Submitted by elisican on Mon, 2011-08-15 06:43
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By: Erin Boudreaux
I-45 sanitary sewer rehabilitation a proactive approach
Conroe, Texas, is a suburban city 40 miles north of Houston with a population approaching 60,000 residents. The city of Conroe has maintenance tasks within its sewer and wastewater system that need to be addressed. One project, the Interstate 45 Sanitary Sewer Rehabilitation, recently was undertaken.
This project rehabilitated the existing 54-in. trunk line. The solution consisted of sliplining with 535 ft of 48-in.-diameter Hobas Centrifugally Cast Fiberglass Reinforced Polymer Mortar pipe. As the main trunk line flowing into the only wastewater treatment plant for Conroe, this line was critical.
Trenchless methods were preferred due to the cover depth, which ranged from 20 to 22 ft, and the amount of surface traffic. The existing line ran underneath a heavily traveled interstate and popular rail line. Lewis Contractors of Bertram, Texas, chose to rehabilitate the pipe by sliplining with Hobas.
Assessing infrastructure
The existing 54-in. reinforced concrete pipe was installed in the late 1970s. An inspection of the line was performed to determine the condition.
“They ran TVs through the line using ultrasonic technology,” said Erwin Burden, assistant public works director, city of Conroe. Evaluation of the existing line by this technology can be used to verify defects and provide information useful in determining the extent of corrosion.
The survey revealed the existing pipe was showing signs of deterioration. The steel reinforcement was visible in the crown of some of the existing pipes. The microorganisms that are naturally present in wastewater systems can convert hydrogen sulfide gas to sulfuric acid, which makes the pipes vulnerable to corrosion. “In addition to the decay, there was joint separation under the railroad crossing,” Burden added.
Quick and easy installation
The project took three weeks to complete with the majority of the time spent preparing the jobsite for the installation and post installation site cleanup. Hobas supplied 20-ft sections of 48-in.-diameter, 36-psi-stiffness pipe. The pipe had a low-profile bell and spigot joint. This joint facilitates a quick installation and requires less joining force. All 535 ft of pipe were installed in a 14-hour period.
The installation pit was installed on the east side of Interstate 45 and the pipe string was pushed west under the main lanes and feeder road of the interstate highway just south of Conroe’s Loop 336. The I-45 is the main interstate highway and a major traffic corridor that travels in a north-south direction across the eastern portion of Texas. Conroe is located on I-45 along the main traffic route between Houston and Dallas.
The existing trunk sewer travels within the Union Pacific Railway easement and, in one location, directly under the railroad crossing. “The pipe was sliplined through an existing line that was in place, and there was no disturbance to the railroad right-of-way,” said Matt Lewis, project manager with Lewis Contractors.
The installation pit and work efforts were located adjacent to the rail line but did not affect the operation of the line. Trains passed through daily, even during the installation of the slipline pipe; there was no interruption to rail service.
The city obtained a permit from the Texas Department of Transportation to slipline the pipe under I-45. In addition to the sliplining directly under the road, “we were abandoning manholes along the frontage road so that we could move them out of the pavement, allowing us future access without having to shut down a lane and create traffic,” Burden said. The high-strength fiberglass composite used for sliplining pipes is designed to withstand the E-80 and HS-20 live loads.
Bypass pumping was necessary due to the manhole rehabilitation and relocation. “The flow was too great so we had to bypass pump, but still had a live flow within the line. It was just decreased, running about half,” Lewis said.
The pipe was installed from the upstream location downstream, with the flow.
The completion of this project will ensure that the line remains operational for the city of Conroe. “The city has been proactive in upgrading our sewer system to corrosion-resistant materials,” Burden said.
Hobas Pipe USA
800.856.7473
www.hobaspipe.com
