bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental study of iron and silica immobilization by bacteria in mixed Fe-Si systems: implications for microbial silicification in hot springs
Authors: Phoenix Vernon R , Konhauser Kurt O , Ferris F Grant
Published: December 2003

The immobilization of silica and iron by the bacteria Bacillus subtilis was monitored in controlled microcosms to elucidate the role iron may play in aiding bacterial silicification in hot springs. Silica and iron immobilization was monitored as a function of bacterial concentration, iron concentration, and silica concentration (both undersaturated and oversaturated with respect to amorphous silica). Results demonstrate that bacterial cells do immobilize more Fe than bacteria-free systems in solutions with iron concentrations [Formula: see text]50 ppm Fe. However, as iron concentrations increase, the difference between Fe immobilization in bacterial and bacteria-free systems decreases as non-bacterially mediated precipitation processes dominate. Additionally, bacterial systems that had immobilized more Fe compared with bacteria-free systems did not immobilize more silica than bacteria-free systems. By comparing molar ratios of (silica in solution)/(bacterially bound Fe), it is evident that insufficient iron is bound to the bacterial surface to act as an effective salt bridge for silica sorption. This appears to be because much of the iron is immobilized by non-bacterially mediated precipitation of phases such as Fe(OH)3 and poorly ordered hydrous iron silicates. It follows that in silica-enriched hot springs, silica and iron immobilization processes are significantly dominated by non-bacterially mediated precipitation. Any bacterially mediated processes are exceedingly small and outside the resolution of these experiments.
Relict tufa at Miette Hot Springs, Jasper National Park, Alberta, Canada
Authors: Bonny Sandy , Jones Brian
Published: December 2003

At the Miette Hot Springs site, relict tufa stretches for nearly 500 m along the west side of Sulphur Creek valley and rises up to 30 m above the valley floor. The tufa, composed of low-Mg calcite, precipitated from waters discharged from a line of perched springs.14C dating of bone material embedded in the tufa indicates that tufa precipitation took place between ~4500 and 2500 years BP under cool and moist climatic conditions. The spring biota was dominated by filamentous microbes (mainly Phormidium and Oscillatoria), with fewer diatoms (including Cymbella), testate protozoans (including Quadrulella), ostracodes (including Darwinula, Heterocypris, Cadonia, and Cyclocypris), and various bryophytes. The ecological preferences of these microbes indicate that the spring water had near-neutral pH, was Ca, HCO3, and H2SSO4rich, and emerged at 5065 °C. Landslides disrupted the west wall of Sulphur Creek valley during and after tufa growth. The relict tufa is divided into six morphotypes that reflect variations in water flow down the steep and rugged flow path. Domal tufa is located around the spring vents, roll-over tufa developed where water flowed over sharp lips or structural barricades, vertical tufa formed where calcite was precipitate from water flowing down steep to vertical inclines, flat-banded tufa reflects precipitation on a gentle slope, and wedge-shaped tufa formed where more rapid downslope calcite precipitation caused a progressive decrease in slope. The tufa contains stromatolitic facies (including streamer, porous laminar, dense laminar) and nonstromatolitic facies (bedded, crenulated) that reflect variations in the biology, water temperature, and style of flow of different parts of the spring flow path.
Deposition and diagenesis of Mammoth Hot Springs travertine, Yellowstone National Park, Wyoming, U.S.A.
Authors: Chafetz Henry S , Guidry Sean A
Published: December 2003

Strata forming a 113 m long core through Mammoth Hot Springs record the Holocene evolution of this travertine accumulation from deposition as part of a lacustrine to a terraced mound environment. The deposit is readily divided into four intervals: 11367 m, carbonate-cemented volcaniclastic with intercalated layers of travertine; 6760 m, moderately pure travertine with some volcaniclastics; 6050 m, carbonate-cemented volcaniclastic-rich interval; and 500 m, essentially pure travertine. Lithologic composition, sedimentary structures, and the rare ostracode fossils indicate that the lower 67 m predominantly accumulated in a lacustrine environment, whereas the upper 40 m are terraced mound deposits. All of the travertine is calcite, some after aragonite. Layers of shrubs, oncoids, and peloids, all bacterial in origin, form the dominant allochems within the travertine. Stable isotopic carbon and oxygen values (n = 128) are strongly positively correlated and decrease up-core ~4 and 8, respectively, reflecting a change in depositional environment from lacustrine to terraced mound upsection. Other stable isotopic trends indicate a pronounced difference between travertine allochems and immediately adjacent spar, e.g., spar averages 0.9 and 0.6, respectively, lower than immediately adjacent shrubs (n = 7 pairs). This difference is interpreted to reflect degassing and evaporation in the surface waters prior to precipitation of the allochems. The trends in stable isotopic values provide valuable corroborative data with regard to the depositional environment and diagenesis of the travertine.
Travertine mounds of the Cave and Basin National Historic Site, Banff National Park
Authors: Grasby Stephen E , van Everdingen Robert O , Bednarski Jan , Lepitzki Dwayne AW
Published: December 2003

The Cave and Basin National Historic Site is a fan-shaped travertine deposit associated with four thermal spring outlets. Tentative age dating of the travertine mound indicates growth initiated with onset of the late Holocene shift to more humid and cool climate conditions and suggests that the flow of thermal waters was limited during the Hypsithermal, which in turn places constraints on the evolutionary biology of endemic species in the spring system. Two large caves and one collapsed cave structure are developed within the deposit. Cave development is in response to both physical erosion of till underlying the travertine and acid gas attack of calcite that makes up the deposit. This process is buffered by formation of reaction crusts of gypsum on the interior cave walls. Only minor modern travertine growth occurs due to historic flow control measures. Understanding the flow of water through the historic site is critical for long-term preservation.
Hot spring sinters: keys to understanding Earth's earliest life forms
Authors: Konhauser Kurt O , Jones Brian , Reysenbach Anna-Louise , Renaut Robin W
Published: December 2003

The question of what composed the Earth's oldest fossils is the subject of current debate. At present, taphonomical determination of Archean silicified microfossils is largely based on morphological comparisons with extant microorganisms. This method has significant shortcomings because little is known about which types of bacteria silicify, what physical changes are induced on those species during mineralization, and, most importantly, what their preservation potential is. Terrestrial hot springs may help resolve these uncertainties because the silica-supersaturated geothermal fluids mineralize a wide variety of natural microbial communities and thus lead to the formation of numerous distinct biofacies. Some of these biofacies are reminiscent of Archean siliceous stromatolites from which the oldest microfossils were recovered. We suggest that by integrating molecular techniques that characterize the indigenous microbial populations growing in different biofacies with electron microscopy, we may be able to assess better what types of ancient microbes could have become fossilized.
Microbes and mineral precipitation, Miette Hot Springs, Jasper National Park, Alberta, Canada
Authors: Bonny Sandy , Jones Brian
Published: December 2003

At Miette Hot Springs, SO42/H2S-, Ca2+-, Sr2+-, and CO32-rich waters with a mean temperature of 51.2 °C are ejected from three spring vents and several minor seeps near the floor of Sulphur Creek valley. Runoff channels from the springs are colonized by cyanobacteria (Oscillatoria, Phormidium, Gloeocapsa, Synechococcus, Xenococcus) that grow in resistant mats and as loose filaments within 0.5 m of the spring vents, diatom assemblages (Cymbella, Mastagloia, Brachysira, Sellaphora, Rhopalodia, Nitzschia, Navicula, Pinnularia) that dominate the flow paths 0.52.0 m from the vents, and microbial mats with cyanobacteria and diatoms in the distal flow paths. Sulphate-reducing bacteria and green algae are also present. Gypsum, elemental sulphur, and lesser quantities of calcite and strontianite precipitate from the spring waters. Microbial populations influence accumulation of mineral precipitates by (i) forming mats close to the spring vents on which crystals grow, (ii) forming mats alongside the flow paths that trap and bind precipitates, and (iii) providing loose filaments to which microscopic gypsum crystals adhere. The microbes also influence crystal habit by (i) creating pores on the surfaces of gypsum crystals where smaller crystal precipitates form, and (ii) producing intercellular mucus in microbial mats, where suspended crystals can grow in all directions to produce polyterminal calcite crystals. Diatoms also mediate corrosion of the faces of calcite and gypsum crystals. Enriched δ13Cinorganicsignatures in the precipitates associated with microbial communities indicate that photosynthesis may promote precipitation of calcite and strontianite.
Petrography and genesis of spicular and columnar geyserite from the Whakarewarewa and Orakeikorako geothermal areas, North Island, New Zealand
Authors: Jones Brian , Renaut Robin W
Published: December 2003

Domal masses of geyserite, which surround many geyser vents in the Whakarewarewa geothermal area, are formed largely of spicules, spicule columns, and shrub columns. The non-branching spicules and the branches of branching spicules, individually up to 3 cm high and 1 mm diameter, have a laminated core encased by siliceous cortex. Silicified microbes are rare in the core but common in the cortex. Silicified microbial mats and pseudodendrites are found in the crevices between neighbouring spicules. Shrub columns, up to 5 cm high and 1.5 cm in diameter, are formed of opal-A that was precipitated around a three-dimensional, branching, shrub-like microbial (?) structure. The shrub branches, which are hollow with scalloped walls, do not contain any evidence of the original microbes or minerals that formed them. Silicified microbial mats are present between the columns. Microbial boring and etching by acidic steam led to local diagenetic degradation of these columns. In the geyserite mounds at Whakarewarewa, spicules and spicule columns are common, whereas shrub columns are rare. Interbedding and intercalation of spicular geyserite with shrub columnar geyserite indicate, however, that these different morphologic entities probably formed under similar environmental conditions on the mounds around the geyser vents. Petrographic evidence shows that the spicules, spicule columns, and shrub columns grew through a combination of biotic and abiotic processes.
Diagenetic transformations (opal-A to quartz) of low- and mid-temperature microbial textures in siliceous hot-spring deposits, Taupo Volcanic Zone, New Zealand
Authors: Lynne Bridget Y , Campbell Kathleen A
Published: December 2003

Silica sinter is a subaerial hot-spring deposit formed upon cooling (<100 °C) of discharging alkali-chloride waters. Silica deposition traps and fossilizes living microbes in low-temperature (<35 °C) to mid-temperature (~3559 °C) apronterrace outflow channels and pools, which record distinctive macrotextures and microtextures along a thermal gradient. Sinters from four geothermal fields, Orakei Korako, northern Waiotapu, Te Kopia, and Umukuri, within the Taupo Volcanic Zone, New Zealand, were sampled from two common microbe-rich microfacies (low-temperature palisade, mid-temperature bubble mat) through a range of ages (modern to ~40 000 years BP). We observed morphologic changes in microbial silicification and stepwise transitions in silica phase mineralogy throughout diagenesis (opal-A to quartz). X-ray powder diffractometry analysis of Taupo Volcanic Zone sinter samples revealed that mode of microbial fossilization is controlled by silica phase mineralogy, which also determines the preservation potential of environmentally significant and measurable filament parameters. Typical low-temperature palisade microfacies display thick sheaths (>3 µm diameter) and coarse tubular filament moulds >5 µm in diameter, whereas mid-temperature bubble mat microfacies characteristically consist of thin sheaths (~1 µm diameter) with fine moulds < 3 µm in diameter. Upon diagenesis and silica phase transformation to opal-CT, the two subenvironments cannot be distinguished based on filament diameter alone. This study of recurring microfacies in sinters of different ages allowed us to systematically track the transformation of mineralogical and morphological changes in bioticabiotic depositional elements during diagenesis of silica sinter, and therefore enhance the paleoenvironmental, paleobiological, and paleohydrologic utility of hydrothermal deposits in the geologic record.
Subaqueous silicification of the contents of small ponds in an Early Devonian hot-spring complex, Rhynie, Scotland
Authors: Trewin Nigel H , Fayers Stephen R , Kelman Ruth
Published: December 2003

The Early Devonian Rhynie and Windyfield cherts of northeast Scotland originated as siliceous sinters deposited by hot springs. Silicification affected both subaerial and subaqueous environments, preserving a diverse terrestrial and freshwater biota. Cherts originally deposited in small shallow pools can be recognised on the basis of both texture and fossil content. Textures comprise clotted and microcoprolitic textures, bacterial coatings on plant axes that can be stromatolitic, and a variety of bacterial and fungal meshworks. The crustacean Lepidocaris, the euthycarcinoid Heterocrania, the charophyte alga Palaeonitella, and chytrid fungi are typical elements of the aquatic biota. Observations of modern hot springs in Yellowstone National Park, Wyoming, U.S.A., demonstrate that shallow ponds and streams on low-angle outwash areas and dormant vent orifices provide suitable environmental analogues. Textures comparable to those described from Rhynie are recorded from Yellowstone sinters, but examples of the rapid and complete silicification of delicate organic structures as seen in a few of the Rhynie chert beds have not been noted. Petrographic textures comparable to those seen in the cherts of freshwater origin from Rhynie occur in modern stream sinters at Yellowstone, where they form from waters at 2028 °C and with a pH of 8.7. This similarity occurs despite differences in environment at Yellowstone, such as the oxidizing surface environment, water table fluctuations, complex modern vegetation, fixing of silica by diatoms, and climatic extremes. Thus there are close similarities between textures seen in the Rhynie cherts and Yellowstone sinters deposited in freshwater pools and streams by hot springs.
Microstructure of high-temperature (>73 °C) siliceous sinter deposited around hot springs and geysers, Yellowstone National Park: the role of biological and abiological processes in sedimentation
Authors: Lowe Donald R , Braunstein Deena
Published: December 2003

Slightly alkaline hot springs and geysers in Yellowstone National Park exhibit distinctive assemblages of high-temperature (>73 °C) siliceous sinter reflecting local hydrodynamic conditions. The main depositional zones include subaqueous pool and channel bottoms and intermittently wetted subaerial splash, surge, and overflow areas. Subaqueous deposits include particulate siliceous sediment and dendritic and microbial silica framework. Silica framework forms thin, porous, microbe-rich films coating subaqueous surfaces. Spicules with intervening narrow crevices dominate in splash zones. Surge and overflow deposits include pool and channel rims, columns, and knobs. In thin section, subaerial sinter is composed of (i) dark brown, nearly opaque laminated sinter deposited on surfaces that evaporate to dryness; (ii) clear translucent silica deposited subaqueously through precipitation driven by supersaturation; (iii) heterogeneous silica representing silica-encrusted microbial filaments and detritus; and (iv) sinter debris. Brownish laminations form the framework of most sinter deposited in surge and overflow zones. Pits and cavities are common architectural features of subaerial sinter and show concave-upward pseudo-cross-laminations and micro-unconformities developed through migration. Marked birefringence of silica deposited on surfaces that evaporate to dryness is probably a strain effect. Repeated wetting and evaporation, often to dryness, and capillary effects control the deposition, morphology, and microstructure of most high-temperature sinter outside of the fully subaqueous zone. Microbial filaments are abundant on and within high-temperature sinter but do not provide the main controls on morphology or structuring except in biofilms developed on subaqueous surfaces. Millimetre-scale lamination cyclicity in much high-temperature sinter represents annual layering and regular seasonal fluctuations in silica sedimentation.
Partitioning of bacterial communities between travertine depositional facies at Mammoth Hot Springs, Yellowstone National Park, U.S.A.
Authors: Fouke Bruce W , Bonheyo George T , Sanzenbacher Beth , Frias-Lopez Jorge
Published: December 2003

A culture-independent molecular survey indicates that the composition of bacterial communities is distinctly partitioned between travertine depositional facies in the surface drainage system of Spring AT-1 at Angel Terrace, Mammoth Hot Springs, Yellowstone National Park. PCR (polymerase chain reaction) amplification and sequencing of 16S rRNA genes with universally conserved bacterial primers has identified over 553 unique partial and 104 complete gene sequences (derived from more than 14 000 clones), affiliated with 221 unique species that represent 21 bacterial divisions. These sequences exhibited < 12% similarity in bacterial community composition between each of the travertine depositional facies. This implies that relatively little downstream bacterial transport and colonization took place despite the rapid and continuous flow of spring water from the high-temperature to low-temperature facies. These results suggest that travertine depositional facies, which are independently determined by the physical and chemical conditions of the hot spring drainage system, effectively predict bacterial community composition as well as the morphology and chemistry of travertine precipitation.
Experimental studies on New Zealand hot spring sinters: rates of growth and textural development
Authors: Mountain B W , Benning L G , Boerema J A
Published: December 2003

To study the rate of growth of sinters in New Zealand hot springs, field experiments were conducted in seven geothermal areas. At Wairakei, fan-shaped subaqueous deposits of amorphous silica grow rapidly (350 kg a1 m2 of drain wall) and are composed of silicified filaments with subordinate bacillus and spirillium-shaped organisms. Characterization of bacteria revealed isolates sharing > 97% 16S rRNA gene sequence homologies affiliated with Thermus, Meiothermus,Bacillus, Tepidomonas, Thermomonas, Porphyrobacter, Thermonema, and, Hydrogenophilus spp., as well as previously uncultured bacteria. At Rotokawa, microstromatolites have a slow growth rate (0.004 mm day1) that is attributed to low pH, capillary rise, and evaporation. At Champagne Pool, sinter growth (0.023 mm day1) is dominated by wave action building alternating microbe-rich and microbe-poor layers. Silica sinter was not observed at Waikite, where slides developed a layer of calcite (0.026 mm day1). Sinter growth at Ngatamariki (0.016 mm day1) forms by capillary rise, evaporation, and diffusion and at Tokaanu, subaqueous growth is slow (0.002 mm day1) and contains silicified microbes. Textures at Orakei Korako indicate similar mechanisms to Ngatamariki, except that growth is more rapid (0.023 mm day1) due to a splash contribution. Silica and calcite saturation indices adequately explain the growth of the sinters and calcite, indicating that microbes are not inducing precipitation where it should not occur. The rate of precipitation is correlated with silica supersaturation, but pH effects can alter this relationship. The degree of preservation of microbial material is explained by the effect of Ostwald ripening on silica spherules. Subaqueous growth allows coarsening of spherules and poor preservation of smaller microbes while subaerial nucleation is rapid, Ostwald ripening is inactive, and better preservation can be expected.
Siliceous shrubs in hot springs from Yellowstone National Park, Wyoming, U.S.A.
Authors: Guidry Sean A , Chafetz Henry S
Published: December 2003

Many of the siliceous hot springs in Yellowstone National Park contain subaqueous, spinose siliceous precipitates up to 5 cm high that occupy shallow terracettes in siliceous terraced mound accumulations, discharge channels, etc. These siliceous "shrubs" are composed of opal-A with an arborescent or branching pattern and have strong morphological similarities to bacterial shrubs from carbonate-precipitating hot springs. Siliceous shrubs constitute a major precipitate style associated with discharge channel  flow-path facies throughout most of the 20 m of flow path at Cistern Spring, Norris Geyser Basin. They are found in siliceous spring waters ranging in temperature from 76.4 to 16.2 °C and pH from 6.0 to 7.4. At every scale, siliceous shrubs contain abundant evidence of microbial life in the form of bacterial body fossils and extracellular polymeric substances. The presence of relict organic constituents and bacterial morphological fossils indicates that the shrub fabric and architecture are dominated by bacteria, i.e., there is potentially a strong biotic effect on the precipitation process. Precipitation of opal in siliceous shrubs is very likely the result of either active bacterially induced precipitation or passive mediation through organic templates. On a larger scale, siliceous shrubs contain abundant evidence of former microbial activity in hot springs, thus they are good microbial biomarkers.
Cyanobacteria associated with hot spring travertines
Authors: Pentecost Allan
Published: December 2003

Cyanobacteria are the major oxygenic photosynthetic microorganisms of hot spring travertines. This review describes the known cyanobacterium flora of travertine-depositing waters > 37 °C. The communities develop either upon (epilithon) or within (endolithon) the travertine surface, where they may influence the travertine fabric by providing nucleation sites for calcium carbonate. Mat photosynthesis locally increases the amount of travertine deposited, but the importance of photosynthesis in travertine deposition is rarely significant because the main loss of CO2is by atmospheric evasion of the hot, CO2-rich waters. The Oscillatoriales are the most important group of cyanobacteria in terms of their biomass, but the taxonomy of the order is in a state of chaos. Molecular methods will ultimately disclose the true affinities of the organisms but, at present, the use of form-taxa based upon morphological characters provides a practical alternative. Identification of fossilized cyanobacteria is problematic since few of the key characters survive as fossils. The known cyanobacterium flora is tabulated and an analytical key provided to identify the form-taxa of hot spring travertines.
Hot spring and geyser sinters: the integrated product of precipitation, replacement, and deposition
Authors: Jones Brian , Renaut R W
Published: December 2003

Complex ornate sinter deposits are found in many hot spring and geysers systems throughout the world, including those located in the Taupo Volcanic Zone on the North Island of New Zealand. Those sinters are formed of opal-A that replaced microbes, opal-A precipitated as cement, accessory minerals (e.g., kaolinite, jarosite, calcite), biological detritus (e.g., leaves, wood, pollen grains), and lithic detritus. The opal-A is compositionally variable because of the amount of water (OH and H2O) and, in some cases, accessory elements (e.g., Au, Ag) bound into its structure. The composition and fabric of the siliceous sinter found at any locality reflect the relative balance among the processes of replacement, precipitation, and deposition. The microbes that inhabit these systems are of critical importance because they are commonly replaced by and (or) encrusted with opal-A. In many settings, copious amounts of opal-A are precipitated as cement around the frameworks of silicified filaments. The cementation process, which continues for as long as waters supersaturated with respect to opal-A flow through the sinter, commonly reduces the porosity of the sinters by as much as 50%. This process is probably of far greater significance than has been previously recognized. The textural and compositional complexity of siliceous sinters found in hot spring and geyser systems reflects the myriad of interrelated processes that control their formation.
FeAs2 biomineralization on encrusted bacteria in hot springs: an ecological role of symbiotic bacteria
Authors: Tazaki Kazue , Rafiqul Islam ABM , Nagai Kaori , Kurihara Takayuki
Published: December 2003

Bacterial FeAs2 mineralization was found in the reddish-brown microbial mats that have grown on the walls of the drainage systems of Masutomi Hot Springs, Yamanashi Prefecture, Japan. The reddish-brown microbial mats, which are mainly composed of bacilliform and coccoid types of bacteria, have been analyzed and observed by microtechniques to interpret the bacterial biomineralization and search for the clues to bioremediation. These bacteria accumulate Fe and As along with other trace elements to form various biominerals. The electron diffraction (ED) pattern of the bacterial capsule identified lollingite (FeAs2) and calcite (CaCO3) on the surface of the cell. Based on Fourier-transform infrared absorbance spectroscopy (FTIR) analysis, the presence of organic components such as CH, C=O, CNH, COOH, and NH in the reddish-brown microbial mats emphasized the metal-binding potential of the bacteria. X-ray diffraction (XRD) data showed the poorly crystalline character of the precipitates, which consist mainly of hydrous iron oxides (2.7 Å (1 Å = 0.1 nm)). The FeAs2 biominerals form by adsorption onto the bacterial cell wall, as demonstrated by microscopic observations and spectroscopic analysis. These showed that bacteria in the reddish-brown microbial mats have the ability to form biominerals with heavy metals and toxic metalloids like As. Particularly significant in hot spring environments is the role of symbiotic and toxic-resistant bacteria, which have the ability to adapt to high As concentrations. Bacterial FeAs2 mineralization might also be considered a mechanism by which toxic As is removed from the aquatic ecosystem. The results provide evidence for detoxification processes and offer clues to possible methods of bioremediation.
What is a hot spring?
Authors: Pentecost Allan , Jones B , Renaut R W
Published: December 2003

The response of researchers to a questionnaire on the definitions of hot, thermal, warm, and cold springs is provided. Two important benchmarks are recognized, the human body temperature and the mean annual local air temperature. While no scheme can claim to provide an objective, unbiased classification, waters emerging with a temperature in excess of the core human body temperature of 36.7 °C should be defined as hot springs. The term "thermal spring" is not recommended as it cannot be defined satisfactorily for all springs. The term "warm spring" is not considered utilitarian.
Performance of instrumented large-scale unreinforced and reinforced embankments loaded by a strip footing to failure
Authors: Bathurst Richard J , Blatz James A , Burger Martin H
Published: December 2003

The paper describes an experimental investigation in which two large-scale geosynthetic reinforced soil embankments and one unreinforced soil embankment were taken to collapse under a strip footing placed close to the crest. One reinforced embankment was constructed with a relatively extensible and weak polypropylene geogrid and the second with a relatively strong and stiff high-density polyethylene geogrid. The geometry of the unfaced embankments, sand soil, and loading arrangement were the same for all three structures. The focus of the paper is on the experimental design, construction, testing, and instrumentation techniques used in the investigation and selected test results. The results of the study show that the ultimate footing load capacity increased with an increase in reinforcement strength (and stiffness) and that the reinforced soil embankments had a load capacity up to 1.62.0 times that of the nominal identical control embankment without reinforcement.Key words: geosynthetics, reinforced embankments, strip footing, large scale, experimental.
Limit equilibrium analysis of large-scale reinforced and unreinforced embankments loaded by a strip footing
Authors: Blatz James A , Bathurst Richard J
Published: December 2003

The paper describes limit equilibrium analyses of two large-scale geosynthetic reinforced soil embankments and one unreinforced soil embankment that were taken to collapse under a strip footing placed close to the crest. One reinforced embankment was constructed with a relatively extensible and weak polypropylene geogrid and the second with a relatively strong and stiff high-density polyethylene geogrid. The geometry of the embankments and the loading arrangement were the same for all three structures. The focus of the paper is on a comparison of the predicted collapse load for the three structures and the actual observed values. A three-dimensional analytical approach is used to account for possible side-wall friction effects due to the test facility in which the large-scale experimental models were built. The paper also reports details on the interpretation of in-isolation constant load tests and strain measurements used to infer tensile loads in the reinforcement at failure. An important conclusion is that a general two-part wedge analysis approach can be used to predict the collapse footing load for both unreinforced and reinforced sand embankments in this investigation provided careful attention is paid to the selection of soil shear strength and reinforcement tensile capacity.Key words: geosynthetics, reinforced embankments, strip footing, large scale, limit equilibrium analyses.
A model to predict the water retention curve from basic geotechnical properties
Authors: Aubertin M , Mbonimpa M , Bussière B , Chapuis R P
Published: December 2003

The water retention curve (WRC) has become a key material function to define the unsaturated behavior of soils and other particulate media. In many instances, it can be useful to have an estimate of the WRC early in a project, when little or no test results are available. Predictive models, based on easy to obtain geotechnical properties, can also be employed to evaluate how changing parameters (e.g., porosity or grain size) affect the WRC. In this paper, the authors present a general set of equations developed for predicting the relationship between volumetric water content, θ, (or the corresponding degree of saturation, Sr) and suction, ψ. The proposed model assumes that water retention results from the combined effect of capillary and adhesion forces. The complete set of equations is given together with complementary relationships developed for specific applications on granular materials and on fine-grained soils. It is shown that the model provides a simple and practical means to estimate the water retention curve from basic geotechnical properties. A discussion follows on the capabilities and limitations of the model, and on additional tools developed to complement its use. Key words: water retention curve, unsaturated soils, prediction, porosity, grain size, liquid limit.
Retaining walls damaged in the Chi-Chi earthquake
Authors: Fang Y S , Yang Y C , Chen T J
Published: December 2003

This paper investigates the failure of three gravity walls due to the 1999 Chi-Chi earthquake. Characteristics of the damaged walls were carefully recorded and backfill materials behind the damaged walls were collected and tested in the laboratory. Both the simplified analysis based on the MononobeOkabe method and the simplified dynamic analysis based on the RichardsElms method were adopted. For the first case, the sliding of concrete wall blocks along the construction joint was observed. It was found that, during the earthquake, the frictional resistance at the untreated construction joint was not sufficient to resist the dynamic lateral thrust. For the second case, the retaining wall settled significantly and tilted about its toe. Seismic analysis of the wall indicated that, under the same horizontal acceleration, the factor of safety against bearing capacity failure was lower than that against overturning and sliding. A stability check against bearing capacity failure for the retaining wall should never be neglected. For the third case, the retaining wall built on top of the Che-Lung-Pu fault was severely damaged by the fault rupture. During the earthquake, the vertical displacement of the hanging wall uplifted the backfill, causing the wall to overturn. Horizontal displacement of the hanging wall caused the wall to slide and the soil in front of the toe to heave.Key words: analysis, bearing capacity, case study, earthquake, failure, retaining wall.
Neural network approach to model the limit state surface for reliability analysis
Authors: Goh Anthony TC , Kulhawy Fred H
Published: December 2003

Structural reliability methods are often used to evaluate the failure performance of geotechnical structures. A common approach is to use the first-order reliability method. Its popularity results from the mathematical simplicity of the method, since only second moment information (mean and coefficient of variation) on the random variables is required. The probability of failure is then assessed by an index known commonly as the reliability index. One critical aspect in determining the reliability index is the explicit definition of the limit state surface of the system. In a problem involving multi-dimensional random variables, the limit state surface is the boundary separating the safe domain from the "failure" (or lack of serviceability) domain. In many complicated and nonlinear problems where the analyses involve the use of numerical procedures such as the finite element method, this surface may be difficult to determine explicitly in terms of the random variables, and therefore the limit state can only be expressed implicitly rather than in a closed-form solution. It is proposed in this paper to use an artificial intelligence technique known as the back-propagation neural network algorithm to model the limit state surface. First, the failure domain is found through repeated point-by-point numerical analyses with different input values. The neural network is then trained on this set of data. Using the optimal weights of the neural network connections, it is possible to develop a mathematical expression relating the input and output variables that approximates the limit state surface. Some examples are given to illustrate the application and accuracy of the proposed approach.Key words: first-order reliability method, geotechnical structures, limit state surface, neural networks, reliability.
Three-dimensional analysis of unlined tunnels in rock subjected to high horizontal stress
Authors: Abdel-Meguid M , Rowe R K , Lo K Y
Published: December 2003

An analysis of the stability of underground openings in weak rock is important to the design of the support requirements near the tunnel face. A detailed three-dimensional (3D) elastoplastic finite element study of face stability and the corresponding stresses around the face is conducted for a large-diameter tunnel in southern Ontario. The effect of the rock mass strength and high horizontal stresses on the tunnel deformation, stability, and distribution of tangential stresses at the tunnel circumference is investigated. To facilitate comparison with plane strain analysis, 3D results are presented for several cross sections across the tunnel. The effect of tunnel construction sequence on the predicted results is discussed.Key words: weak rock, tunnelling, horizontal stresses, three-dimensional, finite element, excavation, face stability, modeling.
Use of laboratory data to confirm yield and liquefied strength ratio concepts
Authors: Olson Scott M , Stark Timothy D
Published: December 2003

A laboratory database of triaxial compression test results was collected to examine the use of strength ratios for liquefaction analysis. Specifically, the database was used to: (i) validate the yield strength ratio concept (or yield friction angle); (ii) demonstrate the parallelism of the consolidation line and steady state line of many sandy soils; and (iii) validate the liquefied strength ratio concept. The yield strength ratio of contractive sandy soils in triaxial compression ranges from approximately 0.29 to 0.42 (corresponding to yield friction angles of 16°23°), while the yield strength ratio from flow failure case histories (which correspond approximately to direct simple shear conditions) ranges from 0.23 to 0.31 (or yield friction angles of 13°17°). As expected, the yield friction angle is greatest in triaxial compression, smaller in direct simple shear, and likely smallest in triaxial extension. The steady state line and consolidation line of many contractive sandy soils are parallel for a wide range effective stresses, steady state line slopes, fines contents, and grain sizes and shapes that are applicable to many civil engineering structures. As such, the liquefied strength ratio is a constant for many sandy soils deposited in a consistent manner. The liquefied strength ratio is inversely related to state parameter and ranges from approximately 0.02 to 0.22 in laboratory triaxial compression tests. Flow failure case histories fall near the middle of this range.Key words: liquefaction, liquefied shear strength, yield shear strength, collapse surface, steady state line, penetration resistance.
Effects of monitoring and pumping well pipe capacities during pumping tests in confined aquifers
Authors: Chapuis Robert P , Chenaf Djaouida
Published: December 2003

This paper establishes how the water stored in the pipes of monitoring and pumping wells influences the drawdown curves of pumping tests in confined aquifers. Experimental and numerical results obtained with a physical model are first studied and then confirmed by field-test data. A large tank was used for fully controlled pumping tests. It contains a lower confined aquifer, an aquitard, and an upper unconfined aquifer. Pumping tests at a constant flow rate in the confined aquifer provided drawdowns that were analyzed for unsteady-state, steady-state, and recovery conditions. For a single monitoring well, the different interpretation methods provided similar values of transmissivity, T, and storativity, S. Drawdown curves gave much too high S values. These S values were equal to those resulting from water storage in the pipes of monitoring and pumping wells, according to the physical definition of storativity. The experimental T and S values were confirmed by two numerical analyses (finite elements) of the pumping test, one considering no water was stored in the pipes and the other considering stored water. Data of real pumping tests in confined aquifers confirmed that the S value calculated from drawdown curves can be influenced by water storage in monitoring and pumping wells for usual pipe diameters.Key words: pumping test, transmissivity, storativity, sandbox, in situ test, pipe capacity.
Electrokinetics-generated pore fluid and ionic transport in an offshore calcareous soil
Authors: Mohamedelhassan E , Shang J Q
Published: December 2003

In this study, the electrokinetics-generated pore fluid transport in an offshore calcareous soil is investigated in three steps. The pore fluid of the soil specimen tested has a salinity equivalent to that of seawater (artificial or A-seawater). The electroosmotic flow rates are measured for the A-seawater and two stabilizing permeating solutions, i.e., 15% CaCl2and 10% Al2(SO4)3·18H2O solutions. The results show that electroosmosis generated significant flow in the soil and can effectively transport the two permeating solutions through soil pores filled with A-seawater. The maximum flow rate is observed in the test conducted with 15% CaCl2solution, followed by those of A-seawater and 10% Al2(SO4)3·18H2O solutions, respectively. The results also show the significant role of electromigration in transporting the cations in the permeating solutions from the anode to the cathode. In particular, it is found that the electrokinetics-generated ionic transport for calcium (Ca2+) is 6.3 times faster than that for aluminum (Al3+). The surface charge properties of the calcareous soil are studied by measuring the zeta potentials of the soil solids suspended in electrolyte solutions of various types, concentrations, and pH values. The relationship between the experimental and theoretical coefficients of electroosmotic permeability, ke, is examined based on the results from the electrokinetic experiments and the HelmholtzSmoluchowski model. It is concluded that the effectiveness of electroosmosis in transporting water can be predicted qualitatively or semiquantitatively from the zeta potential of the soil solids suspension. The influence of pore fluid pH on the zeta potential of the soil is also investigated. The study provides important information for the use of electrokinetics to facilitate in situ artificial cementation of calcareous soils for offshore foundation applications.Key words: calcareous soil, electrokinetics, electroosmosis, electromigration, zeta potential, soilwaterelectrolyte system.
Travel distance angle for "rapid" landslides in constructed and natural soil slopes
Authors: Hunter Gavan , Fell Robin
Published: December 2003

"Rapid" landslides in constructed and natural soil slopes have the potential to cause loss of life, destruction of property, and damage to the natural environment because the velocity of the slide mass is such that persons in the travel path do not have time to evacuate and the kinetic energy is such that even small landslides can severely damage buildings and other structures. This paper presents methods for prediction of the post-failure travel distance for "rapid" landslides from constructed cut and fill slopes and natural soil slopes derived from a database of some 350 "rapid" landslides in predominantly soil slopes. The characteristics of soils, both dilative and contractive on initial shearing, and the slope conditions for which landslides are susceptible to development into slides of "rapid" post-failure velocity are discussed. Methods for estimating the travel distance angle of the post-failure travel of the slide mass have been developed and are based on consideration of the failure mechanics of the initial slide (whether contractive or dilative on initial shearing), the type of slope, the slide volume, the geometry of the slope at and below the slide source area, and the degree of confinement of the travel path of the landslide.Key words: "rapid" landslide, flow slide, debris flow, debris slide, travel distance angle, failure mechanism.
Acidification and release of heavy metals in dredged sediments
Authors: Borma Laura De Simone , Ehrlich Maurício , Barbosa Maria Cláudia
Published: December 2003

The oxidation of iron sulphides in dredged sediments can be a source of long-term contamination of surface and underground water. The adverse effects are related to a decrease in the ability of soil to retain heavy metals, which is caused by acidification. Laboratory tests were conducted, and pH variations and consequent release of heavy metals, especially Zn, Cu, and Pb, into the solution were monitored over time. The rate of pyrite oxidation was determined based on the sulphate production rate, through the stoichiometry of the oxidation reaction. Samples of sediments from the Jacarepaguá lagoon complex, State of Rio de Janeiro, were dried and oxidized over a period of 10 months. During this period the pH fell from 6.9 to 3.3, with oxidation of approximately 20% of the sulphur present in the form of iron sulphide, and 45% of the Zn, 15% of the Pb, and 5% of the Cu contained in the material were released. The oxidation rate at the initial stages was of the order of 1.0 × 104 g(O2)·h1, decreasing to 1.0 × 105 g(O2)·h1 during the test. This study presents the laboratory methodology developed for determining the oxidation rate in a system where the oxygen consumption is governed not only by the pyrite oxidation, but also by the organic matter. In these experiments, a key measure of intrinsic oxidation rate (IOR) is the oxidation rate where oxygen is freely available at normal atmospheric concentration. By comparing the values obtained for the dredged material with the results of the IOR of mining waste materials reported in the literature, it was observed that the oxidation rates of the iron sulphide formed in the Jacarepaguá lagoon environment were one to two orders of magnitude higher than those of mineral iron sulphides from coal wastes. This behavior can be explained considering that the iron sulphides in dredged materials are freshly formed and have more specific surface area exposed to air than the iron sulphide mineral in mining wastes.Key words: sediments, dredging, sulphides, oxidation, acidification, heavy metals.
Use of the ranking distance as an index for assessing the accuracy and precision of equations for the bearing capacity of piles and at-rest earth pressure coefficient
Authors: Orr T LL , Cherubini C
Published: December 2003

In many geotechnical design situations, a number of different calculation models have been developed to predict the value of a particular quantity required for use in design calculations, for example, the bearing capacities of driven and root piles, and K0, the at-rest earth pressure coefficient. In this paper the authors show how the dependability of different calculation methods can be compared and assessed using a synthetic probabilistic approach and the ranking distance (RD) index. Measured values, Qmeas, are compared with calculated values, Qcalc, using the "bias factor," defined as the ratio Qmeas/Qcalc. The bias factor values obtained using a particular calculation method are processed to evaluate the "accuracy" and "precision" by calculating a central tendency and a variability statistical parameter, respectively, from the values. The RD index is a comprehensive statistical parameter for assessing the dependability of a particular calculation method and is based on the central tendency and variability. Using the ratios between calculated and measured bearing capacity and earth pressures values, the RD index is used to assess the accuracy and precision of the most frequently used pile driving formulae, two equations for the bearing capacity of root piles, and seven equations for the at-rest earth pressure coefficient.Key words: accuracy, precision, probabilistic approach, ranking distance.