A plasticity constitutive model for unsaturated,anisotropic, nonexpansive soils     

Panagiotis Sitarenios  Michael Kavvadas 《国际地质力学数值与分析法杂志》2020,44(4):435-454

The paper describes and evaluates an incremental plasticity constitutive model for unsaturated, anisotropic, nonexpansive soils (CMUA). It is based on the modified Cam-Clay (MCC) model for saturated soils and enhances it by introducing anisotropy (via rotation of the MCC yield surface) and an unsaturated compressibility framework describing a double dependence of compressibility on suction and on the degree of saturation of macroporosity. As the anisotropic and unsaturated features can be activated independently, the model is downwards compatible with the MCC model. The CMUA model can simulate effectively: the dependence of compressibility on the level of developed anisotropy, uniqueness of critical state independent of the initial anisotropy, an evolving compressibility during constant suction compression, and a maximum of collapse. The model uses Bishop's average skeleton stress as its first constitutive variable, favouring its numerical implementation in commercial numerical analysis codes (eg, finite element codes) and a unified treatment of saturated and unsaturated material states.  相似文献   

Present climate trend analysis of the Etesian winds in the Aegean Sea     

Anastasia Poupkou  Prodromos Zanis  Panagiotis Nastos  Dimitrios Papanastasiou  Dimitrios Melas  Kleareti Tourpali  Christos Zerefos 《Theoretical and Applied Climatology》2011,104(3-4):459-472

Wildfires are a common experience in Alaska where, on average, 3,775?km² burn annually. More than 90% of the area consumed occurs in Interior Alaska, where the summers are relatively warm and dry, and the vegetation consists predominantly of spruce, birch, and cottonwood. Summers with above normal temperatures generate an increased amount of convection, resulting in more thunderstorm development and an amplified number of lightning strikes. The resulting dry conditions facilitate the spread of wildfires started by the lightning. Working with a 55-year dataset of wildfires for Alaska, an increase in the annual area burned was observed. Due to climate change, the last three decades have shown to be warmer than the previous decades. Hence, in the first 28?years of the data, two fires were observed with an area burned greater than 10,000?km², while there were four in the last 27?years. Correlations between the Palmer Drought Severity Index and the Canadian Drought Code, against both the number of wildfires and the area burned, gave relatively low but in some cases significant correlation values. Special emphasis is given to the fire season of 2004, in which a record of 27,200?km² burned. These widespread fires were due in large part to the unusual weather situation. Owing to the anticyclonic conditions of the summer of 2004, the composite anomaly of the 500?mb geopotential height showed above normal values. The dominance of a ridge pattern during summer resulted in generally clear skies, high temperatures, and below normal precipitation. Surface observations confirmed this; the summer of 2004 was the warmest and third driest for Interior Alaska in a century of climate observations. The fires lasted throughout the summer and only the snowfalls in September terminated them (at least one regenerated in spring 2005). Smoke from the forest fires affected the air quality. This could be demonstrated by measurements of visibility, fine particle matter, transmissivity of the atmosphere, and CO concentration.  相似文献   

Human-biometeorological assessment of heat waves in Athens   总被引：1，自引：1，他引：0  

Andreas Matzarakis  Panagiotis T. Nastos 《Theoretical and Applied Climatology》2011,105(1-2):99-106

The goal of this study is the analysis of heat waves and their impact on humans, using human biometeorological indices, which are based on the energy balance of the human body. The implications for humans are not only described through the intensity of the heat waves, but also through their duration over consecutive days. Both intensity and duration were analyzed for the Greater Athens Area during the period 1955 to 2001. The analysis was carried out using the daily physiologically equivalent temperature and the daily minimum air temperature. Based on these two parameters, the results showed an increase in the average duration of heat waves. Furthermore, the use of the Gaussian filter revealed the intra-annual variation of heat stress conditions and their relevance to humans. The results could be used for the management of the negative consequences of heat waves in cities suffering from environmental pollution and also for climate impact studies.  相似文献   

Local versus regime convergence regression models: a comparison of two approaches     

Panagiotis Artelaris 《GeoJournal》2015,80(2):263-277

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Geotechnical Engineering and Innovative Support System for Shallow Urban Subway Caverns in Rock,in Confined Built Environment     

Panagiotis Spyridis  Petros Fortsakis  Thomas Schwind 《Geotechnical and Geological Engineering》2018,36(5):2967-2983

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Rodingites from the Veria-Naousa ophiolite (Greece): Mineralogical evolution,metasomatism and petrogenetic processes     

Aikaterini Rogkala  Petros Petrounias  Petros Koutsovitis  Panagiota P. Giannakopoulou  Panagiotis Pomonis  Paraskevi Lampropoulou  Konstantin Hatzipanagiotou 《Chemie der Erde / Geochemistry》2022,82(2):125860

In the Veria-Naousa ophiolitic complex (north Greece), rodingite appears mainly in the form of cross cutting dykes within serpentinised peridotites. It is distinguished into three types, based upon the provenance of its protoliths, textural characteristics, mineralogical assemblages and geochemical affinities. Type I rodigites were derived from boninitic diabasic protoliths and their mineralogical assemblage include garnet + clinopyroxene + chlorite. Type II rodingites were formed at the expense of gabbroic precursors, comprising clinopyroxene + garnet + vesuvianite ± quartz, whereas Type III rodingites replaced diabasic tholeiitic protoliths comprising of garnets + vesuvianite + clinopyroxene + chlorite. Rodingitisation resulted in desilification, decrease of alkalies, Al, Fe, Mg and increase in Ca contents. In Type I rodingites the MREE (middle rare earth elements) and HREE (heavy rare earth elements) were slightly reduced. Type II rodingites experienced LREE (light rare earth elements) depletions, whereas MREE and HREE remained fairly stable. Restricted mobility of REE in Type III rodingites is assigned to shallow-level rodingitisation under decreasing pH.Rodingitisation occured in two distinct stages at fore-arc settings. The first stage occured under mildly oxidising conditions and enhanced CO₂/H₂O ratios. This stage affected the protoliths of all rodingite types. The second rodingitisation stage occured under more oxidising conditions and lower CO₂/H₂O ratios, which corresponds to the exhumation stage of the serpentinite-rodingite formations. Types II and III rodingites were subjected to further rodingitisation under the increasing influence of slab-derived hydrous phases at shallower depths, leading to the formation of late-stage andradite and vesuvianite. All stages of rodingitisation are estimated to have occurred under relatively moderate temperatures and pressure (~300 to 450 °C; ~2–6 kbar respectively).  相似文献   

Numerical Modeling of the Long-Term Transport, Dispersion, and Accumulation of Black Sea Pollutants into the North Aegean Coastal Waters     

Kyriakos I. Kopasakis  Anastasios N. Georgoulas  Panagiotis B. Angelidis  Nikolaos E. Kotsovinos 《Estuaries and Coasts》2012,35(6):1530-1550

This study investigates the long-term capacity of the North Aegean coastal systems to transport and store conservative pollutants that originate from the Black Sea. Emphasis is placed on modeling the dispersion and accumulation of a passive tracer that represents a Black Sea pollutant (BSP) substance that continuously discharges from the Dardanelles exit into the North Aegean, for a long period of time (16?years). The effects of the Black Sea water (BSW) inflows, meteorological forcing, and seasonal stratification are assessed with a 3D hydrodynamic model (Estuary, Lake and Coastal Ocean Model), after validation with available field data. The salinity, water temperature, and discharge from the Dardanelles Strait are taken to be seasonally varied. According to the authors' best knowledge, the present paper constitutes the first numerical modeling attempt in the literature that apart from the long-term hydrodynamic characteristics that have also been studied in previous works, a suitable tracer is introduced in order to predict the long-term fate, distribution, and accumulation of pollutants that originate from the Black Sea into the North Aegean coastal regions. The overall results of the present investigation indicate that the BSP concentration is very high at the coastal waters of Thassos, Samothraki, and Limnos islands, as well as along the mainland coastal waters between Alexandroupolis and Strymonikos Gulf, during summer and autumn when strong water column stratification occurs. In general, the BSP concentration in the North Aegean surface waters reaches considerable high values (47?C58?% of the initial pollutant concentration at Dardanelles inflow) within 16?years. Even for depths more than 500?m the BSP concentration is still remarkable, slightly increasing with time. The increase of the BSP concentration with respect to time at various depths (from free surface up to 750?m) is also investigated.  相似文献   

Contribution of electrical tomography methods in geotechnical investigations at Mavropigi lignite open pit mine,Northern Greece     

Hamdan Hamdan  Nikos Andronikidis  George Kritikakis  Nikos Economou  Zacharias Agioutantis  Paul Schilizzi  Chrysanthos Steiakakis  Christodoulos Papageorgiou  Panagiotis Tsourlos  George Vargemezis  Antonis Vafidis 《Environmental Earth Sciences》2014,72(5):1589-1598

In this paper, the application of 2D and 3D electrical resistivity methods in geotechnical investigations is explored through a case study in Northern Greece. These two methods were employed at a lignite surface mining operation where fracture zones and discontinuities have been recently observed close to the pit boundaries. The main aim of the geophysical survey was to estimate the inclination of the contact between the Neogene and Schist/Carbonate formations near the southern limits of the pit, as well as to estimate the thickness of the carbonate rocks on top of the Schist formations to evaluate the stability of the southern slopes. Synthetic data were initially generated to help plan an efficient electrical tomography survey, in a region with complex geology and irregular terrain. Three configurations (Wenner–Schlumberger and dipole–dipole or pole–dipole) proved essential in such conditions and helped improving the resolution of the resistivity section. The sections were then calibrated by boreholes. Finally, the geophysical survey provided invaluable data regarding the geometry of the bedrock and possible faults, which was essential for the slope stability calculations.  相似文献   

Complementing geotechnical slope stability and land movement analysis using satellite DInSAR     

Achilleas Tripolitsiotis  Chrysanthos Steiakakis  Eirini Papadaki  Zacharias Agioutantis  Stelios Mertikas  Panagiotis Partsinevelos 《Central European Journal of Geosciences》2014,6(1):56-66

This paper explores the potential of using satellite radar inteferometry to monitor time-varying land movement prior to any visible tension crack signs. The idea was developed during dedicated geotechnical studies at a large open-pit lignite mine, where large slope movements (10–20 mm/day) were monitored and large fissures were observed in the immediate area outside the current pit limits. In this work, differential interferometry (DInSAR), using Synthetic Aperture Radar (SAR) ALOS images, was applied to monitor the progression of land movement that could potentially thwart mine operations. Early signs of land movements were captured by this technique well before their visual observation. Moreover, a qualitative comparison of DInSAR and ground geodetic measurements indicates that the technique can be used for the identification of high risk areas and, subsequently, for the optimization of the spatial distribution of the available ground monitoring equipment. Finally, quantitative land movement results from DInSAR are shown to be in accordance with simultaneous measurements obtained by ground means.  相似文献   

A large strain theory for the two dimensional problems in geomechanics     

Panagiotis D. Kiousis  George Z. Voyiadjis  Mehmet T. Tumay 《国际地质力学数值与分析法杂志》1986,10(1):17-39

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