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1.
Karst aquifers are characterized by a high degree of hydrologic variability and spatial heterogeneity of transport parameters. Tracer tests allow the quantification of these parameters, but conventional point-to-point experiments fail to capture spatiotemporal variations of flow and transport. The goal of this study was to elucidate the spatial distribution of transport parameters in a karst conduit system at different flow conditions. Therefore, six tracer tests were conducted in an active and accessible cave system in Vietnam during dry and wet seasons. Injections and monitoring were done at five sites along the flow system: a swallow hole, two sites inside the cave, and two springs draining the system. Breakthrough curves (BTCs) were modeled with CXTFIT software using the one-dimensional advection-dispersion model and the two-region nonequilibrium model. In order to obtain transport parameters in the individual sections of the system, a multi-pulse injection approach was used, which was realized by using the BTCs from one section as input functions for the next section. Major findings include: (1) In the entire system, mean flow velocities increase from 183 to 1,043 m/h with increasing discharge, while (2) the proportion of immobile fluid regions decrease; (3) the lowest dispersivity was found at intermediate discharge; (4) in the individual cave sections, flow velocities decrease along the flow direction, related to decreasing gradients, while (5) dispersivity is highest in the middle section of the cave. The obtained results provide a valuable basis for the development of an adapted water management strategy for a projected water-supply system. 相似文献
2.
Under seismic excitation, liquefied clean medium to dense cohesionless soils may regain a high level of shear resistance at large shear strain excursions. This pattern of response, known as a form of cyclic mobility, has been documented by a large body of laboratory sample tests and centrifuge experiments. A plasticity-based constitutive model is developed with emphasis on simulating the cyclic mobility response mechanism and associated pattern of shear strain accumulation. This constitutive model is incorporated into a two-phase (solid–fluid), fully coupled finite element code. Calibration of the constitutive model is described, based on a unique set of laboratory triaxial tests (monotonic and cyclic) and dynamic centrifuge experiments. In this experimental series, Nevada sand at a relative density of about 40% is employed. The calibration effort focused on reproducing the salient characteristics of dynamic site response as dictated by the cyclic mobility mechanism. Finally, using the calibrated model, a numerical simulation is conducted to highlight the effect of excitation frequency content on post-liquefaction ground deformations. 相似文献
3.
Ender Sar&#x;fak&#x;olu Hayrettin
zen Chris Hall 《Journal of Asian Earth Sciences》2009,35(6):502-515
Alkaline lavas were erupted as phonolites and trachytes around Karaburhan (Sivrihisar–Eskisehir, NW Anatolia) within the Izmir–Ankara–Erzincan suture zone. These volcanic rocks were emplaced as domes, close and parallel to the ophiolite thrust line. According to 40Ar/39Ar geochronological analyses of sanidine crystals from the phonolites, the age of the alkaline volcanics is 25 Ma (Late Oligocene–Early Miocene).The flow-textured phonolites are porphyritic and consist mainly of sanidine, clinopyroxene, and feldspathoid crystals. The clinopyroxenes show compositional zoning, with aegirine (Na0.82–0.96Fe+30.68–0.83) rims and aegirine–augite cores (containing calcium, magnesium, and Fe+2). Some aegirine–augites are replaced with sodium-, calcium-, and magnesium-rich amphibole (hastingsite). Feldspathoid (hauyne) crystals enriched with elemental Na and Ca have been almost completely altered to zeolite and carbonate minerals. The fine-grained trachytes with a trachytic texture consist of feldspar (oligoclase and sanidine) phenocrystals and clinopyroxene microphenocrystals within a groundmass made up largely of alkali feldspar microlites.Although there are some differences in their element patterns, the phonolites and trachytes exhibit enrichment in LILEs (Sr, K, Rb, Ba, Th) and LREEs (La, Ce, Pr, Nd) and negative anomalies in Nb and Ta. These geochemical characteristics indicate a lithospheric mantle enriched by fluids extracted from the subduction component. In addition, the high 87Sr/86Sr (0.706358–0.708052) and low 143Nd/144Nd (0.512546–0.512646) isotope concentrations of the alkaline lavas reflect a mantle source that has undergone metasomatism by subduction-derived fluids. Petrogenetic modeling indicates that the alkaline lavas generated from the subduction-modified lithospheric mantle have undergone assimilation, fractional crystallization, and crustal contamination, acquiring high Pb, Ba, Rb, and Sr contents and Pb isotopic compositions during their ascent through the thickened crust in an extensional setting. 相似文献
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5.
Mourad Zeghal Ahmed-W. Elgamal Ender Parra 《Soil Dynamics and Earthquake Engineering》1996,15(8):523-547
Downhole records of seismically-induced soil liquefaction are a valuable source of information on the associated mechanisms of stiffness degradation and lateral spreading. In this paper, free-field downhole array seismic records are employed to identify and model the recorded response at Wildlife Refuge (California, USA) and Port Island (Kobe, Japan) sites. The Wildlife Refuge site was instrumented in 1982 with a two-accelerometer array and six piezometers that recorded a case of seismically induced site liquefaction. At Port Island, a four-accelerometer down-hole array recorded strong motion during the recent 1995 Hyogoken-Nanbu earthquake. This earthquake resulted in widespread liquefaction and major ground deformations at Port Island. Using the recorded downhole accelerations at these two sites, the actual seismic shear stress-strain histories are directly evaluated. These histories provide valuable insight into the mechanisms of site liquefaction and associated loss of stiffness and strength. Based on the identified dynamic soil behaviors, computational simulations of the observed seismic response are performed. Optimization techniques are employed to estimate the necessary computational modeling parameters. This document constitutes the second part of a set of two companion papers about site amplification and liquefaction. 相似文献
6.
I. Srečec A. Ender E. Woermann W. Gans E. Jacobsson G. Eriksson E. Rosén 《Physics and Chemistry of Minerals》1987,14(6):492-498
The equilibrium $${\text{(1}} - y{\text{)Fe}}_{(s)} + \tfrac{{\text{1}}}{{\text{2}}}{\text{O}}_{{\text{2(g)}}} \rightleftarrows {\text{Fe}}_{{\text{1}} - y} {\text{O}}_{{\text{(}}s,{\text{ in MW)}}} $$ was studied by measuring oxygen potentials for a range of different magnesiowüstite compositions relative to those of the iron-wüstite system in an oxygen concentration cell involving yttria stabilized zirconia as the solid electrolyte. The temperature range covered was 1050 to 1400 K. Separate measurements of the mole fraction of trivalent iron in magnesiowüstite (x(Fe3+)) were made and the composition dependence ofx(Fe3+) was taken into account in calculations of the activity-composition relations of FeO, Fe2/3O and MgO. 相似文献
7.
<正>We report here new geochemical and geochronological data from mafic-ultramafic rock suites in the Ankara Mélange in north-central Turkey,and present a new tectonic model for its origin.Considered as one of most important relics of the Neotethyan realm in the region,the Ankara Mélange occurs between the Sakarya Continent 相似文献
8.
Karst aquifers are particularly vulnerable to bacterial contamination. Especially in developing countries, poor microbial water quality poses a threat to human health. In order to develop effective groundwater protection strategies, a profound understanding of the hydrogeological setting is crucial. The goal of this study was to elucidate the relationships between high spatio-temporal variability in microbial contamination and the hydrogeological conditions. Based on extensive field studies, including mapping, tracer tests and hydrochemical analyses, a conceptual hydrogeological model was developed for a remote and geologically complex karst area in Northern Vietnam called Dong Van. Four different physicochemical water types were identified; the most important ones correspond to the karstified Bac Son and the fractured Na Quan aquifer. Alongside comprehensive investigation of the local hydrogeology, water quality was evaluated by analysis for three types of fecal indicator bacteria (FIB): Escherichia coli, enterococci and thermotolerant coliforms. The major findings are: (1) Springs from the Bac Son formation displayed the highest microbial contamination, while (2) springs that are involved in a polje series with connections to sinking streams were distinctly more contaminated than springs with a catchment area characterized by a more diffuse infiltration. (3) FIB concentrations are dependent on the season, with higher values under wet season conditions. Furthermore, (4) the type of spring capture also affects the water quality. Nevertheless, all studied springs were faecally impacted, along with several shallow wells within the confined karst aquifer. Based on these findings, effective protection strategies can be developed to improve groundwater quality. 相似文献
9.
The sorption of Co(II)., Mn(II)- and Fe(II)-ions from aqueous solution on three power plant ashes was investigated in dependence on pH-value and solution concentration. Sorption increases with rising pH-value and increasing solution concentration. The results can be interpreted with the pH-dependent occurrence of the hydrolysis products of the metal ions in solution and their reaction with the ash phase. 相似文献
10.
The sorption of Co(II) from aqueous solutions on granulated titanium dioxide was investigated in dependence on pH-value (pH = 6 … 10) and solution concentration (cL = 10?7 … 10?2 mol/kg) at 83 °C. The precipitation in the solution occurred at high pH-values and solution concentrations was determined by control experiments without the adsorber. The adsorption isotherms are S-shaped. This can be interpreted as transition from chemisorption at the basic material to surface precipitation. 相似文献