North American Special - Trenchless International

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asset management April 2009 - Trenchless International An example graph. but did not have sufficient failure history to warrant a standalone analysis. Sample results of the calibration process are shown in table 1. Results show a relatively long mean time to first failure for ductile iron pipes compared to cast iron pipes. However, for mean time to subsequent failures (especially after the 4th failure) cast iron pipes tend to outperform ductile iron. No significant differences were noticed in the performance of spun and pit cast iron pipes. The performance model was used to predict the following: • Long-term funding requirements for repair and replacement/rehabilitation under different level of service scenarios. Level of service was measured by number of failures experienced on a water main segment. • Using a Monte Carlo simulation to predict future failure patterns on various water main vintages, the optimum time to replace/rehabilitate was computed as a function of the ratio to repair to replacement cost. This minimum expected economic loss (MEEL) was found to be somewhat large for typical cost ratios (8-12 failures on a water main segment). This indicated that the governing criterion is more likely to be a level of service indicator set by the municipality rather than pure economics. In addition to the use of the model at the strategic planning level, the performance model was used to develop two important tools for water main management at the tactical/operational level. The coordinated infrastructure renewal tool and the early replacement tool set. Critical Water Main Management The approach for managing critical water mains differs considerably from that for noncritical mains. Some of these key differences include: • Repair policy: With noncritical water mains, breaks can be tolerated and hence a run-to-end of service life approach can be accepted. Conversely, critical water mains with zero tolerance for failure, a proactive maintenance and rehabilitation policy should be sought. • Tolerance to uncertainty: Whereas with noncritical water mains and their run to failure management approach uncertainty in condition state can be tolerated, no such tolerance can be allowed for critical water mains. This has ramifications on the amount of information being collected and the level of detail at which this information should be stored. The critical water main management framework consists of three main tool sets. 1. Assessment rationalisation framework: 2. Condition rating consolidation framework: This tool set attempts to standardise the way the results of assessment techniques are interpreted and subsequently used to drive decisions. The framework is developed for ductile iron and cast iron water mains as they compose the majority of the city’s critical inventory. The framework utilises Fuzzy Logic and the Analytical Hierarchy Process to combine condition rating results into an overall rating for the condition state as well as the expected deterioration rate of the pipe. 3. Planning cycle decision analysis tool: The purpose of this tool is to equip the asset manager with a consistent methodology for decision-making during each planning cycle. Within a planning cycle, the asset manger must make one of three decisions for the critical water main inventory; schedule intervention, schedule inspection and revisit at next planning cycle. In order to make an informed decision, the asset manager must consider the following aspects: • Condition State. This is analogous to the probability of failure. • Pipeline Risk. This corresponds to the consequence of failure. • Extent of condition/deterioration information currently available. The tool performs a trade-off between the available amount of condition/ deterioration information and the risk associated with operating the pipeline. • Level of uncertainty associated with inferring the condition state. Associated with the condition state that is inferred from the consolidation tool will be a measure of uncertainty. This factor must be considered in the decision process. This study is still ongoing and aims to re-evaluate what information is collected, and the way information is stored and handled throughout the lifecycle of the water main assets. Conclusion With these tools built, the city has established the foundation for the effective management of its watermain infrastructure. Furthermore, as these tools are integrated into the daily business decision process, they will be refined and improved to reflect the increasing knowledge growth within the city. They will also form the basis for clearly articulating the ramifications of decisions. This includes the need to focus resources, particularly financial, on the assessment of critical infrastructure, which in many cases has not yet failed or otherwise caused operational issues. These types of studies are often expensive and do not result in new tangible assets, but rather an improved understanding of the probability of failure. As such, these types of expenditures can often be challenging for cities and utilities to get funding approval for with out being able to demonstrate the non tangible benefits. This article is an edited version of a paper entitled Water Main Asset Management in the City of Hamilton: A Comprehensive Overview of Policies, Practices, Tools, and Technology by Hesham Osman and Kevin Bainbridge. The paper is to be presented at No-Dig 2009 Toronto, Canada. Please refer to the paper for more detailed information, references and acknowledgements. Delivering desalinated water to Sydney The $US419.5 million water delivery infrastructure project, part of the Sydney’s Desalination Project, aims to secure the city's water supply for future generations by constructing about 24 km of pipelines across Botany Bay, Australia. The new pipeline and its associated infrastructure and systems will carry the desalinated water from Kurnell, across Botany Bay, to Sydney's main water supply, the City Water Tunnel at Erskineville. Three tunnel boring machines (TBMs) will be employed to minimise the disturbance to residents and also to protect unique tracts of seagrass on the floor of Botany Bay. TBM: managing the environment The southern shore of Botany Bay contains extensive seagrass beds, which are a valued and protected part of the estuarine environment. Three species of seagrass are present off Silver Beach at Kurnell: zostera capricorni or eelgrass; posidonia australis or strapweed; and halophila ovalis or paddleweed. Posidonia requires the greatest consideration due to its slow reproduction and poor propagation by seed. Stretching about 6,500 metres in a westerly arc from Silver Beach at Kurnell to Lady Robinson’s Beach at Kyeemagh, the twin and single steel pipelines will impact approximately one per cent of the overall area of Botany Bay. Along the entire route, however, less than half of one per cent of existing seagrass along the southern shore (0.45 per cent) and Botany Bay (0.42 per cent) will be removed as a result of pipeline construction. Trenching through these seagrass beds would have required a seagrass management plan to be implemented during and after construction, and a compensatory seagrass package involving steps like transplantation. Instead, Sydney Water has chosen to microtunnel the pipeline from its Silver Beach construction area under Botany Bay for a distance of about 800 metres in order to protect the seagrass. The Water Delivery Alliance will join the single 1,800 mm diameter pipeline from Silver Beach to the twin 1,400 mm diameter pipeline about 800 metres from the shoreline, and (as always) protection of the environment will be a key consideration. Pit construction is nearing completion at the Silver Beach site. This pit is supported by secant piling, has internal jet grouting and is around ten metres deep. Land-based sections of the pipeline will be constructed first. Material that has been dug up from the pit is being used on site where possible, in order to minimise truck movements. Continuous water quality monitoring is being carried out around the Silver Beach construction area. Recent monitoring of the site has indicated good water quality conditions, with similar results both inside and outside the silt curtain. TBM onshore A TBM is also an essential tool to minimise disruption onshore. The bore passes beneath Tasman and Dampier Streets, Kurnell, to install pipeline. The model shown is (page 45) a Herrenknecht earth pressure balance and AVN machine, weighing approximately 100 tonnes. The first microtunnelling drive through a residential area is now complete. The TBM tunnelled 640 metres from the launch pit in Cook Park, under General Holmes Drive and under Tancred Avenue to the receival pit at Muddy Creek. The TBM used was chosen specifically for the conditions at Cook Park. The pipe liner and services will be installed on this section of pipe in the coming months. The TBM has also finished tunnelling 645 metres from Canal Road to Botany Freight Rail Line, which was the first tunnel completed on the project. Microtunnelling from Marsh Street Arncliffe, under the Cooks River to Tempe Recreation Reserve will begin in March. Choosing the route The pipeline route across Botany Bay was chosen because it avoids known areas of contamination. Every practical effort is being made to protect the Bay environment during construction. Water quality monitoring is ongoing during construction activities, in accordance with the Construction Water Quality Management Plan. The results of this monitoring will help the project team manage their work. environment April 2009 - Trenchless International 42 43
environment Supplying the community Water supplied from the desalination plant will increase the total volume of water available to all customers across the whole Sydney Water area, including the Blue Mountains, the Illawarra and Sydney. The desalination plant will be capable of producing up to 250 megalitres of water per day (ML/d), and will be able to be modified to produce 500 ML/d if required. With a nominal capacity of 500 ML/d, the new pipeline will be able to operate for short periods at up to 550 ML/d, to allow the flow to integrate into Sydney Water’s existing water supply network. The pipeline and associated infrastructure is under construction by the Water Delivery Alliance, made up of Bovis Lend Lease, McConnell Dowell, Kellogg Brown & Root, Worley Parsons, Environmental Resources Management and Sydney Water Corporation. All of the parties to the alliance are responsible for the works to be designed, constructed and commissioned. This project is breaking new ground to achieve the distances set for the tunnel drives, while the sizing of the lay barge operations require laying twin 1,400 mm diameter pipe in a predredged trench across the vast Botany Bay waters, which is likely to be challenging. Some of the tunnels will be the longest ever undertaken by pipe jack method in Australia and potentially within the Southern Hemisphere. No twin pipeline of this diameter, laid simultaneously from a barge for 8 km, has been executed previously in Australia. Notwithstanding the considerable challenges that exist, the Water Delivery Alliance team is well-skilled and committed to overcoming them, utilising innovation and a team culture that is striving for the completion of this project on time, in a safe manner and surmounting technical challenges to break new ground. Herrenknecht tunnel boring machine. environment April 2009 - Trenchless International Project scope The main project works are: • A drinking water pumping station on the site of the desalination plant in Kurnell; • Infrastructure from the pumping station to the existing water supply system in Erskineville, via Silver Beach and Kyeemagh, including associated connections and flow and pressure controls; • Marine works consisting of twin 7.5 km long, 1,400 mm diameter steel pipelines across Botany Bay; • Approximately 6.4 km of 1,800 mm diameter mild steel cementlined onshore pipe, slipped inside 2,100 mm diameter concrete pipes and installed by trenchless microtunnelling; and • Approximately 3 km of 1,800 mm diameter onshore pipeline, installed by conventional dig and lay trenching methods, with sheetpile and trench box shoring as required. Overcoming challenges Given the size of the project, and the locations it must traverse, considerable pre-planning and consultation has taken place with various regulatory authorities and the many wider stakeholders, including the community that will be affected by construction operations along the pipeline route. The Water Delivery Alliance has in place a structured team of proven community and environmental personnel, providing support to the wider team and ensuring that all approvals have been obtained and that stakeholders are well informed of both the program and methods of the activities that will take place in their vicinity. Community feedback has been encouraged and adjustments to the method or timing of activities has been made to accommodate their concerns, wherever possible. April 2009 - Trenchless International 44 45
Page 1 and 2: In this issue | Canada | USA | Japa
Page 3 and 4: Dec Downey Istt Chairman Trenchless
Page 5 and 6: EXECUTIVE DIRECTOR'S REPORT John He
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