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121.
Grigorios Tsinidis Kyriazis Pitilakis Christos Anagnostopoulos 《Bulletin of Earthquake Engineering》2016,14(10):2903-2929
The paper discusses the seismic response of circular tunnels in dry sand and investigates the efficiency of current seismic analysis methods at extreme lining flexibilities. Initially, a dynamic centrifuge test on a flexible circular model tunnel, embedded in dry sand, is analyzed by means of rigorous full dynamic analysis of the coupled soil–tunnel system, applying various non-linear soil and soil–tunnel interface models. The numerical results are compared to the experimental ones, aiming to better understand the recorded response and calibrate the numerical models. Then a series of numerical analyses are conducted using the validated numerical model, in order to investigate the effect of the tunnel lining rigidity on the dynamic response of the soil–tunnel system. In parallel, the accuracy of currently used simplified analysis methods is evaluated, by comparing their predictions with the results of the a priori more accurate and well validated numerical models. The comparative analyses allow us to highlight and discuss several crucial aspects of the soil-tunnel system seismic response, including (1) the post-earthquake residual values of the lining forces, which are amplified with the increase of the flexibility of the tunnel and (2) the importance of the soil-tunnel interface conditions. It is finally concluded that simplified analysis methods may provide a reasonable framework for the analysis at a preliminary stage, under certain conditions. 相似文献
122.
Assessment of groundwater vulnerability to pollution: a combination of GIS, fuzzy logic and decision making techniques 总被引:1,自引:0,他引:1
Alexandra Gemitzi Christos Petalas Vassilios A. Tsihrintzis Vassilios Pisinaras 《Environmental Geology》2006,49(5):653-673
The assessment of groundwater vulnerability to pollution aims at highlighting areas at a high risk of being polluted. This
study presents a methodology, to estimate the risk of an aquifer to be polluted from concentrated and/or dispersed sources,
which applies an overlay and index method involving several parameters. The parameters are categorized into three factor groups:
factor group 1 includes parameters relevant to the internal aquifer system’s properties, thus determining the intrinsic aquifer
vulnerability to pollution; factor group 2 comprises parameters relevant to the external stresses to the system, such as human
activities and rainfall effects; factor group 3 incorporates specific geological settings, such as the presence of geothermal
fields or salt intrusion zones, into the computation process. Geographical information systems have been used for data acquisition
and processing, coupled with a multicriteria evaluation technique enhanced with fuzzy factor standardization. Moreover, besides
assigning weights to factors, a second set of weights, i.e., order weights, has been applied to factors on a pixel by pixel
basis, thus allowing control of the level of risk in the vulnerability determination and the enhancement of local site characteristics.
Individual analysis of each factor group resulted in three intermediate groundwater vulnerability to pollution maps, which
were combined in order to produce the final composite groundwater vulnerability map for the study area. The method has been
applied in the region of Eastern Macedonia and Thrace (Northern Greece), an area of approximately 14,000 km2. The methodology has been tested and calibrated against the measured nitrate concentration in wells, in the northwest part
of the study area, providing results related to the aggregation and weighting procedure. 相似文献
123.
Gaye Bayrakci Carla Scalabrin Stéphanie Dupré Isabelle Leblond Jean-Baptiste Tary Nadine Lanteri Jean-Marie Augustin Laurent Berger Estelle Cros André Ogor Christos Tsabaris Marc Lescanne Louis Géli 《Marine Geophysical Researches》2014,35(3):211-229
A rotating, acoustic gas bubble detector, BOB (Bubble OBservatory) module was deployed during two surveys, conducted in 2009 and 2011 respectively, to study the temporal variations of gas emissions from the Marmara seafloor, along the North Anatolian Fault zone. The echosounder mounted on the instrument insonifies an angular sector of 7° during a given duration (of about 1 h). Then it rotates to the next, near-by angular sector and so forth. When the full angular domain is insonified, the “pan and tilt system” rotates back to its initial position, in order to start a new cycle (of about 1 day). The acoustic data reveal that gas emission is not a steady process, with observed temporal variations ranging between a few minutes and 24 h (from one cycle to the other). Echo-integration and inversion performed on the acoustic data as described in the companion paper of Leblond et al. (Mar Geophys Res, 2014), also indicate important variations in, respectively, the target strength and the volumetric flow rates of individual sources. However, the observed temporal variations may not be related to the properties of the gas source only, but reflect possible variations in sea-bottom currents, which could deviate the bubble train towards the neighboring sector. During the 2011 survey, a 4-component ocean bottom seismometer (OBS) was co-located at the seafloor, 59 m away from the BOB module. The acoustic data from our rotating, monitoring system support, but do not provide undisputable evidence to confirm, the hypothesis formulated by Tary et al. (2012), that the short-duration, non-seismic micro-events recorded by the OBS are likely produced by gas-related processes within the near seabed sediments. Hence, the use of a multibeam echosounder, or of several split beam echosounders should be preferred to rotating systems, for future experiments. 相似文献
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126.
Christos Vrettos 《地震工程与结构动力学》1999,28(12):1525-1540
The vertical and rocking response of rigid rectangular foundations resting on a linear-elastic, compressible, non-homogeneous half-space soil model is studied. The non-homogeneity is described by a continuous yet bounded increase of shear modulus with depth. The mixed boundary value problem is solved by means of the semi-analytical method of the subdivision of the foundation/soil contact area whereby the influence functions for the sub-regions are determined by integration of the corresponding surface-to-surface Green's functions for the particular soil model. Impedance functions are given for representative values of the non-homogeneity parameters, the Poisson's ratio and the foundation geometry over a wide range of frequencies. Significant features associated with the soil non-homogeneity are pointed out. Copyright © 1999 John Wiley & Sons Ltd. 相似文献