T.D. Williamson Asia Pacific Pte. Ltd. (TDW) reported completion of a challenging hot tap and folding STOPPLE® plugging operation on a critical water main in Ho Chi Minh City, Vietnam. The operation, carried out for engineering design, construction and supervision consultants CDM International on behalf of Saigon Water Corporation (SAWACO), is the largest STOPPLE plugging operation TDW has performed in the Far East – Asia Pacific region.

Metropolitan cleanup initiative requires canal improvements

The STOPPLE plugging operation was carried out in conjunction with the Ho Chi Minh Environmental Sanitation Project (Nhieu Loc – Thi Nghe Basin). The primary objective of the project is to install a storm water and sewage collector system to alleviate flooding and to correspondingly improve the water quality of one of the city’s primary canals by diverting sewage flows to a pumped collector system and by dredging the canal to promote natural tidal flushing. To achieve this, one million cubic meters of material will be removed from the canal.

Crossing the canal, and laid within the canal bed some 50 years ago, is a primary water supply pipeline that supplies a daily average of 160,000,000 gallons (610,000 cubic meters) to 5,000,000 residents. This pipeline was, however, located within the dredging zone and it therefore had to be removed and re-provided, but without interruption in supply.

North of the canal, the main is a 2m diameter pre-stressed concrete cylinder pipe (PCCP), while to the south it divides into two 1.5m and 1.2m PCCP pipes. CDM proposed sinking two shafts either side of the canal to install a carrier pipe by pipe-jacking it between the shafts. A permanent diversion could then be installed, allowing the existing main to be removed.

The challenge came in maintaining water supply while works were carried out. “There was much at stake,” said Vo Quang Chau, Technical Deputy General Director for SAWACO. “It was the only source of water to the city.”

The solution

Since the main could not be shut down, CDM recommended that SAWACO engage TDW to isolate it while a temporary bypass was installed. This involved inserting folding STOPPLE plugging heads into the three lines to stop the flow through the canal section and diverting it to a temporary bypass pipe on the bridge. The 2m pipeline across the canal could then be isolated for cutting, and new connections made, facilitating the permanent diversion. Supply could thus flow while the permanent main was brought on-stream.

Preparing for hot tapping and folding STOPPLE plugging operation

To ensure that the existing water main operated during tapping, plugging and connection operations, CDM sank shafts on each side of the canal and jacked a carrier pipe between them. A permanent water main was placed in the carrier pipe, and steel pipes laid in the shafts and trenches on each side to connection points on the existing main. At the tapping and STOPPLE plugging points, the existing main was exposed, with concrete piles constructed to support the concrete-encased main, providing a platform for the 15-ton equipment. The water main had to remain perfectly stationary despite the heavy loads; otherwise it might have leaked or failed, interrupting water supply.

Hot tapping on three live water mains

TDW carried out hot tapping procedures on the three live mains using a sterilized cutting head. Three small taps for equalization and three large taps for the folding plugging heads were made. Working at night when water demand was low, engineers reduced the water flow so that the STOPPLE plugging heads could be inserted. TDW inserted three folding plugging heads in just two hours. SAWACO then cut the existing pipe to remove sections and allow new connections. The new pipeline was then connected to the existing pipeline, completing the permanent diversion.

City never without water

Following testing and sterilization, TDW removed the plugging heads, allowing flow to be diverted into the new pipeline. Finally, SAWACO drained, disconnected and removed the temporary bypass, thus completing the operation. “As a result of planning and innovative engineering, the city was never without water,” said George Easo, Project Manager for TDW in India. “Our experience in pressure isolation makes operations of this kind possible, with minimal impact.”

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