Assessment of three interface elements and modification of the interface element in CRISP90

To model the interaction between a buried pipeline and the surrounding soil either special interface elements or thin conventional elements may be used. In this study the CRISP90 interface element, the DRCRISP interface element and a conventional 8-noded quadrilateral element have been examined and their behaviour compared for a variety of loading conditions. Initial studies reveal that all these elements have limitations and are only suitable for monotonic loading and situations where tensile conditions do not occur across the interface. In the light of these findings the CRISP90 interface element has been modified by introducing a limiting adhesive strength in the normal direction; a flag system has also been introduced to track the various conditions of separation and closure for any gap that is formed. The results of single element and other benchmark tests show that the modified element can satisfactorily model the different modes of deformation relevant to soil–structure interface problems.     

Rainfall trend and its implications for water resource management within the Yarra River catchment,Australia

Rainfall is the key climatic variable that governs the regional hydrologic cycle and availability of water resources. Recent studies have analysed the changes in rainfall patterns at global as well as regional scales in Australia. Recent studies have also suggested that any analysis of hydroclimatic variables should be performed at the local scale rather than at a large or global scale because the trends and their effects may be different from one location to the other. Because no studies were found specific to the Yarra River catchment, which is an important catchment in Victoria, Australia, this study performs a spatiotemporal trend analysis on long‐term rainfall records at 15 measuring stations within the catchment. The Mann–Kendall test was used to detect trends, and Sen's slope estimator was used to calculate the slopes in both monthly and annual rainfall. Moreover, a cumulative summation technique was used to identify the trend beginning year, and prewhitening criteria were tested to check for autocorrelation in the data. The results showed that the monthly rainfall has generally decreasing trends except in January and June. Significant decreasing rainfall trends were observed in May (among the autumn months of March, April and May) at most stations and also in some other months at several stations. A decreasing trend was also observed in the annual rainfall at all stations. This study indicates that there has been a consistent reduction in rainfall over the catchment, both spatially and temporally over the past 50 years, which will have important implications for the future management of water resources. Copyright © 2012 John Wiley & Sons, Ltd.     

A study of polychlorinated dibenzo-p-dioxins/furans (PCDD/Fs) and polychlorinated biphenyls (PCBs) in the livestock waste compost of Hong Kong, PR China

Composting is one of the waste disposal methods adopted for disposal of livestock waste in Hong Kong. The composting livestock waste normally undergoes 6-8 weeks fermentation, followed by 16-20 weeks maturation. The matured compost is sold as soil conditioner in the local market. In 2006, feedstock material and a time-series of compost samples were collected throughout the fermentation and maturation process from the Sha Ling Composting Plant in the New Territories. The feedstock material and compost samples were analyzed for contents of three unintentional persistent organic pollutants (POPs), i.e. dioxins/furans, dioxin-like PCBs and total PCBs. These POPs are unintentionally produced by-products of chemical industrial processes and combustion processes. Selected heavy metals were also analyzed, which served as conservative tracers to determine potential mass loss during the composting process. Levels of contamination by these POPs were found to be low in the matured compost for sale. The mean concentrations (lower-upper bound) of total dioxins/furans, total dioxin-like PCBs and total PCBs were 2.01-2.05 ng I-TEQ/kg dw, 0.04-0.05 ng WHO-TEQ/kg dw and 1.55-1.55 microg/kg dw, respectively. Progressively elevated levels of these POPs were observed in the compost samples during the fermentation process. Analysis of the congener profiles revealed that the heptaCDD and octaCDD were the main contributors to the observed increase in dioxin/furan content. The possible sources of dioxins/furans in the compost were discussed. The study results established a local dioxins/furans emission factor specific to the trade and provided a better estimate of the annual dioxins/furans emission for the livestock waste composting activity in Hong Kong.     

华南花岗岩残积土红土化程度的地带性与香港该类土不发育的原因

从华南花岗岩残积土红土化程度的地域变化规律出发 ,通过香港与华南沿海各地花岗岩残积土的化学成分及红土化指标对比 ,作者发现香港花岗岩残积土无论厚度、类型 ,还是红土化程度都具有与所处气候环境不协调的特点。文章进一步讨论了香港花岗岩残积土不发育的原因和对工程性质的影响.     

Effects of the roots of Cynodon dactylon and Schefflera heptaphylla on water infiltration rate and soil hydraulic conductivity

Water infiltration rate and hydraulic conductivity in vegetated soil are two vital hydrological parameters for agriculturists to determine availability of soil moisture for assessing crop growths and yields, and also for engineers to carry out stability calculations of vegetated slopes. However, any effects of roots on these two parameters are not well‐understood. This study aims to quantify the effects of a grass species, Cynodon dactylon, and a tree species, Schefflera heptaphylla, on infiltration rate and hydraulic conductivity in relation to their root characteristics and suction responses. The two selected species are commonly used for ecological restoration and rehabilitation in many parts of the world and South China, respectively. A series of in‐situ double‐ring infiltration tests was conducted during a wet summer, while the responses of soil suction were monitored by tensiometers. When compared to bare soil, the vegetated soil has lower infiltration rate and hydraulic conductivity. This results in at least 50% higher suction retained in the vegetated soil. It is revealed that the effects of root‐water uptake by the selected species on suction were insignificant because of the small evapotranspiration (<0.2 mm) when the tests were conducted under the wet climate. There appears to have no significant difference (less than 10%) of infiltration rates, hydraulic conductivity and suction retained between the grass‐covered and the tree‐covered soil. However, the grass and tree species having deeper root depth and greater Root Area Index (RAI) retained higher suction. Copyright © 2015 John Wiley & Sons, Ltd.     

Influence of structure on the compression and shear behaviour of a saturated lateritic clay

Lateritic clay is well recognized to contain significant amount of iron and aluminium oxides (sesquioxide). These oxides enhance the formation of soil aggregates which would greatly affect soil structure. So far, no study has been carried out purposely to investigate the influence of aggregate-dependent structure on the mechanical behaviour of the lateritic clay. In this study, structure effects on the compression and shear behaviour of a saturated lateritic clay were studied. Intact, recompacted and reconstituted specimens were studied through oedometer, isotropic compression and consolidated undrained shear tests. Microstructure of these specimens was determined using the mercury intrusion porosimetry and scanning electron microscopy (SEM) techniques and then used to explain the observed behaviour. It was found that the compressibility of recompacted/reconstituted specimens was about 90% larger than intact specimen. Different from soft clay, the influence of microstructure does not show an obvious reduction in compressibility after yielding. The peak shear strength of intact specimen was about 100% higher than those of reconstituted/recompacted specimens. The significant difference in compression and shear behaviour is mainly because the aggregates of intact specimen were about 90% larger than those of reconstituted/recompacted specimens, as revealed by the SEM results. As a result, particle contacts forming the force chain were therefore larger in the intact specimen. The intact specimen therefore became less compressible and more dilative.

     

Geochemistry of Lake Sediments as a Record of Environmental Change in a High Arctic Watershed

A 1.93 m long sediment core was obtained from Fish Lake, Truelove Lowland, Devon Island, Nunavut, Canada. Multivariate statistical techniques using a wide range of chemical variables successfully reconstructed the late Holocene history of the Fish Lake watershed. Factor analysis identified six geomorphic mechanisms controlling the formation of sediments. Cluster analysis produced a grouping of core segments and discriminant analysis confirmed that 100% of the samples were correctly classified. The results indicated that the environmental history of the Fish Lake watershed in the past 6500 years can be divided into five phases. These are 6500-5700 years BP, 5700-1700 years BP, 1700-1000 years BP, 1000-600 years BP and 600 years BP to the present. In the Fish Lake watershed, during its time as a terrestrial system, the interactions of erosion, weathering, leaching, soil development, vegetation succession and climatic change have shaped the surrounding landscape as well as determined the evolution of the lake.     

Pesticides in Sediments From Queensland Irrigation Channels and Drains

Pesticide concentration in sediment from irrigation areas can provide information required to assess exposure and fate of these chemicals in freshwater ecosystems and their likely impacts to the marine environment. In this study, 103 sediment samples collected from irrigation channels and drains in 11 agricultural areas of Queensland were analysed for a series of past and presently used pesticides including various organochlorines, synthetic pyrethroids, benzoyl ureas, triazines and organophosphates. The most often detected compounds were endosulphans (, β and/or endosulphan sulphate) which were detectable in 78 of the 103 samples and levels ranged from below the limit of quantification (0.1 ng g⁻¹ dw) up to 840 ng g⁻¹ dw. DDT and its metabolites were the second most often detected pesticide investigated (74 of the 103 samples) with concentrations up to 240 ng g⁻¹ dw of ∑DDTs. Mean ∑endosulphan and ∑DDT concentrations were 1–2 orders of magnitude higher in sediments from the irrigation areas which are dominated by cotton cultivation compared to those which are dominated by sugarcane cultivation. In contrast to these insecticides, the herbicides diuron, atrazine and ametryn were the compounds which were most often detected in sediments from irrigation drains in sugarcane areas with maximum concentrations in areas of 120, 70 and 130 ng g⁻¹ dw, respectively. In particular during flood events, when light is limiting, transport of these photosynthesis inhibiting herbicides from the sugarcane cultivation areas to the marine environment may result in additional stress of marine plants.     

Smooth particle hydrodynamics modelling of liquid-sediment system and coastal wave breaker

Ocean Dynamics - In this paper, a two-phase coastal liquid-sediment system and a wave breaker were numerically simulated using a particle-based smooth particle hydrodynamics (SPH). To verify the...     

Initial Fe/O Enhancements in Large, Gradual, Solar Energetic Particle Events: Observations from Wind and Ulysses

Shocks driven by fast coronal mass ejections (CMEs) are the dominant particle accelerators in large, “gradual” solar energetic particle (SEP) events. In these events, the event-integrated value of the iron-to-oxygen ratio (Fe/O) is typically ～?0.1, at least at energies of a few MeV/nucleon. However, at the start of some gradual events, when intensities are low and growing, initially Fe/O is ～?1. This value is also characteristic of small, “impulsive” SEP events, in which particle acceleration is due to magnetic reconnection. These observations suggested that SEPs in gradual events also include a direct contribution from the flare that accompanied the CME launch. If correct, this interpretation is of critical importance: it indicates a clear path to interplanetary space for particles from the reconnection region beneath the CME. A key issue for the flare origin is “magnetic connectedness”, i.e., proximity of the flare site to the solar footpoint of the observer’s magnetic field line. We present two large gradual events observed in 2001 by Wind at L1 and by Ulysses, when it was located at >?60^° heliolatitude and beyond 1.6 AU. In these events, transient Fe/O enhancements at 5?–?10 MeV/nucleon were seen at both spacecraft, even though one or both is not “well-connected” to the flare. These observations demonstrate that an initial Fe/O enhancement cannot be cited as evidence for a direct flare component. Instead, initial Fe/O enhancements are better understood as a transport effect, driven by the different mass-to-charge ratios of Fe and O. We further demonstrate that the time-constant of the roughly exponential decay of the Fe/O ratio scales as R ², where R is the observer’s radial distance from the Sun. This behavior is consistent with radial diffusion. These observations thus also provide a potential constraint on models in which SEPs reach high heliolatitudes by cross-field diffusion.