Tough Jobs a Focus on First Day of No-Dig

Virginia utility, contractors work through challenges to complete tough HDD job under drinking reservoir

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Tough jobs were a focus of discussion at several of the technical paper sessions Monday at the North American Society for Trenchless Technology’s No-Dig Show in Palm Springs, California.

Many of those sessions — held both in the morning and afternoon — focused on municipalities and contractors facing challenges on jobs over the last several years. Projects highlighted included horizontal directional drilling, sliplining, pipe bursting, CIPP and more.

The Hampton Roads Sanitation District, located in Virginia, was one of those utilities talking about a job they started in 2012 and finished this year in the Suffolk, area. The District undertook a two-phase, 26,000-foot force main replacement project to revitalize an undersized sewer system. A 3,200-foot horizontal directional drill was designed to cross Lake Meade, a drinking reservoir for some communities in Virginia, during installation.

FINDING A PROBLEM

The Hampton Roads Sanitation District is the largest wastewater treatment provider in the state, serving 18 counties and cities with a service area covering about 3,000 square miles. The district serves almost 2 million people with nine major treatment plants and six smaller plants.

The district has about 600 miles of force main and a capacity of about 250 million gallons per day.

“We had built force mains in Suffolk, not anticipating such a rapid growth, but in the year 2000 growth just took off, so our force mains in that area could not meet capacity,” says Tim Marsh, with the Hampton Roads Sanitation District. “We determined the existing pipeline was undersized and needed to be replaced.”

The existing force main was installed in the 1970s with it being a mix of 14- and 18-inch ductile iron and asbestos cement force main, located in a busy corridor with port traffic coming in and out of Norfolk.

The replacement project was going to install 26,000 linear feet of ductile iron force main.

THE PROJECT

The project began in 2012 with a corridor study for the recommended alignment. The new pipe would connect to a portion of the existing pipe, would run through a residential neighborhood, past an active railroad crossing, then it would jump onto an abandoned railroad corridor.

“That was nice because there would be minimal obstructions,” says Brandon Beamon, a project engineer with Michael Baker International, which designed the route.

The pipeline would then cross another active railroad crossing and then to the lake that had to be crossed.

“We had been using microtunneling, tunnel boring machines and guided bores on other parts of this projects, but we determined through a couple analyses that we wanted to cross the lake via horizontal directional drilling.”

DRILLING BEGINS

The drilling work began in 2015 with the selection of the path and location of the drill pad, which would be in a wetland area, so some site prep was needed in advance.

“It was also an historic area as it was once a Civil War battleground,” Beamon says. “We had to put provisions in for if artifacts were found. Fortunately we didn’t recover anything, so it worked out in our favor.”

The drill was determined to go 43 feet below the lakebed because of soil conditions. There were some areas where soils seemed to be good for drilling and others that looked like it could be potential areas for frack-outs. The crews wanted to get deep enough to avoid those issues.

The pipe being used as 24-inch fusible PVC first fused into 600-foot sections and then eventually fused into one long 3,200-foot pipe for the pullback process.

“It was a little over a month from the start of the pilot hole to the time the bore was ready to commence pulling the pipe,” Beamon says. “One of the impressive things was the contractor came within 6 inches of our design drill point.”

PULLBACK PROBLEMS

The initial pullback began on the morning of Aug. 10, 2015. The contractor started the pullback and got in about 150 feet before it was realized the rollers that were set up to help move in the pipe were misaligned.

“They started getting some fishtail at the end of the string, so they stopped and realigned the rollers to be more suitable to keep the pipeline straight,” Beamon says.

The drill continued and with about 85 percent of the pipe pulled through; it all came to a stop as the pipe got stuck. The contractor went through multiple operations of raising the pressure on the drill rig, pulling back and pushing forward on the pipe, but it wouldn’t budge.

“We assume the borehole collapsed there at the east bank of the lake,” Beamon says.

Crews had two options — abandon and drill a new hole with a new easement or just dislodge the pipe, redrill that hole and start over on the pullback. Crews opted for the second option.

“The initial attempt was the contractor hooked up another drill head to the west end of the pipe and they tried to pull it out using a combination of excavators,” Beamon says. “The ended up daisy chaining five excavators together at the chassis and tried, but the chains were snapped as they tried pulling.”

Crews then brought in another rig to try and use the force of that to pull the pipe out, but it didn’t work. After about a week, crews came out with a washer-type tool that would fit around the exterior of the pipe. They fed that through the borehole using drill rods and pumping fluid until they got to where they thought the hole had collapsed.

“After about an hour and a half of pumping fluid they were able to pull the pipe using an excavator,” Beamon says. “They pulled the entire length of pipe out.”

Another contractor washed off the pipe and another inspected the pipe, seeing if there were any imperfections. There were a couple sections that had to be cutout and new pipe was fused in.

After the hole was opened back up, the drilling contractor went from a 38-inch reamer up to a 42-inch. The second attempted at pullback went smoother with the full pipe pulled through in six hours.

ONE MORE ISSUE

Before the Champagne bottles were cracked open, crews pressure tested the new pipe. At 50 psi, an explosion occurred on the west side of the lake as a portion of the pipe fractured sending water into the air.

The location was determined to be about 100 feet from the exit point, so crews dug down 30 feet to find the fracture. They put a cap on the section and repaired it. A second pressure test was done up to 100 psi and passed.

“We then popped the Champagne and congratulated each other on a successful drill,” Beamon says.

The last section of the force main was tied in to complete the project about a month ago, according to Beamon. “We learned some things on this project that we’ll take with us on other projects now,” he says. 



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