P. Le Gauffre

Bio: P. Le Gauffre is an academic researcher from Institut national des sciences Appliquées de Lyon. The author has contributed to research in topics: Visual inspection & Sanitary sewer. The author has an hindex of 4, co-authored 5 publications receiving 126 citations.

The consistency of visual sewer inspection data

Abstract: In common with most infrastructure systems, sewers are often inspected visually. Currently, the results from these inspections inform decisions for significant investments regarding sewer rehabilitation or replacement. In practice, the quality of the data and its analysis are not questioned although psychological research indicates that, as a consequence of the use of subjective analysis of the collected images, errors are inevitable. This article assesses the quality of the analysis of visual sewer inspection data by analysing data reproducibility; three types of capabilities to subjectively assess data are distinguished: the recognition of defects, the description of defects according to a prescribed coding system and the interpretation of sewer inspection reports. The introduced uncertainty is studied using three types of data: inspector examination results of sewer inspection courses, data gathered in day-to-day practice, and the results of repetitive interpretation of the inspection results. After a thorough analysis of the data it can be concluded that for all cases visual sewer inspection data proved poorly reproducible. For the recognition of defects, it was found that the probability of a false positive is in the order of a few percent, the probability of a false negative is in the order of 25%.

Sewer asset management: from visual inspection survey to dysfunction indicators

Abstract: Asset management is an increasing concern for wastewater utilities and companies. Criteria are developed for supporting the definition of investigation and rehabilitation programs. Dysfunction indicators contribute to the calculation of criteria, using expert rules. These indicators are mostly based on visual inspections, which provide major information. However, difficulties remain in the translation of visual inspection survey into dysfunction indicators. This article presents a methodological approach aiming to fill this lack. In the framework of the French RERAU program (Rehabilitation of urban sewer networks) a methodological approach has been developed in order to convert visual inspections of sewer segments into four possible condition grades {1, 2, 3, 4}, grade 4 corresponds to the worse condition. Three complementary procedures are thus executed: (a) expert rules based on sequences of observation codes, (b) comparison of single score to threshold and (c) rules based on analysis of segment profiles (scores distribution). An experiment lead in the Bas-Rhin (France) illustrates the different steps of the methodological approach and the applicability of the RERAU methodology on CCTV data. Moreover, confrontation between expert assessment of sewer segments (condition grade) and calculated scores has demonstrated the necessity of considering diagnosis imperfection, which may lead to misclassification in some cases. The algorithm proposed in this article aims to minimize a cost function with costs assigned to false positive diagnosis test (segment classified in worse condition than experts' opinion) and false negative diagnosis test (segment classified in better condition than experts' opinion). The algorithm is described in detail and applied to an example. Thus imprecision of assessment is taken into account: the threshold is chosen as to be the most efficient (in term of cost). This approach is generally applicable to numerous domains, when levels of performance need to be defined.

Multi-criteria decision support for annual rehabilitation programmes in drinking water networks

Abstract: The selection of projects in the annual rehabilitation plan of a drinking water network requires the consideration of different aspects of existing deficiencies and expected improvements in the water supply system. With a field study of 12 water utilities in Europe, the objectives of drinking water network rehabilitation are identified. These objectives are assigned to a number of “points of view” that can be divided in two types: internal and external points of view. Internal points of view mainly affect the cost and the monetary benefits of rehabilitation measures for the utility. External benefits of rehabilitation result from a better hydraulic performance of the system, from improved system reliability or reduction of risks and therefore, they contribute to customer and third party satisfaction. Nine points of view are rendered more precisely by 17 criteria. The criteria are expressed by detailed cost functions, quantification of current deficiencies, assessment of risks or assessment of the pipe’s potential contribution to zonal problems. Examples are given of criteria definitions and their calculation for using them in procedures of aiding decisions. This paper is a report on ongoing work in the CARE-W European project.

CCTV inspection of sewer segments: calibration of performance indicators based on experts' opinions

Abstract: Asset management is an increasing concern for wastewater utilities and companies. Indicators are developed for supporting the definition of inve stigation and rehabilitation programs. These indicators are mostly based on visual inspect ions, which provide major information. However, difficulty remains in the translation of a visual inspection survey into dysfunction indicators. Condition grade of a sewer segment may be obtained by comparison of a single score to thresholds which must be in accordance wit h practices or opinions of utilities’ experts. The confrontation between expert assessments of sewer segments (condition grade) and calculated scores also demonstrates the necessi ty of considering diagnosis imperfection when establishing thresholds. To fill this niche, a n algorithm has been recently proposed (Ibrahim et al., 2007) in order to fix thresholds by minimizing a c ost function. This article presents a successful application of the proposed a lgorithm on 30 CCTV reports of sewer segments located in the urban community of Strasbourg or in the Departement du Bas-Rhin . For each CCTV, a score is calculated using observat ion codes converted into numerical scores and in parallel, grade is assessed by several exper ts (sewer managers of different French local utilities). This method has proved its interest whe n threshold determination is required to assess indicators. Moreover, this approach is gener ally applicable to numerous domains, when levels of performance need to be defined.

Infiltration in Sewer Systems: Multi-Criteria Comparison of Investment / Rehabilitation Strategies

Abstract: Within the FP5 European APUSS project (Assessing infiltration and exfiltration on the Performance of Urban Sewer Systems), a methodology has been proposed to account for environmental, technical and economic impacts of infiltration or exfiltration on sewer systems, treatment plants and receiving waters, and to evaluate the consequences of possible investment / rehabilitation strategies. The multi-criteria method Electre III is used to compare and to rank the various strategies, as this method has a high potential adaptability to diverse contexts and objectives. An example of application of the proposed methodology is given for a 245 ha residential catchment equipped with a combined sewer system, including scenarios with different infiltration rates. It shows that the methodology is applicable, but also that validated and site specific information (data, measurements, calibrated models, etc.) is necessary in order to carry out a valuable analysis. Results shall be reviewed carefully and the final decision making process should take into account the context of the study. There is no unique best investment strategy, but several options may be considered depending on priorities and criteria of the sewer operator. The methodology is general, but results of the case study are site specific and cannot be extrapolated.

Maintenance, management, life-cycle design and performance of structures and infrastructures: a brief review

Abstract: The optimal decisions to maintain or improve the reliability and functionality of structures and infrastructure systems can only be achieved through proper integrated management planning in a life-cycle comprehensive framework. Structure and Infrastructure Engineering (SIE) is an international journal dedicated to recent advances inmaintenance, management, and life-cycle performance of a wide range of infrastructures. The purpose of this article is to provide a brief review of the recent research accomplishments in the field of design, maintenance, life-cycle management, and optimisation of structures and infrastructures reported in papers published in SIE during the period 2005–2011. The papers are categorised under main topics and very briefly discussed.