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11.
Naturally fractured mine pillars provide an excellent example of the importance of accurately determining rock mass strength.
Failure in slender pillars is predominantly controlled by naturally occurring discontinuities, their influence diminishing
with increasing pillar width, with wider pillars failing through a combination of brittle and shearing processes. To accurately
simulate this behaviour by numerical modelling, the current analysis incorporates a more realistic representation of the mechanical
behaviour of discrete fracture systems. This involves realistic simulation and representation of fracture networks, either
as individual entities or as a collective system of fracture sets, or a combination of both. By using an integrated finite
element/discrete element–discrete fracture network approach it is possible to study the failure of rock masses in tension
and compression, along both existing pre-existing fractures and through intact rock bridges, and incorporating complex kinematic
mechanisms. The proposed modelling approach fully captures the anisotropic and inhomogeneous effects of natural jointing and
is considered to be more realistic than methods relying solely on continuum or discontinuum representation. The paper concludes
with a discussion on the development of synthetic rock mass properties, with the intention of providing a more robust link
between rock mass strength and rock mass classification systems. 相似文献
12.
Structural and engineering geology of the East Gate Landslide, Purcell Mountains, British Columbia, Canada 总被引：3，自引：0，他引：3
The East Gate Landslide is a prehistoric landslide that was reactivated in January 1997. The slope failure took place in the lower greenschist metasedimentary units of the Precambrian Horsethief Creek Group. The Grizzly Creek Thrust is a regional overturned fault that coincides with the location of the headscarp of the East Gate Landslide. Four discontinuity sets were recognised from detailed engineering geological mapping of the headscarp and surrounding area. The main scarp of the section reactivated in 1997 was sub-divided into three structural domains based on its position within the landslide, lithology, and orientation of the discontinuity sets. Limit-equilibrium techniques, finite-difference (FLAC) and distinct-element (UDEC) codes were used to investigate the failure mechanism of the 1997 event. The results of the field observations and numerical models suggest that the 1997 failure involved a complex mechanism incorporating components of rock-slumping, bi-planar, and pseudo-circular failure that was controlled by both the orientation of the discontinuity sets and reduced rock-mass quality due to tectonic deformation. 相似文献
13.
Elevated nutrients have the potential to disrupt reproduction in scleractinian corals, with consequent impacts on population dynamics. Reproduction in broadcast spawning (Montipora capitata) and brooding (Pocillopora damicornis) species was assessed following exposure to elevated ammonium in a microcosm experiment. Planulation in P. damicornis ceased following 4 months of ammonium exposure and did not recover until 3 months after termination of nutrient enrichment. Larval settlement and survivorship were not affected by ammonium enrichment. Few significant changes were found for reproductive parameters of M. capitata. There was a significant but small decrease in egg size (430 microm in control eggs to 408 microm in eggs from ammonium enrichment treatments), but no differences in total fecundity or fertilization success. This may be related to the presence of zooxanthellae in the eggs of M. capitata, in contrast to changes in reproduction previously reported in Acropora species, whose eggs do not contain zooxanthellae. 相似文献
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15.
Marine fish discarding has become a contentious environmental issue, but little attention has been paid to the moral grievances that sometimes underlie discarding practices. This article explores such a moral grievance through a case study of the under-10 m fishery in Sussex, England, where discarding of cod (Gadus morhua) has become a highly charged issue, skippers blaming it on unjust quota allocations. The moral claim to a greater quota allocation is analysed using two conceptions of distributive justice, entitlement and desert. The conclusion reached is that the under-10 m fleet’s entitlement arguments for a higher quota are weaker than their desert arguments, but that entitlement arguments weigh more heavily than desert arguments with government when it allocates quota. 相似文献
16.
Evaluating Kinematic Controls on Planar Translational Slope Failure Mechanisms Using Three-Dimensional Distinct Element Modelling 总被引：1，自引：0，他引：1
This paper investigates the importance of kinematic release mechanisms on planar translational slope failure using three-dimensional distinct element codes. The importance of the dip and dip direction of the rear, basal and lateral release surfaces and their influence on failure mechanism, dilation, and the development of step-path failures is illustrated. The three-dimensional block shape and volume of the unstable rock masses simulated with the different discontinuity set geometries are characterized. Two assumed three-dimensional slope models are investigated in order to assess the importance of varying kinematic confinement/release mechanisms. These two assumed boundary conditions are shown to be critical in the development of asymmetrical rock mass deformation patterns. Scale effects due to the block size and discontinuity persistence are shown to control the calculated displacement and failure mechanisms. The numerical modelling results are also demonstrated to be sensitive to the assumed normal and shear stiffness of the discontinuities. The influence of the factors investigated on the failure of a single rock block versus a rock mass are compared and discussed. 相似文献
17.
The natural phytoplankton was monitored by means of fluorimetric equipment in Vostok Bay of the Sea of Japan. A gradual increase
in the microalgae abundance was revealed in the course of the main water current, which enters the bay and leaves it. The
continuous registration of chlorophyll fluorescence at a fixed point in the bay indicates the significant microscale variation
of the abundance and functional state of the phytoplankton. 相似文献
18.
Vulnerability of coastal communities to key impacts of climate change on coral reef fisheries 总被引：1，自引：0，他引：1
J.E. Cinner T.R. McClanahan N.A.J. Graham T.M. Daw J. Maina S.M. Stead A. Wamukota K. Brown Ö. Bodin 《Global Environmental Change》2012,22(1):12-20
Coral reefs support the livelihood of millions of people especially those engaged in marine fisheries activities. Coral reefs are highly vulnerable to climate change induced stresses that have led to substantial coral mortality over large spatial scales. Such climate change impacts have the potential to lead to declines in marine fish production and compromise the livelihoods of fisheries dependent communities. Yet few studies have examined social vulnerability in the context of changes specific to coral reef ecosystems. In this paper, we examine three dimensions of vulnerability (exposure, sensitivity, and adaptive capacity) of 29 coastal communities across five western Indian Ocean countries to the impacts of coral bleaching on fishery returns. A key contribution is the development of a novel, network-based approach to examining sensitivity to changes in the fishery that incorporates linkages between fishery and non-fishery occupations. We find that key sources of vulnerability differ considerably within and between the five countries. Our approach allows the visualization of how these dimensions of vulnerability differ from site to site, providing important insights into the types of nuanced policy interventions that may help to reduce vulnerability at a specific location. To complement this, we develop framework of policy actions thought to reduce different aspects of vulnerability at varying spatial and temporal scales. Although our results are specific to reef fisheries impacts from coral bleaching, this approach provides a framework for other types of threats and different social-ecological systems more broadly. 相似文献
19.
The recent assessment of the Mitchell Creek Landslide (MCL) in northern British Columbia is a good case history of engineering geomorphological analysis of a large landslide. It was completed using historic aerial photographs, with approximately 20-year time intervals dating back to the mid-twentieth century and field investigations completed between 2008 and 2014. The large bedrock slide initiated between 1956 and 1972 and continues to experience ongoing annual movements. Significant glacial downwasting and retreat has been observed in the photographic record, and it is hypothesized that alpine glaciation has contributed to development of the MCL. This paper documents four aspects of the engineering geomorphological assessment completed at the MCL: (i) topographic evolution, (ii) slope morphology, (iii) deformation features, and (iv) displacement behavior. Four distinct geomorphic zones have been defined at the MCL based on these analyses, controlled by different failure mechanisms. The extents of these zones have changed little over the documented history of the landslide, and rates of movement estimated from aerial photography have been consistent over the last 60 years. Retreat of the Mitchell Valley Glacier appears to have played an important role in landslide initiation, as the ice mass receded the kinematic freedom of the slope increased. This study of the initiation and development of the MCL demonstrates the capabilities of a multi-faceted approach to engineering geomorphology. The combination of historical aerial photographs with digital photogrammetric modeling and point cloud analysis techniques, and geomorphological mapping, allows for development of a robust understanding of landslide behavior. 相似文献
20.
Rare Earth Element Determination in Olivine by Laser Ablation‐Quadrupole‐ICP‐MS: An Analytical Strategy and Applications 
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下载免费PDF全文 Clare V. Stead Emma L. Tomlinson Balz S. Kamber Michael G. Babechuk Cora A. McKenna 《Geostandards and Geoanalytical Research》2017,41(2):197-212
Olivine offers huge, largely untapped, potential for improving our understanding of magmatic and metasomatic processes. In particular, a wealth of information is contained in rare earth element (REE) mass fractions, which are well studied in other minerals. However, REE data for olivine are scarce, reflecting the difficulty associated with determining mass fractions in the low ng g?1 range and with controlling the effects of LREE contamination. We report an analytical procedure for measuring REEs in olivine using laser ablation quadrupole‐ICP‐MS that achieved limits of determination (LOD) at sub‐ng g?1 levels and biases of ~ 5–10%. Empirical partition coefficients (D values) calculated using the new olivine compositions agree with experimental values, indicating that the measured REEs are structurally bound in the olivine crystal lattice, rather than residing in micro‐inclusions. We conducted an initial survey of REE contents of olivine from mantle, metamorphic, magmatic and meteorite samples. REE mass fractions vary from 0.1 to double‐digit ng g?1 levels. Heavy REEs vary from low mass fractions in meteoritic samples, through variably enriched peridotitic olivine to high mass fractions in magmatic olivines, with fayalitic olivines showing the highest levels. The variable enrichment in HREEs demonstrates that olivine REE patterns have petrological utility. 相似文献