Reliability analysis for bearing capacity of surface strip footing using fuzzy finite element method

ABSTRACT

This paper presents the reliability analysis on the basis of the foundation failure against bearing capacity using the concept of fuzzy set theory. A surface strip footing is considered for the analysis and the bearing capacity is estimated using the conventional Finite Element Method (FEM). The spatial variability of the variables is taken into consideration to capture the physical randomness of the soil parameters for an isotropic field. A variation of the probability of failure (P_f) against a varying limiting applied pressure (q) is presented for different Coefficient of Variation (COV) of the variables and different scale of fluctuation (θ). The results reveal that the friction angle of soil (?) is the most influencing parameter among the other variables. Further, the influence of the scale of fluctuation (θ) on the probability of failure (P_f) is also examined. It is observed that for a particular COV of ?, higher value of θ predicts higher P_f whereas, P_f increases as COV of ? increases for a particular θ value. Later, a comparison study is accomplished to verify the viability of the present method and it can be noticed that the present method compares well with the other reliability method (First Order Reliability Method) to a reasonably good extent.     

岩土样本力学参数的模糊统计特征研究

岩土工程参数中的各种信息都存在模糊性。通过对岩土样本力学参数试验值的研究,提出当分析样本统计特征时,应该充分考虑模糊不确定性因素对参数特征值的影响。在确定的参数隶属函数基础上,推导了岩土样本力学参数模糊统计特征值的计算公式,并证明了公式的合理性。应用实例表明,由于文中提出的计算方法考虑了参数模糊性的影响,其计算结果比按常规统计方法得到的结果更具合理性。在任何情况下,模糊方差和模糊变异系数都比常规统计方法得到的方差和变异系数小。分析结果表明,该方法具有广泛的推广价值。     

渭河盆地基底伸展与地裂缝成因关系探讨

渭河盆地是我国乃至世界上地裂缝最为发育,灾害最为严重的地区。本文以渭河盆地为原型,采用有限元数值分析方法,分析了基底伸展作用下盆地浅表层岩土介质和多级破裂系统的应力和变形响应特征,从而揭示基底伸展变形与该区域地裂缝之间的成因关系。结果表明,盆地基底的伸展作用可以引起近地表岩土介质的拉张变形,当这种拉张作用与盆地断裂的上盘正断倾滑式伸展拉张叠加时,必然形成或加剧地表土层的张剪性破裂,从而为地裂缝的发育奠定了构造基础。     

青海省天峻县木里煤田煤层气有利区块的 多层次模糊数学评判

对影响煤层气勘探开发潜力的各种因素进行了综合研究,确定了煤层气勘探开发潜力评价的3个二级指标(生气潜力、储层物性和封盖性能)及对应的三级指标。采用模糊数学方法对各级因素指标赋予权重,建立了用于煤层气勘探开发潜力评价的多层次模糊数学评判模型。利用该模型,对青海木里煤田中低煤阶煤层气资源勘探开发潜力进行了评价,认为江仓矿区是木里煤层气勘探开发的最佳试验区。所建立的评价体系可以作为中低煤阶煤层气资源开发潜力评价的参考体系。     

基于改进型前馈神经网络的流域产流预报模型的研究

在分析流域产流机制、影响因素和现行产流计算方法的基础上,首次取前期影响雨量、主产流历时、全过程面平均雨量和４个代表雨强计７个因子作为神经网络输入,直接以流域产流深作为神经网络输出,并针对传统ＢＰ算法的固有缺陷,采用混合ＧＮ－ＢＦＧＳ算法训练网络。实例验证了所建模型及算法的有效性和可行性。还对神经网络隐层单位数等进行了初步研究。     

晋1-1井水位异常与晋冀蒙交界区中强地震关系简析

通过对晋1-1井22年水位观测资料进行系统清理,对距井区约330km范围一些中强震前的水位资料进行了细致分析。结果表明:晋1-1井地震异常以短临突变异常为主,异常时间多小于80d。根据大量的震例统计结果给出了地震前兆异常定量判别指标,当曲线阶升异常幅度大于30mm或阶降大于40mm时视为震兆异常。     

Radar isochronic layer dating for a deep ice core at Kunlun Station,Antarctica

The ages and accumulation rates of ice are important boundary conditions for paleoclimatic ice models. Radardetected isochronic layers can be used to date the ice column beneath the ice surface and infer past accumulation rates. A Deep Ice-Core Drilling Project has been carried out at Kunlun station in the Dome A region, East Antarctica. Radio echo sounding data are collected during the 2004/2005 Chinese National Research Expedition and the 2007/2008 Dome Connection East Antarctica project of the Alfred Wegener Institute(Germany). Radar isochronic layers from the dataset were linked to compare a new deep ice core site from Kunlun station and the Vostok ice core site. Ten visible layers, accounting for ~50% ice thickness at the Kunlun station ice core site, were dated based on the Vostok ice core chronology. At 1,640 m depth below surface, an age of ~160,400 yr was determined, corresponding to a bright layer at Kunlun station. These layers provided geometric information on the past surface of the ice sheet around the ice core site through the Wisconsin glacial stage, Eemian interglacial and Marine Isotope Stage6. Based on a simple ice flow model and the age-depth relationship, we concluded that the region around the Kunlun ice core site had lower past accumulation rates, consistent with the present pattern. The age-depth relationship would thus be expected to correlate and constrain the chronology of the deep ice core at Kunlun station in the future.     

Geostatistical regionalization of glacial aquitard thickness in northwestern Germany, based on fuzzy kriging

In many instances hydrogeological parameters obtained by conventional methods for selected localities within an aquifer or an aquitard are not sufficient for adequate regionalization at the scale of the entire layer. Here, we demonstrate an application of the fuzzy kriging method in regionalization of hydrogeological data, in which the set of conventional, crisp values is supplemented by imprecise information subjectively estimated by an expert. It is believed that such an approach eventually may reflect the real-world conditions more closely than a traditional crisp-value approach, because the former does not impose exactness artificially on phenomena which are diffuse by their nature. Spatial interpolation was done for the thickness of one of the major aquitards (till and glaciolacustrine clay) in northwestern Germany. The dataset consists of 329 crisp values from boreholes supplemented by 172 imprecise values defined as fuzzy numbers. It is demonstrated that the reliability of regionalization was higher, compared to regionalization performed with the crisp dataset only. Fuzzy kriging was performed with FUZZEKS (Fuzzy Evaluation and Kriging System) developed at the Ecosystem Research Center at the University of Kiel.     

地质动力区划中断裂活动性的模糊综合评判

地质构造尤其是活动断裂控制着动力现象的区域性分布,然而活动断裂与矿井动力现象的关系并不是绝对和完全的。对断裂活动性进行评价,确定断裂的动力活动强度,是进行动力现象的预测与预防的重要内容之一。文章通过分析活动断裂的特征及其对矿区原地应力场的影响,提出了既具有代表性又容易获取的适合多尺度断裂活动性评价的5个主要指标,即活动断裂两侧断块的高程差、活动断裂长度、活动断裂走向与最大主应力的夹角、活动断裂走向与最大剪应力的夹角及断裂地震综合指标。利用模糊数学方法,建立了断裂活动性评价的模糊综合评判模型,确定了隶属函数,并通过层次分析法确定了各个指标的权重,最终获得了断裂活动性的模糊综合评判结果。将该方法应用于新汶矿区协庄矿,结果显示冲击地压多发生于具有强活动性的断裂附近。表明文章建立的评判模型能够较好地对断裂活动性进行分级。文章提出的模糊综合评判方法,改进了地质动力区划中断裂活动性评价方法,提高了评价结果的准确性及合理性。