排序方式: 共有36条查询结果,搜索用时 921 毫秒
31.
Ahmed Abderrahmane Semchaoui Omar Kolli Abdelhak Boutaleb Tarek Zerrouki 《Arabian Journal of Geosciences》2016,9(16):679
The Draïssa barite vein system in the Ougarta district is located in southwestern Algeria. It is the principal mineral deposit of economic interest of the area. The mineralization is hosted by Cambrian sedimentary rocks that unconformably overlie Precambrian formations. The mineralized structures consist mostly of barite and quartz with minor sulfide minerals and trend dominantly NE-SW, NW-SE, and E-W. Siliceous alteration zones are associated with the vein system. Samples of barite ore are characterized by low total REE contents ranging from 9 to 50 ppm and positive Eu (2–2.15 ppm) and Y (1.2–11.1 ppm) anomalies, indicating hydrothermal activity during mineralization. Halogen data of the barite show that the Cl/Br molar ratio is 189:571 and the Na/Br ratio is 34:376, indicating that the sulfur was derived from seawater. The Ba-enrichment trend in the volcanic rocks of Draïssa is interpreted as possible probable source of the Ba (424–3039 ppm Ba). It appears that the barite-quartz deposits were formed in two stages. Endogenous fluids deposited the primary vein materials, consisting of quartz associated with copper sulfides. Exogenous fluids (cold seawater) became heated during ascendant fluid movement. Mineralization was governed by convective motions and the barite and galena fillings were deposited in openings created by normal faulting. 相似文献
32.
River embankments failure due to severe flooding is an extremely complex phenomena triggering permanent or temporary modification
to the river morphology, river flow and sediment movement. Reliable and automatic prediction of these movements is crucial
to properly identify the protective measures for residents living within the inundation flood zones. In this regard, BISHOP,
a decision tool to automatically predict, at multiple river cross-sections, the slope failure circle with the minimum safety
factor has been developed. In this paper, the computer tool BISHOP, named after the simplified Bishop method, is presented.
Its applications have proven to be highly efficient in real case studies, where the stability of multiple slope profiles,
at different river cross-sections, must be analyzed to establish spatial and temporal evolution of the river banks failures.
The integration of the proposed methodology within a comprehensive flow hydrodynamic, sediment transport and landslide calculation
has particularly enhanced the evaluation of the flood-risk zone during major flooding. Typical results demonstrating the effectiveness
of the developed methodology are demonstrated during the analysis of the evolution of a river reach downstream of a dam a
dam break scenario. 相似文献
33.
Physical modeling and visualization of soil liquefaction under high confining stress 总被引:1,自引:0,他引:1
Lenart González 《地震工程与工程振动(英文版)》2005,4(1):47-57
The mechanisms of seismically-induced liquefaction of granular soils under high confining stresses are still not fully understood. Evaluation of these mechanisms is generally based on extrapolation of observed behavior at shallow depths. Three centrifuge model tests were conducted at RPI‘s experimental facility to investigate the effects of confining stresses on the dynamic response of a deep horizontal deposit of saturated sand. Liquefaction was observed at high confining stresses in each of the tests. A system identification procedure was used to estimate the associated shear strain and stress time histories. These histories revealed a response marked by shear strength degradation and dilative patterns. The recorded accelerations and pore pressures were employed to generate visual animations of the models. These visualizations revealed a liquefaction front traveling downward and leading to large shear strains and isolation of upper soil layers. 相似文献
34.
Benamar Ahmed Correia dos Santos Ricardo N. Bennabi Abdelkrim Karoui Tarek 《Acta Geotechnica》2019,14(3):815-823
Acta Geotechnica - An experimental study on internal erosion of coarse-grained soils collected from the Rhine River is presented. The tests performed on laboratory column aim to assess the... 相似文献
35.
36.
Youssef T 《Marine pollution bulletin》2002,44(4):334-339
The germination behavior of Sporobolus iocladus seeds including germination percentage, accumulated germination percentage, the average incubation period to germination and germination velocity was studied under laboratory conditions. Treatments included six salinity regimes (0, 70, 140, 210, 280 and 350 mM NaCI) and three sources of oil hydrocarbons; Light Arabian Crude, polynuclear aromatic hydrocarbons (PAHs) including diaromatic or triaromatic hydrocarbons (in crude oil equivalent concentrations, COEC). The average incubation period needed for seeds to germinate was significantly longer for seeds germinated in 350 mM NaCl (6 +/- 1.16 days) compared with the control (4 +/- 00 days). The accumulated germination percentage gradually decreased with increasing salinity (control: 90 +/- 10, while 350 mM NaCl: 63 +/- 8.8). Oil hydrocarbons significantly affected all germination parameters of S. iocladus seeds regardless of salinity levels. COEC of di- and triaromatic hydrocarbons suppressed seed germination more than crude oil. Seeds exposed to diaromatic hydrocarbons failed to germinate. Hydrocarbon's salinity interaction significantly reduced the number of germinated S. iocladus seeds. It is concluded that hydrocarbon pollutants adversely affect S. iocladus through reducing germination. It is also suggested that the toxic effect of hydrocarbons on seeds is not solely mediated through their interaction with salinity. The ecological implications of these findings are discussed in relation to other studies on the post-spill recovery of halophytes. 相似文献