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81.
The state of land subsidence and prediction approaches due to groundwater withdrawal in China 总被引:13,自引:6,他引:7
This article gives a general introduction to land subsidence with the prediction approaches due to withdrawal of groundwater
in three subsided/subsiding regions in China: the deltaic plain of Yangtse River (YRDP), North China Plain (NCP), and Fenwei
Plain (FP). On YRDP, Shanghai is the typical subsided/subsiding city; on NCP Tianjin is the typical subsided/subsiding city,
and on FP Taiyuan is the typical subsided/subsiding city. The subsided area with subsidence over 200 mm on YRDP is about 10,000 km2 and the maximum subsided value reached 2.9 m at Shanghai; on NCP the subsided area reached 60,000 km2 with the maximum subsidence of 3.9 m at Tianjing; on FP the subsided area is relatively smaller than that on the other two
plains and is about 1,135 km2 with maximum subsidence of 3.7 m at Taiyuan city. In order to protect the civil and industrial facilities, it is necessary
to predict the future development of land subsidence based on present state. Many researchers proposed several approaches
to predict the land subsidence due to groundwater withdrawal according to different geological conditions and groundwater
withdrawal practice. This article classifies these approaches into five categories: (i) statistical methods; (ii) 1D numerical
method; (iii) quasi-3D seepage model; (iv) 3D seepage model; (v) fully coupled 3D model. In China, the former four categories
are presently employed in the prediction practice and their merits and demerits are discussed. According to the prediction
practice, 3D seepage model is the best method presently. 相似文献
82.
83.
84.
苏北盘石山、练山地幔捕虏体的PGE地球化学 总被引:3,自引:0,他引:3
通过锍镍火试金预富集法,分析了位于郯庐断裂带东侧的盘石山、练山地幔橄榄岩包体中铂族元素(PGE)和Au含量.不同于部分熔融残留成因地幔橄榄岩中通常所观察到的负斜率型或平坦型的分布模式,这两地的地幔橄榄岩以Pt、Pd、Ru相对富集,Ir、Rh相对亏损的"燕子型"分布模式为特征.Pt、Pd等不相容元素富集说明上地幔除经历过早期的部分熔融外,还经历了后期富Pt、Pd的高熔/岩比的熔(流)体的层析分离交代作用影响.盘石山地幔橄榄岩的PGE总量比练山高,Os的含量也比原始地幔值高;而练山地幔橄榄岩的Os含量比原始地幔值低,说明交代作用带走了练山地幔橄榄岩中的Os,却没有很大改变盘石山地幔橄榄岩中的Os含量,这可能与交代熔(流)体含硫量饱和程度有关.Rh的负异常可能与部分熔融过程中熔体较低的fo2有关. 相似文献
85.
86.
Numerical estimation of REV and permeability tensor for fractured rock masses by composite element method 总被引:2,自引:0,他引:2
The Monte Carlo method is used to generate parent stochastic discrete fracture network, from which a series of fractured rock samples of different sizes and orientations are extracted. The fracture network combined with a regular grid forms composite element mesh of the fractured rock sample, in which each composite element is composed of sub‐elements incised by fracture segments. The composite element method (CEM) for the seepage is implemented to obtain the nodal hydraulic potential as well as the seepage flow rates through the fractured rock samples. The application of CEM enables a large quantity of stochastic tests for the fractured rock samples because the pre‐process is facilitated greatly. By changing the sizes and orientations of the samples, the analysis of the seepage characteristics is realized to evaluate the variation of the permeability components, the existence of the permeability tensor and the representative element volume. The feasibility and effectiveness are illustrated in a numerical example. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
87.
Biaxial test simulations using a packing of polygonal particles 总被引:1,自引:0,他引:1
The mechanical response of cohesionless granular materials under monotonic loading is studied by performing molecular dynamic simulations. The diversity of shapes of soil grains is modelled by using randomly generated convex polygons as granular particles. Results of the biaxial test obtained for dense and loose media show that samples achieve the same void ratio at large strains independent of their initial density state. This limit state resembles the so‐called critical state of soil mechanics, except for some stress fluctuations, which remain for large deformations. These fluctuations are studied at the micro‐mechanical level, by following the evolution of the co‐ordination number, force chains and the fraction of the sliding contacts of the sample. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
88.
Li Miao Ruisong Xu Yueliang Ma Jinhong Xu Jie Wang Rui Cai Yu Chen 《Journal of Geochemical Exploration》2008,96(1):43-52
In the Hetai goldfield, Guangdong Province, China, samples including rocks, soils and leaves of four plants (Pinus massoniana, Rhodomyrms tomenlosa, D. linearis var. dichotoma and Embelia laeta) collected from the gold mineralization zone and the background area were analyzed for Au, Ag, Cu, Pb, Zn, Hg, As and physiological parameters. The objective of this investigation is to study the geochemical and biogeochemical characteristics of studied plants, aiming at biogeochemical methods in Au exploration. The goldfield region shows geochemical and biogeochemical anomalies. Abundances of Au in rocks, soils, plants and the leaf pigments in the mineralized area are much higher than those in the surrounding region. The plants display unhealthy physiological and ecological characteristics in the Hetai goldfield area. The cell structures of the goldfield plants were anomalous and aberrant, and there were many nano-metal particles diffused in mitochondria and chloroplasts. Macro- and microscopic evidences of the vegetation in the goldfield areas are distinctly different from the background regions. The strongly anomalies in responses to Au are profound in further geochemical and botanic exploration studies. 相似文献
89.
通过对塔里木盆地库车坳陷南天山山前带克孜勒努尔沟与依奇克里克野外露头沉积相的精细研究,结合山前带大量地震剖面分析与迪那201井、东秋5井等多口钻井测井相和岩心精细描述,将古近系库姆格列木群划分为2个层序。层序2低位域以冲积扇沉积为主,自湖侵体系域始,研究区广泛发育退积与进积型扇三角洲沉积。库姆格列木群层序2湖侵体系域内扇三角洲平原砂体以正韵律沉积为主,砂砾岩占地层厚度的(68.4~87)%;扇三角洲前缘砂体正、反韵律均有分布,砂砾岩占地层的百分比有所降低,为(55.2~77)%。高位体系域内主要发育以反韵律砂体为主的扇三角洲前缘沉积。古近系苏维依组只发育一个层序,其低位体系域的砂体为扇三角洲平原与前缘的分流河道砂体,湖侵体系域内扇三角洲前缘砂体正、反韵律均发育,高位体系域内主要发育扇三角洲前缘沉积,以反韵律砂体为主,正韵律砂体相对较少。对比苏维依组不同体系域内砂体储集性,湖侵域内砂体优于高位域内砂体。扇三角洲沉积体中有利储集砂体首选为湖侵体系域内的扇三角洲前缘水下分流河道和河口坝砂体,次之为低位域扇三角洲前缘(平原)分流河道砂体,最后是高位域内的河口坝及席状砂沉积砂体。特别要指出:低位体系域或者湖侵体系域底部发育的扇三角洲前缘(平原)分流河道砂体(底砂砾岩)被快速湖侵的较厚的暗色泥岩所覆盖,可形成较好储集场所。 相似文献
90.
主要通过薄片鉴定、扫描电镜观察、包裹体分析、粘土矿物分析、镜质体反射率测试和岩心物性分析等手段,结合构造发育史和有机质热演化史等研究成果,以揭示东营凹陷北带古近系深部碎屑岩储层成岩环境及演化模式为目的展开研究工作。结果表明:东营凹陷北带古近系深部碎屑岩储层存在酸性、碱性和酸性碱性交替等多重成岩环境。酸性成岩环境以碳酸盐矿物溶解、长石溶解蚀变为高岭石并伴生石英次生加大等为标志,碱性成岩环境以石英质颗粒及其次生加大边溶解、长石次生加大和晚期碳酸盐矿物沉淀为标志。研究区古近系深部碎屑岩储层成岩环境由浅至深大致经历了碱性—酸性—酸性碱性交替(局部碱性较强)—碱性—弱碱性的演化过程,并建立了沙河街组四段的成岩演化和储层改造模式。 相似文献