油罐基础不均匀沉降主要影响因素的敏感性分析

在上部均布荷载作用下柔性基础基底压力是均匀分布的,基底以下土体在同一深度附加应力呈现中间大、周围小的分布规律,导致基础沉降中间大、周围小。刚性基础的沉降是均匀的,必然导致基底压力的分布为周围大、中间小。软基上的油罐筏板基础是具有一定刚度的基础,但并非刚性基础,因而基底压力分布应该介于柔性基础和刚性基础之间,沉降为中间大、周围小的不均匀分布。基于ABAQUS有限元分析,结合工程实际情况,采用UH模型作为土体本构模型进行了模拟分析,对筏板厚度、地基刚度等影响基础不均匀沉降的主要因素进行敏感性分析,探求变刚度地基在油罐基础不均匀沉降中的影响规律。     

控制差异沉降的桩筏基础桩径优化分析方法

桩径优化是桩筏基础以差异沉降最小化为目标的基础优化分析的重要组成部分。基于桩筏基础通用分析方法,结合遗传算法提出了包含非线性约束条件的以差异沉降控制为目标的桩筏基础桩径优化分析模型,并给出了优化分析的实施步骤。通过示例说明了桩径优化的实施情况,对比给出了优化前后基础沉降、桩基荷载分布与筏板分担比、筏板弯矩和剪力结果。最后通过参量分析研究了筏板厚度、桩基参量和土体参量对最优桩径确定的影响程度,桩长和土体特性对桩径优化结果影响显著,而桩体材料特性和筏板厚度对桩径优化结果影响不大。     

灰色预测在软土地基沉降分析中的应用

运用灰色理论建立了软基沉降的不等时距预测 G M ( 1, 1)模型 ,并可用残差的 GM ( 1, 1)模型对其进行修正。工程实例验证结果令人满意。     

Re-assessment of foundation settlements for the Burj Khalifa, Dubai

This paper deals with the re-assessment of foundation settlements for the Burj Khalifa Tower in Dubai. The foundation system for the tower is a piled raft, founded on deep deposits of calcareous rocks. Two computer programs, Geotechnical Analysis of Raft with Piles (GARP) and Non-linear Analysis of Piled Rafts (NAPRA) have been used for the settlement analyses, and the paper outlines the procedure adopted to re-assess the foundation settlements based on a careful interpretation of load tests on trial piles in which the interaction effects of the pile test set-up are allowed for. The paper then examines the influence of a series of factors on the computed settlements. In order to obtain reasonable estimates of differential settlements within the system, it is found desirable to incorporate the effects of the superstructure stiffness which act to increase the stiffness of the overall foundation system. Values of average and differential settlements for the piled raft calculated with GARP and NAPRA were found to be in reasonable agreement with measured data on settlements taken near the end of construction of the tower.     

分层总和法计算沉降的几点改进

利用Matlab6.1平台,通过编制可视化应用程序,对分层总和法计算沉降的传统方法作了较大的改进,地基中的附加应力采用原始积分公式,压缩曲线采用双曲线形式,使用非线性最小二乘法进行拟合处理,压缩层计算深度与分层厚度不再受到限制,数据输入、输出及沉降计算过程均通过可视化界面进行操作,不再需要通过查表、查图计算基础底面的沉降,计算过程简单便利,计算结果重复性好,具有较大的实际应用价值。     

A generalized probabilistic approach for slope analysis

Summary A new probabilistic approach is introduced for slope stability analysis, which is general in types of variable distributions and correlations or dependency between variables, and flexible enough to include any adverse impact analysis for blasting vibrations and groundwater conditions.The material strength within a slope area, given in terms of the internal friction angle (ø) and cohesion (c), is randomized in the bivariate joint probability analysis. To be a completely general engineering method, the new probabilistic approach employs the random variable transformation technique: the Hermite model of the Gaussian transformation function, which transforms the experimental histogram of shear strength parameters to the standard Gaussian distribution (=0, ²=1.0).Because a binormal joint probability is analysed on the true probability region projected on the plane of the Gaussian transformed variables, it is an exact solution of slope stability based on the available sample data. No assumption on the shape of the experimental histogram or independency between two random variables is made as in the current probability methods of slope analysis.     

A framework for the probabilistic analysis of meteotsunamis

A probabilistic technique is developed to assess the hazard from meteotsunamis. Meteotsunamis are unusual sea-level events, generated when the speed of an atmospheric pressure or wind disturbance is comparable to the phase speed of long waves in the ocean. A general aggregation equation is proposed for the probabilistic analysis, based on previous frameworks established for both tsunamis and storm surges, incorporating different sources and source parameters of meteotsunamis. Parameterization of atmospheric disturbances and numerical modeling is performed for the computation of maximum meteotsunami wave amplitudes near the coast. A historical record of pressure disturbances is used to establish a continuous analytic distribution of each parameter as well as the overall Poisson rate of occurrence. A demonstration study is presented for the northeast U.S. in which only isolated atmospheric pressure disturbances from squall lines and derechos are considered. For this study, Automated Surface Observing System stations are used to determine the historical parameters of squall lines from 2000 to 2013. The probabilistic equations are implemented using a Monte Carlo scheme, where a synthetic catalog of squall lines is compiled by sampling the parameter distributions. For each entry in the catalog, ocean wave amplitudes are computed using a numerical hydrodynamic model. Aggregation of the results from the Monte Carlo scheme results in a meteotsunami hazard curve that plots the annualized rate of exceedance with respect to maximum event amplitude for a particular location along the coast. Results from using multiple synthetic catalogs, resampled from the parent parameter distributions, yield mean and quantile hazard curves. Further refinements and improvements for probabilistic analysis of meteotsunamis are discussed.     

A proposed probabilistic seismic tsunami hazard analysis methodology

Natural Hazards - We expand on existing probabilistic tsunami hazard analysis (PTHA) approaches by presenting a methodology wherein the epistemic uncertainties associated with tsunami timing,...     

PSI和CRI联合算法用于苏通大桥基础沉降监测

深厚河床覆盖层地基上建设的超大型群桩基础,其沉降是安全监控的关键问题。针对苏通大桥群桩基础沉降监测中存在的问题,在基础沉降监测中综合运用了永久散射体干涉测量（PSI）和人工角反射器干涉测量（CRI）监测技术。结合大桥自身的永久散射体特性和桥位区重点监测部位安装的人工角反射器,利用EV-InSAR软件的CTM模块对该地区2003－2008年（主体工程施工期间）间获取的20景Envisat卫星单视复数据（SLC）进行差分干涉测量处理,利用PSI和CRI联合算法成功提取出了桥位区的永久散射体点,并解算出各永久散射体点在施工过程不同阶段的变形量,客观、全面地反映了苏通大桥在建设过程中基础的沉降。将获取的主墩处的永久散射体沉降量与有限元计算结果进行了对比,两者相对误差为4.64%。研究结果表明,PSI和CRI联合算法是一种极具潜力的大型桥梁地基基础沉降监测技术。随着监测区合成孔径雷达（SAR）数据的不断累积,利用该技术可以不断获取运营中的苏通大桥基础的高精度沉降量。     

Application of a memory surface model to predict whole-life settlements of a sliding foundation

In this paper a novel modelling procedure is proposed to estimate whole-life settlements of tolerably mobile sliding foundations. A new kinematic hardening-critical state-state parameter constitutive model, the Memory Surface Hardening model, is implemented in a one-dimensional analysis to predict accumulated vertical settlements under drained lateral cyclic loading. The Memory Surface Hardening model performance is compared with the Modified Cam Clay and Severn-Trent Sand models. The Memory Surface Hardening model is adopted to simulate available experimental data from centrifuge tests to predict the settlement of a sliding foundation at the final stable state (i.e. no further volume changes occur).     

Israeli frontier settlements: a cross-temporal analysis

Pragmatic geo-political considerations and a national ideology have guided both pre-1948 and post-1967 Jewish frontier settlements. Each settlement stage was characterized by penetration into remote areas on the periphery of older, established communities.In order to comprehend the development of Jewish frontier settlements, three factors must be analyzed: the historical geographic situation, the method of settlement, and the spatial network of the settlements themselves.Consequently, three waves of frontier settlements are explored in this research: (a) 1907–1916, which marked the first settlement attempt made by the Zionist Organization; (b) 1936–1939, when ‘Tower and Stockade’ settlements emerged as a reaction to the British partition plan; and (c) 1967 to the present, which followed the ‘Third Arab-Israeli’ war.     

A numerical model for foundation settlements due to deformation accumulation in granular soils under repeated small amplitude dynamic loading

Repeated small amplitude dynamic loading of the soil in the vicinity of buildings, as arising from traffic or construction activities, may cause differential foundation settlements and structural damage. In this paper, a numerical model for soils under repeated dynamic loading is formulated. It is assumed that the dynamic part of the loading is small with respect to the static part, reflecting the stress conditions in the soil underneath buildings. As the plastic deformation in the soil is only observed after a considerable amount of dynamic loading cycles, only the accumulation of the average plastic deformation is considered. The model accounts for the dependency of the deformation on the stress conditions and the dynamic loading amplitude. The accumulation model is implemented in a finite element framework, using a consistent tangent approach in combination with a backward Euler integration scheme. A triaxial test is considered in a first numerical example. The available analytical solution for this problem allows to validate the numerical implementation. Second, the differential settlement of a two‐storey building founded on loose sandy soil under repeated vehicle passages is considered. The differential foundation settlement causes the stresses to increase at the bottom of the wall, which may result in damage. Copyright © 2009 John Wiley & Sons, Ltd.     

节理岩体关键块体稳定的概率分析

基于地下岩体受节理面的控制,节理面的几何和力学参数随机分布,从而导致岩体系统具有高度不确定性,提出以关键块体理论为基础,考虑节理几何和力学参数随机性的岩体开挖可靠度分析方法,并给出了块体稳定的总失效概率评价模型。以澳大利亚阿德莱德地区一铜矿地质条件为例,以节理面倾角、倾向、摩擦系数和黏聚力为随机变量,通过Monte Carlo模拟和概率图方法,进行了岩体可靠度和失效概率的计算。最后,采用条件概率的分析方法,计算了单面滑动块体的总失效概率。计算结果表明,块体沿单面滑动并且出现的概率为11.0%,总的失效概率为3.85%,超过一般岩体工程可允许的风险水平,认为该方法可以作为评价块体可靠性的依据。     

Elastoplastic medium for foundation settlements and monotonic soil–structure interaction under combined loadings

Foundation settlements and soil–structure interaction are important problems to structural and geotechnical engineers. This study introduces a novel elastoplastic three‐degree‐of‐freedom medium which models foundations settlements under combined loadings. A soil–structure interaction problem can then be solved by replacing the soil mass with this three‐degree‐of‐freedom elastoplastic medium, thus reducing significantly the size of the problem. The model was developed by extending the classical plasticity concepts to the force‐deformation level. Its ability to predict foundation deformations was evaluated using finite element solutions of a typical shallow foundation problem and was found reasonably accurate while producing significant time savings. Copyright © 2006 John Wiley & Sons, Ltd.     

Territorial settlements and settlements in territories:

Conclusions What is it then that a participant reflects upon as he returns to the less heady realm of his own professional and scholarly activities? First of all, there is conflict. Once the threat of nuclear was rested chiefly in bipolar competition between the U.S. and the Soviet Union. We are now in a multipolar world: infinitely more unpredictable and dangerous, where a lunatic individual could cause as much terror as a whole nation. Institutional arrangements are essential permitting the ebb and flow of conflict. Political geography shows that modern nations are a composite of earlier tribalisms and regional loyalties. Perhaps the same process of increasing consciousness can be expanded to shared responsibility from megalopolitan to global scales. Directly related to this is the issue of population. Anthropos is increasing at the rate of 200,000 more births than deaths a day. Many answers are given by experts, but the main item of consensus appears to be that population will decrease when the lowest-income groups are lifted out of absolute proverty, the darkness of malnutrition, ignorance, and disease.     

Probabilistic foundation stability analysis

A probabilistic model for stability analysis of a deepwater gravity-based platform foundation is defined, based on theory for wave loading in conjunction with conventional slip surface considerations. The model accounts for uncertainties in loading as well as in soil properties, and model uncertainties are also considered. The model is updated through in-service measurements of some of the governing variables, and measurement uncertainties are included. The practical application of the model is illustrated by presentation of calculations for a typical foundation. Probability calculations are performed by first-order reliability methods.     

某基坑位移、沉降和内力实测结果及预警值讨论

以某深基坑支护结构位移、沉降、内力及水位的施工监测数据为依据,探讨了位移、沉降与内力大小及变化规律。实测表明：支护桩及外侧土体各点随着基坑开挖深度和时间的递增,水平位移逐步增大,增大速度由快逐步趋于平稳。另外,位移大小还与周围建筑物位置和支撑条件有关。周围建筑物的沉降随时间增大,且离基坑越近则越大;立柱沉降及土的隆起量与承受的支撑重量及基坑形状有关;支撑轴力的大小及变化与地质条件、支撑刚度和施工开挖顺序及速度等因素有很大关系;桩身偏心较小,底部可按轴心受力计算。最后,对预警值进行了讨论。     

软土地基上建筑物沉降的三维数值模拟分析

受场地地质条件的限制,很多建筑物采用高压缩性的软土作为天然地基,软土地基的不均匀沉降会威胁到结构的安全。不均匀沉降受上部荷载、结构刚度以及土层的不均匀性等因素的影响,传统的分层总和法不能全面地考虑这些因素。因此需要一种更为有效的分析方法来预测建筑物的沉降情况。采用结构、基础与地基共同作用的分析方法,对一栋倾斜的砖混建筑物进行三维数值模拟分析。通过与实际观测结果相比较,证明该方法能很好地分析建筑物的不均匀沉降情况。     

厦门某厂人工挖孔桩质量事故分析

通过静载、钻芯等测试手段对一个人工挖孔桩的桩基工程质量事故进行分析,找出造成质量事故的原因,提出桩基工程中应注意的问题。     

有限压缩层地基上筏基沉降的边界元分析

基于有限压缩层地基模型和Reissner板的边界积分方程,考虑柱荷载作用区域的形状和筏板的横向剪切变形效应,建立了有限压缩层地基上厚筏基础与地基相互作用分析的边界元方程和系统的数值方法。对于弹性半空间模型,其柔度方程可视为有限压缩层模型的特殊情况。把筏板作为自由边界条件处理,被剖分为一系列三角形或矩形网格,假设基底反力在网格内均匀分布,以便与现有的地基沉降计算模式相一致。计算表明,虽然基底反力在内部网格相接处不连续,但并不影响计算结果,反而消除了边界基底压力计算值过大的现象。将该方法与其他方法的计算结果进行比较,显示了该方法的有效性。计算结果表明,对于实际复杂的筏板基础,无需划分太多单元即可得到较高的计算精度