Bortunco Sliplines with HOBAS Pipe

By Liz Moucka | September 28, 2010

When the Montgomery County MUD (Municipal Utility District) No. 9 required the repair of a 72-inch-diameter corrugated stormwater line, they did not know the creativity that this job would entail. The failing corrugated steel pipe ran about 60 feet from the end of the concrete line to an outflow point along the shore of Lake Conroe, beneath residential yards, even directly adjacent to a family's swimming pool.

The engineer, Mike Mathena with Bleyl and Associates, specified HOBAS 60-inch CCFRPM (centrifugally cast fiberglass reinforced pipe) to slipline the failing 72-inch corrugated pipe. Because this was an upscale lakefront residential area, the plan was to slipline the stressed pipe instead of trenching.

Bortunco won the contract to slipline the pipe; however, between the time they bid the project and the time they were awarded the contract, the drought had ended and lake levels were back to normal. No longer could they bring the pipe in by high flotation amphibious vehicle along the shore. They needed a plan B.

Plan B In Action

So as not to ruin the landscaping of these lovely lakeside homes, the decision was made to bring in the pipe across a portion of the lake and into the slip behind these homes. The three 20-foot-long sections of 60-inch CCFRPM HOBAS pipe were delivered to a site about half a mile from the damage area and unloaded with a crane, according to Terry Meador, Bortunco vice president for construction. The Bortunco crew was headed by project manager Holton Ferguson and foreman Mario Torres. Asset Manager Eddie Carter designed and built pontoons to fit inside the pipe so that it would float as it was pulled behind a boat to the job site.

"The pontoons had been rigged with air hoses so we could relieve the pressure in them and introduce water," explained Meador. "We slowly sank the pipe until it had almost zero buoyancy and the top of the pipe was sitting at about lake level."

"The sections of pipe were coupled with flush relining joints to allow them to fit inside a tight application like this," explained Kirk Eager of HOBAS Pipe in Houston. "HOBAS pipe is one of the few products that can be used in sliplining diameters as large as that. Bortunco has worked with HOBAS quite a bit so they were very familiar with the product."

The crew had rigged a winch through a manhole about 80 feet from the outfall, where they could run the cable to pull the 60-inch HOBAS pipe through the 72-inch corrugated pipe to where it joined the concrete stormwater line that was still competent.

Success For All

Bortunco had a 10-foot easement through the residential yards and worked with the property owners to save landscaping not only by bringing the new pipe in via the lake instead of through their yards, but also laid plywood walkways where crews had to work on land. According to Meador, the homeowners were happy to have the problem corrected, and Bortunco kept them informed of work-in-progress.

"Grout bags were slipped around the HOBAS pipe so crew could fill in between the HOBAS and corrugated pipes with high-density grout, a process done in the wet," Meador described. "That created a bulkhead prior to grouting the entire line. Once the grout had set, we put a 60-inch pneumatic air plug in the HOBAS pipe and dewatered everything upstream from the boat slip so that we could get a visual inspection. It was good, as we had anticipated."