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George Skianis Taxiarchis Papadopoulos Dimitrios Vaiopoulos Sotiris Nikolaou 《Geophysical Prospecting》1995,43(5):677-691
A new method is proposed for the quantitative interpretation of SP field data produced by a polarized ore body and simulated by an inclined sheet. The theoretical concept is based on the study of the amplitude Spectrum. It is shown that the SP amplitude Spectrum is not continuous at zero frequency; this leads to the dip angle determination of the inclined sheet. It is also shown that the SP amplitude spectrum is practically nullified at a characteristic amortization frequency that depends on the depth of the polarized body. The maximum amplitude Spectrum value of the SP gradient is used to estimate the depth to the bottom of the polarized body. Thus, the geometrical parameters h and H, the depths to the top and bottom, respectively, as well as the dip angle of the inclined sheet, can be satisfactorily determined. Some problems may arise in the determination of these parameters, affecting their accuracy, whenever unwanted frequency noise is present. 相似文献
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Extending the application of integral frame abutment bridges in earthquake‐prone areas by using novel isolators of recycled materials 
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下载免费PDF全文 Stergios A. Mitoulis Anastasia Palaiochorinou Ilias Georgiadis Sotiris Argyroudis 《地震工程与结构动力学》2016,45(14):2283-2301
Integral abutment bridges (IABs) are jointless structures without bearings or expansion joints which require minimum or zero maintenance. The barrier to the application of long‐span integral abutment bridges is the interaction of the abutment with the backfill soil during the thermal expansion and contraction of the bridge deck, that is, serviceability, or when the bridge is subjected to dynamic loads, such as earthquakes. The interaction of the bridge with the backfill leads to settlements and ratcheting of the soil behind the abutment and, as a result, the soil pressures acting on the abutment build up in the long term. This paper provides a solution for the aforementioned challenges by introducing a novel isolator that is a compressible inclusion of reused tyre‐derived aggregates placed between the bridge abutment and the backfill. The compressibility of typical tyre‐derived aggregates was measured by laboratory tests, and the compressible inclusion was designed accordingly. The compressible inclusion was then applied to a typical integral frame abutment model, which was subjected to static and dynamic loads representing in‐service and seismic loads correspondingly. The response of both the conventional and the isolated abutment was assessed based on the settlements of the backfill, the soil pressures and the actions of the abutment. The study of the isolated abutment showed that the achieved decoupling of the abutment from the backfill soil results in significant reductions of the settlements of the backfill and of the pressures acting on the abutment. Hence, the proposed research enables extending the length limits of integral frame bridges subjected to earthquake excitations. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
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Fragility curves (FCs) constitute an emerging tool for the seismic risk assessment of all elements at risk. They express the probability of a structure being damaged beyond a specific damage state for a given seismic input motion parameter, incorporating the most important sources of uncertainties, that is, seismic demand, capacity and definition of damage states. Nevertheless, the implementation of FCs in loss/risk assessments introduces other important sources of uncertainty, related to the usually limited knowledge about the elements at risk (e.g., inventory, typology). In this paper, within a Bayesian framework, it is developed a general methodology to combine into a single model (Bayesian combined model, BCM) the information provided by multiple FC models, weighting them according to their credibility/applicability, and independent past data. This combination enables to efficiently capture inter-model variability (IMV) and to propagate it into risk/loss assessments, allowing the treatment of a large spectrum of vulnerability-related uncertainties, usually neglected. As case study, FCs for shallow tunnels in alluvial deposits, when subjected to transversal seismic loading, are developed with two conventional procedures, based on a quasi-static numerical approach. Noteworthy, loss/risk assessments resulting from such conventional methods show significant unexpected differences. Conventional fragilities are then combined in a Bayesian framework, in which also probability values are treated as random variables, characterized by their probability density functions. The results show that BCM efficiently projects the whole variability of input models into risk/loss estimations. This demonstrates that BCM is a suitable framework to treat IMV in vulnerability assessments, in a straightforward and explicit manner. 相似文献
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The present study investigates the possible hydrologic effects of the proposed lignite open‐cast mining in Drama lignite field (north Greece). Recent years have seen a rapid increase in surface mining. This activity has generated a growing concern for the potential environmental impacts associated with large scale surface mining. In order to achieve a safe mine operation and allow extraction of lignite to considerable depths, extensive dewatering by pumping will be necessary, while at the same time it is desirable to avoid presence of overpumping conditions in the broader area. Based on stratigrafic, hydrologic and hydrogeologic data, a three‐dimensional finite difference model was developed in order to simulate the dewatering process of the western part of the lignite open‐cast mine in Drama and to predict both spatially and temporally the decline of ground water level down to the lignite surface. The dewatering of the part of the aquifer which underlies the mine area will influence the hydrological conditions of the broader region. The most important anticipated effects will be the abandonment of shallow wells as well as the decrease of ground water pumping rates of deep wells. Aquifer discharge towards the ditches of the study area will cease and there will be an inversion of ground water flow from the ditches towards the underlying aquifer. Dewatering activities will probably result in minor subsidence of the nearby peat deposits of Drama Philippi marshes. Moreover, sand pumping as well as the presence of gasses is likely to cause local subsidence phenomena, mainly in the pit slopes. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
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The town of Edessa is located on Northern Greece at a region that is characterized as low seismicity zone due to the fact
that few moderate events of M < 6 occurred during the last century. According to the Greek Seismic Code, the expected acceleration having a 10% probability
of being exceeded in 50 years is equal to 0.16g. However, an amplification of ground motion is likely to occur due the local geology that is consisted of Holocene fluvio-torrential
deposits. The basic aim of this paper is to evaluate the site amplification due to geological conditions and to assess the
liquefaction hazard. In order to achieve this, 1-D site response analyses were performed. The data that were employed for
the construction of the numerical models have been collected from borings with standard penetrations tests (SPT) that were
drilled for construction purposes. Afterward, the liquefaction potential of the subsoil layers was evaluated taking into consideration
two seismic scenarios. The first scenario was based on the seismic parameters, earthquake magnitude and PGA, assigned by the
Greek Seismic Code. On the second seismic model, we employed the values of acceleration, resulted from the 1-D analyses and
the earthquake magnitude as it was defined by the Greek Seismic Code. In order to compile the liquefaction hazard maps, we
initially estimated the liquefaction potential index (LPI) of the soil columns using the parameters provided by SPT, for both
seismic loadings, and afterward we correlated these values with the proposed classification of the severity of liquefaction-induced
deformations. In addition, having computed the value of probability based on the LPI, liquefaction manifestations probability
maps were compiled for both scenarios. The result of this study was that liquefaction-induced ground disruptions are likely
to occur at the center of the city, among the branches of Voda River, only when the amplified values of acceleration are taken
into account to the computation of liquefaction potential. 相似文献
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A fundamental tool in seismic risk assessment of transportation systems is the fragility curve, which describes the probability that a structure will reach or exceed a certain damage state for a given ground motion intensity. Fragility curves are usually represented by two‐parameter (median and log‐standard deviation) cumulative lognormal distributions. In this paper, a numerical approach, in the spirit of the IDA, is applied for the development of fragility curves for highways and railways on embankments and in cuts due to seismic shaking. The response of the geo‐construction to increasing levels of seismic intensity is evaluated using a 2D nonlinear finite element model, with an elasto‐plastic criterion to simulate the soil behavior. A calibration procedure is followed in order to account for the dependency of both the stiffness and the damping to the soil strain level. The effect of soil conditions and ground motion characteristics on the response of the embankment and cut is taken into account considering different typical soil profiles and seismic input motions. This study will provide input for the assessment of the vulnerability of the road/railway network regarding the performance of the embankments and cuts; therefore, the level of damage is described in terms of the permanent ground displacement in these structures. The fragility curves are estimated based on the evolution of damage with increasing earthquake intensity, which is described by PGA. The proposed approach allows the evaluation of new fragility curves considering the distinctive features of the element's geometry, the input motion, and the soil properties as well as the associated uncertainties. A relationship between the computed permanent ground displacement on the surface of the embankment and the PGA in the free field is also suggested based on the results of the numerical analyses. Finally, the proposed fragility curves are compared with existing empirical data and the limitations of their applicability are outlined. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
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Sotiris Argyroudis Anastasia Palaiochorinou Stergios Mitoulis Dimitris Pitilakis 《Bulletin of Earthquake Engineering》2016,14(12):3573-3590
Reuse of the 1.5 billion waste tyres that are produced annually is a one of the major worldwide challenges, as waste tyres are toxic and cause pollution to the environment. In recognition of this problem, this paper introduces the reuse of tyres, in the form of derived aggregates in mixtures with granulated soil materials, as previous studies indicated the potential benefits of these materials in the seismic performance of structures. The objective of the present research study is to investigate whether use of rubberised backfills benefits the seismic response of Integral Abutment Bridges (IABs) by enhancing soil-structure interaction (SSI) effects. Numerical models including typical integral abutments on surface foundation with nonlinear conventional backfill material and its alternative form as soil-rubber mixtures are analysed and their response parameters are compared. The research is conducted on the basis of parametric analysis, which aims to evaluate the influence of different rubber-soil mixtures on the dynamic response of the abutment-backfill system under various seismic excitations, accounting for dynamic soil-abutment interaction. The results provide evidence that the use of rubberised backfill leads to reductions in the backfill settlements, the horizontal displacements of the bridge deck, the residual horizontal displacements of the top of the abutment and the pressures acting on the abutment, up to 55, 18, 43 and 47 % respectively, with respect to a conventional backfill comprising of clean sand. Small change in bending moments and shear forces on the abutment wall is also observed. Therefore, rubberised backfills offer promising solution to mitigate the earthquake risk, towards economic design with minimal damage objectives for the resilience of transportation networks. 相似文献
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Compaction bands are localized failure patterns that appear in highly porous rock material under the effect of relatively high confining pressure. Being affected mainly by volumetric compression, these bands appear to be almost perpendicular to the most compressive principal stress of a stress state at the so-called “cap” of the yield surface (YS). In this study, we focus on the mechanism that leads to the onset of compaction bands by using a viscoplasticity model able to describe the post-localization response of these materials. The proposed constitutive framework is based on the overstress theory of Perzyna (1966) and the anisotropic clay plasticity model of Dafalias (1986), which provides not only the necessary “cap” of the YS, but introduces a rotational hardening (RH) mechanism, thus, accounting for the effect of fabric anisotropy. Following the analysis of Veveakis and Regenauer-Lieb (2015), we identify the compaction bands as “static” cnoidal wave formations in the medium that occur at a post-yield regime, and we study the effect of rotational and isotropic hardening on their onset. Moreover, we determine a theoretical range of confining pressures in triaxial compression tests for the compaction bands to develop. Under the assumption of coaxiality between stress and anisotropy tensors, the results show that the isotropic hardening promotes compaction localization, whereas the RH has a slightly negative effect on the onset of compaction localization. 相似文献