大变形有限元法分析边坡稳定性     

杨涛  周德培  苏金蓉 《山地学报》2006,24(1):101-104

边坡稳定性分析的重要任务是确定边坡潜在滑面的位置及相应的安全系数,鉴于坡体位移可在现场监测中直接得到,提出边坡潜在滑面确定的位移判据,采用大变形有限元首先计算出边坡的位移场,然后在开挖面的不同高度作塑性区内的水平位移参考线,依次连接参考线上的位移突变点即得到边坡失稳的潜在滑面位置,分析滑面上的应力以及岩体抗剪强度即得到边坡的整体安全系数。  相似文献   

用于湿地气候效应模拟的三江平原下垫面数据获取   总被引：1，自引：0，他引：1  

闫敏华  徐传书  王丹丹  张树清  张耀存 《湿地科学》2006,4(2):108-114

三江平原是我国沼泽湿地的重要分布区。在20世纪的后50 a中,三江平原在经过几次大规模的开荒后,其下垫面发生了明显的阶段性变化,湿地大面积消失,农田面积不断增加。为了认识20世纪下半叶不同时期三江平原湿地的气候效应,拟采用第三代区域气候模式(RegCM3)来开展研究。而目前被广泛用于RegCM3的GL-CC数据,所反映的研究区下垫面几乎不存在沼泽湿地,这与事实严重不符,所以必须获取三江平原有沼泽湿地存在的真实的下垫面数据,才能得到可靠的湿地气候效应的模拟结果。分别选择了4期(1954年、1985年、1996年和2000年)有阶段代表性的航片、TM影像数据为主要数据源,利用ERDAS8.7和Arcview3.2等软件,首先得到4期研究区的土地利用数据,然后通过土地利用数据类型向模式数据类型的转换,从4期研究区土地利用数据中提取出了三江平原下垫面的模式数据。经过误差分析,认为获取的4期三江平原下垫面模式数据准确的反映出研究区几个时期的湿地下垫面实况,可以作为三江平原湿地气候效应模拟的基础数据。  相似文献   

Factors controlling the spatial and temporal variability of dust emissions     

John A. Gillies William G. Nickling Vicken Etyemezian James King Mark Sweeney 《中国地球化学学报》2006,25(B08):219-220

New field measurement techniques are allowing researchers to better understand how surficial properties affect the temporal and spatial variability of dust emissions. In this paper we review the current understanding of the dust emission process and present new field measurements that examine how three surface properties： roughness, crust strength, and temporal changes of surface properties affect dust emissions. These data were collected using three unique measurement systems developed by our team. Roughness exerts considerable control on the entrainment threshold and emissions of dust from a surface. We have carried out a series of experiments designed to quantify roughness effects on aeolian sediment entrainment and transport in a shear stress partitioning framework. Our results show that the model of Raupach et al. （1993） provides very good agreement with available data to predict the amount of shearing stress on the intervening surface among roughness elements, relatively independent of their size and distribution. However, element size affects the aeolian sediment transport process beyond that attributable only to the reduction of surface shear stress caused by the roughness. Additional interactions of the elements with the saltation cloud appear to reduce the transport efficiency and potentially dust emissions as well. The effect of crust strength on dust emissions was assessed using a newly-developed pin penetrometer, which can measure crust strength in-situ. Previous researchers suggested that variation in crust strength even within a small area could lead to considerable spatial variability in dust emissions. Our measurements showed that crust strength is highly variable over a scale of centimeters. This variability may help to explain some of the observed scatter in field measurements of dust emissions for what appear to be homogeneous surfaces. Variability of dust emissions in time and space was also evaluated using a new instrument, the Portable In-Situ Wind Erosion Lab （PI-SWERL） developed to measure dust emissions from soil surfaces.  相似文献   

Investigation of the effect of aggregate shape and surface roughness on the slake durability index using the fractal dimension approach     

Ersin Kolay  Kamil Kayabali   《Engineering Geology》2006,86(4):271-284

Argillaceous rocks cover about one thirds of the earth's surface. The major engineering problems encountered with weak- to medium-strength argillaceous rocks could be slaking, erosion, slope stability, settlement, and reduction in strength. One of the key properties for classifying and determining the behavior of such rocks is the slake durability. The concept of slake durability index (SDI) has been the subject of numerous researches in which a number of factors affecting the numerical value of SDI were investigated. In this regard, this paper approaches the matter by evaluating the effects of overall shape and surface roughness of the testing material on the outcome of slake durability indices.

For the purpose, different types of rocks (marl, clayey limestone, tuff, sandstone, weathered granite) were broken into chunks and were intentionally shaped as angular, subangular, and rounded and tested for slake durability. Before testing the aggregate pieces of each rock type, their surface roughness was determined by using the fractal dimension. Despite the variation of final values of SDI test results (values of I_d), the rounded aggregate groups plot relatively in a narrow range, but a greater scatter was obtained for the angular and subangular aggregate groups. The best results can be obtained when using the well rounded samples having the lowest fractal values. An attempt was made to analytically link the surface roughness with the I_d parameter and an empirical relationship was proposed. A chart for various fractal values of surface roughness to use as a guide for slake durability tests is also proposed. The method proposed herein becomes efficient when well rounded aggregates are not available. In such condition, the approximate fractal value for the surface roughness profile of the testing aggregates could be obtained from the proposed chart and be plugged into the empirical relation to obtain the corrected I_d value. The results presented herein represent the particular rock types used in this study and care should be taken when applying these methods to different type of rocks.  相似文献   

Planation, bauxites and epeirogeny: One or two paleosurfaces on the West African margin?   总被引：3，自引：0，他引：3  

Dominique Chardon  Violaine Chevillotte  Anicet Beauvais  Georges Grandin  Bruno Boulang 《Geomorphology》2006,82(3-4):273-282

Mapping of lateritic bauxites over the West African rifted margin and analysis of the geomorphic properties of these bauxites, combined with available geological data lead to a discussion of the presence of either two Meso-Cenozoic planation surfaces or a single Eocene surface to account for the morphotectonic and paleoclimatic evolution of the Guinean landforms. At large scale, two stepped bauxitic levels are documented. Ongoing or episodic uplift following Gondwana breakup and Meso-Cenozoic climate change are proposed to have allowed the formation and abandonment of an Early mid-Cretaceous surface today preserved as the higher bauxitic level, and the setting of an Eocene planation surface bearing a second generation of bauxites, making the lower bauxitic level. The single Eocene surface hypothesis requires that Paleogene bauxitization preserved large pre-existing relief to explain two stepped bauxitic levels of the same age. The two-surface hypothesis is favored because it would explain rebauxitization of alluvial pebbles of bauxites under the lower lateritic level.  相似文献   

Surface pollen and its relationship to vegetation on the southern slope of the eastern Qilian Mountains     

LU Xinmiao  CHEN Hui  XU Qinghai 《地理学报》2006,16(2):215-222

The objective of this study is to investigate pollen-vegetation relationship in the Qilian Mountains. The eastern Qilian Mountains are located in the transitional zone of the Tibetan Plateau, the Loess Plateau and the arid region of Northwest China, which is one of the key areas of global environmental change. A total of 13 surface pollen samples from main vegetation have been collected. Pollen percentages were calculated in all samples. In order to reveal the relationship between pollen composition and the vegetation types from which the soil samples have been collected, Detrended Correspondence Analysis (DCA) ordination method was employed on the pollen data. The results show that dominating vegetation types can be recognized by their pollen spectra: Picea crassifolia forest, alpine shrub and alpine meadow as well. Altitude and temperature determine the distribution of the surface pollen and the vegetation. The good agreement between modern vegetation and surface samples across this area provides a measure of the reliability of using pollen data to reconstruct paleoenvironment and paleovegetation patterns in this or other similar regions. However the loss of Betula pollen in forest needs further investigation. Pollen oxidation is the most important factor contributing to the damage of modern pollen in the study area. Pollen concentrations decrease with the increase of pH values of soils, and decrease sharply when the pH exceeds 7.6.  相似文献   

The multilevel fast multipole method for forward modelling the multiply scattered seismic surface waves   总被引：1，自引：0，他引：1  

Özcan Çakir 《Geophysical Journal International》2006,167(2):663-678

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Surface waves image the top of the Eifel plume   总被引：1，自引：0，他引：1  

Jan P. Mathar  Joachim R. R. Ritter  Wolfgang Friederich 《Geophysical Journal International》2006,164(2):377-382

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Surface wave tomography: finite-frequency effects lost in the null space   总被引：2，自引：1，他引：2  

Jeannot Trampert  Jesper Spetzler 《Geophysical Journal International》2006,164(2):394-400

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Computation of Large Anisotropic Seismic Heterogeneities (CLASH)     

Éric Beucler  Jean-Paul Montagner 《Geophysical Journal International》2006,165(2):447-468

A general tomographic technique is designed in order (i) to operate in anisotropic media; (ii) to account for the uneven seismic sampling and (iii) to handle massive data sets in a reasonable computing time. One modus operandi to compute a 3-D body wave velocity model relies on surface wave phase velocity measurements. An intermediate step, shared by other approaches, consists in translating, for each period of a given mode branch, the phase velocities integrated along ray paths into local velocity perturbations. To this end, we develop a method, which accounts for the azimuthal anisotropy in its comprehensive form. The weakly non-linear forward problem allows to use a conjugate gradient optimization. The Earth's surface is regularly discretized and the partial derivatives are assigned to the individual grid points. Possible lack of lateral resolution, due to the inescapable uneven ray path coverage, is taken into account through the a priori covariances on parameters with laterally variable correlation lengths. This method allows to efficiently separate the 2ψ and the 4ψ anisotropic effects from the isotropic perturbations. Fundamental mode and overtone phase velocity maps, derived with real Rayleigh wave data sets, are presented and compared with previous maps. The isotropic models concur well with the results of Trampert & Woodhouse. Large 4ψ heterogeneities are located in the tectonically active regions and over the continental lithospheres such as North America, Antarctica or Australia. At various periods, a significant 4ψ signature is correlated with the Hawaii hotspot track. Finally, concurring with the conclusions of Trampert & Woodhouse, our phase velocity maps show that Rayleigh wave data sets do need both 2ψ and 4ψ anisotropic terms.  相似文献