Renovation works in the pipeline16 November 2001
Renovation works were needed on the Izmit domestic and industrial water supply project in Turkey after an earthquake damaged the project's pipelines just seven months after completion
The Izmit domestic and industrial water supply project in Turkey is the largest privately financed water BOOT project in the world. The US$900M project was constructed by a consortium of Thames Water of the UK and two Turkish Contractors - Gama and Güri - with Taylor Woodrow undertaking the project management role. WS Atkins International was the technical adviser to the special purpose company carrying out reviews of the contractor's designs, undertaking a construction monitoring role, administering the contract and providing technical support to the general manager.
The project included the construction of a 108m high clay core earth embankment dam, a 480M l/d water treatment plant, six pumping stations and the installation of over 100km of large diameter steel pipes and nearly 50km of ductile iron pipelines, and a SCADA control system.
The project went into commercial operation on 18 January 1999, three months ahead of schedule and within the budget.
On 17 August 1999, just seven months after completion, a significant earthquake measuring 7.4 on the Richter scale rocked the city of Izmit and the surrounding area. Its epicentre was located approximately 5km from the water treatment works. The earthquake was related to a major fracture of the North Anatolian Fault with lateral displacements of up to 5m across the fault being recorded. Over 15,000 deaths were reported following the earthquake, and 600,000 people needed to be re-housed. The estimated cost of the earthquake was US$16B (7% of Turkey's gross domestic product).
In the immediate aftermath, the water treatment works was shut down for a few hours but then brought back on-line, providing treated water to the disaster area continuously thereafter. The dam wall was apparently unaffected, although subsequent surveys showed that the wall had settled some 190mm, which is well within the overbuild allowance provided for long term consolidation of the dam. Damage at the water treatment works was limited to some of the clarifier distribution pipework shearing: jointing material being squeezed out of movement joints in the water retaining structures; and cracking of architectural finishes.
Two pumps at one of the large pumping stations were also damaged in the quake, and one section of ductile iron pipeline was found to have failed catastrophically, as the fault had crossed a 700mm diameter pipeline where a branch line joined it. The operator repaired this section of pipeline within three days of the earthquake.
The project was insured against earthquake events, so a systematic inspection and repair programme was put in place jointly by Izmit Su and the insurers, Generali. WS Atkins International was appointed to manage the programme and to liaise with the loss adjusters, Crawford, to ensure that all inspection and repair works were pre-agreed to minimise any financial exposure for Izmit Su.
The inspection programme identified the following:
• A700mm ductile iron pipeline was exposed in three locations. It was found to be undamaged with no signs of leakage at joints.
• External damage to the steel branch line was not apparent,although subsequent inspections showed limited failure of the epoxy internal coating adjacent to manufacturing and filed welds.
• A small leak in the main steel pipe line, estimated to be about 20 litre/sec was found on the surface but no other signs of damage were apparent. The pipeline was partially exposed by Gama and three joints were distorted.
The 2.2 m pipeline was under an operating pressure of nearly 9 bar. This was found to be at the limit of traditional line stopping technology but the delay to get the equipment made and shipped to Turkey was not acceptable. A list of options were developed, as detailed in the table below.
The Insurers agreed to proceed with the permanent installation of a bypass and replacement of a damaged pipe line. Although it was the most expensive option, the length of shutdown required was the shortest, and the work required to be undertaken during the shutdown the simplest.
A detailed design, risk assessment and planning exercise was undertaken jointly by Thames Water, Gama, Taylor Woodrow, and WS Atkins with support from the pipe manufacturer, Europipe. The main issues considered were:
• The size of the permanent by-pass for the temporary situation.
• The design of the preparatory works to be undertaken on the live pipeline.
• The draindown and filling times.
• The jointing details required during the shutdown.
The pipeline was fully back into operation in April 2000, seven months after the earthquake event. The investigation, design, approvals and procurement took nearly five months; installation of the by pass and preparation for the shutdown took a month; the shutdown took a day; and the reinstatement of the main pipe a further two weeks.
The repaired pipe is back into full operation with little discernable difference to the operation of the bulk water distribution system.
|In its advisory notes on lifeline earthquake engineering, the American Society of Civil Engineers suggests that identifying active fault zones and avoiding wherever possible, are the best ways to mitigate seismic hazards in a known area of faulting. If, however, a fault zone must be crossed, the following steps are recommended: • The optimum angle of the pipe relative to the strike of the fault should be 70° to 90°. • Slip between the pipe and adjacent soil is desirable. • Slip is encouraged by wrapping with polyvinyl sheathing and shallow burial. • Anchor such as thrust blocks should be excluded within a distance of at least 150m and preferably 300m. • Trenches should have sloping sides rather than vertical sides as they accommodate relative movement between the pipe and the soil better. • Pipes should be strengthened within 15m of the fault zone; ductile iron or extra thickness steel pipe is justified. Butt-welded and double welded joints, restrained-articulated joints and restrained bell and spigot joints with ring gaskets should be considered.|