降雨作用下山区边坡稳定性分析

降雨是诱发边坡失稳破坏的主要原因,本文以坡地水文模型为基础,结合无限边坡稳定计算模型,研究降雨条件下边坡启动的临界降雨条件。通过工程算例表明:降雨量与边坡体稳定系数成反比;滑坡启动的临界降雨量随边坡坡度的增大而减少;随边坡土体内摩擦角的增加而逐渐增加,此分析对降雨型滑坡的研究有借鉴性的意义。     

土体本构模型对强度折减法分析基坑整体稳定性的影响

运用有限元强度折减法对基坑工程进行整体稳定性分析时,已有研究主要采用摩尔-库伦模型对土体进行模拟,由于摩尔-库伦模型给出的基坑变形曲线与实测不符,故据此得到的基坑整体稳定安全系数也不甚合理。采用Plaxis硬化模型模拟开挖过程,在强度折减分析中采用特征点位移突变对基坑整体稳定性进行收敛判断,通过分析对比所选取的不同特征点的位移与折减系数的关系曲线,提出采用挡墙内侧开挖面附近土体作为收敛判断的判别点较为合理,其安全系数的取值与采用极限平衡法得到的结果比较接近,而摩尔-库伦模型所得到的计算结果则偏大。最后分析了基坑宽度、基底软土层厚度、挡墙插入深度和挡墙刚度等因素对基坑整体稳定性的影响,并比较了采用这两种不同土体本构模型对分析结果的影响     

From Predictive Mapping of Mineral Prospectivity to Quantitative Estimation of Number of Undiscovered Prospects

This paper proposes that the spatial pattern of known prospects of the deposit‐type sought is the key to link predictive mapping of mineral prospectivity (PMMP) and quantitative mineral resource assessment (QMRA). This proposition is demonstrated by PMMP for hydrothermal Au‐Cu deposits (HACD) and by estimating the number of undiscovered prospects for HACD in Catanduanes Island (Philippines). The results of analyses of the spatial pattern of known prospects of HACD and their spatial associations with geological features are consistent with existing knowledge of geological controls on hydrothermal Au‐Cu mineralization in the island and elsewhere, and are used to define spatial recognition criteria of regional‐scale prospectivity for HACD. Integration of layers of evidence representing the spatial recognition criteria of prospectivity via application of data‐driven evidential belief functions results in a map of prospective areas occupying 20% of the island with fitting‐ and prediction‐rates of 76% and 70%, respectively. The predictive map of prospective areas and a proxy measure for degrees of exploration based on the spatial pattern of known prospects of HACD were used in one‐level prediction of undiscovered mineral endowment, which yielded estimates of 79 to 112 undiscovered prospects of HACD. Application of radial‐density fractal analysis of the spatial pattern of known prospects of HACD results in an estimate of 113 undiscovered prospects of HACD. Thus, the results of the study support the proposition that PMMP can be a part of QMRA if the spatial pattern of discovered prospects of the deposit‐type sought is considered in both PMMP and QMRA.     

Numerical modeling of multiphase fluid flow in deforming porous media: A comparison between two- and three-phase models for seismic analysis of earth and rockfill dams

In this paper, a fully coupled numerical model is presented for the finite element analysis of the deforming porous medium interacting with the flow of two immiscible compressible wetting and non-wetting pore fluids. The governing equations involving coupled fluid flow and deformation processes in unsaturated soils are derived within the framework of the generalized Biot theory. The displacements of the solid phase, the pressure of the wetting phase and the capillary pressure are taken as the primary unknowns of the present formulation. The other variables are incorporated into the model using the experimentally determined functions that define the relationship between the hydraulic properties of the porous medium, i.e. saturation, relative permeability and capillary pressure. It is worth mentioning that the imposition of various boundary conditions is feasible notwithstanding the choice of the primary variables. The modified Pastor–Zienkiewicz generalized constitutive model is introduced into the mathematical formulation to simulate the mechanical behavior of the unsaturated soil. The accuracy of the proposed mathematical model for analyzing coupled fluid flows in porous media is verified by the resolution of several numerical examples for which previous solutions are known. Finally, the performance of the computational algorithm in modeling of large-scale porous media problems including the large elasto-plastic deformations is demonstrated through the fully coupled analysis of the failure of two earth and rockfill dams. Furthermore, the three-phase model is compared to its simplified one which simulates the unsaturated porous medium as a two-phase one with static air phase. The paper illustrates the shortcomings of the commonly used simplified approach in the context of seismic analysis of two earth and rockfill dams. It is shown that accounting the pore air as an independent phase significantly influences the unsaturated soil behavior.     

双层堤管涌的悬挂型防渗控制实验研究

双层堤基是应用较多的双面层的堤基构造类型,上层为弱透水层,下层为强透水深厚砂层。堤内弱透水层在汛期高水位时面临较高的水头承压,出现管涌的危险性极大。以实验室模拟分析的方式,专题探究双层堤管涌的悬挂型防渗控制规律,结果可知:悬挂型防渗墙在有效截断管涌迁移路径方面具有独特功能和阻滞效果,管涌没有出现之前,悬挂式防渗墙消解水头冲刷的作用一般不很明显,而一旦有管涌发生,防渗墙对透水堤基深入越深,防渗作用将越好,如果保持贯入度相同,则下游布置防渗墙比上游布置防渗墙效果要好。研究结果为同类工程应用提供研究和技术参考。     

基于铜陵矿集区遥感影像的地质解译及成矿远景区圈定研究

本文对铜陵矿集区的landsat 7 ETM+遥感影像进行综合分析,获取影像波谱特性,运用波段比值和主成分分析的方法提取铁染和羟基蚀变信息,利用彩色密度分割得到蚀变异常图像,清晰显示铜陵矿集区的成矿有利区域。并对遥感解译结果和铜陵地区地质构造与现有矿点对比,验证提取结果。圈定的11个成矿有利区域中:3个A类区蚀变信息明显,具备有利成矿条件,成矿潜力巨大;4个B类区蚀变信息中等,具备有利成矿条件,具有一定成矿潜力;4个C类区蚀变信息离散,成矿条件不明显,具有成矿可能,但是潜力不大。     

基坑工程平面竖向弹性地基梁法中土的水平抗力比例系数反分析研究

提出了一种结合Ucode反分析软件和Abaqus有限元分析软件,并根据围护墙实测变形来反分析基坑工程平面竖向弹性地基梁法中土的水平抗力比例系数的方法。重点讨论了反分析的原理和实现流程,给出了反分析过程中迭代控制参数的确定方法及待估参数取值的确定方法。通过参数敏感分析可找到对围护结构变形影响较大的土层,针对起主导作用的土层m值进行反分析,既可提高迭代效率,又能保证反分析结果的准确性。实际工程反分析的结果表明,计算值与实测围护墙变形吻合得很好。在此基础上,根据多个测孔的反分析结果给出了各层土的水平抗力比例系数的建议取值。     

Quantitative evaluation of the biostratigraphic distribution of acanthomorphic acritarchs in the Ediacaran Doushantuo Formation in the Yangtze Gorges area, South China

Doushantuo acanthomorphic acritarchs are large morphologically complex organic-walled microfossils broadly constrained between the 635 Ma Nantuo glaciation and the 551 Ma Miaohe Biota. They are potential biostratigraphic tools for subdivision and correlation of the Ediacaran System in South China. However, major variations in sedimentary facies and stratigraphic thickness present challenges in understanding the spatial and temporal distribution of these acritarchs. Further, the distribution of acritarchs in the Doushantuo Formation is associated with the presence of early diagenetic chert and phosphate, implying a certain degree of preservational bias and/or environmental control. The purpose of this paper is to document the stratigraphic distribution of Doushantuo acritarchs and to quantitatively evaluate their biostratigraphic significance and possible taphonomic–environmental biases, based on high-resolution paleontological data from six sections over 100 km in the Yangtze Gorges area, South China.A total of 1082 acritarch fossils were recorded from 84 chert horizons in the six sections of the study area. These chert horizons are not uniformly distributed throughout the Doushantuo Formation, thus the presence/absence of early diagenetic chert does play a role in controlling the distribution of acritarchs. The sampled chert horizons can be grouped into two stratigraphic intervals in the lower and upper Doushantuo Formation, respectively, based on regional stratigraphic correlation. Quantitative analysis shows that the two intervals are distinct taxonomically and largely independent of taphonomic or facies controls. Thus, the two intervals can be regarded as assemblage biozones. The lower biozone (biozone 1) is numerically dominated by Tianzhushania spinosa (n = 587; 68.3%) and Meghystrichosphaeridium magnificum (n = 74; 8.6%), whereas the upper biozone (biozone 2) is dominated by Ericiasphaera rigida (n = 104; 47.1%) and Tianzhushania spinosa (n = 34; 14.1%). The three most common genera, Meghystrichosphaeridium, Tianzhushania, and Ericiasphaera, have been identified in all sections. Correspondence analysis (CA), detrended correspondence analysis (DCA), discriminant analysis (DA), and pairwise comparisons of samples (Spearman rank coefficient and Jaccard–Chao index), all consistently support biostratigraphic zonations. Thus, the distribution of the Doushantuo acanthomorphs is primarily controlled by biostratigraphic position of samples, with facies and taphonomic differences playing a secondary role. Our case study suggests that acanthomorphic acritarchs can offer a viable tool for regional correlation of the Ediacaran System.     

Stabilization of Expansive Clays Using Granulated Blast Furnace Slag (GBFS) and GBFS-Cement

Expansive clays undergo swelling when subjected to water. This can cause damage, especially to light weight structures, water conveyance canals, lined reservoirs, highways, and airport runways unless appropriate measures are taken. In this study, granulated blast furnace slag (GBFS) and GBFS-cement (GBFSC) were utilized to overcome or to limit the expansion of an artificially prepared expansive soil sample (sample A). GBFS and GBFSC were added to sample A in proportions of 5–25% by weight. The effects of these stabilizers on grain size distribution, Atterberg limits, swelling percentage and rate of swell of soil samples were determined. GBFS and GBFSC were shown to successfully decreasing the total amount of swell while increasing the rate of swell.