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551.
Summary Left in place pillars of abandoned mines are subject to weathering (e.g action of water, bacteria) that degrades their mechanical
strength and eventually leads to collapse. A simple weathering model is proposed, that is governed by two parameters: the
rate of progression of weathered front and the rate of degradation of the compressive strength with time. Both plane strain
and axisymmetric analyses are performed and closed form solutions of the variation with time of the bearing capacity of the
pillar are given. Experimental data of the tests conducted on gypsum and anhydrite specimens attacked by water are presented.
It is shown that in order to fit the experimental data a third parameter must be introduced. New closed form solutions are
given and the data are used for estimating the time to failure of abandoned gypsum mines in Northern Italy.
Authors’ address: Dr. Riccardo Castellanza, Research Assistant, Department of Structural Engineering, Milan University of
Technology (Politecnico), Piazza Leonardo da Vinci 32, 20133 Milan, Italy 相似文献
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Jos M. Marques Paula M. Carreira Maria Rosrio Carvalho Maria J. Matias Fraser E. Goff Maria J. Basto Rui C. Graa Luís Aires-Barros Luís Rocha 《Applied Geochemistry》2008,23(12):3278-3289
This paper reviews the geochemical, isotopic (2H, 18O, 13C, 3H and 14C) and numerical modelling approaches to evaluate possible geological sources of the high pH (11.5)/Na–Cl/Ca–OH mineral waters from the Cabeço de Vide region (Central-Portugal). Water–rock interaction studies have greatly contributed to a conceptual hydrogeological circulation model of the Cabeço de Vide mineral waters, which was corroborated by numerical modelling approaches. The local shallow groundwaters belong to the Mg–HCO3 type, and are derived by interaction with the local serpentinized rocks. At depth, these type waters evolve into the high pH/Na–Cl/Ca–OH mineral waters of Cabeço de Vide spas, issuing from the intrusive contact between mafic/ultramafic rocks and an older carbonate sequence. The Cabeço de Vide mineral waters are supersaturated with respect to serpentine indicating that they may cause serpentinization. Magnesium silicate phases (brucite and serpentine) seem to control Mg concentrations in Cabeço de Vide mineral waters. Similar δ2H and δ18O suggest a common meteoric origin and that the Mg–HCO3 type waters have evolved towards Cabeço de Vide mineral waters. The reaction path simulations show that the progressive evolution of the Ca–HCO3 to Mg–HCO3 waters can be attributed to the interaction of meteoric waters with serpentinites. The sequential dissolution at CO2 (g) closed system conditions leads to the precipitation of calcite, magnesite, amorphous silica, chrysotile and brucite, indicating that the waters would be responsible for the serpentinization of fresh ultramafic rocks (dunites) present at depth. The apparent age of Cabeço de Vide mineral waters was determined as 2790 ± 40 a BP, on the basis of 14C and 13C values, which is in agreement with the 3H concentrations being below the detection limit. 相似文献
555.
T. V. Klets 《Stratigraphy and Geological Correlation》2008,16(5):467-489
Geographic differentiation of conodontophorids between northern and southern latitudes commenced in the Triassic since the early Induan. Cosmopolitan long-lived genera of predominantly smooth morphotypes without sculpturing were characteristic of high-latitude basins of the Panboreal Superrealm. Since the early Olenekian until the Carnian inclusive, this superrealm consisted of the Siberian Realm that extended over Northeast Asia and the Canada-Svalbard Realm that included the Svalbard Archipelago and northern regions of Canada. Throughout the Triassic period, conodontophorids characteristic of the Tethys-Panthalassa Superrealm spanning the Tethys and low-latitude zones of the Pacific were highly endemic, very diverse in taxonomic aspect, having well-developed sculpturing and tempos of morphological transformations. Distinctions between the Early-Middle Triassic conodontophorids from northern and southern zones were not as great as afterward, and their impoverished assemblages from southern Tethyan basins were close in some respects to the Boreal ones. Their habitat basins of that time can be grouped into the Mediterranean-Pacific and India-Pakistan realms. Hence, the extent of geographic differentiation of conodontophorids was not constant and gradually grew, as their taxonomic diversity was reducing in northern basins but relatively increasing in southern ones. The Panboreal e Tethys-Panthalassa superrealms of conodontophorids, which are most clearly recognizable, are close to first-rank paleobiochores (superrealms) established earlier for ammonoids and bivalve mollusks. Main factor that controlled geographic differentiation of Triassic conodontophorids was climatic zoning. Initially lower diversity of southern Tethyan assemblages points probably to relatively cooler water regime in the peri-Gondwanan part of the Tethys. The established patterns in geographic distribution of conodontophorids characterize most likely the real trend of their differentiation and evolution, i.e., the distribution area contraction prior to complete extinction at the end of the Triassic 相似文献
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Feasibility of pre-earthquake strengthening of buildings based on cost-benefit and life-cycle cost analysis, with the aid of fragility curves 总被引:1,自引:1,他引:0
There are two fundamental questions this article aims to deal with. First, whether a pre-earthquake strengthening of a large
and heterogeneous building stock (the emphasis here is on building types common in S. Europe), is economically feasible or
not, and second what is the optimal retrofit level for mitigating the seismic risk. To this purpose contemporary decision
making tools, namely cost-benefit and life-cycle cost analyses, are tailored to the needs of the present study, and implemented
with the aid of an ad-hoc developed new software application (COBE06). A method for estimating the reduction in structural
vulnerability due to retrofit is proposed, as well as a methodology to determine the optimum retrofit level using the fragility
curve approach. Finally, the proposed methodology is used in a pilot application that concerns the city of Thessaloniki, and
results are drawn for the feasibility of strengthening the reinforced concrete building stock in this city. 相似文献
560.
David P. Bacon Nash’at N. Ahmad Thomas J. Dunn Michael C. Monteith Ananthakrishna Sarma 《Natural Hazards》2008,44(3):317-327
By definition, a crisis is a situation that requires assistance to be managed. Hence, response to a crisis involves the merging
of local and non-local emergency response personnel. In this situation, it is critical that each participant: (1) know the
roles and responsibilities of each of the other participants; (2) know the capabilities of each of the participants; and (3)
have a common basis for action. For many types of natural disasters, this entails having a common operational picture of the unfolding events, including detailed information on the weather, both current and forecasted, that may impact on either
the emergency itself or on response activities. The Consequences Assessment Tool Set (CATS) is a comprehensive package of
hazard prediction models and casualty and damage assessment tools that provides a linkage between a modeled or observed effect
and the attendant consequences for populations, infrastructure, and resources, and, hence, provides the common operational
picture for emergency response. The Operational Multiscale Environment model with Grid Adaptivity (OMEGA) is an atmospheric
simulation system that links the latest methods in computational fluid dynamics and high-resolution gridding technologies
with numerical weather prediction to provide specific weather analysis and forecast capability that can be merged into the
geographic information system framework of CATS. This paper documents the problem of emergency response as an end-to-end system
and presents the integrated CATS–OMEGA system as a prototype of such a system that has been used successfully in a number
of different situations. 相似文献