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排序方式: 共有126条查询结果,搜索用时 15 毫秒
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2.
A critical state interpretation for the cyclic liquefaction resistance of silty sands 总被引:1,自引:0,他引:1
George D. Bouckovalas Konstantinos I. Andrianopoulos Achilleas G. Papadimitriou 《Soil Dynamics and Earthquake Engineering》2003,23(2):115-125
Contrary to many laboratory investigations, common empirical correlations from in situ tests consider that the increase in the percentage of fines leads to an increase of the cyclic liquefaction resistance of sands. This paper draws upon the integrated Critical State Soil Mechanics framework in order to study this seemingly not univocal effect. Firstly the effect of fines on the Critical State Line (CSL) is studied through a statistical analysis of a large data set of published monotonic triaxial tests. The results show that increasing the content of non-plastic fines practically leads to a clockwise rotation of the CSL in (e–ln p) space. The implication of this effect on cyclic liquefaction resistance is subsequently evaluated with the aid of a properly calibrated critical state elasto-plastic constitutive model, as well as a large number of published experimental results and in situ empirical correlations. Both sets of data show clearly that a fines content, less than about 30% by weight, may prove beneficial at relatively small effective stresses (p0<50–70 kPa), such as the in situ stresses prevailing in most liquefaction case studies, and detrimental at larger confining stresses, i.e. the stresses usually considered in laboratory tests. To the extent of these findings, a correction factor is proposed for the practical evaluation of liquefaction resistance in terms of the fines content and the mean effective confining stress. 相似文献
3.
Cloud type and cloud cover effects on the surface radiative balance at several Polar sites 总被引:1,自引:0,他引:1
Summary ?The present work concerns measurements performed at five Polar sites in order to study the influence of cloud type and cloud
cover on the surface radiative balance. Cloud cover index was retrieved with the Kasten and Czeplak formula (1980), and comparison
with observed values showed the possibility of applying this formula in Polar regions. The Duchon and O’Malley (1999) methodology
was adopted to estimate the cloud types present during the measurement period for each site. The results show that during
the Antarctic summer clouds have a warming effect on the surface, while during a melting event recorded in the Arctic site
clouds have a net cooling effect on the surface. This result allows us to conclude that, during a melting period a different
cloud type formation, and a lower surface albedo, modify the effects of clouds on the surface radiation balance.
Received April 5, 2002; revised August 1, 2002; accepted August 17, 2002 相似文献
4.
Konstantinos I. Andrianopoulos Achilleas G. Papadimitriou George D. Bouckovalas 《国际地质力学数值与分析法杂志》2010,34(15):1586-1614
This paper presents a new plasticity model developed for the simulation of monotonic and cyclic loading of non‐cohesive soils and its implementation to the commercial finite‐difference code FLAC, using its User‐Defined‐Model (UDM) capability. The new model incorporates the framework of Critical State Soil Mechanics, while it relies upon bounding surface plasticity with a vanished elastic region to simulate the non‐linear soil response. Stress integration of constitutive relations is performed using a recently proposed explicit scheme with automatic error control and substepping, which so far has been employed in the literature only for constitutive models aiming at monotonic loading. The overall accuracy of this scheme is evaluated at element level by simulating cyclic loading along complex stress paths and by using iso‐error maps for paths involving change of the Lode angle. The performance of the new constitutive model and its stress integration scheme in complex boundary value problems involving earthquake‐induced liquefaction is evaluated, in terms of accuracy and computational cost, via a number of parametric analyses inspired by the successful simulation of the VELACS centrifuge Model Test No. 2 studying the lateral spreading response of a liquefied sand layer. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
5.
Pollani Annika Triantafyllou George Petihakis George Nittis Konstantinos Dounas Costas Christoforos Koutitas 《Marine pollution bulletin》2001,43(7-12):270-278
In this work the development and the application of an operational management tool for the Greek Seas is described. This tool consists of a three-dimensional floating pollutant prediction model coupled with a weather, a hydrodynamic and a wave model in order to track the movements and the spreading of the pollutants and indicate those coastal areas which might be affected. The tool is part of the Poseidon system which has been designed to provide real time data and forecasts for marine environmental conditions in the Greek Seas. In this paper, we present four case studies based on realistic scenarios that show the value of the application for long-term strategic planning and short-term decision making in oil spill accidents. 相似文献
6.
The response of adjacent buildings in city blocks to several strong earthquakes is analysed, taking into account the mutual collisions, or pounding, resulting from insufficient or non-existing separation distances. The buildings are idealized as lumped-mass, shear beam type, multi-degree-of-freedom (MDOF) systems with bilinear force-deformation characteristics and with bases supported on translational and rocking spring-dashpots. Collisions between adjacent masses can occur at any level and are simulated by means of viscoelastic impact elements. Using five real earthquake motions the effects of the following factors are investigated: building configuration and relative size, seismic separation distance and impact element properties. It is found that pounding can cause high overstresses, mainly when the colliding buildings have significantly different heights, periods or masses. This suggests a possibility for introducing a set of conditions into the codes, combined with some special measures, as an alternative to the seismic separation requirement. 相似文献
7.
The Pindos Fold-and-thrust belt (Greece): inversion kinematics of a passive continental margin 总被引:1,自引:0,他引:1
Konstantinos?Skourlis Theodor?DoutsosEmail author 《International Journal of Earth Sciences》2003,92(6):891-903
Continuous exposure in the Pindos mountain chain (Greece) and the detailed stratigraphic measurements in the area enable us to construct eight balanced cross sections across the Pindos Fold-and-thrust belt (PFTB) and to approach quantitatively some parameters which controlled foreland evolution. The 160-km-wide passive continental margin of the Apulian continent in Greece was progressively shortened from east to west at rates of 6 mm/year between the Early Oligocene and Late Eocene. From the rear to the frontal part of the wedge, fault-bend folds, duplexes and imbricates were formed, while strain was partitioned into faulting (~34%), layer parallel shortening (~23%) and buckling (~9%). Foreland subsidence and internal deformation of the orogenic wedge are strongly affected by two parameters of equal importance: the thrust load of the overthrusted microcontinents and the rigidity of the underthrusted Apulian passive margin. Changes in the thickness of the pre-orogenic sediments and reactivated transform faults induced salients. During the Lower Miocene, the orogenic wedge in the Peloponnese suffered additional uplift and westward gravitational gliding induced by the intracontinental subduction of the Palaeozoic rift zone of the Phyllite-Quartzite Series, which was reactivated and returned to the earths surface during the Hellenic orogeny. 相似文献
8.
Prior to the 7/9/1999 MS = 5.9 Athens earthquake, regional seismicity has exhibited a power-law increase, of the form = K+A(tc - t)n, where is estimated using an expression log = cM + d and tc is the time of the culminating event. Such changes appeared after the 17/8/1999 M7.4 Izmit event. We quantified the performance of the power law vs. the null hypothesis of constant seismic release rates, by defining the curvature C as the ratio of the power law fit RMS/linear fit RMS, so that the smaller C is, the better the power law behaviour. By mapping C, we have established a critical radius of 110 km and observed that the region of correlated accelerating seismic release extended from the N. Aegean, through Euboea and Attica to the SW Peloponnese. A few days prior to the Athens event, min(C) was centred at the epicentral area and numerical simulation yielded tc = 1999.676 and predicted MS = 5.77. Seismicity rates returned to normal (quasi-constant) after the Athens event. We interpret this effect as critical point behaviour, following remote excitation of a broad area by stress redistribution due to the Izmit event which, at Athens, has triggered `premature' failure of a fault nearing its load bearing capacity. If this is correct, we have documented a case of remote earthquake triggering by another earthquake, as well as insight into the mechanisms producing it. As a corollary, we note that a large event may beget another large event in its broader region of interaction, which may be preceded by characteristic precursory seismicity changes. 相似文献
9.
Argyrios Kapsiotis Tassos A. Grammatikopoulos Basilios Tsikouras Konstantinos Hatzipanagiotou 《Resource Geology》2010,60(2):178-191
The Pindos ophiolite complex, located in the north-western part of continental Greece, hosts various podiform chromite deposits generally characterized by low platinum-group element (PGE) grades. However, a few locally enriched in PPGE + Au (up to 29.3 ppm) chromitites of refractory type are also present, mainly in the area of Korydallos (south-eastern Pindos). The present data reveal that this enrichment is strongly dependant on chromian spinel chemistry and base metal sulfide and/or base metal alloy (BMS and BMA, respectively) content in chromitites. Consequently, we used super-panning to recover PGM from the Al-rich chromitites of the Korydallos area. The concentrate of the composite chromitite sample contained 159 PGM grains, including, in decreasing order of abundance, the following major PGM phases: Pd-Cu alloys (commonly non-stoichiometric, although a few Pd-Cu alloys respond to the chemical formula PdCu4), Pd-bearing tetra-auricupride [(Au,Pd)Cu], nielsenite (PdCu3), sperrylite (PtAs2), skaergaardite (PdCu), Pd-bearing auricupride [(Au,Pd)Cu3], Pt and Pd oxides, Pt-Fe-Ni alloys, hollingworthite (RhAsS) and Pt-Cu alloys. Isomertieite (Pd11Sb2As2), zvyagintsevite (Pd3Pb), native Au, keithconnite (Pd20Te7), naldrettite (Pd2Sb) and Rh-bearing bismuthotelluride (RhBiTe, probably the Rh analogue of michenerite) constitute minor phases. The bulk of PGE-mineralization is dominated by PGM grains that range in size from 5 to 10 µm. The vast majority of the recovered PPGM are associated with secondary BMS and BMA, thus confirming that a sulphur-bearing melt played a very important role in scavenging the PGE + Au content of the silicate magma from which chromian spinel had already started to crystallize. The implemented technique has led to the recovery of more, as well as noble, PGM grains than the in situ mineralogical examination of single chromitite samples. Although, the majority of the PGM occur as free particles and in situ textural information is lost, single grain textural evidence is observed. In summary, this research provides information on the particles, grain size and associations of PGM, which are critical with respect to the petrogenesis and mineral processing. 相似文献
10.