FEM validation of a double porosity elastic model for consolidation of structurally complex clayey soils

Laboratory consolidation of structured clayey soils is analysed in this paper. The research is carried out by two different methods. The first one treats the soil as an isotropic homogeneous equivalent Double Porosity (DP) medium. The second method rests on the extensive application of the Finite Element Method (FEM) to combinations of different soils, composing 2D or fully 3D ordered structured media that schematically discretize the complex material. Two reference problems, representing typical situations of 1D laboratory consolidation of structured soils, are considered. For each problem, solution is obtained through integration of the equations governing the consolidation of the DP medium as well as via FEM applied to the ordered schemes composed of different materials. The presence of conventional experimental devices to ensure the drainage of the sample is taken into account through appropriate boundary conditions. Comparison of FEM results with theoretical results clearly points out the ability of the DP model to represent consolidation processes of structurally complex soils. Limits of applicability of the DP model may arise when the rate of fluid exchange between the two porous systems is represented through oversimplified relations. Results of computations, obtained having assigned reasonable values to the meso‐structural and to the experimental apparatus parameters, point out that a partially efficient drainage apparatus strongly influences the distribution along the sample and the time evolution of the interstitial water pressure acting in both systems of pores. Data of consolidation tests in a Rowe's cell on samples of artificially fissured clays reported in the literature are compared with the analytical and numerical results showing a significant agreement. Copyright © 2000 John Wiley & Sons, Ltd.     

苏锡常地区地面沉降机理及防治措施

地面沉降是一种危害性严重的地质灾害。由于地下水的长期超量开采导致地面沉降不断加剧。然而人们往往总是忽略了地质灾害与地质模式的内在联系,把大多数原因归结为人类活动。事实上地面沉降的发生不仅与地下水水位下降密切相关,而且还与地层岩性结构、水文地质条件、土的类型、厚度、压缩性的大小、固结历史等因素有关。本文以苏锡常地区为例,对地面沉降的机理进行了分析并提出了防治措施。     

Efficient block preconditioners for the coupled equations of pressure and deformation in highly discontinuous media

Large‐scale simulations of flow in deformable porous media require efficient iterative methods for solving the involved systems of linear algebraic equations. Construction of efficient iterative methods is particularly challenging in problems with large jumps in material properties, which is often the case in geological applications, such as basin evolution at regional scales. The success of iterative methods for this type of problems depends strongly on finding effective preconditioners. This paper investigates how the block‐structured matrix system arising from single‐phase flow in elastic porous media should be preconditioned, in particular for highly discontinuous permeability and significant jumps in elastic properties. The most promising preconditioner combines algebraic multigrid with a Schur complement‐based exact block decomposition. The paper compares numerous block preconditioners with the aim of providing guidelines on how to formulate efficient preconditioners. Copyright © 2010 John Wiley & Sons, Ltd.     

A study on one-dimensional consolidation of layered structured aquitard soils in a leakage system

Analytical solutions expressed using the hydraulic head for the one-dimensional consolidation of layered structured aquitard soils in a leakage system are deduced by transforming the n-layered structured soils into n + i (i = 1,2,…, n)-layered soils with gradually changing thicknesses, therein considering the behaviors of structured aquitard soils. The solutions are given in the case of instantaneous and linear decreasing confined aquifer water levels. By comparing three different examples, the effects of the structured behaviors on the consolidation characteristics are analyzed for the instantaneous decline of the confined aquifer water level.     

浅谈灰土挤密桩与DDC桩在工程实践中应用与发展

DDC桩是挤密桩的一种新型桩。根据宝鸡某大型电厂中DDC桩与灰土挤密桩地基处理工程实例,从挤密机理、挤密效果、复合地基承载力与抗变形性状及复合地基浸水稳定性等诸方面进行了系统地分析对比,进而探讨挤密桩地基的应用与发展。     

农地整理对农户农地投入意愿的影响研究——基于农地整理区域农户问卷调查的实证分析

研究农地整理对农户农地投入意愿的影响,对完善农地整理绩效评价和农地整理政策意义重大.依据湖北省3个县(市、区)的188份农地整理区域农户抽样调查数据,构建Logistic模型进行农地整理对农户农地投入意愿的影响分析.结果表明:(1)农户对农地整理的满意度是影响农户流动资本投入意愿和固定资本投入意愿的关键因素,农户对农地整理的满意度越高,其流动资本投入意愿越弱,固定资本投入意愿越强;(2)农地整理的效果在不同土地规模、不同年龄和不同兼业类型农户中有所差异,土地规模大、非老龄、纯农户以及第一类兼业农户的固定资本投入意愿更强.     

土地综合整治项目成功范例分析——以临沂市兰山区李官镇为例

通过阐述临沂市兰山区李官镇土地综合整治项目实施这一成功范例,提出实施土地综合整治项目应抓住的6个关键环节,分析了每个环节的作用和操作方法,希望对破解当前土地综合整治项目实施难的问题有所帮助。     

冻融循环对原状过湿土固结变形特性的影响

为了研究季冻区过湿土的固结变形特性,对黑大公路青冈段路基原状过湿土进行固结试验和渗透试验,研究了冻融循环作用下原状过湿土的固结变形特性。试验结果表明：原状过湿土的含水率越高,土体的压缩性越高;初始孔隙比越大,渗透性越高。冻融循环后,过湿土产生不规则裂缝,土的结构也发生改变,土的压缩系数有所增大,随着冻融循环次数的增加,压缩性先增大后趋于平缓。冻融后过湿土的竖向渗透系数明显增大,且随着冻融循环次数的增加渗透性呈现先增大后趋于平缓的规律,而横向渗透系数冻融前后无明显差异。     

2000年以来中国县级行政区划调整的类型、特征及趋势分析

系统地梳理了2000—2016年中国县级行政区划调整的631个案例,归纳了县级行政区划调整的主要类型,包括撤县（市）设区、撤县设市、行政区合并、增设行政区、边界调整、隶属变更和建制升格7类,发现各种类型变更的背后都隐含着深刻的社会经济背景和特定的需求。详细分析了县级行政区划调整数量和类型的时空分布特征,发现具有时间上集中和空间上聚集相结合的特点,随着不同时期国家或区域发展的战略导向不同,县级行政区划调整的构成和指向会随之发生变化;县级行政区划变更有着明显区域差别,经济发达和城镇化发育较高的地区是调整重点,城镇化导向突出;县级行政区划较多的省份变更频繁,减少了县和县级市数量;注重了民族地区和边疆地区行政区划变革,有利于促进民族和边疆地区发展。立足于空间治理,认为县级行政区划调整和优化基本上围绕城镇化、区域发展、边疆治理和民族地区发展等战略的要求展开,代表了未来调整的趋向。     

地下水位变化对桂林地区地基基础的影响

不同季节桂林地区的地下水位变化较大。通过分析发现,地下水位的变化对地基的稳定不利。地下水位上升将降低地基土承载力特征值f a 和软弱下卧层地基承载力特征值f az ,并影响到地基换土垫层的处理设计; 而地下水位下降将加大地基沉降。因此,《地基规范》第5. 3. 5条地基变形验算没有考虑地下水位变化的影响是不合适的。为此,建议对于受地下水位影响的地基,宜按分层总和法进行地基变形计算。此外,由于桂林漓江沿岸不少的地基主要由砂砾土组成,地下水位上升还会增加砂、砾石土地基基坑主动土压力,但对于粘性土的基坑土压力则影响不明显。