The city of Dallas was renovating its 76-year-old Cotton Bowl. The $50 million facelift included expanding capacity to 92,107, replacing the seats, adding media and VIP facilities, replacing the scoreboard, and upgrading concession areas, lighting, utility and sound systems. Plans also specified enlarging and adding restrooms and upsizing the sanitary sewers to handle the increased flow.
As Wright Construction Co. Inc. in Grapevine, Texas, began open-cutting the trenches for the new pipes, workers found numerous utility and telecommunication lines running over the old service. Project manager John Kolb called John Newell of DigTec in Dallas to review the inspection video and evaluate the situation. Newell declared the 8-inch concrete and SDR lines with CIPP liners good candidates for pipe bursting.
Dense soils, numerous delays, obstructions and unexpected obstacles stretched the three-week project to three months. Newell, however, overcame the challenges using a pipe-pulling system and a proprietary tool, enabling the 100-year-old Red River Shootout between the University of Texas and University of Oklahoma football teams to kick off again in the Cotton Bowl.
Stairway to grief
Wright Construction did all the excavating and set the shoring boxes. The 10-foot-square by 15-foot-deep pulling pits were 10 feet on either side of the stadium stairway. The pits and 3- by 20-foot entry trenches for the fused pipe were in hard clay. Gravel bedding and backfill covered areas of the host pipe. “When dropped into a hole, gravel compacts 85 to 90 percent and is as hard as concrete to expand,” says Newell.
Newell asked Gerry Robinson of Pipe Genie Manufacturing Inc. in Vancouver, B.C., what size bursting machine to use to upsize the 8-inch lined pipe to 12-inch HDPE pipe in such conditions. Robinson recommended an 80-ton machine, but Newell had a 40-ton and 60-ton Pipe Genie system and wanted to use them in tandem.
The chains normally run through the two hollow bursting cones and attach to the pulling head bolted to the HDPE pipe. Robinson, however, custom built a head that connected the chains from the two machines to a 3-inch bar. The cones slid over the bar and attached to the pulling head, allowing the rams to work in unison.
To prepare the pits, Newell’s six men laid two layers of 3/4-inch plywood over the gravel at the bottom to establish a level floor. They stacked railroad ties in front of the bursting machines to form resistance bulkheads. Newell lowered the ties and placed the rams side by side with his Terex backhoe. A chain winch raised and lowered other equipment and removed the 100-foot lengths of 3/4-inch chain as they were pulled into the pit. Each length weighed 618 pounds.
Before Wright Construction could excavate the entry trench on the right side of the stairway, a large crane parked over the location. “A contractor drilling piles needed it to lift rebar into the holes,” says Newell. “That crane put us on hold for weeks.”
Shark attack
Because the liners in the host pipes could come lose and bunch up in front of the breaking cones, Newell first split the lines using the Pipe Genie Shark Fin. As the front of the fin splits the pipe, water sprays out a jetting head at the back, loosening the surrounding bedding and blowing some gravel and sand into the split pipe, creating voids that help with displacement.
“Pulling a 12-inch pipe into an 8-inch pipe bursts and expands it to 15 inches,” says Newell. “Wet dirt and sand compact easier than dry material. In heavy clay and gravel, we jet at 10 or 15 gpm and 3,000 or 4,000 psi.”
Splitting the pipe on the right side took two 10-hour days due to unexpected obstacles. One was in front of the transformer supplying power for most of the Cotton Bowl. An encased duct bank ran directly over the top of the host pipe. Using the backhoe and trailer-mounted SPV800 SpoilVac with 800-gallon tank from Vacmasters, Arvada, Colo., Newell’s crew excavated a 6-foot-square by 10-foot-deep hole, exposed the duct bank, and chipped away enough concrete for the HDPE pipe to pass.
The Shark Fin stopped next at a repaired section of pipe encased in concrete. Newell waited for Wright Construction to open-cut and break it out. “Such an obstruction will stop a pull,” he says. “Time is of the essence then, as the expanded soil collapses slowly around the HDPE pipe, making it difficult to start moving again. Splitting the host pipe first eliminates such surprises.”
We’re off
Lacking sufficient space, the crew fused two 200-foot lengths of 12-inch DR17 HDPE pipe using a McElroy 412 fusion machine. Rollers under the pipe reduced drag and scarring during the pull. After pulling in 150 feet, the men had enough room to fuse the remaining length to the first half.
The first pipe pulled into the right-hand pit ran 275 feet beneath the angular section of Cotton Bowl Circle as it passed the stadium. “Besides pulling around a radius, the line had repairs bedded in gravel,” says Newell. “The pull was so hard that we broke railroad ties and equipment in two places.” Work stopped until Wright Construction open-cut those areas.
Meanwhile, Newell doubled the rows of railroad ties used for bulkheads. Once the pipe entered the pit, crews turned the rams 90 degrees and pulled a 100-foot section straight in from a manhole. When completed, poured-in-place manholes connected the lines in both pulling pits.
Running rams nonstop for eight to 10 hours heats and thins the hydraulic fluid, causing it to lose viscosity. To prevent that from happening and keep the machines pulling at their maximum, Newell alternated between a portable hydraulic power pack and a Bobcat skid-steer’s hydraulic power supply.
The first pipe pulled into the left-hand pit traveled straight from the second entry trench 275 feet away. Crews then turned the equipment 90 degrees and pulled a 100-foot section straight in from a manhole. Once completed, both replacement lines were connected to a new 12-inch pipe auger rammed under Midway Plaza.
Players’ tunnel
The stadium has only one players’ tunnel, and Newell needed a 10-foot-square by 25-foot-deep pulling pit at its outside entrance to upsize 350 feet of 8-inch pipe to 10-inch pipe. However, tons of material for the stadium renovation passed through the tunnel. “We weren’t allowed in there because it would slow progress,” says Newell, who again spent weeks juggling his work schedule while waiting for the all clear.
When the call came, the sand in the area sloughed off so fast that Wright Construction excavated the pulling pit by setting the shore box, digging from inside it, and pushing the box down as the hole deepened. The 15-foot-deep entry trench in the asphalt pavement was dug inside stacked 8- by 20-foot shoring.
Newell’s crew set up one ram and split the pipe the first day with the Shark Fin, jetting at 5 gpm/1,000 psi so as not to make too big a void. That afternoon, they set the second ram, hooked up both chains, and pulled the pipe into the entry trench.
“We starting pulling at seven the next morning and finished at six that evening,” says Newell. “The relief of my business returning to normal was palpable.” The annual Red River Shootout was played at the Cotton Bowl during the State Fair of Texas.
