土工参数不确定性的计算分析

本文根据影响土工参数不确定性的主要因素建立起来的随机模型，探讨了土工参数不确定性的一种计算途径。对土的空间平均特性问题，根据土性随机场理论，就波动幅度（相关距离）的计算提出了曲线极限法。并获得了土工参数空间变异系数的综合计算式。     

杭州地区典型土层抗剪强度指标的变异性研究

根据杭州地区大量实际工程的勘察资料,通过采用土层剖面随机场模型,把土性参数的点变异性和空间变异性联系起来,对几个典型土层强度指标的空间概率特征进行了统计分析,得出了强度指标相关距离和空间变异系数的变化规律。另外,还对杭州地区几个土层强度指标三轴实验和直剪实验的差异性和相关性进行了实验研究。     

软土抗剪强度指标的变异性

引入土层剖面随机场模型 ,把土性参数的点变异性和空间变异性联系起来。利用上海地区 1 7个典型场地的直固快剪试验资料的统计结果 ,提出土层抗剪强度指标点变异系数的置信区间 ,建议在可靠度分析中使用置信上限估计值并考虑空间平均后的折减效应。     

软土地基抗剪强度指标的变异性

引入土层剖面随机场模型,把土性参数的点变异性和空间变异性联系起来。利用上海地区17个典型场地的直固快剪试验资料的统计结果,提出土层抗剪强度指标点变异系数的置信区间,建议在可靠度分析中使用置信上限估计值并考虑空间平均后的折减效应。     

基于随机场理论的盾构隧道地表变形分析

采用随机场理论和数值分析相结合的方法,研究土性参数的空间变异性对盾构隧道施工地表变形的影响。利用协方差矩阵分解法建立描述土性参数空间变异性特征的随机场模型,结合Monte-Carlo策略,采用FLAC3D软件分析弹性模量的变异系数、相关距离对地表变形的影响。研究结果表明:土体弹性模量的空间变异性对地表变形规律有着重要的影响,在变形形态和量值上均有不同程度的体现;根据土体弹性模量的相关距离与隧道直径之间比值的大小关系,总结提出3种地表变形模式;最大地表沉降近似服从对数正态分布,且随着土体弹性模量的变异系数和相关距离的增大,最大地表沉降的概率分布越分散,超出沉降监测控制值的概率逐渐增加。     

基于随机场理论的地基稳定性模糊可靠度分析

根据Vanmarcke提出的随机场理论描述土性参数的空间变异性,建立了考虑土性参数空间变异性的地基失稳模糊概率公式,并通过实例分析了两种情况下地基的模糊失效概率值,得出用随机场理论空间均值方差计算的模糊失效概率值比不考虑土性参数的空间变异性计算模糊失效概率值偏低的结论.     

考虑参数空间变异性的隧道下穿建筑物安全性评价

考虑土性参数的空间变异性,构建了基于随机场理论和数值分析手段的隧道下穿建筑物安全概率评价方法。将土体参数弹性模量视为随机场模型,采用应力释放方法模拟隧道施工,并基于地表建筑物为柔性简支梁的假设,利用极限拉应变作为判定指标对建筑物安全进行概率性评价。结果表明,所提出方法能够在考虑土性参数空间变异性的前提下有效地评价隧道下穿建筑物的安全性。土体弹性模量变异系数和自相关距离对隧道下穿建筑物安全性具有显著的影响;弹性模量的变异程度越高造成建筑物内最大拉应变的概率分布越离散,达到较高破坏等级的概率也越大。     

非均质地基上条形基础沉降的随机有限元分析

针对非均质地基土上条形基础弹性沉降计算的复杂性,建立了无量纲化有限元模型,处理了边界距离和弹性模量变异性问题。在确定性分析基础上,分别运用一阶Taylor展开式随机有限元(简称SFEM)和Monte-Carlo数值模拟随机有限元(简称RFEM)分析了土体弹性模量变异性对基础沉降的影响。结果表明,SFEM低估了基础沉降特征值受弹性模量变异性的影响程度。弹性模量变异系数越大,SFEM对基础沉降均值和标准差低估程度越显著,基础沉降均值随弹性模量空间相关距离逐渐减小。RFEM分析结果则呈现波动性但整体有不断增大趋势,因而基础沉降计算结果更为合理。     

福建沿海地区软土土性参数的空间自相关距离分析

以福建沿海地区软土为研究对象,采用递推平均法对其土性参数的空间自相关距离进行计算分析,研究其土性参数变异性的特征,并指出递推平均法计算中取值应注意的问题.     

基于Kriging法的土性参数估计

讨论了土参数(qc)随机特征，并用半变异函数的球状模型来模拟土参数竖向及水平向的变异特征。基于地质统计学方法，采用随机搜索原理建立估值样本空间，进而用优化解法求解土参数估计的目标函数。本文提出的二维土参数估计方法中考虑了竖向变异特性，用相关距离内的局部均值来代替“点”值，因而更能反映土参数的空间平均特性。本方法适用于岩土工程决策系统中土性参数估计和场地特征的描述。     

Kriging Numerical Models for Geotechnical Reliability Analysis

When the performance function is an implicit numerical model, geotechnical reliability analysis can be challenging due to the coupling between the deterministic numerical evaluation and reliability analysis. Previously, the kriging method was used in geotechnical engineering for modeling the spatial variability of soil properties. In this paper, we illustrate a first-order reliability analysis method based on a kriging approximation of the deterministic numerical model. The key idea in this method is to first calibrate a kriging model to approximate the deterministic numerical model, and then to evaluate the failure probability based on the kriging model. As any stand-alone software for deterministic geotechnical numerical analysis can be potentially used to generate samples for calibrating a kriging model, it can then be ultimately used for a reliability analysis. As such, this method provides a practical way for practitioners to perform reliability analysis based on existing deterministic geotechnical software. The effectiveness of the suggested method is illustrated through a pile foundation example, a shallow foundation example, and a slope example in which the performance functions do not have explicit forms. The kriging method is used here as a tool for interpolating and approximating deterministic numerical models. The present paper does not address any type of spatial variation of soil properties.     

Soil spatial variability impact on the behavior of a reinforced earth wall

This article presents the soil spatial variability effect on the performance of a reinforced earth wall. The serviceability limit state is considered in the analysis. Both cases of isotropic and anisotropic non-normal random fields are implemented for the soil properties. The Karhunen-Loève expansion method is used for the discretization of the random field. Numerical finite difference models are considered as deterministic models. The Monte Carlo simulation technique is used to obtain the deformation response variability of the reinforced soil retaining wall. The influences of the spatial variability response of the geotechnical system in terms of horizontal facing displacement is presented and discussed. The results obtained show that the spatial variability has an important influence on the facing horizontal displacement as well as on the failure probability.     

Utilisation of transparent synthetic soil surrogates in geotechnical physical models: A review

Efforts to obtain non-intrusive measurement of deformations and spatial flow within soil mass prior to the advent of transparent soils have perceptible limitations. The transparent soil is a two-phase medium composed of both the synthetic aggregate and fluid components of identical refractive indices aiming at attaining transparency of the resulting soil. The transparency facilitates real life visualisation of soil continuum in physical models. When applied in conjunction with advanced photogrammetry and image processing techniques, transparent soils enable the quantification of the spatial deformation, displacement and multi-phase flow in physical model tests. Transparent synthetic soils have been successfully employed in geotechnical model tests as soil surrogates based on the testing results of their geotechnical properties which replicate those of natural soils. This paper presents a review on transparent synthetic soils and their numerous applications in geotechnical physical models. The properties of the aggregate materials are outlined and the features of the various transparent clays and sands available in the literature are described. The merits of transparent soil are highlighted and the need to amplify its application in geotechnical physical model researches is emphasised. This paper will serve as a concise compendium on the subject of transparent soils for future researchers in this field.     

压电陶瓷传感器在岩土工程中的应用

压电陶瓷传感器在岩土工程中有很多应用,尤其是通过测量波速来确定土的性质方面。由于材料的物理性质与波速密切相关,压电陶瓷传感器提供了一种简便可靠的无损检测方法。本文报道了压电陶瓷传感器应用于粘土、砂和砾石等不同种类土的研究成果,对应力导致土体各向异性的研究,对路基和地基土的力学特性检测,在离心模型试验中的应用,以及在微重力环境下的粒状材料中波的传播特性的研究等。研究表明,压电陶瓷传感器在岩土力学研究和工程实践中有广阔的应用前景。     

基于高密度电阻率法的水分迁移模型试验研究

在土工模型试验中,常用的应用于水分及溶质迁移过程量测的传感器量测、图像分析及取样分析等方法并不能充分满足三维、无损、实时的量测需求。高密度电阻率成像法为土工模型试验中三维、无损、实时量测需求提供了新的解决思路。基于高密度电阻率成像法发展一套适用于常规物理模型及超重力离心环境中土体电阻率测试设备和分析方法,并通过开展模型试验验证其应用于水分迁移过程量测的适用性及有效性。常规物理模型试验(1g)表明,该设备及方法能够获得模型土体中电阻率的三维时空分布,入渗过程中电阻率与含水率的分布及变化合理反映电阻率与含水率定性关系;在低有效饱和度区间,电阻率法具有很高的灵敏度。离心模型试验结果表明,重力水平的变化可导致水分在模型土柱中的分布发生显著变化;实时量测技术及分析方法可为土工离心环境中渗流及溶质运移过程的分析提供更为准确的依据。高密度电阻率成像法可以成功应用于常规物理模型及超重力离心环境中水分迁移过程量测,并保证一定的精度和灵敏度。     

Expanded reliability-based design of piles in spatially variable soil using efficient Monte Carlo simulations

Inherent spatial variability is considered as a major source of uncertainties in soil properties, and it affects significantly the performance of geotechnical structures. However, research that considers, directly and explicitly, the inherent spatial variability in reliability-based design (RBD) of geotechnical structures is limited. This paper develops a RBD approach that integrates a Monte Carlo Simulation (MCS)-based RBD approach, namely the expanded RBD approach, with random field theory to model, both directly and explicitly, the inherent spatial variability of soil properties in RBD of drilled shafts. The proposed approach is implemented in a commonly-available spreadsheet environment to effectively remove the hurdle of reliability computational algorithms and to provide a user-friendly graphical user interface to practicing engineers. To improve the efficiency and resolution of MCS at small probability levels, the expanded RBD approach is enhanced with an advanced MCS method called “Subset Simulation”. Equations are derived for the integration of the expanded RBD approach and Subset Simulation. The proposed approach is illustrated through a drilled shaft design example, and is applied to explore the effects of inherent spatial variability (including the scale of fluctuation and correlation structure) and to evaluate systematically the equivalent variance technique that is commonly used to indirectly model inherent spatial variability in current RBD approaches. It is found that inherent spatial variability significantly affects the RBD of drilled shafts, and its effects are considered in RBD using the proposed approach in a direct and explicit manner. In addition, the results show that the indirect modeling of inherent spatial variability using the equivalent variance technique with the simplified form of variance reduction function in RBD might lead to relatively conservative designs in design practice.     

考虑参数空间变异性的隧道结构变形分析简化方法

土体参数具有空间变异性是被广泛接受的,而这种变异性对岩土中结构性能有着重要的影响.随机场理论是一种常用的用来模拟土体参数空间变异性的方法.基于随机场理论,以土体弹性模量的空间变异性为切入点,采用蒙特卡罗方法和有限差分模拟计算相结合的方法,开展隧道水平收敛的随机分析.在大量蒙特卡罗计算基础上,提出了3种简单易用的简化考虑...     

地下水环境下地铁车站抗浮离心模型试验研究

离心机模型目前已成为岩土工程中的物理建模的有力工具之一,可将离心场中加速度放大为地球重力加速度的n倍来模拟岩土工程中应力条件。利用相似理论推出相同地下连续墙的挠度相似系数是原型的1/n,可以利用离心模型模拟有地下连续墙的地铁车站的抗浮特性。本文依托宁波轨道交通建设工程,研究覆土厚度、围护结构插入比及土层的含水量对地铁车站浮力和抗浮性状的影响,并进行离心模型试验研究。根据模型试验总结出的结论,可对宁波软土中地铁车站浮力和抗浮性状起指导作用。     

考虑地层变异性和土体参数空间变异性的边坡可靠度全概率设计方法

目前边坡稳定设计研究中大多数考虑了土体参数的空间变异性,但忽略了地层变异性的影响。为此,提出了一种同时考虑这两类变异性的边坡可靠度全概率设计方法。在全概率设计框架内,将广义耦合马尔可夫链模型与随机场模型相耦合用于同时表征地层变异性和土体参数空间变异性,给出了所提方法的计算流程。利用澳大利亚珀斯市钻孔资料,以某边坡为例进行可靠度设计,为说明在边坡可靠度设计中同时考虑地层变异性和土体参数空间变异性的重要性,分析了仅考虑土体参数空间变异的情况,进一步分析了同时考虑两类变异性的情况,并对二者进行了比较。结果表明:所提出的边坡可靠度设计方法能够有效地考虑边坡中存在的地层变异性和土体参数空间变异性。当仅考虑土体参数空间变异性时,边坡可靠度设计结果很大程度上取决于所采用地层的分布情况,特别是地层分布中抗剪强度较强土体类型占比高于真实情况时,将导致得到的最优设计方案偏于危险。反之,若地层分布中抗剪强度较弱的土体类型占比高于真实情况,得到的最优设计方案偏于保守。因此,为准确地得到最优设计方案,在边坡可靠度设计中应同时考虑地层变异性和土体参数空间变异性的影响。     

不同下卧层盾构隧道长期沉降离心模型试验

离心机模型目前已成为岩土工程中的物理建模的有力的工具之一,它的基本原理是将离心场中加速度放大为地球重力加速度的n倍,用来模拟岩土工程中应力条件。根据相似理论可以推出相同土体固结在离心场中固结时间是原型固结时间的1/n2,故可以利用离心模型模拟隧道长期沉降特性。本文依托上海地铁8号线的工程背景,选择两种典型的下卧层来研究不同地质条件下地铁隧道纵向长期沉降特性。根据模型试验结果,得出一些结论,并对软土中盾构隧道的安全性和适用性评价、结构保护起指导作用。