Case Based Reasoning for Prestressed Concrete Cylinder Pipe Condition Assessment

Transcription

1 Case Based Reasoning for Prestressed Concrete Cylinder Pipe Condition Assessment Nada M. Elbouri and Saleh M. Amaitik Operation and Maintenance Department, Building Maintenance Section, Man Made River Project Company, Benghazi, Libya Industrial Engineering Department, Faculty of Engineering, Benghazi University, Benghazi, Libya Abstract: Many owners of Pre stressed Concrete Cylinder Pipe (PCCP) water mains around the world experienced failures in their pipelines. The condition assessment and performance forecasting of the pipelines are the greatest challenges facing owners and users of such pipelines. In this paper, a PCCP condition assessment model was developed using Case- Based Reasoning (CBR) technique and applied to real-world data collected from Man-Made River Project. The developed CBR model involves fifteen input variables that affecting the deterioration process of PCCP. The proposed CBR model demonstrates good and acceptable results of PCCP condition assessment. The developed model can be integrated into the Pipe Management System currently being used by the Man-Made River Authority. It is expected that this model will help decision-makers of Man-Made River Authority or any other owners of PCCP water mains to prioritize their pipeline inspection and rehabilitation planning. Key Words: Pre Stressed Concrete Cylinder Pipe (PCCP), Water Mains, Case Based Reasoning (CBR), Wire Breaks.' Introduction PCCP's are used by many agencies and authorities as a water distribution system. The evaluation of their performance becomes a major concern for owners and operators of these agencies. Due to the limited access to the buried pipes and the high cost associated with conducting non-destructive inspections, this made the evaluation more difficult. Ruptures of PCCP can cause interruption in service, damage to property and repair costs. The Man-Made River Authority (MMRA), that dedicated for the implementation and operation of the Man-Made River Project (MMRP), experienced a series of pipe ruptures in their pipelines. A rehabilitation plans were adopted by MMRA,

2 which involve conducting a comprehensive condition assessment programm based on non-destructive inspections i too identify and treat defective pipes. On site investigations and studies carriedd out by MMRP concluded that ruptures were cause due to corrosion induced failures of pre stressed wires. To minimize the risk of more rupture, a simplified pipe classification model was established andd used to classify the distressedd pipe according to critically. MMRP hass installed an acoustic monitoring system to monitor their pipe lines. A very largee amount of data has been collected showing wire breaks as they occur in real time. This dataa can be exploited with the use of CBR inn order to predict future PCCP P failures. As an alternative to conducting direct inspection (electromagnetic, acoustic monitoring, GPR radar, etc.) which when applied to an entire pipeline can be prohibitively expensive or impossible due to operating conditions, it is possible to use statistical or intelligent models to predict thee condition assessment of the pipelines based on historical condition observations and inspections results. Case-Based Reasoning (CBR), one of artificial intelligence techniques, is a suitable problem solving technique where problems are solved by recalling and adapting the solutions of similar past problems.[2] 2 Overview of Man-Made River Project The MMRP (Man Made River Project) is a water supply project located in North Africa State of Libya. Water is conveyed from well fields deep in the Saharan desert to the population centers that are concentrated on the northern n coastal strip. Almost about 4,000 kilometers of f mainly 4 meters diameterr prestressed concrete cylinder pipe has been laid.[2,7] The MMRP containss 49 production wells, which producing 6.44 million cubic meters of water per day linked together by water holding pipes network having a total length of,988 Km of PCCP's having a diameter of 4m. 4 Phases of MMRP with their pipeline length are shown below: Sarir Sirt Tazerbo Benghazi (900km) ALhasouna Aljeffaraa (277 km) ALgardabia Assdadaa (90 km) Ghdamis-Zouara-Azzawyia(62 km) [6] figure : The Conveyance System of MMRP[7]

3 2. Sarir-Sirt/Tazerbo-Benghazi system The Sarir -Sirt /Tazerbo-Benghazi, which called phase one of o MMRP, consists of two lines and involves conveyingg 2 million cubic meters off water per day from well fields in Sarrir and a Tazerbo to end reservoir at Sirt andd Benghazi. The total length of PCCP used is 900 km, the majority being 4 meters in diameter. The system is designed to ultimately carry a flow of.5 million cubic meters per day in the future with the additional water being drawn from a well field at kufra. 2.2 ALhasouna Aljeffara systemm Phase two of MMRP involves conveying two million cubic meters of water from well fields at East Jabal Hasouna and North East Jabal Hasouna to Tarhouna and Tripoli. 287 production wells willl produce.4 million cubicc meters of water per day and 5 production wells at North East Jabal Hasouna will w produce a total of 0.6 million cubic meters per day. 2. Gardabiya Sedada system This system links phases one andd two, enabling bi-directional flow of water. In addition to the kufraa expansion underway in the phase onee system. Two other major phases are either under construction or water per day. Prestressed Concrete Cylinder Pipe (PCCP) Figure 2: Pre Stressed Concrete Cylinder Pipe Main forms of failuree in PCCP include [6,7]: Broken prestressed wire due to corrosion or poor material quality. Joint leaks. Poor bedding. Excessive external loading. Hydrogen Sulfide (H2S, waste water application). Poor quality mortar coating. Corrosive environment (corrosive, aggressive soil). Constructionn damage (coating damagedd and without repairing).

4 4 Case Based Reasoning Method The CBR Cycle can be described in figure. The main steps of casee based reasoning cycle can be described by four processes: Retrieve the most similar case or cases. Reuse the information andd knowledge in that case to solve the problem. Revise the proposed solution. Retain the parts of this experience likely to be useful for future problem solving.[4] Figure : Case Based Reasoning (CBR) cycle. [] CBR is an Artificial Intelligence technology, and it is a model of human problem solving using prior experience e (called cases). Also it is known as the process of solving new problems by retrieving relevant past cases and adapting them to fit new situation. In CBR system expertise is embodied in a library of past cases, rather than being encodedd in classicall rules. Eachh case typically contains a descriptionn of the problem, plus a solution and thee outcome. The knowledge and the reasoning process used by an expert e to solvee the problem can be implicit in the solution or explicitly recorded ass another component that can be re used. To solve the current problem; the problem is matched againstt the cases in the case base, and similar cases are retrieved. The retrieved cases are a used to suggest a solution which is reused and testedd for success. If necessary, the solution is then revised.finally the current final solutions are retained as a part of new cases thatt is added to case based. Many people like case based reasoning because they feel happier with examples rather than conclusions separated from their context. [8, 9]

5 5 Data Collection and Selection of Model Parameters Results of electromagnetic inspection (Remote Field/Eddy Current Transformer Coupling) technique such as number of wire breaks, number of breaks positions, number of wire breaks in each position are recorded and stored in separate database. This information was available for entire section between Sarir/ Sirt- Tazerbo/ Benghazi, which comprises more than one thousand pipes. It was linked with both Pipe As-Built and Pipe History databases in order to extract the most important design, physical and environmental available data that have the major effect on the deterioration process of PCCP. Action taken for each pipe (monitoring, repairing or replacement) was recorded and linked with other databases. Fifteen variables (parameters) were identified and selected as inputs to the proposed CBR model. Table shows the framework of PCCP parameters used in this research work.[2] Table (): Frame works of PCCP Parameters Cases Input Parameters Parameter unit imp Type Mini Max Station No. m Numeric System Line - Text Pipe Type - 2 Text Pressure Rating Bar 2 Numeric Earth Cover m 2 Numeric Resistivity Ω cm 2 Numeric Wrapping - 2 Text Wire Diameter mm 2 Numeric Distance Between Wires mm 2 Numeric Total # of Turns No. Numeric Pipe Age Days Numeric % of Lost Wire - Numeric # of Break Position No. Numeric Max Breaks No. Numeric Total Breaks No. Numeric 6 Implementation of the CBR Model Therefore CBR depends on the input specification or problem case, the output that defined the suggested solution to the problem and the memory of past cases used. This is known as reasoning mechanism. Each case concerns certain item with input parameters and solution description. Cases may be represented in a variety of ways depending on the requirement of the domain and the structure of available

6 data. Feature-Vector approach is used in this research work. The case is represented as a vector of attribute. When the new case of PCCP is given, memory provides relevant case and searching is done sequentially case after case until the entire case library is researched. The best matching case will always be retrieved adding new case to the library and this new case is added at the end of the list. In order to implement the CBR to aid in assessing PCCP condition, a computer program made MS-Excel with Visual Basic application has been used. Running this program is done by opening the Excel file from the location it saved in or from a shortcut on the desktop. When new case is given, the system will perform case retrieval and case adaption to new problem. Therefore the most important step in the CBR is the retrieval of previous cases that can be used to solve the target problem. Retrieval of cases can be done in different ways. However in this research work retrieving of PCCP cases has been done through similarity assessment, that is the most similar cases are most useful for solving target problem. One of the most important steps in retrieval phase in CBR is to define the degree of similarity between cases. In this research work, the degree of similarity between two items is computed by global similarity function, calculation of global similarity factor can be obtained from the weight of various attribute similarities. Once the similarities between new case and the past cases are calculated, the set of best matching chosen. 7 Nearest Neighbor Retrieval Nearest neighbor retrieval is a technique used for measuring the similarity between the past cases already available in the case base library and the new case given. Sometimes the new case does not match with CBR library, then CBR system will choose the nearest match. To calculate the similarity between the new case and the past cases already exist in the library, the similarity of each input parameter must be calculated, then finally the similarity of a given PCCP case can be calculated as Similarity = Where: Fi: importance factor of each parameters Wi: Similarity factor of each parameter (similarity between old cases and new case). Calculation of Wi: Textual data, if Wi Wcase Wi = 0, otherwise [5]

7 Numerical data: IF Wcase Win Wmax then Wi = IF Wmin Win Wcase Wi= then Where: Win : value of input parameter Wcase : value of given new case parameter Wmax : maximum value of input parameter Wmin : minimum value of input parameter Table( 2): Values of case study no. Parameters Units Values Station No. m 0,60.6 System Line - SS Pipe Type - ST Pressure Rating Bar 6.0 Earth Cover m 2.8 Resistivity Ωcm,700.0 Wrapping Wire Diameter mm 4.88 Distance Between Wires mm 5.58 Total # of Turns Pipe Age Days 4,204.0 % of Lost Wire No.6 # of Break Position No Max Breaks No 65 Total Breaks No 65

8 8 Results and Discussions To implement CBR technique to solve problem of assessing the condition of PCCP, 00 cases of past PCCP problem data have been collected from phase one of MMR project. 70 of these cases have been used as a case base library, and the others (0 cases) were used for validation purposes. The selection of the cases based on two criteria's i.e. pipe type and pipe system. When the new case is entered, the most similar cases will be retrieved and checking the similarity factor, based on the idea that similar problems have similar solution. The values of case study () are shown in table 2. The working steps of the proposed CBR model are summarized in the following steps: First step starts with entering the input parameters of the new problem to the Microsoft Excel program, then Second step is running the program, the similarities between the past cases and the new case are calculated at the end of each case, Third step is the selection of the most similar cases, by checking the similarities between parameters, and Finally, decide which of the retrieved cases best matches with the new case study. Table() shows the results of running the program for case study () Table (): Results of case study () Par. Station No. System Line Pipe Type Pressure Rating Earth Cover Resist.ivity Wrapping Wire Diameter Distance Between Total # of Turns Pipe Age % of Lost Wire # of Break Position Max Breaks Total breaks Similarity Factor Criticality Group Critical Action Uni. m - - Bar m Ω mm mm - Days No No No No Importance Given Data 0,60.2 SS ST , , ,606.6 SS ST , , C 9 Monitor 9 42,67. SS ST , , C 49 Monitor 5 2,62.6 TB ST , , B 74 Repair

9 The first three values of retrieved cases can be seen in Table (), as we can see the first three values of similarities by weighted average are: 0.88, 0.8 and These three cases are against to three cases number, 9 and 5 respectively. From the chart shown by comparing the most three similar cases we suggest that the solution is monitor pipe. Therefore the proposed solution of case study number one is monitoring pipe and when comparing with the actual solution it is the same Case Retrival no5 (solution Repair pipe) Case Retrival no9 (solution Monitor pipe) Case Retrive no (solution Monitor pipe) Figure 4: The chart of the most similar cases This steps are done for the 0 cases (cases used for validation), and comparing the results we concluded that the system is valid for PCCP condition assessment up to 90%. 9 Conclusions and Recommendations It is concluded that the application of CBR technique in assessing PCCP condition is feasible, and the performance of the proposed model is good and acceptable. Therefore, the proposed model can be integrated into the pipe management system currently being used by MMRP to perform the task of condition assessment, which is considered an important function. It is expected that the CBR model developed in this research work will help owners and operators of the PCCP water mains along with other factors such as historical data, knowledge experience, etc, to identify the distressed segments of their pipeline network, and then prioritize inspection and maintenance measures needed to prevent future deterioration and eventual failure of the distressed pipes. Acknowledgement The authors gratefully acknowledge Man-Made River Project (MMRP) and Benghazi University for their support.

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