Introduction of the leak-before-break (LBB) concept for cast iron water pipes on the basis of laboratory experiments

Failure of cast iron water mains in Australia is a common occurrence. Water utilities are seeking solutions to optimise the renewal and rehabilitation of ageing cast iron critical water mains (diameter ≥ 300 mm). Failure pressures of three large-diameter cast iron pipe specimens (600 mm in diameter) were tested. A large corrosion patch was machined onto each pipe section to initiate pipe failure. A large corrosion patch and significant reduction (>90%) of pipe wall thickness were needed to fail the tested pipe specimens. All three pipes under test exhibited leaking before bursting, indicating that the concept of leak-before-break (LBB) could be used for pipe failure prevention. In addition, LBB provides valuable information that could be added to the pipe asset database to make better management decisions on repair or replacement along with all other asset information. The study also found that small corrosion patches (<50 mm) with low remaining wall thickness may cause pipe leaks, but are less likely to cause major pipe bursts.     

Condition grading for dysfunction indicators in sewer asset management

Asset management is an increasing concern for the water and wastewater industry. Condition assessment of sewer segments is an important component of sewer asset management and relies mostly on visual inspection. Observed defects are translated into a score for each segment. Although most protocols give a segment a condition grade by comparing its score with a subjective scale of numerical values, we propose a protocol to calibrate thresholds for each asset stock. Thresholds are calculated according to two sets of parameters: overall condition of the asset stock in question (estimated by a representative sample or provided by the utility manager) and assignment-error weighting (determined by the utility manager) linked to either over-estimation or under-estimation of condition grade. This method is applied to 150 km of sewers from the Greater Lyon asset stock. Sensitivity analyses of these parameters are then implemented. Three hypotheses about overall condition of the asset stock are combined with three matrices of assignment-error weights. Both parameters influence thresholds and change the assessment of the studied segments. The synthesis of such sensitivity analyses can be used to prioritise complementary investigations.     

Simulation-based life cycle cost modeling and maintenance plan for water mains

Life cycle cost (LCC) is an essential approach to decide on alternative rehabilitation strategies for infrastructure systems, such as water mains. The research presented in this article identifies several rehabilitation methods for water mains, which are classified into three main categories: repair, renovation and replacement. A simulation-based LCC (SLCC) model is developed to compare different rehabilitation scenarios/alternatives for various types of water mains (i.e. cast iron, ductile iron, concrete, polyvinyl chloride and asbestos cement). Results show that ‘open trench’ and ‘slip lining’ are the most appropriate methods for the ‘repair’ and ‘renovation’ categories, respectively. However, the most suitable method for the ‘replacement’ category is ‘pipe bursting’ for pipe diameters less than 750 mm (<30″) and ‘open cut’ for pipe diameters greater than 750 mm (>30″). A rehabilitation plan is developed based on the SLCC results. This plan recommends repairing pipes using ‘open trench’ until the breakage rate reaches 0.5 breaks/km/year, then, replace the pipe beyond this threshold. Based on the designed SLCC model, web-based software is developed to determine the optimal rehabilitation scenarios. The developed model and software help academics and practitioners (e.g. municipal engineers) to predict the suitable new installation and/or rehabilitation programs as well as their corresponding costs.     

Using economic asset valuation to meet rehabilitation priority needs in the water sector

ABSTRACT

The current study aims at economic asset valuation of water and wastewater infrastructures to prioritize rehabilitation interventions using the infrastructure value index (IVI) as a key performance indicator. The proposed methodology follows a three-step procedure: (1) identification, characterization and site inspection of existing assets; (2) estimation of the current replacement cost and the current value; and (3) establishment of the priority needs. Data from a utility in the Algarve region of Portugal are used as a case study. The specific objectives are to illustrate the methodology and highlight the inherent challenges and complexities associated with economic asset valuation. Results include the IVI calculation for different assets using scenarios of service lives. Different strategic interventions of rehabilitation in the long term were studied, allowing to assess the evolution of IVI, rehabilitation cost and increased risk assets. Asset valuation is important to establish short-term rehabilitation priorities and to analyse long-term strategies of rehabilitation.     

特高压变压器水喷雾消防管网耐火能力提升措施研究

特高压变电站的固定灭火系统完好是实现其灭火能力的重要前提。首先,通过对现有标准中消防管网耐火能力试验方法进行对比,结合特高压变压器实体火灭火试验数据,明确了特高压变电站水喷雾灭火系统消防管网耐火能力现状。其次,利用气体燃烧器原理设计试验火源,测试结果显示试验火源温度与全尺寸特高压变压器实体火灭火试验中测到的温度较一致,利用该试验火源开展试验能符合实际工况。最后,通过对比试验给出了水喷雾消防管网耐火能力提升建议,为实际工程改造与建设提供参考。     

A data mining approach to modelling of water supply assets

The economic and social costs associated with pipe bursts and associated leakage problems in modern water supply systems are rapidly rising to unacceptably high levels.Pipe burst risks depend on a number of factors which are extremely difficult to characterise. A part of the problem is that water supply assets are mainly situated underground, and therefore not visible and under influence of various highly unpredictable forces. This paper proposes the use of advanced data mining methods in order to determine the risks of pipe bursts. For example, analysis of the database of already occurred bursts events can be used to establish a risk model as a function of associated characteristics of bursting pipe (its age, diameter, material of which it is built, etc.), soil type in which a pipe is laid, climatological factors (such as temperature), traffic loading, etc.In addition to the immediate aid with the the choice of pipes to be replaced, the outlined approach opens completely new avenues in asset management: the one of asset modeling. The condition of an asset such as a water supply network deteriorates with age. With reliable risk models, addressing the evolution of risk with aging asset, it is now possible to plan optimal rehabilitation strategies in advance, before the burst actually occurs.     

Robust Maintenance Policies for Markovian Systems under Model Uncertainty

Abstract:  Asset management systems help public works agencies decide when and how to maintain and rehabilitate infrastructure facilities in a cost-effective manner. Many sources of error, some difficult to quantify, can limit the ability of asset management systems to accurately predict how built systems will deteriorate. This article introduces the use of robust optimization to deal with epistemic uncertainty. The Hurwicz criterion is employed to ensure management policies are never "too conservative." An efficient solution algorithm is developed to solve robust counterparts of the asset management problem. A case study demonstrates how the consideration of uncertainty alters optimal management policies and shows how the proposed approach may reduce maintenance and rehabilitation (M&R) expenditures.     

ELECTRE III model for value engineering applications

Value engineering (VE) programs are implemented to enhance the value received over the life-cycle of constructed assets. It is defined as the process of relating the functions, quality, and costs of the project in the determination of optimum solutions for the project. Value engineering is carried out to optimize the performance and costs of products (e.g., project, service, item, etc.) by identification and removal of unnecessary costs. Such costs include either total life-cycle costs or direct costs of production (e.g., construction, implementation, installation, etc.). This paper considers the application of the ELECTRE III model in the context of value engineering. The steps of the ELECTRE III model include; estimation of concordance indices, estimation of discordance indices, estimation of credibility scores, performing distillation procedure, and performing complete ranking. The proposed methodology is intended to support the decision making on alternatives with an increase in the efficiency of the resolution process. A numerical example is presented to demonstrate the use of the proposed methodology.     

Post-Pareto optimality approach to enhance budget allocation process for bridge rehabilitation management

A variety of conflicting criteria in the form of objective functions exist in budget allocation optimisation problem for bridge rehabilitation projects. Budget allocation decision-making for such transportation assets is generally a combinatorial problem. The nature of the problem is a good reason for decision-makers to apply multi-objective optimisation techniques. However, manually choosing an acceptable solution from a set of optimal solutions is a time-consuming task, which would be avoided if the optimisation technique could be followed by a ranking method to obtain unique acceptable solution. To enhance the budget allocation process, this paper develops a posteriori approach to prioritise Pareto-Optimal (PO) solutions generated by genetic algorithm in order to identify a unique package of bridge rehabilitation activities. By identifying the most conventional objective functions for bridge rehabilitation based on technical and managerial criteria, a multi-objective knapsack problem is constructed. PO solutions will then be prioritised applying ‘Technique for Order Preference by Similarity to an Ideal Solution’. The feasibility of the study will be finally demonstrated through an illustrative example. The proposed ranking approach may facilitate the budget allocation optimisation process for bridge rehabilitation where one or a few acceptable solutions are demanded.     

Time-dependent reliability method for service life prediction of reinforced concrete shield metro tunnels

Ageing and deterioration of underground tunnels is inevitable after their long-time in service. This necessitates a rigorous assessment of the probability of failure due to deterioration with a view to predicting remaining safe life. In the light of considerable research undertaken on prediction of service life of the aboveground structures, e.g. bridges, few such studies dealing with the underground structures, e.g. tunnels, have been carried out. The intention of this paper is to present a time-dependent reliability method to assess the tunnel probability failure due to different mechanisms of deterioration. Stochastic models are developed for four common failure modes of tunnel structures as identified by strength and serviceability criteria. Application of the proposed methodology is demonstrated in a case study. It is found in the paper that the reinforcement corrosion is a key factor that affects the probability of deterioration failure and that all deterioration scenarios need to be considered in the assessment of tunnel failures and prediction of their remaining safe life. The proposed method can help the asset managers and practitioners in developing rehabilitation or replacement strategy for existing tunnels with a view for better management of the valuable tunnel asset.     

A comprehensive criteria-based multi-attribute decision-making model for rehabilitation of water distribution systems

The main objective of this work is to develop a comprehensive criteria-based multi-attribute decision-making model to plan the rehabilitation of water networks. Among the main features of this model is the capability to simultaneously analyse comprehensive criteria for the rehabilitation of water networks; where there is a significant uncertainty within the operational data. In this model, which is called as WDSR model, using a fuzzy TOPSIS technique, it is possible to adjust the criteria based on the local conditions, and to weight them based on the group decision-making of experts. In this paper, using the WDSR model, the rehabilitation plan of the ‘Anytown’ water network is prioritised through two methods. The first method uses a predefined template of WDSR, and the second uses a local template based on the conditions within the study area. The obtained results show the potential of the WDSR in the rehabilitation planning of water networks, where is encountered with numerous criteria, a significant uncertainty in the recorded data and hesitation in group decision-making of experts. It was found that, for rehabilitation of network zones, predefined template of WDSR is preferred, while for pipe rehabilitation, it is essential to use local template layer.     

Economic Feasibility Analysis for Urban Renewal Housing Rehabilitation

Although rehabilitation has become an alternative to new construction in virtually all applicable public policy situations, few guidelines or criteria exist for determining whether rehabilitation or replacement is the most desirable way to improve a given portion of the housing stock. This study develops the idea that the answer depends upon the comparative effects of rehabilitation and new construction on the future maintenance costs, economic life, and shelter amenities of the renewed structure. A model is formulated that determines the feasibility of rehabilitation as compared with new construction and specifies the cost level of renewal that will maximize shelter output per unit of input.     

Multicriteria decision analysis applied to the design of light-frame wood wall assemblies

Designers of light-frame wood wall assemblies should consider several performance criteria simultaneously in addition to minimum requirements set by building codes. Evaluation of various performance characteristics can help select the most suitable configuration for a given project in a given context. In a previous article, we identified appropriate criteria and explored their means of evaluation. Following up, this article integrates the context and the preference of the decision-maker and seeks to obtain a ranking of the various alternatives using quantitative and qualitative information. Four multicriteria decision analysis (MCDA) techniques are explored: weighted sum, MACBETH, ELECTRE II, and PROMETHEE. The approach is applied to a case study where five wall assemblies are compared within six different decision contexts. It shows how the choice of the appropriate aggregation method depends on the nature of the performance evaluation scales and demonstrates the usefulness of MCDA to consider simultaneously different aspects of wall performance.     

基于主动式纠偏的曲线顶管施工力学特性研究

曲线顶管施工技术在市政管线工程中得到越来越广泛的应用。在分析曲线顶管施工机理的基础上,提出并对比分析了3种管节纠偏方案,进而结合主动式纠偏方案的施工特点,对三维曲线顶管施工过程中管土间挤压作用力进行计算分析,并推导了管节顶进摩阻力计算公式,其后对管线平面夹角、管线半径及管径大小3个摩阻力影响因素进行单因素分析。考虑管外注浆对管土接触状态的影响,进而引入土压力作用系数对顶进摩阻力计算公式进行修正,并通过对比分析顶进摩阻力的现场实测值、规范建议值及公式计算值,给出了土压力作用系数的建议取值范围。研究表明:主动式纠偏方案在管节姿态调整、施工扰动控制及管身衬砌受力等方面优于其他两种纠偏方案;顶管施工过程中管土间的挤压作用力呈三维复杂状态,不能进行简单的叠加;管线平面夹角对管节转动摩阻力有显著影响,管线半径对侧向顶推摩阻力和管节转动摩阻力均有一定的影响,而管径大小则主要影响地层土压力摩阻力的数值;管土接触状态是真实存在的,其土压力作用系数的取值范围大致在0.2~0.6之间。     

Cox proportional hazards modelling of blockage risk in vitrified clay wastewater pipes

Older wastewater systems often contain vitrified clay pipes and these pipes are responsible for a significant proportion of blockages. From previous research and site experience, it is known that age, installation period, pipe length, diameter, depth and joint type affect the risk of blockage. Using statistical analysis we extend this list of variables to include soil type, road/rail proximity and road type. The analysis is based on blockage data for 43,976 vitrified clay pipes over a 7 year period. A Cox proportional hazards modelling (PHM) approach using established and new explanatory variables finds that pipe depth, pipe length, pipe gradient, pipe diameter, submergence in water, joint type, pipe installation decade, soil type, road proximity to the pipe, pipe purpose, land use code and road type are associated with risk of blockage. Pipes with the highest risk of failure due to blockage are identified and their locations and risk level are visually represented on a colour coded map. This analysis approach can be used by asset managers working in cost-constrained environments to appropriately target inspection, plan maintenance and replacement programs.     

Functional and residual capital values as criteria for water pipe renewal

Water pipes are considered as tangible assets designed to provide a level of service throughout an expected lifetime. The asset can be characterised by two types of values: capital or accounting value and functional value. The capital value of assets depreciates according to a specific rate per time period. The depreciation is assessed by the annual amortisation of the capital asset, which constitutes a potential self-budgeting for future renewal. The development in the last 20 years of public sector accounting standards boards dedicated to tangible capital assets management has encouraged water and wastewater utilities to consider capital depreciation as a decision-making criterion for asset prioritisation. At the same time, when the capital depreciates the asset function deteriorates, but this deterioration is more difficult to assess. In fact, each asset can be evaluated according to a functional value that indicates the capacity of the asset to deliver the designated service at the required level. This value declines during the service life because of the occurrence of unexpected events (failures, breaks, leaks and degradation). The functional deterioration, also referred to as ‘obsolescence’ or ‘reliability’, is still misunderstood for water pipe assets. This study addresses the following questions: How can the functional value be estimated for water systems both at the pipe and at the network scale? How can the decision-making process for pipe renewal be improved by incorporating specific indicators based on both functional and accounting values? The current research focuses on the definition of an appropriate time-dependent functional value, based on the following hypothesis: the functional value depends on both structural and hydraulic deterioration of the pipe asset, but is partially restored by curative maintenance actions. The calibration of the functional value is mainly based on historical incident data, roughness data and managers' opinions. In order to carry out the decision-making process, the evolution of the functional value is simultaneously analysed with the depreciation of the capital asset value. The implementation of the approach at the pipe and the network level leads to an assessment of innovative criteria for the purpose of assessing possible renewal policies.     

Integrative modeling of performance deterioration and maintenance effectiveness for infrastructure assets with missing condition data

Deterioration modeling is an important analytical component in infrastructure asset management. It concerns the prediction of performance and remaining service life of assets of different designs under omnifarious working environments. For long‐term prediction, it also requires to characterize maintenance effectiveness because maintenance activities do not necessarily bring an asset to a completely renewed status. Deterioration modeling research has for decades been largely focusing on the modeling of the natural deterioration process per se, whereas the modeling of maintenance effectiveness is only a recent focus of investigation, mainly in pavement research. In practice, the asset conditions immediately before and after a given maintenance treatment both are not often known. This has made the modeling of maintenance effectiveness and long‐term deterioration prediction a challenging task. To bridge the gap, this paper presents a novel approach that integrates the modeling of deterioration and maintenance effectiveness into one process. The natural deterioration of asset performance is modeled as a continuous‐time Markov chain, whereas the effectiveness of a maintenance measure is modeled as a discrete‐time Markov chain. To account for missing condition data before and after the maintenance event, the paper also develops a robust statistical method based on Markov chain Monte Carlo simulation. A real‐life case study on a municipal sewer pipe system is carried out for demonstration of the proposed integrated modeling approach. The functional deterioration of sewer pipes and the effectiveness of flushing operations that target to bring flow capacity to intact state are modeled. Influences of pipe length, diameter, slope, and sewershed area are examined. The present work is a valuable step toward development of evidence‐based risk‐informed asset management framework.     

Change program management: Toward a capability for managing value-oriented,integrated multi-project change in its context

Program management has taken its position in project management research and in public and private organizations as a successful method for managing complex, uncertain, and large-scale changes. During the past 25 years, research has evolved from programs as the conceptual extension of projects to a rich field of empirical studies reflecting the special natures and contexts of change programs and their management, with unique theoretical foundations. To take stock of this recent history, in this article we analyze the patterns of previous empirical studies on change program management and their theoretical foundations. The goal is to identify and summarize proposals to guide forthcoming program management research. The results reveal three main themes of ongoing research: managing over the change program lifecycle, managing programs in their context, and program managers' capabilities. The roots of change program management in organization theories are apparent; structural contingency theory and information processing theories have dominated in previous empirical research, but are clearly being extended to agency, stakeholder, and actor-network theories. New research ideas are proposed for the use of programs in various types of changes, value creation and delivery through change programs, the profiles and capabilities of different actors in program management, the coexistence and interplay of multiple programs, and the complex stakeholder networks involved with change programs. When change becomes more prevalent in the organizations' dynamic contexts, there is an increasing need to develop program management toward an organizational capability for managing value-oriented, integrated, and multi-project change in complex stakeholder contexts.     

A relative-risk framework for evaluating transient pathogen intrusion in distribution systems

Hydraulic transients generate significant negative pressures in water systems that may cause intrusion of contaminated water from the environment into the pipe. This paper expands the consideration of transient intrusion events from their purely hydraulic aspects by developing a risk-based framework for comparing the relative risk-reduction achieved by alternative transient-intrusion mitigation strategies. Alternative strategies may be any combination of changes to system operation or surge controls that would reduce the potential for intrusion of contaminants from the soil-groundwater environment surrounding the pipe. A reference groundwater contamination is assumed, and intrusion volumes and time-varying pathogen concentrations are computed respectively using hydraulic transient and water quality models. Risk-based measures are proposed to provide quantitative assessments of the relative reduction in the risk of receptor infection achieved by alternative mitigation strategies.