Tight Urban Directional Drilling

Special Equipment In Restricted Space Aids Project
By Jeff Griffin, Senior Editor | April 2011 Vol. 66 No. 4

CenterPoint Energy Inc., Houston, TX, is a domestic energy delivery company that includes electric transmission and distribution, natural gas distribution, competitive natural gas sales and services, interstate pipelines and field services operations. It serves more than five million metered electric and natural gas customers in six states: Texas, Arkansas, Louisiana, Minnesota, Mississippi and Oklahoma.

The company’s electric transmission and distribution business, CenterPoint Energy Houston Electric LLC, serves two million metered customers with an infrastructure that includes18,995 miles of underground distribution lines, 27,241 miles of overhead distribution cable and 229 substations.

CenterPoint has continuing programs to maintain and upgrade its transmission and distribution infrastructure.

A current project in downtown Houston is to install 12,788 feet of underground duct bank to contain three 8-inch and three 4-inch PVC conduits from the Garrott Street substation to the Midtown substation and ending at the Polk Street substation. Boyer, Inc., Houston, is the general contractor.

Ninety percent of the route is through urban areas, so only 2,200 feet is projected to be open-cut construction, said Shawn Adams, Boyer general foreman. Horizontal directional drilling (HDD) and wood box tunnels will be used for the remainder of the construction.

Restrictive HDD
Two difficult HDD shots in very restrictive areas were completed by subcontractor Laney Directional Drilling Co., Humble, TX.

“Laney drilled two shots -- one for 1,830 feet, the other for 1,300 feet -- in two of the
narrowest streets in the most cramped areas on the project,” said Adams. “For these street crossings, we switched from PVC to HDPE and pulled the bundle of three 8-inch conduits, four four-inch conduits, and added a fourth ‘extra’ 4-inch conduit in the 8-inch bundle to space conduits within the package.”

To handle the weight of the bundles, a powerful drill rig was required.

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A 300,000-pound-pullback drill rig manufactured by Laney was used for both street crossings, said David Poage, Laney surveyor. The HDD unit is powered by a 500-horsepower engine. It develops 47,000 foot pounds of torque. The machine has a footprint of eight by 48 feet, a tight fit on both locations.

“We had very little room for set up on both entry and exit sides of both bores,” said Poage. “Because of restrictions on the amount of time the drill unit could be in the roadway, we had to move the drill rig from the entry to exit side to pull in the bundles on both installations.”