SBUs, Auger Boring Equipment Play Critical Role In Pipeline Expansion

At 260 miles long, Arizona’s Phoenix Expansion Project is a giant in the making.

The natural gas pipeline snakes through challenging terrain and protected lands including two national forests. The most difficult thing about this project has been the terrain: going under rivers, 30-foot side cuts into mountains and very steep slopes,” said Eric Pickett, project engineer for Price Gregory Services, one of two main contractors working on the pipeline. The path of the line, selected to minimize environmental impact, has also required dozens of crossings utilizing both cut and cover and trenchless excavation.

Geological conditions range from soft soils to cobbles to hard rock, requiring auger boring, HDD and rock cutting heads called Robbins Small Boring Units. “The conditions are highly variable. The ground we are working in can change from cemented cobbles, to non cemented ground with little warning,” said Tom Vandyke, president of contractor T&D Services, Inc. Both contractors – T&D Services Inc. of Murrieta, CA, and Price Gregory Services Inc. of Houston – have successfully utilized Small Boring Units on a total of 24 crossings in both hard rock and mixed ground. “The Robbins SBU is one of the few machines we’ve found that will work regardless of the conditions,” continued Vandyke.

Project overview

The Phoenix Expansion Project is being constructed by Transwestern Pipeline Company to service a booming population expected to grow by 38 percent within the next 30 years. By the end of 2008, the pipeline will provide 500 million cubic feet per day of natural gas and will fuel several new power plants in the region, increasing power output from 80,000 GWh in 2008 to 120,000 GWh by 2024.

Gas will be pumped into the Phoenix area using a pre existing 2,400 mile long supply chain of pipelines extending from West Texas and Oklahoma to New Mexico, Arizona and the California border. Much of the gas will come from the Rocky Mountain Basin, as well as the San Juan Basin in northwestern New Mexico and southern Colorado.

The Phoenix Expansion Project traverses rough geography that parallels the existing El Paso Natural Gas line and minimizes environmental impact. The path cuts through two national forests – the Kaibab National Forest (nine miles of pipeline) and the Prescott National Forest (24 miles of pipeline). Much of the protected area did not require additional clearing since it was in close proximity to the already cleared path of the El Paso line; however, a unique crossing was required at the protected Verde River in the Prescott National Forest. Crews used the flume and dam method, constructing a temporary dam across the river to install pipe.

The pipeline project was awarded to two main contractors – Price Gregory Services and Rockford Corporation. Subsequently they have subcontracted some of the work and created hundreds of jobs for contractors since construction began in early 2008. Approximately 114 miles of the pipeline were contracted to Price Gregory Services, who installed both the main pipeline and 40 crossings under roads and canals. Work is ongoing on another 150 mile section of the line contracted to Rockford Corporation of Hillsboro, OR. Rockford then subcontracted T&D Services for a total of 19 crossings, four of which used Small Boring Units.

Choosing effective technology

Given the wide ranging geology, contractor T&D Services had a number of methods to choose from. The contractor elected to use a hard rock cutting head with disc cutters on four crossings ranging from 200 to 310 feet. The crossings passed through a mix of cemented cobbles ranging from six inches to 3 feet in diameter. After an initial bore wore out the cutter heads after only 30 feet, T&D switched to the Robbins equipment, said Rex Vandyke, superintendent for T&D Services.

The company rented a 48 inch diameter SBU A. The circular cutterhead was first welded to an 80-foot length of steel casing. A custom made, 72-inch auger boring machine was then used on the bores to provide both torque and forward thrust to the cutterhead, while allowing for spoils removal through a full face auger. “We’ve averaged about 10 feet per hour,” said Vandyke.

T&D first became interested in small boring units after completing a 54-inch diameter, 250 foot long crossing in Mexico in 2007. “The ground was very bad, mostly solid volcanic rock. We used a roller cone cutting head, which was a disaster – the crossing took about two and a half months,” said Tom Vandyke. After their initial experience, T&D began familiarizing themselves with small boring units.

Excavating the crossings

T&D excavated the first crossing, measuring 260-feet long, in August 2008. The crossing was located under a major aqueduct and required a very long bore pit, measuring 20-feet deep by 60-feet wide by 150- feet long, so the crew could weld 80-foot sections of pipe at the surface and speed up excavation time.

“We did great on the first crossing, only replacing two cutters, which is very good in this abrasive type of ground. For the second bore we added a set of grill bars to keep any large boulders from passing through the head into the auger string. Everything has been working very well,” said Vandyke. As of October, T&D is working on its second 310-foot long crossing, which should take about three weeks working 12 hour shifts, six days per week. The second crossing is also under a major aqueduct and requires an equally long bore pit at 32-feet deep by 60-feet wide by 150 feet long. T&D has plans for two more bores, also under aqueducts, which should be completed by December 2008.

Twenty SBU A crossings were also excavated beginning in March 2008 under Price Gregory Services, with similar advance rates of 10 to 12-feet per hour through lava rock and granite. The bores ranged from 80 feet to 300 feet, and were finished by summer 2008. The contractor was also responsible for laying over 100 miles of the pipeline, using 42-inch diameter, epoxy coated steel pipe in 10-foot deep trenches. The entire pipeline is required to have a minimum 3.5 feet of cover, with some sections going even deeper beneath existing utility lines. All work on the pipeline and two underground compressor stations is scheduled for completion by the end of the year.

Price Gregory Services was established in January 2008 with the merger of two prominent pipeline contractors – H.C. Price Company of Dallas and Gregory & Cook Construction of Houston. Price Gregory Services is now based out of Houston and provides a variety of services for oil and gas pipeline projects.

Rockford Corporation was founded in 1967 in Alaska as a pipeline contractor. The company has been based out of Hillsboro, OR, since 1990. Rockford owns a sizable fleet of pipeline equipment including sidebooms, lowboys, service trucks, skids and mats to perform large and small diameter pipeline work in all types of terrain.

T&D Services has been operating for more than five years out of Murrieta, CA. The company has 14 full time employees in four crews, who work on a variety of projects including road bores, guided auger boring, rock boring, directional drilling and pilot tube boring.
Rockford Corporation, (888) 896-9226,
T&D Services, (941) 304-1190

Price Gregory Services, (281) 362-2877,
Rockford Corporation, (888) 896-9226,
T&D Services, (941) 304-1190
Small Boring Units: Robbins TBM, (440) 248-3303,

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