Evaluating leakages through GMB/GCL composite liners considering random hole distributions in wrinkle networks

This paper presents a study on the development of a hydraulic connectivity analysis-based approach for evaluating leakage rates through geomembrane (GMB)-geosynthetic clay liner (GCL) composite liners considering random hole distributions in a GMB wrinkle network. An algorithm for hydraulic connectivity analysis was developed to find the hydraulically connected wrinkles from a wrinkle network, and an explicitly expressed criterion is proposed to define the hydraulic connection between wrinkles under the assumption that only one of the two adjacent wrinkles is possible to be damaged. A Monte Carlo simulation was used to evaluate the probability weighted average of the total leakage through multiple randomly distributed holes considering numerous possible combinations of locations of holes. The proposed approach was applied to typical examples reported in the literature and shows that it can objectively quantify the effect of the hydraulic properties of the liner and overburden pressure on the hydraulic connectivity between wrinkles in a wrinkle network. The proposed approach also allowed assessing the effect of different probabilities of various hole distributions on the calculated leakage, which was demonstrated to be non-negligible, especially when the hole frequency is small.     

Geomembrane strains from wrinkle deformations

Methods to compute geomembrane strains caused by the deformation of a geomembrane wrinkle when subject to vertical overburden stress are examined. Thin shell theory, small strain-displacement, and large strain-displacement methods are developed to compute geomembrane strains from wrinkle deformations. The implementation of each method is validated for three hypothetical trial cases against results obtained with finite element analysis. It was found that it is necessary to employ large strain-displacement theory and explicitly consider both vertical and horizontal components of wrinkle displacement to compute strain. Results are then presented from six physical experiments where the vertical and horizontal components of wrinkle displacement were measured under simulated landfill base liner conditions. For the particular conditions tested, it was found that without a thick sand protection layer on top of the geomembrane, the largest calculated tensile strain due to wrinkle deformations of 8% was much less than the tensile strain caused by overlying gravel particles, and thus local strains from gravel contacts would govern in the assessment of maximum geomembrane strain; whereas, with a thick sand protection, the maximum tensile strain was from wrinkle deformations, but the measured values were below a proposed long-term allowable strain of 3%.     

裂隙岩体渗流模拟的三维离散裂隙网络数值模型(Ⅰ)：裂隙网络的随机生成

对于裂隙岩体中的渗流来说，离散裂隙网络模型比等效连续体模型更能刻画其基本规律。发展了用于模拟裂隙岩体渗流的三维离散裂隙网络数值模型，并编制了裂隙岩体渗流模拟程序FracFlow。该模型可以利用野外露头上采集到的裂隙的观测数据，通过计算机处理最终形成三维裂隙网络的人工几何模型，然后用边界元法求解所生成的裂隙网络中的渗流问题。在此第一部分中，介绍了利用计算机随机生成三维裂隙网络的详细过程，然后利用算例校核了程序的正确性。     

基于系统可靠度的地下管网抗震设计

地下管网是生命线工程的重要组成部分。文章以地下管网整体有限元分析模型、基于物理机制的随机地震动场和概率密度演化方法为基础,发展地下管网的系统可靠度分析方法和基于可靠度的抗震设计方法。应用该方法,可以得到管网地震反应的概率密度函数和系统可靠度,进而以典型地下管网为例,具体说明这一设计方法。文中方法的创新性：①该方法针对的是整个地下管网结构而非简单的管线结构;②该方法可以完整获得管网结构不同部位和管网整体的随机反应信息,并据此实现管网内部和管网整体的抗震可靠度评价,从而以此实现基于整体可靠度的地下管网抗震设计。     

Numerical simulation of geomembrane wrinkle formation

Three outdoor experiments are reported where a wrinkle was allowed to develop and grow in a narrow strip of 2-mm-thick HDPE geomembrane when subjected to solar heating. The increase in length of the strip was used to obtain an effective coefficient of thermal expansion for the particular configuration tested. That effective coefficient of thermal expansion was then used as input into a finite element model, along with an assumed temperature dependent Young's modulus. The finite element model was able to replicate the formation of a geomembrane wrinkle when subject to solar heating.     

土性参数不确定性描述方法的探讨

通过分析土体自然历史形成条件,从土性参数变异性表现特征着手,对其进行归类分析,初步回答了土性指标变异性的含义;对比分析了土层剖面的两种建模方法,据此提出了基于随机场理论的变异性统计方法,并通过实际工程勘探数据的统计分析,诠释了该方法的优越性所在。结果表明:土性指标变异性并非土体分层后层与层之间土性指标的差异,而是层内土性点与点之间的空间变异;相对于传统随机变量的建模方法,这种空间变异性用随机场理论建模更加科学合理;随机场理论用空间趋势函数和随机波动分量分别表征土性指标的确定性部分和随机扰动部分,通过去趋势化处理,可把握土性参数不确定性的核心;实例分析显示,本文提出的方法可更加精确地了解土性参数的不确定性,为可靠性理念在实际工程中的应用提供有利的途径。     

基于动态可靠性评价的城市地下物流网络设计

基于国内外城市地下物流系统研究实践,提出3种代表性的城市地下物流系统网络原型,对网络布局范式、运作流程和设施配置进行设计。综合拓扑与运行指标,构建城市地下物流网络可靠性评价模型,根据同源案例和现实数据开展随机实验,分析3种网络在设施随机攻击及物流需求激增情景下的动态可靠性。研究表明:线轨式网络在承受高强度随机攻击时易出现突发破坏而失效;连通式网络受攻击时的拓扑可靠性最强,但大范围需求增加易导致管道快速饱和而失效;轴辐式网络在供需水平耦合扰动时的可达性、运输效率、连通性和负载稳定性综合表现最佳,据此提出城市地下物流网络原型的若干应用场景和规划建议。     

Analysis of Bridge Condition Rating Data Using Neural Networks

Currently bridges are evaluated using either a visual inspection process or a detailed structural analysis. When bridge evaluation is conducted by a visual inspection, a subjective rating is assigned to a bridge component. With analytical evaluation, the rating is computed based on the load applied and the resistance of the bridge component. There have been several attempts to correlate the subjective rating to the analytical rating. The conventional statistical analyses, as well as methods based on fuzzy logic, have not been very successful in providing a clear relationship between the two rating systems. This paper describes the application of neural network systems in developing the relation between subjective ratings and bridge parameters as well as that between subjective and analytical ratings. It is shown that neural networks can be trained and used successfully in estimating a rating based on bridge parameters. The specific application problem for railroad bridges in the commuter rail system in the Chicago metropolitan area is presented. The study showed that a successful training of a network can be achieved, especially if the input data set contains parameters with a diverse combination of intercorrelation coefficients. When the relationship between the bridge subjective rating and bridge parameters was investigated, the network had a prediction rating of about 73%. The study also investigated the relation between the subjective and analytical rating. In this case, the prediction rate was about 43%. Compared with conventional statistical methods and the fuzzy‐logic approach, the neural network system had a much better performance ratio in establishing the relation between the bridge rating and bridge parameters.     

Geomembrane strains from coarse gravel and wrinkles in a GM/GCL composite liner

The physical response of a 1.5-mm-thick, high-density polyethylene geomembrane (GM) is reported when placed on top of a needle-punched geosynthetic clay liner (GCL), buried beneath 50-mm coarse gravel and subjected to vertical pressure in laboratory experiments. Local strains in the geomembrane caused by indentations from the overlying gravel and deflections of a wrinkle in the geomembrane are quantified. A peak strain of 20% was calculated when a flat geomembrane was tested without a protection layer at an applied vertical pressure of 250 kPa. Strains were smaller with a nonwoven needle-punched geotextile protection layer between the gravel and geomembrane. Increasing the mass per unit area of the geotextile up to 2200 g/m² reduced the geomembrane strain. However, none of the geotextiles tested were sufficient to reduce the geomembrane strain below an allowable limit of 3%, for the particular 50-mm gravel tested and when subjected to a vertical pressure of 250 kPa. Increasing the initial GCL water content and reducing the stiffness of the foundation layer beneath the GCL were found to increase the geomembrane strains. These local strains were greater when a wrinkle was present in the geomembrane. The wrinkle in the geomembrane experienced a decrease in height and width. The wrinkle deformations lead to larger pressures beside the wrinkle and hence producing larger local strains. A 150-mm-thick sand protection layer was effective in limiting the peak strain to less than 0.3% even with a wrinkle in the geomembrane, at a vertical pressure of 250 kPa.     

Statistical models applied to service life prediction of rendered façades

An approach to the evaluation of the service life of rendered façades applying statistical tools is described. Using multiple linear regression analysis and artificial neural networks, mathematical models are established to estimate the degradation of this type of coating. To devise the models proposed, a sample of 100 rendered façades was subjected to meticulous field work to determine their condition. Some statistical parameters are used to evaluate the validity and efficacy of the models proposed. The service life of the sample of rendered façades is also evaluated, as estimated by the various models, and the result is expressed in histograms. The usefulness of these models to evaluate complex problems, such as the degradation phenomena of rendered façades, is thus demonstrated.     

Random checkerboard based homogenization for estimating effective thermal conductivity of fully saturated soils

This paper proposes homogenization scheme for estimating the effective thermal conductivity of fully saturated soils. This approach is based on the random checkerboard-like microstructure. Two modeling scales and two modeling approaches are distinguished and used, i.e. microscale and mesoscale and 1-step and 2-step homogenizations, respectively. The 2-step homogenization involves sequential averaging procedure, i.e. first, at microscale, a mineralogical composition of soil skeleton is considered and averaging process results in estimation of the skeleton effective thermal conductivity, and then, at mesoscale, a random spatial packing of solid skeleton and pores via random checkerboard microstructure is modeled and leads to evaluation of the soil overall thermal conductivity. The 1-step homogenization starts directly at the mesoscale and homogenization procedure yields evaluation of the overall soil thermal conductivity. At the mesoscale, the distinct nature of soil skeleton, as composed of soil separates, is considered and random variability of soil is modeled via enriched random checkerboard-like structure. Both approaches, i.e. 1-step and 2-step homogenizations, interrelate mineralogical composition with the soil texture characterized by the volume fractions of soil separates, i.e. sand, silt and clay. The probability density functions (PDFs) of thermal conductivity are assumed for each of the separates. The soil texture PDF of thermal conductivity is derived taking into consideration the aforementioned functions. Whenever the random checkerboard-like structure is used in averaging process, the Monte Carlo procedure is applied for estimation of homogenized thermal conductivity. Finally, the proposed methodology is tested against the laboratory data from our measurements as well as those available from literature.     

向量式有限元膜单元及其在膜结构褶皱分析中的应用

向量式有限元法是一种基于点值描述和向量力学理论的分析方法,可有效模拟结构的空间大位移、大转动行为。推导了三角形膜单元的向量式有限元基本公式,详细阐述了通过逆向运动获得单元节点纯变形位移以及在变形坐标系下求解单元节点内力的方法。在此基础上编制了膜单元的计算程序,并通过算例分析验证了理论推导的正确性及所编制程序的可靠性。进一步将向量式有限元引入膜结构的褶皱分析,采用主应力 主应变准则和修正本构矩阵方法处理膜结构的褶皱问题,对一典型膜结构在面外荷载作用下的力学行为及褶皱发展情况进行跟踪分析,成功捕捉了从褶皱出现、褶皱大范围扩展直至褶皱最终消失的全过程,证明了该方法在膜结构皱褶分析中可有效克服传统有限元方法存在的单元刚度矩阵奇异、迭代不易收敛等问题。     

基于贝叶斯更新和信息量分析的边坡钻孔布置方案优化设计方法

为在节省岩土工程勘察成本的前提下获得最有价值的现场试验数据,通常需要事先设计最优的工程勘察方案。提出了基于贝叶斯更新和信息量分析的边坡钻孔布置方案优化设计方法,其中采用贝叶斯方法更新空间变异土体参数统计特征和计算边坡后验失效概率,在此基础上进行场地信息量分析确定边坡最优钻孔位置和最佳钻孔间距。此外,为更加准确地表征土体参数的先验信息,发展了非平稳随机场模型以表征土体参数均值和标准差随埋深逐渐增加的特性。最后通过一个不排水饱和黏土边坡算例验证了提出方法的有效性。结果表明:所提出的方法能够在现场勘察试验之前仅利用现有的土体参数先验信息有效确定边坡最优钻孔位置和最佳钻孔间距。对了解边坡稳定性能所需的试验数据,并不是钻孔间距越小所获得的信息量越大。     

大连地下石油储备库初始渗流场数值反演

 初始渗流场分析是水封式地下石油储备库设计中的重要内容和先决条件,现场压水试验只能提供较准确的各向同性渗透系数,而不能反映各向异性的渗透特征。结合大连地下石油储备库工程,提出一种基于随机节理网络模拟技术反演岩体各向异性渗透特征的方法。首先,采用三维离散元程序3DEC内置的Fish语言,直接生成不同尺寸的三维节理网络模型,通过推导的判别式来统计模型中各组节理的个数及产状信息。其次,利用裂隙介质的渗透张量理论计算不同尺寸的岩体渗透张量,进而确定节理岩体的表征体元(REV)。根据现场压水试验实测资料,修正节理岩体的渗透张量,再利用Matlab软件计算渗透主值及渗透特征向量。最后,考虑渗透系数的空间正交各向异性,采用FLAC3D的Fl_anisotropic的渗流模型反演库区的初始渗流场,为水封式地下石油储备库水幕设计及稳定性分析提供较合理的初始渗流场条件。     

浅谈膜结构褶皱研究

膜结构是一种新型的建筑结构形式；其特点为所用膜材虽然具有很大的张拉强度，但不具有弯曲刚度，当承受压缩应力时膜面会发生局部屈曲，产生褶皱。褶皱的出现既影响膜结构的美观，还对其力学性质产生影响，所以褶皱研究已成为膜结构方向的重要研究课题。文中阐述了膜结构褶皱发生的原理，并简要概括了国内外膜结构褶皱研究的成果和现状，以及对褶皱振幅和波长的预测理论，最后提出了今后的发展方向。     

考虑相关性的地下管网系统抗震可靠度分析方法

城市供水、供气、供热等地下管网是重要的生命线工程系统,由于管网中不同管线的结构属性、场地环境、地震动荷载等参数的相关性,管线结构抗震失效事件存在相关性。文章建立相关失效管网系统抗震可靠度问题的解析模型,给出随机变量相关系数在管线可靠度至管网系统可靠度的传递关系。利用基于Nataf变换和正交变换的一次二阶矩法,建立含相关随机变量的管线结构抗震可靠度解析模型;基于结构体系可靠度理论,求解管线结构失效相关系数;采用网络可靠度算法,计算相关失效管网系统节点连通可靠度。同时,给出基于相关随机变量抽样的Monte Carlo随机模拟解法。算例分析结果表明,在管段结构功能函数起控制作用的随机变量的强相关性,对管网系统可靠度影响较大;与传统的管线失效独立假定相比,管线失效事件的强相关性可使并联管网系统可靠度减小15%以上;管网系统拓扑结构的并联冗余性越高,管线失效相关性对系统可靠度的影响越大。     

Structural Concrete Analysis Using Rigid-Body-Spring Networks

This article presents a new computational approach for supporting the design of structural concrete. The main purpose of this research is to facilitate construction, interpretation, and revision of the analysis model through (1) highly automated mesh generation, (2) discrete modeling of the material components and cracking, (3) dependence on basic material parameters, and (4) graphic rendering of the response quantities, most notably crack locations and widths. Concrete material is represented by a rigid-body-spring network whose geometry is defined by a Voronoi diagram on randomly distributed points. Random geometry of the network reduces mesh bias on potential cracking directions. Concrete cracking is modeled using an energetic fracture mechanics approach that is objective with respect to network component density and random geometry. Reinforcing material may assume any piecewise linear trajectory and is positioned irrespective of the spring network defining the concrete material. Viability of the approach is demonstrated through elastic stress analyses and ultimate failure analyses of T-shape bridge piers subjected to eccentric loading.     

Using the migration of the induced seismicity as a constraint for fractured Hot Dry Rock reservoir modelling

The challenge for Hot Dry Rock technology is to develop a heat exchanger in deep hot rock masses and to circulate a fluid in order to extract its energy to be used at the ground surface. The present day strategy is to take advantage of natural fractures that pre-exist at these depths and to improve their hydraulic properties. The extension of the area with enhanced properties must then be evaluated so that the best locations for further boreholes can be proposed. To date, this development procedure is based on fluid injection at high rates, forcing hydro-mechanical interactions to take place along pressurised fractures. These pore-pressure-driven mechanisms are accompanied by seismic activity. Assuming the validity of poro-elastic theory in the fractured host rock, some authors have derived the virgin hydraulic diffusivity of the fractured reservoir from the analysis of the spatio-temporal growth of the induced seismicity. The present work is aimed at verifying this approach using a numerical code to solve directly for hydro-mechanical interactions in random fracture networks. Our approach assumes that the seismic activity is controlled by a Coulomb shear criterion and we show how the interpretation of spreading rate of the modelled shear activity in a given network coincides with the upscaled virgin hydraulic diffusivity of the same fracture network, calculated from an independent numerical procedure at the reservoir scale. Therefore, it is shown that the direct analysis of the seismicity migration is appropriate to give reliable estimates of virgin hydraulic and mechanic parameters. These parameters can then be used for performing any further quantitative analysis of a reservoir open to the far field. This is of importance, as fluid mass-balance in multi-well exploitation systems will include the contribution from areas surrounding the stimulated zone.     

Geomembrane tensions and strains resulting from differential settlement around rigid circular structures

A simplified model is presented that analyzes tensions and strains in a geomembrane. The membrane analysis is applied to circular structures subjected to differential settlement. It was found that wrinkles are induced in the geomembrane around the circular structure and the associated mechanism was investigated. An improved predictive model was developed based on the wrinkled membrane theory. The model introduced the concept of a “variable Poisson's ratio”, and allowed tensions and strains associated with wrinkles in the geomembrane to be considered. Parametric studies and a comparison between the simplified model and the improved model were performed. Limitations associated with the two models are discussed and some practical recommendations are made with regard to the control of geomembrane tensions and strains around circular structures.     

考虑桨叶旋转效应的海上风力发电高塔系统随机风振响应与动力可靠度分析

研究了考虑桨叶旋转效应的海上风力发电高塔系统随机动力响应与风振可靠度分析.在风场模拟中,桨叶风荷载需要考虑旋转效应的影响.因此,对塔体风荷载,直接采用基于物理机制的随机Fourier谱,而对桨叶风荷载,则采用考虑桨叶旋转机制的随机Fourier谱概念.在此基础上,结合概率密度演化理论,对海上风力发电高塔系统进行了随机动力响应分析以及基于塔顶位移响应的风振动力可靠度分析.结果表明,上述方法能够有效地进行此类结构的随机动力响应及可靠度分析.