Observational method for field performance of prefabricated vertical drains

An exponential formula is used to best-fit theoretical and measured time–settlement (or excess pore pressure) data over the full range of consolidation. The formula fits well theoretical consolidation solutions and measured data regardless of using the incompletely consolidated data, and it is possible to reliably predict the ultimate values. This result has a different trend from those of the hyperbolic and Asaoka (1978) methods. Thus the coefficients of horizontal consolidation and the mobilised discharge capacity q_w(mob) can be expressed in terms of parameters of the exponential formula corresponding to the measured data and the theoretical solutions. The application of the proposed method to six case records on three construction sites (with a maximum drainage path l_m of 7−50 m) indicates that the coefficient of horizontal consolidation for the ideal condition are likely to be used to reconstruct the monitored time–settlement curve and also to adjust the hydraulic and consolidation properties of each monitored point. Based on back-analysis, the mobilised and required discharge capacity for a preliminary design guideline are recommended as: q_w(mob) = (1–5)k_hl_m² and q_w(req) = 19.63k_hl_m², where k_h is the horizontal permeability of soil.     

渗透特性及填筑速率对路基固结的影响

计算软土路基沉降的一般方法没有反映路基渗透系数的变化以及填筑过程的时间效应影响,而大多采用同一渗透系数和一次加载的方式分析路基沉降。笔者采用ABAQUS有限元软件在考虑软粘土渗透系数随孔隙比变化经验公式以及不同填筑速率的基础上分析了软土路基的固结沉降,并进一步研究了填筑阶段路基内竖向有效应力随时间的变化。结果表明:(1)固结随时间的变化跟填筑过程有相关性;(2)渗透系数随深度非线性分布对路基的固结影响不可忽略;(3)加快填筑速率使得竖向有效应力增大的速率加快,沉降也加快;(4)填筑速率对固结沉降的影响主要集中在填筑阶段,对工后沉降影响不大。     

Design chart for the modified hyperbolic method

The modified hyperbolic method is used in practice to predict the ultimate primary consolidation settlement of compressible ground. This paper presents a new relationship between the average degree of consolidation for combined vertical and horizontal consolidation U_vh and the non-dimensional vertical time factor T_v, with a new parameter, ν_hv, introduced. ν_hv is defined as the ratio of the time factor in the horizontal direction to that in the vertical direction. This relationship is then adopted to calculate the slope of the linear segment of the theoretical hyperbolic plot (T_v/U_vh vs T_v), λ, which is a key factor in the modified hyperbolic observational method presented by Tan (1995). A design chart for λ as a function of ν_hv is proposed. Using this design chart, the determination for λ can be simplified from a procedure involving three parameters to only one, ν_hv. A new procedure for the use of the modified hyperbolic method is proposed. The new procedure is verified using a well-documented case history.     

自然通风建筑隔热降温理论与方法 ——陈启高先生学术思想回顾

陈启高先生是我国建筑热工学的创始人之一,他创建了我国南方地区自然通风建筑隔热降温设计理论。围护结构隔热计算理论依据的提出、边界条件的确定、隔热性能的选择,以及蓄水屋面和空气层隔热性能的优化．都反映了陈启高先生以适应气候条件为前提、以建筑热工观测为手段,最大可能地利用气候降温条件、材料性能以及合理组合改善室内热环境的技术思想。     

An option pricing-based model for evaluating the financial viability of privatized infrastructure projects

Privatized infrastructure projects have to demonstrate their financial and technical viability before they are undertaken. Although it is relatively easy to demonstrate the technical viability of an infrastructure project, the evaluation of the financial viability of a privatized infrastructure project is complex and challenging, mainly because of the uncertainties involved due to the project's scale, long concession period and complexity. Traditional methods, such as net present value (NPV) analysis, fall short in reflecting the characteristics of privatized infrastructure projects and the risks involved. This paper presents an option pricing based model, the BOT option valuation (BOT-OV) model, for evaluating the financial viability of a privatized infrastructure project. This quantitative model considers the project characteristics explicitly and evaluates the project from the perspectives of the project promoter and of the government when the project is under bankruptcy risk. Moreover, the model can evaluate the impact of the government guarantee and the developer negotiation option on the project financial viability.     

A framework of critical resource chain for project schedule analysis

Analysing a schedule is beneficial to help stakeholders understand the scheduled project. Project schedules, which create time plans based on the critical path method (CPM) or on resource‐constrained project scheduling problem (RCPSP) optimization, are targets herein. The Theory of Constraints (TOC) treats a schedule as a system. Schedule elements are suspected constraints and a goal depends on the schedule creation policy. Resource information is further surveyed herein to identify true constraints. A framework is proposed to integrate identified constraints on a schedule, and the critical resource chain concept is introduced. Three scenarios illustrate the proposed framework under different scheduling considerations. Results explain schedule constraints, and several schedule analysis issues are discussed.     

Forum The role of CIB: some reflections

An explanation for the low innovation activity in construction is put forward. The central argument is that the current theory of construction is one root cause for low innovation activity. Instead, an explicit and more powerful theory of construction is needed for further innovation, which is ‘to manage new ideas into good currency’. There are three main mechanisms in the current theory of construction which are identified as causing this hindrance. Firstly, production theories in general, as well as construction theories specifically, have been implicit. Therefore, it has not been possible to transfer radical managerial innovations, such as lean production, from manufacturing to construction at a theoretical level. Direct application of this production template to construction has been limited due to the different context of construction in comparison with manufacturing. Secondly, the current theoretical model of construction is based on the transformation model of production. It is argued that the principles of this model are counterproductive, because uncertainty and interdependence are abstracted away. This leads to fragmented and myopic management and inflated variability. Practical examples show that these deficiencies and related practical constraints hinder the implementation of top-down innovations. Thirdly, empirical research shows that also bottom-up innovations - systematic learning and problem solving - are being hindered by the current theory. Thus, the advancement of innovations in construction requires that a new, explicit and valid theory of construction is created, and business models and control methods are developed on the basis of that new theory. Cet article propose une explication concernant le taux bas de l'activité d'innovation dans la secteur du bâtiment. L'argument central étant que la théorie actuelle de la construction est une des raisons fondamentales de cette activité basse d'innover. Au lieu de cela, on a besoin d'une théorie de la construction explicite et plus efficace afin d'innover. Dans la théorie actuelle du bâtiment, il y a trois mécanismes fondamentaux qui sont identifiés comme causes gênant cette innovation. Premièrement, les théories de production en général, ainsi que les théories de la construction en particulier, ont été implicites. Ainsi, il était impossible de transférer des innovations gestionnaires radicales, comme la production allégée (lean production), à partir du domaine de la fabrication à celui du bâtiment à un niveau théorique. L'application directe de ce modèle de production au secteur bâtiment a été limitée à cause du contexte différent de celui-ci en comparaison de celui de la fabrication. Deuxièmement, le modèle théorique actuel de la construction bâtiment est basé sur le modèle de la transformation de production. On avance que les principes de ce modèle agissent négativement sur la productivité parce que l'incertitude et l'interdépendance en sont exclues. Ceci mène à une gestion fragmentée et myope ainsi qu'à une inflation de la variabilité. Des exemples pratiques montrent que ces déficiences et les contraintes pratiques qui leur sont liées, gênent les implémentations des innovations de haut en bas. Troisièmement, une étude empirique montre que les innovations de bas en haut - c'est-à-dire l'apprentissage systématique et la résolution de problèmes - sont gênés par la théorie actuelle. Ainsi, le progrès dan les innovations du secteur bâtiment exige qu'une nouvelle théorie explicite et valide soit créée, et que des modèles d'affaires et des méthodes de contrôle soient développés sur la base de cette nouvelle théorie.     

An industrial organization economic supply chain approach for the construction industry: a review

Understanding industries in terms of the concepts of chains, clusters and networks is becoming increasingly important in economies around the world. Supply chain management for an individual organization is an emerging field of research in the construction management discipline, but less attention has been devoted to investigating the nature of the construction supply chains and their industrial organizational economic environment. This selected review of construction and mainstream management supply chain literature is organized around four themes; distribution, production, strategic procurement management and industrial organization economics, and highlights the need to develop an industrial organization economic supply chain framework for construction. The merging of the supply chain concept with the industrial organization model as a methodology for understanding firm conduct and industry structure and performance is an important contribution to both construction supply chain and construction economic theory. Much of the industrial organization supply chain literature has tended to focus upon manufacturing industries, where typically firms are permanent organizations. This raises issues as to the differences between industries founded upon temporary compared with permanent organizations. There is potential for the development of an industrial organization methodology applicable to the project based industry. Ultimately industrial organization research seeks to have direct implications for industry performance and government policies.     

路基沉降不确定性预测研究

路基沉降计算和预测是工程建设中一个重要的课题,但是很多情况下理论计算的沉降量与实际沉降量有较大的出入。所以必须对路基沉降进行监测,根据实测数据控制填土速率,保证路堤在施工中的安全与稳定;根据实测沉降曲线预测工后沉降,使工后沉降控制在设计允许范围之内。但沉降预测模型的参数是不确定的,用概率和概率分布去描述更加合适,将模型参数视为随机变量,基于贝叶斯理论和MCMC方法,借助WinBUGS软件,建立了贝叶斯沉降时间序列不确定性预测模型。实例分析表明,该方法所得结果合理可信,将其应用于路基沉降预测是可行和值得研究的。     

真空联合堆载预压处理深厚软土效果分析

软土由吹填土和原状淤泥质土构成,平均深度为25m,且表层覆盖回填土层,采用真空联合堆载预压法进行处理。检测结果表明,该场地表层承载力达到100kPa以上,下部淤泥质土层承载力达到80kPa,平均沉降153.14~202.79cm,加固效果非常明显。实践证明,针对该区的深厚淤泥质软土地基,真空联合堆载法具有加固效果好、工期短和施工安全等优点,值得在该地区工程建设中推广应用。