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51.
Knowledge of transport processes of heat and moisture in soils of arid zones is vital to understanding the environmental and economic impacts of many activities: agriculture, waste disposal, geoenvironmental practices and earth sciences. Through extensive review and study on the different aspects of coupled transfer processes in swelling porous media, a general mathematical model for coupled heat, moisture, air flow and deformation problems in clayey soils is proposed in a consistent and unified manner. The model is characterized by the presence of a deformable solid matrix filled with two fluid phases (liquid water and air). In the proposed model, both pore water and air transfers are assumed to be governed by the generalized Darcy’s law. Fully coupled, non-linear partial differential equations are established and then solved by using a Galerkin weighted residual approach in space domain and an implicit integrating scheme in time domain. The obtained model has been finally validated by means of some case tests for the prediction of the thermo-hydro-mechanical behaviour of unsaturated swelling soils. The calculated relative errors between experimental and numerical results are 3% for temperature and 7% for stresses. Consequently, the developed numerical model predicts satisfactory results, compared to experimental test measures. The model is applicable to two-dimensional problems with various initial and boundary conditions; non-linear soil parameters can be easily included in this model.  相似文献   
52.
Madagascar is a complex ‘biodiversity hotspot’ with a rapidly dwindling biota. The Late Quaternary subfossil record includes many extinct species whose loss is attributed to natural climate change and human impacts. Investigation of the chronology of these events is challenging because few localities document pre‐Holocene communities not impacted by humans. Caves with extinct lemurs of large body size comprise some of Madagascar's richest subfossil sites, but provide only a limited window into the island's past. Open highland sites may have fewer primates, but may better document other megafauna, and allow the analysis of the role of the Central Highlands as refugia and as corridors for the dispersal of vertebrates before and after human arrival. Here we present a new subfossil site, Tsaramody (Sambaina basin, Central Madagascar), a high‐altitude wetland area that preserves a diverse late glacial and postglacial vertebrate community. Tsaramody bears testimony to fluctuations in the highland flora during the transition from glacial to postglacial conditions, and the composition of a highland vertebrate community before humans arrived. We compare its biota to those of other sites to begin to document the decline and disappearance of megafauna from some of Madagascar's open ecosystems – wetlands dominated by hippopotamuses and crocodylians. © 2019 John Wiley & Sons, Ltd.  相似文献   
53.
The 8-km2 Morcille catchment, which is a sub-catchment of the 150-km2 Ardières catchment in the Beaujolais region of France, is one of the first sites in Europe where research has been conducted on surface water contamination by pesticides. A consolidated hydrological and chemical dataset has been set up with data collected since 2002 on the Morcille River and since 2011 on the Ardières River. Additional data on the ecotoxicological and ecological impacts of pesticides on aquatic microbial communities and macroinvertebrates has also been recorded in both rivers since 2005. The ‘Site Atelier Ardières-Morcille Dataset’ described here combines rainfall and stream water height measurements at gauged stations with concentrations of two trace elements and nine pesticides (mainly herbicides, fungicides and some of their metabolites) in both the Ardières and Morcille rivers. All contaminant concentration data showed spatial and temporal variability in water quality associated with pesticide use and rainfall patterns. This long-term monitoring framework made it possible to estimate the persistence of two herbicides (diuron and norflurazon) after legislation banning them. It took 4 years for diuron and more than 10 years for norflurazon concentrations to fall below 0.1 μg/L. Concurrent biological data showed a gradient of impacts consistent with chemical anthropogenic pressure, and rapid recovery of phototrophic microbial communities after the diuron ban. Finally, monitoring data on pesticide transport in a grassed strip set on a slope of the Morcille catchment confirmed that vegetative filter strips can effectively reduce diuron fluxes in surface runoff (>80% abatement) and infiltration water (>70% abatement). The full dataset offers a valuable resource for the validation of hydrological models and the development of global approaches to better understand the pressure–transport–exposure–impact chain and aquatic community resilience at the small catchment scale.  相似文献   
54.
Greater Cairo and the Nile Delta are considered very important, high-density population areas. The subject of the research work is dealing with recent crustal movements and its relation to seismicity and tectonics setting. A Global Positioning System (GPS) network consisting of 11 benchmarks covering Greater Cairo and the southern part of the Nile Delta was established in 1996. Different campaigns surveyed the network. In this study, we used ten measurements collected during the period from 2004 to 2010. The data were processed using Bernese 5.0 software to derive velocity vectors and principal components of crustal strains. The horizontal velocity varies in average between 3 and 6 mm per year across the network. Rate of the accumulated strains in the southern part of Greater Cairo varies from low to moderate. The low strain rates and low level of earthquakes occurrence in the present interval in the Nile Delta area indicated that the rate of the deformation in this area is small. The result from coupling GPS and seismic data indicates that the southern part of the area is seismo-active area when compared with the other parts in the network areas. The paper gives information about the present state of the recent crustal movements within Greater Cairo area to understand the geodynamics of that area. This study is an attempt to build a basis for further development of seismic catastrophic risk management models to reduce a risk of large catastrophic losses within the important area.  相似文献   
55.
Climate change caused by anthropogenic activities has generated a variety of research focusing on investigating the past climate, predicting the future climate and quantifying the change in climate extreme events by using different climate models. Climate extreme events are valuable to evaluate the potential impact of climate change on human activities, agriculture and economy and are also useful to monitor the climate change on global scale. Here, a Regional Climate Model (RCM) simulation is used to study the future variations in the temperature extreme indices, particularly change in frequency of warm and cold spells duration over Pakistan. The analyses are done on the basis of simulating two 30 years simulations with the Hadley Center’s RCM PRECIS, at a horizontal resolution of 50 km. Simulation for the period 1961–1990 represents the recent climate and simulation for the period 2071–2100 represents the future climate. These simulations are driven by lateral boundary conditions from HadAM3P GCM of Hadley centre UK. For the validation of model, observed mean, maximum and minimum temperatures for the period 1961–1990 at all the available stations in Pakistan are first averaged and are then compared with the PRECIS averaged grid-box data. Also the observed monthly gridded data set of Climate Research Unit (UK) data is used to validate the model. Temperature indices in the base period as well as in future are then calculated and the corresponding change is observed. Percentile based spatial change of temperature shows that in summer, increase in daily minimum temperature is more as compared to the increase of daily maximum temperature whereas in winter, the change in maximum temperature is high. The occurrence of annual cold spells shows significantly decreasing trend while for warm spells there is slight increasing trend over Pakistan.  相似文献   
56.
57.
The Middle and Upper Jurassic Bathonian-Oxfordian shallow-water carbonate rocks from the Paris Basin, France, consist mainly of oolitic and bioclastic limestones that are hydrocarbon reservoirs in the subsurface. Despite a preliminary positive study, these deposits have been considered to be largely remagnetized (Rochette, private communication), and hence not amenable to palaeomagnetic dating. To establish their magnetic mineralogy and test this remagnetization hypothesis, we have used an integrated investigation combining petrographic, geochemical, rock-magnetic and palaeomagnetic measurements on samples extracted from five cores from the Paris Basin and from outcrops in Burgundy. Magnetic minerals in the Bathonian-Oxfordian carbonates include: (1) primary biogenic single-domain magnetite and detrital multi-domain Ti-magnetite and their oxidized form, maghemite; (2) authigenic spheres of magnetite probably related to hydrocarbons; and (3) goethite, either restricted to ferruginous ooid layers or resulting from surficial alteration, notably replacement of pyrite framboids. Rock-magnetic experiments carried out on 68 samples reveal H cr/ H c and M rs/ M s ratios ranging from 1.88 to 5.58 and 0.017 to 0.314, respectively. These values are clearly distinct from diagnostic values for a chemical remagnetization. Pyrrhotite was not identified within these sediments. Moreover, the average H cr/ H c ratio of 3.14 is significantly different from the value of 1.333 for natural pyrrhotite (Dekkers 1988). These results have a direct implication for the preservation of the primary magnetization; consequently, these deposits are selectively amenable for magnetostratigraphic dating and possible regional correlations.  相似文献   
58.
A transversely isotropic thermo-poroelastic constitutive law is developed and implemented in the finite element code Code_Aster (EDF, France). It is then validated using an analytic solution for an inclined borehole in a transversely isotropic medium. A strategy for identifying the parameters of the transversely isotropic thermo-poroelastic model based on an inverse method is proposed on the basis of different laboratory tests. To demonstrate the efficiency and applicability of the model, it is then applied in a three-dimensional numerical model of an underground structure in a parameter sensitivity study. The results of the modelling highlight the importance of accounting for anisotropic phenomena when determining the dimensions of underground facilities. The whole approach is presented in the paper, from model development to application to 3D numerical modelling to an engineering case study.  相似文献   
59.
Zhang  Zhao  Cui  Yu-Jun  Yang  Jinwen  Mokni  Nadia  Ye  Wei-Min  He  Yong 《Acta Geotechnica》2022,17(6):2435-2447
Acta Geotechnica - Bentonite pellet/powder mixture has been considered as a possible sealing material in deep geological disposal of radioactive waste. As the hydro-mechanical behavior of such...  相似文献   
60.
Ying  Zi  Cui  Yu-Jun  Duc  Myriam  Benahmed  Nadia 《Acta Geotechnica》2022,17(9):3731-3745
Acta Geotechnica - In practice, prior to treating a soil with lime, the optimum lime content required for the cation exchange and for providing sufficient Ca2+ and high pH for pozzolanic reaction...  相似文献   
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