4,643 research outputs found
Guide to the nature and methods of analysis of the clay fraction of tephras from the South Auckland region, New Zealand.
No full textThe manual outlines some of the more common laboratory procedures available for qualitatively and quantitatively analysing the composition of the tephric clays, many of which are difficult to determine because of their short range order or 'amorphous' nature. Techniques described and assessed in terms of their rapidity and quantitativeness include XRD, IR, DTA, TEM and SEM, sodium fluoride reactivity, chemical dissolution analyses, and surface area measurements. No one technique alone produces a definitive clay fraction analysis of tephric deposits. -from Author
Mineral acquisition from clay by Budongo Forest chimpanzees
No full textDate of Acceptance: 06/07/2015Chimpanzees of the Sonso community, Budongo Forest, Uganda were observed eating clay and drinking clay-water from waterholes. We show that clay, clay-rich water, and clay obtained with leaf sponges, provide a range of minerals in different concentrations. The presence of aluminium in the clay consumed indicates that it takes the form of kaolinite. We discuss the contribution of clay geophagy to the mineral intake of the Sonso chimpanzees and show that clay eaten using leaf sponges is particularly rich in minerals. We show that termite mound soil, also regularly consumed, is rich in minerals. We discuss the frequency of clay and termite soil geophagy in the context of the disappearance from Budongo Forest of a formerly rich source of minerals, the decaying pith of Raphia farinifera palms.Peer reviewe
Clay mineralogy of tephras and associated paleosols and soils, and hydrothermal deposits, North Island [New Zealand]
No full textTour themes and itinerary
The tour centres on the occurrence and genesis of clay minerals, especially allophane, halloysite, and ferrihydrite, associated with both Quaternary rhyolitic airfall tephra (volcanic ash) deposits and volcanogenic alluvium, and on mineralisation and thermal activity in hydrothermal fields. After a brief overview of the basaltic volcanoes of Auckland City, our route essentially traverses the Central Volcanic Region by way of a large loop with overnight stops at Rotorua (2 nights), Tokaanu, and Auckland (Fig. 0.1). We have around five stops planned for each day (including lunch), three of these being scientific stops except on Day 4 when we have only one scientific stop because of the need to travel greater distances.
Our route takes us progressively towards the locus of the most recently active volcanic centres of the Central Volcanic Region, and so the surficial tephra deposits and buried paleosols become successively younger and generally less weathered: tephras at the Mangawara section (Day 1) span c. 1 Ma; at Tapapa (Day 2), c. 140 ka; at Te Ngae (Day 2), c. 20 ka; and at De Bretts, c. 10 ka, and Wairakei, c. 2 ka (Day 3). Interspersed with these tephra-paleosol sections are stops to examine an allophane-halloysite soil drainage (leaching) sequence on volcanogenic alluvium (Day 1), hydrothermal activity and mineral deposits at Whakarewarewa (Day 2) and Waiotapu (Day 3), and pure ferrihydrite seepage deposits in Hamilton (Day 4). Following introductory and detailed background review material, the tour guide has been arranged on a day-by-day basis and includes an outline of the route and stops, and several pages describing the stratigraphy, mineralogy, chemistry, and pedology of the deposits or features at each of the main stops. We will attempt to point out and describe geological and other features as appropriate during travel periods.
Other activities
Examples of New Zealand's distinctive fauna and flora, including kiwis and tuataras, will be seen at close quarters at Rainbow Springs (Day 2), where we will also enjoy an agricultural farm show. In Rotorua we will partake in a Maori hangi (steam-cooked feast) and concert including traditional dance forms (hakas) and songs (Day 2). In Tokaanu, hot pools will be available to relax in near the slopes of Mt Tongariro (Day 3). At Waitomo, we will visit the Waitomo Cave and in Hamilton spend a short time at the Waikato Museum of Art and History (Day 4). Finally, the tour will conclude with a farewell dinner in Auckland
Effect of clay amendments on nitrogen leaching and forms in a sandy soil
No full textNitrogen (N) leaching in sandy soil decreases fertiliser use efficiency and may depress plant production. Application of high cation exchange capacity (CEC) materials (e.g. high activity clay minerals) is hypothesized to reduce N leaching and increase plant N uptake in sandy soils. However, the mechanism of leaching in sands with clay amendment is not understood. A column experiment was conducted to determine N leaching and N concentration in soil solution in a sandy soil (1.4 % clay) with three soil amendments (nil, clay soil and bentonite clay) and three fertiliser rates (0, 28 N 17 P 22 K kg/ha and 56 N 34 P 44 K kg/ha). Soil amendments were applied at the rate of 50 Mg/ha. The soil columns were leached with de-ionised water equivalent to 50 mm rainfall every 4 days. Concentrations of soil solution extracted by Rhizon samplers indicated that NH4 leaching was decreased 38-43 % by bentonite addition but little of the soil solution N was in NO3 form and bentonite had no effect on mobility of this form of N. The application of bentonite was able to hold NH4 in soil solution of top soil. Leaching of NH4 was delayed to 15 day after fertiliser application in bentonite-amended sand
Collective effects on the settling of clay flocs
No full textIn this work a high-magnification digital video camera in combination with a settling column is used to study in a first part the influence of the amount of flocs transferred into the settling column on their settling velocity. In a second part, the setup was used to study the properties of flocs prepared at different clay concentrations but at same flocculant to clay ratio (2.5mgg−1). Illite clay was used and flocculated in a 1 L jar with an anionic polyacrylamide (flocculant). Results show that the average settling velocity of flocs is a function of the amount of transferred flocs. It was also found that floc size and settling velocity depend on clay concentration. This is attributed to the fast aggregation happening in the jar when flocculant and clay are mixed: at higher clay concentrations, larger flocs are created in the first minutes of the experiment, with low densities that prevent them from settling to the bottom of the jar.Environmental Fluid MechanicsRivers, Ports, Waterways and Dredging Engineerin
The White Stone Band of the Kimmeridge Clay Formation, an integrated high resolution approach to understanding environmental change
No full textThe Kimmeridge Clay is a Jurassic mudrock succession that shows Milankovitch Band climatic cyclicity. A key issue is to determine how the subtle changes that define this cyclicity result from climatic change. Using material from the Natural Environment Research Council Rapid Global Geological Events (RGGE) Kimmeridge Drilling Project boreholes, the White Stone Band was investigated at the lamination scale using backscattered electron imagery and quantitative palynofacies. Fabric analysis shows the lamination to represent successive deposition of coccolith-rich and organic-matter-rich layers. Individual laminae contain unsorted palynological debris with a consistent ratio of marine and terrestrial components. Such mixed organic matter input is interpreted as the result of storm transport. Linking water column processes to laminae deposition suggests seasonal input with a coccolith bloom followed by a more diverse assemblage including dinoflagellates and photosynthetic chlorobiacean bacteria. As the photic zone extended into the euxinic water column organic matter export to the sea bed underwent minimal cycling through oxidation and subsequently became preserved through sulphurization with greatly increased sequestration of carbon. This was significantlyincreased by late season storm-driven mixing of euxinic water into the photic zone. Increased frequency ofstorm systems would therefore dilute the coccolith input to give an oil shale. Hence climatically induced changes in storm frequency would progressively vary the organic content of the sediment and generate the climate cycle signal. Keywords: Milankovitch theory, Kimmeridge Clay, organic matter, high-resolution methods, climate change
Technology Adoption under Relative Factor Price Uncertainty: The Putty-Clay Investment Model
No full textA plant has more flexibility in choosing among different technologies before undertaking an investment than after installing a specific machine. This paper argues that the irreversibility of factor intensity choice may play an important role in explaining the dynamics of investment in the presence of relative factor price uncertainty. A higher degree of irreversibility in the choice of factor intensity---characterized by the ex ante elasticity of substitution between different factors---leads to a larger negative effect of uncertainty in relative factor prices on investment. The empirical implications of the putty-clay investment model are examined using the plant-level Chilean manufacturing data for the period of time-varying exchange rate volatility. The econometric results show that the elasticity of substitution between imported materials and domestic materials is substantially higher at the time of a large investment and suggest that the irreversibility of factor intensity choice may potentially play an important role in explaining the impact of exchange rate volatility on investmentirreversible investment; putty-clay; technology adoption; uncertainty
Sensitivity and clay mineralogy of weathered tephra-derived soil materials in the Tauranga region
No full textSoil sensitivity is defined as the ratio of peak to remoulded shear strength. Problem soil materials are those that show large strength losses on disruption, resulting in catastrophic failure, liquefaction and long run-out distances. This study focussed on sensitive, weathered, mainly tephra-fall derived soils of mid-Pleistocene age in the Tauranga region. The liquefiable character of these soils is well known, but little detailed study has been directed towards the reasons for sensitivity. The objective of this work was to examine soil sensitivity by investigating geomechanical properties, clay mineralogy, and microfabric, and to determine how these factors combine to develop sensitivity. To achieve these objectives a combination of both field and laboratory investigations was undertaken.
Field investigations indicated that sensitive soils are common in the Tauranga region. Sampling was undertaken at sites in Tauriko and Otumoetai. Selected samples ranged across high (76) and low (≈8) field sensitivity. Stratigraphically, samples from Otumoetai lie below the Rangitawa Tephra (ca. 0.34 Ma), and those from Tauriko underlie the Te Ranga Ignimbrite (ca. 0.27 Ma).
Geomechanical investigation revealed that the sensitive soils had high moisture contents (gt; 60 %), low dry bulk density (lt; 966kg m-3), and high porosity (gt; 60 %). Liquidity index values ranged between 0.27 and 2.41. Plasticity index values ranged from 13.2 % to 42.7 %, with all samples plotting below the A line. Strength tests indicated effective friction angles from 25.7 to 38.5 , effective cohesion from 4.7 kPa to 34.5 kPa, residual friction angles of 19.34 to 33.18 , and cohesions of 0 kPa to 4.87 kPa. Remoulded vane shear strengths ranged between 1 kPa and 36 kPa.
Clay minerals were dominantly hydrated halloysite. Scanning electron microscopy indicated that clay morphology was in the form of hollow tubes, spheres, plates, and platy vermiforms ('books'). Tubes and spheres represent characteristic forms of halloysite in soils, plates are less common, and books have never previously been observed. Hence, these books represent a new morphology for halloysite. Individual plates in each of the books appear to show structural Fe enrichment (~5.2 %). This enrichment indicates that Fe had replaced Al in octahedral positions reducing the mismatch with the tetrahedral sheet, lessening layer curvature and thus generating flat plates.
All microfabrics were continuous with larger sand and silt grains supported in a background of clay minerals. Microfabrics ranged from extremely open with components being loosely packed to those which were dense and tightly packed. A feature common to all structural types was an abundance of extremely small pores (lt; 20 μm) which are capable of tightly retaining water. The loosely packed microfabrics had void ratios that allowed moisture content to exceed liquid limits, producing a liquidity index gt; 1. These open microfabrics are probably a result of quick burial by subsequent pyroclastic beds; hence weathering to clays occurred as a process of subsurface diagenesis. Dense microfabrics with low void ratios and high liquid limits did not have liquidity indexes gt; 1. These dense microfabrics arose as a result of the deposits being at, or near, the land surface for a considerable time, thus allowing strong pedogenic processes to occur, which promoted clay formation and clay migration (illuviation) and reduced void ratios.
Liquidity index was a major control on remoulded strength and sensitivity. Liquidity index is controlled by clay type and content, void ratio, and natural moisture content. When remoulded, structures with natural moisture contents exceeding the liquid limit release a large amount of water, which both dilutes the plasticity of binding clays and supports grains and broken aggregates of clay, allowing the material to flow. The development of sensitivity with low remoulded strength requires a number of factors. These include: a void ratio that is sufficiently high to allow natural moisture content to exceed the liquid limit; the presence of halloysite, which encourages samples to retain a coherent structure when saturated and to ensure the liquid limit remains sufficiently low so that it can be exceeded by natural moisture content; and a saturated environment, which ensures the liquid limit is exceeded
Clay micromechanics: experimental challenges and perspectives
No full textThe importance of physico-chemical processes at the particle scale for the engineering scale behaviour of fine-grained geomaterials is undisputed. Yet, despite great advances in the discipline, experimental evidence that fully resolves the clay micromechanics i.e. linking the evolving microstructure and interparticle actions under loading, is lacking. This paper will discuss the challenges ahead in quantifying the evolving kinematics and interparticle interactions of finegrained geomaterials. As such, the current limitations, and the potential opportunities of experimental methodologies for manipulating, monitoring and (post-mortem) analysing fine-grained materials at the particle scale will be discussed. In addition to the need of integrating multiple experimental techniques that span several length scales and modalities, the critical role of advanced data reduction and analysis is highlighted, as required for a measurement as opposed to qualitative observation. Throughout the paper, the link between experimental clay micromechanics and modelling will be discussed.Geo-engineerin
The prediction and back analysis of excavation behaviour in Oxford Clay.
No full textThe work described in this thesis involved the prediction and back-analysis of ground
movements and pore water pressures around a temporary excavation, lOm deep, 105m long and
35m wide (50m long and lOm wide at its base) in the heavily overconsolidated Oxford Clay.
An experimental programme was carried out which was designed to investigate the nonlinearity and the anisotropy in the soil's response. A series of computer controlled triaxial stress
path tests were carried out on specimens of Oxford Clay trimmed from block samples. The
initial anisotropic stress state resulted in a highly stress path dependent stiffness, and the stressstrain behaviour was closely linked to the time at which the specimen had been held at constant
stress prior to a change in loading.
In the triaxial apparatus, shear wave propagation tests using square wave input functions into
bender element apparatus were significantly affected by near-field effects and by additional
wave components. Tests carried out using sine wave inputs provided a far more consistent
output allowing correlation analyses and easier visual identification of the travelling shear
wave. The shear modulus of the soil at very small strains could then be determined.
A stress path dependent, non-linear, cross-anisotropic elastic model was developed and
implemented into the finite element program CRISP. A genuine prediction of the Elstow
excavation was carried out while the instrumentation data from the site investigation were
temporarily withheld. It was found that the horizontal displacements were modelled
satisfactorily but that the vertical displacements were in error by as much as 2 or 3 times. This
discrepancy was attributed to volumetric changes suggested by the instrumentation data. A
parametric analysis was carried out in which the effects of the initial stress state, the degree of
anisotropy, and the degree of non-linearity were investigated. This showed that although it was
possible to improve the accuracy of the prediction locally, it was not possible to improve on the
overall pattern of behaviour predicted by the first non-linear cross-anisotropic analysis
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