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Complications On The Rio Grande
Storm Sewer Trunk Line Is Successfully Rehabilitated Using Two Trenchless Methods
A preliminary analysis, said Williamson, determined that the most cost effective solution would be to rehabilitate the existing line rather than removing and replacing it.
"The project," he continued, "presented several challenges, including installing a structural liner in the existing line and the use of trenchless construction methods for rehabilitation which included sliplining fiberglass reinforced plastic (FRP) and spiral wound high density polyethylene (HDPE)."
The project required a special outfall design at the Rio Grande in order to comply with U.S. Department of Homeland Security (DHS) requirements. Special provisions were incorporated into the project to address these concerns and minimize impact to local residents and retail businesses.
Ultimately, the decision was made to use two different sliplining methods to rehabilitate the old pipe. General contractor was Huff & Mitchell, Inc., Cypress, TX. Glen Crawford was project manager. Boring & Tunneling Company of America (BorTunCo), was the contractor for sliplining.
Construction was scheduled to begin on the lower section with sliplining of approximately 300 feet of Flowtite glass fiber reinforced thermosetting polymer mortar pipe (FRP). Because the area is in a flood plain of the Rio Grande River, work was scheduled to begin after the end of normal "wet" season, which had been dryer than usual. FRP pipe was chose for the lower segment because it was anticipated the 20 foot sections of pipe could be installed very quickly in case rain did come.
Although the area had been dry preceding the projected starting date of construction, heavy rains came about the time work started, delaying the project from the beginning.
About the time water in the river began to recede, more water came unexpectedly. The Mexican government owed the United States water that it had borrowed during previous drought periods, explained Williamson. With the approval of the International Boundary and Water Commission (IBWC), Mexico released water from dams upstream of the project, and water remained at a level too high to permit construction.
"We considered a coffer dam, but it was determined that would require too much time," said Williamson. "But the water did drop, and we resumed work. The FRP section was cleaned quickly by BorTunCo and 4 inch PVC runners were attached to the host pipe on each side at the 5 o'clock and 7 o'clock positions. This facilitated pushing the 20 foot joints the entire length of the lower section of the project by hand."