearly demonstrated both shallow and deep seated landslides and shows good agreement with the results of landslide investigations

oil bearing co2 ch4 h2o fluid inclusions oil survival since the palaeoproterozoic after high temperature entrapment the 2 45 ga fluvial quartz arenites and conglomerates of the matinenda formation at elliot lake canada contain evidence for two episodes of oil migration with entrapment of oil bearing fluid inclusions the first episode was during diagenesis the second during a subsequent sub greenschist facies metamorphic event at ca 2 2 ga at temperatures exceeding 250 c remnants of the migrating hydrocarbon fluids are preserved as radiogenic pyrobitumen nodules occupying former inter granular pore spaces and as complex fluorescing oil bearing fluid inclusions the latter include two dominant types 1 aqueous oil inclusions with a minor oil phase located within original detrital grains and clasts and within rare quartz overgrowths and 2 aqueous carbonic inclusions with a minor oil phase light hydrocarbons and solids located within microfractures in detrital quartz grains and clasts the majority of type 1 inclusions were trapped with a high salinity fluid up to 25 wt nacl equivalent at relatively low temperatures between 80 and 200 c and pressures of less than 2 kbar early in the burial history of the matinenda formation type 2 inclusions were trapped during metamorphism with a much lower salinity aqueous carbonic fluid 1 2 to 17 wt nacl equivalent at temperatures between 280 and 350 c and pressures between 1 and 1 5 kbar under these conditions oil may have been miscible in the mixed fluid 13c of 25 5 and 24 9 for the pyrobitumen nodules and fluid inclusion hydrocarbon gas indicate a biogenic origin for the petroleum 13c of 16 2 for the bulk inclusion gas suggests a value of 12 for the carbonic phase hence a mix of inorganic co2 and organic co2 from either thermal alteration of organic matter or in situ chemical oxidation of hydrocarbons this study has implications for the depth and temperature at which oil may be present suggesting that deep old reservoirs may not be completely barren of petroleum the fact that hydrocarbons in the matinenda formation fluoresce indicates that aromatic compounds are able to survive temperatures of up to 350 c in a suitable geological environment

prediction of the wetting induced collapse behaviour using the soil water characteristic curve abstract collapsible soils go through three distinct phases in response to matric suction decrease during wetting pre collapse phase collapse phase and post collapse phase it is reasonable and conservative to consider a strain path that includes a pre collapse phase in which constant volume is maintained and a collapse phase that extends to the final matric suction to be experienced by collapsible soils during wetting upon this assumption a method is proposed for predicting the collapse behaviour due to wetting to use the proposed method two parameters critical suction and collapse rate are required the former is the suction value below which significant collapse deformations take place in response to matric suction decease and the later is the rate at which void ratio reduces with matric suction in the collapse phase the value of critical suction can be estimated from the water entry value taking account of both the microstructure characteristics and collapse mechanism of fine grained collapsible soils the wetting soil water characteristic curve thus can be used as a tool five sets of data of wetting tests on both compacted and natural collapsible soils reported in the literature were used to validate the proposed method the critical suction values were estimated from the water entry value with parameter a that is suggested to vary between 0 10 and 0 25 for compacted soils and to be lower for natural collapsible soils the results of a field permeation test in collapsible loess soils were also used to validate the proposed method the relatively good agreement between the measured and estimated collapse deformations suggests that the proposed method can provide reasonable prediction of the collapse behaviour due to wetting

geomorphological control on variably saturated hillslope hydrology and slope instability in steep topography the processes governing variably saturated subsurface hydrologic response and the interparticle stresses leading to shallow landslide initiation are physically linked however these processes are usually analyzed separately here we take a combined approach simultaneously analyzing the influence of topography on both hillslope hydrology and the effective stress fields within the hillslope itself clearly runoff and saturated groundwater flow are dominated by gravity and ultimately by topography less clear is how landscape morphology influences flows in the vadose zone where transient fluxes are usually taken to be vertical we aim to assess and quantify the impact of topography on both saturated and unsaturated hillslope hydrology and its effects on shallow slope stability three real hillslope morphologies concave convex and planar are analyzed using a 3 d physically based distributed model coupled with a module for computation of the probability of failure based on the infinite slope assumption the results of the analyses which included parameter uncertainty analysis of the results themselves show that convex and planar slopes are more stable than concave slopes specifically under the same initial boundary and infiltration conditions the percentage of unstable areas ranges from 1 3 for the planar hillslope 21 for convex to a maximum value of 33 for the concave morphology the results are supported by a sensitivity analysis carried out to examine the effect of initial conditions and rainfall intensity

slope stability analysis under unsaturated conditions case studies of rainfall induced failure of cut slopes abstract we present two case studies of rainfall induced failure of engineered slopes the traditional limit equilibrium and finite element methods are expanded to unsaturated conditions using a generalized effective stress framework because effective stress is represented by the suction stress characteristic curve sscc and the sscc and the soil water retention curve swrc have been unified with the same set of hydromechanical parameters the expanded framework requires only three hydromechanical parameters in addition to those used for saturated slope stability analysis using recorded rainfall measured shear strength parameters and the swrc and site geology transient slope stability analyses are conducted to reconstruct the failure events we find that despite differences in slope geometry hydromechanical properties shear strength and rainfall history the actual failure occurred when the simulated factor of safety approaches its minimum below 1 0 it is shown that the hydromechanical framework under the suction stress based effective stress can reconcile the observed timing of failure

infiltration and instability in dune erosion 1 forecasting dune erosion prior to a storm or over longer periods requires knowledge of the fluid forces on the dune sediments to improve our predictive capability for this process we propose a new model in which dune slumping occurs when water which infiltrates horizontally into the dune increases the overburden sufficiently to destabilize the dune horizontal infiltration is driven by suction of water from swash into the dune via capillary action and is a surprisingly strong process with rapid time scales because the elevated pore water concentrations increase the apparent cohesion of the wetted sediments we also propose that the entire volume of wetted sand slumps as a unit when the dune becomes unstable and erosion can be modeled based on the force balance on a sliding block several versions of this model were tested including a numerical infiltration model a simplified infiltration equation and an equation based on offshore wave forcing rather than known forcing at the dune the model was tested using data from a large scale laboratory experiment with a storm hydrograph to investigate the time dependence of dune erosion predicting slope stability using a numerical infiltration model with known forcing explained 72 of the observed variance in erosion rate while a simplified stability and infiltration model explained 58 error statistics suggest that we captured the majority of the physics controlling dune erosion in this laboratory experiment and that the simplified model will be useful as a forecasting tool

the origin of uraninite bitumen nodules and carbon seams in witwatersrand gold uranium pyrite ore deposits based on a permo triassic analogue permo triassic dongara sandstones from the perth basin of western australia contain solitary bitumen nodules that are analogous to uraniferous bitumen nodules or fly speck carbon in late archean witwatersrand gold uranium pyrite ore deposits nodules in both contain cores of radioactive minerals and occupy depositional sites where heavy minerals were concentrated solitary bitumen nodules in the dongara sandstone formed during burial by radiation induced polymerization of liquid hydrocarbons migrating through primary porosity around detrital monazite grains similar bitumen nodules in witwatersrand ore deposits are likewise interpreted to have formed during burial although the radiation emitting detrital grains were uraninite carbon seams in witwatersrand ore deposits are stratiform bodies of coalesced bitumen nodules by analogy with solitary nodules individual nodules in carbon seams formed during burial as liquid hydrocarbons migrated through primary porosity past detrital uraninite grains but they differ from solitary nodules in that many have been stretched perpendicular to bedding to form an ellipsoidal or columnar structure although a columnar structure is consistent with deformation by vertical extension that deformation clearly postdated nodule formation in some seams elongated nodules are associated spatially with framework hosted bedding parallel microfractures which are commonly filled with fibrous secondary minerals again bedding parallel microfracturing clearly postdated nodule formation columnar textured bitumen and bedding parallel fractures are interpreted to be postdiagenetic structural fabrics whereas carbon seams appear to have been a microfocus of a compressive deformation neither columnar textured bitumen nor bedding parallel fractures are present in the dongara sandstone and they are not present in every witwatersrand carbon seam either supporting the contention that columnar textured bitumen and bedding parallel fractures are focused structural fabrics that postdate nodule formation recognition that solitary bitumen nodules and carbon seam hosted bitumen nodules of witwatersrand ore deposits are analogous in origin to bitumen nodules in the dongara sandstone supports historical mineralogical observations that the witwatersrand basin contained uraninite placers indeed carbon seams are most likely the former sites of heavy mineral uraninite strands given the chemical instability of uraninite under oxidizing conditions detrital uraninite in witwatersrand strata supports the long held contention that the archean atmosphere contained significantly less oxygen than the modern atmosphere

accumulation and mixing of hydrocarbons in oil fields along the murteree ridge eromanga basin south australia abstract the murteree ridge is a focus for up dip migration from two major hydrocarbon kitchens within the intracratonic cooper carboniferous triassic and eromanga jurassic cretaceous basins of south australia the accumulation histories of nine oil fields along and adjacent to the ridge have been reconstructed by sequential solvent extraction and analysis of residual oils in sandstone core plugs from their stacked reservoirs four cretaceous reservoir units received multiple oil charges that varied widely in source affinity from mostly jurassic and or cretaceous to overwhelmingly permian in origin the distributions of residual oil saturations in live and palaeo columns are consistent with the existence of two compartments with the uppermost pools cadna owie murta showing the highest permian inputs these accumulations represent the earliest escape of low maturity cooper sourced oil into overlying eromanga strata this initial charge was displaced upwards into the shallower traps by subsequent hydrocarbon pulses three separate permian charge episodes can be recognised the corresponding dst oils 0 6 0 7 rc represent either the compositional average of all charges to their respective reservoirs or a continuation of the alternating filling pattern observed for successive charges oils in the hutton jurassic reservoir of the outlying kerrina and mudlalee fields to the northeast appear to be mixtures of two distinct early permian oil families variably co mingled with locally derived jurassic and possibly cambrian hydrocarbons

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

hydrological factors affecting rainfall induced shallow landslides from the field monitoring to a simplified slope stability analysis abstract rainfall induced shallow landslides can seriously affect cultivations and infrastructures and cause human losses a continuous monitoring of unsaturated soil hydrological properties is needed to understand the effects of pore water pressure and water content on shallow landslides triggering and slope safety factor in this work the impact of water content pore water pressure and hydrological hysteresis on safety factor reconstruction is analyzed by applying two different models lu and godt s and slip models to a monitored slope located in oltrepo pavese northern italy a shallow landslide event in the studied slope during the monitoring allowed for identifying the triggering mechanism and modeling the safety factor changes the conditions of instability mechanism develop in periods with frequent rainfalls the uprising of a perched water table in the soil profile gets nil or positive pore water pressure which linked with the nil effective soil cohesion of some soil horizons allows for the shallow landslide triggering the safety factor trends correctly predicted unstable conditions safety factor 1 0 in correspondence of the shallow landslide triggering time on the basis of both water content and pore water pressure a better prediction gets when the safety factor is modeled considering the hysteresis effects modeling the safety factor on the basis of water content can make a good assessment of shallow failures triggering conditions only for failures in unsaturated soils and for completely saturated soils instead considering pore water pressure it is possible estimating safety factor changes linked with the development of positive pore water pressures which can be linked in some cases to shallow landslide development

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

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

shear behaviour of rock joints with unsaturated infill behaviour of soil infilled rock joints has significant importance with respect to the strength of fractured rock mass the presence of even a small amount of fine grained infill material within a joint can reduce its shear strength considerably depending on the degree of saturation of infill therefore it is crucial to examine how the infill material can adversely affect the joint shear strength previous studies of infilled joints have mainly been focused on idealised regular joint patterns owing to the simplicity and reproducibility in laboratory testing current literature on infilled rock joints has also neglected the effect of the degree of saturation of infill on the shear behaviour in most instances fully saturated infill has been used or assumed and the contribution of matric suction on the shear strength of joints having unsaturated infill has not been studied in this study a series of triaxial tests on natural joint profiles having joint roughness coefficient jrc of 10 12 is carried out

oil preserved in fluid inclusions in archaean sandstones oil is generally thought to be geologically young as it is thermodynamically unstable when subjected to elevated temperatures over long periods in open systems1 2 indeed almost all petroleum production comes from rocks younger than 400 million years ref 3 although the oldest known oil occurs in rocks 1 650 myr old4 suitable source rocks were abundant in older geological successions5 and circumstantial evidence suggests that some of these generated hydrocarbons early in their history6 here we report the discovery of oil preserved in fluid inclusions in sandstones dating back 3 000 myr most inclusions lie within healed microfractures confined to individual detrital quartz grains indicating that their oil was emplaced before archaean or palaeoproterozoic metamorphism sealed all voids and thus came from older in some cases archaean sources the fluid inclusions apparently acted as inert pressure vessels that protected the oil from subsequent degradation by circulating fluids and mineral catalysts because of its great age this oil can potentially yield valuable information about the size and diversity of the early biosphere particularly if it contains molecular fossils biomarkers of the primordial organisms from which it was derived

gis based prediction method of landslide susceptibility using a rainfall infiltration groundwater flow model this paper describes a physical based model to predict rainfall induced landsides special attention was given to the introduction of a gis based model ys slope model yonsei slope model which can evaluate the susceptibility of landslides the model has been improved by incorporating the combined effects of groundwater flow and rainfall infiltration into the raster model the two dimensional darcy s law was used to reflect the effect of groundwater flow in the soil slope and the modified green ampt model which is a one dimensional infiltration model was selected to capture the effect of rainfall infiltration into the soil mass these elements were integrated into the infinite slope stability model for a rainfall induced landslide the proposed model was verified by comparing the results from existing models as well as an actual slope failure case that occurred in korea with further study the ys model could be adopted as a prediction method for rainfall induced landslides

three detailed radiocarbon dated holocene tufa and alluvial fan mollusc successions from southern ontario the first in northeastern north america abstract fossil mollusc remains particularly those of land snails provide a wealth of detailed information concerning local quaternary paleoenvironments and regional paleoclimatic conditions however this important resource is generally overlooked in north america and consequently quantitative well dated terrestrial mollusc successions are extremely rare here in an attempt to redress this imbalance a project examining the holocene molluscan faunal history of northeastern north america has been initiated thus far detailed mollusc successions and associated radiocarbon age determinations have been obtained from three sites in southern ontario two alluvial fans chine drive fan and cudia park fan both from the scarborough bluffs east of toronto and a tufa west river road near cambridge the observed land snail successions to provide an initial view of the molluscan faunal history of this region during the period from the late glacial to the mid holocene between approximately 10 500 and 5000 radiocarbon years bp yr bp the molluscan data have also been used to reconstruct the paleoenvironmental history of southern ontario during this time documenting the progression from exposed open habitats characterised by species such as vertigo modesta vallonia albula columella columella and vitrina angelicae limpida to closed woodland biotopes indicated by the presence of taxa including carychium nannodes nesovitrea binneyana paravitrea multidenta and helicodiscus parallelus this study has already demonstrated the potential of this technique in the study of quaternary climatic and environmental change in eastern north america and represents a strong foundation for extending the analysis of fossil land snail successions to other sites throughout this region it has also provided new and important insights into the establishment of the modern molluscan fauna which are essential to the understanding of present day distributional patterns and environmental associations

estimation of soil water characteristics using liquid limit state in unsaturated soils the matrix suction creates an additional interparticle force in the soil increasing soil strength the variation in matric suction in a soil is expressed in terms of water content the relationship is known as the soil water characteristic empirical equations for soil water characteristic curves are presented experiments were conducted in granite weathered residual soils from korea to determine the grain size distribution and soil properties and to examine the effect of volume change on the soil water characteristic curve modified pressure cell extractor tests were conducted on the soil at various void ratios which were compressed from the liquid limit state the volume change of the deformable soils could be measured directly the soils showed significant volume change due to matric suction the curves corrected for volume change had higher air entry values flatter slopes and better correlation compared with uncorrected curves the normalised curves had a linear relationship with the normalised void ratio

influence of environmental factors on the wetting front depth a case study in the loess plateau abstract reliable information on the wetting front depth and variation of water contents within the zone of wetting is required for addressing geotechnical problems in loess deposits such as estimation of the collapse deformation and assessment of the slope stability for this reason a field test was conducted at a site in the loess plateau of china to obtain data on soil water contents and temperatures at different depths for a period of one year the variation of water contents was interpreted from the influence of environmental factors and soil temperature and used to determine the maximum wetting front depth in the loess soils in the study region in addition a commercial software vadose w was used to simulate the flow behaviour in unsaturated loess taking account of the influence of environmental factors a reasonable agreement was found between the results of field investigations and numerical simulations the study results are useful as they provide valuable information about the wetting front depth and water content variation in unsaturated loess in response to environmental factors the field investigations and numerical simulations summarized in this paper can serve as a reference for future studies on other soils

effects of radiation exposure on indicators of thermal maturity abstract study of fossil wood samples with varying contents of uranium suggests that radiation exposure over geologic time results in alteration of vitrinite the alteration is shown by increased reflectance of vitrinite increased values of thermal alteration index decreased atomic h c ratios and by loss of fluorescence each of these parameters is used to estimate the thermal maturity of kerogen unless recognized during interpretation of analytical results radiation damage of vitrinite results in over estimation of thermal maturity

stability analysis of unsaturated soil slopes considering water air flow caused by rainfall infiltration abstract even though soil is a mixture of solids with voids that are filled by air and water most previous studies on rainfall infiltration and its influence on slope stability were based on a single phase water flow model by assuming that the pore air pressure was atmospheric the purpose of this study is to examine the effect of interactions between air and water flow due to heavy rainfall on the mechanical stability of an unsaturated soil slope water air two phase flow analyses were conducted to investigate the contribution of pore air pressure on infiltration by rainfall in order to study the infiltration behavior with respect to soil type flow analyses were performed with two types of soil under similar settings results obtained from the two phase infiltration analysis were then used as input to the stability analysis by the strength reduction method infiltration and stability analyses based on a single phase water flow model were also carried out which helped clarify the effects of air flow induced by rainfall infiltration on an unsaturated soil slope the results showed an increase in pore air pressure during infiltration because rainwater displaced the air in the unsaturated zone hence remarkable delaying effects on water flow were induced such water air interactions in the pore space of soil significantly affected the stability and behavior of the soil slope