Fast track solution to trenchless pipeline build

According to Jim Stilling, marketing services manager at Plexco Performance Pipe, location can mean everything when it comes to the pipeline installation business.

Pipe rollers greatly minimised resistance during pullback

Pipe rollers greatly minimised resistance during pullback

The offices and main pumping station of the Leucadia County Water District in Southern California are located in La Costa, one of North San Diego County's most rapidly developing and environmentally sensitive areas. The district serves 52,000 people and expects a 30% jump in usage by 2020.

One block away from the district facilities is La Costa Resort and Golf Course. On a high cliff overlooking the district facilities sits the Four Seasons Resort. Surrounding it are expensive new housing developments.

Across the street lies the scenic Batiquitos Lagoon, which connects directly to the Pacific Ocean - the product of a high profile $50M wetlands restoration. The district's sewer forcemain runs along the entire south shore of the lagoon and crosses its western end on a Pacific Coast Highway bridge.

Forcemain Break
In December 1998, the district was in the middle of a capital improvement project. It had already constructed more than 2.4km of parallel pipeline in combination with state and city road improvement projects along La Costa Avenue, when an unexpected forcemain break occurred near the Leucadia Pump Station.

Utilising a 305mm diameter reclaimed water pipeline put into service during an earlier road project, the district was able to bypass the larger diameter forcemain.

Immediately, the district decided to accelerate the remaining 365m of parallel forcemain near the pump station. When a second forcemain break occurred in March in the same general vicinity, the pressure was on to complete the missing link as quickly as possible.

Instead of taking over a year to study and redesign the job, the project took two months for new geotechnical and redesign work and another two months for construction.

The district installed 335m of high density Plexco Green Stripe by directional drilling, parallelling the old ductile iron forcemain. The project served a dual purpose - advancing the district's long-term plan for redundant systems and solving its short-term dilemma.

In southern California, directional drilling is a fairly new method of installation. The project team included Plexco Performance Pipe, P&F Distributors, ARB Inc and Dudek and Associates.

Fast-track project
Accelerating the design and bidding process, the district replaced 335m of 610mm ductile iron pipeline with a 710mm pipeline in 33 days - 16 days ahead of schedule.

Among the methods considered for the project were horizontal direct drilling and micro-tunnelling. When it came to pipe for directional drilling, polyethylene was the only consideration.

The district decided to limit bids to select directional drilling contractors after working with Plexco on a small, but environmentally sensitive, directionally drilled project between La Costa Resort and a manhole on the district site.

The district took a number of steps to ensure the project's success:

  • It discussed the availability of materials and services with suppliers and drillers;
  • The district's attorney determined it could select a contractor on qualifications basis in addition to bid price;
  • It decided to offer contractors a substantial bonus for early completion and an equally substantial penalty for finishing the job late.

Quick start
"They wanted the pipe as fast as possible," said Josh Randell, sales/fusion technician for P&F Distributors.

"In response to the customer's urgent need, we ordered the pipe from Plexco's Reno plant and had the pipe on site in seven days."

P&F ordered green stripe pipe for easy identification underground. "This is a really strong, sturdy pipe - precisely suited for a relatively long run like this," added Randell.

"Of course, when you are going under an existing road, there are always concerns about lifting the road. With directional drilling, you're interested in keeping the pipe in good condition during and after the pull back. That's why we settled on the 710mm SR11 - its wall thickness is just over 63mm." Additionally, the pipe was positioned above ground on large diameter pipe rollers which greatly minimised the resistance during the pullback.

A staging area was set up in the district's car park, where fusion training took place. With a street-widening project proceeding at the same time on La Costa Avenue, the crew was able to utilise expanded median areas to help with equipment placement.

"The project went smoothly," said David Arthurs, ARB division manager. "The soil is a fairly consistent sandstone that held together quite well during the drill and pullback. The only problem we encountered was when we began to drill the pilot hole.

"We hit rock and started having minor frac-outs (drilling fluids coming to the surface due to cracks in the soil) in three or four locations. We were able to vacuum up and sandbag to completely contain the thin film of bentonite. The frac-outs cost us five days.

"We slowed down the pilot hole drilling, eventually going down 12mm, far below the spaghetti of utilities we found under the intersection. Traffic drove through unimpeded and we never had to stop working, except to clear the frac-outs."

Smooth pull-back
"We had a fairly smooth pull-back," said Arthurs. "Although the pipe is designed to withstand up to 2700kN of tensile force, we never exceeded 270kN during pull-back. The hole stayed open and we didn't encounter any problems - it took five hours for pull-back, which is excellent.

"Plexco and P&F made sure we had the materials, machinery and technical assistance on site when we needed it.

"We learned how to handle the pipe to keep it from floating - we were in a wet environment in the water table. To keep the pipe from riding up to the top of the hole, we filled it with water.

"The crew had not worked with this size polyethylene before. Polyethylene is more flexible, easier to get into the hole and more forgiving than the steel we have worked with in the past. The steel itself is more rigid, heavier," added Arthurs. "Everything went well and the district was satisfied with the progress of the job."

"We like the pipe," said district capital projects manager Denis Pollak. "It was clearly the technically superior material for this application. Combined with the horizontal directional drill installation method, we effectively avoided environmental impacts and disruption to the surrounding community."



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